Don’t look back in space-time

New research was unveiled in the study of time. As reported in ArsTechnica, “Unlike our daily experience, the world of elementary particle physics is mostly symmetrical in time. Run the clock backward on your day and it won’t work; run the clock backward on a process in particle physics and things are just fine. However, to preserve certain fundamental aspects of space-time the Standard Model predicts that certain reversible events nevertheless have different probabilities, depending on which way they go. This time-reversal asymmetry is remarkably hard to observe in practice since it involves measurements of highly unstable particles.

“New results from the BaBar detector at the Stanford Linear Accelerator Center (SLAC) have uncovered this asymmetry in time. Researchers measured transformations of entangled pairs of particles, including the rates at which these transformations occurred. Through analyzing over 10 years of data, they found clear time-reversal asymmetry with an error of only one part in 1043, a clear discovery by any standard. These results are a strong confirmation of predictions of the Standard Model, filling in one of the final missing details of that theory.

“A direct consequence of relativity in particle physics is the presence of three related symmetries, known as CPT: charge, parity, and time. Charge symmetry (C) involves operations wherein particles are swapped with their antiparticles; parity (P) deals with interactions that may depend on which direction in space they take place. Time reversal (T) is perhaps the most subtle of the three: some processes are predicted to occur differently depending on their order in time. While our everyday lives demonstrate that time has a definite direction (we get older and more decrepit, a tragically dropped pizza will not spontaneously reform itself and become edible again, etc.), fundamental processes involving particles are almost all reversible.”


For full story see, “Finding a direction of time in exotic particle transformations” in ArsTechnica.

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