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Anna Phan | USLHC | USA

View Blog | Read Bio

If I could turn back time…

I’m going to do something different today and discuss a result from another experiment… I saw the result this morning and thought the topic would be an interesting one for a blog post.

So what will I be talking about? Time reversal violation!

You might be wondering why I would consider this an interesting topic, we all experience time reversal violation in our lives, everyday events definitely are not symmetric in time – we can always tell when a video is being played backwards. This isn’t the case in the world of particle physics however, where most interactions are symmetric under time reversal.

So why do we expect time reversal violation in particle interactions? It’s related to the underlying structure of the Standard Model, which relies on interactions being CPT symmetric.

What is CPT you ask? It’s the combination of three other more fundamental symmetries, Charge conjugation, Parity and Time reversal. I’ve described C and P previously and also presented results of CP violation in the B and D meson systems.

Now if we expect the Standard Model to be CPT symmetric and we’ve observed CP violation, it follows that we should also observe T violation.

And this is exactly the result that the BaBar collaboration released this morning, where they report “the first direct observation of T violation in the B meson system.”

I’m not going to go through the details of the analysis, it’s quite clever and complicated, instead here is a set of plots from the paper:

The points are the data, the blue line is the model without T violation and the red line is the model with T violation. As you can see, the model with T violation matches the data much better than the model without.

And voila, here you have it! Observation of T violation in the B meson system…



  • The principle of microscopic reversibility goes macroscopic given entropy and the law of large numbers. They sum to a weak arrow of time for, as you say, running the video backwards is an unlikely but not impossible progression. Feynman’s sprinkler (angular momentum) is a strong arrow of time. Playing that video backwards affords an impossible progression.

    Physics postulates vacuum mirror symmetry. A large fraction of physical theory is symmetry-breaking curve fittings to that empirically defective postulate. T-violation is more curve fitting. Massless boson photons demonstrate the vacuum is parity-even achiral f(x) = f(-x). Fermionic matter (angular momentum) detects a trace, selective, fundamental parity-odd chiral f(x) = -f(-x) additional vacuum background.

    Test it on a bench top. An Eotvos experiment has 5×10^(-14) difference/average sensitivity, suggesting geometric Equivalence Principle (EP) violation is large signal above noise: The EP is blind to everything physics can measure. Physical chirality cannot be measured. (Optical chirality is irrelevant, http://www.mazepath.com/uncleal/norbors.gif , J. Phys. Chem. A 111(48), 12057 (2007); A 110(51), 13995 (2006)). Single crystals of left-handed versus right-handed alpha-quartz violate the Equivalence Principle in trace left-handed vacuum selective toward matter. Trace anisotropic vacuum plus Noether’s theorems allow trace non-conservation of angular momentum, hence MOND’s 1.2×10^(-10) m/s^2 Milgrom acceleration (not dark matter).

    Empirical failures of SUSY, quantum gravitation, matter-antimatter abundance, neutrino-antineutrino reaction channel divergence, dark matter; C,P,T,CP,CT,PT violations are naturally explained. Parity-even, achiral general relativity gives way to parity-odd, chiral ECSK gravitation, its superset. Physics should challenge spacetime geometry with orthogonal atomic mass distribution geometries – not just photons – then stop writing journal hectares of apologia.

  • rezvane

    what is the “At”?

  • Rick

    A dumb question maybe, but why do we expect the SM to be CPT symmetric?
    Thank you very much for this post!

  • Anna Phan

    The A_T are time-dependent time reversal violating asymmetries. I encourage you to look at the paper for their definitions. It’s a little too difficult to write out the formulas here.

  • Anna Phan

    Dear Rick,

    Thanks for the question. I’m sorry, but the answer is a little technical. The SM is a local Lorentz invariant quantum field theory. Local Lorentz invariance implies CPT invariance. Lorentz invariance comes from relativity – that the relevant laws of physics are unaffected by Lorentz transformations (rotations and/or changes in position and velocity). This website explains it much better than I can.


  • Ezequiel Alvarez

    Hi Anna,

    I think that your post should mention some things about the Babar article:

    1) this measurement was explicitly proposed in hep-ph/0611370 in a model independent way, and independent of CPT. (Not mentioned in the paper.)
    2) in fact, the Babar article says that CPT is assumed in the construction of the observable, henceforth one should not expect nothing different as CP violation from that construction.

    Let me stress that there is a subtle, but important contribution in this ideas, since it shows that this same observable is a T-violating observable without any assumption, nor of CPT, nor of the SM, nor of QFT. Just Quantum Mechanics.

    Cheers, Ezequiel.