Category: accelerated expansion

The Universe Is Disappearing, And There’s Nothing We Can Do To Stop It

“Of the estimated two trillion galaxies in our Universe today, only about 3% of them are still reachable from the point of view of the Milky Way. This also means that 97% of the galaxies in our observable Universe are already out of humanity’s reach, owing to the accelerated expansion of the Universe caused by dark energy. Every galaxy beyond our local group, as time goes on, is destined for that same fate.

Unless we develop the capacity for intergalactic travel and head out to other galaxy groups and clusters, humanity will forever be stuck in our local group. As time goes on, our ability to even send or receive signals to what lies beyond in the great cosmic ocean will fade from view. The accelerated expansion of the Universe is relentless, and the gravity we have isn’t strong enough to overcome it. The Universe is disappearing, and there’s nothing we can do to stop it.”

One of the most profound discoveries about the Universe occurred just 20 years ago. Not only was the Universe expanding, with distant galaxies getting farther and farther away as time goes on, but that expansion was accelerating. Take a look at any galaxy that isn’t gravitationally bound to our own, and if you watch it as time goes on, it will appear to move away from us faster and faster. At some point, when it gets to about 15 billion light years away from us, it will appear to recede faster than the speed of light. When it reaches that point, it means that anything that occurs within it won’t be viewable by us, and that if we left immediately, even at the speed of light, we’d never reach it.

Moreover, with every second that goes by, approximately 20,000 new stars cross that threshold into unreachability. The Universe is disappearing, and there’s nothing we can do about it.

Ask Ethan: Could The Energy Loss From Radiating Stars Explain Dark Energy?

“What happens to the gravity produced by the mass that is lost, when it’s converted by nuclear reactions in stars and goes out as light and neutrinos, or when mass accretes into a black hole, or when it’s converted into gravitational waves? […] In other words, are the gravitational waves and EM waves and neutrinos now a source of gravitation that exactly matches the prior mass that was converted, or not?”

For the first time in the history of Ask Ethan, I have a question from a Nobel Prize-winning scientist! John Mather, whose work on the Cosmic Microwave Background co-won him a Nobel Prize with George Smoot, sent me a theory claiming that when matter gets converted into radiation, it can generate an anti-gravitational force that might be responsible for what we presently call dark energy. It’s an interesting idea, but there are some compelling reasons why this shouldn’t work. We know how matter and radiation and dark energy all behave in the Universe, and converting one into another should have very straightforward consequences. When we take a close look at what they did, we can even figure out how the theory’s proponents fooled themselves.

Radiating stars and merging black holes do change how the Universe evolves, but not in a way that can mimic dark energy! Come find out how on this week’s Ask Ethan.

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!