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  • We know about our universe's past:

  • the Big Bang theory predicts that all matter, time, and space

  • began in an incredibly tiny, compact state about 14 billion years ago.

  • And we know about the present:

  • scientists' observations of the movement of galaxies

  • tell us that the universe is expanding at an accelerated rate.

  • But what about the future?

  • Do we know how our universe is going to end?

  • Cosmologists have three possible answers for this question,

  • called the Big Freeze,

  • the Big Rip and the Big Crunch.

  • To understand these three scenarios,

  • imagine two objects representing galaxies.

  • A short, tight rubber band is holding them together

  • that's the attractive force of gravity.

  • Meanwhile, two hooks are pulling them apart

  • that's the repulsive force expanding the universe.

  • Copy this system over and over again,

  • and you have something approximating the real universe.

  • The outcome of the battle between these two opposing forces

  • determines how the end of the universe will play out.

  • The Big Freeze scenario is what happens if the force pulling the objects apart

  • is just strong enough to stretch the rubber band until it loses its elasticity.

  • The expansion wouldn't be able to accelerate anymore,

  • but the universe would keep getting bigger.

  • Clusters of galaxies would separate.

  • The objects within the galaxies

  • suns, planets, and solar systems

  • would move away from each other,

  • until galaxies dissolved into lonely objects

  • floating separately in the vast space.

  • The light they emit would be redshifted to long wavelengths

  • with very low, faint energies,

  • and the gas emanating from them would be too thin to create new stars.

  • The universe would become darker and colder,

  • approaching a frozen state

  • also known as the Big Chill,

  • or the Heat Death of the Universe.

  • But what if the repulsive force is so strong

  • that it stretches the rubber band past its elastic limit,

  • and actually tears it?

  • If the expansion of the universe continues to accelerate,

  • it will eventually overcome not only the gravitational force

  • tearing apart galaxies and solar systems

  • but also the electromagnetic, weak, and strong nuclear forces

  • which hold atoms and nuclei together.

  • As a result, the matter that makes up stars breaks into tiny pieces.

  • Even atoms and subatomic particles will be destroyed.

  • That's the Big Rip.

  • What about the third scenario,

  • where the rubber band wins out?

  • That corresponds to a possible future

  • in which the force of gravity brings the universe's expansion to a halt

  • and then reverses it.

  • Galaxies would start rushing towards each other,

  • and as they clumped together

  • their gravitational pull would get even stronger.

  • Stars too would hurtle together and collide.

  • Temperatures would rise as space would get tighter and tighter.

  • The size of the universe would plummet

  • until everything compressed into such a small space

  • that even atoms and subatomic particles would have to crunch together.

  • The result would be an incredibly dense, hot, compact universe

  • a lot like the state that preceded the Big Bang.

  • This is the Big Crunch.

  • Could this tiny point of matter explode in another Big Bang?

  • Could the universe expand and contract over and over again,

  • repeating its entire history?

  • The theory describing such a universe is known as the Big Bounce.

  • In fact, there's no way to tell how many bounces could've already happened

  • or how many might happen in the future.

  • Each bounce would wipe away any record of the universe's previous history.

  • Which one of those scenarios will be the real one?

  • The answer depends on the exact shape of the universe,

  • the amount of dark energy it holds,

  • and changes in its expansion rate.

  • As of now, our observations suggest that we're heading for a Big Freeze.

  • But the good news is that we've probably got about 10 to the 100th power years

  • before the chill sets in

  • so don't start stocking up on mittens just yet.

We know about our universe's past:

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B2 US TED-Ed universe rubber band rubber expansion big bang

TED-ED | Three ways the universe could end - Venus Keus

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    11101130 posted on 2019/11/27
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