Arrow of Time II
in [Physics]
|
Prev: folks really believe that oilcos hate cap&trade on fossilized fuels TM?
Next: BP's the Man in Moon, Gulf, Alaska, ARCO etc. -- go with their cap&trade, or nationalize?
From: Robert L. Oldershaw on 23 Jun 2010 23:04 On Jun 21, 4:26 pm, Tom Roberts <tjroberts...(a)sbcglobal.net> wrote: > > If you don't believe me, just try to resolve the issue I brought > up earlier using any of those theories: what is the "cause" of > the fire on this match? ---------------------------------------------------------------- Well, for starters how about: motion, then friction, then heat, then chemical reactions, then fire? Are you saying that going from an unlit match to a flaming match is an ACAUSAL process? What exactly is your point? Can you specify any physical system undergoing any specific physical interaction that violates causality. Please skip the Platonic obfuscation and deal with real systems doing real testable things. RLO www.amherst.edu/~rloldershaw
From: Tom Roberts on 24 Jun 2010 01:06 Robert L. Oldershaw wrote: > On Jun 21, 4:26 pm, Tom Roberts <tjroberts...(a)sbcglobal.net> wrote: >> If you don't believe me, just try to resolve the issue I brought >> up earlier using any of those theories: what is the "cause" of >> the fire on this match? > ---------------------------------------------------------------- > > Well, for starters how about: motion, then friction, then heat, then > chemical reactions, then fire? > Are you saying that going from an unlit match to a flaming match is an > ACAUSAL process? No. > What exactly is your point? That you cannot actually specify the cause of that fire. And therefore, you cannot construct a sensible physical theory based on such "causes". Your usage of "causality" is NAIVE, and no modern physical theory has it, except possibly as an approximation. > Can you specify any physical system undergoing any specific physical > interaction that violates causality. I'm not sure what "violates causality" means. There are certainly many non-causal systems for which we have good physical models. Such as classical electrodynamics, in which charge does not "cause" the field, and the field does not "cause" the charge, and yet charge and field are 100% correlated via Maxwell's equations. Note that classical electrodynamics does indeed have causality in the modern sense -- it is not naive, and is not subjective like your usage: the field at a given point depends only on the charges and field within its past light cone, and is completely independent of everything outside its past light cone. Another aspect is that timelike-separated events have a definite order (independent of frame), while spacelike-separated events do not. Note that this meaning separates things which can affect the fields at a given point from things which cannot. But it makes no attempt to specify what "is" the "cause" of the field(s) at that point. Indeed in GR and classical electrodynamics, the relevant field(s) everywhere within the past lightcone can be said to "cause" the field(s) at that point (but one must be speaking rather loosely). This is not at all what you mean by "causality". So beware of PUNs. The NAIVE causality you espouse arises in these theories when there is only a single object within the past lightcone that has nonzero field(s), so it is the only thing which can affect the field(s) at the point in question, and thus can be said to be the "cause" of those field(s) in the naive sense. Tom Roberts
From: eric gisse on 24 Jun 2010 02:32 Robert L. Oldershaw wrote: [...] Robert, have you actually studied enough {gravitationa, electromagnetic, quantum} field theory to have _seen_ retarded/advanced potentials?
From: BURT on 24 Jun 2010 14:25 On Jun 23, 10:06 pm, Tom Roberts <tjroberts...(a)sbcglobal.net> wrote: > Robert L. Oldershaw wrote: > > On Jun 21, 4:26 pm, Tom Roberts <tjroberts...(a)sbcglobal.net> wrote: > >> If you don't believe me, just try to resolve the issue I brought > >> up earlier using any of those theories: what is the "cause" of > >> the fire on this match? > > ---------------------------------------------------------------- > > > Well, for starters how about: motion, then friction, then heat, then > > chemical reactions, then fire? > > Are you saying that going from an unlit match to a flaming match is an > > ACAUSAL process? > > No. > > > What exactly is your point? > > That you cannot actually specify the cause of that fire. And therefore, you > cannot construct a sensible physical theory based on such "causes". Your usage > of "causality" is NAIVE, and no modern physical theory has it, except possibly > as an approximation. > > > Can you specify any physical system undergoing any specific physical > > interaction that violates causality. > > I'm not sure what "violates causality" means. There are certainly many > non-causal systems for which we have good physical models. Such as classical > electrodynamics, in which charge does not "cause" the field, and the field does > not "cause" the charge, and yet charge and field are 100% correlated via > Maxwell's equations. > > Note that classical electrodynamics does indeed have causality in the modern > sense -- it is not naive, and is not subjective like your usage: the field at a > given point depends only on the charges and field within its past light cone, > and is completely independent of everything outside its past light cone. Another > aspect is that timelike-separated events have a definite order (independent of > frame), while spacelike-separated events do not. > > Note that this meaning separates things which can affect the > fields at a given point from things which cannot. But it makes > no attempt to specify what "is" the "cause" of the field(s) at > that point. Indeed in GR and classical electrodynamics, the > relevant field(s) everywhere within the past lightcone can be > said to "cause" the field(s) at that point (but one must be > speaking rather loosely). > > This is not at all what you mean by "causality". So beware of PUNs. > > The NAIVE causality you espouse arises in these theories when > there is only a single object within the past lightcone that > has nonzero field(s), so it is the only thing which can affect > the field(s) at the point in question, and thus can be said > to be the "cause" of those field(s) in the naive sense. > > Tom Roberts Time is always flowing ahead energy floating in it. MItch Raemsch
From: hanson on 24 Jun 2010 21:40
"Tom Roberts" <tjroberts137(a)sbcglobal.net> wrote: > Robert L. Oldershaw wrote: >> Tom Roberts <tjroberts...(a)sbcglobal.net> wrote: [snip bantering over timely minutia] > hanson wrote: It all boils and gets down to the properties of a definition for time, which is by definition anthropic & hence questionable in the greater and deeper scheme of things. ... So, for human povs and purposes, if you elect to define that = Time is the sequential occurrence or manifestation = of events, items or processes in nature = then all your petty arguments fall away. You can even set restrictive sub-definition that allows time to be what is useful in your experiment... since sequences can go back and/or forwards, (arrow of time), accelerate or dilate, be periodic or aperiodic etc, etc... Why all the big deal about time. Thanks for the laughs, though... ahahahaha...ahahanson |