Y Cosmos: Diwedd y Bydysawd Y Cosmos

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-All living things eventually die.

-So how and when will the cosmos end?

-How will the universe end?

-It's the big question in astronomy.

-Two cosmic heavyweights

-wrestle for control.

-The winner decides our future.

-Expansion makes everything bigger

-and gravity pulls things together.

-Will gravity be the winner...

-..or will other forces

-rip the universe apart?

-The universe will change

-into a dark, cold place.

-Freezing is the likely ending

-for the universe.

-In this programme,

-we will discover...

-..how and when the cosmos

-will come to an end.

-The cosmos is everything.

-Earth is a tiny grain of rock...

-..amongst the billions of stars

-in the Milky Way.

-The Milky Way is just one of

-hundreds of millions of galaxies.

-And all of this will one day die.

-Since its birth...

-..the fuel that lights the stars

-has been gradually burning.

-But what happens

-when the fuel runs out?

-As the stars disappear,

-they will leave behind black holes.

-Those black holes

-will mop up what's left...

-..leaving a universe

-full of black holes.

-The universe may then gather

-everything into one big black hole.

-Scientists used to think...

-..the cosmos would cruise slowly

-into old age.

-But astronomers

-have revealed a different picture.

-The cosmos is fighting for its life.

-The universe is dynamic,

-with things changing constantly.

-Two forces fight for control.

-Expansion pulls galaxies apart...

-..threatening to freeze the cosmos

-to its death.

-Gravity tries to

-crush everything back together...

-..threatening to compress the

-universe into a large ball of fire.

-Two forces,

-but which one will triumph?

-One is the big freeze.

-Expansion wins.

-The universe expands forever.

-The second is a delicate balance...

-..between expansion

-and gravitational attraction.

-The universe gets to a

-particular size and it stays there.

-The third outcome is that

-gravitational attraction wins.

-Expansion stops

-and the universe gets smaller...

-..until eventually

-it goes back to a big crunch.

-The cosmos seems balanced

-between these two forces.

-Will it keep its equilibrium

-or will something tip the balance?

-What will happen to the universe?

-It's the big question in astronomy.

-To predict the future,

-cosmologists look to the past.

-Back to the beginning of everything.

-Billions of years ago...

-..a dense, hot speck ignites

-and suddenly expands...

-..creating the Big Bang.

-This starts the building blocks

-for the cosmos.

-All energy, all space

-and all matter.

-Think of everything

-you see around us...

-..concentrated into a primordial

-fireball that exploded...

-..sending all the galaxies

-into motion.

-The effects of the blast

-continue today.

-Things are still expanding.

-Without it, we wouldn't have

-a universe big enough...

-..for the stars and galaxies.

-Astonishingly, expansion works...

-..by inflating

-the fabric of space and time.

-Compare it to a balloon expanding.

-If you mark the balloon

-to represent the galaxies...

-..and then expand the balloon...

-..the marks don't move

-on the surface.

-The surface expands and that's

-what's happening to the universe.

-Expansion has led to

-the existence of the cosmos...

-..but it needs to be controlled

-or it could destroy everything.

-Without pressure...

-..the universe

-would have expanded forever.

-We're still here,

-so what put on the brakes?

-Another force - the glue

-which keeps everything together.

-Gravity.

-Gravity is crucial.

-It draws atom to atom,

-particle to particle...

-..building stars, galaxies,

-the whole universe.

-But even more crucial

-is the amount of gravity.

-Too much gravity

-could end the universe.

-Many things must remain constant

-for us to be here...

-..to ask questions

-about the universe.

-There's a perfect balance here.

-No force

-is greater than the other...

-..so the expansion

-is entirely balanced.

-The universe has lasted

-because of the opposing forces.

-Gravity and expansion

-controlling each other.

-But how long will this balance last?

-Scientists have worked on the maths

-and the results were unexpected.

-The more matter you have,

-the more gravity you have.

-If you have lots of matter

-in a very dense universe...

-..the universe may recollapse.

-If you have very little matter,

-the universe would freeze to death.

-What is the critical density -

-the border between the two?

-We know the strength of gravity...

-..so we can calculate

-the critical density.

-It equates to around five

-hydrogen atoms per cubic meter.

-This discovery seems to suggest the

-universe is balanced on a tightrope.

-But when astronomers

-took additional measurements...

-..they were more hopeful.

-The universe contained

-the right amount of matter...

-..to stay at the critical density.

-The universe would have either

-shrunk rapidly or expanded quickly.

-It would not have lasted

-for close to 14 billion years...

-..without this perfect balance.

-It would have mushroomed quickly

-or shrunk.

-Everything seemed good and the

-universe seemed perfectly balanced.

-But 40 years ago, astronomers

-made a shocking discovery.

-The cosmos

-was filled with invisible stuff...

-..and its gravity

-could be lethal for the universe.

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-The cosmos

-is balanced on a tightrope.

-On each side lies an early death.

-A big freeze,

-fuelled by the stretching of space.

-Or a big crunch.

-In the mid-1970s and early 1980s,

-astronomers tried to calculate...

-..how many galaxies there are

-in the universe.

-They wanted to see if the universe

-would expand forever...

-..or stop and shrink.

-Astronomers were stunned...

-..to discover the universe was full

-of an unknown, invisible matter.

-And lots of it.

-We used to think that gravity came

-from stars and objects you can see.

-End of story.

-Now we realize that naive picture

-is actually wrong.

-Astronomers made the discovery when

-studying movement in the cosmos.

-The huge gravity of the sun holds

-the earth and planets in place.

-The sun's mass

-controls the speed of these orbits.

-If the sun were bigger,

-the planets would orbit quicker.

-If the sun were smaller,

-they would slow down.

-Galaxies work in the same way.

-The vast mass at the centre...

-..pulls the outer stars

-to orbit like planets.

-In the 1970s, precise measurements

-of these galactic orbits were taken.

-The results changed everything.

-We know the sun's mass.

-We can also measure its effect

-on the planets.

-By the same token, we can measure

-the mass of a galaxy.

-But when we do so,

-there's something missing.

-It doesn't make mathematical sense.

-The galaxies were spinning too fast.

-Way too fast.

-They would have been torn apart.

-You couldn't explain why they

-had lasted for such a long time.

-It was impossible

-for them to exist...

-..unless some other matter

-was creating gravity.

-Something else must be

-holding the galaxies together.

-But despite looking,

-nothing was found.

-This new stuff doesn't emit light,

-reflect light or even block light.

-It's now known as dark matter.

-We don't know what dark matter is.

-But the galaxies don't behave

-in the way we expect them to...

-..if they only consisted

-of the matter we see.

-We therefore think there's something

-else there, but we don't know what.

-It doesn't belong

-to the matter we know.

-The 92 elements

-we're taught about at school.

-It's something beyond that.

-Some kind of matter

-that's parallel to our own.

-Dark matter leaves scientists

-scratching their heads.

-The fate of the universe hangs on

-how much of it fills space.

-But how do you measure

-something you can't even see?

-There are many ways

-to see things around us.

-Firstly, things which emit light.

-The sun emits light.

-The light from a city at night

-and the stars emit light.

-Then there are things

-which reflect light.

-That's what allows us

-to see the moon.

-There are also things

-which block light...

-..like a shadow

-or a passing silhouette.

-But what if there's something...

-..which doesn't reflect light,

-emit light or block light?

-That's a description of dark matter.

-So how do we know it's there?

-Galaxies are so massive...

-..their gravity

-actually bends passing light.

-Astronomers see these cosmic mirages

-with telescopes.

-Sometimes, they see the same bent

-light around apparently empty space.

-Could dark matter be to blame?

-When light travels through glass,

-it bends.

-That's how we can see it.

-In the same way,

-when light from a star...

-..travels through dark matter

-in the universe, it also bends.

-That's how we map dark matter.

-Astronomers have mapped out

-the distribution of dark matter...

-..using the same technology...

-..and the results are mind-blowing.

-Dark matter fills the universe.

-It outstrips normal matter

-by five to one.

-And bright galaxies cluster

-where dark matter is thickest.

-Around a quarter of the matter

-in the universe is dark matter.

-There's much more of it

-than visible matter...

-..and its framework

-keeps galaxies stable.

-Without dark matter,

-we would have no galaxies.

-There is a theory that dark matter

-came first, before the universe.

-That it was the first thing to form.

-So dark matter

-has shaped the cosmos.

-We know that gravity pulls things

-together if they have mass...

-..and we now know

-that dark matter also has mass.

-Dark matter

-holds the cosmos together...

-..but it also

-threatens to destroy it.

-One of the most amazing discoveries

-of the past decades is dark matter.

-There's much more matter in the

-universe than we were aware of.

-That matter has a lot of gravity.

-This new matter, this new gravity,

-slows the expansion of the universe.

-Dark matter could destroy

-the balance in the cosmos.

-Gravity could defeat expansion...

-..turning the entire universe

-into a ball of fire.

-It's called the big crunch

-and this is how it would happen.

-For a fraction of a second,

-the universe stops...

-..poised between the two forces.

-Then gravity wins.

-In the big crunch, the opposite

-of an explosion would happen.

-All matter would come together and

-disappear into a big black hole.

-As space contracts,

-the density of matter increases.

-Gravity gets stronger.

-Galaxies begin to collide,

-gas clouds begin to collide...

-..and planets slam into the earth.

-Black holes will execute

-a death dance around each other.

-Temperatures

-will continue to skyrocket.

-At the point when the universe

-is at its biggest...

-..and folds into itself,

-everything changes.

-The direction of time even changes.

-So rather than lighting a match

-and watching it burn...

-..the heat, smoke and gasses would

-come together and create a match.

-Like watching a film in rewind mode.

-Everything in the universe...

-..is compressed into a tiny speck

-of mass, heat and pressure.

-For the last stages

-of the big crunch...

-..galaxies will collide

-and form a primordial atom.

-Then life, as we know it,

-will be impossible.

-We're back to where it all began -

-at the Big Bang.

-The universe that we live in

-will cease to exist.

-But some believe the big crunch

-could herald a new beginning.

-Many people like the idea...

-..that you start a new universe

-with a clean slate...

-..and that everything

-starts from scratch.

-As scientists came to terms

-with the big crunch...

-..they came across another problem.

-Another force

-which could send the cosmos...

-..towards a completely

-different death.

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-Over billions of years...

-..the balance of two forces

-has controlled our universe.

-Expansion pushing it outward

-and gravity pulling it in.

-And the significant discovery -

-dark matter...

-..suggesting that gravity

-will triumph in the end.

-Its force dragging the cosmos

-into the big crunch.

-Until another discovery was made.

-Around 1990,

-two teams of researchers...

-..decided to measure the

-expansion history of the universe...

-..to determine if it's slowing down

-so much it'll have a big crunch...

-..or it hasn't been slowing down

-and will eternally expand.

-Astronomer Alexei Filippenko

-was on one team.

-Saul Perlmutter led the other.

-We realized it was possible

-for the first time...

-..to make a direct measurement...

-..of how much the universe

-had slowed down in the past.

-Both teams wanted to measure

-the speed of distant galaxies.

-But because the galaxies

-are too dim and far away...

-..they looked

-for something brighter.

-A star detonates

-in the far reaches of the cosmos.

-This is a supernova.

-It burns five billion times brighter

-than the sun.

-Scientists had a window

-of just two weeks to see this light.

-Before it disappeared...

-..they measured how quickly

-the galaxy moved away from us.

-For eight years, the team searched

-for supernova stars.

-They measured 42

-and the results seemed impossible.

-The shock was that,

-rather than slow down...

-..the expansion of the universe

-is accelerating.

-Since the Big Bang,

-the universe has been expanding.

-Gravity is a force which brings

-everything back together...

-..so you'd expect

-the rate of expansion to slow down.

-But in 1997-1998, we discovered

-that the expansion is accelerating.

-The acceleration

-bewilders the scientists.

-The power of gravity

-pulls things together.

-If Leigh Halfpenny

-kicks a rugby ball to the sky...

-..even with his strong left foot,

-gravity will bring it back down.

-With dark energy, it's like gravity

-working in the opposite direction...

-..and pushing things apart.

-If dark energy

-were stronger than gravity...

-..rather than the rugby ball

-coming back down...

-..Leigh Halfpenny could kick the

-ball and it would never come down.

-The new energy seemed to be coming

-from nothing - the vacuum of space.

-One of the facts we now accept

-about vacuum is that it isn't empty.

-In any empty space,

-even in the depth of space...

-..matter is produced and destroyed

-all the time.

-Without a clue what this force is

-or how it works...

-..it is called dark energy.

-We seek an energy

-of which there is no evidence.

-It is, of course, dark energy.

-NASA used its finest telescopes

-to measure dark energy.

-The result is mind-blowing.

-There is more dark matter

-in the cosmos than anything else.

-The more space expands, the more

-dark energy there seems to be.

-If this dark energy becomes

-more important in the future...

-..and, according to some theories,

-it's linked to a vacuum.

-As the universe expands...

-..the percentage of dark energy

-in the universe will increase.

-At the moment, it's 75%.

-In the future it could be more...

-..and as a result, the expansion

-of the universe will accelerate.

-This discovery

-seems to kill the big crunch theory.

-But many questions remain

-about dark energy.

-If a volume of space grows...

-..does the dark energy inside it

-grow at the same rate?

-If so, the cosmos continues

-to expand until it freezes.

-But if dark energy increases

-above and beyond expansion...

-..a more terrifying end

-awaits the universe.

-It will be ripped apart.

-It pushes things.

-Things contract, defying gravity.

-You get a sort of antigravity...

-..as dark energy

-pushes everything further apart.

-So what will rip apart?

-One by one, the galaxies

-in the night sky will disappear.

-They will be pushed apart

-by the dark energy.

-In a big rip scenario,

-the expansion is so great...

-..that even the galaxies

-begin to expand, internally.

-Our bodies

-are going to be ripped apart.

-What we'll see in the distant future

-is just a vacuum with no stars.

-In the end,

-there will be nothing left to see.

-The end will be quick.

-In a matter of minutes, all the

-stars and planets in the cosmos...

-..will be destroyed.

-Their remains pulled apart

-into ever-smaller pieces.

-Until the final second...

-..when the small particles that made

-all matter will be destroyed.

-All that remains

-will be individual photons...

-..becoming scarcer

-as the space between them expands.

-And the last thing to go will be

-the empty vacuum of space itself.

-Will the universe end

-with a big rip or a big freeze?

-The answer is

-inside the mystery of dark energy.

-We don't know

-which of these things will happen.

-However, the evidence now suggests

-not only the expansion theory...

-..but the big rip, with dark energy

-becoming more important.

-For the cosmos to explode, it needs

-a huge increase in dark energy.

-For the cosmos to freeze,

-the expansion has to be consistent.

-Dark energy is one of the

-great mysteries of our time.

-We know something is there,

-but we don't know what it is.

-May 2009, the European Space Agency

-launches the Plank satellite...

-..to search for dark energy.

-Its sensitive telescope peers back

-through billions of years...

-..towards the beginning of time.

-This is the cosmos

-at the beginning of time.

-Soon after the Big Bang.

-These experiments have searched

-in every direction.

-They've mapped the small differences

-in the background.

-The early cosmos...

-..is a hot soup of protons,

-electrons and photons.

-Hydrogen atoms

-have just started to form.

-Blue areas are colder.

-Reds are warmer.

-The red spots

-represent denser areas.

-Areas where galaxies have formed.

-The blue areas are less dense...

-..and those would be the vacuums

-between the galaxies.

-Gravity and expansion...

-..appear to drive

-the formation of these galaxies.

-There's no sign

-of the dark energy yet.

-So when did dark energy

-take control of the cosmos?

-Scientists

-need a series of snapshots...

-..as the universe starts to grow.

-Astronomer, David Schlegal...

-..looks into the first three billion

-years after the Big Bang.

-Galaxies from this time

-are too dim and distant to see.

-David looks for something

-much larger.

-Enormous clouds of hydrogen gas

-illuminated by quasars.

-Quasars are convenient objects

-that the universe has given us.

-The brightest objects

-that we can see.

-Quasars are high energy zones that

-surround the massive black holes.

-They're much brighter

-than our sun.

-They illuminate gas clouds...

-..in the same way

-as clouds pass in front of our moon.

-We've been making a very peculiar,

-three-dimensional map...

-..of the gas in the universe...

-..along the line of sight

-to each one of these quasars.

-Plank provided a snapshot

-of the early cosmos.

-Mapping early gas clouds

-with quasars...

-..reveals a glimpse

-of the cosmos starting to grow.

-By mapping the cosmos today...

-..scientists start to understand

-the influence of Dark Energy.

-Astronomer, Brenda Fry

-is part of a team...

-..using ground-based telescopes,

-like this one at Kitt Peak, Arizona.

-She peers back in time to capture

-the cosmos through its childhood.

-This is an aluminium plate.

-Into it are drilled

-640 individual holes.

-Each at a specific place which will

-correspond to one particular galaxy.

-The light from

-hundreds of galaxies is collected...

-..using fibre optic cables.

-The speed and position

-of each galaxy is measured...

-..to pinpoint where it is in space.

-So far, the team has mapped

-around a million galaxies in 3D...

-..and this is how they look.

-Each one of these fuzzy patches

-is a fully-grown galaxy...

-..containing

-around two hundred billion stars.

-It's the very basic measurement

-and we think it can help us...

-..get a grasp

-into the nature of dark energy.

-Scientists compare

-the early and later pictures.

-It shows dark energy emerging...

-..when the cosmos

-is half as old as it is today.

-About 8 billion years

-after the Big Bang...

-..this expansion of the universe

-begins to accelerate.

-We're in the middle

-of this acceleration.

-The data also shows that,

-as space expands...

-..dark energy increases

-at the same rate.

-It appears we should be safe

-from a big rip.

-Dark energy

-will continue to increase gradually.

-It seems the cosmos

-is heading for a big freeze.

-Scientists can calculate

-when this is likely to happen.

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-It seems we live

-in an almost perfect universe.

-Just enough gravity

-to hold the galaxies together...

-..and just enough dark energy

-that it will expand slowly.

-Cosmologists can finally envision

-the end of everything.

-We'll finish in a big freeze.

-Everything will expand

-and everything will get colder.

-In a big freeze, dark energy pushes

-galaxies further and further apart.

-The stars inside them fade away.

-The stars will run out of fuel and

-their lights will be extinguished.

-Looking far to the future...

-..the biggest stars

-will be the first to go.

-The star's core collapses,

-unleashing a supernova.

-Gravity then crushes the dead star

-down to a single, dense spot.

-The bright star is now a black hole.

-Medium-sized stars such as our sun

-will go next.

-As their supply of hydrogen

-runs out...

-..they swell to a bloated fireball

-over 200 times their current size.

-Red giants are stars

-reaching the end of their lives.

-They're unstable

-and expanded massively.

-The gases in the stars will expand

-to the earth's orbit or beyond.

-With no more fuel, stars like

-our sun shrinks to a dense ball.

-But there's no need to worry.

-It will provide heat

-for a further ten billion years...

-..before cooling

-to a ball of compressed carbon.

-As the biggest stars die,

-the universe will slowly turn red.

-Some stars will cool

-over billions of years.

-Some small stars will lose

-their energy very slowly.

-They'll be around billions

-of years after the big stars.

-Red stars are the smallest

-and coolest in the universe.

-They burn their fuel slowly.

-But even these smallest

-of dwarf stars will die.

-Stars as we know them

-will cease to burn energy.

-The night sky will turn black.

-Black holes, corpses of dead stars

-and cold clouds of gas and dust...

-..are all that remain.

-The age of stars is over.

-The age of black holes begins.

-It seems there's a huge black hole

-at the centre of every galaxy.

-The age of the black holes

-is a long way away.

-All that's left in the universe

-will be these black holes.

-Dead galaxies, filled with

-black holes continue to evolve.

-They sweep up

-the dead remains of stars.

-Black holes merge.

-As the stars disappear...

-..all that's left is black holes

-mopping up what left.

-The universe

-will be full of black holes.

-Maybe you can see a situation...

-..where the universe mops them

-all up into one big black hole.

-Any material that evades the

-black hole eventually dies away...

-..as its protons disintegrate.

-A proton is one of the

-particles in the nucleus of an atom.

-Some suggest these protons in the

-end break down into other things.

-All that will be left

-is a sea of black holes.

-But even these will one day die.

-We're talking about timescales

-of unimaginable length.

-Quadrillions of years

-into the future.

-But, on that timescale, even

-the black holes begin to evaporate.

-The universe will expand and expand.

-Like a cloud, it will grow and grow

-until it eventually disappears.

-The cosmos will end when

-the last remaining black hole dies.

-It gets smaller...

-..and eventually the last black hole

-will be less than an inch in size.

-At that instant,

-the laws of physics break down.

-The last black hole explodes

-in a flash of gamma rays...

-..leaving nothing.

-Once everything

-is in the black hole, that's it.

-The end of the universe.

-The cosmos will freeze.

-The universe will suffer

-a cold, slow, dark death...

-..which will happen

-over trillions of years.

-But the end could be very different.

-An event so powerful,

-so destructive...

-..it could destroy everything

-in the blink of an eye.

-And it could happen tomorrow.

-Phase Transition

-is the name for the monster.

-In the same way as water

-changes its properties in heat...

-..the same thing

-could happen to space.

-Water can be found in many forms.

-Solid - ice.

-Liquid - water.

-Gas - steam.

-Moving from one to the other

-requires a Phase Transition.

-Some people suggest in the distant

-future, as the universe expands...

-..the vacuum will expand and

-this vacuum will change its state.

-A small change in the temperature

-of space could start this process.

-A tiny bubble of a new universe

-could swallow the old.

-We know it can happen

-because it's happened before...

-..during the Big Bang.

-Something similar happened before...

-..as the universe cooled

-and lost energy...

-..during the first few seconds

-of its existence.

-The cosmos that's created

-at the start of the Big Bang...

-..is totally different

-from the one we see today.

-Hot and without form,

-there's no matter, no time.

-The laws of physics

-are completely different.

-A fraction of a second later...

-..something triggers

-a Phase Transition.

-A tiny bubble of the universe

-we live in today forms.

-It races outwards,

-destroying everything it touches.

-The energy that spills out...

-..creates the space and time

-in which we exist.

-That energy was released, producing

-all the matter and radiation...

-..we observe in the universe today.

-The old universe gives up but

-it holds back some of its energy.

-The vacuum of space

-also keeps some of its energy.

-Perhaps this is the dark energy

-we see today.

-Physicists believe that

-one day in the future...

-..it could happen again.

-A small change may trigger

-another Phase Transition.

-One that turns everything

-on its head.

-This is a way

-to destroy an entire universe.

-Within your universe are the seeds

-of its own destruction.

-It tends to start in one place,

-at first...

-..and then it expands,

-like a bubble...

-..at the speed of light,

-in this system.

-Nothing can survive

-this transition.

-Planets and galaxies are all ripped

-apart as the bubble reaches them.

-If the bubble hits an atom,

-it's destroyed...

-..and transformed

-into something totally different.

-If the laws of physics change with

-Phase Transition in the vacuum...

-..then everything will change.

-Gravity and electromagnetism

-would change.

-Almost all the assumptions

-of physics would change...

-..and you would be in a very alien,

-completely different universe.

-This bubble

-will expand at the speed of light.

-As the bubble passes you, the atoms

-of your body rearrange themselves...

-..and you would never know it.

-You have no warning...

-..because the bubble is expanding

-at the speed of light.

-When will this happen?

-Very far in the future.

-It will not happen tomorrow,

-the day after or next week!

-If it happens at all,

-and we're not certain...

-..it's much more likely

-to happen far in the future.

-The cosmos is full of secrets.

-Like dark energy, there may be

-more surprises still to come.

-Surprises that will only

-add to the wonder of the cosmos.

-The death of energy,

-the death of heat, will be the end.

-That is something new.

-Five years ago,

-we would not have said that.

-Today, I think that is the message

-from those working in this field.

-S4C subtitles by Eirlys A Jones

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