On Monday 02 October 2006 21:25, jimbo wrote: > Brian Beesley wrote: > > [Off topic, but seems to merit a reply] > > > > We are unable to track any events prior to the Big Bang (or the local > > Little Bang, in the colliding brane model). So the time we are able to > > use up to the present is indeed finite. > > Given a ray with a starting point and another point, is the ray finite > or infinite? It's infinitely long.
Yes. But the time that the photon has been travelling from the instant it was emitted until the instant it is detected is strictly finite, whatever your frame of reference, and even if your frame of reference is accelerating, rotating or being distorted in any manner free of actual discontinuities. (Travelling time is always _zero_ if you're actually riding on the photon!) > Same holds for time. Well, if you mean time as a component of an N-dimensional space-time manifold, then what you say is correct. (Special Relativity). However there is a philosophical problem here - how do you define either time or space, except as an abstract manifold, unless there is something measurable in it? > > Didn't that big paper in 1905 redefine time in terms of the speed of > light in a roundabout fashion? Even without baryon interaction > assuming no collapse photons will still travel ... oh, wait, you > said, "... there will come a point when time effectively ..." > Never mind. Yes. If the photons never interact you have no means of determining relative position or recording a history, which means that space-time has effectively come to an end. The problems with Einstein's Special Relativity stem from the fact that it is a description of a content-free universe. It's not wrong, it's just that models based purely on Special Relativity become increasingly inaccurate as density (mass-energy content) increases. If you think of space-time in this way then it becomes clear that a photon (or other particle) has _no_ position except when it is interacting with something. Actually interacting, not just potentially interacting. Experiments like the single-photon variant of the two-slit interferometer set-up (where an interference pattern exists in the apparent absence of anything to cause it) become easy to explain. > > Is there a physical law which demands that time must stop in any > universe? Depends on those initial conditions of total energy and > fundamental constant values, they say. Well ... if there is content (matter+energy, both "real" and "dark", i.e. everything which has a mass) and everything starts from a singularity of some sort, then gravitational collapse is ensured unless the total content is less than a critical value dependent on the boundary conditions. Again space-time is destroyed as the singularity is approached. A steady-state universe avoids the initial singularity and can therefore avoid these problems. Unfortunately no steady-state model so far invented appears to be compatible with observational evidence, as well as theoretical problems caused by violation of e.g. the Second Law of Thermodynamics ... in a steady-state universe, it ought to be possible to construct a perpetual-motion machine powered by continuous spontaneous creation of new space-time, which removes entropy from the universe as a whole, allowing meaningful space-time to continue to persist to infinity. > > So, although time in this universe appears to have a beginning, > we can't conclude that it's finite today. Hitch-hikers' Guide to the Galaxy: "History is an illusion caused by the passage of time, whilst time is an illusion caused by the existence of history". Very deep. Think about it. Regards Brian Beesley _______________________________________________ Prime mailing list [email protected] http://hogranch.com/mailman/listinfo/prime
