Is the consensus of the fate of the universe still eternal expansion and heat death

[Wesley_Clark]

I’ve heard some recent theories about how higgs particles may enter a lower energy state, causing everything to be destroyed at light speed.

Or how dark energy may slow the expansion.

So is eternal expansion and heat death still the agreed upon fate of the universe as of 2018?

need answer fast. not really.

[Chronos]

The consensus is that it probably will, but with a lot of caveats reflecting our ignorance. The biggest one is that, if the dark energy continues to behave how it does now, then we’ll get eternal expansion and heat death. But we know almost nothing about the dark energy, and nothing at all about what manner of stuff it is or by what mechanisms it works, and so we can’t be confident that it’ll continue to behave how it does now. It might weaken in the future enough to allow for a re-collapse. It might even reverse sign, and force a re-collapse. Or it might actually increase in strength, resulting in a Universe that still expands forever but which never has a chance to go through heat death, because it instead expands so fast that it literally tears apart atoms: This is what’s called a “big rip”.

It’s also possible that what we think of as the vacuum state of the Universe is only a “false vacuum”, that could collapse to a lower energy state (you allude to this, but it’s not specific to the Higgs field). We believe that such false vacuum collapses have happened before. The fact that we’ve gone 13 billion years without such a collapse suggests that either our vacuum is the true one after all, or that we’re in a false vacuum state that’s very stable. But if the latter, if it (somehow) collapses at just one point, that would provide the impetus to collapse the rest, expanding outward at the speed of light. This is what’s called a “thunderbolt” end, because we wouldn’t see it coming, and one possible trigger might be the complete decay of a black hole.

But while these ideas do exist and are taken seriously by cosmologists, nobody really thinks that any of them is more likely than the consensus view of boring perpetual expansion.

[Jasmine]

**This is a good blurb. **

Update by Christopher Springob: Astronomers’ understanding of this problem has changed dramatically since we first answered this question in January 1999. There’s now convincing evidence that the expansion of the universe is actually accelerating, not decelerating. This cannot be due to gravity. It must be due to “dark energy”, a repulsive force of empty space that counteracts gravity on large scales. (You can read more about this here.)

Assuming astronomers’ interpretations of the data are correct, and the universe is indeed accelerating at an ever-faster rate, we still don’t know what the ultimate fate of the universe is going to be because we don’t know if the dark energy will always be repulsive. There are some models that allow for it to become attractive in the future, which would cause the universe to ultimately recontract. But if dark energy is real, then the density of matter will no longer have much impact on the final fate of the universe, because dark energy tends to win out over gravity in the long run.

In other words, right now it appears as if it will expand faster and faster forever, but we aren’t totally sure that it will.