Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Fate of The Universe

  1. Sep 24, 2007 #1
    When I read thermodynamics in my college coursebook since then I had got a new idea to explain the ultimate fate of universe according to Second Law of Thermodynamics. According to second law of thermodynamics "the entropy(measure of disorder) of a closed system is always increasing and reaches the maximum thenafter a state of equilibrium is reached then entropy of such system doesn't change anymore". So univetse can also be considered as a closed system and self contained like a upside black hole according to Dr. Hawking's work. So the entropy of the universe is increaing now. All the phenomenon that are going in the universe like formation of stars, death of stars, evolution of we like creatures, collisin of galaxies etc. increases the entropy of the universe and finally from billions of years from now a state of equlibirium is reached. In such a condition each point in the space will have same temperature and pressure so that no further evolution occurs. How is my idea. Please someone suggest me how can i prove it mathematically by using the laws of physics?
  2. jcsd
  3. Sep 25, 2007 #2


    User Avatar
    Staff Emeritus
    Science Advisor

    Your conclusion relies on your assumption that the universe is both closed and finite; something which may not necessarily be true.
  4. Sep 25, 2007 #3
    It's very good that you're starting to independently apply ideas you've learnt. But you've yet to discover that almost everything you've been taught has been thoroughly thought through... :wink: This particular one has been around since 1850.

    See: http://en.wikipedia.org/wiki/Heat_death_of_the_universe

    However! Do not be disheartened! Keep trying to be innovative, and learn as much of everything as possible. Sooner or later, you'll manage to think of something that's genuinely new, and then you'll have managed to do real research. :approve:
  5. Sep 28, 2007 #4


    User Avatar
    Science Advisor

    Yes, as genneth said this idea is known as "heat death", but good work on coming up with the idea independently. Also, one thing to notice is that the maximum entropy state for a gravitating system is a little different, if you have a giant box filled with an even, cold, distribution of gas, and then gravity causes most of the gas to pull together into a hotter ball, this actually represents an increase in entropy (basically because gravitational potential energy has been converted to kinetic energy in the form of heat, so there are more states available to the system in the form of different possible ways of distributing the added momentum among all the different particles). So, in the very far future, the increase of entropy may mean that most of the matter of the universe is collapsed into black holes. But then even farther in the future, these black holes could radiate all their mass away as Hawking radiation, so the universe would basically just end up as just very cold and mostly empty distribution of photons and other particles emitted by the Hawking radiation process.

    Here's a good article on what cosmologists currently think about the fate of the universe:

    Last edited: Sep 28, 2007
  6. Sep 28, 2007 #5
    Man then what the creator would do? As you said all the matter will be converted into radiation through Hawking Radiation then there isn't any possbility that again it would convert into matter as mass and energy are interconvertable?
  7. Sep 28, 2007 #6


    User Avatar
    Science Advisor

    Well, according to the "chaotic inflation" theory which we were talking about on another thread, even if this universe went into permanent heat death it might have spawned "baby universes" which inflated up from tiny regions of it and created new Big Bangs, and they in turn might spawn new universes, with the process going on forever so there are always plenty of "young" universes far from heat death. Also, if the universe really lasts forever eventually quantum fluctuations could create large chunks of matter, although it would be extremely improbable and thus extremely rare...as the article I linked to above says:
  8. Oct 2, 2007 #7
    No man the universe must be afterall a finite place. The infinity of the universe means the infinity of density mass and enery in the universe which is not possible. Beside this if the universe is really infinte then we won't be here to observe it beacause in such a infinite universe the collective light from infinite no. of galaxies would have heated the earth and other parts of the universe so much that all the things in the universe would have boiled down. Isn't is?:?
  9. Oct 2, 2007 #8


    User Avatar
    Science Advisor

    But mass and energy could be infinite without the density of mass and energy being infinite--after all, density is mass/volume, so if you have two containers of water, and one has both twice the volume and twice the amount of water as the other, then their densities are equal. General relativity does in fact allow you to model the universe as being infinite extent with a uniform density everywhere, and this is actually the assumption made by 2 out of the possible 3 cosmologies in the Friedmann-Lemaître-Robertson-Walker model of the universe which was the starting point for applying general relativity to an expanding big-bang universe. It turns out that according to general relativity, a finite "closed" universe with positive spatial curvature is actually associated a density that's higher than a certain critical value "Omega", while an infinite flat universe with zero spatial curvature is associated with a density exactly equal to the critical value Omega, and an infinite open universe with negative spatial curvature is associated with a density lower than Omega. Take a look at wikipedia's shape of the universe article or this section of Ned Wright's cosmology tutorial for some more information on this (both pages have illustrations showing 2-dimensional analogues of the three different possible curvatures of our 3D space).
    Have you read about http://en.wikipedia.org/wiki/Olbers'_paradox]Olbers'[/PLAIN] [Broken] paradox? This is pretty much exactly what you're describing, a problem noticed in the 1800s by an astronomer named Wilhelm Olbers...but the paradox only applies if the universe is both infinite in size and infinite in age, if the universe has a finite age as in the Big Bang cosmology, then there's only a finite number of stars whose light will have had time to reach us (if the universe is 14 billion years old, then if it were not expanding the maximum distance a star could be and still have light reach us by today would be 14 billion light-years away, although figuring out the maximum distance is more complicated if you take into account the expansion of space).
    Last edited by a moderator: May 3, 2017
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook