What's Causing The Universe To Expand? The Mystery of Dark Energy

We've all heard that the Universe is expanding, but why is it expanding? What's the force pushing everything outwards?

Follow us on Twitter: @universetoday

Team:
Fraser Cain - @fcain
Jason Harmer - @jasoncharmer
Susie Murph - @susiemmurph
Brian Koberlein - @briankoberlein
Kevin Gill - @kevinmgill

Created by:
Fraser Cain and Jason Harmer

Edited by:
Chad Weber

Music:
Left Spine Down - “X-Ray”

If still you don’t know that we live in an expanding Universe, then I’m clearly not doing my job.

And so once more, with feeling... the Universe is expanding.

But that certainly doesn’t answer all the questions that go along with the it.

Like what’s the Universe expanding into? Which we did in another video, which I’ll list at the end of this episode.

You might also want to know why is the Universe expanding? What’s making this happen?

Did it give up its gym membership? Did it sign up for the gallon of ice cream of the month club? Has it completely embraced the blerch?

Edwin Hubble, the astronomer made famous by being named after a space telescope, provided the definitive evidence that the Universe was expanding.

Observing distant galaxies, he observed they were fleeing outwards, in fact he was able to come up with calculations to show just how fast they were moving away from us.

Or to be more precise, he was able to show how fast all the galaxies are moving away from each other.

Which was your question! Just like a minute ago! See you’re just as smart as Hubble!

So up until about 15 years ago, the only answer was momentum.

The idea was that the Universe received all the energy it needed for its expansion in the first few moments after the Big Bang.

Imagine the beginning of the Universe, BOOM, like an explosion from a gun. And all the rest of the expansion is the Universe coasting outwards.

For the longest time, astronomers were trying to figure out what this momentum would mean for the future of the Universe.

Would the mutual gravity of all the objects in the Universe cause it to slow to a halt at some point in the distant future, or maybe even collapse in on itself, leading to a Big Crunch? Or just clump up in piles and stay on the couch all summer because it’s maybe a little lazy and isn’t ready to start going back to the gym yet?

In 1999, astronomers discovered something completely unexpected... dark energy.

As they were doing their observations to figure out exactly how the Universe would coast to a stop, they discovered that it’s actually speeding up.

It’s as if that bullet is actually a rocket and it’s accelerating.

Now it appears that the Universe will not only expand forever, but the speed of its expansion will continue to accelerate faster and faster.

So what’s causing this expansion?

Currently, we believe it’s mostly momentum left over from the Big Bang, and the force of dark energy will be accelerating this expansion.

Forever.

How do you feel about a rapidly accelerating expanding Universe? Tell us in the comments below.

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[memelovergirl]

THANK YOU FOR THIS. IVE HAD IT HARD FINDING SOMEONE WHO COULD EXPLAIN THESE THINGS FOR MY SLOW BRAIN AND I FINALLY FOUND IT!

[SeeroBoarder]

It's amazing how people can still deny the big bang from ever have existing, when there's so much science around us to prove it, and they just blind themselves from it. Thank you, Fraser, so opening some people's eyes with making space science enjoyable, easy, and fun to learn.

[EricCharland]

Hubble, a man made famous after being named after a space telescope. LOL

[curalicentia]

A good question could also be: Is Dark Energy independent or is it "working together" with some other matter(s) to obtain this expansion of the Universe?

[eschelar]

Edward Hubble, the physicist made famous by being named after a space telescope.

I lol'd far more than appropriate.

[primorec]

OH MY GOOD; THANKK I WAS WAITING FOR CHANNELS LIKE THIS <3

[dittoford]

stupid question here, but how do we know that the "space" that's actually expanding?
and not just the galaxies moving away from each other just-because

[TheOneAndOnlySame]

Problem with that explanation is that the galaxies are not traveling through space from each other, it is actually the space in between them that expands...and it does so faster than the speed of light, and still accelerating...

[bryanncampbellca]

Did Fraser just say Hubble was named AFTER a space telescope?

[garetclaborn]

I keep thinking that, along with the initial momentum and symettry breaking, the observable universe would have been more effected by the gravity of now external parts of universe. As everything is spreading out, wouldn't there be a Doppler shift in gravitational waves causing acceleration beyond initial escape velocity?

If that were so, then I've also thought that as each other part of the total universe spread out, the different waves would have to combine from all angles and contribute a nonlinear shift, resulting in localized spin. If you see where I'm going with that, I've wondered if that spin could have been translated into the rotational energy of galaxies rather than needing dark matter. In that case filaments could come naturally from the shifting gravitational interference.

its probably nutty and bad physics but the thought keeps itching my brain

[FourthRoot]

I don't see how the expansion can be attributed to momentum, space itself doesn't have momentum.

[mnpuri]

Hi. As a layman. May I ask a question? The observable universe is expanding. There are forces pushing and causing the expansion. Is there a chance that something very very big is outside the universe, which is attracting everything outwards leading to the expansion? Closer the galaxies are to this huge puller they speed up more. I shall be ever ready to learn.

[jabelltulsa]

I wonder if the big bang was just an intersection point of two extra dimensional planes or spheres that are in motion relative to each other that have a shape which corresponds to the shape/time/speed of the expansion we see.  There could be changes in the rate of expansion because the two objects or extra dimensional universes act like bubbles merging together.

[ytkerfuffles]

I hope we can still look super far away to see the very early universe

[RoyBasty]

If you think of our universe as a soap bubble that expands forever having its interior going cold and black because of entropy but you belive in the multiverse theory, then our universe is a soap bubble that's eventually going to collide with another very old and giant soap bubble. When two big bubbles collide, they are ripped apart and some smaller and young bubbles are created in the process.
But we're taling about soap here.

[tedgetschman]

Not a scientist, but why do we need a reason for the expansion of the universe to be accelerating. If the edge of the universe (edge of space-time) is accelerating away from the big bang center at the speed of light, all matter is trapped in spacetime and will go along for the ride. Thus things farther from us will look to be accelerating because they are. There is also the fact that things further from us should be experiencing time slower than us. As light, however, must travel at the same rate, it means it will be red-shifted. So, just as there is no gravity to bring objects together, it is rather the warpage of space-time, why isn't just the expansion of space-time that is responsible for objects accelerating away from each other?

[sparkymahoney]

The largest problem with explaining physics to laymen are the limitations of language and the choices physicists use. People think an expanding universe means it's expanding into some kind of weird empty space that surrounds it. Whereas what physicists really mean is the space between galaxies is increasing. They should learn to take better care in their explanations. I could never wrap my head around the "expanding universe" until a physicist friend of mine explained it in more precise terms. Needless confusion, as it were. That still does not explain the Big Bang however.

I still think dark matter is jive. It reeks of Deus Ex Machina. and I won't accept it until it can be revealed. Yet, I really can't believe it's expanding - and speeding up - on momentum alone so something is attracting/repelling it. I've read some articles in SciAm that postulate given the physical limitations of our brains we perceive space-time incorrectly anyway. And as we constantly revise our tools we see a lot of theories that were once gospel fall by the wayside too. And lastly, what about the unified field theory? How can we have two mutually exclusive theories - realtivity and quantum - that are both right but negate the other? We're definitely missing a lot of the big picture methinks.

[PoPeration]

If the universe is expanding and getting faster and faster does the matter within the expansion eventually surpass light speed as it did shortly after the Big Bang? ...and if so - what effect does that have on the matter dragging behind in it's wake?

[blitherbox]

Why did the universe ask us this question? Or did we just make it up from nothing?

[byalfredis]

Does it means one day we are going to float alone somewhere in the universe or it does mean we are going to be expanded atom by atom until nothing left from the planets, sun etc. and anything ever existed will be gone forever without any trace?