expanding universe. will it keep expanding, or "bounce back" the other way?

[cameron marical]

i read an article a while back that stated that the universe doesnt have enough of anything to make it stop exploding and start inploding, including even speculative things like dark matter and stuff too. is this true? if so, is this a good thing? that means that life could exist even when all the galaxies are so strung apart its unmeasurable. it would have to be intelligent and more advanced life than us right now of course, but if they already had a space ship, and found a way to recycle everything, life could make it yet, right?

[npts2020]

At this point in time, most cosmologists believe the universe will expand forever (in human terms) until in something like 10 to the hundredth power years there will be a uniform steady state of immeasurability (or nothingness to some). Of course this view is always subject to change as we get better and different measurements of the universe around us.

[Klaynos]

We don't know, the nature of dark energy is unknown, and until we work that one out it is impossible to say whether it'll keep going forever, slow down and stop, or slow down and bounce back.

[Martin]

i read an article a while back that stated that the universe doesnt have enough of anything to make it stop exploding and start inploding, including even speculative things like dark matter and stuff too. is this true? if so, is this a good thing? that means that life could exist even when all the galaxies are so strung apart its unmeasurable. it would have to be intelligent and more advanced life than us right now of course, but if they already had a space ship, and found a way to recycle everything, life could make it yet, right?

 

I don't understand what you mean by bounce back.

 

When you throw a ball up in the air and it gradually slows down and reaches its max and starts falling back, that's not what is usually called a bounce.

 

In the current model called LCDM (Lambda-cold-dark-matter) expansion doesn't ever finish and give way to re-collapse. So it's worth considering the fate of life in the circumstances you imagine.

 

That doesn't mean we know for certain that LCDM is right or that expansion will never end, but it's a reasonable possibility.

 

If LCDM is right, then dark energy will stay the same density it is today, namely 0.6 nanojoule per cubic meter. And acceleration will not compromise basic structures like our local group of galaxies. Milky and

Andromeda will eventually merge, together with some of the other local group. So we will be in one big galaxy. Other more distant galaxies will drift off beyond our horizon.

 

Stars will eventually burn out and people will have to learn to convert matter into energy or extract gravitational potential energy efficiently by lowering stuff into black holes, or something. They'll have to figure out some way to get the energy they need. And it will probably consume matter or gravitational potential. I'm not well enough informed to be able to speculate about how life will cope.

 

I suspect nature will remain beautiful for a long long time.

[cameron marical]

why cant we just recycle every form of energy we produce?

[Klaynos]

why cant we just recycle every form of energy we produce?

 

The universe is BIG there's nothing we can do to change anything about it on a large scale....

[Airbrush]

Nice explanation Martin.

 

I would add that currently cosmologists believe in an open universe, and the expansion will only accelerate due to dark energy and never bounce-back whatever "bounce-back" means. The next Dark Age will begin after the red dwarf stars slowly burn out over the next Trillions of years. Then there will be only cold dead stars and black holes. The last supermassive black holes will evaporate over Googles of years.

 

Unless something interesting happens during those vast time spans, like another Big Bang or something.

[Martin]

Nice explanation Martin...

 

Thanks!

 

I would add that currently cosmologists believe in an open universe,

 

I agree pretty much entirely with the concrete detail you mention, but please tell me what you mean by "open universe".

 

Since 1998 there has been a lot of confusion and misunderstanding about the terms "open" and "closed" applied to universe models.

 

Back when I learned cosmology, which was before 1998, it was clear what the terms meant.

A closed universe had finite spatial volume. (And because noone dreamed there might be dark energy, it was a side consequence that she would eventually collapse. But that wasn't the root meaning. The root idea of closed was that space closed around on itself and was finite volume, but no boundaries, like a sphere.)

 

An open universe had infinite spatial volume. And incidentally a mathematical consequence was endless expansion (given what we assumed before 1998.)

 

====================

 

Now you say the universe is not "closed". But we don't actually know that. The authoritative WMAP report that came out 2008 with the best data so far allows for the universe to be closed---that is finite spatial volume. And it also allows for it to be open---infinite spatial volume.

 

In the closed case, the data implies that it will expand forever.

 

WMAP does not treat the case of an open universe that collapses, but it is physically possible that a universe might be open (spatial infinite) and yet destined to eventually collapse. Depends on the character of the dark energy.

 

So it can lead to confusion when you use these terms, which were perfectly fine before 1998 and which unfortunately are still used some in pop science journalism and at some outreach websites.

 

I'm curious what you mean by "open".

[Airbrush]

By "open universe" I had always supposed that it meant the universe would never stop expanding and eventually become either a Big Rip or it would expand to a point and stop, but never contract. "Closed universe" meant that gravity would win out in the end and expansion would slow down, stop, and begin contracting into a Big Crunch.

 

Other terms used were bounded or unbounded, finite or infinite, and flat or curved. I am confused about how all these qualities interact. What's your best guess?

[Martin]

"Closed universe" meant that gravity would win out in the end and expansion would slow down, stop, and begin contracting into a Big Crunch.

...

 

Well now the data suggests that we may be in a spatially finite universe that will expand forever.

 

What do you want to call that case, "closed" or "open"?

 

Either way you are going to confuse and possibly mislead some of your audience.

 

The last time this came up at another forum I take part in, folks settled down to the usage that closed meant spatially closed.

 

So you could have a universe that is expected to expand forever and if a certain parameter which can be measured these days to within a few percent uncertainty, namely Omega_k turns out to be less than zero then you have spatial closure----basically space like a 2D sphere surface except its 3D. So that would be a closed universe destined to expand endlessly. As the term is used on that forum.

 

At that point we had a Princeton astrophysics grad student helping us get our terminology straight.

 

Maybe the thing to do is never use a term like "closed" by itself.

Always say things like "spatially closed" and "eternally expanding".

Use enough words to be clear.

 

I'd like to know your opinion.

[Airbrush]

I will try to be more precise in my use of terminology. I dabble only very casually in cosmology. It all started when I saw Carl Sagan's "Cosmos" series long ago. More recently the History Channel's "The Universe".

[cameron marical]

ya. those two shows really helped me get into science. more of the universe than the cosmos though. michio kaku rocks.

 

i posted this on another forum so this is a little of course, but this question has been buging me ever since i came up with it.

 

say we put solar panels all throughout space surrounding our planet, and also put lightbulbs in the atmosphere {for artificial sunlight of course}, could we literally recylce everything that happens on our planet energy-wise? would we still eventually run out of energy somehow?

 

this is future tense, im just pondering ideas that might help out us later on...

---

Merged post follows:

Consecutive posts merged

if anyone answers it, thanks. if not, its cool.

[Airbrush]

Not to get off topic of universe expansion and "bounce back"!

 

But why put lightbulbs in the atmosphere? Solar panels could collect all the energy humans could need, positioned right here on Earth, IF there were not too many people on Earth, and IF there were enough solar panels. That power source will last as long as the Sun does, Billions more years, and it is totally benign environmentally, except for the process of their manufacture?

 

Anyhow, it is fun to wonder what the universe will do over astronomical time scales and hear educated guesses.

[cameron marical]

i agree. i do it alot im my... well, in my every minute of the day and sometimes at night time.

 

i think that the universe is still going to contract, just as a little trick to get all the energy back in one place to spread it out again, renew the stars, etc...

maybe mankind, and all existing lifekind advanced enough to do it, could burn holes in spacetime{im not trying to pass this off as my idea, i know, i heard it off the universe}, and get to alternate states of reality, or maybe the space between spaces as is suggested there is in the membrane theory, and live off total recyclemt. just a biodynamic, floating in space, and harboring advanced and intelligent life, ecosystem.

 

i know, im very imaginative. but in the words of einstein, imagination is more important than knowlege. id like to kind of meet that halfway.