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NICHOLAS DIBELLA: Over
the past couple of weeks,

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I talked about this thing
called the universe, which

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is pretty big.

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I talked about the possible
beginnings of the universe,

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whether there was a
big beginning of time,

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whether there will be an end,
whether the universe is finite,

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what its shape is.

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00:00:41,633 --> 00:00:44,000
Hello.

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00:00:44,000 --> 00:00:46,800
And I described this
basic picture that's--

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00:00:46,800 --> 00:00:49,874
we've begun to form over
the past 100 years or so.

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And the basic picture
is that yes, there

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was a beginning of time.

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00:00:52,690 --> 00:00:54,344
We call it the big bang.

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There won't be an end.

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The universe will live forever.

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And the universe is also
infinite and flat, in the sense

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that I described last time.

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Flat means that if
you form a triangle

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and you added up the
angles in the triangle,

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then you can get 180 degrees.

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00:01:08,820 --> 00:01:10,830
How I also talked about
how we didn't fully

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00:01:10,830 --> 00:01:14,534
understand the beginning what
this big bang really was,

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and actually, when you think
a little bit harder about it,

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we don't really
understand the big bang.

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00:01:18,180 --> 00:01:20,630
Our current physics theories
basically, break down.

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00:01:20,630 --> 00:01:22,296
And so it's entirely
possible that there

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00:01:22,296 --> 00:01:25,295
wasn't a beginning and
most of our modern theories

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00:01:25,295 --> 00:01:27,055
to explain this beginning--

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00:01:27,055 --> 00:01:28,680
I'll say, that it
wasn't the beginning,

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00:01:28,680 --> 00:01:29,869
there was time beforehand.

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00:01:29,869 --> 00:01:31,910
So you don't really know
if there is a beginning,

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00:01:31,910 --> 00:01:33,951
but we're pretty sure that
there won't be an end.

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00:01:36,330 --> 00:01:38,220
And it's certainly
also very plausible

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00:01:38,220 --> 00:01:40,020
that the universe is infinite.

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00:01:40,020 --> 00:01:41,895
We don't know for sure,
but it's definitely--

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00:01:46,470 --> 00:01:48,120
all the observational
data that we have

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00:01:48,120 --> 00:01:49,745
is totally consistent
with the universe

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00:01:49,745 --> 00:01:54,784
being infinite and flat,
in that sense I described.

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00:01:54,784 --> 00:01:55,950
That was the last two weeks.

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00:01:55,950 --> 00:01:57,283
Does anybody have any questions?

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00:02:00,380 --> 00:02:01,320
OK.

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00:02:01,320 --> 00:02:04,350
Now, today, I'd like to describe
some very interesting things

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00:02:04,350 --> 00:02:09,900
that happen as result of
the universe being very big.

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00:02:09,900 --> 00:02:12,030
I'll assume for the
rest of the class

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00:02:12,030 --> 00:02:13,920
the universe is
in fact, infinite.

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00:02:13,920 --> 00:02:17,310
It might not be infinite,
it might just be very large,

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but all the data
seems to indicate

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that the universe is infinite.

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In an infinite universe,
the craziest things happen.

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Anything that's
possible happens.

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00:02:29,540 --> 00:02:31,650
I mean, right now,
there's a possibility

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that I'll just get
bored with this class.

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00:02:34,200 --> 00:02:36,034
You know, I'm teaching,
but maybe I'm bored.

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There's a possibility
that I'll get bored

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and just want to leave.

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So in another universe-- we
say, in a parallel universe,

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I just leave the class.

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Bye.

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AUDIENCE: Bye.

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AUDIENCE: [INAUDIBLE]

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NICHOLAS DIBELLA: Hi.

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Fortunately, we're
not in that universe,

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we're in this universe.

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And I don't--

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AUDIENCE: [INAUDIBLE]

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NICHOLAS DIBELLA: How do I
know this universe, what?

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AUDIENCE: Isn't parallel
universe [INAUDIBLE]??

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NICHOLAS DIBELLA: Well, it is.

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I'll describe what I mean
by parallel universes

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in more detail, more
precisely, in a little bit.

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Yeah.

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I mean, certainly,
our universe could be

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parallel to another universe.

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What's that?

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AUDIENCE: Nothing.

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NICHOLAS DIBELLA: OK.

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So let me be a little
more precise now.

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So we have to make a distinction
between the whole universe

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and the observed universe.

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Whole versus observed.

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Now, the whole universe
is exactly what

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00:03:54,400 --> 00:03:57,710
it sounds like, it's
the whole universe,

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but unfortunately, we can't
observe the whole universe

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because the light was emitted
only a finite amount of time

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00:04:05,710 --> 00:04:09,060
ago from all the
points in universe.

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In particular, about
13.7 billion years ago.

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So light hasn't had
time to reach us

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for the most
distant of galaxies,

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00:04:17,230 --> 00:04:19,870
but it has had time to reach
us from less distant galaxies,

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00:04:19,870 --> 00:04:23,470
in particular the galaxies whose
light has had time to reach us

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00:04:23,470 --> 00:04:25,360
in the past 13.7 years.

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00:04:25,360 --> 00:04:26,642
And we call the points--

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00:04:26,642 --> 00:04:27,850
called the regions of space--

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00:04:27,850 --> 00:04:31,930
the region of space that we
can see the observed universe.

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00:04:31,930 --> 00:04:34,480
And the observed universe has
been increasing in size ever

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since the beginning.

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So a long time ago, on the
point where we are right now,

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00:04:43,780 --> 00:04:46,745
had observed universe
that was not very big.

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I'll just draw it like this.

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00:04:48,380 --> 00:04:51,410
Let's say this is us.

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It's spherical.

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00:04:52,660 --> 00:04:54,930
The observing
universe is spherical.

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00:04:54,930 --> 00:04:57,260
Any direction is as
good as any other.

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If light has had time
to reach us from there,

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00:04:59,990 --> 00:05:02,250
then it has had time of
year is just from there,

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00:05:02,250 --> 00:05:03,620
and it's had time to reach
us from there, and so

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00:05:03,620 --> 00:05:04,330
all directions.

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00:05:04,330 --> 00:05:07,400
So the observed
universe is spherical.

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And is increasing in time.

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00:05:08,510 --> 00:05:10,850
So maybe-- let's say
maybe, a billion years

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00:05:10,850 --> 00:05:14,040
after the Big Bang, the
observed universe was this size.

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Maybe after a little
bit more time--

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let's say this is 10 billion
years after the Big Bang.

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00:05:21,600 --> 00:05:23,790
So this is us.

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00:05:23,790 --> 00:05:29,150
And it should continue to
grow in size for a long time.

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00:05:29,150 --> 00:05:29,734
So us.

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00:05:29,734 --> 00:05:31,400
And the universe--
the observed universe

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00:05:31,400 --> 00:05:33,570
just keeps growing
and growing in size.

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00:05:33,570 --> 00:05:35,660
It's obviously, very big.

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00:05:35,660 --> 00:05:38,920
It's about 40 billion
light years across.

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00:05:38,920 --> 00:05:42,340
Well actually, 40
billion times two.

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A light year is just how long--

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00:05:44,990 --> 00:05:46,640
a light year just
how long light--

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how far light travels in a year.

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And the radius of
the observed universe

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is about 40 billion light years.

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That's a little bit greater
than 13.7 billion light years.

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13.7 billion years being
the age of the universe.

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That's a detail that comes
in from general relativity.

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00:06:04,880 --> 00:06:08,220
Distances get
stretched to detail.

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OK.

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So the observed
universe is smaller

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than the whole universe,
and you might wonder well,

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if you can't observe anything
outside this observed

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universe then how do we know--

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how do we know for sure if
anything exists outside of it?

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I mean, we can't see it.

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So it's entirely possible
that the universe just

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stops right there.

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00:06:32,570 --> 00:06:34,630
I mean, it could just
conceivably stop.

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00:06:34,630 --> 00:06:37,210
There could be some kind of
a boundary, some kind of a--

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maybe some kind of a stop sign.

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But as I talked
about last time, none

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of the predictions
of general relativity

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about the overall size
and shape of the universe

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predicts a universe like this.

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This kind of finites.

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General relativity does
predict a kind of finite,

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but it's the kind
of finite that's

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my vitamin water bottle is.

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The kind of finite
that's closed.

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So you're still standing
on one part of the universe

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and you keep walking, and
eventually, you make a circle.

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00:07:07,275 --> 00:07:08,900
Or it could mean more
like the universe

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at the surface of a sphere.

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00:07:10,024 --> 00:07:13,490
You keep walking on the
surface of this hypersphere,

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00:07:13,490 --> 00:07:15,140
and then you eventually reach--

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you return to your
original point.

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But as I talked
about last time, it

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doesn't look like the
universe is like that.

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Our data is not consistent
with that kind of finites.

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It's certainly not consistent
with that kind of finite.

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And it's actually consistent
with an infinite universe

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that's flat.

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So all of our data
seems to indicate

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that the universe is infinite.

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And that's exactly what
I'll assume for this class.

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So we have indirect evidence
that the universe is infinite.

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Direct evidence would
be that we somehow

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measure that it's infinite.

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But how would you measure
that it's infinite?

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The best we can ever do is
really have indirect evidence.

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00:07:54,470 --> 00:07:55,590
Any questions about that?

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Now, according to our
best modern theories

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about the very early
universe, there

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00:08:05,590 --> 00:08:07,164
is matter and energy present.

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00:08:07,164 --> 00:08:08,330
The energies were very high.

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The temperatures were very high.

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00:08:09,950 --> 00:08:11,870
And all the matter
and energy were

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spread around pretty randomly
in the very beginning,

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right after the Big Bang.

189
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And this process of spreading
everything around, actually

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led to pretty much all
possible initial arrangements

191
00:08:24,620 --> 00:08:25,920
of matter and energy.

192
00:08:25,920 --> 00:08:28,920
I'll just a matter, just
to keep things simple.

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00:08:28,920 --> 00:08:31,550
So you can imagine, for example,
having some kind of a box.

194
00:08:35,620 --> 00:08:37,809
Some kind of a finite box.

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00:08:37,809 --> 00:08:40,809
Let's say, it's a very small
box and only has room for say,

196
00:08:40,809 --> 00:08:42,440
four atoms.

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00:08:42,440 --> 00:08:45,510
So one atom could go here,
another atom can go here,

198
00:08:45,510 --> 00:08:49,390
another one can go here,
another one can go here.

199
00:08:49,390 --> 00:08:53,389
So you have four
slots for atoms.

200
00:08:53,389 --> 00:08:55,180
So how many different
possible arrangements

201
00:08:55,180 --> 00:08:56,350
are there in this box?

202
00:08:56,350 --> 00:08:58,820
You can only fit four.

203
00:08:58,820 --> 00:09:00,129
Does anybody have an answer?

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00:09:00,129 --> 00:09:00,670
AUDIENCE: 16.

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00:09:00,670 --> 00:09:01,360
NICHOLAS DIBELLA: Yes, 16.

206
00:09:01,360 --> 00:09:02,776
There are 16
possible arrangements

207
00:09:02,776 --> 00:09:04,437
because you can fit two--

208
00:09:04,437 --> 00:09:05,770
you have two possibilities here.

209
00:09:05,770 --> 00:09:07,542
The atoms there are not.

210
00:09:07,542 --> 00:09:08,500
Two possibilities here.

211
00:09:08,500 --> 00:09:09,010
Two there.

212
00:09:09,010 --> 00:09:09,580
Two there.

213
00:09:09,580 --> 00:09:12,910
So two, times two, times two,
times two, 16 possibilities.

214
00:09:12,910 --> 00:09:14,770
And so it's a finite
number of possibilities

215
00:09:14,770 --> 00:09:17,460
of different arrangements
you can have in this box.

216
00:09:17,460 --> 00:09:20,263
So 16 possible arrangements.

217
00:09:30,910 --> 00:09:34,670
You can also think
of a bigger box that

218
00:09:34,670 --> 00:09:38,720
maybe has 100 slots for atoms,
then that would lead to two,

219
00:09:38,720 --> 00:09:41,690
times two, times two, times two.

220
00:09:41,690 --> 00:09:45,120
A hundred two's, which
is a very large number,

221
00:09:45,120 --> 00:09:47,520
but it's still a finite number.

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00:09:47,520 --> 00:09:51,380
Now, in an infinite universe--

223
00:09:51,380 --> 00:09:53,390
in infinite universe,
these arrangements

224
00:09:53,390 --> 00:09:54,860
will start to repeat each other.

225
00:09:54,860 --> 00:09:56,480
They'll start to repeat.

226
00:09:56,480 --> 00:10:01,260
I mean, there are only
16 possible arrangements

227
00:10:01,260 --> 00:10:04,310
in this box, for example.

228
00:10:04,310 --> 00:10:08,420
Now, if you have many of
these boxes in the universe,

229
00:10:08,420 --> 00:10:11,720
each arrangement having
some possibility of arising,

230
00:10:11,720 --> 00:10:14,510
then eventually, you're going
to start getting repeats.

231
00:10:14,510 --> 00:10:17,390
Some of them are going to recur.

232
00:10:17,390 --> 00:10:21,800
And in infinite universe, every
possible arrangements recurs

233
00:10:21,800 --> 00:10:24,502
and in fact, it occurs
infinitely many times.

234
00:10:24,502 --> 00:10:26,960
So there are infinitely many
possible different occurrences

235
00:10:26,960 --> 00:10:28,520
of every single
possible arrangement

236
00:10:28,520 --> 00:10:33,590
of matter and energy at the
beginning of the universe.

237
00:10:33,590 --> 00:10:41,486
And that also should mean that
today, there should be also,

238
00:10:41,486 --> 00:10:42,860
every single
possible arrangement

239
00:10:42,860 --> 00:10:44,734
of matter and energy in
the universe as well,

240
00:10:44,734 --> 00:10:47,760
for every single
kind of a finite box.

241
00:10:47,760 --> 00:10:50,120
Because if you start off
with one arrangement,

242
00:10:50,120 --> 00:10:51,830
you start with
one configuration,

243
00:10:51,830 --> 00:10:54,317
then there's a chance that
it will become another one.

244
00:10:54,317 --> 00:10:56,900
There's a chance it will become
another one and every single--

245
00:10:56,900 --> 00:10:58,775
pretty much every single
possible arrangement

246
00:10:58,775 --> 00:11:00,230
has some chance of arising.

247
00:11:00,230 --> 00:11:03,290
So in infinite universe,
you get them all.

248
00:11:06,010 --> 00:11:11,240
In this room, for example, there
are air molecules in the room,

249
00:11:11,240 --> 00:11:15,110
and it's theoretically possible
that all the air in the room

250
00:11:15,110 --> 00:11:19,940
will somehow randomly
spontaneously rush towards me,

251
00:11:19,940 --> 00:11:21,630
and they'll all rush
towards right here,

252
00:11:21,630 --> 00:11:22,463
suffocating you all.

253
00:11:22,463 --> 00:11:24,507
That's totally possible.

254
00:11:24,507 --> 00:11:26,090
It's not going to
happen in a billion,

255
00:11:26,090 --> 00:11:28,250
billion, billion
years, actually,

256
00:11:28,250 --> 00:11:31,650
many more years than that,
but it's totally possible.

257
00:11:31,650 --> 00:11:36,410
And in fact, let's say the
chances of that happening

258
00:11:36,410 --> 00:11:39,077
are one in a billion,
billion, billion.

259
00:11:39,077 --> 00:11:40,160
Let's say that's a chance.

260
00:11:40,160 --> 00:11:41,618
They're much, much
lower than that,

261
00:11:41,618 --> 00:11:45,080
but let's say that's the chances
of the air rushing towards me.

262
00:11:45,080 --> 00:11:46,600
It's theoretically possible.

263
00:11:46,600 --> 00:11:49,310
Let's say that's the chances
of the air rushing towards me.

264
00:11:49,310 --> 00:11:50,690
Now, if I had a
billion, billion,

265
00:11:50,690 --> 00:11:52,520
billion copies of
this room that are

266
00:11:52,520 --> 00:11:54,920
exactly the same, the same
distribution of matter

267
00:11:54,920 --> 00:11:58,780
and energy and same
motions and everything then

268
00:11:58,780 --> 00:12:01,745
eventually, if that's really
the chance is one in a billion,

269
00:12:01,745 --> 00:12:04,200
billion, billion, eventually
that would happen.

270
00:12:04,200 --> 00:12:06,350
You would eventually
get a repeat.

271
00:12:06,350 --> 00:12:07,127
And if you look--

272
00:12:07,127 --> 00:12:09,710
I mean, you would probably get
a repeat if you have a billion,

273
00:12:09,710 --> 00:12:12,039
billion, billion
different copies.

274
00:12:12,039 --> 00:12:13,580
Now, if you look at
even more copies,

275
00:12:13,580 --> 00:12:15,746
if you look at a billion,
billion, billion, billion,

276
00:12:15,746 --> 00:12:20,540
copies then the chances
of a repeat happening

277
00:12:20,540 --> 00:12:22,050
are even higher.

278
00:12:22,050 --> 00:12:25,650
And then you look at even
more samples, more copies,

279
00:12:25,650 --> 00:12:27,140
the chances are even higher.

280
00:12:27,140 --> 00:12:29,450
And if you have an
infinite number of copies,

281
00:12:29,450 --> 00:12:33,770
an infinite number of
boxes like this, then

282
00:12:33,770 --> 00:12:36,530
boxes that form the volume
of a room, an infinite number

283
00:12:36,530 --> 00:12:40,580
of copies then the chances
of getting a repeat

284
00:12:40,580 --> 00:12:43,060
are complete certainty.

285
00:12:43,060 --> 00:12:46,040
It must happen in
infinite universe.

286
00:12:46,040 --> 00:12:47,165
You will get these repeats.

287
00:12:53,740 --> 00:12:58,210
Now, we can look at the
distribution of matter

288
00:12:58,210 --> 00:13:01,570
and energy in this
room, for example

289
00:13:01,570 --> 00:13:03,940
and its universe is infinite.

290
00:13:03,940 --> 00:13:06,250
We'll eventually
find a copy of it.

291
00:13:06,250 --> 00:13:10,480
We eventually find a copy
of every single aspect

292
00:13:10,480 --> 00:13:12,490
of this room.

293
00:13:12,490 --> 00:13:15,530
Everything is made up of atoms
and electrons and everything,

294
00:13:15,530 --> 00:13:18,460
and if the universe is infinite
then this whole arrangement

295
00:13:18,460 --> 00:13:19,604
will repeat.

296
00:13:19,604 --> 00:13:21,520
So if you travel far
enough, you'll eventually

297
00:13:21,520 --> 00:13:25,570
find a copy of room 4270
on a campus like MIT

298
00:13:25,570 --> 00:13:27,820
on a pile like earth,
and eventually, you'll

299
00:13:27,820 --> 00:13:32,295
get a complete repeat of the
entire observed universe.

300
00:13:32,295 --> 00:13:33,170
AUDIENCE: [INAUDIBLE]

301
00:13:33,170 --> 00:13:34,420
NICHOLAS DIBELLA: What's that?

302
00:13:34,420 --> 00:13:37,460
AUDIENCE: So are we alive again?

303
00:13:37,460 --> 00:13:41,420
AUDIENCE: So yeah, if
you travel far enough.

304
00:13:41,420 --> 00:13:44,650
I mean, our current
understanding of modern biology

305
00:13:44,650 --> 00:13:50,680
is that humans are made up
of molecules and atoms, which

306
00:13:50,680 --> 00:13:56,590
are in turn made up of
electrons and protons and quarks

307
00:13:56,590 --> 00:13:59,230
and photons and whole lot
of other small things.

308
00:14:02,140 --> 00:14:04,780
I mean, these different
particles interact

309
00:14:04,780 --> 00:14:07,090
in a very complex
way to give rise

310
00:14:07,090 --> 00:14:11,620
to the very vast
experience that we know

311
00:14:11,620 --> 00:14:13,850
as being the human experience.

312
00:14:13,850 --> 00:14:16,540
But in principle, we're
completely reconstructed

313
00:14:16,540 --> 00:14:18,780
both from these
fundamental pieces.

314
00:14:18,780 --> 00:14:20,450
And so yeah, if you
travel far enough,

315
00:14:20,450 --> 00:14:22,150
you'll eventually
find a complete repeat

316
00:14:22,150 --> 00:14:24,280
of all the matter and
energy that make us up,

317
00:14:24,280 --> 00:14:25,539
that make up humans.

318
00:14:25,539 --> 00:14:27,580
And you'll find-- yeah,
if you travel far enough,

319
00:14:27,580 --> 00:14:29,140
you'll find exact copy of you.

320
00:14:29,140 --> 00:14:30,910
You, the student
in the green shirt.

321
00:14:33,540 --> 00:14:34,320
You, yeah.

322
00:14:34,320 --> 00:14:36,730
The one that asked the question.

323
00:14:36,730 --> 00:14:39,690
And I mean, he's not really you.

324
00:14:39,690 --> 00:14:40,980
You're you.

325
00:14:40,980 --> 00:14:43,630
He's really a clone
of you, a copy of you,

326
00:14:43,630 --> 00:14:45,460
a counterpart of you.

327
00:14:45,460 --> 00:14:46,002
Yes?

328
00:14:46,002 --> 00:14:48,210
AUDIENCE: Isn't there a
chance when he finds himself,

329
00:14:48,210 --> 00:14:49,400
he might not be
wearing a green shirt

330
00:14:49,400 --> 00:14:51,765
because he might have chosen
a blue shirt or something?

331
00:14:51,765 --> 00:14:52,404
[INAUDIBLE]

332
00:14:52,404 --> 00:14:54,070
NICHOLAS DIBELLA:
Yeah, there's a chance

333
00:14:54,070 --> 00:14:55,903
that instead of wearing
a green shirt today,

334
00:14:55,903 --> 00:14:57,100
he wore blue shirt today.

335
00:14:57,100 --> 00:15:01,740
So not only will
he find the exact--

336
00:15:01,740 --> 00:15:02,470
in a second.

337
00:15:02,470 --> 00:15:05,380
Not only will he find
the exact distribution

338
00:15:05,380 --> 00:15:07,600
of matter and energy--

339
00:15:07,600 --> 00:15:10,060
I mean, if I don't find the
green shirt that's a little bit

340
00:15:10,060 --> 00:15:12,360
different, but let's say I
still find the same human.

341
00:15:12,360 --> 00:15:16,390
But not only will I find the
same distribution of matter,

342
00:15:16,390 --> 00:15:18,610
I'll also find every
single possible history

343
00:15:18,610 --> 00:15:20,980
and every single
possible future.

344
00:15:20,980 --> 00:15:25,950
Now, if I look at a air molecule
right here, sitting over here,

345
00:15:25,950 --> 00:15:28,390
and I follow its path,
it might do something.

346
00:15:28,390 --> 00:15:30,300
It might do some kind of weird--

347
00:15:30,300 --> 00:15:32,930
some kind of a
weird path and then

348
00:15:32,930 --> 00:15:35,161
eventually land
up on his glasses.

349
00:15:35,161 --> 00:15:35,660
All right.

350
00:15:35,660 --> 00:15:37,090
There might do some kind
of weird path like that

351
00:15:37,090 --> 00:15:39,070
or it could instead
of doing that, it

352
00:15:39,070 --> 00:15:44,950
could walk in this direction
and then just go into the vent.

353
00:15:44,950 --> 00:15:48,220
There are a lot
of possible paths

354
00:15:48,220 --> 00:15:50,310
that a given atom could take.

355
00:15:50,310 --> 00:15:52,960
There all possible histories
that an atom can take.

356
00:15:52,960 --> 00:15:56,170
And really, pretty much
every conceivable path

357
00:15:56,170 --> 00:15:59,780
that something can take is
possible, theoretically.

358
00:15:59,780 --> 00:16:00,700
And so for any--

359
00:16:00,700 --> 00:16:02,320
if something is
possible, then it

360
00:16:02,320 --> 00:16:04,100
will happen in an
infinite universe.

361
00:16:04,100 --> 00:16:05,851
So you can think of not just--

362
00:16:05,851 --> 00:16:07,600
I mean, it's certainly
true that an atom--

363
00:16:07,600 --> 00:16:10,160
a given atom will do infinitely
many different things

364
00:16:10,160 --> 00:16:12,701
in infinite universe, but you
can look at more complex things

365
00:16:12,701 --> 00:16:15,860
like, look at a system of five
atoms or of 10 atoms or 10

366
00:16:15,860 --> 00:16:18,680
to the 23 atoms or even more.

367
00:16:18,680 --> 00:16:21,770
And so you can look at all
the atoms to make up a person.

368
00:16:21,770 --> 00:16:24,350
So while in our
universe you decided

369
00:16:24,350 --> 00:16:26,770
to wear the green shirt
today and another universe,

370
00:16:26,770 --> 00:16:29,440
you decided to wear
a blue shirt today.

371
00:16:29,440 --> 00:16:33,461
At least your clone decided
to wear a blue shirt today.

372
00:16:33,461 --> 00:16:35,294
AUDIENCE: [INAUDIBLE]
everything is supposed

373
00:16:35,294 --> 00:16:37,246
to repeat itself [INAUDIBLE].

374
00:16:37,246 --> 00:16:39,545
But then wouldn't the
clone [INAUDIBLE]??

375
00:16:39,545 --> 00:16:40,420
NICHOLAS DIBELLA: OK.

376
00:16:40,420 --> 00:16:41,230
So yes.

377
00:16:41,230 --> 00:16:43,419
Some of your clones will
pick out the green shirts.

378
00:16:43,419 --> 00:16:45,460
Some of your clones will
pick out the blue shirt.

379
00:16:45,460 --> 00:16:47,126
It really depends on
how you define you.

380
00:16:47,126 --> 00:16:50,260
If you define you as
being you must necessarily

381
00:16:50,260 --> 00:16:53,897
wear a green shirt
on July 13, 2008,

382
00:16:53,897 --> 00:16:56,230
then obviously, those guys
that don't wear a green shirt

383
00:16:56,230 --> 00:16:58,540
aren't you or at least
they're not clones of you,

384
00:16:58,540 --> 00:16:59,740
how you define them.

385
00:16:59,740 --> 00:17:01,660
But you might define
a clone if you

386
00:17:01,660 --> 00:17:05,079
as having some kind of essential
characteristics that you share.

387
00:17:05,079 --> 00:17:06,266
For example, maybe--

388
00:17:06,266 --> 00:17:08,349
I'm not going to speculate
about your personality,

389
00:17:08,349 --> 00:17:10,319
but let's say,
you're a happy guy.

390
00:17:10,319 --> 00:17:12,579
You're a smart guy.

391
00:17:12,579 --> 00:17:15,040
You have certain idiosyncrasies.

392
00:17:15,040 --> 00:17:17,560
But there are certain
non-essential characteristics

393
00:17:17,560 --> 00:17:19,685
of you, like the shirt you
decide to wear in a day,

394
00:17:19,685 --> 00:17:22,605
but you'd still consider
it as being you.

395
00:17:22,605 --> 00:17:23,619
So yeah, clones of you--

396
00:17:23,619 --> 00:17:25,369
yeah, some of them
will wear green shirts.

397
00:17:25,369 --> 00:17:27,430
Some of them will
wear blue shirts.

398
00:17:27,430 --> 00:17:29,770
Some of them won't
wear any shirts at all,

399
00:17:29,770 --> 00:17:33,820
and then I'd have to direct you
to the office to find a shirt.

400
00:17:33,820 --> 00:17:34,780
Yes, certainly.

401
00:17:34,780 --> 00:17:35,290
Question?

402
00:17:35,290 --> 00:17:37,610
Or actually, you had
a question first.

403
00:17:37,610 --> 00:17:39,110
AUDIENCE: It was
along those lines.

404
00:17:39,110 --> 00:17:42,610
It's just if in an alternate--

405
00:17:42,610 --> 00:17:45,110
on an alternate
planet, such as ours,

406
00:17:45,110 --> 00:17:47,610
and you have the
exact same situation,

407
00:17:47,610 --> 00:17:50,610
wouldn't his mind think
in the exact same way?

408
00:17:50,610 --> 00:17:52,360
So we may see the
exact same decisions

409
00:17:52,360 --> 00:17:54,152
to wear a green shirt?

410
00:17:54,152 --> 00:17:55,110
NICHOLAS DIBELLA: Yeah.

411
00:17:55,110 --> 00:17:57,337
So the question
is if he's really

412
00:17:57,337 --> 00:17:59,420
a clone of him then wouldn't
he think the same way

413
00:17:59,420 --> 00:18:01,604
and make the same
decisions he made?

414
00:18:01,604 --> 00:18:02,270
Well, maybe not.

415
00:18:02,270 --> 00:18:04,340
I mean, very often, I'm
uncertain about what

416
00:18:04,340 --> 00:18:05,561
I should do.

417
00:18:05,561 --> 00:18:08,060
And like, should I wear this
shirt, should I wear the shirt,

418
00:18:08,060 --> 00:18:10,190
and sometimes I just kind
of randomly choose it.

419
00:18:10,190 --> 00:18:11,834
And so-- I mean,
there's a chance

420
00:18:11,834 --> 00:18:13,250
he would wear the
blue shirt, then

421
00:18:13,250 --> 00:18:15,083
in another universe he
wears the blue shirt.

422
00:18:17,677 --> 00:18:18,260
Yes, question?

423
00:18:18,260 --> 00:18:21,599
AUDIENCE: [INAUDIBLE]
repeat itself,

424
00:18:21,599 --> 00:18:23,507
if you made certain
mistakes, would you

425
00:18:23,507 --> 00:18:24,950
be able to change them?

426
00:18:24,950 --> 00:18:26,400
NICHOLAS DIBELLA: If he
made certain mistakes--

427
00:18:26,400 --> 00:18:28,140
if everything repeats itself
and you made certain mistakes,

428
00:18:28,140 --> 00:18:29,070
would you be able
to change them?

429
00:18:29,070 --> 00:18:29,695
AUDIENCE: Yeah.

430
00:18:29,695 --> 00:18:32,032
Then everything
wouldn't repeat itself

431
00:18:32,032 --> 00:18:33,490
because the situation
[INAUDIBLE]..

432
00:18:33,490 --> 00:18:35,160
NICHOLAS DIBELLA: Then
everything wouldn't what?

433
00:18:35,160 --> 00:18:36,951
AUDIENCE: Everything
wouldn't repeat itself

434
00:18:36,951 --> 00:18:39,384
because the situation would
be different, like after you

435
00:18:39,384 --> 00:18:40,880
change [INAUDIBLE].

436
00:18:40,880 --> 00:18:43,350
NICHOLAS DIBELLA: Well, what
you can do is you can travel--

437
00:18:43,350 --> 00:18:46,960
I mean, these parallel universes
are so far away from us

438
00:18:46,960 --> 00:18:49,280
that we probably wouldn't
be able to reach them

439
00:18:49,280 --> 00:18:51,430
in a billion, billion, billion--

440
00:18:51,430 --> 00:18:52,850
many lifetimes.

441
00:18:52,850 --> 00:18:55,420
But let's say you did reach
one of these parallel universes

442
00:18:55,420 --> 00:18:58,316
where there's a clone of you,
and you have the experience

443
00:18:58,316 --> 00:18:59,440
in knowing oh, he's going--

444
00:18:59,440 --> 00:19:02,179
she's going to make this
mistake, let me prevent it.

445
00:19:02,179 --> 00:19:03,970
And then you decide to
prevent this mistake

446
00:19:03,970 --> 00:19:05,899
that your clone makes.

447
00:19:05,899 --> 00:19:07,690
Well, you're not really
changing your past,

448
00:19:07,690 --> 00:19:12,460
you're changing the
future of the clone.

449
00:19:12,460 --> 00:19:17,140
I mean, in that particular
universe your past doesn't

450
00:19:17,140 --> 00:19:18,130
repeat itself.

451
00:19:18,130 --> 00:19:20,140
But if you travel
to another universe,

452
00:19:20,140 --> 00:19:21,730
you'll find someone
who does repeat

453
00:19:21,730 --> 00:19:22,900
that mistake that you made.

454
00:19:25,600 --> 00:19:29,080
But you might not really care
about these counterparts,

455
00:19:29,080 --> 00:19:30,124
these clones of yours.

456
00:19:30,124 --> 00:19:30,790
They're not you.

457
00:19:30,790 --> 00:19:31,870
I mean, I care about my past.

458
00:19:31,870 --> 00:19:32,828
I care about my future.

459
00:19:32,828 --> 00:19:34,415
I don't care about his or hers.

460
00:19:34,415 --> 00:19:35,290
AUDIENCE: [INAUDIBLE]

461
00:19:35,290 --> 00:19:36,534
NICHOLAS DIBELLA: Yeah.

462
00:19:36,534 --> 00:19:37,825
I mean, they're not really you.

463
00:19:37,825 --> 00:19:38,800
You're you.

464
00:19:38,800 --> 00:19:41,640
Those are just clones of
you that think similarly,

465
00:19:41,640 --> 00:19:43,870
but fundamentally differently.

466
00:19:43,870 --> 00:19:45,090
Yes?

467
00:19:45,090 --> 00:19:47,727
AUDIENCE: How do we know these
parallel universes exists?

468
00:19:47,727 --> 00:19:49,560
NICHOLAS DIBELLA: How
do we know they exist?

469
00:19:49,560 --> 00:19:52,620
Well, these parallel universes
are really just a prediction

470
00:19:52,620 --> 00:19:55,680
of assuming that the
universe is infinite,

471
00:19:55,680 --> 00:19:58,830
and assuming that all
possible initial conditions,

472
00:19:58,830 --> 00:20:01,350
all possible initial
arrangements of matter

473
00:20:01,350 --> 00:20:03,090
were present in the
very early universe.

474
00:20:03,090 --> 00:20:05,640
And those are two pretty
reasonably uncontroversial

475
00:20:05,640 --> 00:20:07,800
assumptions.

476
00:20:07,800 --> 00:20:11,304
Yeah, we don't know for sure
that the universe is infinite.

477
00:20:11,304 --> 00:20:12,720
We certainly know
it's very large,

478
00:20:12,720 --> 00:20:15,060
but it's totally conceivable
that the universe is infinite.

479
00:20:15,060 --> 00:20:16,476
And all the lines
of evidence seem

480
00:20:16,476 --> 00:20:19,780
to be pointing that
it is infinite.

481
00:20:19,780 --> 00:20:22,790
So the infinity assumption--

482
00:20:22,790 --> 00:20:24,240
some people don't believe it.

483
00:20:24,240 --> 00:20:28,350
Some people think that our
evidence points towards it.

484
00:20:28,350 --> 00:20:30,942
But it's reasonably
uncontroversial.

485
00:20:30,942 --> 00:20:32,400
You might be you
might be wondering

486
00:20:32,400 --> 00:20:34,150
about this other
assumption the assumption

487
00:20:34,150 --> 00:20:36,330
of all possible
initial conditions.

488
00:20:36,330 --> 00:20:40,050
That's really a
prediction of a theory

489
00:20:40,050 --> 00:20:44,785
about the variable universe that
hasn't totally been tested yet.

490
00:20:44,785 --> 00:20:45,660
It makes predictions.

491
00:20:45,660 --> 00:20:48,120
It's called-- it's a
version of inflation, which

492
00:20:48,120 --> 00:20:49,985
I was describing last time.

493
00:20:49,985 --> 00:20:51,360
It makes predictions
about things

494
00:20:51,360 --> 00:20:55,069
that we can observe like the
cosmic microwave background.

495
00:20:55,069 --> 00:20:56,610
It makes predictions
that are totally

496
00:20:56,610 --> 00:20:59,100
confirmed by the cosmic
microwave background.

497
00:20:59,100 --> 00:21:02,880
If you look at this radiation,
these microwaves that permeates

498
00:21:02,880 --> 00:21:05,370
all of space, you'll see
that the temperature is

499
00:21:05,370 --> 00:21:07,550
very uniform, pretty
much the same,

500
00:21:07,550 --> 00:21:08,742
but it changed a little bit.

501
00:21:08,742 --> 00:21:10,200
And the precise
way that it changes

502
00:21:10,200 --> 00:21:12,480
is exactly what
inflation predicts.

503
00:21:12,480 --> 00:21:16,830
And so the fact that
inflation makes predictions

504
00:21:16,830 --> 00:21:19,020
that are confirmed
in one case should

505
00:21:19,020 --> 00:21:23,190
make us at least suspect that
other predictions that it makes

506
00:21:23,190 --> 00:21:24,450
are also true.

507
00:21:24,450 --> 00:21:26,550
I mean, we don't have
to totally believe them,

508
00:21:26,550 --> 00:21:30,170
but it's totally
plausible that--

509
00:21:30,170 --> 00:21:32,620
well, this prediction of all
possible initial conditions

510
00:21:32,620 --> 00:21:33,810
in fact, true.

511
00:21:33,810 --> 00:21:36,060
And later, I'll talk about
even more predictions

512
00:21:36,060 --> 00:21:38,070
that inflation makes,
that are even stranger

513
00:21:38,070 --> 00:21:39,528
than what I'm
describing right now.

514
00:21:41,597 --> 00:21:42,180
Is that clear?

515
00:21:42,180 --> 00:21:42,990
Does that answer your question?

516
00:21:42,990 --> 00:21:43,980
AUDIENCE: Yeah.

517
00:21:43,980 --> 00:21:45,216
NICHOLAS DIBELLA: Question?

518
00:21:45,216 --> 00:21:46,680
AUDIENCE: If
everything is possible

519
00:21:46,680 --> 00:21:49,120
because there's chances of
[INAUDIBLE],, wouldn't there

520
00:21:49,120 --> 00:21:53,879
be a universe that-- parallel
universes don't exist?

521
00:21:53,879 --> 00:21:55,420
NICHOLAS DIBELLA:
Wouldn't there be--

522
00:21:55,420 --> 00:21:57,295
if everything's possible,
then wouldn't there

523
00:21:57,295 --> 00:22:00,070
be a parallel universe, such
that other parallel universes

524
00:22:00,070 --> 00:22:02,600
don't exist?

525
00:22:02,600 --> 00:22:03,100
No.

526
00:22:03,100 --> 00:22:07,240
I mean, so I have to be a
little more precise by what I

527
00:22:07,240 --> 00:22:09,290
mean by everything is possible.

528
00:22:09,290 --> 00:22:16,380
So I define occurrences as
being what matter and energy do.

529
00:22:16,380 --> 00:22:19,391
How they move, where
they are located.

530
00:22:19,391 --> 00:22:21,640
All the different possible
ways that matter and energy

531
00:22:21,640 --> 00:22:24,130
can move and be
distributed, that's

532
00:22:24,130 --> 00:22:26,410
what I define as a possibility.

533
00:22:26,410 --> 00:22:32,090
I mean, the theory says that
these parallel universes

534
00:22:32,090 --> 00:22:33,760
necessarily exist.

535
00:22:33,760 --> 00:22:37,660
I mean, it would be a
contradiction if one parallel

536
00:22:37,660 --> 00:22:41,280
universe, people don't--

537
00:22:41,280 --> 00:22:45,790
there aren't other parallel
universes parallel to that.

538
00:22:45,790 --> 00:22:47,890
Well, it's certainly
true that there

539
00:22:47,890 --> 00:22:51,250
will exist parallel
universes where there

540
00:22:51,250 --> 00:22:52,884
exist scientists like us that--

541
00:22:52,884 --> 00:22:55,300
I mean, none of them believe
in parallel universes, that's

542
00:22:55,300 --> 00:22:57,760
totally possible, but
just because somebody

543
00:22:57,760 --> 00:23:00,940
doesn't believe in something
doesn't make it false.

544
00:23:00,940 --> 00:23:04,870
So it's possible that there are
reasonably intelligent beings,

545
00:23:04,870 --> 00:23:07,559
just like us, but they haven't--

546
00:23:07,559 --> 00:23:09,850
they've been around for a
long, long time, maybe longer

547
00:23:09,850 --> 00:23:12,016
than us, and they haven't
even figured anything out.

548
00:23:12,016 --> 00:23:13,930
I mean, that's totally possible.

549
00:23:13,930 --> 00:23:14,524
Yeah?

550
00:23:14,524 --> 00:23:16,440
AUDIENCE: Wouldn't there
also be a possibility

551
00:23:16,440 --> 00:23:18,310
that humans wouldn't exist
right now in that universe?

552
00:23:18,310 --> 00:23:18,640
NICHOLAS DIBELLA: Yeah.

553
00:23:18,640 --> 00:23:20,015
There's also a
possibility humans

554
00:23:20,015 --> 00:23:21,604
don't exist in that universe.

555
00:23:21,604 --> 00:23:23,770
Yeah, I mean, you can't you
can use your imagination

556
00:23:23,770 --> 00:23:25,603
to think of a lot of
very interesting things

557
00:23:25,603 --> 00:23:26,720
that could happen.

558
00:23:26,720 --> 00:23:30,970
I mean, seemingly
magical worlds that we

559
00:23:30,970 --> 00:23:34,360
see in the movies like
the magical worlds--

560
00:23:34,360 --> 00:23:37,510
the magical world
of Harry Potter.

561
00:23:40,210 --> 00:23:44,730
If everything-- if all those
magical events that happen

562
00:23:44,730 --> 00:23:47,171
in the books can be described--

563
00:23:47,171 --> 00:23:49,420
if you can think of a physical
mechanism by which they

564
00:23:49,420 --> 00:23:51,170
can work, if you don't
postulate some kind

565
00:23:51,170 --> 00:23:52,780
of a nonphysical
thing, but if you

566
00:23:52,780 --> 00:23:55,000
try to describe them
physically and if you

567
00:23:55,000 --> 00:23:59,920
can think of a mechanism
by which they can work then

568
00:23:59,920 --> 00:24:01,810
it would totally
happen somewhere else.

569
00:24:05,660 --> 00:24:08,570
At least if you really believe
in quantum mechanics, which

570
00:24:08,570 --> 00:24:09,820
I haven't really talked about.

571
00:24:09,820 --> 00:24:11,320
If you really believe in
quantum mechanics then

572
00:24:11,320 --> 00:24:13,600
the magical world of
Harry Potter should exist.

573
00:24:13,600 --> 00:24:17,920
Star Wars, Star Trek,
all these magical worlds

574
00:24:17,920 --> 00:24:19,900
should exist somewhere.

575
00:24:19,900 --> 00:24:20,515
Yes?

576
00:24:20,515 --> 00:24:23,170
AUDIENCE: So basically, what
you mean by parallel universes

577
00:24:23,170 --> 00:24:29,295
is since space is infinite, but
matter arrangement is finite,

578
00:24:29,295 --> 00:24:34,424
there's an infinite number of
arrangements that we are on?

579
00:24:34,424 --> 00:24:35,340
NICHOLAS DIBELLA: Yes.

580
00:24:35,340 --> 00:24:37,180
So by parallel universe--

581
00:24:37,180 --> 00:24:38,830
so what I mean--

582
00:24:38,830 --> 00:24:41,230
I mean, we can define
our observed universe

583
00:24:41,230 --> 00:24:43,870
as being our universe,
and then another--

584
00:24:43,870 --> 00:24:47,560
a parallel universe
is a region of space

585
00:24:47,560 --> 00:24:49,185
equal in size to our
observed universe,

586
00:24:49,185 --> 00:24:51,768
but where things are different,
where the matter and energy is

587
00:24:51,768 --> 00:24:52,300
difference.

588
00:24:52,300 --> 00:24:54,976
Where there are no humans.

589
00:24:54,976 --> 00:24:57,100
Where there are maybe, more
humans, smarter humans,

590
00:24:57,100 --> 00:24:59,190
better humans, faster
humans, et cetera.

591
00:24:59,190 --> 00:25:02,110
Yeah, that's what I mean
by parallel universe.

592
00:25:02,110 --> 00:25:03,372
Questions?

593
00:25:03,372 --> 00:25:07,990
AUDIENCE: [INAUDIBLE]

594
00:25:07,990 --> 00:25:09,900
NICHOLAS DIBELLA: Oh, OK.

595
00:25:09,900 --> 00:25:11,440
OK.

596
00:25:11,440 --> 00:25:17,890
So as I said, these very
strange parallel worlds

597
00:25:17,890 --> 00:25:21,130
are really the result of two
reasonably uncontroversial

598
00:25:21,130 --> 00:25:22,600
assumptions.

599
00:25:22,600 --> 00:25:26,780
And so it's quite amazing that
these predictions would happen,

600
00:25:26,780 --> 00:25:27,970
but they do.

601
00:25:27,970 --> 00:25:33,820
And actually, we call this whole
ensemble of parallel universes,

602
00:25:33,820 --> 00:25:37,750
as I've described them, we
call them level one multiverse.

603
00:25:37,750 --> 00:25:40,280
We come up with a
better name, multiverse.

604
00:25:40,280 --> 00:25:42,575
So this whole thing is
a level and multiverse.

605
00:25:54,724 --> 00:25:56,890
Any final questions before
I move onto the level two

606
00:25:56,890 --> 00:25:57,550
multiverse?

607
00:26:00,460 --> 00:26:01,970
OK.

608
00:26:01,970 --> 00:26:03,880
The level 2 multiverse--

609
00:26:03,880 --> 00:26:05,860
AUDIENCE: Can I go
to the bathroom?

610
00:26:05,860 --> 00:26:07,740
NICHOLAS DIBELLA: Oh, let's see.

611
00:26:07,740 --> 00:26:10,150
I mean, yeah, you can
certainly go to the bathroom.

612
00:26:10,150 --> 00:26:12,954
I was going to have a
break in about 15 minutes.

613
00:26:12,954 --> 00:26:13,495
AUDIENCE: OK.

614
00:26:13,495 --> 00:26:15,416
I'll wait.

615
00:26:15,416 --> 00:26:16,290
NICHOLAS DIBELLA: OK.

616
00:26:16,290 --> 00:26:18,820
We can have a break
now, but there won't--

617
00:26:18,820 --> 00:26:20,540
well, we have a five
minute break now,

618
00:26:20,540 --> 00:26:22,998
but there won't be another
break for the rest of the class.

619
00:26:22,998 --> 00:26:25,209
AUDIENCE: No, I'd rather
have a 15-minute break.

620
00:26:25,209 --> 00:26:27,500
NICHOLAS DIBELLA: No, there
won't be a 15-minute break.

621
00:26:27,500 --> 00:26:30,270
There will be a
five minute break.

622
00:26:30,270 --> 00:26:33,965
I was planning on having a five
minute break in 15 minutes.

623
00:26:33,965 --> 00:26:35,360
AUDIENCE: Oh.

624
00:26:35,360 --> 00:26:36,755
[INAUDIBLE]

625
00:26:36,755 --> 00:26:38,051
NICHOLAS DIBELLA: You sure?

626
00:26:38,051 --> 00:26:38,502
AUDIENCE: Yeah.

627
00:26:38,502 --> 00:26:39,377
NICHOLAS DIBELLA: OK.

628
00:26:42,170 --> 00:26:56,420
Onto the level to multi-verse
The level one multi-verse

629
00:26:56,420 --> 00:26:59,810
certainly sounds strange with
all these parallel people,

630
00:26:59,810 --> 00:27:02,390
these parallel magical
worlds and places

631
00:27:02,390 --> 00:27:04,675
where really good
things happens to me,

632
00:27:04,675 --> 00:27:06,800
really bad things happens
to me, really good things

633
00:27:06,800 --> 00:27:08,360
happen to you, and so forth.

634
00:27:08,360 --> 00:27:11,040
Certainly sounds strange that
these things could exist,

635
00:27:11,040 --> 00:27:12,860
but the level two
multi-verse, you actually

636
00:27:12,860 --> 00:27:17,000
have universes
just like our own,

637
00:27:17,000 --> 00:27:22,940
but the very constants
of nature are different.

638
00:27:22,940 --> 00:27:27,020
Things like the speed of light.

639
00:27:27,020 --> 00:27:29,490
Things like the mass
of the electron.

640
00:27:29,490 --> 00:27:31,009
The mass of a proton.

641
00:27:31,009 --> 00:27:32,300
The number of space dimensions.

642
00:27:32,300 --> 00:27:34,490
The number of time dimensions.

643
00:27:34,490 --> 00:27:37,080
And parallel level
two universes,

644
00:27:37,080 --> 00:27:39,500
they are universes that
have different [INAUDIBLE],,

645
00:27:39,500 --> 00:27:41,930
different constants,
different speeds of light.

646
00:27:41,930 --> 00:27:43,430
So I'll write some examples.

647
00:27:43,430 --> 00:27:44,601
It's a different--

648
00:27:56,160 --> 00:27:58,140
In our universe,
the speed of light

649
00:27:58,140 --> 00:28:03,940
is 299,790,458
meters per second.

650
00:28:03,940 --> 00:28:07,380
It's good to know
that for parties.

651
00:28:07,380 --> 00:28:09,060
But in other universes,
you can conceive

652
00:28:09,060 --> 00:28:11,400
of the speed of
light being something

653
00:28:11,400 --> 00:28:13,560
like 25 miles per hour.

654
00:28:13,560 --> 00:28:15,169
That's certainly possible.

655
00:28:15,169 --> 00:28:17,210
You can also have different
mass of the electron.

656
00:28:26,900 --> 00:28:28,650
The abbreviation for electron.

657
00:28:28,650 --> 00:28:31,590
I mean, in this universe,
it's about 9.1 times 10

658
00:28:31,590 --> 00:28:34,000
to the minus 31 kilograms,
but in another universe,

659
00:28:34,000 --> 00:28:36,950
it might be something
like 30 pounds.

660
00:28:36,950 --> 00:28:37,450
Who knows?

661
00:28:40,140 --> 00:28:43,060
You could also have, as
I said, different number

662
00:28:43,060 --> 00:28:47,078
of dimensions of space and time,
different dimensionalities.

663
00:29:04,964 --> 00:29:07,380
I know we're all familiar with
the three space dimensions.

664
00:29:07,380 --> 00:29:13,370
I mean, we can move forward
and backwards, left and right,

665
00:29:13,370 --> 00:29:15,500
and down and up.

666
00:29:15,500 --> 00:29:18,530
We're all familiar with three
space dimensions, and the one

667
00:29:18,530 --> 00:29:20,600
time dimension that
just moves forward.

668
00:29:20,600 --> 00:29:25,220
I mean, I just look at my
watch or my cell phone,

669
00:29:25,220 --> 00:29:26,510
time marches on.

670
00:29:26,510 --> 00:29:28,630
So one time dimension.

671
00:29:28,630 --> 00:29:31,760
But other universes you can
actually have different space

672
00:29:31,760 --> 00:29:32,930
time dimensionalities.

673
00:29:32,930 --> 00:29:35,060
Different from three plus one.

674
00:29:35,060 --> 00:29:36,570
You had a question?

675
00:29:36,570 --> 00:29:39,720
AUDIENCE: I was wondering if in
parallel universes if possible,

676
00:29:39,720 --> 00:29:42,040
that the universe was made
at different [INAUDIBLE]..

677
00:29:42,040 --> 00:29:43,415
NICHOLAS DIBELLA:
Was made, what?

678
00:29:43,415 --> 00:29:46,282
AUDIENCE: You know, we
think that the universe

679
00:29:46,282 --> 00:29:47,728
was made by [INAUDIBLE].

680
00:29:47,728 --> 00:29:51,102
Is it possible that in another
universe that, that universe

681
00:29:51,102 --> 00:29:55,186
was made in a different way?

682
00:29:55,186 --> 00:29:57,060
NICHOLAS DIBELLA: So
that's really a matter--

683
00:29:57,060 --> 00:29:58,130
so the question
is, is it possible

684
00:29:58,130 --> 00:29:59,740
that in other
universes, the universe

685
00:29:59,740 --> 00:30:02,190
was made in a different way.

686
00:30:02,190 --> 00:30:06,580
So it's really a matter of
how you're defining universe.

687
00:30:06,580 --> 00:30:09,960
I'll describe how these universe
come about in a little bit.

688
00:30:09,960 --> 00:30:13,310
Actually, let me just describe
how these universes come about,

689
00:30:13,310 --> 00:30:15,220
then I'll come back
to your question.

690
00:30:15,220 --> 00:30:16,670
OK.

691
00:30:16,670 --> 00:30:19,790
So these things
sound crazy, right?

692
00:30:19,790 --> 00:30:22,610
So why should we
even believe them?

693
00:30:22,610 --> 00:30:27,070
Because there are
predictions of this model.

694
00:30:27,070 --> 00:30:28,910
A particular version
of inflationary theory,

695
00:30:28,910 --> 00:30:33,040
that I mentioned before, called
chaotic eternal inflation.

696
00:30:33,040 --> 00:30:34,040
I'll just write it down.

697
00:30:39,500 --> 00:30:42,964
[INAUDIBLE] Prediction of--

698
00:31:07,690 --> 00:31:14,760
And this is probably the best--

699
00:31:14,760 --> 00:31:16,500
there's so many
versions of inflation,

700
00:31:16,500 --> 00:31:18,430
but this certainly looks
the most promising.

701
00:31:21,110 --> 00:31:25,660
And so I was talking about the
microwave background, the way

702
00:31:25,660 --> 00:31:27,220
it has these fluctuations.

703
00:31:27,220 --> 00:31:29,980
It has these slight
deviations in uniformity.

704
00:31:29,980 --> 00:31:36,880
And this kind of inflation can
exactly explain that deviation

705
00:31:36,880 --> 00:31:39,760
from uniformity.

706
00:31:39,760 --> 00:31:41,830
With inflation, you
can also explain

707
00:31:41,830 --> 00:31:45,070
why the universe is flat.

708
00:31:45,070 --> 00:31:47,770
I mean, I mentioned last time
that the observation seems

709
00:31:47,770 --> 00:31:49,540
to indicate that the
universe is flat,

710
00:31:49,540 --> 00:31:51,331
but you might still be
scratching your head

711
00:31:51,331 --> 00:31:53,080
and wondering well,
why is it flat?

712
00:31:53,080 --> 00:31:54,920
I mean, why did that
have to be the case?

713
00:31:54,920 --> 00:31:57,190
Inflation provides an answer.

714
00:31:57,190 --> 00:32:01,730
It also provides an answer as to
why the universe is so uniform.

715
00:32:01,730 --> 00:32:03,880
It explains this
cosmological principle

716
00:32:03,880 --> 00:32:06,160
that I talked about
last time, where

717
00:32:06,160 --> 00:32:07,980
the universe is really boring.

718
00:32:07,980 --> 00:32:10,480
You just travel and you see
a galaxy here, see a galaxy

719
00:32:10,480 --> 00:32:11,380
there.

720
00:32:11,380 --> 00:32:12,310
Things don't really
change very much.

721
00:32:12,310 --> 00:32:14,226
The density doesn't
really change a whole lot.

722
00:32:14,226 --> 00:32:17,420
So inflation can also explain
the uniformity of the universe.

723
00:32:17,420 --> 00:32:21,490
It can also explain
some other things like,

724
00:32:21,490 --> 00:32:23,020
why there are no
magnetic monopoles,

725
00:32:23,020 --> 00:32:24,690
if you've heard of that.

726
00:32:24,690 --> 00:32:25,648
Yes, question?

727
00:32:25,648 --> 00:32:27,148
AUDIENCE: When you
said, [INAUDIBLE]

728
00:32:27,148 --> 00:32:31,576
why is the universe
[INAUDIBLE] earth is so flat.

729
00:32:31,576 --> 00:32:33,052
You said [INAUDIBLE].

730
00:32:33,052 --> 00:32:36,990
It's also because
of the gravity.

731
00:32:36,990 --> 00:32:38,785
NICHOLAS DIBELLA: Why
is the earth so flat?

732
00:32:38,785 --> 00:32:40,270
AUDIENCE: You said, why
the earth is so flat?

733
00:32:40,270 --> 00:32:41,311
NICHOLAS DIBELLA: No, no.

734
00:32:41,311 --> 00:32:43,288
Why is the universe so flat?

735
00:32:43,288 --> 00:32:44,122
AUDIENCE: Oh, sorry.

736
00:32:44,122 --> 00:32:45,246
NICHOLAS DIBELLA: Oh, yeah.

737
00:32:45,246 --> 00:32:47,039
I mean, but it's all
related to gravity.

738
00:32:47,039 --> 00:32:48,580
I mean, these all
come from theories.

739
00:32:48,580 --> 00:32:51,040
All these predictions
are theories of gravity,

740
00:32:51,040 --> 00:32:51,912
essentially.

741
00:32:54,160 --> 00:32:54,660
Yeah.

742
00:32:57,110 --> 00:32:57,610
Right.

743
00:32:57,610 --> 00:33:01,780
So inflation can explain a lot
of features about our world

744
00:33:01,780 --> 00:33:05,830
and things that we
observe, but also makes

745
00:33:05,830 --> 00:33:07,960
interesting predictions.

746
00:33:07,960 --> 00:33:08,650
Hello.

747
00:33:08,650 --> 00:33:10,316
They also makes
interesting predictions.

748
00:33:10,316 --> 00:33:14,650
Like, it predicts the existence
of these parallel universes.

749
00:33:14,650 --> 00:33:16,840
So it's-- I'll just
describe, very briefly,

750
00:33:16,840 --> 00:33:19,990
how these universes come about.

751
00:33:19,990 --> 00:33:23,350
So in this chaotic
eternal inflation,

752
00:33:23,350 --> 00:33:26,500
the universe is infinite
and it's expanding,

753
00:33:26,500 --> 00:33:29,420
and it's going to continue
expanding forever,

754
00:33:29,420 --> 00:33:30,670
but there are some--

755
00:33:30,670 --> 00:33:32,540
so let's say, this is
the whole universe.

756
00:33:32,540 --> 00:33:38,770
But there is some patches, some
pockets that eventually form.

757
00:33:38,770 --> 00:33:44,440
Some pocket universes
that you actually form,

758
00:33:44,440 --> 00:33:48,470
and that stop expanding,
and when these pockets--

759
00:33:48,470 --> 00:33:54,970
the forming of these pockets are
really big bangs in themselves.

760
00:33:54,970 --> 00:33:57,310
You get these really
weird particles

761
00:33:57,310 --> 00:34:00,250
that I was describing before
that have repulsive gravity,

762
00:34:00,250 --> 00:34:03,670
and they form these
pockets and when

763
00:34:03,670 --> 00:34:05,922
this happens, when these
pockets form-- well,

764
00:34:05,922 --> 00:34:06,880
we call them universes.

765
00:34:06,880 --> 00:34:08,940
We call these pocket universes.

766
00:34:08,940 --> 00:34:12,280
And so this is really how we
define a universe in the level

767
00:34:12,280 --> 00:34:13,550
two multiverse.

768
00:34:13,550 --> 00:34:16,900
So I mean, if you're talking
about a pocket that formed,

769
00:34:16,900 --> 00:34:18,670
then that's a universe.

770
00:34:18,670 --> 00:34:20,770
And these pockets form--

771
00:34:20,770 --> 00:34:26,960
the way they form is by
a big bang kind of thing.

772
00:34:26,960 --> 00:34:29,110
And so it's really
kind of by definition

773
00:34:29,110 --> 00:34:31,659
that universes have
formed by big bang.

774
00:34:31,659 --> 00:34:34,600
I mean, you can ask
questions about the space

775
00:34:34,600 --> 00:34:37,270
in between these universes.

776
00:34:37,270 --> 00:34:39,790
Obviously, no big
bangs happened there,

777
00:34:39,790 --> 00:34:41,739
but they could happen there.

778
00:34:41,739 --> 00:34:43,830
You can call those
universes if you want,

779
00:34:43,830 --> 00:34:46,900
but they would be completely
devoid of observers

780
00:34:46,900 --> 00:34:48,110
and intelligent life.

781
00:34:48,110 --> 00:34:52,550
And so no one would be there
to call it the universe.

782
00:34:52,550 --> 00:34:56,170
So these pockets form and it's
really like a random process

783
00:34:56,170 --> 00:34:58,880
that they form.

784
00:34:58,880 --> 00:35:01,560
I mean, I'll talk more
about quantum mechanics

785
00:35:01,560 --> 00:35:04,180
in a little bit, and even
more in another lecture,

786
00:35:04,180 --> 00:35:07,630
but it's really fluctuations,
quantum fluctuations

787
00:35:07,630 --> 00:35:10,670
that give rise to the
existence of these pockets,

788
00:35:10,670 --> 00:35:12,730
these bubbles.

789
00:35:12,730 --> 00:35:14,680
And so occasionally,
you'll get a bubble

790
00:35:14,680 --> 00:35:19,192
that forms and that's
really our universe.

791
00:35:19,192 --> 00:35:20,650
Our universe formed
by the creation

792
00:35:20,650 --> 00:35:22,720
of one of these bubbles.

793
00:35:22,720 --> 00:35:27,610
And when these bubbles form,
a process occurs called--

794
00:35:27,610 --> 00:35:28,892
oh, let's see.

795
00:35:28,892 --> 00:35:29,850
Oh, I'll just tell you.

796
00:35:29,850 --> 00:35:31,430
It's called symmetry breaking.

797
00:35:31,430 --> 00:35:34,335
A process occurs called,
symmetry breaking.

798
00:35:34,335 --> 00:35:36,460
But you can't really go
into a lot of detail about,

799
00:35:36,460 --> 00:35:39,670
but when this process occurs,
each one of these bubbles

800
00:35:39,670 --> 00:35:42,670
is endowed with its own
set of physical constants.

801
00:35:42,670 --> 00:35:43,990
It's own mass of electrons.

802
00:35:43,990 --> 00:35:44,989
It's own speed of light.

803
00:35:44,989 --> 00:35:47,860
It's own space time
dimensionality.

804
00:35:47,860 --> 00:35:50,410
And so you have an infinite
number of universes forming.

805
00:35:50,410 --> 00:35:51,910
These are really--
each one of these

806
00:35:51,910 --> 00:35:54,910
is really-- it's really
level one multiverse.

807
00:35:54,910 --> 00:35:57,160
So the level two
multiverse consists

808
00:35:57,160 --> 00:36:02,110
of an infinite ensemble
of level one multiverses,

809
00:36:02,110 --> 00:36:04,930
and each one has its
own set of constants.

810
00:36:04,930 --> 00:36:10,210
So some will form with three
space dimensions and one time

811
00:36:10,210 --> 00:36:11,280
dimension.

812
00:36:11,280 --> 00:36:14,640
The electron mass will be the
same mass that we have here.

813
00:36:14,640 --> 00:36:17,170
Speed of light will be the speed
of light that we have here.

814
00:36:17,170 --> 00:36:19,620
And the universe would
be just as we observe it.

815
00:36:19,620 --> 00:36:23,560
But in others, you'll get maybe
five space dimensions in, four

816
00:36:23,560 --> 00:36:25,630
time dimensions
and others, you'll

817
00:36:25,630 --> 00:36:29,350
get maybe a 25 mile per
hour speed of light.

818
00:36:29,350 --> 00:36:30,200
They'll happen.

819
00:36:30,200 --> 00:36:32,200
There's some kind
of distribution

820
00:36:32,200 --> 00:36:34,850
of all these
different constants,

821
00:36:34,850 --> 00:36:37,900
some kind of distribution of
all these physical parameters.

822
00:36:37,900 --> 00:36:38,686
Yes?

823
00:36:38,686 --> 00:36:43,510
AUDIENCE: [INAUDIBLE] like a
different dimensional space

824
00:36:43,510 --> 00:36:44,480
dimensions.

825
00:36:44,480 --> 00:36:47,530
How would time dimensions work?

826
00:36:47,530 --> 00:36:51,880
NICHOLAS DIBELLA: How would
different time dimensions work?

827
00:36:51,880 --> 00:36:55,720
Well, it's hard to imagine
what it would be like.

828
00:36:55,720 --> 00:36:59,590
We observe change
in one direction.

829
00:36:59,590 --> 00:37:02,650
So it's kind of hard to imagine
intuitively how it would work,

830
00:37:02,650 --> 00:37:05,530
but you can certainly
work out the consequences

831
00:37:05,530 --> 00:37:07,797
by looking at your
equations and adding

832
00:37:07,797 --> 00:37:09,880
in another extra dimension,
adding in another time

833
00:37:09,880 --> 00:37:11,527
dimension and
seeing what happens.

834
00:37:11,527 --> 00:37:12,610
You can certainly do that.

835
00:37:12,610 --> 00:37:13,990
It's easy to change
the equations

836
00:37:13,990 --> 00:37:16,570
and try to understand
mathematically

837
00:37:16,570 --> 00:37:19,540
what a universe with extra
space dimension or extra time

838
00:37:19,540 --> 00:37:20,620
dimension is.

839
00:37:20,620 --> 00:37:23,120
But it turns out that if
you make these changes,

840
00:37:23,120 --> 00:37:23,887
if you change--

841
00:37:23,887 --> 00:37:25,720
if you tweak the number
of space dimensions,

842
00:37:25,720 --> 00:37:27,740
and you tweak the number
of time dimensions,

843
00:37:27,740 --> 00:37:29,910
it turns out that
the combination

844
00:37:29,910 --> 00:37:32,970
that we live in today, three
space dimensions and one time

845
00:37:32,970 --> 00:37:35,490
dimension is the only
combination that's

846
00:37:35,490 --> 00:37:38,270
suitable for intelligent life.

847
00:37:38,270 --> 00:37:42,080
It turns out-- let's see,
I had something written.

848
00:37:42,080 --> 00:37:42,580
Oh, yeah.

849
00:37:42,580 --> 00:37:45,880
So yeah, if you live in a
world with five space dimension

850
00:37:45,880 --> 00:37:49,184
and four time dimensions for
example, atoms couldn't exist.

851
00:37:49,184 --> 00:37:50,850
You can just work
through the equations.

852
00:37:50,850 --> 00:37:51,480
Atoms couldn't exist.

853
00:37:51,480 --> 00:37:53,070
They would be
completely unstable.

854
00:37:53,070 --> 00:37:56,070
They would decay
in a split second.

855
00:37:56,070 --> 00:38:00,000
If you had one extra
time dimension,

856
00:38:00,000 --> 00:38:02,760
events would be
completely unpredictable.

857
00:38:02,760 --> 00:38:04,920
And when we do
experiments, we always

858
00:38:04,920 --> 00:38:08,100
have some kind of an arrow
bar, some kind of uncertainty

859
00:38:08,100 --> 00:38:09,190
attached to them.

860
00:38:09,190 --> 00:38:11,100
Well, if you had
more time dimensions,

861
00:38:11,100 --> 00:38:13,359
then the arrow bar
would become infinite.

862
00:38:13,359 --> 00:38:14,900
So you couldn't make
any predictions.

863
00:38:14,900 --> 00:38:17,420
The world would be
completely unpredictable.

864
00:38:17,420 --> 00:38:19,080
And you can also
think about what

865
00:38:19,080 --> 00:38:21,000
would happen if the
electromagnetic force was

866
00:38:21,000 --> 00:38:22,200
stronger than--

867
00:38:22,200 --> 00:38:24,150
was stronger than nuclear
force, for example.

868
00:38:24,150 --> 00:38:27,240
And it could work
what happened, carbon

869
00:38:27,240 --> 00:38:28,630
would be unstable, for example.

870
00:38:32,030 --> 00:38:35,330
And so are our universe
seems to be really--

871
00:38:35,330 --> 00:38:38,460
seems to be magically
fine tuned--

872
00:38:38,460 --> 00:38:41,020
magically fit for life to form.

873
00:38:41,020 --> 00:38:43,470
AUDIENCE: Maybe we were
created as a backup.

874
00:38:43,470 --> 00:38:47,337
NICHOLAS DIBELLA: Maybe we were
created so that we could exist.

875
00:38:47,337 --> 00:38:49,549
AUDIENCE: Like, maybe we
were created because-- like,

876
00:38:49,549 --> 00:38:51,840
this universe was the only
one that could support life.

877
00:38:51,840 --> 00:38:52,964
NICHOLAS DIBELLA: Oh, yeah.

878
00:38:52,964 --> 00:38:54,480
Yeah.

879
00:38:54,480 --> 00:38:57,090
So people were puzzled
by this for a long time.

880
00:38:57,090 --> 00:38:59,820
So why do we three
space dimensions

881
00:38:59,820 --> 00:39:00,750
or one tiny dimension?

882
00:39:00,750 --> 00:39:02,458
Why is this-- why does
this be like this?

883
00:39:02,458 --> 00:39:04,770
Why is the mass of electron
this, and so forth?

884
00:39:04,770 --> 00:39:06,630
People are puzzled by
this for a long time.

885
00:39:06,630 --> 00:39:08,880
Well, the chaotic
eternal inflation

886
00:39:08,880 --> 00:39:11,160
provides any answer for it.

887
00:39:11,160 --> 00:39:13,800
Universes with other
constants and dimensionalities

888
00:39:13,800 --> 00:39:16,950
do exist, they do form, but
in those universes you just

889
00:39:16,950 --> 00:39:18,380
don't have intelligent life.

890
00:39:18,380 --> 00:39:19,890
Or you don't have stable system.

891
00:39:19,890 --> 00:39:21,600
You don't have complexity.

892
00:39:21,600 --> 00:39:24,560
They're baron, their
dead, basically.

893
00:39:24,560 --> 00:39:28,020
And so we shouldn't be surprised
to find ourself in a universe

894
00:39:28,020 --> 00:39:28,770
where we exist.

895
00:39:28,770 --> 00:39:30,186
I mean, obviously,
we shouldn't be

896
00:39:30,186 --> 00:39:31,980
surprised to find
ourself in a universe

897
00:39:31,980 --> 00:39:34,410
where we exist because we exist.

898
00:39:34,410 --> 00:39:35,940
Yeah, we just look at ourselves.

899
00:39:35,940 --> 00:39:37,840
But we also shouldn't be
surprised to find ourselves

900
00:39:37,840 --> 00:39:40,048
in a universe with three
space dimension and one time

901
00:39:40,048 --> 00:39:41,360
dimension.

902
00:39:41,360 --> 00:39:44,239
As for the other constants--

903
00:39:44,239 --> 00:39:46,030
and the other constant
like speed of light,

904
00:39:46,030 --> 00:39:51,540
mass the electron,
it's a little unclear

905
00:39:51,540 --> 00:39:53,190
what different
combinations would

906
00:39:53,190 --> 00:39:57,690
be able to support intelligent
life and complexity,

907
00:39:57,690 --> 00:39:59,100
and so forth.

908
00:39:59,100 --> 00:40:03,510
But we certainly might be
able to answer these questions

909
00:40:03,510 --> 00:40:06,000
by just looking
at a distribution

910
00:40:06,000 --> 00:40:09,150
of different constants
and whatever,

911
00:40:09,150 --> 00:40:12,960
and say, well, the ones
that can support life,

912
00:40:12,960 --> 00:40:14,784
the ones that can
support observers,

913
00:40:14,784 --> 00:40:16,200
would be ones that
we shouldn't be

914
00:40:16,200 --> 00:40:17,820
surprised to find ourselves in.

915
00:40:17,820 --> 00:40:19,080
So the hope is that--

916
00:40:19,080 --> 00:40:21,030
I mean, so this is
actually a testable theory.

917
00:40:21,030 --> 00:40:22,770
The hope is that
if we actually form

918
00:40:22,770 --> 00:40:25,150
this distribution of
constants and dimensionalities

919
00:40:25,150 --> 00:40:27,930
and everything, the hope is
that we would find ourselves

920
00:40:27,930 --> 00:40:32,370
in a universe that is
consistent with our existence

921
00:40:32,370 --> 00:40:34,770
and that is typical
among members

922
00:40:34,770 --> 00:40:37,800
that have constants and
dimensionalities that

923
00:40:37,800 --> 00:40:39,220
can support life.

924
00:40:39,220 --> 00:40:42,630
So if we find ourselves
in a universe that

925
00:40:42,630 --> 00:40:44,490
isn't typical among
these universes that

926
00:40:44,490 --> 00:40:47,610
can support life,
then that would

927
00:40:47,610 --> 00:40:49,740
be a defect of the theory.

928
00:40:49,740 --> 00:40:53,790
So it actually has
predictive power.

929
00:40:53,790 --> 00:40:55,625
Well, it's actually,
it's falsifiable.

930
00:40:55,625 --> 00:40:57,000
I mean, it predicts
the existence

931
00:40:57,000 --> 00:41:00,820
of these other universes,
and also predicts

932
00:41:00,820 --> 00:41:03,399
that the universe should be
flat, and so on and so forth,

933
00:41:03,399 --> 00:41:05,940
but these other universes are
so far away that we really have

934
00:41:05,940 --> 00:41:08,249
no hope of ever observing them.

935
00:41:08,249 --> 00:41:09,540
But it's certainly falsifiable.

936
00:41:09,540 --> 00:41:11,370
The theory is
certainly falsifiable.

937
00:41:11,370 --> 00:41:13,740
And one way that
people often define

938
00:41:13,740 --> 00:41:16,620
science, a scientific theory, is
that it has to be falsifiable,

939
00:41:16,620 --> 00:41:19,920
that you can do an experiment
or you can do an observation

940
00:41:19,920 --> 00:41:22,050
that, if it
contradicted the theory,

941
00:41:22,050 --> 00:41:25,050
would automatically say,
the theory is false.

942
00:41:25,050 --> 00:41:27,300
And that's true of this theory.

943
00:41:27,300 --> 00:41:29,010
It's possible that it's false.

944
00:41:29,010 --> 00:41:33,300
And we can test it by working
through these distributions

945
00:41:33,300 --> 00:41:36,749
and seeing if our universe
is a typical member.

946
00:41:36,749 --> 00:41:37,790
And people working on it,

947
00:41:37,790 --> 00:41:38,640
Don't know the answer.

948
00:41:38,640 --> 00:41:39,681
People are working on it.

949
00:41:39,681 --> 00:41:40,680
So it's unknown.

950
00:41:44,240 --> 00:41:49,020
And there are actually
a lot of people that

951
00:41:49,020 --> 00:41:51,020
really don't like the solution.

952
00:41:51,020 --> 00:41:52,260
I mean, we explain--

953
00:41:52,260 --> 00:41:56,130
I mean, chaotic eternal
inflation explains away

954
00:41:56,130 --> 00:41:58,200
previously puzzling
facts about our universe

955
00:41:58,200 --> 00:42:02,970
by saying that these features
of our universe like,

956
00:42:02,970 --> 00:42:07,230
speed of light, and so forth,
they were just randomly created

957
00:42:07,230 --> 00:42:08,460
without any real cause.

958
00:42:08,460 --> 00:42:10,350
They're just randomly created.

959
00:42:10,350 --> 00:42:12,400
But a lot of people are
unsatisfied by this.

960
00:42:12,400 --> 00:42:14,780
They think it's
kind of a cop out.

961
00:42:14,780 --> 00:42:17,340
Many people feel
that we should be

962
00:42:17,340 --> 00:42:18,990
able to derive
these things like,

963
00:42:18,990 --> 00:42:21,630
three space dimensions and one
time dimension, and so forth,

964
00:42:21,630 --> 00:42:23,040
from fundamental principles.

965
00:42:23,040 --> 00:42:26,160
A lot of people think we
should able to drive it.

966
00:42:26,160 --> 00:42:28,305
But we're having a hard
time deriving them.

967
00:42:28,305 --> 00:42:31,540
And currently, it looks
like the multiverse--

968
00:42:31,540 --> 00:42:35,040
these multiverse theories offer
the best hope of explaining it.

969
00:42:35,040 --> 00:42:37,010
But it's certainly
possible that it

970
00:42:37,010 --> 00:42:40,780
could be derivable in principle
from fundamental principles,

971
00:42:40,780 --> 00:42:42,260
but we don't know.

972
00:42:42,260 --> 00:42:47,470
But inflation certainly
offers an answer.

973
00:42:47,470 --> 00:42:48,200
OK.

974
00:42:48,200 --> 00:42:52,410
Are there any questions about
the level two multiverse?

975
00:42:52,410 --> 00:42:53,060
OK.

976
00:42:53,060 --> 00:42:56,740
So just described the
level two multiverse,

977
00:42:56,740 --> 00:42:59,860
and now we're going to march
forward onto the level three

978
00:42:59,860 --> 00:43:00,852
multiverse.

979
00:43:13,880 --> 00:43:16,710
And this is a prediction of
the so-called many worlds

980
00:43:16,710 --> 00:43:19,890
interpretation of
quantum mechanics.

981
00:43:19,890 --> 00:43:21,240
So a prediction of many worlds.

982
00:43:37,820 --> 00:43:40,850
Quantum mechanics,
is a theory that

983
00:43:40,850 --> 00:43:44,810
was developed in
the 1920s and it's

984
00:43:44,810 --> 00:43:49,410
been enormously successful in
the describing the very small.

985
00:43:49,410 --> 00:43:51,200
In fact, it's one
of the two most

986
00:43:51,200 --> 00:43:55,070
successful physical
theories ever proposed.

987
00:43:55,070 --> 00:44:00,690
The other I talked about last
time was general relativity.

988
00:44:00,690 --> 00:44:03,050
Now, we've only tested
quantum mechanics

989
00:44:03,050 --> 00:44:08,000
on small things like molecules
and atoms and electrons,

990
00:44:08,000 --> 00:44:11,900
but it's certainly
believable, reasonable

991
00:44:11,900 --> 00:44:15,890
to think that quantum mechanics
applies to bigger objects.

992
00:44:15,890 --> 00:44:19,087
After all, bigger objects are
made of smaller objects, right?

993
00:44:19,087 --> 00:44:20,670
I mean, I'm made up
of a lot of atoms.

994
00:44:20,670 --> 00:44:22,564
This table is made
up of a lot of atoms.

995
00:44:22,564 --> 00:44:24,230
And each of these
atoms can be described

996
00:44:24,230 --> 00:44:25,661
using quantum mechanics.

997
00:44:28,310 --> 00:44:32,924
And so it's reasonable to think
that pretty much every system

998
00:44:32,924 --> 00:44:34,340
is described by
quantum mechanics,

999
00:44:34,340 --> 00:44:35,975
including the universe itself.

1000
00:44:39,670 --> 00:44:53,030
So many worlds interpretation
of quantum mechanics.

1001
00:44:59,990 --> 00:45:01,250
OK.

1002
00:45:01,250 --> 00:45:04,400
In quantum mechanics, there
is a fundamental randomness

1003
00:45:04,400 --> 00:45:04,910
to nature.

1004
00:45:07,622 --> 00:45:09,080
According to quantum
mechanics, you

1005
00:45:09,080 --> 00:45:15,020
don't know for sure what you'll
get as a result of experiments.

1006
00:45:15,020 --> 00:45:18,707
For example, if you measured
the position of an electron,

1007
00:45:18,707 --> 00:45:21,290
you don't know if you'll find
it to be here, or here, or here,

1008
00:45:21,290 --> 00:45:25,410
or here, or so forth.

1009
00:45:25,410 --> 00:45:29,337
Well, there are some
things that we know,

1010
00:45:29,337 --> 00:45:31,670
some things that we can predict
with a reasonable degree

1011
00:45:31,670 --> 00:45:35,780
of certainty like, if I drop
this chalk it will probably

1012
00:45:35,780 --> 00:45:36,330
fall.

1013
00:45:36,330 --> 00:45:36,990
It did.

1014
00:45:36,990 --> 00:45:39,170
That proves quantum mechanics.

1015
00:45:39,170 --> 00:45:40,930
But in general, you
don't know for sure

1016
00:45:40,930 --> 00:45:42,650
what you'll get
in an experiment.

1017
00:45:42,650 --> 00:45:44,108
You don't know for
sure what you'll

1018
00:45:44,108 --> 00:45:46,100
get when you measure something.

1019
00:45:46,100 --> 00:45:49,520
Now, we have a tool
in quantum mechanics

1020
00:45:49,520 --> 00:45:52,880
to help us calculate the
probabilities, and it's called,

1021
00:45:52,880 --> 00:45:53,630
the wave function.

1022
00:46:02,210 --> 00:46:05,180
And this wave function
tells us the probability

1023
00:46:05,180 --> 00:46:08,480
of observing certain things.

1024
00:46:08,480 --> 00:46:10,730
Probability of observing
a certain speed

1025
00:46:10,730 --> 00:46:14,430
of an electron or [INAUDIBLE]
principal of a person,

1026
00:46:14,430 --> 00:46:15,155
and so forth.

1027
00:46:15,155 --> 00:46:17,780
But it's hard to do experiments,
quantum mechanical experiments

1028
00:46:17,780 --> 00:46:20,780
with people and larger objects.

1029
00:46:20,780 --> 00:46:23,030
But this wave function
tells us everything

1030
00:46:23,030 --> 00:46:25,100
we want to know about
probabilities of a given

1031
00:46:25,100 --> 00:46:26,145
system.

1032
00:46:26,145 --> 00:46:28,520
What speed you'll measure,
what positions you'll measure,

1033
00:46:28,520 --> 00:46:32,230
what energy you'll
measure, and so forth.

1034
00:46:32,230 --> 00:46:36,920
Now, this wave function, there's
nothing peculiar about the way

1035
00:46:36,920 --> 00:46:40,520
that this wave function changes.

1036
00:46:40,520 --> 00:46:42,380
So every object has
its own wave function.

1037
00:46:42,380 --> 00:46:43,010
I have a wave function.

1038
00:46:43,010 --> 00:46:44,020
You have a wave function.

1039
00:46:44,020 --> 00:46:45,353
An electron has a wave function.

1040
00:46:45,353 --> 00:46:46,640
An atom has a wave function.

1041
00:46:46,640 --> 00:46:49,121
In principle, the universe
has a wave function.

1042
00:46:49,121 --> 00:46:51,620
There's nothing-- and there's
nothing peculiar about the way

1043
00:46:51,620 --> 00:46:54,202
that it changes under
most circumstances.

1044
00:46:57,570 --> 00:46:59,070
The wave function just obeys--

1045
00:46:59,070 --> 00:47:01,980
it generally just
obeys a simple equation

1046
00:47:01,980 --> 00:47:05,074
and tells the wave
function how to change.

1047
00:47:05,074 --> 00:47:07,240
It completely tells the
wave function how to change.

1048
00:47:07,240 --> 00:47:10,140
You can totally predict how
the wave function changes

1049
00:47:10,140 --> 00:47:11,502
under most circumstances.

1050
00:47:11,502 --> 00:47:13,710
The circumstances where you
don't know how it changes

1051
00:47:13,710 --> 00:47:17,890
is when you make a
measurement on something.

1052
00:47:17,890 --> 00:47:21,210
So there are two
fundamental processes.

1053
00:47:21,210 --> 00:47:23,550
There is measurement and
there's non-measurement.

1054
00:47:23,550 --> 00:47:25,716
When you're not measuring
something, when you're not

1055
00:47:25,716 --> 00:47:30,370
looking at it, you're for sure
how its wave function changes.

1056
00:47:30,370 --> 00:47:32,760
But when you measure
something the wave function

1057
00:47:32,760 --> 00:47:36,690
is set to collapse, and you
don't know for certainty

1058
00:47:36,690 --> 00:47:37,740
what it will collapse to.

1059
00:47:37,740 --> 00:47:40,080
You don't know if you'll measure
one speed or another, if you'll

1060
00:47:40,080 --> 00:47:41,580
measure one energy or another.

1061
00:47:41,580 --> 00:47:44,437
You have some kind of a
probability for each speed

1062
00:47:44,437 --> 00:47:46,020
and for each possible
outcome, but you

1063
00:47:46,020 --> 00:47:48,570
don't know what it will be.

1064
00:47:48,570 --> 00:47:52,076
You don't know what the result
of your experiments will be.

1065
00:47:52,076 --> 00:47:53,700
So there are two
fundamental processes.

1066
00:48:07,500 --> 00:48:19,223
There is non-measurement
and measurement.

1067
00:48:29,370 --> 00:48:33,040
Now, for a long time, physicists
have scratched their heads

1068
00:48:33,040 --> 00:48:36,190
to figure out what this
measurement really is.

1069
00:48:36,190 --> 00:48:39,870
I mean, what this collapse of
the wave function really is.

1070
00:48:39,870 --> 00:48:40,814
It collapses randomly.

1071
00:48:40,814 --> 00:48:42,730
You don't know what it's
going to collapse to.

1072
00:48:42,730 --> 00:48:44,020
What does it mean?

1073
00:48:44,020 --> 00:48:48,190
And people for a long time have
tried to come up with theories

1074
00:48:48,190 --> 00:48:51,400
to explain what measurement is.

1075
00:48:51,400 --> 00:48:56,650
And in the 1950s, an
alternative interpretation

1076
00:48:56,650 --> 00:48:58,585
of quantum mechanics came out.

1077
00:48:58,585 --> 00:49:01,210
What I've described so far is by
the traditional interpretation

1078
00:49:01,210 --> 00:49:04,675
of quantum mechanics or really,
the traditional formulation

1079
00:49:04,675 --> 00:49:05,550
of quantum mechanics.

1080
00:49:05,550 --> 00:49:07,820
They're really
different formulations.

1081
00:49:07,820 --> 00:49:10,060
This is the traditional
way the quantum mechanics

1082
00:49:10,060 --> 00:49:10,980
is formulated.

1083
00:49:10,980 --> 00:49:14,630
But in the 1950s,
a new formulation

1084
00:49:14,630 --> 00:49:17,956
was hypothesized,
and that today,

1085
00:49:17,956 --> 00:49:20,080
goes by the name of the
many world interpretations.

1086
00:49:20,080 --> 00:49:24,790
In 1950s, many world
interpretation came out.

1087
00:49:38,640 --> 00:49:40,840
It's actually probably
not the best name

1088
00:49:40,840 --> 00:49:44,460
for the interpretation.

1089
00:49:44,460 --> 00:49:46,480
It's a very
misleading name that's

1090
00:49:46,480 --> 00:49:48,760
confused a lot of people.

1091
00:49:48,760 --> 00:49:52,720
All it says-- all the many
world interpretation says,

1092
00:49:52,720 --> 00:49:54,910
is that the wave
function just changes

1093
00:49:54,910 --> 00:49:58,760
by this predictable
equation that I described.

1094
00:49:58,760 --> 00:50:01,060
There's no more
of this collapse.

1095
00:50:01,060 --> 00:50:02,890
There's no more of this
mysterious collapse

1096
00:50:02,890 --> 00:50:04,340
that occurs in measurement.

1097
00:50:04,340 --> 00:50:06,640
Measurement is now
this process that

1098
00:50:06,640 --> 00:50:09,610
occurs according to
this equation, which

1099
00:50:09,610 --> 00:50:13,090
I won't write down,
and there's nothing

1100
00:50:13,090 --> 00:50:14,140
very mysterious about it.

1101
00:50:14,140 --> 00:50:16,750
I mean, there are certain
types of interactions

1102
00:50:16,750 --> 00:50:19,720
that a system can
undergo, and some of these

1103
00:50:19,720 --> 00:50:23,920
are just favorable
to this measurement

1104
00:50:23,920 --> 00:50:26,230
appearance, this collapse
appearance that we see.

1105
00:50:29,620 --> 00:50:31,887
And so that's what the many
worlds interpretation is.

1106
00:50:31,887 --> 00:50:33,970
It's just-- you just have
one fundamental process.

1107
00:50:33,970 --> 00:50:37,870
You just have the
type of process

1108
00:50:37,870 --> 00:50:41,320
that was supposed to happen
with this non-measurement.

1109
00:50:41,320 --> 00:50:42,475
So one fundamental process.

1110
00:50:54,510 --> 00:50:55,740
OK.

1111
00:50:55,740 --> 00:50:59,870
Now, in both of these
interpretations,

1112
00:50:59,870 --> 00:51:03,770
both the traditional and the
many worlds interpretation,

1113
00:51:03,770 --> 00:51:07,370
you have something
called a superposition.

1114
00:51:07,370 --> 00:51:09,847
Now, I know I'm introducing
a lot of terms today.

1115
00:51:09,847 --> 00:51:11,180
I'm introducing a lot of terms--

1116
00:51:11,180 --> 00:51:13,760
I mean, to describe this kind
of level three multiverse,

1117
00:51:13,760 --> 00:51:15,800
but it'll be worth it.

1118
00:51:15,800 --> 00:51:17,994
You have something
called superposition.

1119
00:51:29,130 --> 00:51:31,870
And this is really a mixture of
state, mixture between states.

1120
00:51:31,870 --> 00:51:33,635
I'll describe a little
more in one second.

1121
00:51:46,750 --> 00:51:47,250
OK.

1122
00:51:47,250 --> 00:51:49,770
One possible state
is that you've got

1123
00:51:49,770 --> 00:51:51,620
a cat, if a cat that's alive--

1124
00:51:54,280 --> 00:51:56,990
that's totally a
possible physical state.

1125
00:51:56,990 --> 00:51:58,560
AUDIENCE: [INAUDIBLE]

1126
00:51:58,560 --> 00:51:59,970
NICHOLAS DIBELLA: We can--

1127
00:51:59,970 --> 00:52:02,424
I'll get to that in a second.

1128
00:52:02,424 --> 00:52:03,840
You can have a
state that's alive.

1129
00:52:03,840 --> 00:52:05,548
So you have a state
where a cat is alive.

1130
00:52:05,548 --> 00:52:06,810
That's one possibility state.

1131
00:52:06,810 --> 00:52:09,210
And you can also conceive
of a cat being dead.

1132
00:52:09,210 --> 00:52:11,070
That's another possible state.

1133
00:52:11,070 --> 00:52:14,010
Now, according to
quantum mechanics,

1134
00:52:14,010 --> 00:52:18,090
you can also have a cat
that's both alive and dead.

1135
00:52:18,090 --> 00:52:20,312
The technical term,
it's a superposition.

1136
00:52:20,312 --> 00:52:22,020
You can have a cat
that's a superposition

1137
00:52:22,020 --> 00:52:24,960
of being alive and dead.

1138
00:52:24,960 --> 00:52:27,570
And you can also
have superpositions

1139
00:52:27,570 --> 00:52:29,670
of other crazy states.

1140
00:52:29,670 --> 00:52:32,550
You can have a superposition
of a cat and a dog.

1141
00:52:32,550 --> 00:52:37,980
A superposition of an
airplane and a planet.

1142
00:52:37,980 --> 00:52:41,320
For any two physical states
that you can think of,

1143
00:52:41,320 --> 00:52:43,320
if you just combine
the two, if you just

1144
00:52:43,320 --> 00:52:47,130
form a superposition
of the two, then that's

1145
00:52:47,130 --> 00:52:52,110
also a physically valid state
according to quantum mechanics.

1146
00:52:52,110 --> 00:52:55,110
Anybody have a
question about that?

1147
00:52:55,110 --> 00:52:55,782
Yes?

1148
00:52:55,782 --> 00:52:58,720
AUDIENCE: It's just weird
having a cat alive and dead

1149
00:52:58,720 --> 00:52:59,546
at the same time.

1150
00:52:59,546 --> 00:53:00,504
NICHOLAS DIBELLA: Yeah.

1151
00:53:00,504 --> 00:53:02,440
AUDIENCE: [INAUDIBLE]
be possible?

1152
00:53:02,440 --> 00:53:03,890
NICHOLAS DIBELLA: OK.

1153
00:53:03,890 --> 00:53:05,900
So quantum mechanics
predicts that these are

1154
00:53:05,900 --> 00:53:08,435
totally valid physical states.

1155
00:53:08,435 --> 00:53:10,490
But yeah, we don't
observe things--

1156
00:53:10,490 --> 00:53:14,110
we don't observe
dead alive cats.

1157
00:53:14,110 --> 00:53:17,690
We don't observe dog
cats, and so forth.

1158
00:53:17,690 --> 00:53:21,480
And so you might be wondering
why is that the case.

1159
00:53:21,480 --> 00:53:24,890
Well, let's suppose you did have
a superposition of a cat being

1160
00:53:24,890 --> 00:53:25,560
alive and dead.

1161
00:53:25,560 --> 00:53:28,160
Suppose you had a cat that
was both alive and dead

1162
00:53:28,160 --> 00:53:30,200
at the same time.

1163
00:53:30,200 --> 00:53:31,430
The way to do this--

1164
00:53:31,430 --> 00:53:34,230
the way to actually
get a superposition--

1165
00:53:34,230 --> 00:53:39,080
well, I'll describe this
famous thought experiment.

1166
00:53:39,080 --> 00:53:41,690
It's called, the shredding
your cat thought experiment.

1167
00:53:41,690 --> 00:53:43,475
And what you do
is you take a cat,

1168
00:53:43,475 --> 00:53:47,330
you put the cat inside of a
box, put some radioactive poison

1169
00:53:47,330 --> 00:53:50,840
in the box, and
then you close it.

1170
00:53:50,840 --> 00:53:52,100
OK.

1171
00:53:52,100 --> 00:53:55,490
And let's say that there is a
50% chance that after an hour

1172
00:53:55,490 --> 00:53:57,620
the poison will have decayed.

1173
00:53:57,620 --> 00:54:00,560
It might decay, it might
not decay, we don't know.

1174
00:54:00,560 --> 00:54:03,080
There's some probability
that it will decay.

1175
00:54:03,080 --> 00:54:05,780
Well, after an hour, the cat--

1176
00:54:05,780 --> 00:54:07,640
you don't know if
the thing-- you don't

1177
00:54:07,640 --> 00:54:09,170
know if the poison has decayed.

1178
00:54:09,170 --> 00:54:11,270
So according to quantum
mechanics, after an hour,

1179
00:54:11,270 --> 00:54:13,690
the cat is both alive and dead.

1180
00:54:13,690 --> 00:54:16,070
It's in a superposition
of being alive and dead,

1181
00:54:16,070 --> 00:54:17,900
and only when you
open it will you

1182
00:54:17,900 --> 00:54:20,870
find the cat to
be alive or dead.

1183
00:54:20,870 --> 00:54:23,810
So in the traditional
interpretation

1184
00:54:23,810 --> 00:54:27,770
of quantum mechanics,
once you open up the box,

1185
00:54:27,770 --> 00:54:30,860
you give the cat
aliveness or deadness.

1186
00:54:30,860 --> 00:54:33,170
So once you open the
box, you'll either

1187
00:54:33,170 --> 00:54:36,620
see a dead cat or an alive cat.

1188
00:54:36,620 --> 00:54:40,430
And I guess if you found a dead
cat then someone can accuse you

1189
00:54:40,430 --> 00:54:42,920
of killing the cat.

1190
00:54:42,920 --> 00:54:46,009
But that's one of
the reasons that this

1191
00:54:46,009 --> 00:54:48,050
is a thought experiment,
we don't actually do it.

1192
00:54:51,290 --> 00:54:53,810
So in this traditional
interpretation,

1193
00:54:53,810 --> 00:54:58,310
you give the cat aliveness or
deadness by opening up the box

1194
00:54:58,310 --> 00:54:59,132
and measuring it.

1195
00:54:59,132 --> 00:55:00,090
It's as simple as that.

1196
00:55:00,090 --> 00:55:01,904
The cat is either alive or dead.

1197
00:55:01,904 --> 00:55:03,320
In the many worlds
interpretation,

1198
00:55:03,320 --> 00:55:05,480
once you open the box,
you'll find the cat

1199
00:55:05,480 --> 00:55:08,390
to be either alive or
dead, but in reality,

1200
00:55:08,390 --> 00:55:13,880
in true quantum reality, the
cat is both alive and dead.

1201
00:55:13,880 --> 00:55:17,720
We only perceive a small
fraction of this true quantum

1202
00:55:17,720 --> 00:55:18,890
reality.

1203
00:55:18,890 --> 00:55:20,420
And we perceive one of them.

1204
00:55:20,420 --> 00:55:21,950
We perceive one or the other.

1205
00:55:21,950 --> 00:55:24,610
The alive cat or the dead cat.

1206
00:55:24,610 --> 00:55:30,020
And according to this many
worlds interpretation,

1207
00:55:30,020 --> 00:55:33,380
other parts of this
true quantum reality,

1208
00:55:33,380 --> 00:55:36,250
you can call them parallel
universes, parallel worlds.

1209
00:55:36,250 --> 00:55:41,690
In other parts of
the true reality,

1210
00:55:41,690 --> 00:55:44,485
you will measure
the cat to be dead

1211
00:55:44,485 --> 00:55:46,860
or you'll measure it to be
the opposite where you measure

1212
00:55:46,860 --> 00:55:49,850
it to be in this universe.

1213
00:55:49,850 --> 00:55:52,977
We can't perceive this
true quantum reality,

1214
00:55:52,977 --> 00:55:54,810
we can only perceive a
small fraction of it.

1215
00:55:54,810 --> 00:55:56,309
I mean, these
experiences that we're

1216
00:55:56,309 --> 00:56:00,260
having really represent the
small piece of the true quantum

1217
00:56:00,260 --> 00:56:02,930
reality.

1218
00:56:02,930 --> 00:56:10,960
And we can't-- we
have a hard time--

1219
00:56:10,960 --> 00:56:12,710
well, it's quite
possible that we'll never

1220
00:56:12,710 --> 00:56:15,050
be able to interact with
these other universes,

1221
00:56:15,050 --> 00:56:18,980
other universes where there's a
counterpart of me and I measure

1222
00:56:18,980 --> 00:56:21,824
has to be alive or I
measure the cat to be dead.

1223
00:56:21,824 --> 00:56:23,990
But if you believe in the
many worlds interpretation

1224
00:56:23,990 --> 00:56:26,600
of quantum mechanics
then in fact,

1225
00:56:26,600 --> 00:56:30,542
these universes do exist in a
very real way in a kind of--

1226
00:56:30,542 --> 00:56:32,000
I mean, it's called,
Hilbert space.

1227
00:56:32,000 --> 00:56:34,220
That's the name of this
true quantum reality.

1228
00:56:34,220 --> 00:56:38,360
I mean, these other universes,
they don't exist in the sense

1229
00:56:38,360 --> 00:56:40,400
that if you travel very
far you'd get to them.

1230
00:56:40,400 --> 00:56:44,480
They exist in more of an
abstract mathematical sense.

1231
00:56:44,480 --> 00:56:46,730
It's called the Hilbert space.

1232
00:56:46,730 --> 00:56:48,050
It's the quantum space.

1233
00:56:48,050 --> 00:56:49,700
The quantum-- the
true quantum reality

1234
00:56:49,700 --> 00:56:53,312
is more of an abstract
mathematical thing.

1235
00:56:53,312 --> 00:56:55,520
And if you believe in the
many worlds interpretation,

1236
00:56:55,520 --> 00:57:02,390
then you should also believe
in these parallel universes

1237
00:57:02,390 --> 00:57:06,140
where instead of measuring
the cat to be alive,

1238
00:57:06,140 --> 00:57:07,520
you measure the cat to be dead.

1239
00:57:07,520 --> 00:57:09,764
Instead of coming to
this class and teaching,

1240
00:57:09,764 --> 00:57:11,180
I walked out and
left you all here

1241
00:57:11,180 --> 00:57:13,270
for an hour and a
half to waste time.

1242
00:57:13,270 --> 00:57:18,010
Or you wore a blue shirt
today instead of green,

1243
00:57:18,010 --> 00:57:19,382
and other things happened.

1244
00:57:19,382 --> 00:57:21,840
In other universes, in other
universes in this true quantum

1245
00:57:21,840 --> 00:57:25,430
reality, those things
do happen if you

1246
00:57:25,430 --> 00:57:27,740
believe in the many
worlds interpretation.

1247
00:57:27,740 --> 00:57:30,410
So should you believe in the
many worlds interpretation?

1248
00:57:30,410 --> 00:57:34,280
Well, the traditional
interpretation

1249
00:57:34,280 --> 00:57:37,264
of quantum mechanics,
to me, it doesn't really

1250
00:57:37,264 --> 00:57:38,930
make any sense because
it doesn't really

1251
00:57:38,930 --> 00:57:40,640
describe what measurement is.

1252
00:57:40,640 --> 00:57:42,786
So we-- I mean,
that's my own opinion.

1253
00:57:42,786 --> 00:57:44,660
So we need to understand
what measurement is.

1254
00:57:44,660 --> 00:57:46,680
We have to have some
kind of idea what it is.

1255
00:57:46,680 --> 00:57:48,138
And this many worlds
interpretation

1256
00:57:48,138 --> 00:57:49,560
does describe what
measurement is.

1257
00:57:49,560 --> 00:57:52,150
It's the dynamical process.

1258
00:57:52,150 --> 00:57:54,290
It's not some kind of a weird--

1259
00:57:54,290 --> 00:57:56,990
it's kind of a weird,
mysterious, collapse

1260
00:57:56,990 --> 00:57:58,310
type of thing.

1261
00:57:58,310 --> 00:58:00,200
And this many worlds
interpretation

1262
00:58:00,200 --> 00:58:03,420
really describes things--

1263
00:58:03,420 --> 00:58:07,080
really describes the way things
are in a very abstract sense.

1264
00:58:07,080 --> 00:58:11,600
And actually, we can
do experiments now

1265
00:58:11,600 --> 00:58:15,410
where we follow how the
wave functions of things

1266
00:58:15,410 --> 00:58:18,810
change in time, the
smallest things.

1267
00:58:18,810 --> 00:58:22,760
And we can actually
see the wave functions

1268
00:58:22,760 --> 00:58:24,680
start to have this
appearance of collapse.

1269
00:58:24,680 --> 00:58:26,510
I mean, usually
happens very fast,

1270
00:58:26,510 --> 00:58:29,420
but we can actually, kind of see
how this wave function starts

1271
00:58:29,420 --> 00:58:30,660
to collapse.

1272
00:58:30,660 --> 00:58:33,530
It's called de-coherence,
and it's a very active topic

1273
00:58:33,530 --> 00:58:37,040
in quantum research today.

1274
00:58:37,040 --> 00:58:39,440
There's also support for the
many worlds interpretation

1275
00:58:39,440 --> 00:58:43,910
quantum computing where you
have interference effects

1276
00:58:43,910 --> 00:58:47,600
in a variety of superpositions.

1277
00:58:47,600 --> 00:58:50,249
So if you believe in
this interpretation--

1278
00:58:50,249 --> 00:58:52,040
on the face of it is
a very sensible thing.

1279
00:58:52,040 --> 00:58:53,456
You just have one
kind of process.

1280
00:58:53,456 --> 00:58:55,490
You just have an equation
to govern everything,

1281
00:58:55,490 --> 00:58:58,446
but it has very
weird prediction.

1282
00:58:58,446 --> 00:59:00,320
But if you believe the
fundamental principle,

1283
00:59:00,320 --> 00:59:03,180
then you should believe
the very weird predictions.

1284
00:59:03,180 --> 00:59:05,140
I'm not going to tell
you what to believe.

1285
00:59:05,140 --> 00:59:08,157
I could of course, said the
same thing for the other.

1286
00:59:08,157 --> 00:59:09,740
I could of course,
said the same thing

1287
00:59:09,740 --> 00:59:12,170
for the other parallel
universes as well.

1288
00:59:14,980 --> 00:59:17,020
I'm not going to tell
you what to believe.

1289
00:59:17,020 --> 00:59:18,590
You can choose for yourself.

1290
00:59:18,590 --> 00:59:22,430
But these theories that we
have, they look very sensible

1291
00:59:22,430 --> 00:59:23,180
on the face of it.

1292
00:59:23,180 --> 00:59:24,721
You just have these
simple equations,

1293
00:59:24,721 --> 00:59:26,720
but they predict
very weird things,

1294
00:59:26,720 --> 00:59:29,511
very wild and crazy things.

1295
00:59:29,511 --> 00:59:32,010
But if you really believe the
theories, if you look at them,

1296
00:59:32,010 --> 00:59:36,090
you say, well, they
agree with experiments.

1297
00:59:36,090 --> 00:59:38,660
They saw the experiments
that we've done,

1298
00:59:38,660 --> 00:59:40,745
but they predict
some weird things.

1299
00:59:43,786 --> 00:59:45,410
It might take a lot
of emotional effort

1300
00:59:45,410 --> 00:59:50,030
or psychological
dissonance to get rid of,

1301
00:59:50,030 --> 00:59:51,800
but if you believe
in the foundations,

1302
00:59:51,800 --> 00:59:53,800
then you should also
believe in the predictions.

1303
00:59:53,800 --> 00:59:55,040
That's my view of it.

1304
00:59:55,040 --> 00:59:58,940
Whether you believe in the
foundations is up to you.

1305
00:59:58,940 --> 01:00:01,100
So in this many
worlds interpretation,

1306
01:00:01,100 --> 01:00:03,740
of our world that we experience,
is just a small fraction

1307
01:00:03,740 --> 01:00:05,520
of the true quantum reality.

1308
01:00:05,520 --> 01:00:08,120
And there are a
number of parallel--

1309
01:00:08,120 --> 01:00:10,970
infinitely many parallel
universes in addition to ours

1310
01:00:10,970 --> 01:00:13,950
that we can't interact with,
but they're really there

1311
01:00:13,950 --> 01:00:18,960
in a very kind of abstract
sort of way, but they do exist.

1312
01:00:18,960 --> 01:00:20,600
Think about that tonight.

1313
01:00:20,600 --> 01:00:23,240
Does anybody have any
questions about the level three

1314
01:00:23,240 --> 01:00:24,206
multiverse?

1315
01:00:28,060 --> 01:00:28,560
OK.

1316
01:00:28,560 --> 01:00:30,390
Do I have any more time?

1317
01:00:30,390 --> 01:00:32,560
I have five minutes.

1318
01:00:32,560 --> 01:00:34,012
There's one more.

1319
01:00:34,012 --> 01:00:34,970
There's one more level.

1320
01:00:37,880 --> 01:00:39,180
I suppose I can--

1321
01:00:39,180 --> 01:00:42,360
yeah, I can describe
it pretty briefly.

1322
01:00:42,360 --> 01:00:44,030
And I'll come back
to it actually,

1323
01:00:44,030 --> 01:00:48,890
in a later lecture when I
discuss the nature of gallity.

1324
01:00:48,890 --> 01:00:54,937
But in this final level,
this level four multiverse,

1325
01:00:54,937 --> 01:00:57,020
this is the most controversial
and the most weird.

1326
01:01:14,530 --> 01:01:15,030
OK.

1327
01:01:15,030 --> 01:01:17,050
So in all these
previous levels you

1328
01:01:17,050 --> 01:01:20,730
get a variety of an infinitude
of different universes,

1329
01:01:20,730 --> 01:01:22,100
parallel universes.

1330
01:01:22,100 --> 01:01:24,710
But in each one of them, you
have the same physical laws.

1331
01:01:24,710 --> 01:01:26,355
You have the same
laws of nature.

1332
01:01:26,355 --> 01:01:28,230
It might be that the
constants are different,

1333
01:01:28,230 --> 01:01:30,390
the masses are different, the
speed of lights are different,

1334
01:01:30,390 --> 01:01:31,848
the dimensionalities
are different,

1335
01:01:31,848 --> 01:01:34,810
but the underlying laws,
they are all the same.

1336
01:01:34,810 --> 01:01:38,560
So the obvious step is say,
well, let's change the laws.

1337
01:01:38,560 --> 01:01:39,365
Right?

1338
01:01:39,365 --> 01:01:41,490
So in the level four
multiverse, you have universes

1339
01:01:41,490 --> 01:01:43,050
with different laws of physics.

1340
01:01:56,310 --> 01:01:57,300
OK.

1341
01:01:57,300 --> 01:01:59,520
And this level four
multiverse really

1342
01:01:59,520 --> 01:02:03,570
stems from a very simple
question that you can ask.

1343
01:02:03,570 --> 01:02:06,650
We have certain laws that
describe the universe,

1344
01:02:06,650 --> 01:02:08,860
and you can look at
those laws and say, well,

1345
01:02:08,860 --> 01:02:10,740
that's very interesting,
these are the laws.

1346
01:02:10,740 --> 01:02:14,230
But you might be wondering,
why are these the laws?

1347
01:02:14,230 --> 01:02:16,480
Why these laws of physics
and why not others?

1348
01:02:16,480 --> 01:02:18,010
I mean, you could ask the
same questions about--

1349
01:02:18,010 --> 01:02:20,070
you can ask the same
questions about the constants

1350
01:02:20,070 --> 01:02:22,403
and the dimensionalities, and
chaotic internal inflation

1351
01:02:22,403 --> 01:02:24,040
provide an answer for that.

1352
01:02:24,040 --> 01:02:27,790
But didn't provide answer for
why these laws and not others.

1353
01:02:27,790 --> 01:02:29,750
And so you might--

1354
01:02:29,750 --> 01:02:31,360
yeah so it's a puzzle.

1355
01:02:31,360 --> 01:02:33,030
It's a puzzle about--

1356
01:02:33,030 --> 01:02:36,160
it's a puzzle.

1357
01:02:36,160 --> 01:02:37,240
It's a puzzle.

1358
01:02:37,240 --> 01:02:40,870
Why these laws and not others?

1359
01:02:40,870 --> 01:02:43,600
What you can do to answer
this question is you can say,

1360
01:02:43,600 --> 01:02:48,990
well, maybe there's a vast
ensemble of parallel universes

1361
01:02:48,990 --> 01:02:51,780
that are actually described by a
different set of physical laws,

1362
01:02:51,780 --> 01:02:54,330
and we just happened to
find ourselves in one where

1363
01:02:54,330 --> 01:02:58,470
the laws allow life to form,
allow stability of matter,

1364
01:02:58,470 --> 01:03:01,140
and allow complexity to
form, and there are actually

1365
01:03:01,140 --> 01:03:04,720
universes that have
other laws of physics.

1366
01:03:04,720 --> 01:03:08,170
So I mean, in our
universe, we have,

1367
01:03:08,170 --> 01:03:12,840
for example, a law of gravity
whereby, every mass is

1368
01:03:12,840 --> 01:03:14,934
attracted to every other mass.

1369
01:03:14,934 --> 01:03:16,350
Although, I mention
inflation, you

1370
01:03:16,350 --> 01:03:18,141
can actually have your
[INAUDIBLE] gravity,

1371
01:03:18,141 --> 01:03:19,440
but forget that.

1372
01:03:19,440 --> 01:03:22,170
Every mass is attracted to
every mass, every other mass.

1373
01:03:22,170 --> 01:03:23,259
So things pull each other.

1374
01:03:23,259 --> 01:03:24,300
That's one law of nature.

1375
01:03:27,350 --> 01:03:29,830
The correct theory to describe
is general relativity,

1376
01:03:29,830 --> 01:03:33,944
but it's easy to understand
basic things about it.

1377
01:03:33,944 --> 01:03:35,610
You know, an object
falls down, an apple

1378
01:03:35,610 --> 01:03:37,151
falls down to the
center of the earth

1379
01:03:37,151 --> 01:03:40,560
because it's gravitationally
attracted to it.

1380
01:03:40,560 --> 01:03:46,939
Now, without law of gravity,
it's certainly true that--

1381
01:03:46,939 --> 01:03:49,230
well, gravity is responsible
for things being attracted

1382
01:03:49,230 --> 01:03:51,521
to each other, but certainly
not responsible for people

1383
01:03:51,521 --> 01:03:52,999
falling in love.

1384
01:03:52,999 --> 01:03:54,540
It could be that in
another universe,

1385
01:03:54,540 --> 01:03:56,957
you have some laws
of physics where

1386
01:03:56,957 --> 01:03:59,040
gravity is responsible for
people falling in love.

1387
01:04:02,130 --> 01:04:03,540
I thought it was funny.

1388
01:04:03,540 --> 01:04:05,590
But you can also have--

1389
01:04:05,590 --> 01:04:08,100
you can also have set
of laws of physics

1390
01:04:08,100 --> 01:04:20,340
where instead of gravity
becoming weaker and weaker

1391
01:04:20,340 --> 01:04:22,680
and weaker as you go far
away, it could become stronger

1392
01:04:22,680 --> 01:04:23,763
and stronger and stronger.

1393
01:04:23,763 --> 01:04:25,340
That's another possible theory.

1394
01:04:25,340 --> 01:04:28,390
And you could think
of many, many others.

1395
01:04:28,390 --> 01:04:29,970
And so in this level
four multiverse,

1396
01:04:29,970 --> 01:04:33,510
you have universes
where there are actually

1397
01:04:33,510 --> 01:04:35,190
different laws of physics.

1398
01:04:35,190 --> 01:04:41,820
And there's a lot more to be
said about this multiverse.

1399
01:04:41,820 --> 01:04:42,629
I don't have time--

1400
01:04:42,629 --> 01:04:44,920
maybe if I had a little more
time, I could describe it,

1401
01:04:44,920 --> 01:04:48,450
but I'll describe it later.

1402
01:04:48,450 --> 01:04:51,660
And the nature of
these universes

1403
01:04:51,660 --> 01:04:54,180
is very different from the
nature of the universes

1404
01:04:54,180 --> 01:04:55,980
that I've been describing.

1405
01:04:55,980 --> 01:05:01,710
In these universes, their nature
is completely mathematical.

1406
01:05:01,710 --> 01:05:06,110
So the level four
multiverse, every universe,

1407
01:05:06,110 --> 01:05:07,860
every universe with
its own law of physics

1408
01:05:07,860 --> 01:05:11,690
is completely mathematical,
and they're actually

1409
01:05:11,690 --> 01:05:13,620
called mathematical structures.

1410
01:05:13,620 --> 01:05:16,170
And so our universe has a
certain mathematical structure.

1411
01:05:16,170 --> 01:05:18,540
Well, our universe is a
certain mathematical structure,

1412
01:05:18,540 --> 01:05:19,560
and there are other
universes that

1413
01:05:19,560 --> 01:05:21,518
are different mathematical
structures, and only

1414
01:05:21,518 --> 01:05:24,030
in the mathematical structures
that are complex enough

1415
01:05:24,030 --> 01:05:28,140
to contain self-aware
observers, will there

1416
01:05:28,140 --> 01:05:34,680
be an appearance of a thing
that we call, physical reality.

1417
01:05:34,680 --> 01:05:37,680
Yeah, there's a lot more
to be said about this.

1418
01:05:37,680 --> 01:05:42,419
And I will do that
in the following--

1419
01:05:42,419 --> 01:05:42,960
I don't know.

1420
01:05:42,960 --> 01:05:44,501
I don't know when
I'll talk about it,

1421
01:05:44,501 --> 01:05:47,990
but I'll talk more about
this in the future OK.

1422
01:05:47,990 --> 01:05:50,140
So that's it for today.