Apply u r physics knowledge...

Hello "Guest".

No puzzle at all.

With these type of so-called puzzle questions it is always best to go back to first principles, reason it out, and forget the complicated equations.

Nothing we know of in this physical Universe is able to travel faster than the speed of light, relative to any observer.

If something does actually travel faster than the speed of light, relative to any observer, the observer cannot actually perceive it by any means, and to that observer therefore, the object can not actually exist.

So in the case of the two torches, the photons of light project out from each torch at the speed of light, but to a observer standing by, one torch goes minutely faster than the other.

So....part of the photon stream from that torch will exceed the speed of light, and not exist any more for that observer.

So...simple deductive reasoning shows that the running man's torch light beam will reach the wall first.

However, because the increase in speed from the man's running, compared with the speed of light, is so extremely small, I would think that there is no present set of instruments which could actually measure the difference in time between the two torch beams arrival at the wall.

Kind Regards....

Wrong.

The speed of light is constant. So if the two beams start at the same distance from the wall and the same time they will reach the wall at the same time. The beam from the moving totch will be blue shifted due to the doppler effect.

Peter.

Hello plbplb

Evidently you have not read about the speed of light being slowed down by both temperature and the medium in which the light is travelling.

The convention that the "Speed of light is constant" only applies in theory, not in practice.

The convention was assumed, so that other theories could be "parked on some definite figure", which at the time, did not appear to change.

The speed of light in a vacuum being a large amount, it was convenient to use that large number as the base for further theories and calculations.

It is a common misunderstanding that the "Speed of Light is constant".

Albert Einstein knew this well, when he formed his "Theory of Relativity", but used the large number for convenience, as stated earlier.

Kind Regards....

Sparky, the speed of light is constant, though it does vary slightly, in a medium or in the presence of a massive gravitational field. As I said in my previous post, if this were ever found to be untrue, General Relativity would come crashing down. Trust me, this is bedrock.

Evidently you have not read about the speed of light being slowed down by both temperature and the medium in which the light is travelling.

The apparent slowdown of light in various media is due to photons colliding with atoms and getting consequently retransmitted. Between collisions, the photons travel at the speed of light.

Excellent point! That's one of the difficulties in discussing the speed of light: Are we talking speed of the photon or propagation velocity of the wave?

The speed of light is relativistic - Not constant. That is the premise of relativity. The absolute speed is relative to the speed of the observer.

Now, it is possible to postulate that the speed of light is in fact constant. However, that is not what Einstein did postulate. His theory that curvature of space time caused the mass attraction effects we know as gravitation post dated his work light speed. Because all the experiments showing very slow speeds of light involve extremely dense media like Einstein-Bose condensates it is very tempting to hypothesize that the speed of light is constant and that the "density" of materials influences the amount of "space-time" for a give volume of material. However, you will have to extensively rework general relativity and most of the rest of physics in order to quantify this intriguing possibility.

I wish you the best in this undertaking. Einstein spent much of the last half of his life trying to crack this nut and I have given it a go myself. Neither one of us has any tangible results to publish and the odds are pretty good you won't either. If anyone young and brilliant wants to give it a go, let me know, I will be happy to pass on my thoughts and offer to review anyone's progress.

Best wishes,

Mr. Gee

You are correct of course. What General Relativity says is in fact that "c" is constant for all observers, regardless of their frame of reference relative to any other frame. At it's most basic, that there is no privileged frame of reference. As to an absolute value for "c", I can think of no way to measure it, since we run up against the relativistic issue of the observer, who will undoubtedly measure it the same as any other observer. Hmmmm... What a thorny problem.

About the only way I could think of to actually measure the thing would require reliable superluminal communications. Not to mention the fact that the yardsticks themselves are now defined in terms of "c". Without some privileged frame of reference to gauge it against... Pity space-time is such a slippery thing. Makes one wish for the luminiferous aether.

I admit I am intrigued. I would love to hear your thoughts on the subject.

We can always go back to the same simple reasoning that Einstein used.

Imagine that half way between the two men and the wall, there is an observer who is stationary with respect to the wall. There is a curtain so arranged that this observer can see the light beams and the wall, but not the two men.

IF this observer were to detect any difference in the speed of the light beams, this would mean that he could tell which man had absolute motion. This would be a violation of relativity and cannot occur.

Therefore, the beams must reach the wall at the same time.

but, he can detect a difference in the wavelength, with the violet shift giving him a metric

"There are two men with torch in hand one is standing 100m ahead with same direction and in front of both there is wall."

In this situation itself, lights from both the persons' torches should have reached the wall, right?

Of course the torch nearer to wall should have reached first than the one at farther, however small the time difference be...

He cannot. The man with the torch is running toward the wall, perpendicular to the observer (Well, I didn't say that explicitly, did I ?).

The man standing far from the wall (2^nd man) have a constant speed at the same moment of meeting with the man standing 100 m ahead (1^st man) who starts his speed from zero value. So the resultant speed of light of 2^nd man (speed of man + speed of light) shall be greater than resultant speed of light of 1^st man (0 + speed of light).

How can the speed of light (from the 2^nd torch) be equal to the speed man + speed of light?! This is absurd. Speed of light is equal to the speed of light, and it is constant and irrespective of the frame of reference. (Maybe this also sounds absurd, but at least, it is experimentally verified!)

I liked especially TVP45's answer so far. He gives a nice simple example of what relativity is all about.

Sorry, can anyone repeat this question in proper English?

Two men are facing a wall with one man 100 m ahead of the other. Each holds a flashlight. The man farthest from the wall begins running toward the wall and as he reaches the closer man, they both turn on their flashlights, directing the beams toward the wall. Which beam will strike the wall first?

I think that's the gist of it.

So the idea is does the man running towards the wall increase the velocity of the the beams of light from a flashlight that is turned on at the same distance as the man standing stationary.

My answer is no.

The light from both flashlights hit the wall at the same time.

Otherwise, I'm going to stand around and push my hands through the air pushing towards a dark area.

When someone asks me what am I doing. I'm going to answer that I'm pushing the light particals over there where it's dark.

That guy is going to tell me, "Oh well, good luck with that."

Thanks, got it now.

Since the speed of light is constant, they would reach at the same time. However, since E1 does not equal E2, the transfer of energy would not increase speed, but the amplitude of the light. Therefore, one light would be brighter than the other, but would arrive at the same time.

The man running will have a compression wave in front of him which makes the air in front of him more dense. In denser materials light travels slower, therefore the stationary man's light will hit the wall first.

lol...what IF they were in a vacuum?

I do not believe moving the source of the light will influence the speed at which the light propagates from that source. One source may reach the wall first, depending on the speed of the runners, but the light will be traveling from sources postulated to be at identical distances from the wall, so will be traversing the same distance. Running with a light does not influence the speed at which the light itself moves through that identical distance. If it does, then prove it by passing me some photons, please.

I stand corrected. What we are discussing here is Special Relativity, not General Relativity as I had previously specified. For this error I appologize.

Maybe I'm reading too little into the problem. As stated, person #2 turns his light on at the instant he reaches person #1. At that instant the relative velocity of #2 to that of #1 is zero. The lights reach the wall at the same time.