Ok so C is independent of the sources speed, but

[Gullemsmcgee]

But I don't see where that clashes with galilean transformations :s

 

Hello, new here, today is the day before my physics exams and I am having a few mental problems with my relativity study . Sorry if I seem newbish, I am but a 17 year old student.

 

Anyway, on with the question.

 

According to one of maxwell's equations, the speed of light depends only on the electromagnetic constants of what its travelling through. No problem there, but then I dont see why this causes a clash with classic transformations.

 

We say that A is cycling at 0.5c towards observer B, and shines a flashlight. Then we say that both see the light travelling at speed c. I can understand why light cannot exceed c, but the way I see it light doesnt necessarily have to appear to be c for observer A?

 

If it is thought of as totally independant of A's velocity, then why cant it just take off and travel 0.5c faster than observer A, so to him it appears to move away at 0.5c whereas to B it appears to be c?

 

In effect I suppose, I am challenging the second postulate. What proof is there for it, because as I see it simply that the speed of light is independant of the source is insufficient to say it is the same for all inertial observers.

 

Furthermore, why couldnt someone move away from light at speed 0.5c and have it catch up to them at c?

 

So basically, why must light appear to be c and not less than c? And if that can be proven with some explanation, then why does it occur in this scenario?

 

Thanks

[Gullemsmcgee]

woops. gah, cant delete post D:

[Klaynos]

But I don't see where that clashes with galilean transformations :s

 

If you are travelling on a train at 20mpg and you through a ball backwards at 5mph, it has a velocity relative to the ground of, 15mpg. If you where moving at 0.9c, and you through a photon off of the back at c relative to yourself, relative to the ground it would also be moving at c. This has been experimentally confirmed.

 

Hello, new here, today is the day before my physics exams and I am having a few mental problems with my relativity study . Sorry if I seem newbish, I am but a 17 year old student.

 

Anyway, on with the question.

 

According to one of maxwell's equations, the speed of light depends only on the electromagnetic constants of what its travelling through. No problem there, but then I dont see why this causes a clash with classic transformations.

 

This doesn't really the velocity is only changing because of absorption and readdmittance of the photons, each photon moves at c. The reason that maxwells equations lead to lorentz transforms is that they have to be invariant at every point in space, as the first postulate of special relativity states.

 

We say that A is cycling at 0.5c towards observer B, and shines a flashlight. Then we say that both see the light travelling at speed c. I can understand why light cannot exceed c, but the way I see it light doesnt necessarily have to appear to be c for observer A?

 

It does have to appear as c in all inertia reference frames, the only way something can be travelling at c is because it started off at c, if you run through the equations that is.

 

If it is thought of as totally independant of A's velocity, then why cant it just take off and travel 0.5c faster than observer A, so to him it appears to move away at 0.5c whereas to B it appears to be c?

 

In effect I suppose, I am challenging the second postulate. What proof is there for it, because as I see it simply that the speed of light is independant of the source is insufficient to say it is the same for all inertial observers.

 

The Michelson-Morley experiment shows that c is an invariant.

 

http://en.wikipedia.org/wiki/Michelson-Morley_experiment

 

It does not change no matter what you try, if c is not the same everywhere then the laws of physics differ on your location in space.

 

Furthermore, why couldnt someone move away from light at speed 0.5c and have it catch up to them at c?

 

So basically, why must light appear to be c and not less than c? And if that can be proven with some explanation, then why does it occur in this scenario?

 

Thanks

 

It all stems from the laws having to be constant, so when you alter maxwells equations to maintain this invariance you get some nice equations which have the implication that c has to be invariance. You then run some experiments trying to disprove this and find you can't.

 

You must remember that with relativity you can't just got 0.5c + 0.7c = 1.2c, things do not combine in such a way...

[Gullemsmcgee]

Ok well im still a bit confused, but thanks that cleared it up a bit.

[Ragib]

Why can't light go at less then C? Because if it did, then that would be C. If you mean, simultaineously, which is probably what you do, ill try to explain. Easiest explaination. If we had two light beams. Ones 0.5c, other c. Now, Your standing still. Your brother can see both beams. He can only travel at below c, as he has mass. But, he could go at 0.6 c, faster than the other light beam. In his point of view he just went faster than light, when this should not be possible as he has mass. Not to mention, theres lots of problems going faster than light, ie imaginary time/mass, negative length

[Ragib]

O btw, just to explain, you would be pretty scared seeing..well not seeing because the light wont reach your eyes if its going faster than light..well sorta seeing a negative lengthed...object with imaginary mass, therefore imaginary momentum, and since theres the law of conservation of momentum, suddenly everyother mass has to become imaginary...eep