Category: big crunch

Ask Ethan: If The Universe Ends In A Big Crunc…

Ask Ethan: If The Universe Ends In A Big Crunch, Will All Of Space Recollapse?

“When you describe the Big Crunch, you talk about a race between gravity and the expansion of space. It’s not clear to me that if gravity wins that race, whether space stops expanding, or simply that the matter in space stops expanding. I’d love to hear your explanation of this.”

The Universe is expanding, and we can confirm this by looking at the relationship between how redshifted a galaxy’s light is compared with how far away it is from us. But if these galaxies, at some point in the far future, stop being redshifted and start moving closer and closer to us again, does that necessarily mean that the fabric of space is contracting? Is all of space necessarily recollapsing? Or could the galaxies simply be moving towards us, owing to some massive attraction, while the fabric of space doesn’t recollapse at all? Does a Big Crunch necessarily equate to a recollapsing Universe?

Even though we don’t know whether dark energy will reverse itself or not, we do know the answer to this question, and yes, a Big Crunch does mean recollapse! Find out why on this edition of Ask Ethan.

The Five Ways The Universe Might End

The Five Ways The Universe Might End

4.) Dark energy could transition into another form of energy, rejuvenating the Universe. If dark energy doesn’t decay, but instead remains constant or even strengthens, there’s another possibility that arises. This energy, inherent to the fabric of space today, may not remain in that form forever. Instead, it could get converted into matter-and-radiation, similar to what occurred when cosmic inflation ended and the hot Big Bang began.

If dark energy remains constant until that point, it will create a very, very cold and diffuse version of the hot Big Bang, where only neutrinos and photons can self-create. But if dark energy increases in strength, it could lead to an inflation-like state followed by a new, truly hot Big Bang once again. This is the most straightforward way to rejuvenate the Universe, and create a cyclic-like set of parameters, where the Universe gets another chance to behave like ours did.”

Based on the best knowledge and data that we have today, it’s clear that the Universe isn’t just expansion, but the expansion is accelerating. Does this determine the fate of our Universe unambiguously? If we extrapolate what the data indicates about dark energy into the future, we fully expect that structures (like our local group) that are gravitationally bound today will remain so into the future, but that larger-scale structures which are unbound (like our supercluster, Laniakea) will eventually dissociate. But extrapolation is tricky, and assumes that dark energy doesn’t change over time.

If we allow the possibility of change, though, many more possibilities arise. Here are the five most likely, and how we’ll distinguish between them!

Ask Ethan: Can The Universe Still End In A Big Crunch? “You…

Ask Ethan: Can The Universe Still End In A Big Crunch?

“You [wrote] that the Universe is expanding at a decreasing rate. I thought a Nobel Prize was awarded for the “discovery” that the Universe was expanding at an increasing rate. Can you please clarify the leading theories? Is the “Big Crunch” still a possibility?”

Have you heard about the accelerating Universe? What about dark energy, vacuum energy, or a cosmological constant? These are terms we throw around to talk about one of the strangest observations ever made in the Universe: that the more distant a galaxy is from us, the faster it appears to be receding from us. Not only that, but the rate of recession appears to actually increase over time, which is the biggest puzzle of all. But what does this mean for the expansion rate of the Universe? While you might think, as many do, that this means the expansion rate itself is accelerating, that’s not how it works at all. The expansion rate is dropping today, and will continue to drop, eventually asymptoting to a constant value. So how does this cause acceleration, and what does that mean for the fate of the Universe?

Find out on this week’s Ask Ethan, and learn how a Big Crunch and a Big Rip are not only still possibilities, but how we’re going to attempt to find out whether either one might be real!