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Consider Einstein's development of SR and his thought experiment on the train to Berlin.

The clock towers at station X and station Y are synchronized in the rest frame of the earth.

Einstein's watch is synchronized with X as he passes heading toward Y.

According to experiment, no matter how fast he travels the light from both clock towers reaches him at light speed. Thus he cannot pass light coming from X no matter how fast he goes so he will never observe it ticking backwards. The minimum time for the trip is in the earth frame is x/c. In this case, the time seen at X from Y is the same as when he passed X.

The difficulty here is not so much a difficulty with special relativity, it is a difficulty with how things are. If experiment is correct, his watch must be slow by x/c since it cannot go backwards when seen from X or Y if light speed is constant and light cannot pass light as experiment reveals. Einstein derived all the equations of SR are derived from this, t-t' = x/c.

While this may seem very strange, but the alternative is also very strange. If Einstein could exceed light speed, he could arrive at station Y and then watch himself arrive. Experiment reveals that nature conspires to keep causes and effects is strict order such that an effect before a cause is never observed and no clock can be directly observed going backwards.

In every case at any speed his watch must be slow by x/c. In the extreme case, at light speed, the travel time will also be x/c, (x/c)-(x/c)=0 such that zero time passed on his watch exhibiting an infinite proper velocity not limited by light speed for the traveler.

But all observers in the earths frame see a travel time of x/c and never anything faster than light. Physics for the traveler seem difference from the fixed observers. SR resolves this difficulty by allowing relative distance to contract along with time. The faster he goes, the shorter the distance, and at light speed the distance is zero such that light speed is not exceeded and the laws of physics remain the same for everyone.

However, this distance contraction is only a relative effect. It is just a mathematical devise. The actual absolute effect is the clock discrepancy of x/c when arriving at Y.

I am not sure you can convince the traveler who goes one light year in one minute on his watch that he did not travel faster than light and the distance for him was different than the distance for everyone else. To believe that he did not travel 60*24*365 times the speed of light, the traveler must swallow SR hook, line and sinker.

There is ZERO ambiguity as to which clock is slow or which clock is moving with respect to any reference frame, but it seems absurd initially.

Consider a second train travelling the same speed and direction as Einstein's train leaving Y at the same time he leaves X.. In this rest frame, the clock tower Y is effectively moving from train 2, to train 1 and therefore Y must be slow by x/c when it arrives at train 1.

Many people stop their analysis here. This is an apparent contradiction, either his watch is slow, or the clock tower is slow, you can't have it both ways. Or can you?

At near light speed the clock tower apparently arrives at Einstein's train immediately, but must have taken x/c time to get there in contracted time and space. But since the clock did not change it must be slow by x/t.

This can be true because each rest frame has its own clock and each clock is slower in the other frame. There is no contradiction, the clock discrepancy is actual from both frames. Relative time is always slower and never faster and time between clocks is independent by x/c.

Experiment confirms that relative clocks are always slower and never faster. Our idea that if one clock is slow, the other must be fast is wrong. Thus the idea that some absolute clock can resolve the issue is also wrong.

The reference frame of the big bang may be an exception. Relativity may not be perfect and the big bang reference frame may be absolute. This may account for some anomalies in the constant speed of light. However, because we are accelerating away from the big bang frame at close to light speed, it's clock is effectively stopped with respect to ours and vise verse. It is thus not very useful when considering trains or space travel.

The fact is that relative space and time is largely how things work. We need only consider a clock moving from A to B and it must be slow if event orderings are preserved.

How this happens cannot be conceptualized without considering general relativity and the "bending", or construction and destruction of space time.

It was Wheeler who said matter tells space how to bend, and space tell matter how to move. This may be true, but I do not believe it is the complete picture.

If we consider space time to be the enforcer of the absolute ordering of causes and effects, then we can think of it as being composed of the information about events (e.g. photons) it orders. This may seem to contradict the postulate of quantum theory that vacuum fluctuations are purely random by imposing a definite ordering of quantum potentials in space but it is not contradicted by measurement. If space is energetic, as Dirac and Wheeler suggest and the propagation speed of light implies, it is not nothing, it is energy. We would expect that when energy is released it becomes space, when it is absorbed it is mass. Free energy is space and trapped energy is matter.

The problem people have with this view is because the energy of the vacuum is cold, 3 degrees Kelvin, microwave and below, how can it have so much energy? Well, it takes more colder photons than it would take hot photons, but if there is no limit to how how many cold photons there may be there is no limit to how much total energy there is. And how could so much energy seem like nothing? It is the zero point because there is no lower temperature where it can flow. But it can be absorbed by matter contracting local spacetime, while expanding future spacetime. The contraction bends local space geodesics towards masses. Masses will absorb a range of low energy frequencies according to their mass. It is as though 32 feet of spacetime ordering information falls into the earth each second by local reception of vacuum energy pushing things down with it, imparting acceleration.

If the universe is electrodynamical, than the only thing that can push back and resist acceleration is the vacuume energy, in that case it is no surprize, as Wheeler put it, the vacuum is only marginally less energy dense than matter. I may be thought of as a cold plasma, the coldest around, the zero point ZPE.

The beauty of spacetime made of energy is that energy always defines both space as wavelengths x=e/c and time inversely to frequency t=x/c together, and we would expect there to be huge amounts of low energy red shifted energy from the big bang. There is no bases to presume space and time exist independently or by any other means than as it is manifest electrodynamically. The model is exceedingly simple and uncontradicted by experiment.

Because space time itself can contract and expand by absorptions and emissions there is no need for the classical notion of repulsion and attraction. Instead there are quantum bi-local up or down spin expansions and contractions without the need for other magic at a distance.

See QuantumRelativity RelativeStateSpace ElectrodynamicalUniverse

This is a very satisfying answer for me personally. I just accept what we know from experiment and it turns out to be enough to explain most everything. The only problem I see is getting rid of our preconceived notions and accepting nature as she reveals herself to us. Looking back, the notion of magical forces at a distance is silly and is not supported by general relativity or quantum mechanical logic. 13:41, 1 January 2007 (EST)

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