If (hypothetically), someone managed to create a vehicle that travels EXACTLY at the speed of light, (not one m/s more or one m/s less) and they turned the headlights on, what would happen to the light? Would it never come out of the light bulbs, or slowly shoot out of the vehicle?

Until we build a vehicle that can do this (which currently isn't believed to be possible) no one can reasonably answer this.

Well, you'd travel at the same speed of the light irradiating from bulbs. My guess is you'd not see the light in the same axis you're traveling in but you'd see the light around that axis.

If you were going 1 mph above it, the light would go back inside the light bulb almost like it never even happened. However if you are going 1mph slower, your headlights would eventually come out in front of you.

But just going at the same speed, youd see a faint light and the reflection of it in the back of it, just not infront of it

You can't travel exactly at the speed of light.

Also light moves at the same speed in all reference frames, so if a spaceship was traveling at half the speed of light, and they turned on their headlights, from the spaceships perspective the light would move away from them at the speed of light.

EDIT: Everyone else in this thread is wrong.

Once again light travels at the same speed in all reference frames.

Ok, I'm not really sure what a fast traveling spaceship would see although I'm pretty sure it would be weird. For instance I'm pretty sure that the perceived lengths of stuff changes, and extremely sure that time passes slower for fast moving objects than for other things.

What I am sure 100% of is that light travels at the same speed in all reference frames.

This is from my physics textbook:
A rocket is headed away from earth at a a speed of 0.80c. The rocket fires a missile at a speed of 0.70c (the missile is aimed away from the earth and leaves the rocket at 0.70c relative to the rocket). How fast is the missile moving relative to the earth?
a. 1.50c
b. a little less than 1.50c
c a little over c
d a little under c
e 0.75c

Post has been edited 2 time(s), last time on Jun 14 2009, 6:13 am by scwizard.

The speed of light is a fixed constant, so if the space ship was moving at half the speed of light, and it shot out lights, they would move away from at the speed of light, however, because it is moving at half that speed, the light would be moving away from it at half the speed of light, if you were to subtract half the speed of light from both, leaving the space ship at 0 and the light now at half. It's basic algebra.

No, because light is also a fixed constant in the spaceships's inertial reference frame. Therefore the light moves at c away from the spaceship relative to the spaceship.

According to classical physics what your saying makes sense, however classical physics don't apply at these speeds.

This is how you're thinking:
"the spaceship moves at .6c relative to me, and the light that the spaceship emits moves at c relative to me. Therefore the light must move at .4c relative to the spaceship, because 1 - .6 = .4"
Relativity doesn't work like that. "Light moves at c" is a law of physics, and if I'm moving at .6c relative to you, any light I see is moving at c relative to me. Is the spaceship moving at .6c away from the observer, or is the observer moving at .6c away from the spaceship? You can't define which one is standing still and which one is moving, so if they both shine a flashlight, there's no way to decide for which person the light is "moving slow" for. The answer that both people see both beams of light moving at c may seem contradictory. And it is, which is why a new branch of physics had to be crated so that that result wasn't contradictory.

Post has been edited 2 time(s), last time on Jun 14 2009, 6:41 am by scwizard.

No, it moves at .5c relative to the spaceship, and it is moving at c.


Not with that data, but we know both are moving in the same direction, so the faster one is slowly pulling away from the slower one.

How do you know the spaceship isn't standing still, and the human is moving away from the spaceship at .6c?

It's impossible to define which one is standing still, and which one is moving no matter how much data you have.


So if the spaceship is standing still, then the spaceships sees the light moving at c away from it. It says here that a person traveling away from the spaceship (at .6c in this case) will measure the same speed for that light as the spaceship.

Neither is standing still, both are moving..

I edited my above post a bit.

Also if both are moving then lets construct a person who is standing still. At what speed is the spaceship moving away from that person. At what speed is the previous person we constructed who was standing still moving away from this person?

Falkoner believes that there is an absolute reference frame, and that light moves at c relative to that absolute reference frame.

However an experiment was done, they measured the speed of light as the earth turned around the globe, and they always measured it to be c. Scientists were very confused by this "null result" at the time.

If such an absolute reference frame existed, then if you measured the light at one time of year, it would be 100,000kmph less than c, because the earth would be moving 100,000kmph towards this standing still being. And at another time of the year, it would be 100,000kmph greater than c, because the earth would be moving 100,000kmph away from this standing still being.

Scientists can measure the speed of light very exactly, and they've never measured a value different than c.

IMPORTANT READ THIS: I don't get why this is something people are arguing with me about. If you were to read about realativity on wikipedia, or in a textbook or anywhere, you would see that it's an accepted fact that I'm right when I say that light moves at c in all reference frames. Saying "omg this contradicts classical physics, therefore your wrong, here's how it contradicts classical physics" won't prove you right, it will just prove classical physics wrong.

I don't do relativistic mathematics, but to answer the original question, those aboard the spaceship would observe their headlights to be projecting light out in front of them at c, by Einstein's Second Postulate.

Quote

Falkoner believes that there is an absolute reference frame, and that light moves at c relative to that absolute reference frame.

However an experiment was done, they measured the speed of light as the earth turned around the globe, and they always measured it to be c. Scientists were very confused by this "null result" at the time.

If such an absolute reference frame existed, then if you measured the light at one time of year, it would be 100,000kmph less than c, because the earth would be moving 100,000kmph towards this standing still being. And at another time of the year, it would be 100,000kmph greater than c, because the earth would be moving 100,000kmph away from this standing still being.

Scientists can measure the speed of light very exactly, and they've never measured a value different than c.

The Michelson-Morley experiment defies all reason, and bothers me. Still, you can't argue with results =/

Relativity actually makes a sick sort of sense when you think about it a whole lot. As you can see, with me, it's to the point where I'm like "omg how can you say light moves at different speeds in difference reference frames, isn't it obvious how silly the idea of an absolute observer or reference frame would be."

However quantum physics makes me cry. Compared to quantum physics, relativity is simple and intuitive ;_;

The world will blow up.

gg

... no but seriously. Like Vrael said we can never know. We can't really discuss things like that until we find some way of even achieving speeds exactly at the speed of light.

Post has been edited 1 time(s), last time on Jun 14 2009, 6:56 pm by MillenniumArmy.

First of all, Falkoner, you have absolutely no idea what you are talking about. Please be quiet or at least try to inform yourself.

Second of all, traveling at the speed of light is impossible for any object that has mass. But still I like the idea of this question.

You are moving on a train and shoot a bullet backwards off the train. The train is going 1000 mph, and the muzzle velocity of the bullet is 1000 mph.

Who is driving the train?

j/k. This is a more believable strange situation.

You will observe the bullet to fly away from you at 1000 mi/h, and a stationary observer on the trackside will (hypothetically) watch as if a bullet were dropped from rest in front of them. This is nearly impossible to reproduce because it is very difficult to ensure these precise velocities.