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[Phys-L] Re: "moving clock runs slower" (yes)



Bob Sciamanda wrote:

"Michael has said much of what I want to say. The problem is purely
semantic - a question of what to call *real*. I too single out the *proper*
length of a "rigid" object and the *proper* period of a clock as useful
invariant properties of certain objects. I have a problem when "proper" is
used as a synonym for "real", rendering other length and period measurements
unreal and only appearances. Is this real/appearance distinction restricted
to only clocks and "rigid" rods?

I would indeed find this language more meaningful if one could give it a
universal definition - ie. if one could define the "proper/real" time and
distance separations between two arbitrary events in space time. This would
give the concepts "proper/real" a universal philosophical meaning rather
than restrict the "reality" concept to events on the world lines of clocks
and "rigid" rods. "


I agree with this 100%, especially with the emphasis on the word "universal" (about definitions) in the second paragraph.
As I had suspected, and said in one of my previous messages, the discussion turns out to be semantic and is zeroing down onto basic definitions of what we mean when we say "mass", "time", or "real", for that matter. If John had said from the very beginning that a moving clock does not tick slower because "we" no longer want to call "time" what we measure to have elapsed in our Lab between its two ticks, only to preserve this term for the rest frame of the clock, then a question about the rate of the clock's tickings in any other RF would just loose its meaning, and there would probably be no discussion (at least I would not go into it). Terminology is a matter of taste. But even when choosing terminology, we must be careful for it not to be misleading or too restrictive. I think the examples my Michael Edmiston illustrate this point very well, and deserve more serious consideration.
The minor axis on the Saturn ring's projection is NOT the diameter of the Saturn's ring (here I agree with John 100%). In contrast, the projection of the proper time of moving clock onto the temporal axis of my Lab IS the time interval between its ticks in my Lab (here John disagrees with me 100%.) But so far the aspect of reality called time is accessible to direct measurement in my lab, with clearly defined experimental procedure, and John has to state clearly that he does not agree with this conventional operational definition of measurement of property called time.
Nobody argues against the importance of the "proper" or "invariant" characteristics of an object or process. But sometimes (and it is rather amusing in view of the way the whole discussion took) these "real" characteristics can only be found from the "less real" non-invariant characteristics. For instance, the rest mass of a newly observed high-energy particle mc^2 = sqrt{E^2 - P^2c^2} can be inferred from the measurements of the particle's energy and momentum in our lab. Even more so for the cases when, as Bob has pointed out, we do not deal with something "solid". For instance, consider just two events in spacetime (say, two separate collisions). We can measure in our lab the time interval and spatial separation between them, but these, being merely the "projections" of something really "real", are not really important characteristics, all the more so that they will be different in another lab moving with respect to our. What is this "really real" about the two events?
The invariant 4-interval? To me
A couple of more examples. Imagine that the Earth became transparent so that John and I (vacationing on the opposite sides of the globe) can see each other. I see John upside down, and he sees me upside down. We record the events, making photographs etc. We can then present our scientific evidence to a higher arbiter. What would the arbiter's verdict be - who is really upside down? Here we do not have a situation when we can appeal to a special RF where corresponding characteristic is a proper characteristic. If only proper is real, but there is no "proper" here, then neither orientation is real in this case? I would rather say that either one is real, but neither is absolute.
I had once read about an exotic hypothesis that the whole universe was created in the collision of only two ultra-high energy particles. A proper rest frame of this system (admittedly coinciding with the one where the current background radiation is isotropic) was the one where their net momentum was zero, and therefore neither of their energies was really energy. However, the net energy of current universe where we live is energy, assuming that we live in its rest frame. Is it that something real has been cooked up from something less real? Are we real?
Let us make this example even more exotic, assuming that the initial particles were just two photons. The rest energy of each is zero; the actual energy and momentum of a photon, being only a geometrical projection of the zero, surely cannot be considered as real energy and momentum (according to proposed new terminology). It follows that even if we still admit the reality of our world, then its "good, new" rest mass consists 100% of "bad, old" relativistic mass, and the same for its energy.
If relativistic energy and mass in E = mc^2 E are not really energy and mass, than what is this relationship about?
Only because "good, new" terminology is being currently used by majority (which statement has not been statistically confirmed), does not necessarily mean that it is better than the "bad, old" terminology so effectively used in time of development of Special Relativity.

Moses Fayngold,
NJIT


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