On Feb 23, 8:42 pm, Brent Meeker <meeke...@dslextreme.com> wrote: >I think > it's an example of the radiation arrow of time making a time-reversed > process impossible - or maybe just vanishingly improbable. Bruce Kellet > has written a paper about these problems, see pp 35. > > http://members.optusnet.com.au/bhkellett/radasymmetry.pdf
I am reading this, and have just come across this passage: "One possibility that is sometimes raised is that the overall expansion of the universe provides the local arrow for the direction of time. While cosmology, particularly the cosmological initial conditions, might be relevant to any final understanding of the arrow of time, particularly the thermodynamic arrow, it is difficult to see the expansion of the universe as being sufficient to explain the local asymmetry of every single independent radiation event. The basic reason is that the expansion of the universe is a cosmological phenomenon; the usual understanding of the Friedmann-Roberston-Walker solution to Einstein’s equations of General Relativity that governs the overall evolution of the universe is that, although the fabric of spacetime expands on the large scale, individual galaxies do not expand, they merely move apart. The expansion actually takes place only on the scale at which the universe can be seen as homogeneous and isotropic. This is the scale of galaxies and galactic clusters—only there is the ‘Friedmann dust’ model applicable. The model that describes the expansion of the universe simply does not apply within galaxies, much less within the solar system or on the surface of the earth. So the universal expansion is simply unable to provide an effective arrow of time that is locally available for every independent radiation event." This seems to me to miss a fundamental point, namely that emission and absorption events are only local if you ignore what happens to the photon beforehand or afterwards. If you trace the trajectory of the photon, you will arrive at some other event, and this event in turn is linked to a previous / future one. Ultimately all chains of trajectories of photons, electrons, quarks and so on connect to either the Big Bang or the distant future (timelike infinity, say). If the trajectories (or, presumably, waves) are constrained by whatever is at either end of their trajectory, as time-symmetry implies, then this stops them being local. They are part of a universe-filling web, which is "anchored" to whatever boundary conditions obtain on the universe as a whole. Charles -- You received this message because you are subscribed to the Google Groups "Everything List" group. To post to this group, send email to everything-l...@googlegroups.com. To unsubscribe from this group, send email to everything-list+unsubscr...@googlegroups.com. For more options, visit this group at http://groups.google.com/group/everything-list?hl=en.