· 7 min read · Jul 16, 2018
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Physicists have often been amazed at the invariance of the speed of light. This means that regardless of whether the source is moving or the destination is moving or even if both are moving, the speed of light remains constant at 3 x 10^5 km/s approx. What is so unusual about this? It goes absolutely against every practical experience known to mankind! In the normal world things obey what are known as Galilean transformations. Thus take two fast cars 150 Km apart and travelling towards each other; car (a) travelling at 150 kmh and car (b) at 100 kmh. If they both start off at exactly the same time when will they meet? It might surprise you at first to learn that the time at which they will meet is governed by their combined speed or 100 kmh + 150 kmh = 250 kmh. They will therefore meet after 36 minutes during which time car (a) would have covered 90 Km and car (b) would have covered 60 km. The same would apply if the cars were moving away from each other here, the speed of the two cars is again combined but this time they are moving away from each other, thus they are departing from each other at a relative speed of 100 km + 150 kmh = 250 kmh. If both cars are moving in the same direction then the speed of car (a) relative to the speed of car (b) would be the difference in speed 150 kmh — 100 kmh = 50 kmh. These cars are moving according to Galilean transformations.
Imagine then the surprise of scientists when they found that light does not obey these Galilean transformations . Take the following case. Suppose you have a light at a fixed source (A) shining towards a point (B) that is 100,000 Kms. away then we know that since the speed of light is 300,000 km/sec that it should take 0.33 secs for the light to travel from point A to Point B. And this is how long it does take. (note: Actually according to relativity this is by no means certain). Now suppose you fit the light onto a superfast train travelling at 150,000 km/s then the combined speed would be 300,000 km/s + 150,000 km/s = 450,000 km/s and it should now take the light only 0.222 s to reach point B! Wrong! Say the scientists, it would still take the light 0.33 secs to cover the distance from (A) to (B)!
How could this be true? More important how could it be proved to be either true or false? One possible proof is that that of the speed of sound because it is also invariant. Just like light the speed of sound is also independent of the speed of the source or of the destination or even if both were moving together. How could this be ? Look at this problem. First you have a stationary sound at (A) travelling towards a point (B) which is 600 m distant. Consider that sound travels at 1257.12 Kmh therefore it will take approximately 1.72 secs to cover the distance to (B). Now imagine that the sound (Siren or whatever) is fitted onto a car travelling at 150 Kmh , then if they both start off together from point (A) the sound should now take 600/ (150 Kmh + 1257.12 Kmh) = 1.53 sec to cover the distance to B, right? Wrong say the physicists the sound will still take 1.72 sec to travel from point A to point B. The sound (i.e the frequency might change but the velocity of the sound would remain the same)would still take 1.72 sec to reach point B. Therefore it doesn’t matter what at what speed the vehicle is moving with the siren attached to it, sound will travel at a fixed speed. In the present case sound will take 1.72 sec to reach from A to B. If the vehicle on which the siren is fitted is travelling faster than the speed of sound, then the sound will arrive after the vehicle reaches point B. The fact that the speed of sound does not follow Galilean transformations is the only reason that the sound barrier can be broken! How could this be ?
It becomes very simple to understand once it is realised that the speed of the car depends on its mass, the force with which it can press onto the tarmac, the force of gravity etc., While the speed of sound is solely dependent on the properties of the medium it is travelling through. The two velocities have nothing to do with each other. It is like comparing apples and oranges you can’t do it! So the sound will still take 1.72 secs to travel from point (A) to point (B) while the car would still take 14.35 secs to cover the distance form (A) to (B). How fast the car is travelling has absolutely no effect on how fast the sound is travelling the two are independent and arrive at point B independent of each other.
The speed of sound is a property of the medium. Sound is not an object, but a disturbance in a given medium, so it will always travel at the rate the medium prescribes. The only way to change its speed is to change the medium somehow (typically temperature in air). This means that the fact a person is moving or not is immaterial to the speed that the sound travels with providing that the medium remains unchanged. If you are moving relative to the sound the frequency might change but the velocity of the sound will remain the same.
The question here is why if the speed of sound so closely emulates the speed of light isn’t the question of a medium through which light propagates examined more closely or re-examined more closely. Surely the similarities are too great for it to be coincidence? (n.b. As to why the speed of light is the limiting speed of the Universe, that is a different question and will be answered in due course).Think of the highly convoluted ( some would say) illogical reasoning of special relativity. The average distance from the earth to the moon is 384,403 km. the speed of light is 299,784 km/s , therefore it should take a radio transmission exactly 1.28223099 seconds to cover this distance and this is the time that a radio transmission does take. But here is the catch, according to special relativity the two way distance, earth to moon and back again, takes the same time as the one way distance, earth to moon. Therefore according to special relativity we are wrong when we measure the time taken for a radio signal to travel from earth to the moon and back again as being 2.56446 seconds, in actual fact it takes only 1.28223099 seconds but due to time dilation and length contraction we register the time taken as 2.56446 seconds. This has to be true if the speed of light is taken to be constant and this is how the Michelson & Morley experiment was rationalised. Einstein used the constancy of the speed of light to rationalise the results of the Michelson & Morley experiment, while Lorentz used the aether to rationalise the results of the Michelson & Morley experiment. In both cases, time dilation and length contraction were used. If you find it difficult to believe look up Einstein synchronisation and two way distance same as one way distance. Isn’t this highly convoluted, after all in terms of today’s time measurements where it is possible to measure time intervals of 10–15 s. a difference of 1.2822 seconds is huge? On the other hand if a medium such as a universal field or an aether, hitherto undetected, does exist then it would serve as a Universal frame of reference and also account for the speed of light being constant. Travelling in a medium light would not be able to go either any faster or slower than it does.
In Special Relativity light is viewed as a solid that obeys Galilean transformations. This almost certainly wrong and it is strange to think that this faulty understanding underlies most of modern physics today. Michelson & Morley discovered that light always moves at the same speed no matter which way it is moving relative to the earth. In this article I have attempted to explain this seeming anomaly. According to the special theory of relativity, light travels at the speed c in all inertial frames of reference. It implied there wasn’t any special frame called ether through which light travelled at c. In fact, light travelled at c in all frames of references. The result was extraordinary and so were the consequences of it. The only way in which this axiom would hold true is if light were not, in fact, a wave travelling through a medium is if length contracted and time dilated. To understand how grievous are the consequences of this theory imagine a space ship leaving the vicinity of the earth at 0.95c on the way to a planet that is 9.5 light years distant from earth. To the observer watching from earth it would appear that the spaceship takes 10 years to reach the star. To the observer on the star it would take only 3.122 years. This apparently is the correct time. So between the two measurements of time a total of 6.28 years and a distance of 61,500,000,000,000 Km has somehow been lost! Imagine that massive distance and that amount of time vanishing from someone’s account of things. That is relativity and it does not really reflect reality at all. It is no excuse to state that that will never happen since nothing can travel at the speed of light. Every time we watch a sunrise some one watching from another planet is seeing something different, at least according to relativity.
On the other hand, replace this weird concept with a medium and everything falls into place, just as Poincare, Lorentz, Fitzgerald, Maxwell, and other great scientists from the time of Aristotle had visualised. Time once more takes on its measured course and lengths stay constant all over the Universe.
