Cosmic background radiation 2

WEBVTT
Kind: captions
Language: en

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In the last video, we
learned that 380,000 years

00:00:04.320 --> 00:00:06.580
after the Big Bang,
which is still

00:00:06.580 --> 00:00:10.910
roughly 13.7 billion years
ago, every point-- I shouldn't

00:00:10.910 --> 00:00:13.270
say every point--
every atom in space

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that was kind of at this
roughly 3,000 Kelvin temperature

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was emitting this
electromagnetic radiation.

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Since every point in space was,
there were points in space,

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or there was points
in the universe,

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that that radiation is
only just now reaching us.

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It has been traveling
for 13.7 billion years.

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So when we look at
radiation that's

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been traveling for that long,
we can look at any direction

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and we'll see this
uniform radiation.

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And that radiation has been
red-shifted into the microwave

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range from the
higher frequencies

00:00:46.080 --> 00:00:48.000
that it was actually emitted at.

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Now, a question that
might pop in your brain

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is, well, what happens if
we wait a billion years?

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Because if we wait
a billion years,

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if we have 1,000,380,000
years after the beginning

00:00:59.480 --> 00:01:02.730
of the universe, this stuff
won't just be atoms anymore.

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It will have started to
condense into actual stars.

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The universe at
every point in space

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will no longer be this uniform.

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We'll actually start having
condensation into stars.

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So if we move forward a little
bit, the universe will expand.

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Maybe I'll just draw a half
of it since it's expanded.

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It's obviously
expanded much more.

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But now all of a sudden,
we actually have stars.

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These are no longer
just uniform atoms

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spread through the universe.

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We actually have
condensation into stars.

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And so if you look at
what is being emitted

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from the points in space from
which we're only now getting

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this cosmic background
radiation, if we wait

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a billion years,
the light that we

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see from those points
in space will not

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look like this
uniform radiation.

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It'll start to look
a little bit more

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like the more mature
parts of the universe.

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We'll essentially be
looking at the universe

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a billion years after the Big
Bang, when stars have formed,

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other structures have formed.

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So the question is
in a billion years,

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will this cosmic microwave
background radiation disappear.

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And I'm using billion just
to arbitrarily use a number.

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But will it
eventually disappear?

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And the answer to
that is yes and no.

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So to think about it, it is
true that this point in space

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will mature.

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It will mature in
a billion years.

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It will no longer
be this uniform--

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I guess this uniform haze
of hot hydrogen atoms.

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But what you have
to think about is

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there were further
points in the universe.

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At that same time, there
were further points

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that were also emitting
this radiation.

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And the original photons
from those original points

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still haven't gotten to us.

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So from those further
out points-- right now,

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the observable universe
is-- we can only

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see electromagnetic
radiation that's

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been traveling for
13.7 billion years.

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In another billion
years, the universe

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will be a billion years older.

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And then there will
be radiation that

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has been traveling for
14.7 billion years.

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And so we will start
to observe that.

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And we'll start to observe that
radiation from the same time

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period in the universe.

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It'll just be from further out.

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Now, what I want
to make clear is,

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is that since those points
were even further out, where

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that radiation was emitted,
the stuff that we'll

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see in a billion years, it
will be even more red-shifted.

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So at that point, the cosmic
background radiation we see

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will have longer wavelengths
than the radio spectrum.

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It will be redder

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And I should say redder
because we're already more--

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would "redder" have two Ds?

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I've never written "redder."

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Well, it would be more red
than the microwave radiation.

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And, of course,
that's a funny thing

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because microwave
radiation is already

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more red than actual
visible red light.

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It has a longer wavelength.

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Now, this will keep happening.

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And it'll keep happening.

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We'll keep getting radiation
as we go further and further

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into the future.

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We'll keep getting
radiation from further out

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points in space.

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And it'll get more
and more red-shifted.

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The actual wave lengths of
that electromagnetic light

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will be bigger, and
bigger, and bigger.

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Until we really aren't
able to even see it

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as electromagnetic
light because it'll

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be red-shifted to infinity.

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It'll have an
infinite wavelength.

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And to make that
point clear, I want

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to show you that at
some point, there

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will be kind of a threshold
where we can't even

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get radiation from further out.

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And let me draw a
diagram of that.

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So let's say that
this is the universe.

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Let's say that this is the
universe 13.7 billion years

00:04:50.200 --> 00:04:52.300
ago, right when that
radiation, what we

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now see as cosmic microwave
background radiation,

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right when it started
to be admitted.

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And let's say that
this is the point

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in the universe
where we are now.

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So this is us.

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Let's say that this is the point
in the universe where we now

00:05:07.720 --> 00:05:10.430
observe the background
radiation-- or this is

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one of the points.

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We obviously could form
a circle around us.

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It could be any of
these points over here,

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where the photons, the
electromagnetic radiation that

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were emitted from this
point, 380,000 years

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after the beginning
of the universe,

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is only just now reaching us.

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So this is the point in
the universe from which we

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are observing the cosmic
background radiation.

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And let me be very clear.

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That point in the
universe has now

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matured into things that
look-- into stars and galaxies

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and planets.

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And if they were to look
at our point in space,

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they are also going to see
cosmic background radiation

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from us.

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It's not like some type
of permanently old place.

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It's just the light we're
getting from them right now is

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old light, light that
that point in space

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emitted way before
it was able to mature

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into actual structures.

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So this is the point
in space from which

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we are receiving cosmic
background radiation right now.

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I don't want to write all that.

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It'll take me forever.

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Now, let's take
another point in space

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that's whatever
this distance is.

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Well, it's actually
estimated to be about-- now,

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it's estimated to be about
46 billion light years.

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At that time, when things were
just beginning to be emitted,

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this was only about 36
million light years.

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And this is a very
rough estimate.

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I shouldn't even write it down.

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Because that's really based on
how fast we assume the universe

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is expanding and all
of that type of thing.

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But it was just a lot smaller
than 46 billion light years.

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Now let's go that same distance
again from this point in space.

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So let me make it clear.

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This is 380,000 years ago.

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Now let's fast forward.

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Let's fast forward-- sorry,
not 380,000 years ago,

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380,000 years
after the Big Bang,

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which is approximately-- it's
still 13.7 billion years ago.

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So that's then.

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Now let's look at now.

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And now I'll just draw
it a little bit bigger.

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It's actually going to
be much, much bigger now.

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Now, if we do it a little
bit bigger-- so when

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I draw it like this,
this is where we are now.

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This point in space from which
we are only now receiving

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that cosmic background
radiation is over here.

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And then this other point in
space is going to be over here.

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And we saw in the video on the
actual size of the observable

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universe, not just what it
appears to be based on how long

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the light's been travelling,
this is now on the order of 46

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or 47 billion light years.

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And so this distance
is also going

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to be 46 billion light years.

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Now, every point in
space, back then,

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was emitting this radiation.

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We have this uniform radiation.

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It was just hydrogen atoms
everywhere, these hot hydrogen

00:08:05.120 --> 00:08:06.767
atoms.

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Maybe I should just do it in
the color of the radiation.

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So this guy's
receiving-- I'm just

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showing it's coming
from this guy.

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We're only now, 13.7 billion
years in the future, receiving

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photons from this guy, only
now are we receiving it.

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And frankly, this
green guy, only

00:08:22.240 --> 00:08:24.630
now is going to be
receiving photons.

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When he looks at the point
in space, or the things

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that he thinks are points
in space out there,

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he will see that
uniform radiation.

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And likewise, this guy
over here will only now

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be receiving photons
from the point

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in space for where we are now.

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He'll see the universe
where we are now

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as it was 380,000 years
after the Big Bang.

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And same thing from that
point in space, the photons

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will only just now reach.

00:08:50.707 --> 00:08:51.790
Now, let's think about it.

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It took this guy's photons--
let me make it clear.

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It took him 13.7 billion
years to reach this point

00:09:03.290 --> 00:09:06.920
over here, which is now 46
billion light years away

00:09:06.920 --> 00:09:08.080
from us.

00:09:08.080 --> 00:09:10.990
And the universe
continues to expand.

00:09:10.990 --> 00:09:13.650
Depending on if the universe
expands fast enough,

00:09:13.650 --> 00:09:17.580
there's no way that that
photon that got to this guy,

00:09:17.580 --> 00:09:19.000
will eventually get to this.

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The universe is expanding
faster than the light can never

00:09:21.920 --> 00:09:22.870
even catch up to us.

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And this light will never,
ever, ever get to us.

00:09:26.180 --> 00:09:28.430
And so there is some
threshold, some distance,

00:09:28.430 --> 00:09:31.980
from which we will never get
light during this time period

00:09:31.980 --> 00:09:34.490
or actually from which
we will never, ever get

00:09:34.490 --> 00:09:36.380
any electromagnetic radiation.

00:09:36.380 --> 00:09:39.400
So the simple answer is the
cosmic background radiation

00:09:39.400 --> 00:09:42.430
from this-- or the cosmic
background radiation

00:09:42.430 --> 00:09:44.460
from this point, yes,
it will start to mature.

00:09:44.460 --> 00:09:48.480
It won't be as uniform if we go
fast forward 400 million years

00:09:48.480 --> 00:09:49.500
or a billion years.

00:09:49.500 --> 00:09:52.120
But we will get uniform
radiation from further out.

00:09:52.120 --> 00:09:53.720
But it will be even
more red-shifted.

00:09:53.720 --> 00:09:55.807
And the further forward
we get into the future,

00:09:55.807 --> 00:09:57.640
the background radiation
we get will be from

00:09:57.640 --> 00:09:59.390
further and further
out and it will

00:09:59.390 --> 00:10:01.854
be more and more and
more red-shifted.

00:10:01.854 --> 00:10:03.270
Until some point,
where it's going

00:10:03.270 --> 00:10:05.380
to be so red-shifted that
we won't even observe it

00:10:05.380 --> 00:10:07.060
as electromagnetic radiation.

00:10:07.060 --> 00:10:09.740
And there's some threshold where
we won't even observe anything

00:10:09.740 --> 00:10:12.150
anymore because beyond
that, the light wasn't

00:10:12.150 --> 00:10:15.090
able to actually get to us.


Cosmic background radiation

WEBVTT
Kind: captions
Language: en

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Let's think a little bit
about what the Big Bang

00:00:02.740 --> 00:00:04.030
theory suggests.

00:00:04.030 --> 00:00:05.770
And then based on
the theory, what

00:00:05.770 --> 00:00:07.370
we should be observing today.

00:00:07.370 --> 00:00:11.660
So the Big Bang starts with
all of the mass in space

00:00:11.660 --> 00:00:15.465
in the universe, an
infinitely, an infinitely dense

00:00:15.465 --> 00:00:15.965
singularity.

00:00:15.965 --> 00:00:17.630
And a singularity
is just something

00:00:17.630 --> 00:00:19.270
that the math doesn't
even apply to it.

00:00:19.270 --> 00:00:21.510
We don't even know how
to understand that.

00:00:21.510 --> 00:00:23.140
But immediately
after the Big Bang,

00:00:23.140 --> 00:00:29.830
so this occurred 13.7 billion
years ago, 13.7 billion years

00:00:29.830 --> 00:00:34.390
ago, immediately after it, this
little tiny infinitely small

00:00:34.390 --> 00:00:36.750
singularity begins to expand.

00:00:36.750 --> 00:00:39.780
And so the first 100,000
years, it's still pretty dense.

00:00:39.780 --> 00:00:41.550
So let me just to
show this right now.

00:00:41.550 --> 00:00:43.770
So then it starts to expand.

00:00:43.770 --> 00:00:47.790
So maybe it gets to this
level right over here.

00:00:47.790 --> 00:00:54.890
And I do not know if the entire
universe is infinite or finite,

00:00:54.890 --> 00:00:57.210
whether it's a four-dimensional
sphere, whether it goes

00:00:57.210 --> 00:00:59.490
infinitely in every directions,
or whether it's just

00:00:59.490 --> 00:01:02.320
slightly curved here and there
and maybe flat everywhere else.

00:01:02.320 --> 00:01:03.670
I won't go into all of that.

00:01:03.670 --> 00:01:05.140
But then it starts to
expand a little bit

00:01:05.140 --> 00:01:06.015
from the singularity.

00:01:06.015 --> 00:01:09.610
But it's still extremely dense.

00:01:09.610 --> 00:01:10.850
It's still extremely dense.

00:01:10.850 --> 00:01:13.210
So dense that atoms
can't even form.

00:01:13.210 --> 00:01:16.500
So you just have the basic
fundamental building blocks

00:01:16.500 --> 00:01:17.000
of atoms.

00:01:17.000 --> 00:01:18.500
They're just all flying around.

00:01:18.500 --> 00:01:21.780
Electrons and protons, they're
just flying around in just

00:01:21.780 --> 00:01:26.180
this ultra-hot, ultra-hot,
white hot I could say,

00:01:26.180 --> 00:01:29.540
or maybe even white hot plasma.

00:01:29.540 --> 00:01:33.815
So I'll call it
white hot plasma.

00:01:37.380 --> 00:01:39.430
And then if we fast
forward a little bit more.

00:01:39.430 --> 00:01:42.599
And now this is a point that
we think we understand well.

00:01:42.599 --> 00:01:44.890
But this number-- I actually
looked at some old physics

00:01:44.890 --> 00:01:45.389
books.

00:01:45.389 --> 00:01:48.700
And this number has changed in
really the last 15, 20 years.

00:01:48.700 --> 00:01:50.300
So maybe it'll change more.

00:01:50.300 --> 00:01:56.070
But after 380,000 years from
the beginning of the Big Bang,

00:01:56.070 --> 00:02:02.420
300,000 years after
the Big Bang--

00:02:02.420 --> 00:02:06.460
I'll call it the BB-- 380,000
years after the Big Bang,

00:02:06.460 --> 00:02:09.139
and obviously this is give
or take a couple of years,

00:02:09.139 --> 00:02:12.669
the universe expands enough, the
universe is now large enough--

00:02:12.669 --> 00:02:14.210
and obviously, I'm
not drawing things

00:02:14.210 --> 00:02:21.930
to scale-- the universe is now
large enough and sparse enough

00:02:21.930 --> 00:02:23.740
that it can cool
down a little bit.

00:02:23.740 --> 00:02:25.540
You don't have as
much bumping around.

00:02:25.540 --> 00:02:27.160
It's still a hot place.

00:02:27.160 --> 00:02:30.820
But now, it cools down
enough that electrons

00:02:30.820 --> 00:02:32.870
can be captured by a proton.

00:02:32.870 --> 00:02:36.360
And you could actually
have-- the first hydrogen

00:02:36.360 --> 00:02:39.310
atoms can begin to form.

00:02:39.310 --> 00:02:41.430
The first hydrogen
atoms begin to form.

00:02:41.430 --> 00:02:42.755
They actually condense.

00:02:42.755 --> 00:02:46.130
And we estimate this temperature
to be around 3,000 Kelvin.

00:02:46.130 --> 00:02:48.197
So we've cooled to 3,000 Kelvin.

00:02:48.197 --> 00:02:50.280
But this is still a
temperature that you would not

00:02:50.280 --> 00:02:51.113
want to hang out in.

00:02:51.113 --> 00:02:53.440
It's still extremely,
extremely hot.

00:02:53.440 --> 00:02:56.670
Now why is this moment
important, the first atoms

00:02:56.670 --> 00:02:57.170
forming?

00:02:57.170 --> 00:02:58.961
So let's think about
what's happening here.

00:02:58.961 --> 00:03:00.980
You have all of this
bumping and interactions.

00:03:00.980 --> 00:03:03.670
And if because of a bump,
or some energy release,

00:03:03.670 --> 00:03:05.270
or because of the
heat temperature,

00:03:05.270 --> 00:03:08.220
if a photon is released
it'll be immediately absorbed

00:03:08.220 --> 00:03:09.840
by something else.

00:03:09.840 --> 00:03:11.472
If some energy gets
released, it'll

00:03:11.472 --> 00:03:13.180
immediately be absorbed
by something else

00:03:13.180 --> 00:03:15.800
because the universe
is so dense,

00:03:15.800 --> 00:03:17.680
especially with
charged particles,

00:03:17.680 --> 00:03:19.767
Here, all of a sudden,
it's not that dense.

00:03:19.767 --> 00:03:21.600
So over here, things
that were being emitted

00:03:21.600 --> 00:03:23.390
could not travel long distances.

00:03:23.390 --> 00:03:25.790
They would immediately
bump into something else.

00:03:25.790 --> 00:03:27.830
Well, you go over
here and the universe

00:03:27.830 --> 00:03:31.650
is starting to look like
the universe we recognize.

00:03:31.650 --> 00:03:34.580
All of a sudden, if one
of these really hot--

00:03:34.580 --> 00:03:37.290
and it's still nowhere near
as hot as this universe

00:03:37.290 --> 00:03:40.870
over here-- but if one of
these hot atoms emits a photon,

00:03:40.870 --> 00:03:43.767
and they would because
they are at 3,000 Kelvin,

00:03:43.767 --> 00:03:45.350
if they emit a photon,
all of a sudden

00:03:45.350 --> 00:03:49.312
there's actually space
for that photon to travel.

00:03:49.312 --> 00:03:51.520
So for the first time in
the history of the universe,

00:03:51.520 --> 00:03:55.960
380,000 years after the Big
Bang, you now have photons.

00:03:55.960 --> 00:03:58.530
You now have
electromagnetic radiation.

00:03:58.530 --> 00:04:00.500
You now have
information that can

00:04:00.500 --> 00:04:03.545
travel over long,
long distances.

00:04:03.545 --> 00:04:04.920
So given that this
happened, it's

00:04:04.920 --> 00:04:07.600
still roughly 13.7
billion years ago.

00:04:07.600 --> 00:04:12.230
380,000 years is not a lot
when you're talking about 13.7.

00:04:12.230 --> 00:04:14.545
It still wouldn't even
really change the dial

00:04:14.545 --> 00:04:16.670
because we're talking in
the hundreds of thousands.

00:04:16.670 --> 00:04:18.644
0.7 is 700 million years.

00:04:18.644 --> 00:04:20.310
So this is actually
a very small number.

00:04:20.310 --> 00:04:23.870
So it's still
approximately 13.7 billion.

00:04:23.870 --> 00:04:27.820
It's really 13.7
minus 380,000 years.

00:04:27.820 --> 00:04:30.560
But given that this was the
first time that information

00:04:30.560 --> 00:04:33.490
could travel, that photons
could travel through space

00:04:33.490 --> 00:04:36.262
without most of them having to
bump into something, especially

00:04:36.262 --> 00:04:37.720
something that's
probably charged--

00:04:37.720 --> 00:04:40.178
the other interesting thing is
that these atoms that formed

00:04:40.178 --> 00:04:43.025
are now neutral-- what could
we expect to see today?

00:04:43.025 --> 00:04:44.150
Well, let's think about it.

00:04:44.150 --> 00:04:45.240
These left.

00:04:45.240 --> 00:04:49.230
These photons were emitted
13.7 billion years ago.

00:04:49.230 --> 00:04:52.680
And they were emitted from
every point in the universe.

00:04:52.680 --> 00:04:54.595
So this is every
point in the universe.

00:05:00.230 --> 00:05:01.950
The universe was a
pretty uniform place

00:05:01.950 --> 00:05:04.404
at that time, very
minor irregularities.

00:05:04.404 --> 00:05:06.820
But you could see because it
was this white-hot thing that

00:05:06.820 --> 00:05:07.945
had just began to condense.

00:05:07.945 --> 00:05:10.519
It hadn't formed a
lot of the structures

00:05:10.519 --> 00:05:12.185
that we now associate
with the universe.

00:05:12.185 --> 00:05:15.570
It was just kind of a
fairly uniform spread of,

00:05:15.570 --> 00:05:18.655
at that time, reasonably
hot hydrogen atoms.

00:05:18.655 --> 00:05:20.280
So this is every
point in the universe.

00:05:20.280 --> 00:05:22.029
So let's think about
what's going on here.

00:05:22.029 --> 00:05:24.915
Let me draw another diagram.

00:05:24.915 --> 00:05:26.290
So we're talking
about this point

00:05:26.290 --> 00:05:28.870
in the universe right over here.

00:05:28.870 --> 00:05:32.350
The universe is, at even 380,000
years after the Big Bang,

00:05:32.350 --> 00:05:35.000
still much, much,
much, much smaller

00:05:35.000 --> 00:05:36.460
than the universe today.

00:05:36.460 --> 00:05:44.210
But let's say that this is the
point in the universe where

00:05:44.210 --> 00:05:45.530
we happen to be now.

00:05:45.530 --> 00:05:48.260
At this point in time,
there was no Earth,

00:05:48.260 --> 00:05:50.420
there was no solar system,
there was no Milky Way.

00:05:50.420 --> 00:05:54.270
It was just a bunch
of hot hydrogen atoms.

00:05:54.270 --> 00:05:56.370
Now if we were at this
point in the universe,

00:05:56.370 --> 00:06:01.340
there must been
points in the universe

00:06:01.340 --> 00:06:07.995
at that exact same time that
were emitting this radiation.

00:06:11.702 --> 00:06:13.410
And actually, every
point in the universe

00:06:13.410 --> 00:06:14.300
was emitting this radiation.

00:06:14.300 --> 00:06:16.050
The point of the
universe where we are now

00:06:16.050 --> 00:06:19.000
is emitting this radiation.

00:06:19.000 --> 00:06:23.280
So the points that
were closer to us,

00:06:23.280 --> 00:06:24.750
it was emitting that radiation.

00:06:24.750 --> 00:06:27.500
But it got to us much sooner.

00:06:27.500 --> 00:06:29.750
It got to us billions
of years ago.

00:06:29.750 --> 00:06:31.755
But there are some points
that were far enough

00:06:31.755 --> 00:06:36.205
that that radiation must
be getting to us right now.

00:06:36.205 --> 00:06:37.663
Or another way to
think about it is

00:06:37.663 --> 00:06:41.820
that radiation has taken 13.7
billion years to reach us.

00:06:41.820 --> 00:06:42.970
So let me draw.

00:06:42.970 --> 00:06:45.499
So if I were to draw the
visible universe today--

00:06:45.499 --> 00:06:47.290
and you know from the
video about the size.

00:06:47.290 --> 00:06:48.550
So it's not going
to be to scale.

00:06:48.550 --> 00:06:50.064
It would have to
be far, far larger

00:06:50.064 --> 00:06:51.230
than the circle I drew here.

00:06:51.230 --> 00:06:54.020
But let's say that this
is the visible universe.

00:06:54.020 --> 00:06:56.810
Let's say this is the
visible universe today.

00:06:56.810 --> 00:06:59.340
We should be receiving-- and
we're in the center of it

00:06:59.340 --> 00:07:01.660
because we can always look
roughly the same distance

00:07:01.660 --> 00:07:02.280
in every direction.

00:07:02.280 --> 00:07:03.470
We're not the center
of the universe.

00:07:03.470 --> 00:07:04.270
I want to be clear.

00:07:04.270 --> 00:07:06.810
We're the center of the
observable universe because we

00:07:06.810 --> 00:07:09.710
can only observe the same
distance in all directions.

00:07:09.710 --> 00:07:15.590
Now, we're receiving some light
from 100,000 light years away.

00:07:15.590 --> 00:07:17.940
And then we're looking
100,000 years in the past.

00:07:17.940 --> 00:07:22.430
We should be receiving
some light that was first

00:07:22.430 --> 00:07:24.284
emitted a million
light years before.

00:07:24.284 --> 00:07:26.450
And that's like looking a
million years in the past.

00:07:26.450 --> 00:07:29.539
Because the light we see was
emitted a million years ago.

00:07:29.539 --> 00:07:30.830
I think that's a bit redundant.

00:07:30.830 --> 00:07:34.150
We could see light
that's just getting

00:07:34.150 --> 00:07:36.570
to us after traveling
for a billion years.

00:07:36.570 --> 00:07:38.544
And so we're actually
looking at those objects

00:07:38.544 --> 00:07:39.960
a billion years
ago because that's

00:07:39.960 --> 00:07:41.126
when they emitted the light.

00:07:41.126 --> 00:07:43.390
So the same way, we
could look at objects

00:07:43.390 --> 00:07:47.400
that emitted their light
13.7 billion years ago,

00:07:47.400 --> 00:07:48.910
right at the beginning.

00:07:48.910 --> 00:07:50.650
Right at this stage
over here, right

00:07:50.650 --> 00:07:53.620
after 380,000 years
after the Big Bang.

00:07:53.620 --> 00:07:57.020
And so since that light
is only just reaching us,

00:07:57.020 --> 00:08:02.920
we will see it as it was
13.7 billion years ago.

00:08:02.920 --> 00:08:05.370
So we should see this
type of radiation.

00:08:05.370 --> 00:08:08.620
Now the other thing to remember,
the universe was expanding.

00:08:08.620 --> 00:08:11.030
When this was emitted, the
universe was expanding.

00:08:11.030 --> 00:08:14.090
The universe was expanding
at a very-- well,

00:08:14.090 --> 00:08:16.320
it's all relative what's a
fast rate and all of that.

00:08:16.320 --> 00:08:17.410
But it was expanding.

00:08:17.410 --> 00:08:19.560
And we learned on the
video in red shift

00:08:19.560 --> 00:08:23.996
that when the source of the
light is moving away from you,

00:08:23.996 --> 00:08:26.440
or the source of the
electromagnetic radiation

00:08:26.440 --> 00:08:29.670
is moving away from you,
the radiation itself get red

00:08:29.670 --> 00:08:30.490
shifted.

00:08:30.490 --> 00:08:33.289
So even though this is at a
relatively high frequency--

00:08:33.289 --> 00:08:36.559
you can almost imagine it
was kind of red-hot gas.

00:08:36.559 --> 00:08:39.890
It was at 3,000 Kelvin--
because it was moving away

00:08:39.890 --> 00:08:43.159
from us, these things--
and we learned in the video

00:08:43.159 --> 00:08:48.739
on the actual size of
the observable universe,

00:08:48.739 --> 00:08:50.530
even though these
electromagnetic waves are

00:08:50.530 --> 00:08:52.960
taking 13.7 billion
years to reach us,

00:08:52.960 --> 00:08:56.190
in that time, this point in
space, the point in space that

00:08:56.190 --> 00:08:58.390
emitted those
electromagnetic waves are

00:08:58.390 --> 00:09:01.124
about 46 billion
light years away.

00:09:01.124 --> 00:09:02.290
So that's our best estimate.

00:09:02.290 --> 00:09:05.120
So this is still
stretching away.

00:09:05.120 --> 00:09:07.225
So theory, if you
believe all of this,

00:09:07.225 --> 00:09:10.490
that this was about 3,000
Kelvin and it gets red shifted,

00:09:10.490 --> 00:09:12.250
theory would have
it that we should

00:09:12.250 --> 00:09:19.370
see not something analogous
to electromagnetic waves being

00:09:19.370 --> 00:09:23.440
released from a 3,000
degree temperature atom.

00:09:23.440 --> 00:09:25.980
We should see
something red shifted

00:09:25.980 --> 00:09:28.200
into the radio spectrum.

00:09:28.200 --> 00:09:33.020
So we should be
observing radio waves.

00:09:33.020 --> 00:09:35.270
And the reason why we're
observing radio waves and not

00:09:35.270 --> 00:09:38.580
something of a higher frequency
is because it got red shifted.

00:09:38.580 --> 00:09:40.600
It got red shifted down
into a lower frequency.

00:09:40.600 --> 00:09:42.230
And remember, we
should be seeing it

00:09:42.230 --> 00:09:45.260
from every point in the universe
where the photons have been

00:09:45.260 --> 00:09:48.040
traveling for 13.7
billion years.

00:09:48.040 --> 00:09:51.290
We should see it all around us.

00:09:51.290 --> 00:09:52.690
This is almost a
necessity for us

00:09:52.690 --> 00:09:55.730
to really believe in the
current Big Bang theory.

00:09:55.730 --> 00:09:58.130
And it turns out that
we did observe this.

00:09:58.130 --> 00:09:59.690
And this is very unintuitive.

00:09:59.690 --> 00:10:02.270
Because you look at any
other point in the universe,

00:10:02.270 --> 00:10:03.104
it's nonuniform.

00:10:03.104 --> 00:10:04.520
Every other point
in the universe,

00:10:04.520 --> 00:10:06.176
you have stars and galaxies.

00:10:06.176 --> 00:10:07.300
These aren't atoms anymore.

00:10:07.300 --> 00:10:10.190
These are stars, and
galaxies, and whatnot.

00:10:10.190 --> 00:10:11.940
And so there's some
points in the universe

00:10:11.940 --> 00:10:13.750
where you see a
lot of radiation.

00:10:13.750 --> 00:10:16.375
And there's other points in the
universe where you see nothing.

00:10:16.375 --> 00:10:17.090
It's just black.

00:10:17.090 --> 00:10:20.900
But if this is correct,
if this really did happen,

00:10:20.900 --> 00:10:23.850
we should be able to
observe uniform radio

00:10:23.850 --> 00:10:26.290
waves from every
direction around us.

00:10:26.290 --> 00:10:29.150
And you go 300-- or
more than 360 degrees.

00:10:29.150 --> 00:10:32.030
We're going in three dimensions.

00:10:32.030 --> 00:10:35.540
Any direction you point an
antenna, a radio antenna,

00:10:35.540 --> 00:10:37.852
you should be receiving
these radio waves that

00:10:37.852 --> 00:10:40.060
were at much higher frequency
when they were emitted.

00:10:40.060 --> 00:10:41.351
They had been red shifted then.

00:10:41.351 --> 00:10:44.020
But they were emitted
13.7 billion years ago.

00:10:44.020 --> 00:10:46.810
And, it turns out
in the late 1960s,

00:10:46.810 --> 00:10:50.080
they did find these radio
waves from every direction.

00:10:50.080 --> 00:10:53.250
And these are
called the cosmic--

00:10:53.250 --> 00:10:54.440
let me write this down.

00:10:54.440 --> 00:11:06.600
This is the cosmic microwave
background radiation.

00:11:06.600 --> 00:11:11.729
And it's this in combination--
so it's this data

00:11:11.729 --> 00:11:13.270
that we're getting,
this observation,

00:11:13.270 --> 00:11:15.380
in combination with the
fact that the further

00:11:15.380 --> 00:11:19.810
we look out to galaxies
and clusters of galaxies,

00:11:19.810 --> 00:11:21.640
they all seem to be
moving away from us.

00:11:21.640 --> 00:11:22.430
They're all red shifted.

00:11:22.430 --> 00:11:24.013
And they get red
shifted more and more

00:11:24.013 --> 00:11:25.170
the further we look out.

00:11:25.170 --> 00:11:28.410
So this and everything being
redshifted away from us

00:11:28.410 --> 00:11:31.150
are the best two points of
evidence for the actual Big

00:11:31.150 --> 00:11:31.920
Bang.

00:11:31.920 --> 00:11:35.510
So hopefully, you found
that reasonably interesting.


Four fundamental forces

WEBVTT
Kind: captions
Language: en

00:00:00.294 --> 00:00:01.710
What I want to do
in this video is

00:00:01.710 --> 00:00:08.160
give a very high-level overview
of the four fundamental forces

00:00:08.160 --> 00:00:09.280
of the universe.

00:00:09.280 --> 00:00:10.795
And I'm going to
start with gravity.

00:00:14.210 --> 00:00:17.310
And it might surprise some of
you that gravity is actually

00:00:17.310 --> 00:00:19.640
the weakest of the four
fundamental forces.

00:00:19.640 --> 00:00:21.590
And that's surprising
because you say, wow,

00:00:21.590 --> 00:00:24.220
that's what keeps us glued--
not glued-- but it keeps us

00:00:24.220 --> 00:00:25.800
from jumping off the planet.

00:00:25.800 --> 00:00:28.220
It's what keeps the Moon
in orbit around the Earth,

00:00:28.220 --> 00:00:31.770
the Earth in orbit around
the Sun, the Sun in orbit

00:00:31.770 --> 00:00:35.290
around the center of
the Milky Way galaxy.

00:00:35.290 --> 00:00:36.970
So if it's a little
bit surprising

00:00:36.970 --> 00:00:39.810
that it's actually the
weakest of the forces.

00:00:39.810 --> 00:00:43.110
And that starts to make
sense when you actually

00:00:43.110 --> 00:00:45.460
think about things on maybe
more of a human scale,

00:00:45.460 --> 00:00:47.840
or a molecular scale,
or even atomic scale.

00:00:47.840 --> 00:00:52.190
Even on a human scale, your
computer monitor and you,

00:00:52.190 --> 00:00:54.290
have some type of
gravitational attraction.

00:00:54.290 --> 00:00:55.540
But you don't notice it.

00:00:55.540 --> 00:00:57.450
Or your cell phone and
your wallet, there's

00:00:57.450 --> 00:00:58.590
gravitational attraction.

00:00:58.590 --> 00:01:00.923
But you don't see them being
drawn to each other the way

00:01:00.923 --> 00:01:03.830
you might see two magnets
drawn to each other

00:01:03.830 --> 00:01:05.140
or repelled from each other.

00:01:05.140 --> 00:01:06.723
And if you go to
even a smaller scale,

00:01:06.723 --> 00:01:08.800
you'll see the it
matters even less.

00:01:08.800 --> 00:01:10.840
We never even talk about
gravity in chemistry,

00:01:10.840 --> 00:01:12.950
although the gravity is there.

00:01:12.950 --> 00:01:15.370
But at those scales,
the other forces really,

00:01:15.370 --> 00:01:17.580
really, really
start to dominate.

00:01:17.580 --> 00:01:19.020
So gravity is our weakest.

00:01:19.020 --> 00:01:21.950
So if we move up a
little bit from that,

00:01:21.950 --> 00:01:25.510
we get-- and this is maybe
the hardest force for us

00:01:25.510 --> 00:01:27.190
to visualize.

00:01:27.190 --> 00:01:30.540
Or it's, at least, the least
intuitive force for me--

00:01:30.540 --> 00:01:34.820
is actually the weak
force, sometimes called

00:01:34.820 --> 00:01:38.210
the weak interaction.

00:01:38.210 --> 00:01:41.250
And it's what's responsible
for radioactive decay,

00:01:41.250 --> 00:01:43.850
in particular beta minus
and beta plus decay.

00:01:43.850 --> 00:01:47.720
And just to give you an example
of the actual weak interaction,

00:01:47.720 --> 00:01:55.660
if I had some cesium-137--
137 means it has 137 nucleons.

00:01:55.660 --> 00:01:58.230
A nucleon is either a
proton or a neutron.

00:01:58.230 --> 00:02:00.310
You add up the protons
and neutrons of cesium,

00:02:00.310 --> 00:02:01.970
you get 137.

00:02:01.970 --> 00:02:07.301
And it is cesium, because
it has exactly 55 protons.

00:02:07.301 --> 00:02:08.759
Now, the weak
interaction is what's

00:02:08.759 --> 00:02:12.260
responsible for one of
the neutrons-- essentially

00:02:12.260 --> 00:02:14.690
one of its quarks flipping
and turning into a proton.

00:02:14.690 --> 00:02:16.940
And I'm not going to go into
detail of what a quark is

00:02:16.940 --> 00:02:18.090
and all of that.

00:02:18.090 --> 00:02:20.347
And the math can
get pretty hairy.

00:02:20.347 --> 00:02:21.930
But I just want to
give you an example

00:02:21.930 --> 00:02:23.346
of what the weak
interaction does.

00:02:23.346 --> 00:02:26.630
So if one of these neutrons
turns into a proton,

00:02:26.630 --> 00:02:28.815
then we're going to
have one extra proton.

00:02:28.815 --> 00:02:31.930
But we're going to have the
same number of nucleons.

00:02:31.930 --> 00:02:34.370
Instead of an
extra neutron here,

00:02:34.370 --> 00:02:36.420
you now have an
extra proton here.

00:02:36.420 --> 00:02:38.260
And so now this is
a different atom.

00:02:38.260 --> 00:02:40.430
It is now barium.

00:02:40.430 --> 00:02:42.480
And in that flipping,
it will actually

00:02:42.480 --> 00:02:49.550
emit an electron and an
anti-electron neutrino.

00:02:49.550 --> 00:02:52.290
And I'm not going to go
into the details of what

00:02:52.290 --> 00:02:54.670
an anti-electron neutrino is.

00:02:54.670 --> 00:02:56.430
These are fundamental particles.

00:02:56.430 --> 00:02:58.690
But this is just what
the weak interaction is.

00:02:58.690 --> 00:03:00.830
It's not something that's
completely obvious to us.

00:03:00.830 --> 00:03:03.960
It's not the kind of this
traditional things pulling

00:03:03.960 --> 00:03:06.730
or pushing away from
each other, like we

00:03:06.730 --> 00:03:09.964
associate with the other forces.

00:03:09.964 --> 00:03:11.630
Now, the next strongest
force-- and just

00:03:11.630 --> 00:03:14.080
to give a sense of
how weak gravity

00:03:14.080 --> 00:03:18.020
is even relative to
the weak interaction,

00:03:18.020 --> 00:03:23.035
the weak interaction
is 10 to the 25th times

00:03:23.035 --> 00:03:24.035
the strength of gravity.

00:03:26.780 --> 00:03:29.080
And you might be saying,
if this is so strong, how

00:03:29.080 --> 00:03:30.890
come this does it
operate on planets

00:03:30.890 --> 00:03:35.470
or us relative to the Earth?

00:03:35.470 --> 00:03:38.902
Why doesn't this apply to
intergalactic distances

00:03:38.902 --> 00:03:39.776
the way gravity does?

00:03:39.776 --> 00:03:43.310
And the reason is the weak
interaction really applies

00:03:43.310 --> 00:03:50.100
to very small distances,
very, very small distances.

00:03:50.100 --> 00:03:53.280
So it can be much
stronger than gravity,

00:03:53.280 --> 00:03:55.380
but only over very,
very-- and it really

00:03:55.380 --> 00:03:57.520
only applies on the
subatomic scale.

00:03:57.520 --> 00:03:59.690
You go anything beyond
that, it kind of

00:03:59.690 --> 00:04:03.870
disappears as an actual force,
as an actual interaction.

00:04:03.870 --> 00:04:07.430
Now, the next force
up the hierarchy,

00:04:07.430 --> 00:04:10.530
which is one that we
are more familiar with,

00:04:10.530 --> 00:04:13.540
it's what actually dominates
most of the chemistry

00:04:13.540 --> 00:04:16.760
that we deal with
and electromagnetism

00:04:16.760 --> 00:04:19.975
that we deal with, and that's
the electromagnetic force.

00:04:19.975 --> 00:04:29.820
Let me write it in magenta,
electromagnetic force.

00:04:29.820 --> 00:04:34.541
And just to give a sense,
this is 10 to the 36 times

00:04:34.541 --> 00:04:35.540
the strength of gravity.

00:04:38.082 --> 00:04:40.040
So it kind of puts the
weak force in its place.

00:04:40.040 --> 00:04:42.540
It's 10 to the 12th times
stronger than the weak force.

00:04:42.540 --> 00:04:44.040
So these are huge
numbers that we're

00:04:44.040 --> 00:04:45.831
talking about, either
this relative to that

00:04:45.831 --> 00:04:48.539
or even this
relative to gravity.

00:04:48.539 --> 00:04:50.080
And so you might be
saying, well, you

00:04:50.080 --> 00:04:53.150
know the electromagnetic force,
that's unbelievably strong.

00:04:53.150 --> 00:04:58.890
Why doesn't that apply over
these kind of macro scales

00:04:58.890 --> 00:04:59.790
like gravity?

00:04:59.790 --> 00:05:03.310
Let me write it
there, macro scales.

00:05:03.310 --> 00:05:05.170
Why doesn't it apply
to macro scales?

00:05:05.170 --> 00:05:08.595
And there's nothing about the
electromagnetic force, why

00:05:08.595 --> 00:05:12.830
it can't, or it actually does
apply over large distances.

00:05:12.830 --> 00:05:16.550
The reality though, is you don't
have these huge concentrations

00:05:16.550 --> 00:05:23.830
of either Coulomb charges or
magnetism the way you do mass.

00:05:23.830 --> 00:05:26.310
So the mass that you have
such huge concentrations,

00:05:26.310 --> 00:05:28.690
it can operate over
huge, huge distances,

00:05:28.690 --> 00:05:31.450
even though it's
way, way, way weaker

00:05:31.450 --> 00:05:32.850
than the electromagnetic force.

00:05:32.850 --> 00:05:34.650
The electromagnetic
force, what happens

00:05:34.650 --> 00:05:37.740
is because it's both
attractive and repulsive,

00:05:37.740 --> 00:05:39.440
it tends to kind
of sort itself out.

00:05:39.440 --> 00:05:41.970
So you don't have these huge,
huge, huge concentrations

00:05:41.970 --> 00:05:42.930
of charge.

00:05:42.930 --> 00:05:44.971
Now, the other thing you
might be wondering about

00:05:44.971 --> 00:05:47.820
is, why is it called the
electromagnetic force?

00:05:47.820 --> 00:05:52.130
In our everyday life, there's
things like the Coulomb force

00:05:52.130 --> 00:05:55.740
or the electrostatic force,
which we're familiar with.

00:05:55.740 --> 00:05:58.810
Positive charges or
like charges want

00:05:58.810 --> 00:06:00.810
to repel-- if both of
these were negative,

00:06:00.810 --> 00:06:02.280
the same thing
would be happening--

00:06:02.280 --> 00:06:06.170
and different charges
like to attract.

00:06:06.170 --> 00:06:07.500
We've seen this multiple times.

00:06:07.500 --> 00:06:10.330
This is the Coulomb force
or the electrostatic force.

00:06:13.220 --> 00:06:16.240
And then on the other
side of the word, I guess,

00:06:16.240 --> 00:06:17.720
you have the magnetic part.

00:06:17.720 --> 00:06:21.710
And magnets, you've played
with magnets on your fridge.

00:06:21.710 --> 00:06:23.850
If they're the same
side of the magnet,

00:06:23.850 --> 00:06:25.364
they're going to
repel each other.

00:06:25.364 --> 00:06:27.280
If they're the opposite
sides, opposite poles,

00:06:27.280 --> 00:06:28.780
they're going to
attract each other.

00:06:28.780 --> 00:06:30.332
So why is it called one force?

00:06:30.332 --> 00:06:32.290
And it's called one
force-- and once again, I'm

00:06:32.290 --> 00:06:34.970
not going to go into
detail here-- it's

00:06:34.970 --> 00:06:37.670
called one force
because it turns out,

00:06:37.670 --> 00:06:41.180
that the Coulomb force,
the electrostatic force

00:06:41.180 --> 00:06:44.210
and magnetic force are
actually the same thing viewed

00:06:44.210 --> 00:06:46.922
in different frames
of references.

00:06:46.922 --> 00:06:48.380
So I won't go into
a lot of detail.

00:06:48.380 --> 00:06:49.880
But just keep that in the
back of your mind, that they

00:06:49.880 --> 00:06:50.520
are connected.

00:06:50.520 --> 00:06:51.978
And in a future
video, I'll go more

00:06:51.978 --> 00:06:54.330
into the intuition of
how they are connected.

00:06:54.330 --> 00:07:00.800
And it's more apparent
when the charges are moving

00:07:00.800 --> 00:07:03.550
at relativistic frames
and you have-- well,

00:07:03.550 --> 00:07:05.350
I won't go into a
lot of detail there.

00:07:05.350 --> 00:07:06.933
But just keep in
mind that they really

00:07:06.933 --> 00:07:10.060
are the same force, just
viewed from different frames

00:07:10.060 --> 00:07:11.010
of reference.

00:07:11.010 --> 00:07:13.060
Now, the strongest of
the force is probably

00:07:13.060 --> 00:07:15.480
the best named of them all.

00:07:15.480 --> 00:07:18.770
And that's the strong force.

00:07:18.770 --> 00:07:24.340
That is the strong force.

00:07:24.340 --> 00:07:26.670
And although you probably
haven't seen this yet

00:07:26.670 --> 00:07:28.320
in chemistry
classes, it actually

00:07:28.320 --> 00:07:30.040
applies very strongly
in chemistry.

00:07:30.040 --> 00:07:34.450
Because from the get-go, when
you first learn about atoms--

00:07:34.450 --> 00:07:35.580
let me draw a helium atom.

00:07:35.580 --> 00:07:42.350
A helium atom has two
protons in its nucleus

00:07:42.350 --> 00:07:45.380
and it has two neutrons.

00:07:45.380 --> 00:07:47.920
And then it also has two
electrons circulating around.

00:07:47.920 --> 00:07:48.850
So it has an electron.

00:07:48.850 --> 00:07:50.890
And I could draw the
electron as much smaller.

00:07:50.890 --> 00:07:53.890
Well, I won't try to do
anything in relative size.

00:07:53.890 --> 00:07:55.830
But it has two electrons
floating around.

00:07:55.830 --> 00:07:58.730
And one question that may or may
not have jumped into your mind

00:07:58.730 --> 00:08:01.610
when you first saw
this model of an atom

00:08:01.610 --> 00:08:04.290
is like, well, I see
why the electrons are

00:08:04.290 --> 00:08:05.780
attracted to the nucleus.

00:08:05.780 --> 00:08:07.680
It has a negative
Coulomb charge.

00:08:07.680 --> 00:08:10.570
The nucleus has a net
positive Coulomb charge.

00:08:10.570 --> 00:08:12.140
But what's not so
obvious and what

00:08:12.140 --> 00:08:14.790
tends not to sometimes be
explained in chemistry class

00:08:14.790 --> 00:08:16.410
is these two
positive charges are

00:08:16.410 --> 00:08:17.970
sitting right next
to each other.

00:08:17.970 --> 00:08:21.257
If the electromagnetic force
was the only force in play,

00:08:21.257 --> 00:08:23.340
if the Coulomb force was
the only thing happening,

00:08:23.340 --> 00:08:26.280
these guys would just
run away from each other.

00:08:26.280 --> 00:08:27.874
They could repel each other.

00:08:27.874 --> 00:08:29.290
And so the only
reason why they're

00:08:29.290 --> 00:08:31.680
able to stick to each
other is that there's

00:08:31.680 --> 00:08:34.730
an even stronger force than
the electromagnetic force

00:08:34.730 --> 00:08:37.900
operating at these very,
very, very small distances.

00:08:37.900 --> 00:08:42.000
So if you get two of these
protons close enough together,

00:08:42.000 --> 00:08:45.090
and the strong force only
applies over very, very, very

00:08:45.090 --> 00:08:47.760
small distances,
subatomic or I should even

00:08:47.760 --> 00:08:52.480
say subnucleic distances,
then the strong interaction

00:08:52.480 --> 00:08:53.460
comes into play.

00:08:53.460 --> 00:08:56.360
So then you have the strong
interaction actually keeping

00:08:56.360 --> 00:08:57.880
these charges together.

00:08:57.880 --> 00:09:02.100
And once again, just to keep
it in mind relative to gravity,

00:09:02.100 --> 00:09:09.100
it is 10 to the 38th times
the strength of gravity.

00:09:09.100 --> 00:09:12.505
Or it's about 100 times stronger
than the electromagnetic force.

00:09:12.505 --> 00:09:13.880
So once again,
the reason why you

00:09:13.880 --> 00:09:15.710
don't see the
strong force, which

00:09:15.710 --> 00:09:17.360
is the strongest
of all the forces,

00:09:17.360 --> 00:09:20.310
or the weak interaction,
applying over huge scales

00:09:20.310 --> 00:09:24.700
is that their strength
dies off super, super fast.

00:09:24.700 --> 00:09:28.630
Even when you start going
to a larger radius nucleuses

00:09:28.630 --> 00:09:30.920
of atoms, the strength
starts to die off,

00:09:30.920 --> 00:09:32.674
especially for the strong force.

00:09:32.674 --> 00:09:35.340
The reason why you don't see the
electromagnetic force operating

00:09:35.340 --> 00:09:38.050
over large distances, even
though in theory it can,

00:09:38.050 --> 00:09:40.230
like gravity, is
that you don't see

00:09:40.230 --> 00:09:42.370
the type of charge
concentrations the way

00:09:42.370 --> 00:09:45.130
you see mass concentrations
in the universe.

00:09:45.130 --> 00:09:46.820
Because the charge
concentrations

00:09:46.820 --> 00:09:47.917
tend to sort them out.

00:09:47.917 --> 00:09:48.875
They start to equalize.

00:09:52.210 --> 00:09:55.020
If I have a huge
positive charge there

00:09:55.020 --> 00:09:57.130
and a huge negative
charge there,

00:09:57.130 --> 00:10:00.890
they will attract each
other and then become

00:10:00.890 --> 00:10:04.110
essentially a big lump
of neutral charge.

00:10:04.110 --> 00:10:06.280
And once they're a big
lump of neutral charge,

00:10:06.280 --> 00:10:08.100
they won't interact
with anything else.

00:10:08.100 --> 00:10:11.170
And gravity, if you have
one mass and another mass,

00:10:11.170 --> 00:10:13.540
and they attract
each other, then you

00:10:13.540 --> 00:10:15.040
have another mass
that's even better

00:10:15.040 --> 00:10:17.480
to attracting at other masses.

00:10:17.480 --> 00:10:19.810
And so it'll keep
attracting things to it.

00:10:19.810 --> 00:10:21.690
So it kind of
snowballs the process.

00:10:21.690 --> 00:10:24.440
And that's why gravity operates
on these really, really

00:10:24.440 --> 00:10:26.710
large, large objects
in our universe

00:10:26.710 --> 00:10:29.290
and on the universe as a whole.


Cosmological time scale 2

WEBVTT
Kind: captions
Language: en

00:00:00.650 --> 00:00:04.890
In the last video, we tried to
relate what 13.7 billion years

00:00:04.890 --> 00:00:07.530
really means by compressing
it to 10 years, which is still

00:00:07.530 --> 00:00:10.390
a pretty long time, at
least from our perspective.

00:00:10.390 --> 00:00:13.840
And we saw that these huge
periods of time, everything

00:00:13.840 --> 00:00:16.890
that's happened since
the United States

00:00:16.890 --> 00:00:19.470
Declaration of
Independence, all gets

00:00:19.470 --> 00:00:21.220
compressed into
just five seconds.

00:00:21.220 --> 00:00:25.170
And that's not much when
you think about 10 years.

00:00:25.170 --> 00:00:27.230
I mean 10 years, you
could wait around a lot.

00:00:27.230 --> 00:00:29.130
That's a huge amount of time.

00:00:29.130 --> 00:00:31.979
So hopefully, that put things
in perspective a little bit.

00:00:31.979 --> 00:00:34.520
What I want to do in this video
is kind of do the same thing,

00:00:34.520 --> 00:00:37.950
but relate the 13.7
billion years, if that were

00:00:37.950 --> 00:00:40.470
a distance or the
length of a time line,

00:00:40.470 --> 00:00:44.070
how big each of these
periods would be.

00:00:44.070 --> 00:00:46.280
So just to start off,
at the timeline--

00:00:46.280 --> 00:00:48.710
I'm recording this in
high definition right now.

00:00:48.710 --> 00:00:51.187
There should be
1,280 pixels wide,

00:00:51.187 --> 00:00:52.770
depending on where
you're watching it.

00:00:52.770 --> 00:00:55.060
So maybe you're watching
it on a high def TV.

00:00:55.060 --> 00:00:58.650
If the timeline was
width of my screen right

00:00:58.650 --> 00:01:02.130
over here, if the timeline was
the width of my screen here,

00:01:02.130 --> 00:01:04.900
so if that was
13.7 billion years,

00:01:04.900 --> 00:01:08.122
from there-- let's say this is
the beginning of the universe

00:01:08.122 --> 00:01:09.330
and this is our present time.

00:01:09.330 --> 00:01:13.730
If that was 13.7 billion
years, the amount

00:01:13.730 --> 00:01:18.180
of time that humans have been
on this planet-- modern humans,

00:01:18.180 --> 00:01:21.290
so people who look and think
like us-- the amount of time

00:01:21.290 --> 00:01:24.840
that we have been on this
planet will not even be a pixel.

00:01:24.840 --> 00:01:27.180
This little dot I drew
is multiple pixels.

00:01:27.180 --> 00:01:30.730
The amount of time we've been
here would not even be a pixel.

00:01:30.730 --> 00:01:32.630
In fact, a pixel--
and that dot I

00:01:32.630 --> 00:01:34.590
drew here is about four pixels.

00:01:34.590 --> 00:01:38.810
But a pixel, just one
little pixel on my screen,

00:01:38.810 --> 00:01:42.179
would represent
11 million years.

00:01:42.179 --> 00:01:43.095
Let me scroll over it.

00:01:43.095 --> 00:01:49.960
It would represent
11 million years.

00:01:49.960 --> 00:01:53.700
So if this was the
timeline, the dinosaurs

00:01:53.700 --> 00:01:57.580
would have been extinct about
six pixels from the end.

00:01:57.580 --> 00:02:01.280
So it would be right about--
so six pixels from the end

00:02:01.280 --> 00:02:03.762
is when the dinosaurs
would have gotten extinct.

00:02:03.762 --> 00:02:06.220
And the amount of time that
modern humans are on the planet

00:02:06.220 --> 00:02:07.630
wouldn't even register here.

00:02:07.630 --> 00:02:11.100
It would be 1/20 of
that pixel over there.

00:02:11.100 --> 00:02:14.840
In fact, if we just expanded
that very last pixel--

00:02:14.840 --> 00:02:17.800
if we were to expand
that very last pixel--

00:02:17.800 --> 00:02:21.010
I'll do it in yellow-- that very
last tiny pixel that you can't

00:02:21.010 --> 00:02:24.250
see, if we were expand
that to the entire length

00:02:24.250 --> 00:02:28.700
of this screen again-- so
if we were to just expand

00:02:28.700 --> 00:02:31.530
just that very last pixel--
so I'm saying everything

00:02:31.530 --> 00:02:35.280
on this yellow line could be
contained in that very last dot

00:02:35.280 --> 00:02:41.150
right over there, then
every pixel in this

00:02:41.150 --> 00:02:45.160
would still be 8,000 years.

00:02:45.160 --> 00:02:47.320
So the entire period
of time that humanity

00:02:47.320 --> 00:02:51.150
has been on this
planet on this scale--

00:02:51.150 --> 00:02:53.700
so we've broken out this
little tiny pixel here all

00:02:53.700 --> 00:02:59.280
the way out here, 200,000 years,
that's on the order of about 25

00:02:59.280 --> 00:03:00.490
of these pixels.

00:03:00.490 --> 00:03:06.840
So 25 of these pixels would
be something like that,

00:03:06.840 --> 00:03:08.870
not even that, not even that.

00:03:08.870 --> 00:03:12.450
So 25 pixels on this screen--
at least at my resolution,

00:03:12.450 --> 00:03:14.230
is about that distance.

00:03:14.230 --> 00:03:17.980
So this is the fraction
of just that pixel that

00:03:17.980 --> 00:03:20.820
is the amount of time humans
have been on the planet.

00:03:20.820 --> 00:03:22.970
If you want the
time since Jesus,

00:03:22.970 --> 00:03:27.120
it would be 1/4 of a pixel
on this yellow scale.

00:03:27.120 --> 00:03:30.376
On this yellow scale, it
would be 1/4 of a pixel.

00:03:30.376 --> 00:03:32.750
And the amount of time to the
Declaration of Independence

00:03:32.750 --> 00:03:36.121
would be even a more
minuscule amount of time.

00:03:36.121 --> 00:03:37.620
So that's one way
to think about it.

00:03:37.620 --> 00:03:40.430
But these timelines to some
degree also don't give justice.

00:03:40.430 --> 00:03:41.805
So another way to
think about it,

00:03:41.805 --> 00:03:44.450
what if we had a time line
that stretched from here,

00:03:44.450 --> 00:03:46.270
where I am, in this
San Francisco Bay

00:03:46.270 --> 00:03:50.320
Area, if it stretched 1,300
kilometers to Seattle?

00:03:50.320 --> 00:03:52.950
So if this thing
stretched 1,300 kilometers

00:03:52.950 --> 00:03:56.610
all the way to Seattle, so
this thing, the Big Bang,

00:03:56.610 --> 00:03:59.010
would be sitting in Seattle.

00:03:59.010 --> 00:04:01.150
This would be
sitting in Seattle.

00:04:01.150 --> 00:04:05.790
The universe--
well, the formation

00:04:05.790 --> 00:04:07.910
of the Earth and the
solar system, this

00:04:07.910 --> 00:04:11.360
would be about 200
kilometers away,

00:04:11.360 --> 00:04:13.610
a little over 200 kilometers.

00:04:13.610 --> 00:04:15.820
And in the direction of
Seattle, I don't know,

00:04:15.820 --> 00:04:17.519
that would get us in
probably some part

00:04:17.519 --> 00:04:20.429
of northern California
with redwoods and whatnot.

00:04:20.429 --> 00:04:22.220
But just to give an
idea of 200 kilometers,

00:04:22.220 --> 00:04:25.550
that would get me from where I
am near the coast of California

00:04:25.550 --> 00:04:27.050
to about the Nevada border.

00:04:27.050 --> 00:04:30.070
So still a pretty
good distance relative

00:04:30.070 --> 00:04:32.030
to the entire timeline.

00:04:32.030 --> 00:04:37.360
The dinosaurs, the
last land dinosaurs,

00:04:37.360 --> 00:04:40.480
when the Earth got hit by an
asteroid this-- so remember,

00:04:40.480 --> 00:04:43.670
our whole timeline now stretches
all the way to Seattle.

00:04:43.670 --> 00:04:47.310
This event now would
have only occurred

00:04:47.310 --> 00:04:52.180
about 3,000 meters away.

00:04:52.180 --> 00:04:55.500
Or maybe I should just say
three kilometers away or roughly

00:04:55.500 --> 00:04:56.457
about two miles.

00:04:56.457 --> 00:04:58.540
So that's still seems like
a pretty good distance.

00:04:58.540 --> 00:05:01.300
But remember, our timelines
stretches all the way

00:05:01.300 --> 00:05:03.960
to Seattle from the
San Francisco area.

00:05:03.960 --> 00:05:05.430
So it's a pretty big timeline.

00:05:05.430 --> 00:05:08.350
So this is already a
pretty small distance.

00:05:08.350 --> 00:05:09.800
But it gets even smaller.

00:05:09.800 --> 00:05:13.640
Australopithecus,
this right over here,

00:05:13.640 --> 00:05:16.367
when they were roaming the
Earth 3 million years ago,

00:05:16.367 --> 00:05:17.950
this gets reduced
to a little bit more

00:05:17.950 --> 00:05:25.040
than a football field, about
150 meters, not kilometers.

00:05:25.040 --> 00:05:28.100
Let me write that in a color
where there's some contrast.

00:05:28.100 --> 00:05:33.370
150 meters is
where-- so 150 meters

00:05:33.370 --> 00:05:34.960
in the direction of
Seattle, if that's

00:05:34.960 --> 00:05:36.870
the timeline that
we're talking about.

00:05:36.870 --> 00:05:38.590
And then the first
humans, even shorter.

00:05:38.590 --> 00:05:42.330
It's only going to be 10 meters,
10 meters of this timeline that

00:05:42.330 --> 00:05:46.300
stretches all the
way to Seattle.

00:05:46.300 --> 00:05:52.110
The birth of Jesus,
2,000 years ago,

00:05:52.110 --> 00:05:56.210
would be 10 centimeters, 10
centimeters on a time line

00:05:56.210 --> 00:05:59.060
that stretches from San
Francisco to Seattle.

00:05:59.060 --> 00:06:01.380
And then finally, the
Declaration of Independence,

00:06:01.380 --> 00:06:03.300
the American Declaration
of Independence,

00:06:03.300 --> 00:06:09.760
would be 1 centimeter on a time
line that stretches to Seattle.

00:06:09.760 --> 00:06:12.410
Anyway, I don't know
if that put things

00:06:12.410 --> 00:06:13.660
in more or less perspective.

00:06:13.660 --> 00:06:16.730
But it was worth
giving it a shot.


Cosmological time scale 1

WEBVTT
Kind: captions
Language: en

00:00:00.616 --> 00:00:02.490
What I've done here is
I've copied and pasted

00:00:02.490 --> 00:00:05.760
a bunch of pictures
that signify events

00:00:05.760 --> 00:00:08.180
in our history, when
you think about history

00:00:08.180 --> 00:00:12.290
on a grander scale, that most
of us have some relation to

00:00:12.290 --> 00:00:14.890
or we kind of have heard it
talked about a little bit.

00:00:14.890 --> 00:00:16.820
And the whole point
of this is to try

00:00:16.820 --> 00:00:19.880
to understand, or try
to begin to understand,

00:00:19.880 --> 00:00:23.280
how long 13.7 billion years is.

00:00:23.280 --> 00:00:26.090
So just to start off,
I have here-- this

00:00:26.090 --> 00:00:27.967
is the best depiction
I could find

00:00:27.967 --> 00:00:29.300
where it didn't have copyrights.

00:00:29.300 --> 00:00:31.940
This is from NASA--
of the Big Bang.

00:00:31.940 --> 00:00:33.890
And I've talked about
it several times.

00:00:33.890 --> 00:00:39.140
The Big Bang occurred
13.7 billion years ago.

00:00:39.140 --> 00:00:40.950
And then if we go a
little bit forward,

00:00:40.950 --> 00:00:43.040
actually a lot forward,
we get to the formation

00:00:43.040 --> 00:00:45.950
of our actual solar
system and the Earth.

00:00:45.950 --> 00:00:48.050
This is kind of the
protoplanetary disk

00:00:48.050 --> 00:00:50.790
or a depiction of a
protoplanetary disk forming

00:00:50.790 --> 00:00:52.460
around our young Sun.

00:00:52.460 --> 00:00:58.006
And so this right here
is 4.5 billion years ago.

00:00:58.006 --> 00:01:00.630
Now this over here-- once again,
these aren't pictures of them.

00:01:00.630 --> 00:01:02.713
These are just depictions
because no one was there

00:01:02.713 --> 00:01:03.650
with a camera.

00:01:03.650 --> 00:01:05.440
This is what we think
the asteroid that

00:01:05.440 --> 00:01:08.890
killed the dinosaurs looked like
when it was impacting Earth.

00:01:08.890 --> 00:01:12.110
And it killed the dinosaurs
65 million years ago.

00:01:19.200 --> 00:01:21.100
So until then, we
had land dinosaurs.

00:01:21.100 --> 00:01:24.330
And then this, as far as
the current theories go,

00:01:24.330 --> 00:01:25.650
got rid of them.

00:01:25.650 --> 00:01:27.590
Now, we'll fast forward
a little bit more.

00:01:27.590 --> 00:01:32.520
At about 3 million years ago--
let me do this in a color

00:01:32.520 --> 00:01:35.590
that you can see--
about 3 million,

00:01:35.590 --> 00:01:43.100
so three million years ago,
our ancestors look like this.

00:01:43.100 --> 00:01:45.956
This is Australopithecus
afarensis.

00:01:45.956 --> 00:01:48.355
This is I think a depiction
of-- this is Lucy.

00:01:51.890 --> 00:01:57.210
I believe the theory is that all
of us have some DNA from her.

00:01:57.210 --> 00:01:59.402
But this was 3
million years ago.

00:01:59.402 --> 00:02:01.360
And you fast forward some
more and you actually

00:02:01.360 --> 00:02:05.100
have the first modern humans
appearing on the planet, people

00:02:05.100 --> 00:02:07.450
that looked and thought
like you and me.

00:02:07.450 --> 00:02:12.790
This is 200,000 years ago.

00:02:12.790 --> 00:02:14.000
That's right over here.

00:02:14.000 --> 00:02:16.320
Obviously, this drawing
was done much later.

00:02:16.320 --> 00:02:19.650
But this is a depiction of
a modern human, so 200,000

00:02:19.650 --> 00:02:20.820
years ago.

00:02:20.820 --> 00:02:22.651
And then you fast
forward even more.

00:02:22.651 --> 00:02:24.400
And I don't want to
keep picking on Jesus.

00:02:24.400 --> 00:02:26.460
I did that with him
getting on the jet liner.

00:02:26.460 --> 00:02:29.320
And I genuinely don't mean
any offense to anyone.

00:02:29.320 --> 00:02:33.930
I just keep picking Jesus
because frankly our calendar is

00:02:33.930 --> 00:02:39.680
kind of-- he's a good person
that most people know about,

00:02:39.680 --> 00:02:40.860
2,000 years ago.

00:02:40.860 --> 00:02:43.390
And so when we
associate kind of a lot

00:02:43.390 --> 00:02:46.450
of modern history
occurring after his birth.

00:02:46.450 --> 00:02:49.890
So this right here is
obviously a painting

00:02:49.890 --> 00:02:51.220
of the birth of Jesus.

00:02:51.220 --> 00:02:56.250
And this is 2,000 years ago.

00:02:56.250 --> 00:03:00.950
And then this might be a
little bit American-centric.

00:03:00.950 --> 00:03:02.960
But the Declaration
of Independence, it

00:03:02.960 --> 00:03:03.790
was a major event.

00:03:03.790 --> 00:03:05.570
Actually even on
a worldwide basis,

00:03:05.570 --> 00:03:08.780
it was the first
secular democracy

00:03:08.780 --> 00:03:11.490
based on a kind of a
constitutional democracy that

00:03:11.490 --> 00:03:14.050
showed up on the planet.

00:03:14.050 --> 00:03:16.460
They said we don't want the
king of England anymore.

00:03:16.460 --> 00:03:21.170
And this was about
234 years ago.

00:03:21.170 --> 00:03:23.680
And I always remembered
because I was born almost

00:03:23.680 --> 00:03:25.010
on the 200th anniversary.

00:03:25.010 --> 00:03:26.760
So you just have to
add my age to 200.

00:03:26.760 --> 00:03:29.690
So this is 234 years ago.

00:03:29.690 --> 00:03:33.550
So these are all events
or periods of time

00:03:33.550 --> 00:03:35.470
that we've heard about
and we've talked about.

00:03:35.470 --> 00:03:37.950
And people throw around
these type of years.

00:03:37.950 --> 00:03:39.680
But what I want to
do in this video

00:03:39.680 --> 00:03:43.140
is relate it to time scales
that we can comprehend.

00:03:43.140 --> 00:03:47.660
So instead of the Big Bang
occurring 13.7 billion years

00:03:47.660 --> 00:03:51.080
ago, let's pretend like
it occurred 10 years ago.

00:03:51.080 --> 00:03:53.810
Because most of us, especially
if you're over the age of 10,

00:03:53.810 --> 00:03:55.780
can kind of understand
what 10 years is.

00:03:55.780 --> 00:03:58.000
It's a very, very
long period of time.

00:03:58.000 --> 00:04:00.190
But something that's well
within our lifetimes,

00:04:00.190 --> 00:04:01.560
well within our experience.

00:04:01.560 --> 00:04:04.980
So let's say the 13.7 billion--
instead of saying the Big

00:04:04.980 --> 00:04:07.540
Bang occurred 13.7
billion years ago, let's

00:04:07.540 --> 00:04:11.690
pretend like it
occurred 10 years ago.

00:04:11.690 --> 00:04:14.280
And if we pretend that
it occurred 10 years ago,

00:04:14.280 --> 00:04:17.200
let's think about how many
years, or minutes, or hours

00:04:17.200 --> 00:04:20.940
ago each of these events
would have occurred.

00:04:20.940 --> 00:04:24.380
So if Big Bang, which is
really 13.7 billion years,

00:04:24.380 --> 00:04:26.890
if it really had
occurred 10 years ago,

00:04:26.890 --> 00:04:30.280
and we scaled everything down,
if we had scaled everything

00:04:30.280 --> 00:04:33.580
down, then the Earth
would have been

00:04:33.580 --> 00:04:36.690
created about 3.3 years ago.

00:04:36.690 --> 00:04:41.300
So this would have
been 3.3 years ago.

00:04:41.300 --> 00:04:44.960
So there's nothing kind
of amazing about this.

00:04:44.960 --> 00:04:47.570
This is a significant fraction
of the age of the universe.

00:04:47.570 --> 00:04:51.430
So not that mind
blowing just yet.

00:04:51.430 --> 00:04:54.770
But if we go all the way to
when the dinosaurs were extinct,

00:04:54.770 --> 00:04:58.815
the last land dinosaurs, now
the 65 million years-- and this

00:04:58.815 --> 00:05:01.440
will give you an appreciation of
the difference between million

00:05:01.440 --> 00:05:05.220
and billion-- if the universe
was only 10 years old,

00:05:05.220 --> 00:05:09.450
then the dinosaurs would have
been extinct 17 days ago.

00:05:09.450 --> 00:05:11.211
Not even a month
ago, the dinosaurs

00:05:11.211 --> 00:05:12.210
would have been extinct.

00:05:12.210 --> 00:05:15.680
So if the universe was created
when I was just graduated--

00:05:15.680 --> 00:05:18.570
well, I'm in my '30s
now, so when I was 24--

00:05:18.570 --> 00:05:22.510
just last month, the dinosaurs
would have gone extinct.

00:05:22.510 --> 00:05:24.620
And it gets even crazier.

00:05:24.620 --> 00:05:27.500
17 days ago, the dinosaurs
would have extinct.

00:05:27.500 --> 00:05:29.420
Australopithecus
afarensis would have

00:05:29.420 --> 00:05:32.300
walked on the Earth 19
hours ago, yesterday.

00:05:35.940 --> 00:05:39.080
19 hours ago, she would
have been walking around

00:05:39.080 --> 00:05:39.900
on the planet.

00:05:39.900 --> 00:05:48.550
And modern humans wouldn't have
shown up until 80 minutes ago,

00:05:48.550 --> 00:05:51.050
80 minutes, a
little over an hour.

00:05:51.050 --> 00:05:52.430
There wasn't even
a modern human.

00:05:52.430 --> 00:05:54.550
Then the universe
was 10 years, it

00:05:54.550 --> 00:05:56.280
didn't take until
just very recently,

00:05:56.280 --> 00:05:59.620
the last hour, for us to see
someone that looks something

00:05:59.620 --> 00:06:02.500
like us, looks and
thinks something like us.

00:06:02.500 --> 00:06:05.430
Fast forward even more,
the birth of Jesus,

00:06:05.430 --> 00:06:09.620
if the universe was 10 years
old instead of 13.7 billion--

00:06:09.620 --> 00:06:12.540
and we scaled everything
down-- then the birth of Jesus

00:06:12.540 --> 00:06:15.680
would have been 46 seconds ago.

00:06:19.530 --> 00:06:21.250
And then if we fast
forward all the way

00:06:21.250 --> 00:06:23.750
to the Declaration
of Independence,

00:06:23.750 --> 00:06:29.850
this would have occurred
five seconds ago.

00:06:29.850 --> 00:06:33.900
So this isn't quite
as mind blowing

00:06:33.900 --> 00:06:35.850
as the scale of the universe.

00:06:35.850 --> 00:06:37.950
But in my mind, this is
still pretty amazing.

00:06:37.950 --> 00:06:43.450
I mean all that's happened
since 1776 on a global basis

00:06:43.450 --> 00:06:46.570
could have been
encapsulated in five seconds

00:06:46.570 --> 00:06:49.570
if the age of the
universe was 10 years.

00:06:49.570 --> 00:06:52.030
So hopefully, that gives you
a little bit of a perspective.

00:06:52.030 --> 00:06:56.180
In the next video, instead
of condensing things in time,

00:06:56.180 --> 00:06:58.740
I'm going to compare this scale
to kind of a distance scale.

00:06:58.740 --> 00:07:01.570
So we can kind of say,
hey, if the universe was

00:07:01.570 --> 00:07:03.490
the number of
pixels on my screen,

00:07:03.490 --> 00:07:06.890
how big would each
of these things be?


Red shift

WEBVTT
Kind: captions
Language: en

00:00:00.760 --> 00:00:01.850
Let's say I'm over here.

00:00:01.850 --> 00:00:03.110
I'm going to do two scenarios.

00:00:03.110 --> 00:00:04.650
So I'm an observer over here.

00:00:04.650 --> 00:00:06.990
This is me.

00:00:06.990 --> 00:00:10.730
And then maybe even better,
I should just draw my eyeball

00:00:10.730 --> 00:00:12.920
because we're going
to be observing light.

00:00:12.920 --> 00:00:15.130
So I'm just going
to draw my eyeball.

00:00:15.130 --> 00:00:18.530
So this is me in the
first scenario or this

00:00:18.530 --> 00:00:20.120
is one of my eyeballs.

00:00:20.120 --> 00:00:21.830
And then this is
one of my eyeballs

00:00:21.830 --> 00:00:24.192
in the second scenario.

00:00:24.192 --> 00:00:26.150
Now in the first scenario--
so let me draw it--

00:00:26.150 --> 00:00:28.316
so in both scenarios, we're
going to have an object.

00:00:28.316 --> 00:00:31.820
We're going to have some
type of source of light.

00:00:31.820 --> 00:00:35.080
But in the first
scenario, relative to me,

00:00:35.080 --> 00:00:37.070
the source of light
will not be moving.

00:00:37.070 --> 00:00:38.740
While in the second
scenario, the source

00:00:38.740 --> 00:00:43.590
of light-- just for the sake
of discussion, just for fun--

00:00:43.590 --> 00:00:45.600
will be moving at half
the speed of light.

00:00:45.600 --> 00:00:49.260
Unimaginably fast speed, but
let's just assuming that it is.

00:00:49.260 --> 00:00:52.530
So it's moving at-- it
has a velocity of 1/2

00:00:52.530 --> 00:01:02.760
the speed of light, 1/2
light speed away from me

00:01:02.760 --> 00:01:05.220
who is the observer.

00:01:05.220 --> 00:01:07.190
Now let's just imagine
what would happen.

00:01:07.190 --> 00:01:08.490
They're both emitting light.

00:01:08.490 --> 00:01:09.906
So and they're
both going to start

00:01:09.906 --> 00:01:12.150
emitting light at
the exact same time.

00:01:12.150 --> 00:01:14.220
And when they start
emitting light,

00:01:14.220 --> 00:01:18.090
they're both at the exact
same distance from my eye.

00:01:18.090 --> 00:01:19.940
The only difference
is is that this

00:01:19.940 --> 00:01:23.850
is stationary, relative to
me, while this is moving away

00:01:23.850 --> 00:01:26.950
from me at half
the speed of light.

00:01:26.950 --> 00:01:29.500
So let's say that after
some period of time,

00:01:29.500 --> 00:01:35.150
that the light wave from
this source reaches my eye.

00:01:35.150 --> 00:01:36.930
And then it looks
something like this.

00:01:36.930 --> 00:01:40.060
I'll try my best to draw it.

00:01:40.060 --> 00:01:42.761
So let's say I have-- I want
to draw a couple of wavelengths

00:01:42.761 --> 00:01:43.260
here.

00:01:43.260 --> 00:01:45.830
So let's say that's
half a wavelength.

00:01:45.830 --> 00:01:47.030
That's a full wavelength.

00:01:47.030 --> 00:01:51.080
That's another half, a full
wavelength, another half,

00:01:51.080 --> 00:01:53.631
full wavelength, and
then a half, and then

00:01:53.631 --> 00:01:54.380
a full wavelength.

00:01:54.380 --> 00:01:55.920
So let me see if
I can draw that.

00:01:55.920 --> 00:02:00.920
So it would look
like full wavelength,

00:02:00.920 --> 00:02:04.480
full wavelength,
full wave length.

00:02:04.480 --> 00:02:05.610
This is not easy to do.

00:02:05.610 --> 00:02:07.470
And then you got
another full wavelength.

00:02:07.470 --> 00:02:11.650
So it would look something
like that, the actual waveform.

00:02:11.650 --> 00:02:16.370
And so the front of the wave
form is just getting to my eye.

00:02:16.370 --> 00:02:20.440
And then as the wave forms
keep going past my eye,

00:02:20.440 --> 00:02:23.470
my eye will perceive some type
of a wave length or frequency

00:02:23.470 --> 00:02:25.490
and perceive it to be
some type of color,

00:02:25.490 --> 00:02:27.360
assuming that we're
in the visible part

00:02:27.360 --> 00:02:28.694
of the electromagnetic spectrum.

00:02:28.694 --> 00:02:30.110
Now let's think
about what's going

00:02:30.110 --> 00:02:31.770
to happen with this source.

00:02:31.770 --> 00:02:34.610
So the first thing is is that
the front of the wave form

00:02:34.610 --> 00:02:36.930
is going to reach me
at the exact same time.

00:02:36.930 --> 00:02:41.300
One of those neat and amazing
things about light travelling

00:02:41.300 --> 00:02:43.860
in general, or
especially in a vacuum,

00:02:43.860 --> 00:02:47.520
it doesn't matter that this
is moving away from me at half

00:02:47.520 --> 00:02:48.690
the speed of light.

00:02:48.690 --> 00:02:50.900
The light will still
move towards me

00:02:50.900 --> 00:02:52.477
at the speed of light.

00:02:52.477 --> 00:02:53.060
It's absolute.

00:02:53.060 --> 00:02:55.749
It doesn't matter if
this is going away at 0.9

00:02:55.749 --> 00:02:56.540
the speed of light.

00:02:56.540 --> 00:03:00.217
The light will still travel
to me at the speed of light.

00:03:00.217 --> 00:03:01.300
And it's very unintuitive.

00:03:01.300 --> 00:03:05.140
Because in our everyday sense,
if I'm moving away from you

00:03:05.140 --> 00:03:07.330
at half the speed of a
bullet and I shoot a bullet,

00:03:07.330 --> 00:03:09.730
the bullet will only
move towards you

00:03:09.730 --> 00:03:12.694
at-- it'll kind of--
that half of its velocity

00:03:12.694 --> 00:03:13.485
will be subtracted.

00:03:13.485 --> 00:03:17.357
And it'll only move towards me
at half of its normal velocity,

00:03:17.357 --> 00:03:18.940
relative to whether
it was stationary,

00:03:18.940 --> 00:03:20.524
but not the case with the light.

00:03:20.524 --> 00:03:22.190
So with that out of
the way, let's think

00:03:22.190 --> 00:03:24.460
about what the wave
form would look like.

00:03:24.460 --> 00:03:27.251
So by the time the
light reached here,

00:03:27.251 --> 00:03:29.750
we need to think of-- let me
actually redraw this over here.

00:03:29.750 --> 00:03:37.360
Let me redraw this
eyeball right over here.

00:03:37.360 --> 00:03:38.690
So this is me again.

00:03:38.690 --> 00:03:42.500
So by the time the light reaches
my eye-- so they both started

00:03:42.500 --> 00:03:44.660
emitting the light at
the exact same time--

00:03:44.660 --> 00:03:47.570
this guy has traveled
half this distance.

00:03:47.570 --> 00:03:52.150
If it took light a certain
amount of time to get this far,

00:03:52.150 --> 00:03:54.740
this guy will get half as far
in that same amount of time.

00:03:54.740 --> 00:03:57.810
So by the time the
light reaches my eye,

00:03:57.810 --> 00:04:00.560
this guy will have traveled
about half that distance.

00:04:00.560 --> 00:04:03.740
So he would have
traveled about that far.

00:04:03.740 --> 00:04:06.090
They started emitting the
light at the same time.

00:04:06.090 --> 00:04:10.600
So that very first photon, if
you view light as a particle,

00:04:10.600 --> 00:04:13.180
will reach my eye at
the very same time

00:04:13.180 --> 00:04:16.040
as the very first
photon from this guy.

00:04:16.040 --> 00:04:19.550
So the wave form is going
to essentially be stretched.

00:04:19.550 --> 00:04:22.560
So instead of having--
so we're still

00:04:22.560 --> 00:04:28.352
going to have one, two,
three, four full wavelengths,

00:04:28.352 --> 00:04:29.560
but they'll now be stretched.

00:04:29.560 --> 00:04:31.650
Let me see if I can draw
four full wavelengths.

00:04:31.650 --> 00:04:34.040
So let me cut this
in half over here.

00:04:34.040 --> 00:04:37.800
And let me cut each
of those in half.

00:04:37.800 --> 00:04:40.670
So each of these are going
to be a full wavelength.

00:04:40.670 --> 00:04:47.030
And then they're going to have
a half wavelength in between.

00:04:47.030 --> 00:04:49.295
And so the wave form is
going to look like this.

00:04:52.340 --> 00:04:55.200
Let me try my best to draw it.

00:04:55.200 --> 00:04:58.800
This is the hardest part,
drawing the stretched out wave

00:04:58.800 --> 00:05:00.302
form.

00:05:00.302 --> 00:05:01.010
And there you go.

00:05:01.010 --> 00:05:02.450
It's going to look like this.

00:05:02.450 --> 00:05:04.740
And so when it gets
to my eye, my eye

00:05:04.740 --> 00:05:07.790
is going to perceive it as
having a longer wavelength,

00:05:07.790 --> 00:05:09.990
even though from the
perspective of each

00:05:09.990 --> 00:05:12.410
of these objects, if you're
traveling with each of them,

00:05:12.410 --> 00:05:15.550
the frequency and the
wavelength of the light emitted

00:05:15.550 --> 00:05:16.380
is the same.

00:05:16.380 --> 00:05:18.910
The only difference is this
guy's moving away from me--

00:05:18.910 --> 00:05:20.490
or I'm moving away
from it, depending

00:05:20.490 --> 00:05:23.600
on how you want to view
it-- while I am stationary,

00:05:23.600 --> 00:05:26.310
while in this first case,
the observer and the source

00:05:26.310 --> 00:05:27.660
are both stationary.

00:05:27.660 --> 00:05:29.940
Now, in this situation,
what's my eye going to say?

00:05:29.940 --> 00:05:33.170
Well, my eye will get each
of these successive pulses,

00:05:33.170 --> 00:05:35.400
or each of these
successive wave trains.

00:05:35.400 --> 00:05:37.740
And it's going to say, hey,
there's a longer wavelength

00:05:37.740 --> 00:05:46.280
here, a perceived
longer wavelength--

00:05:46.280 --> 00:05:51.680
let me write that-- perceived
longer wavelength here,

00:05:51.680 --> 00:05:55.265
and also, a perceived
lower frequency.

00:06:00.990 --> 00:06:03.220
So what would that do to
the perception of the light?

00:06:03.220 --> 00:06:06.440
Let's say that this
is green light.

00:06:06.440 --> 00:06:08.330
So if you are stationary
with the observer,

00:06:08.330 --> 00:06:09.684
it would be green light.

00:06:09.684 --> 00:06:11.600
So let's look at the
electromagnetic spectrum.

00:06:11.600 --> 00:06:13.750
I got this off of Wikipedia.

00:06:13.750 --> 00:06:16.850
So if I were stationary
towards-- with the observer,

00:06:16.850 --> 00:06:20.190
we'd be in the green light
part of the spectrum,

00:06:20.190 --> 00:06:23.970
so a 500 nanometer wavelength.

00:06:23.970 --> 00:06:26.380
But if all of a sudden,
because the object

00:06:26.380 --> 00:06:29.800
is moving away from me
at this huge velocity,

00:06:29.800 --> 00:06:32.560
the perceived wavelength
becomes wider.

00:06:32.560 --> 00:06:34.420
So from my perception,
it is going

00:06:34.420 --> 00:06:36.495
to have a wider wavelength.

00:06:36.495 --> 00:06:37.870
And you can see
what's happening.

00:06:37.870 --> 00:06:39.270
It will look redder.

00:06:39.270 --> 00:06:42.480
It will move towards the
red part of the spectrum.

00:06:42.480 --> 00:06:44.850
And this phenomenon
is called redshift.

00:06:53.560 --> 00:06:55.974
And I've done a bunch of
videos of the physics playlist

00:06:55.974 --> 00:06:56.890
on the Doppler effect.

00:06:56.890 --> 00:06:59.890
And over there, I talk about
sound waves and the perceived

00:06:59.890 --> 00:07:02.310
frequency of sound-- if
something travels towards you

00:07:02.310 --> 00:07:05.280
verses away from you--
as the exact same idea.

00:07:05.280 --> 00:07:07.380
This is the Doppler
effect applied to light.

00:07:07.380 --> 00:07:09.600
And the reason why
the Doppler effect

00:07:09.600 --> 00:07:12.100
works for light
traveling through space

00:07:12.100 --> 00:07:15.350
and for sound
traveling through air

00:07:15.350 --> 00:07:17.640
is because the sound
wave in air, regardless

00:07:17.640 --> 00:07:19.910
of whether the
source is moving away

00:07:19.910 --> 00:07:21.290
or towards you,
the sound wave is

00:07:21.290 --> 00:07:23.970
going to move at the
speed of sound in air

00:07:23.970 --> 00:07:25.910
at a certain pressure
and all of that.

00:07:25.910 --> 00:07:27.250
And light is the same thing.

00:07:27.250 --> 00:07:32.310
But in a vacuum, It will always,
regardless of the source,

00:07:32.310 --> 00:07:34.740
regardless of what
the source is doing,

00:07:34.740 --> 00:07:36.910
the actual light wave
itself will always

00:07:36.910 --> 00:07:39.130
travel at the same velocity.

00:07:39.130 --> 00:07:42.260
The only difference is is
that its perceived frequency

00:07:42.260 --> 00:07:43.676
and wavelength will change.

00:07:43.676 --> 00:07:45.800
And now the whole reason
why I'm talking about this

00:07:45.800 --> 00:07:49.460
is you can use this
property of light,

00:07:49.460 --> 00:07:52.510
that it gets redshift, to see
whether things are traveling

00:07:52.510 --> 00:07:55.140
away or towards you.

00:07:55.140 --> 00:07:57.690
And people talk about redshift
because, frankly, most things

00:07:57.690 --> 00:07:59.020
are traveling away from us.

00:07:59.020 --> 00:08:00.802
And that's one of
the reasons why

00:08:00.802 --> 00:08:02.260
we tend to believe
in the Big Bang.

00:08:02.260 --> 00:08:05.660
The opposite, if something
is traveling towards me

00:08:05.660 --> 00:08:07.946
at super high
velocities, then we

00:08:07.946 --> 00:08:09.320
would have something
called-- you

00:08:09.320 --> 00:08:11.236
don't hear the word--
it would be violetshift.

00:08:11.236 --> 00:08:12.450
The frequency would increase.

00:08:15.040 --> 00:08:17.470
So it would look
bluer or more purple.

00:08:17.470 --> 00:08:19.110
Now the other thing
I want to highlight

00:08:19.110 --> 00:08:21.930
is this redshift
phenomenon, this idea,

00:08:21.930 --> 00:08:24.830
it doesn't apply only
to visible light.

00:08:24.830 --> 00:08:27.240
So it could even apply the
things that we can't even see.

00:08:27.240 --> 00:08:29.770
So it would only-- it
would become redder.

00:08:29.770 --> 00:08:31.354
But it's not like
you can even see.

00:08:31.354 --> 00:08:32.770
It could even be
applied to things

00:08:32.770 --> 00:08:34.280
that are even more red than red.

00:08:34.280 --> 00:08:37.030
So maybe it's a microwave
that is being emitted.

00:08:37.030 --> 00:08:40.080
But because the source is
moving away from us so fast,

00:08:40.080 --> 00:08:44.354
it could be perceived
as an actual radio wave.

00:08:44.354 --> 00:08:46.770
And actually, I should have
talked about this in the video

00:08:46.770 --> 00:08:49.630
on the microwave
background radiation

00:08:49.630 --> 00:08:52.820
is that we're perceiving
it as microwaves.

00:08:52.820 --> 00:08:55.830
But these sources were
moving away from us.

00:08:55.830 --> 00:08:57.290
They were being redshift.

00:08:57.290 --> 00:09:00.870
So they were not actually
emitting microwave radiation.

00:09:00.870 --> 00:09:03.420
It's just what we observe--
and this is actually

00:09:03.420 --> 00:09:07.200
what would be predicted based
on the Big Bang-- is actually

00:09:07.200 --> 00:09:08.551
microwave radiation.

00:09:08.551 --> 00:09:10.050
So anyway, hopefully,
that gives you

00:09:10.050 --> 00:09:11.860
a sense of what redshift is.

00:09:11.860 --> 00:09:16.450
And now we can use
this tool to explain

00:09:16.450 --> 00:09:19.180
why we think many, many things
are moving away from us.

00:09:19.180 --> 00:09:22.810
And now let me just actually
make sure you get that idea.

00:09:22.810 --> 00:09:25.990
If I have two objects, let's
say that these are suns.

00:09:25.990 --> 00:09:29.620
Let's say that these are
both suns, or both galaxies,

00:09:29.620 --> 00:09:30.510
either way.

00:09:30.510 --> 00:09:32.000
And because of
other properties--

00:09:32.000 --> 00:09:33.625
and I won't talk
about them right now--

00:09:33.625 --> 00:09:37.400
we know that they
are probably emitting

00:09:37.400 --> 00:09:39.179
light of the same color.

00:09:39.179 --> 00:09:41.220
They're probably emitting
light of the same color

00:09:41.220 --> 00:09:45.930
because we know other properties
of that star or of that galaxy.

00:09:45.930 --> 00:09:48.080
Now, if what we
actually perceive

00:09:48.080 --> 00:09:51.440
is that this one looks
redder to us than this one,

00:09:51.440 --> 00:09:55.090
then we know that it is
traveling away from us.

00:09:55.090 --> 00:09:57.100
And the redder it looks,
the more its wavelength

00:09:57.100 --> 00:10:00.540
is spread out relative to this
other star, the faster we know

00:10:00.540 --> 00:10:03.310
that this is moving
away from us.