[Script Info]
Title: 
[Events]
Format: Layer, Start, End, Style, Name, MarginL, MarginR, MarginV, Effect, Text
Dialogue: 0,0:00:06.49,0:00:07.89,Default,,0000,0000,0000,,Looking up at the night sky,
Dialogue: 0,0:00:07.89,0:00:10.91,Default,,0000,0000,0000,,we are amazed by how it seems to go on forever.
Dialogue: 0,0:00:10.91,0:00:12.40,Default,,0000,0000,0000,,But what will the sky look like
Dialogue: 0,0:00:12.40,0:00:13.86,Default,,0000,0000,0000,,billions of years from now?
Dialogue: 0,0:00:13.86,0:00:15.37,Default,,0000,0000,0000,,A particular type of scientist,
Dialogue: 0,0:00:15.37,0:00:16.62,Default,,0000,0000,0000,,called a cosmologist,
Dialogue: 0,0:00:16.62,0:00:19.53,Default,,0000,0000,0000,,spends her time thinking about that very question.
Dialogue: 0,0:00:19.53,0:00:21.92,Default,,0000,0000,0000,,The end of the universe is intimately linked
Dialogue: 0,0:00:21.92,0:00:23.87,Default,,0000,0000,0000,,to what the universe contains.
Dialogue: 0,0:00:23.87,0:00:25.17,Default,,0000,0000,0000,,Over 100 years ago,
Dialogue: 0,0:00:25.17,0:00:27.88,Default,,0000,0000,0000,,Einstein developed the Theory of General Relativity,
Dialogue: 0,0:00:27.88,0:00:29.92,Default,,0000,0000,0000,,formed of equations that help us
Dialogue: 0,0:00:29.92,0:00:31.26,Default,,0000,0000,0000,,understand the relationship
Dialogue: 0,0:00:31.26,0:00:33.46,Default,,0000,0000,0000,,between what a universe is made of
Dialogue: 0,0:00:33.46,0:00:34.51,Default,,0000,0000,0000,,and its shape.
Dialogue: 0,0:00:34.51,0:00:36.12,Default,,0000,0000,0000,,It turns out that the universe
Dialogue: 0,0:00:36.12,0:00:38.18,Default,,0000,0000,0000,,could be curved like a ball or sphere.
Dialogue: 0,0:00:38.18,0:00:40.68,Default,,0000,0000,0000,,We call this positively curved or closed.
Dialogue: 0,0:00:40.68,0:00:42.23,Default,,0000,0000,0000,,Or it could be shaped like a saddle.
Dialogue: 0,0:00:42.23,0:00:44.49,Default,,0000,0000,0000,,We call this negatively curved or open.
Dialogue: 0,0:00:44.49,0:00:46.03,Default,,0000,0000,0000,,Or it could be flat.
Dialogue: 0,0:00:46.03,0:00:47.16,Default,,0000,0000,0000,,And that shape determines
Dialogue: 0,0:00:47.16,0:00:49.54,Default,,0000,0000,0000,,how the universe will live and die.
Dialogue: 0,0:00:49.54,0:00:52.63,Default,,0000,0000,0000,,We now know that the universe is very close to flat.
Dialogue: 0,0:00:52.63,0:00:54.34,Default,,0000,0000,0000,,However, the components of the universe
Dialogue: 0,0:00:54.34,0:00:56.45,Default,,0000,0000,0000,,can still affect its eventual fate.
Dialogue: 0,0:00:56.45,0:00:58.03,Default,,0000,0000,0000,,We can predict how the universe
Dialogue: 0,0:00:58.03,0:00:59.61,Default,,0000,0000,0000,,will change with time
Dialogue: 0,0:00:59.61,0:01:01.79,Default,,0000,0000,0000,,if we measure the amounts or energy densities
Dialogue: 0,0:01:01.79,0:01:04.59,Default,,0000,0000,0000,,of the various components in the universe today.
Dialogue: 0,0:01:04.59,0:01:06.73,Default,,0000,0000,0000,,So, what is the universe made of?
Dialogue: 0,0:01:06.73,0:01:09.39,Default,,0000,0000,0000,,The universe contains all the things that we can see,
Dialogue: 0,0:01:09.39,0:01:11.56,Default,,0000,0000,0000,,like stars, gas, and planets.
Dialogue: 0,0:01:11.56,0:01:14.73,Default,,0000,0000,0000,,We call these things ordinary or baryonic matter.
Dialogue: 0,0:01:14.73,0:01:16.59,Default,,0000,0000,0000,,Even though we see them all around us,
Dialogue: 0,0:01:16.59,0:01:18.70,Default,,0000,0000,0000,,the total energy density of these components
Dialogue: 0,0:01:18.70,0:01:20.44,Default,,0000,0000,0000,,is actually very small,
Dialogue: 0,0:01:20.44,0:01:23.53,Default,,0000,0000,0000,,around 5% of the total energy of the universe.
Dialogue: 0,0:01:23.53,0:01:26.68,Default,,0000,0000,0000,,So, now let's talk about what the other 95% is.
Dialogue: 0,0:01:26.68,0:01:29.08,Default,,0000,0000,0000,,Just under 27% of the rest
Dialogue: 0,0:01:29.08,0:01:30.91,Default,,0000,0000,0000,,of the energy density of the universe
Dialogue: 0,0:01:30.91,0:01:33.82,Default,,0000,0000,0000,,is made up of what we call dark matter.
Dialogue: 0,0:01:33.82,0:01:36.93,Default,,0000,0000,0000,,Dark matter is only very weakly interacting with light,
Dialogue: 0,0:01:36.93,0:01:39.21,Default,,0000,0000,0000,,which means it doesn't shine or reflect light
Dialogue: 0,0:01:39.21,0:01:41.19,Default,,0000,0000,0000,,in the way that stars and planets do,
Dialogue: 0,0:01:41.19,0:01:42.29,Default,,0000,0000,0000,,but, in every other way,
Dialogue: 0,0:01:42.29,0:01:44.26,Default,,0000,0000,0000,,it behaves like ordinary matter --
Dialogue: 0,0:01:44.26,0:01:46.13,Default,,0000,0000,0000,,it attracts things gravitationally.
Dialogue: 0,0:01:46.13,0:01:48.76,Default,,0000,0000,0000,,In fact, the only way we can detect this dark matter
Dialogue: 0,0:01:48.76,0:01:51.05,Default,,0000,0000,0000,,is through this gravitational interaction,
Dialogue: 0,0:01:51.05,0:01:52.34,Default,,0000,0000,0000,,how things orbit around it
Dialogue: 0,0:01:52.34,0:01:53.60,Default,,0000,0000,0000,,and how it bends light
Dialogue: 0,0:01:53.60,0:01:56.01,Default,,0000,0000,0000,,as it curves the space around it.
Dialogue: 0,0:01:56.01,0:01:58.34,Default,,0000,0000,0000,,We have yet to discover a dark matter particle,
Dialogue: 0,0:01:58.34,0:02:00.82,Default,,0000,0000,0000,,but scientists all over the world are searching
Dialogue: 0,0:02:00.82,0:02:02.95,Default,,0000,0000,0000,,for this elusive particle or particles
Dialogue: 0,0:02:02.95,0:02:05.84,Default,,0000,0000,0000,,and the effects of dark matter on the universe.
Dialogue: 0,0:02:05.84,0:02:08.26,Default,,0000,0000,0000,,But this still doesn't add up to 100%.
Dialogue: 0,0:02:08.26,0:02:09.78,Default,,0000,0000,0000,,The remaining 68%
Dialogue: 0,0:02:09.78,0:02:11.68,Default,,0000,0000,0000,,of the energy density of the universe
Dialogue: 0,0:02:11.68,0:02:13.76,Default,,0000,0000,0000,,is made up of dark energy,
Dialogue: 0,0:02:13.76,0:02:16.46,Default,,0000,0000,0000,,which is even more mysterious than dark matter.
Dialogue: 0,0:02:16.46,0:02:18.42,Default,,0000,0000,0000,,This dark energy doesn't behave
Dialogue: 0,0:02:18.42,0:02:20.59,Default,,0000,0000,0000,,like any other substance we know at all
Dialogue: 0,0:02:20.59,0:02:23.01,Default,,0000,0000,0000,,and acts more like anti-gravity force.
Dialogue: 0,0:02:23.01,0:02:25.42,Default,,0000,0000,0000,,We say that it has a gravitational pressure,
Dialogue: 0,0:02:25.42,0:02:28.33,Default,,0000,0000,0000,,which ordinary matter and dark matter do not.
Dialogue: 0,0:02:28.33,0:02:30.21,Default,,0000,0000,0000,,Instead of pulling the universe together,
Dialogue: 0,0:02:30.21,0:02:32.00,Default,,0000,0000,0000,,as we would expect gravity to do,
Dialogue: 0,0:02:32.00,0:02:34.29,Default,,0000,0000,0000,,the universe appears to be expanding apart
Dialogue: 0,0:02:34.29,0:02:36.11,Default,,0000,0000,0000,,at an ever-increasing rate.
Dialogue: 0,0:02:36.11,0:02:37.94,Default,,0000,0000,0000,,The leading idea for dark energy
Dialogue: 0,0:02:37.94,0:02:40.15,Default,,0000,0000,0000,,is that it is a cosmological constant.
Dialogue: 0,0:02:40.15,0:02:42.24,Default,,0000,0000,0000,,That means it has the strange property
Dialogue: 0,0:02:42.24,0:02:45.43,Default,,0000,0000,0000,,that it expands as the volume of space increases
Dialogue: 0,0:02:45.43,0:02:47.61,Default,,0000,0000,0000,,to keep its energy density constant.
Dialogue: 0,0:02:47.61,0:02:49.44,Default,,0000,0000,0000,,So, as the universe expands
Dialogue: 0,0:02:49.44,0:02:50.77,Default,,0000,0000,0000,,as it is doing right now,
Dialogue: 0,0:02:50.77,0:02:52.74,Default,,0000,0000,0000,,there will be more and more dark energy.
Dialogue: 0,0:02:52.74,0:02:54.57,Default,,0000,0000,0000,,Dark matter and baryonic matter,
Dialogue: 0,0:02:54.57,0:02:55.28,Default,,0000,0000,0000,,on the other hand,
Dialogue: 0,0:02:55.28,0:02:56.62,Default,,0000,0000,0000,,don't expand with the universe
Dialogue: 0,0:02:56.62,0:02:58.41,Default,,0000,0000,0000,,and become more diluted.
Dialogue: 0,0:02:58.41,0:02:59.34,Default,,0000,0000,0000,,Because of this property
Dialogue: 0,0:02:59.34,0:03:00.69,Default,,0000,0000,0000,,of the cosmological constant,
Dialogue: 0,0:03:00.69,0:03:03.45,Default,,0000,0000,0000,,the future universe will be more and more dominated
Dialogue: 0,0:03:03.45,0:03:04.59,Default,,0000,0000,0000,,by dark energy,
Dialogue: 0,0:03:04.59,0:03:06.33,Default,,0000,0000,0000,,becoming colder and colder
Dialogue: 0,0:03:06.33,0:03:08.72,Default,,0000,0000,0000,,and expanding faster and faster.
Dialogue: 0,0:03:08.72,0:03:10.74,Default,,0000,0000,0000,,Eventually, the universe will run out of gas
Dialogue: 0,0:03:10.74,0:03:11.84,Default,,0000,0000,0000,,to form stars,
Dialogue: 0,0:03:11.84,0:03:13.94,Default,,0000,0000,0000,,and the stars themselves will run out of fuel
Dialogue: 0,0:03:13.94,0:03:15.19,Default,,0000,0000,0000,,and burn out,
Dialogue: 0,0:03:15.19,0:03:18.06,Default,,0000,0000,0000,,leaving the universe with only black holes in it.
Dialogue: 0,0:03:18.06,0:03:19.26,Default,,0000,0000,0000,,Given enough time,
Dialogue: 0,0:03:19.26,0:03:21.61,Default,,0000,0000,0000,,even these black holes will evaporate,
Dialogue: 0,0:03:21.61,0:03:24.52,Default,,0000,0000,0000,,leaving a universe that is completely cold and empty.
Dialogue: 0,0:03:24.52,0:03:28.13,Default,,0000,0000,0000,,That is what we call the heat death of the universe.
Dialogue: 0,0:03:28.13,0:03:29.57,Default,,0000,0000,0000,,While it might sound depressing
Dialogue: 0,0:03:29.57,0:03:30.69,Default,,0000,0000,0000,,living in a universe
Dialogue: 0,0:03:30.69,0:03:32.74,Default,,0000,0000,0000,,that will end its lifetime cold
Dialogue: 0,0:03:32.74,0:03:34.24,Default,,0000,0000,0000,,and devoid of life,
Dialogue: 0,0:03:34.24,0:03:36.03,Default,,0000,0000,0000,,the end fate of our universe
Dialogue: 0,0:03:36.03,0:03:37.94,Default,,0000,0000,0000,,actually has a beautiful symmetry
Dialogue: 0,0:03:37.94,0:03:40.09,Default,,0000,0000,0000,,to its hot, fiery beginning.
Dialogue: 0,0:03:40.09,0:03:41.100,Default,,0000,0000,0000,,We call the accelerating end state
Dialogue: 0,0:03:41.100,0:03:44.11,Default,,0000,0000,0000,,of the universe a de Sitter phase,
Dialogue: 0,0:03:44.11,0:03:46.08,Default,,0000,0000,0000,,named after the Dutch mathematician
Dialogue: 0,0:03:46.08,0:03:47.93,Default,,0000,0000,0000,,Willem de Sitter.
Dialogue: 0,0:03:47.93,0:03:49.68,Default,,0000,0000,0000,,However, we also believe
Dialogue: 0,0:03:49.68,0:03:51.52,Default,,0000,0000,0000,,that the universe had another phase
Dialogue: 0,0:03:51.52,0:03:52.83,Default,,0000,0000,0000,,of de Sitter expansion
Dialogue: 0,0:03:52.83,0:03:54.61,Default,,0000,0000,0000,,in the earliest times of its life.
Dialogue: 0,0:03:54.61,0:03:57.23,Default,,0000,0000,0000,,We call this early period inflation,
Dialogue: 0,0:03:57.23,0:03:58.89,Default,,0000,0000,0000,,where, shortly after the Big Bang,
Dialogue: 0,0:03:58.89,0:04:01.22,Default,,0000,0000,0000,,the universe expanded extremely fast
Dialogue: 0,0:04:01.22,0:04:02.86,Default,,0000,0000,0000,,for a brief period.
Dialogue: 0,0:04:02.86,0:04:04.39,Default,,0000,0000,0000,,So, the universe will end
Dialogue: 0,0:04:04.39,0:04:06.86,Default,,0000,0000,0000,,in much the same state as it began,
Dialogue: 0,0:04:06.86,0:04:08.77,Default,,0000,0000,0000,,accelerating.
Dialogue: 0,0:04:08.77,0:04:10.78,Default,,0000,0000,0000,,We live at an extraordinary time
Dialogue: 0,0:04:10.78,0:04:12.35,Default,,0000,0000,0000,,in the life of the universe
Dialogue: 0,0:04:12.35,0:04:13.86,Default,,0000,0000,0000,,where we can start to understand
Dialogue: 0,0:04:13.86,0:04:15.15,Default,,0000,0000,0000,,the universe's journey
Dialogue: 0,0:04:15.15,0:04:16.44,Default,,0000,0000,0000,,and view a history
Dialogue: 0,0:04:16.44,0:04:18.52,Default,,0000,0000,0000,,that plays itself out on the sky
Dialogue: 0,0:04:18.52,0:04:20.62,Default,,0000,0000,0000,,for all of us to see.