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Quantum Mechanics and Thermodynamics Explain Us!

  1. May 12, 2012 #1
    Quick theory for you folks to knock down...

    Laws of Thermodynamics:
    1) Energy is conserved,
    2) As time passes, energy tends to be located in increasingly complex masses.

    Matter and energy are essentially the same thing; as time progresses, the universe consists of less 'pure' energy and more energy in the form of matter.

    Logical conclusions:
    The universe began as pure energy and will end in pure matter ('heat death').

    Add in quantum mechanics:
    1) Energy only has a location when 'observed' (where 'observed' means any contact or association with any other photon).


    Before the universe there was only pure energy in some kind of non-uniform distribution; once photons began 'observing' one-another, they coalesced into matter, instantaneously creating massive coalescence, or 'big bang', and the beginning of time.

    The universe will end when time ends, which will be when all energy is locked into matter.

    Phew! That is the best I can do. Any ideas??
  2. jcsd
  3. May 12, 2012 #2
    RAuld, welcome to PF!
    The first law doesn't apply on cosmological scales - energy is an undefinable quantity in general relativity, there simply is no term for it. Especially in an expanding universe

    The second point there is not true. The second law states that entropy will always increase. Entropy is a measure of the number of ways you can re-arrange the microscopic constituents of an object without altering its macroscopic appearance. So, for example, an ice cube in water has a low entropy. If you started exchanging molecules, you will eventually destroy the ice cube. However, a cool glass of water has a high entropy - you can mix the molecules around, and it will remain the same for quite a while. (until, of course, you start mixing water molecules with the molecules of the glass.)

    Also, note that this applies to closed systems. Your body can break down the constituents of food and organize them. But to do so, you must waste energy in the form of heat, which has a very high entropy.
    Why do you conclude this? Eventually, the universe will experience heat death - it will be dominated by very low energy photons.
    See the reply above. In a heat death scenario, photons will dominate.
    That isn't true. Quantum mechanics says that nothing ever has a defined position. However, particles evolve in accordance with the Schrodinger Equation as 'wavefunctions'. Interacting with a particle's wavefunction forces it to lose its wavelike behavior, and behave (for the most part) classically.
    As of now, it doesn't make sense to speak of 'before the universe'. As far as we know, the big bang was the beginning of time itself.

    There are two things the term 'big bang' refers to. Firstly, there is the initial singularity - this is the point at which the universe was infinitely dense, and physics is, for now, unknowable. Secondly, it refers to the Hot Big Bang - the evolution of the universe from a hot, dense, state, into a cool one. Also, it refers to the primordial nucleosynthesis - the creation of the standard model particles and the elements.

    Next, radiation doesn't 'coalesce' into matter. Matter can be created from radiation via particle pair production. A photon can emit two particles - a particle, and anti-particle. Somehow, the particles gained an advantage over the anti-particles, about one part in a billion.
  4. May 16, 2012 #3
    Mark M - thanks for your thorough introduction! One or two points...

    It seems to me that the laws of thermodynamics must apply on a cosmological scale, otherwise they are not consistent or complete; either they apply or they are incoherent.

    Matter-energy is a standard conclusion from the Laws; heat transfers, potential energy to kinetic, etc. The universe ending with low-energy photons is the same as saying that there is no available energy for use - i.e. 'heat death'.

    Entropy is the correct term for the process of energy being located in more and more complex matter; in the largest open system of all, at cosmological scales, eventually there can be no more relying on larger systems for energy as we do on Earth with the Sun - in other words the universe will end in 'heat death' of no availabe energy.

    Logically, the opposite must be true of the beginning of the universe - i.e. all energy and no matter.

    Also, is there any rationale for saying that it doesn't make any sense to speak of 'before the universe'? The very point I am making is that there must have been something before the big bang. The fact that matter won out over anti-matter is tautologous since we do, in fact, exist!

    Finally, your interpretation of quantum mechanics is simply incorrect; the location of energy-matter at these scales is observer dependent. If nothing ever had a defined location, well, it seems that our material existence disproves that thoroughy!
  5. May 16, 2012 #4


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    Many things are not consistent and incomplete. Many laws and theories only apply in specific situations. This just happens to be one of the situations that the standard view of conservation of energy does not apply.
    Some of the theories on possible futures for the universe take into account effects such as Proton Decay. If this does happen, then over huge amounts of time matter itself will decay into photons and leptons, leaving no "normal" matter, only a sea of very low energy photons and leptons.
    The early universe was so hot and dense that matter and antimatter were constantly being created from interacting photons and then nearly instantly annihilated with each other, creating an endless chain of photons-matter-photons. Both matter and light have been here the whole time. (I dislike using the term energy to refer to electromagnetic radiation, as I believe it implies that energy is something it isn't.)

    I would tend to agree, but then having the universe as existing for an infinite amount of time makes just as much sense. We simply don't know.

    His interpretation is one of the standard ones of QM and is perfectly fine. The fact that the position of a particle is probabilistic explains a great many effects, such as Quantum Tunneling and certain decay processes.
  6. May 16, 2012 #5
    Did you read the FAQ? They have a thread about conservation of energy in cosmology. Energy is not defined on global scales. How could you conserve what is undefined?

    Not as you said. You may believe in a multiverse that existed prior to our universe, or a universe that contracted and bounced, but you can't propose it was just 'filled with energy'. This energy would just drive the expansion of the universe as the big bang model predicts. And it most certainly has nothing to do with photons 'observing' each other.

    That is the Copenhagen Interpretation. Considering it has always been the most widely accepted interpretation, I wouldn't say it is 'simply incorrect'. It's also basic quantum field theory - particles are just excitations of fields- they don't have absolute positions.
  7. May 17, 2012 #6


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    "Finally, your interpretation of quantum mechanics is simply incorrect; the location of energy-matter at these scales is observer dependent. If nothing ever had a defined location, well, it seems that our material existence disproves that thoroughy!"
    I couldn't help but notice you failed to offer any observational evidence supporting this bold assertion, RAuld.
  8. May 17, 2012 #7
    Okay folks, I know when i'm beaten! From the replies here it looks as though i've quite a bit of reading to do to get up to speed. Enjoyed the discussion though, cheers!
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