Back to the future

Time to Reverse Time
This is all sorts of mental gymnastics. I can't quite pin down what's happening with the particles and the significance of their interactions and decay. But I'll be damned if I don't try to get better a better grip on it.
#time   #timetravel   #science   #knowledgefrontiers  

Jonathan Langdale originally shared this post:

Back to the future

I've been trying to come to grips with the idea of time symmetry and time-reversal.  +Sean Carroll writes an interesting post about the recent B meson "arrow of time" experimental result that was announced recently. 

"The reason why it’s an impressive experiment is that it’s very difficult to directly compare the rate of one process to its precise time-reverse. You can measure the lifetime of a muon, for example, as it decays into an electron, a neutrino, and an anti-neutrino. But it’s very difficult (utterly impractical, actually) to shoot a neutrino and an anti-neutrino directly at an electron and measure the probability that it all turns into a muon."

What I'm struggling with is the idea of time reversal as distinguished by

1.  Going forward in time and constructing a muon from by-products coming together in the same way they decay


2.  Going backwards in time from the by-products to a muon. 

There seems to be a fundamental difference between these two ideas.  If you're still going forward in time, is that really a time symmetry? It seems like it would be a different process than actual time-reversal. 

Time-Reversal Violation Is Not the “Arrow of Time” | Cosmic Variance | Discover Magazine

arxiv | Looks like the good folks at the BaBar experiment at SLAC, feeling that my attention has been distracted by the Higgs boson, decided that they might be able to