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Heat Death

  1. Mar 15, 2005 #1
    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. :surprised

    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.
  2. jcsd
  3. Mar 15, 2005 #2
    Heat Death is the most likely fate of the universe, atoms would be so spread apart, very spread apart
  4. Mar 15, 2005 #3


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    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.
  5. Mar 15, 2005 #4


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    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.
  6. Mar 15, 2005 #5


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

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

    All converted to heat (lower and lower frequency as this background radiation keeps cooling toward absolute zero).
  7. Mar 15, 2005 #6
    Could absolute zero theoretically be achieved in the universe?
  8. Mar 15, 2005 #7
    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?
  9. Mar 15, 2005 #8
    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? :tongue:
  10. Mar 15, 2005 #9
    If there is Zero-Point-Energy, no. I need to check that up myself.
  11. Mar 15, 2005 #10
    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 :tongue2:.
  12. Mar 15, 2005 #11
    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. :smile:
  13. Mar 15, 2005 #12
    Could we have some expanision on the second idea?
  14. Mar 15, 2005 #13


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    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.
  15. Mar 15, 2005 #14
    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. :wink:
    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.
  16. Mar 15, 2005 #15


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    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.

    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.

    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.
  17. Mar 16, 2005 #16
    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"?
  18. Mar 16, 2005 #17
    So let me see if I understand this correctly; the universe is continually accelerating but the rate it is accelerating at is decelerating?
  19. Mar 16, 2005 #18


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    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.


    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 recieve 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.
  20. Mar 16, 2005 #19


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

    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 :wink:). 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).

    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.
  21. Mar 16, 2005 #20
    Pardon my ignorace, what is the "zeroth order"?
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