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0:00:02 > 0:00:06- All living things eventually die.
0:00:08 > 0:00:11- So how and when will the cosmos end?
0:00:12 > 0:00:16- How will the universe end? - It's the big question in astronomy.
0:00:17 > 0:00:20- Two cosmic heavyweights - wrestle for control.
0:00:21 > 0:00:24- The winner decides our future.
0:00:25 > 0:00:30- Expansion makes everything bigger - and gravity pulls things together.
0:00:33 > 0:00:35- Will gravity be the winner...
0:00:35 > 0:00:39- ..or will other forces - rip the universe apart?
0:00:42 > 0:00:46- The universe will change - into a dark, cold place.
0:00:47 > 0:00:50- Freezing is the likely ending - for the universe.
0:00:51 > 0:00:53- In this programme, - we will discover...
0:00:54 > 0:00:57- ..how and when the cosmos - will come to an end.
0:01:12 > 0:01:13- The cosmos is everything.
0:01:19 > 0:01:22- Earth is a tiny grain of rock...
0:01:22 > 0:01:26- ..amongst the billions of stars - in the Milky Way.
0:01:34 > 0:01:38- The Milky Way is just one of - hundreds of millions of galaxies.
0:01:43 > 0:01:46- And all of this will one day die.
0:01:59 > 0:02:00- Since its birth...
0:02:01 > 0:02:05- ..the fuel that lights the stars - has been gradually burning.
0:02:07 > 0:02:10- But what happens - when the fuel runs out?
0:02:13 > 0:02:17- As the stars disappear, - they will leave behind black holes.
0:02:17 > 0:02:21- Those black holes - will mop up what's left...
0:02:22 > 0:02:25- ..leaving a universe - full of black holes.
0:02:25 > 0:02:31- The universe may then gather - everything into one big black hole.
0:02:34 > 0:02:36- Scientists used to think...
0:02:37 > 0:02:41- ..the cosmos would cruise slowly - into old age.
0:02:41 > 0:02:45- But astronomers - have revealed a different picture.
0:02:46 > 0:02:49- The cosmos is fighting for its life.
0:02:49 > 0:02:54- The universe is dynamic, - with things changing constantly.
0:02:56 > 0:02:58- Two forces fight for control.
0:03:01 > 0:03:03- Expansion pulls galaxies apart...
0:03:05 > 0:03:09- ..threatening to freeze the cosmos - to its death.
0:03:11 > 0:03:15- Gravity tries to - crush everything back together...
0:03:16 > 0:03:21- ..threatening to compress the - universe into a large ball of fire.
0:03:25 > 0:03:28- Two forces, - but which one will triumph?
0:03:32 > 0:03:34- One is the big freeze.
0:03:34 > 0:03:37- Expansion wins. - The universe expands forever.
0:03:37 > 0:03:39- The second is a delicate balance...
0:03:39 > 0:03:42- ..between expansion - and gravitational attraction.
0:03:43 > 0:03:46- The universe gets to a - particular size and it stays there.
0:03:46 > 0:03:50- The third outcome is that - gravitational attraction wins.
0:03:50 > 0:03:53- Expansion stops - and the universe gets smaller...
0:03:53 > 0:03:56- ..until eventually - it goes back to a big crunch.
0:03:58 > 0:04:01- The cosmos seems balanced - between these two forces.
0:04:04 > 0:04:09- Will it keep its equilibrium - or will something tip the balance?
0:04:12 > 0:04:15- What will happen to the universe?
0:04:15 > 0:04:18- It's the big question in astronomy.
0:04:24 > 0:04:28- To predict the future, - cosmologists look to the past.
0:04:33 > 0:04:35- Back to the beginning of everything.
0:04:43 > 0:04:44- Billions of years ago...
0:04:45 > 0:04:49- ..a dense, hot speck ignites - and suddenly expands...
0:04:49 > 0:04:51- ..creating the Big Bang.
0:04:56 > 0:05:00- This starts the building blocks - for the cosmos.
0:05:00 > 0:05:03- All energy, all space - and all matter.
0:05:07 > 0:05:09- Think of everything - you see around us...
0:05:10 > 0:05:14- ..concentrated into a primordial - fireball that exploded...
0:05:14 > 0:05:17- ..sending all the galaxies - into motion.
0:05:22 > 0:05:25- The effects of the blast - continue today.
0:05:27 > 0:05:29- Things are still expanding.
0:05:29 > 0:05:33- Without it, we wouldn't have - a universe big enough...
0:05:33 > 0:05:36- ..for the stars and galaxies.
0:05:36 > 0:05:39- Astonishingly, expansion works...
0:05:39 > 0:05:42- ..by inflating - the fabric of space and time.
0:05:45 > 0:05:48- Compare it to a balloon expanding.
0:05:49 > 0:05:53- If you mark the balloon - to represent the galaxies...
0:05:53 > 0:05:55- ..and then expand the balloon...
0:05:55 > 0:05:58- ..the marks don't move - on the surface.
0:05:59 > 0:06:04- The surface expands and that's - what's happening to the universe.
0:06:04 > 0:06:07- Expansion has led to - the existence of the cosmos...
0:06:08 > 0:06:13- ..but it needs to be controlled - or it could destroy everything.
0:06:18 > 0:06:20- Without pressure...
0:06:21 > 0:06:24- ..the universe - would have expanded forever.
0:06:28 > 0:06:31- We're still here, - so what put on the brakes?
0:06:33 > 0:06:37- Another force - the glue - which keeps everything together.
0:06:39 > 0:06:41- Gravity.
0:06:43 > 0:06:44- Gravity is crucial.
0:06:46 > 0:06:50- It draws atom to atom, - particle to particle...
0:06:50 > 0:06:55- ..building stars, galaxies, - the whole universe.
0:07:01 > 0:07:04- But even more crucial - is the amount of gravity.
0:07:06 > 0:07:11- Too much gravity - could end the universe.
0:07:16 > 0:07:20- Many things must remain constant - for us to be here...
0:07:20 > 0:07:22- ..to ask questions - about the universe.
0:07:24 > 0:07:27- There's a perfect balance here.
0:07:27 > 0:07:30- No force - is greater than the other...
0:07:31 > 0:07:35- ..so the expansion - is entirely balanced.
0:07:42 > 0:07:47- The universe has lasted - because of the opposing forces.
0:07:48 > 0:07:52- Gravity and expansion - controlling each other.
0:07:55 > 0:07:57- But how long will this balance last?
0:07:59 > 0:08:04- Scientists have worked on the maths - and the results were unexpected.
0:08:06 > 0:08:10- The more matter you have, - the more gravity you have.
0:08:10 > 0:08:14- If you have lots of matter - in a very dense universe...
0:08:14 > 0:08:16- ..the universe may recollapse.
0:08:16 > 0:08:21- If you have very little matter, - the universe would freeze to death.
0:08:21 > 0:08:25- What is the critical density - - the border between the two?
0:08:26 > 0:08:28- We know the strength of gravity...
0:08:28 > 0:08:32- ..so we can calculate - the critical density.
0:08:33 > 0:08:37- It equates to around five - hydrogen atoms per cubic meter.
0:08:45 > 0:08:51- This discovery seems to suggest the - universe is balanced on a tightrope.
0:08:51 > 0:08:55- But when astronomers - took additional measurements...
0:08:55 > 0:08:57- ..they were more hopeful.
0:08:58 > 0:09:02- The universe contained - the right amount of matter...
0:09:02 > 0:09:05- ..to stay at the critical density.
0:09:08 > 0:09:13- The universe would have either - shrunk rapidly or expanded quickly.
0:09:13 > 0:09:17- It would not have lasted - for close to 14 billion years...
0:09:18 > 0:09:20- ..without this perfect balance.
0:09:21 > 0:09:25- It would have mushroomed quickly - or shrunk.
0:09:31 > 0:09:36- Everything seemed good and the - universe seemed perfectly balanced.
0:09:37 > 0:09:42- But 40 years ago, astronomers - made a shocking discovery.
0:09:44 > 0:09:47- The cosmos - was filled with invisible stuff...
0:09:47 > 0:09:52- ..and its gravity - could be lethal for the universe.
0:09:54 > 0:09:55- .
0:10:00 > 0:10:00- Subtitles
0:10:00 > 0:10:02- Subtitles- - Subtitles
0:10:11 > 0:10:14- The cosmos - is balanced on a tightrope.
0:10:15 > 0:10:18- On each side lies an early death.
0:10:19 > 0:10:23- A big freeze, - fuelled by the stretching of space.
0:10:25 > 0:10:26- Or a big crunch.
0:10:36 > 0:10:40- In the mid-1970s and early 1980s, - astronomers tried to calculate...
0:10:41 > 0:10:44- ..how many galaxies there are - in the universe.
0:10:44 > 0:10:48- They wanted to see if the universe - would expand forever...
0:10:49 > 0:10:50- ..or stop and shrink.
0:10:52 > 0:10:54- Astronomers were stunned...
0:10:55 > 0:11:00- ..to discover the universe was full - of an unknown, invisible matter.
0:11:00 > 0:11:02- And lots of it.
0:11:04 > 0:11:08- We used to think that gravity came - from stars and objects you can see.
0:11:09 > 0:11:10- End of story.
0:11:11 > 0:11:14- Now we realize that naive picture - is actually wrong.
0:11:17 > 0:11:22- Astronomers made the discovery when - studying movement in the cosmos.
0:11:25 > 0:11:30- The huge gravity of the sun holds - the earth and planets in place.
0:11:31 > 0:11:35- The sun's mass - controls the speed of these orbits.
0:11:39 > 0:11:43- If the sun were bigger, - the planets would orbit quicker.
0:11:45 > 0:11:48- If the sun were smaller, - they would slow down.
0:11:51 > 0:11:53- Galaxies work in the same way.
0:11:54 > 0:11:56- The vast mass at the centre...
0:11:56 > 0:12:00- ..pulls the outer stars - to orbit like planets.
0:12:02 > 0:12:07- In the 1970s, precise measurements - of these galactic orbits were taken.
0:12:08 > 0:12:10- The results changed everything.
0:12:10 > 0:12:13- We know the sun's mass.
0:12:13 > 0:12:17- We can also measure its effect - on the planets.
0:12:18 > 0:12:21- By the same token, we can measure - the mass of a galaxy.
0:12:22 > 0:12:25- But when we do so, - there's something missing.
0:12:25 > 0:12:28- It doesn't make mathematical sense.
0:12:29 > 0:12:31- The galaxies were spinning too fast.
0:12:32 > 0:12:33- Way too fast.
0:12:35 > 0:12:37- They would have been torn apart.
0:12:38 > 0:12:43- You couldn't explain why they - had lasted for such a long time.
0:12:44 > 0:12:46- It was impossible - for them to exist...
0:12:47 > 0:12:51- ..unless some other matter - was creating gravity.
0:12:54 > 0:12:58- Something else must be - holding the galaxies together.
0:12:59 > 0:13:02- But despite looking, - nothing was found.
0:13:06 > 0:13:12- This new stuff doesn't emit light, - reflect light or even block light.
0:13:16 > 0:13:19- It's now known as dark matter.
0:13:20 > 0:13:23- We don't know what dark matter is.
0:13:24 > 0:13:28- But the galaxies don't behave - in the way we expect them to...
0:13:29 > 0:13:32- ..if they only consisted - of the matter we see.
0:13:32 > 0:13:38- We therefore think there's something - else there, but we don't know what.
0:13:41 > 0:13:43- It doesn't belong - to the matter we know.
0:13:44 > 0:13:48- The 92 elements - we're taught about at school.
0:13:48 > 0:13:51- It's something beyond that.
0:13:51 > 0:13:55- Some kind of matter - that's parallel to our own.
0:13:59 > 0:14:03- Dark matter leaves scientists - scratching their heads.
0:14:04 > 0:14:08- The fate of the universe hangs on - how much of it fills space.
0:14:08 > 0:14:12- But how do you measure - something you can't even see?
0:14:13 > 0:14:16- There are many ways - to see things around us.
0:14:16 > 0:14:19- Firstly, things which emit light.
0:14:20 > 0:14:22- The sun emits light.
0:14:22 > 0:14:27- The light from a city at night - and the stars emit light.
0:14:30 > 0:14:33- Then there are things - which reflect light.
0:14:33 > 0:14:36- That's what allows us - to see the moon.
0:14:37 > 0:14:40- There are also things - which block light...
0:14:41 > 0:14:43- ..like a shadow - or a passing silhouette.
0:14:44 > 0:14:46- But what if there's something...
0:14:47 > 0:14:51- ..which doesn't reflect light, - emit light or block light?
0:14:51 > 0:14:54- That's a description of dark matter.
0:14:54 > 0:14:56- So how do we know it's there?
0:15:02 > 0:15:04- Galaxies are so massive...
0:15:05 > 0:15:08- ..their gravity - actually bends passing light.
0:15:10 > 0:15:14- Astronomers see these cosmic mirages - with telescopes.
0:15:16 > 0:15:21- Sometimes, they see the same bent - light around apparently empty space.
0:15:21 > 0:15:23- Could dark matter be to blame?
0:15:26 > 0:15:29- When light travels through glass, - it bends.
0:15:30 > 0:15:31- That's how we can see it.
0:15:33 > 0:15:35- In the same way, - when light from a star...
0:15:36 > 0:15:40- ..travels through dark matter - in the universe, it also bends.
0:15:40 > 0:15:42- That's how we map dark matter.
0:15:46 > 0:15:50- Astronomers have mapped out - the distribution of dark matter...
0:15:51 > 0:15:53- ..using the same technology...
0:15:53 > 0:15:56- ..and the results are mind-blowing.
0:15:59 > 0:16:01- Dark matter fills the universe.
0:16:02 > 0:16:05- It outstrips normal matter - by five to one.
0:16:09 > 0:16:14- And bright galaxies cluster - where dark matter is thickest.
0:16:17 > 0:16:21- Around a quarter of the matter - in the universe is dark matter.
0:16:24 > 0:16:27- There's much more of it - than visible matter...
0:16:27 > 0:16:31- ..and its framework - keeps galaxies stable.
0:16:33 > 0:16:37- Without dark matter, - we would have no galaxies.
0:16:38 > 0:16:43- There is a theory that dark matter - came first, before the universe.
0:16:44 > 0:16:46- That it was the first thing to form.
0:16:48 > 0:16:51- So dark matter - has shaped the cosmos.
0:16:56 > 0:17:01- We know that gravity pulls things - together if they have mass...
0:17:02 > 0:17:05- ..and we now know - that dark matter also has mass.
0:17:11 > 0:17:14- Dark matter - holds the cosmos together...
0:17:14 > 0:17:17- ..but it also - threatens to destroy it.
0:17:19 > 0:17:23- One of the most amazing discoveries - of the past decades is dark matter.
0:17:23 > 0:17:26- There's much more matter in the - universe than we were aware of.
0:17:26 > 0:17:29- That matter has a lot of gravity.
0:17:29 > 0:17:33- This new matter, this new gravity, - slows the expansion of the universe.
0:17:36 > 0:17:39- Dark matter could destroy - the balance in the cosmos.
0:17:40 > 0:17:42- Gravity could defeat expansion...
0:17:43 > 0:17:46- ..turning the entire universe - into a ball of fire.
0:17:48 > 0:17:52- It's called the big crunch - and this is how it would happen.
0:17:56 > 0:17:59- For a fraction of a second, - the universe stops...
0:17:59 > 0:18:02- ..poised between the two forces.
0:18:03 > 0:18:05- Then gravity wins.
0:18:06 > 0:18:11- In the big crunch, the opposite - of an explosion would happen.
0:18:12 > 0:18:17- All matter would come together and - disappear into a big black hole.
0:18:19 > 0:18:23- As space contracts, - the density of matter increases.
0:18:24 > 0:18:25- Gravity gets stronger.
0:18:29 > 0:18:33- Galaxies begin to collide, - gas clouds begin to collide...
0:18:36 > 0:18:38- ..and planets slam into the earth.
0:18:42 > 0:18:45- Black holes will execute - a death dance around each other.
0:18:46 > 0:18:49- Temperatures - will continue to skyrocket.
0:18:51 > 0:18:54- At the point when the universe - is at its biggest...
0:18:55 > 0:18:58- ..and folds into itself, - everything changes.
0:18:59 > 0:19:01- The direction of time even changes.
0:19:03 > 0:19:07- So rather than lighting a match - and watching it burn...
0:19:08 > 0:19:12- ..the heat, smoke and gasses would - come together and create a match.
0:19:13 > 0:19:15- Like watching a film in rewind mode.
0:19:16 > 0:19:18- Everything in the universe...
0:19:19 > 0:19:23- ..is compressed into a tiny speck - of mass, heat and pressure.
0:19:27 > 0:19:30- For the last stages - of the big crunch...
0:19:30 > 0:19:33- ..galaxies will collide - and form a primordial atom.
0:19:34 > 0:19:37- Then life, as we know it, - will be impossible.
0:19:38 > 0:19:41- We're back to where it all began - - at the Big Bang.
0:19:43 > 0:19:46- The universe that we live in - will cease to exist.
0:19:50 > 0:19:55- But some believe the big crunch - could herald a new beginning.
0:20:00 > 0:20:02- Many people like the idea...
0:20:03 > 0:20:06- ..that you start a new universe - with a clean slate...
0:20:07 > 0:20:10- ..and that everything - starts from scratch.
0:20:12 > 0:20:16- As scientists came to terms - with the big crunch...
0:20:16 > 0:20:19- ..they came across another problem.
0:20:22 > 0:20:25- Another force - which could send the cosmos...
0:20:26 > 0:20:29- ..towards a completely - different death.
0:20:29 > 0:20:30- .
0:20:38 > 0:20:38- Subtitles
0:20:38 > 0:20:40- Subtitles- - Subtitles
0:20:47 > 0:20:49- Over billions of years...
0:20:50 > 0:20:54- ..the balance of two forces - has controlled our universe.
0:20:55 > 0:20:59- Expansion pushing it outward - and gravity pulling it in.
0:21:04 > 0:21:07- And the significant discovery - - dark matter...
0:21:08 > 0:21:12- ..suggesting that gravity - will triumph in the end.
0:21:13 > 0:21:16- Its force dragging the cosmos - into the big crunch.
0:21:19 > 0:21:21- Until another discovery was made.
0:21:23 > 0:21:26- Around 1990, - two teams of researchers...
0:21:26 > 0:21:30- ..decided to measure the - expansion history of the universe...
0:21:30 > 0:21:34- ..to determine if it's slowing down - so much it'll have a big crunch...
0:21:35 > 0:21:39- ..or it hasn't been slowing down - and will eternally expand.
0:21:40 > 0:21:43- Astronomer Alexei Filippenko - was on one team.
0:21:44 > 0:21:46- Saul Perlmutter led the other.
0:21:47 > 0:21:50- We realized it was possible - for the first time...
0:21:50 > 0:21:52- ..to make a direct measurement...
0:21:52 > 0:21:55- ..of how much the universe - had slowed down in the past.
0:21:57 > 0:22:01- Both teams wanted to measure - the speed of distant galaxies.
0:22:02 > 0:22:06- But because the galaxies - are too dim and far away...
0:22:07 > 0:22:11- ..they looked - for something brighter.
0:22:16 > 0:22:19- A star detonates - in the far reaches of the cosmos.
0:22:21 > 0:22:22- This is a supernova.
0:22:23 > 0:22:27- It burns five billion times brighter - than the sun.
0:22:30 > 0:22:35- Scientists had a window - of just two weeks to see this light.
0:22:35 > 0:22:37- Before it disappeared...
0:22:38 > 0:22:42- ..they measured how quickly - the galaxy moved away from us.
0:22:48 > 0:22:52- For eight years, the team searched - for supernova stars.
0:22:52 > 0:22:58- They measured 42 - and the results seemed impossible.
0:23:02 > 0:23:05- The shock was that, - rather than slow down...
0:23:05 > 0:23:09- ..the expansion of the universe - is accelerating.
0:23:11 > 0:23:15- Since the Big Bang, - the universe has been expanding.
0:23:15 > 0:23:20- Gravity is a force which brings - everything back together...
0:23:20 > 0:23:24- ..so you'd expect - the rate of expansion to slow down.
0:23:24 > 0:23:30- But in 1997-1998, we discovered - that the expansion is accelerating.
0:23:34 > 0:23:37- The acceleration - bewilders the scientists.
0:23:40 > 0:23:43- The power of gravity - pulls things together.
0:23:44 > 0:23:48- If Leigh Halfpenny - kicks a rugby ball to the sky...
0:23:48 > 0:23:52- ..even with his strong left foot, - gravity will bring it back down.
0:23:53 > 0:24:00- With dark energy, it's like gravity - working in the opposite direction...
0:24:01 > 0:24:03- ..and pushing things apart.
0:24:04 > 0:24:08- If dark energy - were stronger than gravity...
0:24:09 > 0:24:12- ..rather than the rugby ball - coming back down...
0:24:13 > 0:24:17- ..Leigh Halfpenny could kick the - ball and it would never come down.
0:24:23 > 0:24:29- The new energy seemed to be coming - from nothing - the vacuum of space.
0:24:31 > 0:24:36- One of the facts we now accept - about vacuum is that it isn't empty.
0:24:36 > 0:24:39- In any empty space, - even in the depth of space...
0:24:40 > 0:24:43- ..matter is produced and destroyed - all the time.
0:24:46 > 0:24:50- Without a clue what this force is - or how it works...
0:24:51 > 0:24:53- ..it is called dark energy.
0:24:56 > 0:24:59- We seek an energy - of which there is no evidence.
0:25:00 > 0:25:02- It is, of course, dark energy.
0:25:05 > 0:25:09- NASA used its finest telescopes - to measure dark energy.
0:25:11 > 0:25:13- The result is mind-blowing.
0:25:15 > 0:25:19- There is more dark matter - in the cosmos than anything else.
0:25:20 > 0:25:25- The more space expands, the more - dark energy there seems to be.
0:25:26 > 0:25:30- If this dark energy becomes - more important in the future...
0:25:31 > 0:25:35- ..and, according to some theories, - it's linked to a vacuum.
0:25:36 > 0:25:38- As the universe expands...
0:25:39 > 0:25:43- ..the percentage of dark energy - in the universe will increase.
0:25:48 > 0:25:49- At the moment, it's 75%.
0:25:50 > 0:25:52- In the future it could be more...
0:25:53 > 0:25:58- ..and as a result, the expansion - of the universe will accelerate.
0:26:00 > 0:26:04- This discovery - seems to kill the big crunch theory.
0:26:05 > 0:26:09- But many questions remain - about dark energy.
0:26:09 > 0:26:11- If a volume of space grows...
0:26:12 > 0:26:16- ..does the dark energy inside it - grow at the same rate?
0:26:17 > 0:26:21- If so, the cosmos continues - to expand until it freezes.
0:26:23 > 0:26:28- But if dark energy increases - above and beyond expansion...
0:26:28 > 0:26:31- ..a more terrifying end - awaits the universe.
0:26:32 > 0:26:34- It will be ripped apart.
0:26:34 > 0:26:36- It pushes things.
0:26:39 > 0:26:41- Things contract, defying gravity.
0:26:42 > 0:26:44- You get a sort of antigravity...
0:26:44 > 0:26:48- ..as dark energy - pushes everything further apart.
0:26:49 > 0:26:50- So what will rip apart?
0:26:56 > 0:27:00- One by one, the galaxies - in the night sky will disappear.
0:27:01 > 0:27:05- They will be pushed apart - by the dark energy.
0:27:09 > 0:27:13- In a big rip scenario, - the expansion is so great...
0:27:13 > 0:27:17- ..that even the galaxies - begin to expand, internally.
0:27:18 > 0:27:20- Our bodies - are going to be ripped apart.
0:27:21 > 0:27:27- What we'll see in the distant future - is just a vacuum with no stars.
0:27:28 > 0:27:31- In the end, - there will be nothing left to see.
0:27:37 > 0:27:38- The end will be quick.
0:27:40 > 0:27:45- In a matter of minutes, all the - stars and planets in the cosmos...
0:27:45 > 0:27:47- ..will be destroyed.
0:27:47 > 0:27:51- Their remains pulled apart - into ever-smaller pieces.
0:27:51 > 0:27:53- Until the final second...
0:27:53 > 0:27:58- ..when the small particles that made - all matter will be destroyed.
0:27:59 > 0:28:02- All that remains - will be individual photons...
0:28:02 > 0:28:06- ..becoming scarcer - as the space between them expands.
0:28:09 > 0:28:14- And the last thing to go will be - the empty vacuum of space itself.
0:28:19 > 0:28:23- Will the universe end - with a big rip or a big freeze?
0:28:24 > 0:28:27- The answer is - inside the mystery of dark energy.
0:28:30 > 0:28:33- We don't know - which of these things will happen.
0:28:34 > 0:28:39- However, the evidence now suggests - not only the expansion theory...
0:28:40 > 0:28:44- ..but the big rip, with dark energy - becoming more important.
0:28:46 > 0:28:50- For the cosmos to explode, it needs - a huge increase in dark energy.
0:28:51 > 0:28:56- For the cosmos to freeze, - the expansion has to be consistent.
0:28:59 > 0:29:03- Dark energy is one of the - great mysteries of our time.
0:29:04 > 0:29:08- We know something is there, - but we don't know what it is.
0:29:13 > 0:29:19- May 2009, the European Space Agency - launches the Plank satellite...
0:29:20 > 0:29:22- ..to search for dark energy.
0:29:25 > 0:29:30- Its sensitive telescope peers back - through billions of years...
0:29:30 > 0:29:33- ..towards the beginning of time.
0:29:36 > 0:29:39- This is the cosmos - at the beginning of time.
0:29:39 > 0:29:41- Soon after the Big Bang.
0:29:47 > 0:29:51- These experiments have searched - in every direction.
0:29:52 > 0:29:56- They've mapped the small differences - in the background.
0:29:58 > 0:29:59- The early cosmos...
0:30:00 > 0:30:03- ..is a hot soup of protons, - electrons and photons.
0:30:06 > 0:30:09- Hydrogen atoms - have just started to form.
0:30:13 > 0:30:16- Blue areas are colder. - Reds are warmer.
0:30:19 > 0:30:23- The red spots - represent denser areas.
0:30:23 > 0:30:25- Areas where galaxies have formed.
0:30:26 > 0:30:29- The blue areas are less dense...
0:30:29 > 0:30:33- ..and those would be the vacuums - between the galaxies.
0:30:37 > 0:30:39- Gravity and expansion...
0:30:39 > 0:30:43- ..appear to drive - the formation of these galaxies.
0:30:45 > 0:30:47- There's no sign - of the dark energy yet.
0:30:49 > 0:30:53- So when did dark energy - take control of the cosmos?
0:30:57 > 0:31:00- Scientists - need a series of snapshots...
0:31:01 > 0:31:04- ..as the universe starts to grow.
0:31:04 > 0:31:06- Astronomer, David Schlegal...
0:31:07 > 0:31:12- ..looks into the first three billion - years after the Big Bang.
0:31:13 > 0:31:17- Galaxies from this time - are too dim and distant to see.
0:31:17 > 0:31:20- David looks for something - much larger.
0:31:20 > 0:31:25- Enormous clouds of hydrogen gas - illuminated by quasars.
0:31:29 > 0:31:33- Quasars are convenient objects - that the universe has given us.
0:31:34 > 0:31:36- The brightest objects - that we can see.
0:31:39 > 0:31:44- Quasars are high energy zones that - surround the massive black holes.
0:31:46 > 0:31:48- They're much brighter - than our sun.
0:31:54 > 0:31:56- They illuminate gas clouds...
0:31:57 > 0:32:01- ..in the same way - as clouds pass in front of our moon.
0:32:03 > 0:32:08- We've been making a very peculiar, - three-dimensional map...
0:32:08 > 0:32:10- ..of the gas in the universe...
0:32:10 > 0:32:14- ..along the line of sight - to each one of these quasars.
0:32:15 > 0:32:18- Plank provided a snapshot - of the early cosmos.
0:32:19 > 0:32:22- Mapping early gas clouds - with quasars...
0:32:22 > 0:32:27- ..reveals a glimpse - of the cosmos starting to grow.
0:32:27 > 0:32:29- By mapping the cosmos today...
0:32:31 > 0:32:35- ..scientists start to understand - the influence of Dark Energy.
0:32:41 > 0:32:45- Astronomer, Brenda Fry - is part of a team...
0:32:45 > 0:32:50- ..using ground-based telescopes, - like this one at Kitt Peak, Arizona.
0:32:52 > 0:32:57- She peers back in time to capture - the cosmos through its childhood.
0:33:00 > 0:33:02- This is an aluminium plate.
0:33:02 > 0:33:06- Into it are drilled - 640 individual holes.
0:33:07 > 0:33:13- Each at a specific place which will - correspond to one particular galaxy.
0:33:16 > 0:33:20- The light from - hundreds of galaxies is collected...
0:33:20 > 0:33:22- ..using fibre optic cables.
0:33:27 > 0:33:30- The speed and position - of each galaxy is measured...
0:33:31 > 0:33:33- ..to pinpoint where it is in space.
0:33:35 > 0:33:39- So far, the team has mapped - around a million galaxies in 3D...
0:33:40 > 0:33:41- ..and this is how they look.
0:33:43 > 0:33:48- Each one of these fuzzy patches - is a fully-grown galaxy...
0:33:48 > 0:33:51- ..containing - around two hundred billion stars.
0:33:52 > 0:33:56- It's the very basic measurement - and we think it can help us...
0:33:56 > 0:33:59- ..get a grasp - into the nature of dark energy.
0:34:01 > 0:34:05- Scientists compare - the early and later pictures.
0:34:07 > 0:34:09- It shows dark energy emerging...
0:34:09 > 0:34:12- ..when the cosmos - is half as old as it is today.
0:34:13 > 0:34:15- About 8 billion years - after the Big Bang...
0:34:16 > 0:34:19- ..this expansion of the universe - begins to accelerate.
0:34:20 > 0:34:24- We're in the middle - of this acceleration.
0:34:24 > 0:34:27- The data also shows that, - as space expands...
0:34:28 > 0:34:31- ..dark energy increases - at the same rate.
0:34:35 > 0:34:39- It appears we should be safe - from a big rip.
0:34:41 > 0:34:44- Dark energy - will continue to increase gradually.
0:34:45 > 0:34:49- It seems the cosmos - is heading for a big freeze.
0:34:50 > 0:34:54- Scientists can calculate - when this is likely to happen.
0:34:55 > 0:34:56- .
0:35:01 > 0:35:01- Subtitles
0:35:01 > 0:35:03- Subtitles- - Subtitles
0:35:10 > 0:35:13- It seems we live - in an almost perfect universe.
0:35:13 > 0:35:17- Just enough gravity - to hold the galaxies together...
0:35:18 > 0:35:22- ..and just enough dark energy - that it will expand slowly.
0:35:26 > 0:35:30- Cosmologists can finally envision - the end of everything.
0:35:32 > 0:35:34- We'll finish in a big freeze.
0:35:36 > 0:35:41- Everything will expand - and everything will get colder.
0:35:44 > 0:35:49- In a big freeze, dark energy pushes - galaxies further and further apart.
0:35:51 > 0:35:54- The stars inside them fade away.
0:35:57 > 0:36:02- The stars will run out of fuel and - their lights will be extinguished.
0:36:10 > 0:36:12- Looking far to the future...
0:36:12 > 0:36:15- ..the biggest stars - will be the first to go.
0:36:17 > 0:36:20- The star's core collapses, - unleashing a supernova.
0:36:26 > 0:36:31- Gravity then crushes the dead star - down to a single, dense spot.
0:36:31 > 0:36:34- The bright star is now a black hole.
0:36:37 > 0:36:41- Medium-sized stars such as our sun - will go next.
0:36:42 > 0:36:45- As their supply of hydrogen - runs out...
0:36:45 > 0:36:51- ..they swell to a bloated fireball - over 200 times their current size.
0:36:55 > 0:36:58- Red giants are stars - reaching the end of their lives.
0:37:01 > 0:37:04- They're unstable - and expanded massively.
0:37:05 > 0:37:10- The gases in the stars will expand - to the earth's orbit or beyond.
0:37:13 > 0:37:18- With no more fuel, stars like - our sun shrinks to a dense ball.
0:37:19 > 0:37:22- But there's no need to worry.
0:37:22 > 0:37:26- It will provide heat - for a further ten billion years...
0:37:26 > 0:37:30- ..before cooling - to a ball of compressed carbon.
0:37:39 > 0:37:43- As the biggest stars die, - the universe will slowly turn red.
0:37:45 > 0:37:48- Some stars will cool - over billions of years.
0:37:49 > 0:37:52- Some small stars will lose - their energy very slowly.
0:37:52 > 0:37:56- They'll be around billions - of years after the big stars.
0:37:57 > 0:38:01- Red stars are the smallest - and coolest in the universe.
0:38:02 > 0:38:04- They burn their fuel slowly.
0:38:06 > 0:38:10- But even these smallest - of dwarf stars will die.
0:38:10 > 0:38:13- Stars as we know them - will cease to burn energy.
0:38:14 > 0:38:16- The night sky will turn black.
0:38:18 > 0:38:23- Black holes, corpses of dead stars - and cold clouds of gas and dust...
0:38:23 > 0:38:24- ..are all that remain.
0:38:27 > 0:38:29- The age of stars is over.
0:38:31 > 0:38:33- The age of black holes begins.
0:38:35 > 0:38:39- It seems there's a huge black hole - at the centre of every galaxy.
0:38:39 > 0:38:42- The age of the black holes - is a long way away.
0:38:43 > 0:38:47- All that's left in the universe - will be these black holes.
0:38:49 > 0:38:53- Dead galaxies, filled with - black holes continue to evolve.
0:38:54 > 0:38:57- They sweep up - the dead remains of stars.
0:38:58 > 0:38:59- Black holes merge.
0:38:59 > 0:39:01- As the stars disappear...
0:39:01 > 0:39:05- ..all that's left is black holes - mopping up what left.
0:39:07 > 0:39:09- The universe - will be full of black holes.
0:39:10 > 0:39:12- Maybe you can see a situation...
0:39:12 > 0:39:16- ..where the universe mops them - all up into one big black hole.
0:39:18 > 0:39:23- Any material that evades the - black hole eventually dies away...
0:39:23 > 0:39:25- ..as its protons disintegrate.
0:39:26 > 0:39:31- A proton is one of the - particles in the nucleus of an atom.
0:39:31 > 0:39:36- Some suggest these protons in the - end break down into other things.
0:39:40 > 0:39:43- All that will be left - is a sea of black holes.
0:39:45 > 0:39:47- But even these will one day die.
0:39:51 > 0:39:55- We're talking about timescales - of unimaginable length.
0:39:55 > 0:39:58- Quadrillions of years - into the future.
0:39:58 > 0:40:02- But, on that timescale, even - the black holes begin to evaporate.
0:40:03 > 0:40:06- The universe will expand and expand.
0:40:06 > 0:40:11- Like a cloud, it will grow and grow - until it eventually disappears.
0:40:13 > 0:40:17- The cosmos will end when - the last remaining black hole dies.
0:40:18 > 0:40:20- It gets smaller...
0:40:20 > 0:40:25- ..and eventually the last black hole - will be less than an inch in size.
0:40:28 > 0:40:32- At that instant, - the laws of physics break down.
0:40:32 > 0:40:36- The last black hole explodes - in a flash of gamma rays...
0:40:37 > 0:40:40- ..leaving nothing.
0:40:41 > 0:40:44- Once everything - is in the black hole, that's it.
0:40:44 > 0:40:46- The end of the universe.
0:40:48 > 0:40:49- The cosmos will freeze.
0:40:50 > 0:40:53- The universe will suffer - a cold, slow, dark death...
0:40:54 > 0:40:57- ..which will happen - over trillions of years.
0:40:59 > 0:41:02- But the end could be very different.
0:41:02 > 0:41:05- An event so powerful, - so destructive...
0:41:06 > 0:41:09- ..it could destroy everything - in the blink of an eye.
0:41:11 > 0:41:14- And it could happen tomorrow.
0:41:21 > 0:41:25- Phase Transition - is the name for the monster.
0:41:26 > 0:41:30- In the same way as water - changes its properties in heat...
0:41:30 > 0:41:33- ..the same thing - could happen to space.
0:41:38 > 0:41:41- Water can be found in many forms.
0:41:41 > 0:41:42- Solid - ice.
0:41:43 > 0:41:44- Liquid - water.
0:41:45 > 0:41:46- Gas - steam.
0:41:47 > 0:41:52- Moving from one to the other - requires a Phase Transition.
0:41:57 > 0:42:02- Some people suggest in the distant - future, as the universe expands...
0:42:03 > 0:42:07- ..the vacuum will expand and - this vacuum will change its state.
0:42:10 > 0:42:15- A small change in the temperature - of space could start this process.
0:42:15 > 0:42:20- A tiny bubble of a new universe - could swallow the old.
0:42:23 > 0:42:26- We know it can happen - because it's happened before...
0:42:27 > 0:42:28- ..during the Big Bang.
0:42:35 > 0:42:38- Something similar happened before...
0:42:38 > 0:42:41- ..as the universe cooled - and lost energy...
0:42:41 > 0:42:45- ..during the first few seconds - of its existence.
0:42:47 > 0:42:51- The cosmos that's created - at the start of the Big Bang...
0:42:51 > 0:42:54- ..is totally different - from the one we see today.
0:42:55 > 0:42:58- Hot and without form, - there's no matter, no time.
0:42:58 > 0:43:02- The laws of physics - are completely different.
0:43:02 > 0:43:04- A fraction of a second later...
0:43:05 > 0:43:08- ..something triggers - a Phase Transition.
0:43:09 > 0:43:12- A tiny bubble of the universe - we live in today forms.
0:43:12 > 0:43:16- It races outwards, - destroying everything it touches.
0:43:18 > 0:43:20- The energy that spills out...
0:43:20 > 0:43:24- ..creates the space and time - in which we exist.
0:43:24 > 0:43:28- That energy was released, producing - all the matter and radiation...
0:43:28 > 0:43:31- ..we observe in the universe today.
0:43:33 > 0:43:38- The old universe gives up but - it holds back some of its energy.
0:43:39 > 0:43:42- The vacuum of space - also keeps some of its energy.
0:43:43 > 0:43:46- Perhaps this is the dark energy - we see today.
0:43:48 > 0:43:51- Physicists believe that - one day in the future...
0:43:51 > 0:43:53- ..it could happen again.
0:43:55 > 0:43:58- A small change may trigger - another Phase Transition.
0:43:59 > 0:44:01- One that turns everything - on its head.
0:44:02 > 0:44:05- This is a way - to destroy an entire universe.
0:44:05 > 0:44:10- Within your universe are the seeds - of its own destruction.
0:44:10 > 0:44:13- It tends to start in one place, - at first...
0:44:13 > 0:44:17- ..and then it expands, - like a bubble...
0:44:18 > 0:44:23- ..at the speed of light, - in this system.
0:44:29 > 0:44:32- Nothing can survive - this transition.
0:44:32 > 0:44:37- Planets and galaxies are all ripped - apart as the bubble reaches them.
0:44:39 > 0:44:42- If the bubble hits an atom, - it's destroyed...
0:44:42 > 0:44:46- ..and transformed - into something totally different.
0:44:47 > 0:44:53- If the laws of physics change with - Phase Transition in the vacuum...
0:44:54 > 0:44:56- ..then everything will change.
0:44:57 > 0:45:00- Gravity and electromagnetism - would change.
0:45:00 > 0:45:04- Almost all the assumptions - of physics would change...
0:45:04 > 0:45:09- ..and you would be in a very alien, - completely different universe.
0:45:11 > 0:45:15- This bubble - will expand at the speed of light.
0:45:15 > 0:45:19- As the bubble passes you, the atoms - of your body rearrange themselves...
0:45:19 > 0:45:21- ..and you would never know it.
0:45:21 > 0:45:23- You have no warning...
0:45:23 > 0:45:27- ..because the bubble is expanding - at the speed of light.
0:45:28 > 0:45:32- When will this happen? - Very far in the future.
0:45:32 > 0:45:37- It will not happen tomorrow, - the day after or next week!
0:45:38 > 0:45:41- If it happens at all, - and we're not certain...
0:45:41 > 0:45:45- ..it's much more likely - to happen far in the future.
0:45:55 > 0:45:58- The cosmos is full of secrets.
0:46:04 > 0:46:09- Like dark energy, there may be - more surprises still to come.
0:46:11 > 0:46:15- Surprises that will only - add to the wonder of the cosmos.
0:46:19 > 0:46:23- The death of energy, - the death of heat, will be the end.
0:46:23 > 0:46:25- That is something new.
0:46:25 > 0:46:28- Five years ago, - we would not have said that.
0:46:29 > 0:46:33- Today, I think that is the message - from those working in this field.
0:47:13 > 0:47:15- S4C subtitles by Eirlys A Jones
0:47:15 > 0:47:15- .