Some time ago I read Einsteins biography and was interested to discover that the more I understood Relativity, the less I agreed with it. At least, the more I disagreed with anything involving time. Everything else seems ok.
In his theory of Special Relativity he refers to the special case of objects travelling through spacetime at a constant velocity relative to each other, in a straight line. He postulates that spacetime is not absolute and the only thing that matters is the relative velocity between the two objects. He seems to have come to this conclusion by assuming that because inertial effects remain the same regardless of the velocity of the object then the same must apply to any light emitted by the object. He uses the thought experiment of a very fast train with mirrors on the floor and roof and a light beam bouncing between them. The inference would be that if one can bounce a ball up and down in a very fast train travelling at a constant speed without any difference to when the train is stationary, then the same must apply to a beam of light doing the same thing. He postulated that if an observer in the train saw the beam going up and down at the speed of light, and an observer outside the train saw the beam doing the same thing in the same time interval, there was a problem because the beam was travelling much further in the same interval due to the forward motion of the train, according to the outside observer. He saw only two possibilities;
1. The light beam travelling faster than light to the outside observer, which is impossible because light cannot travel faster than light, or,
2. Actual time on the train as observed by the outside observer slowing down so that both observers saw the light travelling at 186,000 miles/sec.
I believe that there is another, correct, possibility. Einstein saw the two observers as being in two different inertial frames of reference, which is correct. What he mustnt have taken into account is that, unlike a bouncing ball, light has no inertia. Light is but a disturbance in a medium, called at this point, spacetime. Einstein is correct in saying that the speed of light is constant regardless of the speed of the emitter and receiver relative to each other. This is because the speed of any wave through a medium is dependant of the properties of the medium. For example, sound travels through air at about 720 miles/hour at sea level and about 600 miles/hour at 60,000 feet, depending on ambient temperature, pressure, humidity and the exact proportions of the gasses in the atmosphere at that moment. Regardless whether its a SR71 travelling above mach 1 or a Piper Cub at 80 knots, the sound at the same altitude travels at the same speed. A pulse of light leaving moving object A and travelling to moving object B, travels at 186,000 miles per hour through spacetime, relative to spacetime, from the exact point in spacetime that it left A to the exact point in spacetime that it encounters B.
3. The third possibility, I believe, is that both observers agree that they saw the same thing. This is, that they both saw the light bounce between the roof and the floor while also travelling sideways whatever distance the train managed to go during that period of time. No time dilation. The reason for this is that the train does not carry its own spacetime inside it as it travels, unlike its ability to carry its own atmosphere. Whilst travelling with no relative motion between each other, the mirrors are both travelling through spacetime. In other words the light beam leaves one mirror and travels through spacetime to the next one. By the time the beam gets to where the other mirror was, its not there, having travelled forward through spacetime some distance during the time it took for the light beam to get there.
One can talk to ones fellow travellers in the train quite easy because there is very little relative motion between the travellers and the medium that carries sound, air. If there was a certain amount of air movement in the cabin it would have the effect of making the observers seem closer together, or further away, depending on the direction of the air movement relative to the observers and disregarding wind noise. The mirrors, however, are both independently travelling through spacetime while maintaining the same distance in all axis relative to each other. This suggests that there is absolute space time, at least absolute to this universe. Recent experiments, while not actually proving it, do suggest that this might be so. The Cosmic Background Emission experiment conducted by George Smoot and others in the late 70s showed that we, together with our galaxy, had a real motion of some 600 kilometres/ sec in the direction of Leo through our universe.
If an observer (listener) was travelling at the same speed as an aircraft, some distance away from the aircraft but close enough to hear it, the engine noise would sound the same as it would on the ground with the same power settings etc, in other words with no relative motion between the aircraft and the observer. If, however there was relative motion between the two then there is an effect. This is a change of pitch of the sound heard by the observer. The greater the relative motion the greater the pitch change. If the aircraft is approaching the pitch becomes higher, if retreating then it becomes lower. I am sure that everyone has heard this effect. It is called the Doppler Effect. This effect is also observed to occur with light. With light it is called Red Shift if the emitter and observer are diverging, or Blue Shift if they are converging. If Einstein is correct and time is dilated for an object travelling at very high speeds relative to an observer then all the processes in that object must be slowed, according to that observer. For instance, all light emitted by the object must ALREADY be red shifted regardless of whether the object is travelling towards or away from the observer, due to time dilation. Then the light must be further red shifted if the object is travelling away from, or blue shifted if travelling towards the observer. This may possibly now be tested using the Hubble telescope. If a suitable binary white dwarf system could be found with very high rotational speeds then the difference in red/blue shifts of the two stars would give some indication of the validity of time dilation.
Lets have a look at a version of the much publicised twin paradox. Normally one twin gets on a spacecraft, leaves Earth and departs for some distant part of the Universe at a high speed, approaching that of light. Now, Special Relativity takes the special case of two objects that are travelling at a constant high speed relative to each other in a straight line. There is no acceleration or turning involved. If only Special Relativity was involved then these two objects would never see each other ever again, so different laws must be involved if the twins are ever to see each other again. Fortunately, Einstein developed his theory of General Relativity which takes into account acceleration, positive and negative. Acceleration is deemed to be equivalent to a gravitational field which also dilates time. So, one twin stays on Earth and the other accelerates away on its journey. Upon achieving its cruising speed it maintains constant velocity and heading until it needs to decelerate to reach its destination. Then it picks up its soil samples or whatever, accelerates back towards Earth until reaching cruising speed, decelerates so that it can land on Earth and greet its twin that has presumably aged far faster than he has and is on the pension In my version BOTH twins get to go on an interstellar journey. Twin A does what I just described, but twin B, as per prearrangement does exactly the same thing but in the opposite direction. They both have exactly the same type of ship. They both take off at the same time and accelerate at exactly the same rate to achieve the exact same velocity at the same time, but in opposite directions. They stay at this speed for the same time etc, etc. I am sure you get my drift. They both arrive back on Earth with As stop watch showing the exact same elapsed time as Bs, and vice versa. Which one arrived back on Earth first? According to Einsteins laws there must have been a fair amount of time dilation experienced between them. I suspect that in a practical example in the real world there is no such thing as time dilation as a result of relative speed, or acceleration. I suspect that only an actual gravitational field can produce time dilation.
Einstein developed his theories after the famous Michelson - Morley experiments of the late 19th century. These experiments were designed to show the existence of the Aether, the medium through which light travels. They failed to discover the slightest indications of this Aether, so the presumption is that it doesnt exist. Well, it may not exist exactly as they thought it should back in 1895, but light does travel through something. We call this something, spacetime, today. It is possible, however, that there is something there but the experiment wasnt good enough to find it. The method that they used was to split a beam of light, send one half in the direction of Earths rotation to a mirror and return it to the source where it was combined with the other half which was sent in a direction 90deg to the Earths rotation. One beam should have travelled further than the other which would have resulted in the beams being out of phase when recombined. They were still in phase so, no Aether. However this experiment seems very similar to one used to demonstrate the nonlocal quantum effect, although I believe they change the polarisation of one beam which affects the other. It MAY be possible that there are quantum effects that interfere with the Michelson Morley types of experiments. Regardless, there is no doubt that we have barely scratched the surface of Quantum science.