Speed of light

If you're moving at the speed of light and turn on your headlights, what happens?

Now this may seem childish at first, but give it some thought. Can photons carry momentum? If so, how long before they slow? All of this in space, or what about in a stable atmosphere? Or an unstable one for that matter.

If you're moving at the speed of light and turn on your headlights, what happens?
Moving at the speed of light is impossible. The best any matter or things with mass can do is get close to the speed of light. This is because mass of an object increases with speed. As you approach the speed of light, mass approach infinity. Try to push something with infinite mass and see what will happen!

Can photons carry momentum?
Yes and No. They have no mass but they do have energy. light can be converted to kinetic energy when it hits an atom. This is like a transfer of momentum, but it is really just transfer of energy.

If so, how long before they slow?
They travel for billions of light years away and still are just as fast as when the started. They slow when traveling through matter like a colorless glass or water or glass. Glass slows matter down at a different rate then water. Colder glass slows light down even more.


[Edited on 30-10-2003 by TheManWithThePlan]

Originally posted by Pherophile
If you're moving at the speed of light and turn on your headlights, what happens?

Now this may seem childish at first, but give it some thought. Can photons carry momentum? If so, how long before they slow? All of this in space, or what about in a stable atmosphere? Or an unstable one for that matter.

I'm sure some more up to date Physics Genius will find flaws in this but I'll give it a shot.

Turning on your headlights while going the speed of light is not really a logical problem since going the speed of light in the first place in a vehicle that would retain it's structure first needs to be explained.

A photon moving at light speed is also moving at the speed of Time so I don't think momentum would apply since there would be no time allowed for any build up of momentum to occur.

A photon also has no Volume or Mass either and as far as I know we can't stop one completely either. We recently slowed them way down though but since it's location and volocity can't be known both 100% at the same time. It almost stopped at 0. It's Volocity was known at near 99% and location was the 1%. Speeding them up and smashing them to find smaller particles also does no good as I know of since the energy that is used in speeding it up is used to create duplicate photons upon it being smashed.

Also a photon seems to exist as a particle (actual) and a wave (probability). Also distance between two photons does not seem to matter as if a photon is not only itself but also other photons as well in a weird kinda way.

Did I miss anything or do I need to be updated on my photon physics?? Any professionals out there wanna help me out??

Originally posted by Pherophile
Can photons carry momentum?

I would say that it depends mostly on what the *viewer* would think would happen. There's been an experiment that refracted a single beam of light into two beams...And the weird thing is that one of those refracted beams acted like a "waveform" & the other acted like a "particle stream".
So how could the same photons from the same original beam of light react *both* ways? It comes down to the Quantum Theory that the expectations of the *observer* have an effect on that which is *observed*.

First of all you can go faster than the speed of light.

When you are travelling at such speeds the basis of physics changes.

Gravity is the only force that is constant and it allows speeds faster than light.

Saying that you car can not approach the speed of light and its structural integrity would break down does not help. Basically the question can be simplified to: if I am travelling in my car at 100 mph and turn on my lights, what happens? Are the photons then going the speed of light + 100 mph. The answer to this is simply no, they still travel at the speed of light.

If 2 people stand a mile apart and simaltaniously turn on their flashlights, do the light beams approach each other faster than the speed of light, the answer again is no.

Einstein's theory of relativity explains all of this. That is why it is called relativity, it talks about the movement of one object compared to another at speeds around that of light. But it is a theory after all.

[Edited on 31-10-2003 by greenkoolaid]

This might help:

Theoretical Basis for Special Relativity

Einstein's theory of special relativity results from two statements -- the two basic postulates of special relativity:

The speed of light is the same for all observers, no matter what their relative speeds.
The laws of physics are the same in any inertial (that is, non-accelerated) frame of reference. This means that the laws of physics observed by a hypothetical observer traveling with a relativistic particle must be the same as those observed by an observer who is stationary in the laboratory.

Given these two statements, Einstein showed how definitions of momentum and energy must be refined and how quantities such as length and time must change from one observer to another in order to get consistent results for physical quantities such as particle half-life. To decide whether his postulates are a correct theory of nature, physicists test whether the predictions of Einstein's theory match observations. Indeed many such tests have been made -- and the answers Einstein gave are right every time!

www2.slac.stanford.edu...

Originally posted by greenkoolaid
Saying that you car can not approach the speed of light and its structural integrity would break down does not help. Basically the question can be simplified to: if I am travelling in my car at 100 mph and turn on my lights, what happens? Are the photons then going the speed of light + 100 mph. The answer to this is simply no, they still travel at the speed of light.

If 2 people stand a mile apart and simaltaniously turn on their flashlights, do the light beams approach each other faster than the speed of light, the answer again is no.

Einstein's theory of relativity explains all of this. That is why it is called relativity, it talks about the movement of one object compared to another at speeds around that of light. But it is a theory after all.

[Edited on 31-10-2003 by greenkoolaid]

Oh, ok.....So you're going 100mph and hit the lights. Still, the photons would be going C. (C=Speed of Light)
The photon traveling at C would also be equal to the speed of Time. So basically all time would stop from the Perspective of the photon from the moment it shot from the headlight.

I've also read the Relativity Theory. I'm not sure but the example I think I read was with a Train and Lightning striking the front of it. There is a guy in the back of the train that passes another guy standing on the ground just as the lightning hits.
Does that sound familiar??

By the way. I have the the pdf document of Einstein's General and Special Theory of Relativity if anyone would like to check it out. It's 85pgs but only 227k which makes it very easy and quick to email.

Makes for some nice "light" reading!! (Pun intended )

[Edited on 31-10-2003 by mOjOm]

I am not familiar with the example of the lighting, but there have been lots of examples used to explain it. But I think the jist of what you are saying is that the man standing beside the train and the man on the train both experience the light travelling at the speed C, even though one is on a moving train.

I would like to see a copy of that document if you wouldn't mind emailing it. thanks.

Originally posted by greenkoolaid
I am not familiar with the example of the lighting, but there have been lots of examples used to explain it. But I think the jist of what you are saying is that the man standing beside the train and the man on the train both experience the light travelling at the speed C, even though one is on a moving train.

I would like to see a copy of that document if you wouldn't mind emailing it. thanks.

Yah, that's the idea. So imagine the train being really, really, really long so that the light takes some small amount of time to reach each guy. Well since the one on the train is moving forward toward the light at the same time he would see the lightning hit before the one standing off to the side. So the exact moment of the lighting strike then becomes Relative to the observer as to when it hit.

It was something similar to that anyway, It's been a while, but I think it's in this pdf as well. I actually read it on the net when I came across it first.

U2U me with an email.