1. Limited time only! Sign up for a free 30min personal tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Why did entropy decrease after the big bang?

  1. Feb 2, 2012 #1
    According to the big bang model, the very early universe was at one time filled with energy. The cosmic microwave background radiation shows that the energy of the universe was very uniform. The deviation of energy in the famous CMB radiation picture taken was on average just 1 in 100,000 the average temperature.

    So why did uniformity decrease as galaxies were formed in the very early universe? Does this contradict the 2nd law of thermodynamics?
  2. jcsd
  3. Feb 2, 2012 #2
    Contrary to popular opinion, uniformly distributed matter is unstable in presence of gravitation and is actually the least likely state with very low entropy. Most probable high-entropy states are those where matter is all lumped together in massive objects, culminating in the creation of black holes.
  4. Feb 2, 2012 #3
    Now that I think about it, gravitation does turn the tables. It would be impossibly improbable for objects such as planets/stars to uniformly distribute back in space again. So yeah, I would agree that entropy of the early universe was very low and has only increased since so the 2nd law of thermodynamics isn't wrong.
  5. Feb 2, 2012 #4
    Consider that all matter and energy in the early universe was closer together than it is now. But at the same time moving away from the center.

    Entropy might have a dependance on the curve of space/time, as the less curve the more entropy. So matter and energy that are not as close together have a lower gravity and thus appear to the observer to be unstable and a low entropy. But the higher density space/time with the matter and energy closer together has a higher entropy. It could be then that distance has a lot to do with it along with gravity and space/time as factors. In higher energy states we find that space/time can separate into space and time.

    Your automotive engine for example is density packed with metals and uses high energy or heat from explosions of gasoline to push pistons and give you the ability to turn the wheels. In this high energy state, we have high energy but we still have Earth's gravity as well as high entropy. Which is why your fuel efficiency goes down so heat is a form of energy that has to do with it.

    Then I'd say that stars generate heat to cause higher entropy and in the early universe there wasn't much heat as stars didn't form yet and provide the heat and higher gravity for higher entropy.

    Just a theory, I could be wrong.
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook