Layman: In the light of the observations on cosmic ray muons, why don’t we believe that muons could travel at 8×109 meters/sec having observed them travel 16000meters in 2 microseconds?
Scientist: because that exceeds the speed of light
Layman: then what?
Scientist: Special relativity (SR) prohibits speeds faster than light which is 3×108meters/sec.
Layman: on what grounds?
Scientist: From the law of constant speed of light
Layman: What is that?
Scientist: Speed of light is constant to all observers i.e light always travels at velocity ‘c’ i.e. 3×108meters/sec with reference to all observers irrespective of their own motion. A ‘stationary’ observer, a fast moving electron or the cosmic ray muon, all ‘measure’ the same speed of light.
Layman: how weird!
Scientist: Yes, it is weird but proven by many experiments including the muon’s time dilation.
Scientist: So if light travels at speed ‘c’ with reference to the cosmic ray muon, how can the latter travel faster than light? Obviously it can’t. If at all something (e.g. cosmic ray muon) appears to travel faster than light, it is just an illusion. What actually happens there is time dilation and space contraction in muon’s reference frame. Obviously we can’t appreciate this in our reference frame.
Layman: Why should we believe in time dilation which we can’t appreciate, and ignore what we actually appreciate?
Scientist: Because that’s what is exactly predicted by the theory of special relativity.
Layman: Pardon me sir; but muon’s time dilation is a prediction or a proof of special relativity?
Scientist: The problem is you neither understand the mathematics nor the reference frames. Though the muon appears to travel 16000 meters in 2 microseconds, it is impossible according to special relativity and the law of constant speed of light. What actually happens is time dilation and space contraction in muon’s reference frame. So this muon’s time dilation proves special relativity.
Layman: I am feeling dizzy; it appears to me that we are going round and round. That could be my ignorance. May be muon’s time dilation is in fact true and possibly proves special relativity!
Scientist: Of course, numerous experiments have proven special relativity beyond doubt.
Layman: Now I am getting the gist of relativity. Everything in relativity is counterintuitive, isn’t it?
Scientist: Well, you are right but there is a lot more to go through before you can even dream of understanding relativity. Even I didn’t believe in it initially, but having seen the vast support and evidence, I had no choice but to accept it. And over the course of time, as I thoroughly understood the theory and the maths, I got converted and became a believer of relativity.
Layman: So, cosmic ray muons prove time dilation because nothing can travel faster than light. Is there an equally strong proof for the idea of constant speed of light?
Scientist: Well, plenty. Neutral pion decay and Michelson-Morley experiments are among the top. The former proves that the photon’s velocity is unaffected by that of the source. The latter proves many aspects of SR, but as a layman it will be too much for you to grasp.
Layman: I accept my ignorance. May be you can tell me about the pion’s story.
Scientist: You know, the velocity of a stone thrown out of a moving train depends upon the train’s velocity. That is, the velocity of any projectile/ emitted body depends upon the velocity of the source/ emitter.
Layman: Of course!
Scientist: But that’s not the case with light photons. We know velocity of light is ‘c’. Neutral pions are fundamental particles with a high velocity and emit photons as they decay. If the neutral pion’s velocity is ‘x’, we would expect the emitted photons to move at speed ‘c+x’. But the photons were noted to travel at just ‘c’ in an experiment studying the decay of neutral pions. This proved beyond doubt that velocity of light is indeed constant and unaffected by that of the source.
Layman: Well, the speed of an engine (photon) obviously doesn’t depend upon the vehicle (pion) it was driving.
Scientist: What do you mean?
Layman: If the lone speed of a rail engine is 100kmph, this remains the same even when the engine gets detached from the moving train it was driving.
Imagine a horse which runs at 50kmph when free of load. Also imagine that this horse is pulling a cart at 40kmph. If the horse gets ‘released’ from this moving cart, it will only run at its original speed of 50kmph and not at 50+40kmph.
So like SOL, the speed of a horse and the speed of a rail engine are also constant!
Scientist: Neutral pion decay was a real observation which proved that the speed of light is constant. You are equating a real experiment and published evidence with your imaginary and silly experiments on bullock carts and rail engines.
Layman: I am only…
Scientist: You can’t make wild propositions without published evidence from peer reviewed journals and strong mathematics.
Layman: Sorry sir, I didn’t mean to dishonour science. I am just thinking that photons may be behaving just like horses and rail engines for the particles in the quantum world. If so, then we don’t need the weird law of constant speed of light to explain the observations on neutral pion decay!
Scientist: But that’s not what special relativity (SR) predicts.
Layman: I am again feeling giddy. I am not able to appreciate whether something is a logical conclusion, a proof or a prediction.
Scientist: Well, don’t forget that relativity is counterintuitive, so commonsense obviously fails. The problem is you don’t understand the maths. We the scientists are not fools to believe in relativity if this was wrong.
Layman: I realise that we the lay people shouldn’t try to understand Relativity but religiously believe in what the great scientists like you preach. Thank you sir.
(So we must not believe in what we have observed because that is simply prohibited by some weird theory. And we should believe in the weird phenomenon of time dilation, though we haven’t observed – because that is what is proposed by SR. Note the awkward logic here- Special relativity proposes time dilation. Time dilation then proves special relativity!!!