# Speed of Light problem

uzless
Posers and Puzzles 04 May '06 15:06
1. uzless
The So Fist
04 May '06 15:06
If you were closely following your friend in his car and you were in your car, and the two of you were in outerspace, and could somehow get your cars to travel at the speed of light and then you turned on your headlights, would your headlights light up the back of your friends car, or would they do nothing?
2. 04 May '06 16:231 edit
Originally posted by uzless
... could somehow get your cars to travel at the speed of light ...
That would violate the law of nature, it's impossible.
I think you'd rather mean, near the speed of light.
You would, from your point of view (front seat), not see anything funny. Everything should appear quite normal.
However - from an outside still sitting observer you just have a very high speed (if he sees you at all.
3. sonhouse
Fast and Curious
04 May '06 17:462 edits
Originally posted by FabianFnas
That would violate the law of nature, it's impossible.
I think you'd rather mean, near the speed of light.
You would, from your point of view (front seat), not see anything funny. Everything should appear quite normal.
However - from an outside still sitting observer you just have a very high speed (if he sees you at all.
Like he says, AT the speed of light is impossible. Anything under the speed of light and you turn on the headlights, from your point of view, the light goes away from you at the speed of light. The thing is, time has slowed down for you and it looks like the speed of light.
Its going at the speed of light from an outsider POV also.
One thing that happens though, if you point the light away from your direction of travel, it still is emitted at the speed of light but doppler shift will take it towards the red end of the spectrum. Suppose its an ultraviolet light, depending on how close to the speed of light you are, the light going out to your rear may even end up being infrared or longer wavelength than that. It could end up being a radio wave if you are close enough to the speed of light. And conversely, doppler shift will make the beam going in front change to the blue end of the spectrum, it could end up as an X ray if you were close enough to C.
4. uzless
The So Fist
04 May '06 20:27
Originally posted by FabianFnas
That would violate the law of nature, it's impossible.
I think you'd rather mean, near the speed of light.
You would, from your point of view (front seat), not see anything funny. Everything should appear quite normal.
However - from an outside still sitting observer you just have a very high speed (if he sees you at all.
A light beam travels at the speed of light so if you were somehow able to attach your car to a beam of light, you would be carried along with it at the speed of light too!

The question is a theoretical problem.

By the way, Gravitrons move faster than the speed of light. The gravity influence of stars and planets are transferred across galaxies almost instantaneously, much faster than the speed of light.
5. sonhouse
Fast and Curious
04 May '06 21:162 edits
Originally posted by uzless
A light beam travels at the speed of light so if you were somehow able to attach your car to a beam of light, you would be carried along with it at the speed of light too!

The question is a theoretical problem.

By the way, Gravitrons move faster than the speed of light. The gravity influence of stars and planets are transferred across galaxies almost instantaneously, much faster than the speed of light.
News to me. Gravitational influence and gravitons both travel at the speed of light. If you somehow instantly transported the sun out of the solar system to somewhere a million ly away, the earth would not start out in a tangential movement for 8 minutes because the wave of warped space that would be the gravitational equivalent of cutting a stretched rubber band would not be able to effect earth for about 8 minutes, the same as we would not see the loss of light from the sun in that time either. We would suddenly be plunged into darkness and the earth would no longer be in a curved orbit but after that 8 minute delay would continue on a straight path aiming wherever it was moving to when the word finally got here there was no more gravity from the sun.
Planets like Pluto would be fat dumb and happy for a few hours because thats how far it is from the sun, 3 odd light hours away. So its orbit would continue to be elliptical just like the earth't but it would take three hours before Pluto would start in on a straight path.
Interesting idea: If the timing was right, Mercury would go in a straight path first and a few minutes later the earth would also. I wonder if there was a scenario where Merc and Earth could collide? I bet there is a non-zero probability that could happen.
6. 04 May '06 22:04
Originally posted by uzless
A light beam travels at the speed of light so if you were somehow able to attach your car to a beam of light, you would be carried along with it at the speed of light too!

The question is a theoretical problem.

By the way, Gravitrons move faster than the speed of light. The gravity influence of stars and planets are transferred across galaxies almost instantaneously, much faster than the speed of light.
Gravitrons are a theoretical, bosonic particle required by a quantum theory of gravity. They have not yet been detected and so we don't know at what speed they travel. Experiments are currently being devised and constructed to measure the speed of gravity waves. Until the results come in it's best not to speculate on the "speed of gravity".
7. 04 May '06 22:06
Originally posted by uzless
If you were closely following your friend in his car and you were in your car, and the two of you were in outerspace, and could somehow get your cars to travel at the speed of light and then you turned on your headlights, would your headlights light up the back of your friends car, or would they do nothing?
Assuming both cars are moving at a constant velocity, then your headlights would light up the back of your friends car. Just like the other thread (sonhouse's): that's the whole idea behind special relativity.
8. sonhouse
Fast and Curious
05 May '06 03:34
Gravitrons are a theoretical, bosonic particle required by a quantum theory of gravity. They have not yet been detected and so we don't know at what speed they travel. Experiments are currently being devised and constructed to measure the speed of gravity waves. Until the results come in it's best not to speculate on the "speed of gravity".
If the speed of gravitational radiation were to go faster than C, it would break causality, you could theoretically see into the future or maybe change the past if you could send information back in time or for instance, if you were light years away from earth and a black hole crashed into the sun causing a gravitational disturbance, you could maybe send a message back to earth that 'hey, don't look now but the earth is due to be destroyed in 8 minutes" That could give the earthlings, who by this time have interstellar craft capable of going near infinite speed, a chance to get away, a chance they would not have had when gravity only travels at the speed of light.
9. 05 May '06 06:301 edit
Originally posted by uzless
The question is a theoretical problem.
The theory says no.

No, you can't ever reach the speed of light, theoretically. Near but not at.
If you do you'll violate the laws of nature. The nature will not allow that.
10. uzless
The So Fist
05 May '06 17:15
Originally posted by FabianFnas
The theory says no.

No, you can't ever reach the speed of light, theoretically. Near but not at.
If you do you'll violate the laws of nature. The nature will not allow that.
I'm no physics major so please correct me where I'm wrong here....

A light beam is made up of photons. Therefore photons travel at the speed of light. If a photon is a particle, then why can't other particles travel at light speed also?
11. sonhouse
Fast and Curious
05 May '06 17:22
Originally posted by uzless
I'm no physics major so please correct me where I'm wrong here....

A light beam is made up of photons. Therefore photons travel at the speed of light. If a photon is a particle, then why can't other particles travel at light speed also?
Photons are sneaky bastards: No mas! Its only a bundle of electromagnetic fields so its got no actual matter to slow it down.
However, Mr E=MC^2 says that energy can be converted to mass if they collide with enough energy but when it turns into other stuff like electrons or whatever, they DO have mass so can't go at light speed.
According to some photons I know, they tell me matter is SUCH a drag!
12. 05 May '06 17:41
If, for the sake of argument, we let the cars be travelling at the speed of light, I would say the light does not reach the car in front.
The photons do not even get out of the headlights. They can go backwards or sideways but not forwards (relative to the car). They bounce around inside the headlights and are eventually converted to heat.
Then the car battery runs flat and the lights turn off.

umm, will electricity be able to flow to the headlights?
13. uzless
The So Fist
05 May '06 18:00
Originally posted by aging blitzer
If, for the sake of argument, we let the cars be travelling at the speed of light, I would say the light does not reach the car in front.
The photons do not even get out of the headlights. They can go backwards or sideways but not forwards (relative to the car). They bounce around inside the headlights and are eventually converted to heat.
Then the ...[text shortened]... y runs flat and the lights turn off.

umm, will electricity be able to flow to the headlights?
Even better, if you were a passenger in the car in front and looked behind at the car behind you, when he turned on the headlights I don't think you would even see a difference!

In fact, I don't think you'd even see the car!
14. sonhouse
Fast and Curious
05 May '06 19:35
Originally posted by aging blitzer
If, for the sake of argument, we let the cars be travelling at the speed of light, I would say the light does not reach the car in front.
The photons do not even get out of the headlights. They can go backwards or sideways but not forwards (relative to the car). They bounce around inside the headlights and are eventually converted to heat.
Then the ...[text shortened]... y runs flat and the lights turn off.

umm, will electricity be able to flow to the headlights?
But in the real world, only massless particles can go exactly at the speed of light, so its more like metaphsyics to talk about it. Maybe you could make a car of photons but other than that, you are out of luck. Even if you were within a mm/second of C, then you would still be within Big Al's speed limit and therefore the time flow inside the spacecraft would slow down to almost nothing and assuming both cars are going at the same velocity, the people in both cars would see nothing out of the ordinary and see the lights shining on them.
15. 05 May '06 20:31
Originally posted by sonhouse
Photons are sneaky bastards: No mas! Its only a bundle of electromagnetic fields so its got no actual matter to slow it down.
However, Mr E=MC^2 says that energy can be converted to mass if they collide with enough energy but when it turns into other stuff like electrons or whatever, they DO have mass so can't go at light speed.
According to some photons I know, they tell me matter is SUCH a drag!
Strictly speaking they have no rest mass. When they are travelling at the speed of light they do have a mass. Or at least they behave as if they do. Two for instances: The so called "solar sail" - the momentum of photons from the sun is used to drive a ship with a huge reflective sail. And, light is affected by gravity.

How they get from have no rest mass to having mass when moving is yet another facet of their sneakiness. Along with all that wave/partical duality stuff.