[Script Info]
Title: 
[Events]
Format: Layer, Start, End, Style, Name, MarginL, MarginR, MarginV, Effect, Text
Dialogue: 0,0:00:07.88,0:00:11.02,Default,,0000,0000,0000,,The Universe is really big.
Dialogue: 0,0:00:11.02,0:00:13.85,Default,,0000,0000,0000,,We live in a galaxy, the Milky Way Galaxy.
Dialogue: 0,0:00:13.85,0:00:17.70,Default,,0000,0000,0000,,There are about a hundred billion stars\Nin the Milky Way Galaxy,
Dialogue: 0,0:00:17.70,0:00:21.41,Default,,0000,0000,0000,,and if you take a camera and you point it\Nat a random part of the sky,
Dialogue: 0,0:00:21.41,0:00:23.67,Default,,0000,0000,0000,,and you just keep the shutter open,
Dialogue: 0,0:00:23.68,0:00:26.73,Default,,0000,0000,0000,,as long as your camera is attached\Nto the Hubble Space Telescope
Dialogue: 0,0:00:26.73,0:00:29.28,Default,,0000,0000,0000,,it will see something like this.
Dialogue: 0,0:00:29.28,0:00:32.17,Default,,0000,0000,0000,,Every one of these little blobs\Nis a galaxy,
Dialogue: 0,0:00:32.17,0:00:33.81,Default,,0000,0000,0000,,roughly the size of our Milky Way.
Dialogue: 0,0:00:33.81,0:00:36.62,Default,,0000,0000,0000,,A hundred billion stars\Nin each of those blobs,
Dialogue: 0,0:00:36.62,0:00:40.97,Default,,0000,0000,0000,,there are approximately a hundred billion\Ngalaxies in the observable Universe.
Dialogue: 0,0:00:40.97,0:00:43.59,Default,,0000,0000,0000,,A hundred billion is the only number\Nyou need to know,
Dialogue: 0,0:00:43.59,0:00:46.18,Default,,0000,0000,0000,,the age of the Universe\Nbetween now and the Big Bang
Dialogue: 0,0:00:46.18,0:00:48.64,Default,,0000,0000,0000,,is a hundred billion in dog years
Dialogue: 0,0:00:48.64,0:00:50.28,Default,,0000,0000,0000,,(Laughter)
Dialogue: 0,0:00:50.28,0:00:53.18,Default,,0000,0000,0000,,which tells you something\Nabout our place in the Universe.
Dialogue: 0,0:00:53.18,0:00:56.38,Default,,0000,0000,0000,,One thing you can do with a picture\Nlike this is simply admire it,
Dialogue: 0,0:00:56.38,0:00:58.76,Default,,0000,0000,0000,,it's extremely beautiful,\Nand I've often wondered
Dialogue: 0,0:00:58.76,0:01:02.33,Default,,0000,0000,0000,,what is the evolutionary pressure\Nthat made our ancestors develop,
Dialogue: 0,0:01:02.33,0:01:07.16,Default,,0000,0000,0000,,adapt, and evolve to really enjoy pictures\Nof galaxies, when they didn't have any.
Dialogue: 0,0:01:07.16,0:01:09.10,Default,,0000,0000,0000,,But we would also like to understand it,
Dialogue: 0,0:01:09.10,0:01:12.84,Default,,0000,0000,0000,,as a cosmologist I want to ask,\N"Why is the Universe like this?"
Dialogue: 0,0:01:12.84,0:01:16.29,Default,,0000,0000,0000,,One big clue we have is\Nthat the Universe is changing with time.
Dialogue: 0,0:01:16.30,0:01:19.44,Default,,0000,0000,0000,,If you looked at one of these galaxies\Nand measured its velocity,
Dialogue: 0,0:01:19.44,0:01:21.41,Default,,0000,0000,0000,,it would be moving away from you,
Dialogue: 0,0:01:21.41,0:01:25.24,Default,,0000,0000,0000,,and if you look at a galaxy even further\Naway, it will be moving away faster.
Dialogue: 0,0:01:25.24,0:01:27.60,Default,,0000,0000,0000,,So we say\Nthat the Universe is expanding.
Dialogue: 0,0:01:27.60,0:01:29.92,Default,,0000,0000,0000,,What that means, of course,\Nis that in the past,
Dialogue: 0,0:01:29.92,0:01:31.54,Default,,0000,0000,0000,,things were closer together.
Dialogue: 0,0:01:31.54,0:01:34.75,Default,,0000,0000,0000,,In the past, the Universe \Nwas more dense, and it was also hotter,
Dialogue: 0,0:01:34.75,0:01:37.40,Default,,0000,0000,0000,,if you squeeze things together\Nthe temperature goes up.
Dialogue: 0,0:01:37.40,0:01:39.02,Default,,0000,0000,0000,,That makes sense to us.
Dialogue: 0,0:01:39.02,0:01:41.42,Default,,0000,0000,0000,,The thing that doesn't make sense\Nto us as much is
Dialogue: 0,0:01:41.42,0:01:43.89,Default,,0000,0000,0000,,that the Universe at early times,\Nnear the Big Bang,
Dialogue: 0,0:01:43.89,0:01:46.68,Default,,0000,0000,0000,,was also very, very smooth.
Dialogue: 0,0:01:46.68,0:01:50.39,Default,,0000,0000,0000,,You might think that's not a surprise;\Nthe air in this room is very smooth,
Dialogue: 0,0:01:50.39,0:01:53.17,Default,,0000,0000,0000,,you might say: "Well, these things\Nsmooth themselves out."
Dialogue: 0,0:01:53.17,0:01:56.16,Default,,0000,0000,0000,,But the conditions near the Big Bang\Nwere very, very different
Dialogue: 0,0:01:56.17,0:01:58.10,Default,,0000,0000,0000,,than those of the air in this room.
Dialogue: 0,0:01:58.10,0:02:00.37,Default,,0000,0000,0000,,In particular, things were a lot denser,
Dialogue: 0,0:02:00.37,0:02:04.69,Default,,0000,0000,0000,,the gravitational pull of things\Nwas a lot stronger near the Big Bang.
Dialogue: 0,0:02:04.69,0:02:06.58,Default,,0000,0000,0000,,What you have to think about is,
Dialogue: 0,0:02:06.58,0:02:09.01,Default,,0000,0000,0000,,we had a Universe\Nwith a hundred billion galaxies,
Dialogue: 0,0:02:09.01,0:02:10.76,Default,,0000,0000,0000,,a hundred billion stars each,
Dialogue: 0,0:02:10.76,0:02:13.67,Default,,0000,0000,0000,,at early times,\Nthose hundred billion galaxies
Dialogue: 0,0:02:13.67,0:02:18.05,Default,,0000,0000,0000,,were squeezed into a region\Nabout this big, literally at early times;
Dialogue: 0,0:02:18.05,0:02:22.51,Default,,0000,0000,0000,,you had to imagine doing\Nthat squeezing without any imperfections,
Dialogue: 0,0:02:22.51,0:02:26.38,Default,,0000,0000,0000,,without any little spots where there were\Na few more atoms than somewhere else,
Dialogue: 0,0:02:26.38,0:02:28.84,Default,,0000,0000,0000,,because if there had been,\Nthey would've collapsed
Dialogue: 0,0:02:28.85,0:02:31.75,Default,,0000,0000,0000,,under the gravitational pull\Ninto a huge black hole.
Dialogue: 0,0:02:31.76,0:02:35.45,Default,,0000,0000,0000,,Keeping the Universe very, very smooth\Nat early times is not easy.
Dialogue: 0,0:02:35.45,0:02:37.04,Default,,0000,0000,0000,,It's a delicate arrangement.
Dialogue: 0,0:02:37.04,0:02:40.39,Default,,0000,0000,0000,,It's a clue that the early Universe\Nis not chosen randomly,
Dialogue: 0,0:02:40.40,0:02:42.42,Default,,0000,0000,0000,,there was something\Nthat made it that way,
Dialogue: 0,0:02:42.42,0:02:44.29,Default,,0000,0000,0000,,and we would like to know what.
Dialogue: 0,0:02:44.29,0:02:47.85,Default,,0000,0000,0000,,So part of our understanding of this\Nwas given to us by Ludwig Boltzmann,
Dialogue: 0,0:02:47.85,0:02:50.64,Default,,0000,0000,0000,,an Austrian physicist in the 19th century,
Dialogue: 0,0:02:50.64,0:02:54.23,Default,,0000,0000,0000,,and Boltzmann's contribution was\Nthat he helped us understand entropy.
Dialogue: 0,0:02:54.23,0:02:55.61,Default,,0000,0000,0000,,You've heard of entropy,
Dialogue: 0,0:02:55.63,0:02:59.38,Default,,0000,0000,0000,,it's the randomness, the disorder,\Nthe chaoticness of some systems.
Dialogue: 0,0:02:59.38,0:03:02.82,Default,,0000,0000,0000,,Boltzmann gave us a formula,\Nengraved on his tombstone now,
Dialogue: 0,0:03:02.83,0:03:05.21,Default,,0000,0000,0000,,that really quantifies what entropy is.
Dialogue: 0,0:03:05.21,0:03:08.72,Default,,0000,0000,0000,,It's basically just saying\Nthat entropy is the number of ways
Dialogue: 0,0:03:08.73,0:03:12.54,Default,,0000,0000,0000,,we can rearrange the constituents\Nof a system so that you don't notice.
Dialogue: 0,0:03:12.54,0:03:14.68,Default,,0000,0000,0000,,So that macroscopically,\Nit looks the same.
Dialogue: 0,0:03:14.68,0:03:18.51,Default,,0000,0000,0000,,In the air in this room,\Nyou don't notice each individual atom.
Dialogue: 0,0:03:18.51,0:03:20.57,Default,,0000,0000,0000,,A low entropy configuration is one
Dialogue: 0,0:03:20.57,0:03:23.45,Default,,0000,0000,0000,,where there are only a few arrangements\Nthat look that way.
Dialogue: 0,0:03:23.45,0:03:25.07,Default,,0000,0000,0000,,A high entropy arrangement is one
Dialogue: 0,0:03:25.07,0:03:27.54,Default,,0000,0000,0000,,that there are many arrangements\Nthat look that way.
Dialogue: 0,0:03:27.54,0:03:29.36,Default,,0000,0000,0000,,This is a crucially important insight,
Dialogue: 0,0:03:29.36,0:03:32.64,Default,,0000,0000,0000,,because it helps us explain\Nthe second law of thermodynamics;
Dialogue: 0,0:03:32.64,0:03:35.66,Default,,0000,0000,0000,,the law that says that entropy\Nincreases in the Universe,
Dialogue: 0,0:03:35.66,0:03:38.30,Default,,0000,0000,0000,,or in some isolated bit of the Universe.
Dialogue: 0,0:03:38.30,0:03:42.46,Default,,0000,0000,0000,,The reason why the entropy increases\Nis simply because there are many more ways
Dialogue: 0,0:03:42.46,0:03:45.51,Default,,0000,0000,0000,,to be high entropy than to be low entropy.
Dialogue: 0,0:03:45.51,0:03:48.95,Default,,0000,0000,0000,,That's a wonderful insight,\Nbut it leaves something out.
Dialogue: 0,0:03:48.96,0:03:51.37,Default,,0000,0000,0000,,This insight that entropy\Nincreases, by the way,
Dialogue: 0,0:03:51.37,0:03:54.22,Default,,0000,0000,0000,,is what's behind what we call\N'the arrow of time, '
Dialogue: 0,0:03:54.22,0:03:56.41,Default,,0000,0000,0000,,the difference between the past\Nand the future.
Dialogue: 0,0:03:56.41,0:03:59.66,Default,,0000,0000,0000,,Every difference that there is\Nbetween the past and the future
Dialogue: 0,0:03:59.66,0:04:01.89,Default,,0000,0000,0000,,is because entropy is increasing.
Dialogue: 0,0:04:01.89,0:04:04.79,Default,,0000,0000,0000,,The fact that you can remember\Nthe past but not the future.
Dialogue: 0,0:04:04.79,0:04:07.41,Default,,0000,0000,0000,,The fact that you are born,\Nand then you live,
Dialogue: 0,0:04:07.41,0:04:09.91,Default,,0000,0000,0000,,and then you die, always in that order,
Dialogue: 0,0:04:09.91,0:04:11.82,Default,,0000,0000,0000,,that's because entropy is increasing.
Dialogue: 0,0:04:11.82,0:04:14.74,Default,,0000,0000,0000,,Boltzmann explained\Nthat if you start with low entropy,
Dialogue: 0,0:04:14.74,0:04:16.48,Default,,0000,0000,0000,,it's very natural for it to increase
Dialogue: 0,0:04:16.48,0:04:18.97,Default,,0000,0000,0000,,because there are more ways\Nto be high entropy.
Dialogue: 0,0:04:18.97,0:04:24.20,Default,,0000,0000,0000,,What he didn't explain was why the entropy\Nwas ever low in the first place.
Dialogue: 0,0:04:24.20,0:04:26.93,Default,,0000,0000,0000,,The fact that the entropy\Nin the Universe was low,
Dialogue: 0,0:04:26.93,0:04:30.45,Default,,0000,0000,0000,,is a reflection of the fact\Nthat the early Universe was very smooth,
Dialogue: 0,0:04:30.45,0:04:34.13,Default,,0000,0000,0000,,we would like to understand that,\Nthat's our job as cosmologists.
Dialogue: 0,0:04:34.13,0:04:38.11,Default,,0000,0000,0000,,Unfortunately, it's actually not a problem\Nwe've been giving enough attention to.
Dialogue: 0,0:04:38.11,0:04:41.00,Default,,0000,0000,0000,,It's not one of the first things\Npeople would say if you ask
Dialogue: 0,0:04:41.00,0:04:44.28,Default,,0000,0000,0000,,a modern cosmologist what are\Nthe problems we're trying to address.
Dialogue: 0,0:04:44.28,0:04:47.100,Default,,0000,0000,0000,,One of the people who did understand\Nthis was a problem was Richard Feynman.
Dialogue: 0,0:04:47.100,0:04:50.59,Default,,0000,0000,0000,,50 years ago, he gave\Na series of different lectures
Dialogue: 0,0:04:50.60,0:04:52.27,Default,,0000,0000,0000,,- you've heard about them already -
Dialogue: 0,0:04:52.27,0:04:55.46,Default,,0000,0000,0000,,popular lectures that became\N"The Character of physical law,"
Dialogue: 0,0:04:55.46,0:04:57.59,Default,,0000,0000,0000,,he gave lectures to Caltech undergrads
Dialogue: 0,0:04:57.59,0:05:00.30,Default,,0000,0000,0000,,that became\N"The Feynman lectures on physics,"
Dialogue: 0,0:05:00.30,0:05:03.66,Default,,0000,0000,0000,,to Caltech graduate students,\N"The Feynman lectures on gravitation."
Dialogue: 0,0:05:03.66,0:05:06.75,Default,,0000,0000,0000,,In every one of these books,\Nevery one of these sets of lectures,
Dialogue: 0,0:05:06.75,0:05:08.49,Default,,0000,0000,0000,,he emphasized this puzzle:
Dialogue: 0,0:05:08.49,0:05:11.66,Default,,0000,0000,0000,,why did the early Universe\Nhave such a small entropy?
Dialogue: 0,0:05:11.66,0:05:14.25,Default,,0000,0000,0000,,So he says:\N- and I'm not going to do the accent -
Dialogue: 0,0:05:14.25,0:05:18.02,Default,,0000,0000,0000,,"For some reason, the Universe,\Nat one time, had a very low entropy
Dialogue: 0,0:05:18.02,0:05:21.66,Default,,0000,0000,0000,,for its energy content,\Nand since then, the entropy has increased.
Dialogue: 0,0:05:21.66,0:05:24.75,Default,,0000,0000,0000,,The arrow of time cannot be\Ncompletely understood
Dialogue: 0,0:05:24.75,0:05:27.88,Default,,0000,0000,0000,,until the mystery of the beginnings\Nof the history of the Universe
Dialogue: 0,0:05:27.88,0:05:32.25,Default,,0000,0000,0000,,are reduced still further\Nfrom speculation to understanding."
Dialogue: 0,0:05:32.25,0:05:34.26,Default,,0000,0000,0000,,So that's our job, we want to know.
Dialogue: 0,0:05:34.26,0:05:36.50,Default,,0000,0000,0000,,This is 50 years ago,\Nsurely, you're thinking,
Dialogue: 0,0:05:36.51,0:05:37.95,Default,,0000,0000,0000,,we've figured it out by now.
Dialogue: 0,0:05:37.95,0:05:40.34,Default,,0000,0000,0000,,It's not true\Nthat we've figured it out by now.
Dialogue: 0,0:05:40.34,0:05:42.72,Default,,0000,0000,0000,,In fact, it's more\Nthan a fifty-year old problem,
Dialogue: 0,0:05:42.72,0:05:45.20,Default,,0000,0000,0000,,Boltzmann understood\Nthat this was a problem,
Dialogue: 0,0:05:45.20,0:05:47.34,Default,,0000,0000,0000,,and he suggested an answer to it.
Dialogue: 0,0:05:47.34,0:05:48.87,Default,,0000,0000,0000,,Before I get to that,
Dialogue: 0,0:05:48.87,0:05:53.18,Default,,0000,0000,0000,,I should say that the reason the problem\Nhas gotten worse, rather than better,
Dialogue: 0,0:05:53.19,0:05:56.77,Default,,0000,0000,0000,,is because in 1998, we learned something\Ncrucial about the Universe,
Dialogue: 0,0:05:56.78,0:05:58.07,Default,,0000,0000,0000,,that we didn't know before.
Dialogue: 0,0:05:58.07,0:05:59.84,Default,,0000,0000,0000,,We learned that it's accelerating.
Dialogue: 0,0:05:59.84,0:06:01.56,Default,,0000,0000,0000,,The Universe is not only expanding,
Dialogue: 0,0:06:01.56,0:06:03.70,Default,,0000,0000,0000,,if you look at that galaxy,\Nit's moving away,
Dialogue: 0,0:06:03.71,0:06:06.52,Default,,0000,0000,0000,,you come back a billion years later\Nand look at it again,
Dialogue: 0,0:06:06.52,0:06:08.41,Default,,0000,0000,0000,,it'll be moving away faster.
Dialogue: 0,0:06:08.41,0:06:11.89,Default,,0000,0000,0000,,Individual galaxies are speeding\Naway from us, faster and faster,
Dialogue: 0,0:06:11.89,0:06:14.46,Default,,0000,0000,0000,,so we say the Universe is accelerating.
Dialogue: 0,0:06:14.46,0:06:16.73,Default,,0000,0000,0000,,Unlike the low entropy\Nof the early Universe,
Dialogue: 0,0:06:16.73,0:06:20.42,Default,,0000,0000,0000,,even though we don't know the answer\Nfor this we at least have a good theory,
Dialogue: 0,0:06:20.42,0:06:22.59,Default,,0000,0000,0000,,that can explain it\Nif that theory is right,
Dialogue: 0,0:06:22.59,0:06:24.52,Default,,0000,0000,0000,,and that's the theory of dark energy.
Dialogue: 0,0:06:24.52,0:06:27.63,Default,,0000,0000,0000,,It's just the idea\Nthat empty space itself has energy,
Dialogue: 0,0:06:27.63,0:06:29.72,Default,,0000,0000,0000,,and every little cubic centimeter of space
Dialogue: 0,0:06:29.72,0:06:31.45,Default,,0000,0000,0000,,whether or not there's stuff,
Dialogue: 0,0:06:31.45,0:06:34.30,Default,,0000,0000,0000,,whether there's particles,\Nmatter, radiation, or whatever,
Dialogue: 0,0:06:34.31,0:06:37.16,Default,,0000,0000,0000,,there's still energy,\Neven in the space itself.
Dialogue: 0,0:06:37.16,0:06:41.14,Default,,0000,0000,0000,,This energy, according to Einstein,\Nexerts a push on the Universe,
Dialogue: 0,0:06:41.14,0:06:45.58,Default,,0000,0000,0000,,it's a perpetual impulse that pushes\Ngalaxies apart from each other.
Dialogue: 0,0:06:45.58,0:06:49.32,Default,,0000,0000,0000,,Because dark energy,\Nunlike matter radiation,
Dialogue: 0,0:06:49.32,0:06:52.58,Default,,0000,0000,0000,,does not dilute away\Nas the Universe expands.
Dialogue: 0,0:06:52.58,0:06:55.84,Default,,0000,0000,0000,,The amount of energy in each cubic\Ncentimeter remains the same,
Dialogue: 0,0:06:55.84,0:06:58.26,Default,,0000,0000,0000,,even as the Universe\Ngets bigger and bigger.
Dialogue: 0,0:06:58.26,0:07:02.30,Default,,0000,0000,0000,,This has crucial implications\Nfor what the Universe is going to do
Dialogue: 0,0:07:02.31,0:07:03.45,Default,,0000,0000,0000,,in the future.
Dialogue: 0,0:07:03.45,0:07:06.09,Default,,0000,0000,0000,,For one thing, the Universe\Nwill expand forever.
Dialogue: 0,0:07:06.09,0:07:07.59,Default,,0000,0000,0000,,Back when I was your age,
Dialogue: 0,0:07:07.59,0:07:10.16,Default,,0000,0000,0000,,we didn't know what\Nthe Universe was going to do,
Dialogue: 0,0:07:10.17,0:07:12.88,Default,,0000,0000,0000,,some people thought it would\Nrecollapse in the future,
Dialogue: 0,0:07:12.88,0:07:14.81,Default,,0000,0000,0000,,Einstein was fond of this idea.
Dialogue: 0,0:07:14.82,0:07:18.21,Default,,0000,0000,0000,,But if there's dark energy\Nand the dark energy does not go away,
Dialogue: 0,0:07:18.21,0:07:21.56,Default,,0000,0000,0000,,the Universe is just going\Nto keep expanding for ever and ever.
Dialogue: 0,0:07:21.56,0:07:24.67,Default,,0000,0000,0000,,14 billion years in the past,\Na hundred billion dog years,
Dialogue: 0,0:07:24.67,0:07:27.96,Default,,0000,0000,0000,,but an infinite number\Nof years into the future.
Dialogue: 0,0:07:27.96,0:07:33.09,Default,,0000,0000,0000,,Meanwhile, for all intents and purposes,\Nspace looks finite to us.
Dialogue: 0,0:07:33.09,0:07:35.11,Default,,0000,0000,0000,,Space may be finite or infinite,
Dialogue: 0,0:07:35.11,0:07:37.30,Default,,0000,0000,0000,,but because the Universe is accelerating
Dialogue: 0,0:07:37.30,0:07:40.57,Default,,0000,0000,0000,,there are parts of it\Nwe cannot see and never will see.
Dialogue: 0,0:07:40.57,0:07:43.20,Default,,0000,0000,0000,,There's a finite region of space\Nthat we have access to,
Dialogue: 0,0:07:43.20,0:07:44.69,Default,,0000,0000,0000,,surrounded by a horizon,
Dialogue: 0,0:07:44.69,0:07:48.68,Default,,0000,0000,0000,,so even though time goes on forever,\Nspace is limited to us.
Dialogue: 0,0:07:48.68,0:07:52.10,Default,,0000,0000,0000,,Finally, empty space has a temperature.
Dialogue: 0,0:07:52.10,0:07:55.21,Default,,0000,0000,0000,,In the 1970s, Stephen Hawking\Ntold us that a black hole,
Dialogue: 0,0:07:55.21,0:07:58.08,Default,,0000,0000,0000,,even though you think it's black,\Nit actually emits radiation
Dialogue: 0,0:07:58.08,0:08:00.27,Default,,0000,0000,0000,,when you take into account\Nquantum mechanics.
Dialogue: 0,0:08:00.27,0:08:02.75,Default,,0000,0000,0000,,The curvature of space-time\Naround the black hole
Dialogue: 0,0:08:02.76,0:08:07.87,Default,,0000,0000,0000,,brings to life the quantum mechanical\Nfluctuation that the black hole radiates.
Dialogue: 0,0:08:07.88,0:08:11.20,Default,,0000,0000,0000,,A precisely similar calculation\Nby Hawking and Gary Gibbens
Dialogue: 0,0:08:11.21,0:08:14.22,Default,,0000,0000,0000,,shows that if you have\Ndark energy in empty space,
Dialogue: 0,0:08:14.22,0:08:17.08,Default,,0000,0000,0000,,then the whole Universe radiates.
Dialogue: 0,0:08:17.08,0:08:20.71,Default,,0000,0000,0000,,The energy in empty space brings\Nto life quantum fluctuations,
Dialogue: 0,0:08:20.71,0:08:23.26,Default,,0000,0000,0000,,so even though the Universe\Nwill last forever,
Dialogue: 0,0:08:23.26,0:08:25.52,Default,,0000,0000,0000,,and ordinary matter radiation\Nwill dilute away,
Dialogue: 0,0:08:25.52,0:08:30.02,Default,,0000,0000,0000,,there will always be some radiation,\Nsome thermal fluctuations,
Dialogue: 0,0:08:30.02,0:08:32.08,Default,,0000,0000,0000,,even in empty space.
Dialogue: 0,0:08:32.08,0:08:37.69,Default,,0000,0000,0000,,So what this means is that, the Universe\Nis like a box of gas that lasts forever.
Dialogue: 0,0:08:37.69,0:08:39.91,Default,,0000,0000,0000,,What are the implications of that?
Dialogue: 0,0:08:39.91,0:08:43.11,Default,,0000,0000,0000,,That implication was studied by Boltzmann,\Nback in the 19th century.
Dialogue: 0,0:08:43.11,0:08:48.17,Default,,0000,0000,0000,,He said, well, entropy increases\Nbecause there are many many more ways
Dialogue: 0,0:08:48.17,0:08:51.04,Default,,0000,0000,0000,,for the Universe to be high entropy\Nrather than low entropy.
Dialogue: 0,0:08:51.04,0:08:53.55,Default,,0000,0000,0000,,But that's a probabilistic statement.
Dialogue: 0,0:08:53.55,0:08:55.55,Default,,0000,0000,0000,,It will probably increase,
Dialogue: 0,0:08:55.55,0:08:57.62,Default,,0000,0000,0000,,and the probability is enormously huge,
Dialogue: 0,0:08:57.62,0:08:59.64,Default,,0000,0000,0000,,it's not something\Nyou have to worry about,
Dialogue: 0,0:08:59.64,0:09:02.92,Default,,0000,0000,0000,,the air in this room all gathering over\None part of the room,
Dialogue: 0,0:09:02.92,0:09:06.46,Default,,0000,0000,0000,,and suffocating us,\Nit's very, very unlikely.
Dialogue: 0,0:09:06.46,0:09:10.42,Default,,0000,0000,0000,,Except if they lock the doors\Nand kept us here, literally forever,
Dialogue: 0,0:09:10.42,0:09:11.93,Default,,0000,0000,0000,,that would happen.
Dialogue: 0,0:09:11.93,0:09:13.53,Default,,0000,0000,0000,,Everything that is allowed,
Dialogue: 0,0:09:13.53,0:09:17.40,Default,,0000,0000,0000,,every configuration that is allowed to be\Nattained by the molecules in this room,
Dialogue: 0,0:09:17.40,0:09:18.81,Default,,0000,0000,0000,,would eventually be attained.
Dialogue: 0,0:09:18.81,0:09:23.42,Default,,0000,0000,0000,,So Boltzmann says, you can start\Nwith a Universe in thermal equilibrium,
Dialogue: 0,0:09:23.43,0:09:26.77,Default,,0000,0000,0000,,he didn't know about the Big Bang\Nor the expansion of the Universe,
Dialogue: 0,0:09:26.77,0:09:29.77,Default,,0000,0000,0000,,he thought that space and time were\Nexplained by Isaac Newton,
Dialogue: 0,0:09:29.78,0:09:32.26,Default,,0000,0000,0000,,they were absolutely,\Njust stuck there forever.
Dialogue: 0,0:09:32.26,0:09:36.10,Default,,0000,0000,0000,,So his idea that natural Universe\Nwas one in which the air molecules
Dialogue: 0,0:09:36.10,0:09:39.82,Default,,0000,0000,0000,,were just spread out evenly everywhere,\Neverything molecules.
Dialogue: 0,0:09:39.82,0:09:42.82,Default,,0000,0000,0000,,But if you're Boltzmann,\Nyou know that if you wait long enough,
Dialogue: 0,0:09:42.82,0:09:44.85,Default,,0000,0000,0000,,the random fluctuations of those molecules
Dialogue: 0,0:09:44.85,0:09:50.26,Default,,0000,0000,0000,,will occasionally bring them into lower\Nenergy, lower entropy configurations.
Dialogue: 0,0:09:50.26,0:09:54.08,Default,,0000,0000,0000,,And then of course, in the natural course\Nof things, they will expand back.
Dialogue: 0,0:09:54.08,0:09:56.59,Default,,0000,0000,0000,,So it's not that entropy\Nmust always increase,
Dialogue: 0,0:09:56.59,0:09:59.32,Default,,0000,0000,0000,,you can get fluctuations\Ninto lower entropy,
Dialogue: 0,0:09:59.32,0:10:02.72,Default,,0000,0000,0000,,more organized situations.
Dialogue: 0,0:10:02.72,0:10:07.02,Default,,0000,0000,0000,,Boltzmann then goes on to invent\Ntwo very modern-sounding ideas,
Dialogue: 0,0:10:07.02,0:10:10.04,Default,,0000,0000,0000,,the multiverse and the entropic principle.
Dialogue: 0,0:10:10.04,0:10:13.73,Default,,0000,0000,0000,,He says, the problem with thermal\Nequilibrium is that we can't live there.
Dialogue: 0,0:10:13.73,0:10:16.88,Default,,0000,0000,0000,,Remember, life itself\Ndepends on the arrow of time.
Dialogue: 0,0:10:16.88,0:10:19.68,Default,,0000,0000,0000,,We would not be able to process\Ninformation, to metabolize,
Dialogue: 0,0:10:19.68,0:10:22.80,Default,,0000,0000,0000,,walk and talk if we lived in\Nthermal equilibrium.
Dialogue: 0,0:10:22.80,0:10:26.63,Default,,0000,0000,0000,,So, if you imagine a very big Universe,\Nan infinitely big Universe,
Dialogue: 0,0:10:26.63,0:10:29.38,Default,,0000,0000,0000,,with randomly bumping into\Neach other particles,
Dialogue: 0,0:10:29.38,0:10:32.69,Default,,0000,0000,0000,,there will occasionally be\Nsmall fluctuations to lower entropy states
Dialogue: 0,0:10:32.69,0:10:34.27,Default,,0000,0000,0000,,and then they would relax back.
Dialogue: 0,0:10:34.27,0:10:36.40,Default,,0000,0000,0000,,But there would also be\Nlarge fluctuations,
Dialogue: 0,0:10:36.40,0:10:40.59,Default,,0000,0000,0000,,occasionally you'll make a planet,\Nor a star, or a galaxy,
Dialogue: 0,0:10:40.59,0:10:43.13,Default,,0000,0000,0000,,or a hundred billion galaxies.
Dialogue: 0,0:10:43.13,0:10:47.64,Default,,0000,0000,0000,,So Boltzmann says, we will only live\Nin the part of the multiverse,
Dialogue: 0,0:10:47.64,0:10:51.62,Default,,0000,0000,0000,,the part that has an infinitely big set\Nof fluctuating particles,
Dialogue: 0,0:10:51.62,0:10:55.12,Default,,0000,0000,0000,,where life is possible, that's the regions\Nwhere entropy is low,
Dialogue: 0,0:10:55.12,0:10:59.98,Default,,0000,0000,0000,,maybe our Universe is just one of those\Nthings that happens, from time to time.
Dialogue: 0,0:10:59.98,0:11:03.05,Default,,0000,0000,0000,,Now, your homework assignment is\Nto really think about this,
Dialogue: 0,0:11:03.05,0:11:04.70,Default,,0000,0000,0000,,to contemplate what it means.
Dialogue: 0,0:11:04.70,0:11:08.54,Default,,0000,0000,0000,,Carl Sagan once famously said\Nthat in order to make an apple pie,
Dialogue: 0,0:11:08.54,0:11:10.92,Default,,0000,0000,0000,,you must first invent the Universe.
Dialogue: 0,0:11:10.93,0:11:13.04,Default,,0000,0000,0000,,But he was not right.
Dialogue: 0,0:11:13.04,0:11:16.55,Default,,0000,0000,0000,,In Boltzmann's scenario, if you want\Nto make an apple pie you just wait
Dialogue: 0,0:11:16.55,0:11:20.12,Default,,0000,0000,0000,,for the random motion of atoms\Nto make you an apple pie.
Dialogue: 0,0:11:20.12,0:11:21.13,Default,,0000,0000,0000,,(Laughter)
Dialogue: 0,0:11:21.13,0:11:23.53,Default,,0000,0000,0000,,That will happen much more frequently
Dialogue: 0,0:11:23.53,0:11:27.20,Default,,0000,0000,0000,,than the random motions of atoms\Nmaking you an apple orchard,
Dialogue: 0,0:11:27.20,0:11:31.38,Default,,0000,0000,0000,,and some sugar, and an oven,\Nand then making you an apple pie.
Dialogue: 0,0:11:31.38,0:11:35.97,Default,,0000,0000,0000,,So this scenario makes predictions,\Nand the predictions are
Dialogue: 0,0:11:35.97,0:11:39.47,Default,,0000,0000,0000,,that the fluctuations\Nthat make us are minimal.
Dialogue: 0,0:11:39.47,0:11:43.64,Default,,0000,0000,0000,,Even if you imagine that this room\Nwe are in now exists and is real,
Dialogue: 0,0:11:43.64,0:11:46.57,Default,,0000,0000,0000,,and here we are and we have\Nnot only our memories,
Dialogue: 0,0:11:46.57,0:11:49.64,Default,,0000,0000,0000,,but our impression that outside there is\Nsomething called Caltech
Dialogue: 0,0:11:49.64,0:11:52.08,Default,,0000,0000,0000,,and the United States\Nand the Milky Way Galaxy.
Dialogue: 0,0:11:52.09,0:11:56.05,Default,,0000,0000,0000,,It's much easier for all those impressions\Nto randomly fluctuate into your brain
Dialogue: 0,0:11:56.05,0:11:58.97,Default,,0000,0000,0000,,than for them to actually randomly\Nfluctuate into Caltech,
Dialogue: 0,0:11:58.97,0:12:00.82,Default,,0000,0000,0000,,the United States and the galaxy.
Dialogue: 0,0:12:00.82,0:12:04.17,Default,,0000,0000,0000,,The good news is that, therefore,\Nthis scenario does not work,
Dialogue: 0,0:12:04.17,0:12:05.62,Default,,0000,0000,0000,,it is not right.
Dialogue: 0,0:12:05.62,0:12:08.74,Default,,0000,0000,0000,,This scenario predicts that we should be\Nin minimal fluctuation,
Dialogue: 0,0:12:08.74,0:12:10.41,Default,,0000,0000,0000,,even if you left our galaxy out,
Dialogue: 0,0:12:10.41,0:12:12.95,Default,,0000,0000,0000,,you would not get\Na hundred billion other galaxies.
Dialogue: 0,0:12:12.95,0:12:15.46,Default,,0000,0000,0000,,Feynman also understood this,\NFeynman says:
Dialogue: 0,0:12:15.46,0:12:18.70,Default,,0000,0000,0000,,"From the hypothesis\Nthat the world is a fluctuation,
Dialogue: 0,0:12:18.70,0:12:21.63,Default,,0000,0000,0000,,all the predictions are\Nthat if we look at a part of the world
Dialogue: 0,0:12:21.64,0:12:24.06,Default,,0000,0000,0000,,we have never seen before,\Nwe will find it mixed up,
Dialogue: 0,0:12:24.07,0:12:26.50,Default,,0000,0000,0000,,not like the piece we just looked at."\NHigh entropy.
Dialogue: 0,0:12:26.50,0:12:30.18,Default,,0000,0000,0000,,"If our order were due to a fluctuation,\Nwe would not expect order anywhere,
Dialogue: 0,0:12:30.18,0:12:31.82,Default,,0000,0000,0000,,but where we have just noticed it.
Dialogue: 0,0:12:31.82,0:12:35.43,Default,,0000,0000,0000,,We therefore conclude\Nthe Universe is not a fluctuation."
Dialogue: 0,0:12:35.43,0:12:38.66,Default,,0000,0000,0000,,So that's good, the question is then,\Nwhat is the right answer?
Dialogue: 0,0:12:38.66,0:12:42.60,Default,,0000,0000,0000,,If the Universe is not a fluctuation, why\Ndid the early Universe have low entropy?
Dialogue: 0,0:12:42.60,0:12:45.97,Default,,0000,0000,0000,,And I would love to tell you the answer\Nbut I'm running out of time.
Dialogue: 0,0:12:45.97,0:12:47.80,Default,,0000,0000,0000,,(Laughter)
Dialogue: 0,0:12:47.81,0:12:50.43,Default,,0000,0000,0000,,Here is the Universe\Nthat we tell you about
Dialogue: 0,0:12:50.43,0:12:52.80,Default,,0000,0000,0000,,versus the Universe that really exists.
Dialogue: 0,0:12:52.81,0:12:54.93,Default,,0000,0000,0000,,I just showed you this picture,
Dialogue: 0,0:12:54.93,0:12:58.98,Default,,0000,0000,0000,,the Universe is expanding for the last\Nten billion years or so, it's cooling off.
Dialogue: 0,0:12:58.98,0:13:02.66,Default,,0000,0000,0000,,But we now know enough about the future\Nof the Universe to say a lot more.
Dialogue: 0,0:13:02.66,0:13:05.42,Default,,0000,0000,0000,,If the dark energy remains around,
Dialogue: 0,0:13:05.42,0:13:09.05,Default,,0000,0000,0000,,the stars around us will use up\Ntheir nuclear fuel, they'll stop burning,
Dialogue: 0,0:13:09.05,0:13:10.88,Default,,0000,0000,0000,,they will fall into black holes.
Dialogue: 0,0:13:10.88,0:13:14.60,Default,,0000,0000,0000,,We will live in a Universe\Nwith nothing in it but black holes.
Dialogue: 0,0:13:14.60,0:13:18.11,Default,,0000,0000,0000,,That Universe will last\N10 to the 100 years,
Dialogue: 0,0:13:18.12,0:13:20.50,Default,,0000,0000,0000,,a lot longer than\Nour little Universe has lived.
Dialogue: 0,0:13:20.51,0:13:22.77,Default,,0000,0000,0000,,The future is much longer than the past.
Dialogue: 0,0:13:22.77,0:13:25.68,Default,,0000,0000,0000,,But even black holes\Ndon't last forever, they will evaporate,
Dialogue: 0,0:13:25.68,0:13:28.79,Default,,0000,0000,0000,,and we will be left with nothing\Nbut empty space.
Dialogue: 0,0:13:28.80,0:13:32.18,Default,,0000,0000,0000,,That empty space lasts\Nessentially forever.
Dialogue: 0,0:13:32.18,0:13:35.66,Default,,0000,0000,0000,,However, you notice that\Nsince empty space gives off radiation,
Dialogue: 0,0:13:35.66,0:13:38.97,Default,,0000,0000,0000,,there's actually thermal fluctuations\Nand it cycles around
Dialogue: 0,0:13:38.97,0:13:42.97,Default,,0000,0000,0000,,all the different possible combinations\Nof the degrees of freedom
Dialogue: 0,0:13:42.98,0:13:44.97,Default,,0000,0000,0000,,that exist in empty space.
Dialogue: 0,0:13:44.98,0:13:46.98,Default,,0000,0000,0000,,So even though the Universe lasts forever,
Dialogue: 0,0:13:46.98,0:13:50.56,Default,,0000,0000,0000,,there's only a finite number of things\Nthat can possibly happen in it,
Dialogue: 0,0:13:50.56,0:13:55.74,Default,,0000,0000,0000,,they all happen over a period of time\Nequal to 10 to the 10 to the 120 years.
Dialogue: 0,0:13:56.28,0:13:58.34,Default,,0000,0000,0000,,So here are two questions for you:
Dialogue: 0,0:13:58.34,0:14:01.74,Default,,0000,0000,0000,,number one, if the Universe lasts\Nfor 10 to the 10 to the 120 years,
Dialogue: 0,0:14:01.74,0:14:05.66,Default,,0000,0000,0000,,why are we born\Nin the first 14 billion years of it,
Dialogue: 0,0:14:05.66,0:14:09.27,Default,,0000,0000,0000,,in the warm, comfortable\Nafterglow of the Big Bang?
Dialogue: 0,0:14:09.28,0:14:11.78,Default,,0000,0000,0000,,Why aren't we in empty space?
Dialogue: 0,0:14:11.78,0:14:15.23,Default,,0000,0000,0000,,You might say, there's nothing there\Nto be living, but that's not right.
Dialogue: 0,0:14:15.24,0:14:18.25,Default,,0000,0000,0000,,You could be a random fluctuation\Nout of the nothingness.
Dialogue: 0,0:14:18.25,0:14:19.56,Default,,0000,0000,0000,,Why aren't you?
Dialogue: 0,0:14:19.56,0:14:21.67,Default,,0000,0000,0000,,More homework assignments for you.
Dialogue: 0,0:14:21.67,0:14:24.14,Default,,0000,0000,0000,,So, like I said,\NI don't actually know the answer,
Dialogue: 0,0:14:24.14,0:14:26.38,Default,,0000,0000,0000,,I'm going to give you\Nmy favorite scenario;
Dialogue: 0,0:14:26.38,0:14:29.09,Default,,0000,0000,0000,,either it's just like that,\Nthere is no explanation,
Dialogue: 0,0:14:29.09,0:14:32.28,Default,,0000,0000,0000,,it's a brute fact about the Universe\Nthat we should learn to accept
Dialogue: 0,0:14:32.28,0:14:34.47,Default,,0000,0000,0000,,and stop asking questions.
Dialogue: 0,0:14:34.87,0:14:39.05,Default,,0000,0000,0000,,Or maybe the Big Bang is\Nnot the beginning of the Universe.
Dialogue: 0,0:14:39.05,0:14:42.17,Default,,0000,0000,0000,,An unbroken egg is\Na low entropy configuration
Dialogue: 0,0:14:42.17,0:14:44.61,Default,,0000,0000,0000,,and yet when we open\Nour refrigerator we do not go:
Dialogue: 0,0:14:44.61,0:14:48.93,Default,,0000,0000,0000,,"How surprising to find this low entropy\Nconfiguration in our refrigerator."
Dialogue: 0,0:14:48.93,0:14:51.47,Default,,0000,0000,0000,,That's because an egg\Nis not a closed system.
Dialogue: 0,0:14:51.47,0:14:53.43,Default,,0000,0000,0000,,It comes out of a chicken.
Dialogue: 0,0:14:53.43,0:14:57.04,Default,,0000,0000,0000,,Maybe the Universe\Ncomes out of a Universal chicken.
Dialogue: 0,0:14:57.04,0:14:57.99,Default,,0000,0000,0000,,(Laughter)
Dialogue: 0,0:14:57.100,0:14:59.93,Default,,0000,0000,0000,,Maybe there is something that naturally,
Dialogue: 0,0:14:59.93,0:15:02.85,Default,,0000,0000,0000,,through the growth of the laws of physics,
Dialogue: 0,0:15:02.85,0:15:07.09,Default,,0000,0000,0000,,gives rise to a Universe like ours\Nin low entropy configuration.
Dialogue: 0,0:15:07.09,0:15:09.24,Default,,0000,0000,0000,,If that's true it would happen\Nmore than once,
Dialogue: 0,0:15:09.25,0:15:11.52,Default,,0000,0000,0000,,we would be part\Nof a much bigger multiverse.
Dialogue: 0,0:15:11.52,0:15:13.08,Default,,0000,0000,0000,,That's my favorite scenario.
Dialogue: 0,0:15:13.08,0:15:16.58,Default,,0000,0000,0000,,So the organizers asked me to end\Nwith a bold speculation;
Dialogue: 0,0:15:16.58,0:15:21.12,Default,,0000,0000,0000,,my bold speculation is that I will be\Nabsolutely vindicated by history,
Dialogue: 0,0:15:21.12,0:15:26.90,Default,,0000,0000,0000,,and 50 years from now all of my current\Nwild ideas will be accepted as truths
Dialogue: 0,0:15:26.90,0:15:29.09,Default,,0000,0000,0000,,by the scientific and external communities
Dialogue: 0,0:15:29.09,0:15:31.82,Default,,0000,0000,0000,,who will all believe\Nthat our little Universe
Dialogue: 0,0:15:31.82,0:15:34.38,Default,,0000,0000,0000,,is just a small part\Nof a much larger multiverse,
Dialogue: 0,0:15:34.38,0:15:38.48,Default,,0000,0000,0000,,and even better, we will understand\Nwhat happened at the Big Bang
Dialogue: 0,0:15:38.48,0:15:42.03,Default,,0000,0000,0000,,in terms of a theory that we will be able\Nto compare to observations.
Dialogue: 0,0:15:42.03,0:15:45.26,Default,,0000,0000,0000,,It's a prediction, I might be wrong,\Nbut we've been thinking,
Dialogue: 0,0:15:45.26,0:15:48.36,Default,,0000,0000,0000,,as a human race,\Nabout what the Universe was like,
Dialogue: 0,0:15:48.37,0:15:51.02,Default,,0000,0000,0000,,why it came to be the way it did,\Nfor many many years.
Dialogue: 0,0:15:51.02,0:15:54.09,Default,,0000,0000,0000,,It's exciting to think, we may finally\Nknow the answer some day.
Dialogue: 0,0:15:54.09,0:15:55.21,Default,,0000,0000,0000,,Thank you.
Dialogue: 0,0:15:55.21,0:15:56.75,Default,,0000,0000,0000,,(Applause)