What Happens to Matter and Energy at the End of the Universe?

[misskitty]

My physics class is currently studying thermodynamics. As I was reading my assignment I came across something very intriguing. Eventually, approximately 100 trillion years from now, the universe will reach thermal equilibrium and maximum entropy. When this happens all physical, chemical, and biological processes will cease to exsist. Work will be impossible. All energy will still exsist, but it will all be unusable energy.

I thought this was pretty amazing. Let me know what you think about the topic. This is some pretty heavy stuff. One thing I would like to know is what will happen to all matter? Things that we use everyday and us...I know we'll all die, but how would it be. What happens to all the energy? The universe is such a vast place to reach thermal equilibrium.

 

[Gold Barz]

Heat Death is the most likely fate of the universe, atoms would be so spread apart, very spread apart

 

[SpaceTiger]

My physics class is currently studying thermodynamics. As I was reading my assignment I came across something very intriguing. Eventually, approximately 100 trillion years from now, the universe will reach thermal equilibrium and maximum entropy. When this happens all physical, chemical, and biological processes will cease to exsist. Work will be impossible. All energy will still exsist, but it will all be unusable energy.

I would be extremely hesitant to extrapolate our current knowledge of cosmology that far into the future. However, given the most popular models and their simplest extrapolation, that is correct.

 

[ohwilleke]

Let's just say, it doesn't keep me up at night worrying. :P Call me parochial, but I'm far more concerned about asteroids striking Earth and the Sun discontinuing its business as usual operations (not that either of those are insomnia pill generators themselves) which are far nearer term, than I am about the heat death of the universe.

 

[Phobos]

When this happens all physical, chemical, and biological processes will cease to exsist.

Biology will likely be gone long before then. Most chemistry too (atoms too far apart).

One thing I would like to know is what will happen to all matter?

Eventually, matter will fall apart (decay into its subatomic particles...maybe further to fundamental particles?).

What happens to all the energy?

All converted to heat (lower and lower frequency as this background radiation keeps cooling toward absolute zero).

 

[misskitty]

Could absolute zero theoretically be achieved in the universe?

 

[misskitty]

How long does anyone think it might take for the biological and chemical processes to fall apart? How would these processes cease? Would the atoms just break down one subatomic particle at a time? What would happen to the neutrons, protons and electrons? Would they break down too?

 

[Lord Flasheart]

I've been reading some of Stephen Baxter's Manifold and Xeelee Sequence stories, and quite a few of them deal with the "upcoming" Heat Death. What a depressing future.

Personally, I've always felt a bit skeptical about the Heat Death. Although the surviving particles are still rather far apart, I'd think that gravity would actually shift them together again. Anyway, it's about time (er, not for a few ten-to-the-umptillion years) that the weakling force found his destiny: The reconstruction/crunch of the Universe!

Now where did my drasted marbles go?

 

[Lord Flasheart]

Could absolute zero theoretically be achieved in the universe?

If there is Zero-Point-Energy, no. I need to check that up myself.

 

[misskitty]

How would the universe reconstruct itself after reaching maximum entropy? When maximum entropy is reached, particles have a high tendency to remain in maximum entropy.

How far apart are we talking when we say far apart?

Check under your bed for the missing marbles .

 

[Andromeda321]

You have to remember at this point that there are a few outcomes for what can happen in the universe based on its acceleration and how much mass there is in it to slow down the acceleration. Right now we can't definitively rule any of these out, although most cosmologists believe that #s 1 and 2 in the following list aren't the likely outcomes.
1. The universe collapses back in on itself. In this case you don't really need to worry about the entropy thing as it'll all end in the Big Crunch anyway.
2. The universe stops expanding and just stays the way it is. If this happens then eventually it will all just get more and more disordered: stars will stop being formed because there's nothing left for fusion and it'll all just be sitting around more or less, decaying into smaller and smaller particles.
3. The universe keeps expanding the way it is now. If this happens then all the matter in the universe will just keep going further and further away from everything else. There's nothing really to stop the distances between masses to be infinite. So you'll have absolute entropy but it's not like anything's going to have the ability to collide with everything else anyway.
4. The universe begins accelerating at a faster pace. Known as "The Big Rip" in cosmology, if the universe increases its expansion acceleration atoms themselves will literally become ripped apart due to the forces involved (as implied by the name). Sort of like number 3 but a heck of a lot more brutal.
I think that's it... if I messed up somewhere someone please point it out.

 

[misskitty]

Could we have some expanision on the second idea?

 

[SpaceTiger]

Could we have some expanision on the second idea?

I suppose it's possible, in theory, but I haven't seen it suggested in respected circles. It would require a delicate balance akin to that present in Einstein's original formulation of the cosmological constant.

 

[Andromeda321]

Sure thing.
Basically right now it's been observed that the universe is expanding with a certain amount of acceleration and in order to reverse this acceleration you would need a sufficient amount of mass in order to slow down and stop the acceleration. If you don't have this mass then the universe just keeps going and going in expansion. In order to slow down the expansion of the universe to a constant you need an exact amount of matter: a little more then that and it'll collapse into the Big Crunch, a little less and it'll just keep expanding. Think Goldielocks only finding one mass value that's just right.
The problem with this is right now we really don't know how much mass there is out there because the baryonic stuff (ie what we're made out of in the form of ordinary atoms and such) make up only 3% of the stuff in the universe. We don't know much about the grand majority of the matter and as a result can't tell what's going to happen just yet.

 

[SpaceTiger]

Basically right now it's been observed that the universe is expanding with a certain amount of acceleration and in order to reverse this acceleration you would need a sufficient amount of mass in order to slow down and stop the acceleration. If you don't have this mass then the universe just keeps going and going in expansion.

Ok, I thought this might be what you were talking about. In actuality, with what we currently know, the acceleration implies that it's already too late and there's not enough matter to slow the expansion. The models you're referring to would require that the universe be decelerating, something we simply assumed until the Type 1a supernova measurements.

However, we don't know anything about the dark energy, so there's no way to say how it will behave in the future. It might continue inducing acceleration or it might change its behavior and begin slowing the expansion. Until we figure out what it is, it's anybody's guess.

In order to slow down the expansion of the universe to a constant you need an exact amount of matter: a little more then that and it'll collapse into the Big Crunch, a little less and it'll just keep expanding.

Even in the old models, that wasn't quite the case. A perfectly balanced universe, as you describe, would still expand forever, it would just do so at an ever-decreasing rate. In mathematical terms, the limit of the scale factor as time goes to infinity would be infinity in both open and perfectly balanced universes.

The problem with this is right now we really don't know how much mass there is out there because the baryonic stuff (ie what we're made out of in the form of ordinary atoms and such) make up only 3% of the stuff in the universe. We don't know much about the grand majority of the matter and as a result can't tell what's going to happen just yet.

If WMAP is to be believed, we do know how much mass is out there and it adds up to about 27% (mostly dark matter). Most of the rest is dark energy.

 

[misskitty]

I don't know much about astronomy, physics is more my forte. What is a Type 1a supernova? What does WMAP and what do you mean by "dark energy"?

 

[misskitty]

So let me see if I understand this correctly; the universe is continually accelerating but the rate it is accelerating at is decelerating?

 

[Janus]

I don't know much about astronomy, physics is more my forte. What is a Type 1a supernova? What does WMAP and what do you mean by "dark energy"?

A type 1A supernova is a type of exploding star. What makes them unique is that they all have a certain absolute luminosity. This makes them perfect as distance yardsticks. If we see one type 1A that is 1/4 as bright as another we know that it is 2 times further away.

WMAP:
http://map.gsfc.nasa.gov/

Dark energy is the hypothesised mechanism that is powering the acceleration of the expansion of the universe.

The supernovae measurements come into the picture like this:

There were generally two models to predict the future of the Universe;

In the First, there was enough matter in the universe for mutual gravitational attraction to eventually slow the expansion to the point that it would reverse and the universe would collaspse.

In the second, there wasn't enough matter, and the universe would continue to expand forever.( though the rate of expansion would decrease with time, it would never drop to zero.)

To try and determine which was correct, an experiment was done. The idea was to meaasure the brightness of type 1A supernovae in distant galaxies, which would give us a distance measurement to these galaxies. These were then compared to the red-shift of those galaxies, which told us how fast they were receding. Since the light we receive from these galaxies are dleyed by the time it takes light to reach us, the further the galaxy, the longer ago the information about it left. This gives us a plot of recession speed vs time. The researchers hope to use this plot to measure the rate at which the universes expansion was slowing.

The surprise was that they found that it wasn't slowing at all, it was increasing. The universe was expanding faster now than it was in the past!

Something had to be powering that increase, and thus the conception of dark energy.

 

[SpaceTiger]

If I may add to Janus' excellent description (my apologies to misskitty for being terse).

A type 1A supernova is a type of exploding star. What makes them unique is that they all have a certain absolute luminosity. This makes them perfect as distance yardsticks. If we see one type 1A that is 1/4 as bright as another we know that it is 2 times further away.

It's worth noting that we don't treat Type 1As as all being the same luminosity, though that was the zeroth order assumption at first. It turned out later that we could determine their actual luminosity even more precisely by considering the shape of their light curve (i.e. the variation of their brightness as a function of time).

As for WMAP, that is one of the greatest experiments of our time (though I'm a bit biased on this issue ). It measured the cosmic microwave background (a radiation field that was predicted by the big bang model) to very high precision and succeeded in pinning down some of the fundamental cosmological parameters (including the total density of matter in the universe).

So let me see if I understand this correctly; the universe is continually accelerating but the rate it is accelerating at is decelerating?

The cosmological constant alone would induce an acceleration and we believe that its influence is still increasing with time, so I guess the rate of acceleration is accelerating. We haven't actually measured this, though. Our techniques are too crude to get such high order moments.

 

[misskitty]

Pardon my ignorace, what is the "zeroth order"?

 

[SpaceTiger]

Pardon my ignorace, what is the "zeroth order"?

I just meant it was the first approximation we made. When that turned out to be inadequate, we had to be more precise, much as when you use a Taylor Series and consider higher-order terms. It's lingo I picked up as an undergrad, but perhaps it's less common than I thought.

 

[misskitty]

How would you even go about measuring something like that? What unit of measure would you use?

 

[SpaceTiger]

How would you even go about measuring something like that? What unit of measure would you use?

Measure what? The luminosity? The light curve? The acceleration?

 

[misskitty]

I would think the acceleration would be measured in meters per second squared because that's the unit you would use to measure acceleration, unless there is a unit used in astronomy that we don't use in physics.

Sure, how would you measure all of that? Where would you even know where to start? What would you do with the data you collected?

 

[SpaceTiger]

I would think the acceleration would be measured in meters per second squared because that's the unit you would use to measure acceleration, unless there is a unit used in astronomy that we don't use in physics.

I rarely see an actual value for the acceleration quoted, it's just how we describe how the universe is behaving. Usually, we express the universe's parameters in terms of fractional densities (e.g. density of matter, dark energy, etc.). The value for the apparent acceleration of an object away from us can be derived from that.

I'll say more tomorrow, when I'm less sleepy.

 

[hellfire]

I would think the acceleration would be measured in meters per second squared because that's the unit you would use to measure acceleration, unless there is a unit used in astronomy that we don't use in physics.

You can measure it in m/s², but you have to specify for which distance this value applies, e.g. m/s² for each km (similar as for the Hubble parameter). According to the currently accepted cosmological parameters (Hubble parameter H = 71 km/s Mpc and deceleration parameter q = - 0.55), this value is around 3 × 10^-33 m / s² for every km. However, usually, when talking about the acceleration of expansion, the deceleration parameter q is used (which is dimensionless).

 

[Chronos]

misskitty, those were excellent answers. I can't add much - aside that ST is sleep deprived and hellfire gave a detailed, and correct answer. I'm sleep deprived too. Anyways, supernova are mainly classified according to their spectral lines. Certain varieties display certain metallicities. The ones most interesting to astronomers are the 'candles' [i.e., having the same intrinsic brightness and spectral profiles.]. Ia supernova are believed to be white dwarfs in binary systems that leech the fuel needed to go Ia. Sometimes they destroy themselves, or their companions, sometimes they repeat the cycle.

 

[misskitty]

How much 'fuel' (I think that's right) does a star need to explode/implode? How dense is an exploding star? Does it gain matter after it explodes and repeats the process?

 

[Andromeda321]

A star doesn't need "fuel" to go nova/supernova in the sense I believe you're thinking of it. In both cases this happens to a star when the star has reached the end of its life which means it has run out of fuel to maintain fusion. It's when it can no longer maintain that fusion to combat gravity that the star collapses.
As for the density of the star when this happens, I can't really remember off the top of my head but I'm sure someone else knows that fact...

 

[Billy T]

A star doesn't need "fuel" to go nova/supernova in the sense I believe you're thinking of it. In both cases this happens to a star when the star has reached the end of its life which means it has run out of fuel to maintain fusion. It's when it can no longer maintain that fusion to combat gravity that the star collapses.
As for the density of the star when this happens, I can't really remember off the top of my head but I'm sure someone else knows that fact...

If not big enough to make a black hole when star has no more fusion cycles possible (core is largely iron which is bottom of the nuclear well - takes energy not releases it if fused) then a neutron star will usually form. As it is collapsing, the potentail energy of the gravitational field is heating it and the barrions and electrons both increase in temperature. The electrons, being lighter, need to have much higher average speed to have same averarage energy (same temperature), but they can't go faster than speed of light. So they disappear by merger with the protons to form neutrons.

The strong nuclear forces are very short range, but they stop the collapse and a neutron star is formed. - normally it is a "pulsar". The intense magnet field at the polar regions (Original stellar field is very much compressed during the collapse) is typically rotating around the axis of rotation and acting like a poweful electric field generator which accelerate charges making a continuous beam of radiation. On Earth, if we happen to be in the part of the heavens this beams sweeps by, then we "see" measure microwave pulses. If you have read this far, you are probbly interested in this sort of thing. Visit site www.DarkVisitor.com where you can learn much more without effort as all the physics is woven into a scary story of a coming cosmic disaster. (You'll learn how to read book for free as well and why it was written - trying to save good jobs from going to Asia etc.)

 

[misskitty]

Thanks for the link.

So the matter that made up the star, after it explodes, becomes so miniscule that it joins with protons to become a neutron? That's kinda confusing because I thought neutrons were neutral atmoic particles by themselves. Not new atoms...unless I misinterperted what you posted. How short is the range of a nuclear force? How does it stop the collapse of the star?

 

[Billy T]

Thanks for the link.

So the matter that made up the star, after it explodes, becomes so miniscule that it joins with protons to become a neutron? That's kinda confusing because I thought neutrons were neutral atmoic particles by themselves. Not new atoms...unless I misinterperted what you posted. How short is the range of a nuclear force? How does it stop the collapse of the star?

(1)It is the electrons that join with the protons to make neutral neutrons.
(2) the strong force is very short range - can't even reach across the larger nucleus of the higher Z elements - that is in fact why elements with z greater than about 100 are not stable. The mutual repulsion between the protons falls off only as the inverse square - reaches all the way out to the orbiting electrons, but the short range strong force can only reach across a few baryon diameters - not even to the other side of a high Z nucleus!

So long as the mutual gravitation is not too great, the short range force is able to prevent complet collapse into a black hole because it is very strong (why they call it the strong force) That is as gravity tries to force the baryones (or just neutrons) into smaller volume, (compress them) each one is "pushing on its neighbor", who in turn piushes on its neighbor etc, just like a bunch of marbles in a box.

 

[misskitty]

Oh ok, I think I got about half of that. Spock, translation please!

 

[Chronos]

For those of you who are disconsolate over the prospect of heat death - there's still hope:
Spontaneous Inflation and the Origin of the Arrow of Time
http://arxiv.org/abs/hep-th/0410270

 

[misskitty]

I'm not worried about it. (Its 100 TRILLION years away...talk about stressing for no reason ) I'm just curious about all this stuff. Pretty interesting! Hey Spock, how bout that translation please.

 

[Billy T]

...Hey Spock, how bout that translation please.

Not sure I am your "spock" but if you did not understand what I was saying in post 32, please ask some specific question(s) - I thought I was relatively straight forward and clear - compared to what I am like often

 

[misskitty]

We are just starting to talk about this stuff in my physics class. We haven't hit relativity yet, but we're getting there within the next week and a half or so.

I'm not sure if it was you Billy, it might be me. The electrons joining with the protons to make a neutral nucleus was ok I think. The elements above z aren't stable thing, you lost me there. The short range thing also comes into that too. Baryon diameters? I don't know what that is. Mutual repulsion of protons was confusing because I'm not sure I know where that fits into everything, especially the inverse square thing. What did you mean by protons "falling off"? Do they literally fall off of an atom that is trying to form?

What did you mean about the prevention of a black hole? There is a force in space that can prevent a black hole? I know very little about this stuff, but I do know that light can not even escape a black hole.

Anyone else who might be able to explain any of this please do! Your input would be an excellent addition to the thread.

Billy your information is great. I'm not saying it isn't. I just don't want this to turn into a thread where you and I are the only people posting. Keep posting.

 

[Janus]

We are just starting to talk about this stuff in my physics class. We haven't hit relativity yet, but we're getting there within the next week and a half or so.

I'm not sure if it was you Billy, it might be me. The electrons joining with the protons to make a neutral nucleus was ok I think. The elements above z aren't stable thing, you lost me there. The short range thing also comes into that too. Baryon diameters? I don't know what that is. Mutual repulsion of protons was confusing because I'm not sure I know where that fits into everything, especially the inverse square thing. What did you mean by protons "falling off"? Do they literally fall off of an atom that is trying to form?

Z = atomic number = number of protons in the nucleus.
Baryon diameters: Essentially the diameters of the Neutron and Proton.

Nuclei are composed of protons and neutrons. The Protons all have a postive charge thus they mutually repel each other. Something has to hold the nucleus together against this tendency to fly apart. Thus the strong force which is acts between the Neutrons and protons. This forms the nuclear "glue" that holds the nucleus together.

Now, the repulsion between the Protons "falls off" (gets weaker) by the inverseof the square of the distance. (two protons that are separated by a given distance will repel each other by 1/4 as much as two protons that are half as far apart from each other.)

The strong force, while stronger than this repulsion at short range, gets weaker a lot faster with distance. As the number of protons increase in a nucleus ( As you move up the periodic table of elements) the nuclei tend to get larger. As they get larger, it becomes harder for the strong force to "reach across" the entire width of the nucleus with enough strength to hold all the protons from flying off. The nuclei tend to become unstable and undergo radioactive decay. (There are also other reasons for radioactive decay of nuclei, such as neutron deficiency or excess in certain isotopes, etc, but that's another discussion)

 

[misskitty]

Ah, ok that makes sense. Thanks Janus.

Stupid questions for 100: Is there anyway to reduce the entropy of a substance that has reached maximum entropy? How do you do it?

 

[Nereid]

Someone else earlier said it - our understanding of cosmology is sufficiently new, and its history shows sufficiently drastic changes, that anything we think now about 100 trillion years in the future is as close to 100% wrong as to not matter!

Perhaps it's fun to look at what our current best theories say ... about the distant future, and whether there are inconsistencies? I have a soft spot for neutrinos - shall the meek inherit the universe?

 

[Billy T]

Z = atomic number = number of protons in the nucleus.
Baryon diameters: Essentially the diameters of the Neutron and Proton.

Nuclei are composed of protons and neutrons. The Protons all have a postive charge thus they mutually repel each other. Something has to hold the nucleus together against this tendency to fly apart. Thus the strong force which is acts between the Neutrons and protons. This forms the nuclear "glue" that holds the nucleus together.

Now, the repulsion between the Protons "falls off" (gets weaker) by the inverseof the square of the distance. (two protons that are separated by a given distance will repel each other by 1/4 as much as two protons that are half as far apart from each other.)

The strong force, while stronger than this repulsion at short range, gets weaker a lot faster with distance. As the number of protons increase in a nucleus ( As you move up the periodic table of elements) the nuclei tend to get larger. As they get larger, it becomes harder for the strong force to "reach across" the entire width of the nucleus with enough strength to hold all the protons from flying off. The nuclei tend to become unstable and undergo radioactive decay. (There are also other reasons for radioactive decay of nuclei, such as neutron deficiency or excess in certain isotopes, etc, but that's another discussion)

Well said. Thanks for saving me the trouble. I have been quite busy at a higher level in the thread "First Stars - how big - Black Holes now?" which has warped into another thread about small black holes evaporating away etc. Perhaps you should have also helped misskitty on her confusion:
"The elements above z aren't stable thing, you lost me there."
but I am not sure if it is about iron being the most stable or fact that few (if any) with z>100 are at all stable. The "iron is the bottom of the stability well" is very important as this is why no stellar fusion is possible even in big stars after they have fused elements with z less than iron. And why the they then implode as the still fusing layers above the core press down on the core.
"

 

[misskitty]

Billy, I understand your dilemma. A friend of mine had been involved in higher courses of study for so long he had begun to do simple steps in his head and word explanations in such a way that would confuse me because I was not well versed in that level of vocabulary yet. Its ok, not big thing.

My class mentioned the Z particle thing a few days ago. It sort of made sense, but not at the same time. It had something to do with the big bang theory and how we can get within 10^-43 seconds of the actual event.

 

[Crosson]

Stupid questions for 100: Is there anyway to reduce the entropy of a substance that has reached maximum entropy? How do you do it?

Sure, you refridgerator reduces the entropy (and with it the temperature) of your food.

It is just that the process of cooling your food makes more entropy than the food decreases by. So the net change is an increase.

 

[misskitty]

Crosson, funny you should mention a refridgerator. My latest physics test had a question asking us (the test takers) to describe how a refridgerator works and what states the refridgerant was in through every step of the process.

The ONE THING I continuously reviewed and thought about...and then moved on to the other equations and material and such...ended up MISSING an imortant step of the process. I wanted to kick myself for that! Probably a good thing I can't. Thank goodness for partial credit.

 

[misskitty]

By the way, if we can reduce the entropy of the refriderant and increase the entropy of the surrounding environment, can we do that to space too? I don't know if my question makes sense...

 

[moving finger]

For those of you who are disconsolate over the prospect of heat death - there's still hope:
Spontaneous Inflation and the Origin of the Arrow of Time
http://arxiv.org/abs/hep-th/0410270

I still have a problem reconciling the 2nd Law of Thermodynamics and the prospect of eternal inflation.

Briefly : The entropy of the universe tends to increase over time. This implies that the entropy at the beginning of the universe (Big Bang) should be much (much!) lower than towards the end. Carroll & Chen in the cited paper estimate that the present-day entropy is some 10^22 lower than it will be when most matter ends up in black holes, and the entropy of the early universe was probably some 10^11 lower than today. And their guesstimate for the entropy of the "proto-inflationary" universe (some 10^6 Planck lengths in size) that is supposed to have existed at the time of inflation is at least some 10^70 lower still. Even if the final state of our universe is one of increasingly rarified radiation and no black holes (which would be the case for a space containing a finite amount of mass-energy which is continually expanding), Carroll & Chen show that this is then actually the state with larger entropy.

If there is some mechanism of 'eternal inflation', what is the origin (cause) of the low entropy starting conditions each time a new universe is created?

Are we simply a statistical fluctuation?

I know Carroll & Chen go into this issue in great depth in their paper - but I haven't been able to fathom the solution to the problem yet - can anyone summarise it?

Thanks!

MF

 

[misskitty]

MF, I don't think we are just a statistical fluctuation.

I'm not sure I completely comprehend what you are getting at though. The second law of thermo makes sense to me. I'm not sure I see where you are having an issue.

 

[selfAdjoint]

Are we simply a statistical fluctuation?

I know Carroll & Chen go into this issue in great depth in their paper - but I haven't been able to fathom the solution to the problem yet - can anyone summarise it?

Thanks!

Look at section four and the beginning of section five of their paper. In section four they review Penrose's argument that in a universe with gravity and zero vacuum energy, the evolution inevitable takes you to isolated black holes. Here there are a lot of diagrams to help you follow the argument.

In section five they show that in the special but plausible deSitter case of general relativity, a slight vacuum energy, caused by a small cosmological constant, is "unstable toward inflation". Fluctuations from average behavior will tend to fall into inflation states. And they show that inflation pumps entropy into the universe, providing that arrow of time they mention. And of course this gives a sort of anthropic reason for that small cosmological constant (which has been measured from the CMB but which is regarded as a problem for theory); we see the c.c. as positive but small because that is what it had to be in order to produce the arrow of time, which in turn was necessary for the physics, chemistry, and evolution which produced us.

 

[DaveC426913]

Could absolute zero theoretically be achieved in the universe?

It's not that the universe will eventually cool to absolute zero, it's that it will reach equilibrium. Cooling can only happen when heat flows from a hotter place to a cooler place. But eventually all atoms will have the same amount of energy and there will be no further transfer.

That is, unless we account for infinite expansion. If we presume universe expands infinitely, then it will continue to cool, merely because there will be fewer atoms in any given volume of space.

 

[1123581321]

right now, we really don't know what will happen. if you are familiar with the Hubble constant/ deceleration parameter are, you will understand what will happen. the huble constant says that the universe is expanding anywhere from 50 km/s to 70 km/s per 3.2 million lightyears. (which means that every 3.2 mill lightyears, the universe is expanding 50 to 70 km/s faster than the last 3.2. the deceleration parameter measures the rate at which cosmic expansion is slowing. as far as i know, we don't know the answer to this, but if we did, we could know what the mass density of the universe is. with all of this we could determine the fate of the universe. to make things simple, all this mumbo-jumbo was condensed into 'omega'. if omega is under 1, then the universe will endlessly expand (because the expansion is too great for deceleration or something like that) and will suffer a heat death. if it is over one, the universe will suffer a big crunch, the big bang in reverse. if one, than the universe will be critical density, and i don't know what that is. I got that almost directly from the book "the big shebang", so if i am wrong, don't yell at me.

Regards,
Fabinacci