This is actually my field of study! The universe has been on the downswing, star-formation wise, since redshift 2 (10 billion years ago). Plus the SMBHs have more or less stopped growing, so we don't really get quasars anymore. This has nothing to do with the universe dying any more than the end of an ice age means the earth is dying. Just moving into another stage of cosmic evolution.

Since its your area, are you in the mindset that it wills slowly fizzle out eventually, or that it will eventually reach a point where expansion will stop and gravity will cause a "big crunch" into a new singularity, causing the cycle to repeat?

I just remembered one time when I was a kid, I was lying in bed and thought "what if the universe collapses into another black hole, and starts over again?" and I thought I was the only person who had ever come up with that.

Luke & Starfox are correct. 20 years ago, we didn't know the density (and therefore destiny) of the universe. We know know that Omega (the dimensionless density parameter which is just the total density divided by the critical density needed to make the universe flat) is one, so gravity will never win. The universe will expand forever, actually accelerating as it goes (since we now live in the Lambda dominated epoch, and will forever more).

Nah, because gravity falls off per the square of distance -- a massive object can form from a dense cluster of material, but everything outside the cluster is accelerating away fast enough that it never gets drawn in.

Linkigi is correct. Think about just your own daily life. You feel a strong, 9.81m/s^2 pull from the Earth, but only 0.6 cm/s^2 from the sun, even though the sun is a third of a million times more massive than the Earth.

Stuff's too separated for the universe to ever collapse.

We know know that Omega is one, so gravity will never win. The universe will expand forever, actually accelerating as it goes (since we now live in the Lambda dominated epoch, and will forever more).

It's for real 1 now? Last I read about it, it was suspiciously close, but not a sure thing. That's a huge development. Any papers about it?

Linkigi is correct. Think about just your own daily life. You feel a strong, 9.81m/s^2 pull from the Earth, but only 0.6 cm/s^2 from the sun, even though the sun is a third of a million times more massive than the Earth.

Stuff's too separated for the universe to ever collapse.

That's because distance and speed, the forces are in equilibrium (sort of), but not forever. Eventually the Earth will fall into the Sun as it's orbit slows. Unless the sun dies out/ explodes before that time.

Linkigi is correct. Think about just your own daily life. You feel a strong, 9.81m/s^2 pull from the Earth, but only 0.6 cm/s^2 from the sun, even though the sun is a third of a million times more massive than the Earth.

Stuff's too separated for the universe to ever collapse.

That's because distance and speed, the forces are in equilibrium, but not forever. Eventually the Earth will fall into the Sun as it's orbit slows. Unless the sun dies out/ explodes before that time.

The Earth will not fall into the sun, as there are no processes in the solar system currently that can transport angular momentum away from the sun. We likely did lose planets to ejections/stellar cannibalism early in the solar system's history though, when 3-body scattering was common and a thick dust disc was still around. And that 0.6 cm/s^2 force from the sun is just the straight number you get out of Newton's law. We feel none of that small value because of Earth's orbit, but even if Earth wasn't in orbit around the sun, we would still experience orders of magnitude more gravitational acceleration from the Earth, simply by virtue of the distances involved.

Linkigi is correct. Think about just your own daily life. You feel a strong, 9.81m/s^2 pull from the Earth, but only 0.6 cm/s^2 from the sun, even though the sun is a third of a million times more massive than the Earth.

Stuff's too separated for the universe to ever collapse.

That's because distance and speed, the forces are in equilibrium (sort of), but not forever. Eventually the Earth will fall into the Sun as it's orbit slows. Unless the sun dies out/ explodes before that time.

It takes a finite amount of energy to move two objects infinitely far apart. There's no inherent reason why everything needs to eventually collapse.

This is where stuff gets weird. Energy and mass in the universe is finite, however mass can, and does, come into "existence" randomly, and the same goes for energy. Sometimes it's a quick flip-flop between energy and mass, and sometimes it's a Boltzmann brain. At the same time as well, mass and energy have a direct affect on space-time, but it's hard to justify that their relationship is causative, that is that mass and energy create space or that space creates mass and energy. However, it should be noted that we are only capable, according to my knowledge, of observing space if mass and/or energy exist within it in some way.

Space is only finite to the degree that we can't really percieve space we haven't seen/generated yet, so at any point in time there is a finite amount of known space (ie. observable universe), however there is a potential for infinite amounts of it, which I hope answers your question.

As always, please correct me if I'm wrong or feel free to clarify any points I don't explain particularly well.

This is where stuff gets weird. Energy and mass in the universe is finite, however mass can, and does, come into "existence" randomly, and the same goes for energy. Sometimes it's a quick flip-flop between energy and mass, and sometimes it's a Boltzmann brain. At the same time as well, mass and energy have a direct affect on space-time, but it's hard to justify that their relationship is causative, that is that mass and energy create space or that space creates mass and energy. However, it should be noted that we are only capable, according to my knowledge, of observing space if mass and/or energy exist within it in some way.

Space is only finite to the degree that we can't really percieve space we haven't seen/generated yet, so at any point in time there is a finite amount of known space (ie. observable universe), however there is a potential for infinite amounts of it, which I hope answers your question.

As always, please correct me if I'm wrong or feel free to clarify any points I don't explain particularly well.

If we are talking space in a "Einstein's General Relativity" sense, the amount of space you have is only somewhat related to how much mass-energy your universe has, and not in a finite mass/finite space sort of way. Most of the solutions to the Einstein Field Equations are that people are familiar with are actually vacuum solutions, and so contain no matter at all! Some of them have infinite volume (the Milne model), others have finite volume (the anti-De Sitter space). The size & shape of your universe is a function of how much mass, energy, pressure, and curvature it has. Only in the last 20 years have we been able to measure the contents of our universe well enough to determine what its shape is (today, it is best approximated as a De Sitter, or dark-energy dominated, space). We still don't know the source of the cosmological constant, but once we do, assuming we don't introduce new questions, we will know the future evolution of the universe pretty much to a tee.

The biggest let down that the universe won't crunch, is that Marathon was wrong.

At least Halo still has one of the best examples of an artificial-gravity-generating space station with the Halo rings, even if all the space ships have bullshit AG just cuz.

Has anyone ever bothered to illustrate or depict what an ever expanding universe would actually sort of look like as it ages? What would we see as things cool and get pulled further apart?

Would be interesting to simulate a galaxy being torn apart by a "big rip" scenario.

Has anyone ever bothered to illustrate or depict what an ever expanding universe would actually sort of look like as it ages? What would we see as things cool and get pulled further apart?

Would be interesting to simulate a galaxy being torn apart by a "big rip" scenario.

The universe is going to get redder, and dimmer, as it ages. Eventually, we won't see any galaxies, since their will be redshifted out of the visible. It will look as though our galaxy is all there is (which, funnily enough, is what it people thought ~100 years ago)

## Comments

Refresher:

> 1: runaway expansion forever

= 1: expansion slows forever but never stops

< 1: big crunch

Note, < 1 does not necessarily imply the cycle repeats, just that the universe is closed. It may or may not bang again after crunching.

Bang> Cloud> Condensation> Compression > Bang

Eventually something will grow big enough till nothing can escape. Perhaps

Stuff's too separated for the universe to ever collapse.

suspiciouslyclose, but not a sure thing. That's a huge development. Any papers about it?noneof that small value because of Earth's orbit, but even if Earth wasn't in orbit around the sun, we would still experience orders of magnitude more gravitational acceleration from the Earth, simply by virtue of the distances involved.Space is only finite to the degree that we can't really percieve space we haven't seen/generated yet, so at any point in time there is a finite amount of known space (ie. observable universe), however there is a potential for infinite amounts of it, which I hope answers your question.

As always, please correct me if I'm wrong or feel free to clarify any points I don't explain particularly well.

At least Halo still has one of the best examples of an artificial-gravity-generating space station with the Halo rings, even if all the space ships have bullshit AG just cuz.

Has anyone ever bothered to illustrate or depict what an ever expanding universe would actually sort of look like as it ages? What would we see as things cool and get pulled further apart?

Would be interesting to simulate a galaxy being torn apart by a "big rip" scenario.