# Relativity for people who insist on having a true physical time

1. Sep 12, 2004

### pervect

Staff Emeritus
Relativity for people who insist on having a "true physical time"

OK, here is the promised thread, on how to have both relativity and a "true physical time" and "true physical distance". The basic idea is really quite simple.

Pick a frame of reference. Pick any frame of reference.. Say that that particular frame of reference is the one that keeps "true physical time". Say that the rods in that particular frame of reference have "their true physical length".

Treat lorentz contraction and time dilation as "true physical effects". Use the usual equations for them. Any rod that is not in the "one true physical frame" has it's length contracted by virtue of its motion by a factor of gamma = 1/sqrt(1-(v^2/c^2) (the lengthis divided by gamma). A clock that's moving is slowed down by the factor of gamma as well.

Make sure that all clocks are synchronized in the "true physical frame".

Make sure that if you apply Newton's laws of motion, you only do so in the "true physical frame".

The result will be equivalent to relativity. The biggest drawback is being able to apply Newton's laws only in the one frame. There may be a way to fix this, but it's not clear to me yet what it is.

Of course, the choice of which particular frame is the "true physical frame' is completely arbitrary, as long as one is consistent. The "true physical frame" must of course never accelerate, it must always be a frame in the Newtonian sense.

ps - personaly, I think this approach is a bit of a dead end, though it does have a very few proponents, such as Bell, who insists that this general approach helped him formulate the Bell inequality. But we seem to see a small but significant number of peole who seem to be "stuck" in absolute time, this viewpoint would be one way for them to do special relativity correctly. (I don't think the approach will generalize well to general relativity, however).

2. Sep 12, 2004

### robphy

And just how is this "equivalent to relativity"?
In your reply, it might be helpful if you include the definition of "relativity" you are trying to use, as well as definitions for "true physical time" and "true physical distance". (Operational definitions and mathematical definitions are preferred.)

3. Sep 12, 2004

### Tide

pervect,

Newton's Laws only approximate reality when things aren't moving very fast. That fact will not be changed in any inertial reference frame you wish to choose. For example, if you have two charged particles approaching each other at relativistic speeds you cannot find any inertial frame of reference in which the interaction is Newtonian.

4. Sep 12, 2004

### pervect

Staff Emeritus
Pick a frame, any frame, and declare it to be the "one true frame". That's the definition. (We know that the aether isn't detectable, so the good news is we can define it any way we like -- since it has no physical consequences, it's basically a mental crutch for those who need crutches).

It's equivalent to relativity because we are essentially using the Lorentz transformations, just changing the philosophical baggage around a bit.

i.e.
x' = gamma*(x-vt), t'=gamma*(t-vx)

It doesn't really matter what we call 'real', as long as we can get the right answer.

My particular formulation didn't really address the clock synchronization issue, except by not allowing people to use anything other than one frame. This could probably be improved, it's extremely useful to be able to use more than one frame. Since I personally don't use this formulation (I think it's a bit of a dead end if one wants to progress beyond special relativity), I'd have to think some more about the best way to "wrap it up". I'm not sure of the origin of this formulation, but one of its main proponents was Bell.

5. Sep 12, 2004

### pervect

Staff Emeritus
A couple of good points, as if we can't switch frames, we'll always have to deal with situations where things are moving very fast. So I think we'd have to re-define momentum to be gamma*m*v, instead of m*v.

We don't currently teach people electrodynamics until after they've had basic relativity, so I'm not sure how much of this I would want to explain. We'd basically have the usual effects of electric field lines getting "squished", we'd just describe this as being a "real" squish. We'd still need the magnetic field, and we'd still need the electromagnetic field to carry energy and momentum to "balance the books", but we already need that.

Probably I'd need to be able to provide at least a consistent philosophical interpretation of Maxwell's equations to make the scheme viable. Since I don't actually think about relativity in this way, I'd have to scratch my head for a bit to come up with this, but I'm pretty sure it's possible.

,

6. Sep 12, 2004

### Tide

That was just an example. Replace the charged particles with relativistic billiard balls and you're back to the same problem! :-)

7. Sep 13, 2004

### yogi

Your suggestion is that in order to arrive at the same result as SR we use instead the modified Lorentz Ether Theory (actual physical contraction and actual time dilation). Since this theory uses the same equations as SR, you get the same answers - at least in most cases. This theory still has a following though it be a minority - it does simplify the twin and triplet problem because there is no need to speculate as to the effects of acceleration - time dilation being actual, the moving twin's clock always runs slow relative to the universal ether frame where light is defined as isotropic. The hard part to swallow is just what is themechanism responsible for actual physical contraction - this so bothered the early thinkers that they rapidly gravitated toward SR as a better way to envision the world (to make a pun).