Does a photon know how fast to leave its emitter?

[nitsuj]

I thought someone above said that length contraction and time dilation would make the corrections required to bring light speed for a moving object to c . I tried to make those corrections and could not get it to work.

It seems to me that both length contraction and time dilation, if applied to the light in my frame which flies into the moving object from behind and from in front, will raise the speeds of these two lights. (contraction means the moving measuring rod gets shorter and takes less time to pass the light (although no one can actually measure it); time dilation means less time elapses on the moving object for a given distance of the light passage, hence more apparent speed for the light. Correct me if I'm wrong on either of those)

I can't understand what you are referring to in the second paragraph; can you re-word that?

 

[stever]

I will try to re-word it, but not right now. I have to think about it. Do you have some idea of what part is not clear?

 

[nitsuj]

"...both length contraction and time dilation, if applied to the light in [one] frame which flies into the moving object from behind and from in front, will raise the speeds of these two lights."

That's the part; I don't understand what you mean.

 

[Qzit]

Hi, I have been reading this post and find it interesting. I believe I might understand the wording as it stands. If I may try and change the wording a little stever, correct me if I am wrong. Objects moving away from you appear longer and objects moving toward you appear shorter. Now here is the statement about time "(contraction means the moving measuring rod gets shorter and takes less time to pass the light.)". This I suspect to be an incorrect statement. The rod going towards you will always appear shorter because of the finite speed of light. One moving away can never pass you and will always appear lenghened but once again I believe this is because of the finite speed of light. I suspect it is just a strobe like effect using light as a measuring device. The rod will be the same size in either direction if going at the same speed. Let me explain. A rod going 1/2 the speed of light towards you will have a reflective mirror on the front and the back. Your using light to measure the rod. Light hits the front mirror and moves towards the back mirror. Now the rod is moving at 1/2 the speed of light so it closes at 1/2 the distance that light is traveling toward the back mirror and gets reflected. The rod appears to be 1/3 shorter than its actual size. If this is correct the contraction is a optical effect and not a physical effect.

 

[nitsuj]

If this is correct the contraction is a optical effect and not a physical effect.

I am not sure what you mean by "physical effect", I think I understand what you mean by "optical effect". Given the little bit I understand about SR I still feel length contraction is a physical effect as much as time dilation. i.e. it's not just optical.

If you'd agree that time dilation is a physical effect, I am unsure how you could say length contraction isn't.

I wonder if it's ever been discussed here on PF

 

[Qzit]

Time dilation is a physical effect. The rod going towards you and away from you are dilated to the same length. That is the time dilation part possibly a longer distance for the electron to travel slowing time wrt resting electron path distance. What does it matter which direction a rod travels for its length? SR does not care about direction so the contraction and lengthening of the rod in my opinion has to be an optical effect caused by the finite speed of light. I mentioned that the rods were going the same speed I believe to defuse the time dilation and optical contraction.

 

[nitsuj]

What does it matter which direction a rod travels for its length? SR does not care about direction so the contraction and lengthening of the rod in my opinion...

I see direction being fundamental to relative motion, all else (SR) "builds" on that.

Length contraction is in the direction of motion. A length measurement taken perpendicular to the direction of motion will be the same value as measured when at "rest".

I have not heard of length "lengthening".

Thank you for the explination of your comments

 

[stever]

I am assuming that the contraction is real; I don't know how it happens or if it really happens, but both Lorentz and Einstein and others use it for reasons I don't understand. But I take it as a given and try to see if it helps the conceptual problem I have with relativity: namely, that light moves at c for all regardless of movement. However, Lorentz apparently explained the same phenomena as Einstein but said the speed of light can vary in one direction, but not on round trips. Apparently Lorentz assumes some kind of imperceptible ether and an imperceptible reference frame where the speed of light is the same in both directions. I am only looking at the light in my frame as it goes by or through a moving object and considering whether that object's dilation and contraction have a chance to make the light calculate roughly to be c in either or both directions parallel to the travel direction. I assume that the light would look, if I could measure or see it, to be going at unequal velocities past the moving object, that is, plus from the front and minus from the rear. This might not be a problem for the moving object as the round trip speed of light could perhaps be c, but I wondered what the effect of contraction and dilation would be in regard to this inequality of light speed. My conclusion was that contraction and dilation do not aid in equalizing the speeds. They make the speeds greater, which is OK for the light that catches up to the moving object, but not for the light that is oncoming. And they might make the round trip speed of light too high. I think that contraction and dilation create greater light speeds because the shorter the measuring stick or the slower the clock, the greater becomes the speed of any moving thing they measure, assuming independence of the factors. The independence of the physical movement of photons, the speed of a clock, and the length of matter is questionable though, and I don't know what the dependencies might be. If a moving object really does shrink, the light that enters its space is probably affected in some way, for example.

One thing that could be interesting is that time dilation would affect the calculation of light speed and velocities in all directions equally, while contraction would would work most in the travel line and diminishingly so at angles off the travel line.

 

[Qzit]

Back to the original question "How does a photon "know" how fast to leave its emitter?" In our current knowledge a photon created from an electron going slower than the speed of light than speeding up to "C" and maintaining that speed. WOW! What a question. If it worked in the rules we know then we would need to add speed and add maintenance to stop entropy. We would need roller bearings going faster than the electron and maintain those rollers at "C". How does the micro world do it? It must have different rules than ours.

 

[Qzit]

OK Stever while on the rotating Earth atomic clocks (Einstein said they could be used in the place of the speed of light) going west there is about a 14 Nano second difference in NY to San Francisco - for the Western direction and + for the Eastern direction. It is 0 differences if you go straight up to the North Pole from NY and straight down to San Francisco. Airplanes also have done the same experiment with the same conclusions. It is explained with the rotation of the Earth going west we reduce our speed of rotation going east we increase our speed of rotation. If you believe atomic clocks and the speed of light are interchangeable than the speed of light does have different speeds. Kind of like a flowing river of rotating Earth. All of our minds are shut off to that idea because there is no substance to space. Hence no difference in speeds.

 

[technician]

If time dilation and length contraction are taken to a logical conclusion and applied to light then, since light travels at the speedof light ! Time is zero... has no meaning for light and distance = zero... has no meaning for light.
Light takes no time to travel from (our) A to B and the distance from (our) A to B is zero for light.
Light just links everything together.

 

[Qzit]

Technician I do not understand your post. Mathematically you are saying position A = position B? What was the point?