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  • One day the universe will die.

  • But why? And how? And will the universe be dead forever?

  • And how do we know that?

  • First of all, the universe is expanding.

  • And not only that, the rate of its expansion is accelerating.

  • The reason: dark energy.

  • Dark energy is a strange phenomenon that scientists believe permeates the universe.

  • Until 1998 we thought that the universe must work a bit like

  • a ball that you throw into the sky.

  • The ball moves up, but at some point it has to come down again.

  • But the expansion of the universe is actually speeding up.

  • That’s like throwing a ball up and watching it fly away

  • faster and faster and faster.

  • Where is this acceleration coming from?

  • Well, we don’t know, but we call itdark energy”.

  • Einstein thought of it first and then decided it was stupid.

  • Now, astrophysicists have decided it is plausible.

  • Trouble is, this is all very theoretical, and we don’t actually know

  • what the properties of dark energy are.

  • But there are various theories and they lead us to three scenarios

  • for the end of the universe.

  • One: the Big Rip.

  • Since its birth, the universe has been expanding.

  • For unknown reasons new spaces created everywhere equally.

  • The space between galaxies expands, so they move apart.

  • The space inside galaxies also expands, but here, gravity is strong enough

  • to keep them together.

  • In the Big Rip scenario, the expansion accelerates up to a point where

  • space expands so fast that gravity can’t compensate for this effect anymore.

  • The result is a Big Rip.

  • At first, only large structures like galaxies are torn apart,

  • since space between the single objects expands very fast.

  • Next, big bodies like black holes, stars, and planets die.

  • Their gravity isn’t strong enough to keep them together,

  • so they dissolve into their components.

  • In the end, space would expand faster than the speed of light.

  • Atoms would now be affected, and they would just disband.

  • Once space is expanding faster than light, no particle in the universe can interact

  • with any other particle anymore.

  • The universe would dissolve into countless lonely particles that won’t be able to

  • touch anything else in a strange, timeless universe.

  • Hmm, and you thought you felt lonely!

  • Two: Heat death or a Big Freeze.

  • In a nutshell, the difference between the Big Rip and heat death is that

  • in a heat death scenario matter stays intact and is converted

  • over an incredibly long but finite period of time into radiation,

  • while the universe expands forever.

  • But how does this work? Let’s talk about entropy.

  • Every system tends towards the state of highest entropy,

  • like when we have a latte macchiato.

  • Initially, it has different regions, but over time, they will

  • cool down and disintegrate, until it’s uniform.

  • And this also applies to the universe.

  • So, while the universe gets bigger and bigger,

  • matters slowly decays and spreads out.

  • At some point, after lots of generations of stars, all the gas clouds necessary

  • to form stars will be exhausted, so the universe will turn dark.

  • The remaining suns will die;

  • black holes will slowly degenerate and evaporate over trillions of years

  • due to what’s known as Hawking radiation.

  • When this process is complete, only a dilute gas of photons and light particles

  • remains, until even this decays.

  • All activity in the universe ceases at this point;

  • entropy is at its maximum and the universe is dead forever.

  • Unlesstheoretically, it might be possible

  • that after an incredibly long amount of time,

  • there might be a spontaneous entropy decrease as a result of something called

  • quantum tunneling”, leading to a new Big Bang.

  • Three: Big Crunch and Big Bounce.

  • This is the most uplifting scenario.

  • If there is less dark energy than we think or it decreases over time, gravity will be

  • the dominating force in the universe one day.

  • In a few trillion years, the rate of expansion of the universe

  • will slow down and stop.

  • After that, it reverses.

  • Galaxies will race at each other, merging as the universe becomes

  • smaller and smaller.

  • Since a smaller universe also means a hotter universe, temperatures rise

  • everywhere all at once.

  • One hundred thousand years before the Big Crunch, background radiation would be

  • hotter than the surfaces of the most stars, which means that

  • they would be cooked from the outside.

  • Minutes before the Big Crunch happens, atom cores are ripped apart,

  • before supermassive black holes devour everything.

  • Finally, all black holes would emerge into a supermassive mega-black hole

  • that contains the entire mass of the universe,

  • and in the last moment before the Big Crunch

  • it would devour the universe, including itself.

  • The Big Bounce theory states that this has happened a lot of times

  • and that the universe goes through an infinite cycle of

  • expansion and contraction.

  • Well, wouldn’t that be nice?

  • So what will actually happen to the universe in the end?

  • At the moment, heat death seems the most likely, but we at Kurzgesagt hope that

  • thisdead foreverstuff is wrong and the universe will start over and over again.

  • We don't know for sure either way, so let’s just assume

  • the most uplifting theory is true.

  • By the way, we have a Twitter account.

  • Subtitles by the Amara.org community

One day the universe will die.

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B2 UK universe dark energy expands expansion entropy crunch

Three Ways to Destroy the Universe

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    Lypan posted on 2015/06/15
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