(dramatic music) - If the universe as we know it started with the Big Bang, will it also have an end?

And if it's going to end someday, how?

(computer beeping) (upbeat electronic music) There are four main ideas about the future of our universe: the big rip, (fabric ripping) the big crunch, (objects thumping) the big freeze, (ice clinking) and vacuum decay.

(air whooshing) All of these ideas come from our understanding of how the universe is evolving, and that's where we find the clues for how it could end.

(air whooshing) (upbeat electronic music) So here's what scientists know.

(upbeat electronic music continues) The universe is expanding, (computer beeping) and that expansion is happening faster and faster.

(air whooshing) Scientists think this is caused by a mysterious force called dark energy.

Think of it as the universe's invisible pump, (pump whooshing) stretching space.

(bubbles popping) So what would happen if this mysterious force keeps creating new space?

(mysterious music) Let's start with the big freeze.

(ice rustling) (mysterious music) If the universe keeps accelerating in its expansion thanks to dark energy, everything will get farther and farther apart.

(screen hissing) (bubbles popping) The space between galaxies will increase, stars will eventually die, and the materials needed to form new stars will be too spread out that star formation just can't happen.

(screen hissing) Picture the universe as an endless winter, (wind whooshing) where everything is at its absolute coldest possible temperature, a frozen, lifeless void.

(mysterious music) That's one idea.

(bubbles popping) (alarm sounding) (cash register ringing) The second way is the big rip.

(fabric ripping) Imagine the universe expanding faster and faster, so fast that eventually, it tears everything apart.

(fabric ripping) Dark energy or maybe even a stronger form of dark energy called phantom energy could increase the distance between everything, pulling galaxies, stars, and even atoms apart until nothing's left but shreds.

(bubble popping) All that remains will be fundamental particles floating alone in a destroyed universe.

Pretty tragic.

And then, there's the big crunch.

(light music) This idea says, What if the universe stops expanding and starts shrinking instead?

(objects thumping) Gravity could overpower dark energy, pulling everything back together in a cosmic collapse, kinda like a giant rubber band that stretches as it expands (rubber band squeaking) but eventually (rubber band snapping) snaps back.

(air whooshing) (mysterious music) As the universe collapses, galaxies will collide and merge.

Temperatures will skyrocket, (thermometer beeping) and all matter will be squeezed into an impossibly small volume.

In the final stages, atoms will crush together, pressures will become infinitely intense, and the laws of physics as we know them might break down entirely.

(mysterious music) The big crunch might even give way to a new beginning, possibly leading to another Big Bang.

(star exploding) And finally, there's vacuum decay.

(air whooshing) Now this one's a bit of a wild card.

(screen hissing) Imagine you could find the darkest, coldest, (computer beeping) quietest place in the universe.

No photons zipping around, so there's no light.

No protons or electrons around, so there's no matter.

You're pretty sure that except for you, there's nothing there.

(mysterious music) But wait, that's not true.

Even the emptiness of space contains a certain minium amount of energy, like a background hum.

So steady and faint that even if you could hear it, you wouldn't notice it.

That's called the vacuum energy state.

And it's like the floor that the entire universe stands on.

But what if even that goes away?

Then there'd truly be nothing.

And scientists think that could happen.

Maybe gradually, maybe really, really fast, that one minute the universe will be here and the next, (objects whooshing) it'll be gone.

But how exactly would this even happen?

(mysterious music) A type of energy field called the Higgs field that gives mass to particles in the universe, and scientists think it's possible, but unlikely, that the vacuum energy of the Higgs field could change.

And this very change could produce a bubble of a true vacuum to form and grow at the speed of light, destroying everything in its path and leaving behind a fateful universe with no Higgs field, where atoms can't even hold together.

(mysterious music) So which theory is the most likely?

(drum sounding) Right now, the big freeze is the most supported.

(ice clinking) (brass instruments sounding) And observations suggest the universe will keep expanding, getting colder and darker until it reaches maximum entropy, a chaotic equilibrium where everything is as random and spread out as possible until an ultimate frozen silence.

But don't worry, none of this will happen for at least a few trillion years.

So if you plan (computer beeping) to be around, maybe bring a sweater.

(mysterious music) (logo chiming)