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

T-symmetry violation: any leads?

  1. Mar 12, 2009 #1
    For me it is the most mysterious violation, because it is anisotropy of space-time. It does not look so weird for Time, because we intuitively accept an “arrow of time”, but as space is the same as time it is weird.

    In LQG or superstrings, are there any leads which might help to explain that phenomena? In particular, is that asymmetry "per se", or is it a weak “echo” of the Big bang/initial/boundary conditions of our Universe? If so, can it vary in time?
     
  2. jcsd
  3. Mar 12, 2009 #2

    jambaugh

    User Avatar
    Science Advisor
    Gold Member

    What makes you think there is T-symmetry violation?
    Remember symmetry of the dynamics is not the same as symmetry of a given system.

    If you are referring to entropy then look closely at its definition which is itself time asymmetric and not a function of some t-asymmetry of the universe.

    2nd law of thermodynamics: Our knowledge about the state of a system in isolation cannot increase.

    Entropy is a measure of our ignorance about the state of a system. This doesn't make entropy mystical because in physics knowledge only comes from physical measurement. Thus as well the last act of measurement about the system from which this entropy is defined is itself by definition prior to the time at which we are referring to the system.

    Ultimately we are saying that our ability to predict a future state based on measurements made at present must decrease in fidelity as we extend farther into the future due to unknown interactions with the environment. This manifests in the entropy of a prepared system going up over time.

    But if we look at the true time reversed case we find a similar increase in ignorance. The past state of a system becomes increasingly uncertain in terms of what we observe at present as we project farther back in time.

    Thus if we start with a googleplex of jars with salt and water in solution which we allow to be in thermal equilibrium with the environment back into the arbitrary past and find one which has a salt crystal in the shape of Abe Lincoln we can say definitively that as we project back into the past the entropy increases. But this is a trick in selecting a low entropy system for our final system. It is the time reversed case of preparing an initial system with an Abe Lincoln salt crystal in a brine solution and a trick of how we define what we mean by "the system".

    We impose implicit T-symmetry breaking assumptions when we define a physical system in isolation. The system is "arbitrary" at the beginning and thenceforth placed in isolation. If you consider an "arbitrary" final configuration and prior isolation then for the "arbitrary" configuration the past entropy must be greater. But to instantiate the full range of such arbitrary configurations we must play the googleplex game of measuring enough systems to find cases of each "arbitrary" configuration we enumerate. The 2nd law is not violated because we are not invoking the requisite assumptions for the 2nd law to apply.

    Let me also point out that entropy is not additive. The entropy of the whole is not the entropy of the sum of the parts, especially when you invoke quantum theory. So it is not proper to speak of "the entropy of the universe always increasing". You must define a system and in so doing you establish an arrow of time.
     
  4. Mar 12, 2009 #3
    Hm, I was thinking it is a well known fact
    I am not talking about the macroscopic world, but the fundamental T-symmetry violation

    http://en.wikipedia.org/wiki/T-symmetry

     
    Last edited: Mar 12, 2009
  5. Mar 12, 2009 #4
    And Wikipedia proves yet again the utter incompetence of its editors...
     
  6. Mar 12, 2009 #5
    Really?
    So what is wrong? CPT theorem, or there is no CP violation, or Standard Model does not explicitly includes CP/T violation phase parameter = 0.995?
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook




Similar Discussions: T-symmetry violation: any leads?
  1. Z2 symmetry (Replies: 1)

  2. Symmetry Groups (Replies: 4)

Loading...