On 4 January 2014 00:10, Bruno Marchal <[email protected]> wrote: > We cannot observed something like time reversibility. We can only inferred > it from a finite number of observations, and then assume a theory which > either assumes it at the start, or explains it from other assumptions, or > perhaps refute it. We can observe facts, not theories. I guess you were > just in the hyperquick mode of talk :) > > Hmm. Weeeeeeeeeeell, there are inferences involved, of course, but I'm not sure what you mean by "not observe". We observe emission and absorption spectra, for example, and we deduce that atoms emit and absorb photons - but we are only inferring from observation. But we are inferring all the time, e.g. we assume the spectra we observe are real and not implanted in our minds by malevolent scientists keeping our brains in vats. At that level, of course, everything is inference, but...
Emission and absorption spectra indicate that the process of an atom absorbing a photon and emitting one are time symmetric processes. Kinetic theory explains the properties of gases by assuming that they engage in time-symmetric collisions (once they reach thermal equilibrium). The equations of Newtonian dynamics are time-symmetric and appear to accord very well with observation (modulo dissipative processes and the existence of an entropy gradient, hypothetically due to boundary conditions on the universe). I agree that from a philosophy of science viewpoint we have to make caveats, but they apply to everything, not just this one feature of physics! -- You received this message because you are subscribed to the Google Groups "Everything List" group. To unsubscribe from this group and stop receiving emails from it, send an email to [email protected]. To post to this group, send email to [email protected]. Visit this group at http://groups.google.com/group/everything-list. For more options, visit https://groups.google.com/groups/opt_out.
