# Speed of Light

1. Jan 31, 2004

### theurinal

Firstly, just a high to everyone, (first post, aye).

Now, everyone has been saying that FTL Travel (Faster than Light) and even the speed of light is impossible. (dammit... ) than how is it that light can go at the speed of light.

Now, for some touching back on the SOL theory. As you approach the SOL time gets slower and the energy needed for the speed gets higher. AT the SOL energy is infinite and time is held. (e.g 12:00 forever: never even hitting 1 ms later)

Now, if the energy required is infinite than how can Light itself go that fast.

Is the secret hidden in Light??!

2. Feb 1, 2004

### Staff: Mentor

The secret is that light has no mass.

3. Feb 1, 2004

### franznietzsche

AS he said light has no mass. It is an electromagnetic fluctuation. think of light as an increase in the electromagnetic field that moves throuhg space. This fluctuation can only propagate at the speed of light. It has no mass so the rules about accelerating to that speed are irrelevant. Also there is no known reason why it travels at that speed, it just does.

4. Feb 1, 2004

### theurinal

oh ok. i didn't really know that... well a day in which you learn something isn't a day wasted...

thanx guys

5. Feb 1, 2004

### Nudnik

There is a common misunderstanding about the speed of light being the limit of all physical speed. The actual limit is the the speed that a mass can be accelerated relative to the accelerating energy source. Since electromagnetic waves (light) is the fastest means of transferring energy it appears to the energy source as if the mass is increasing without bound as speed approaches light speed. Actually if some energy source is already travelling near the speed of light relative to some other object it can still accelerate another mass in the same direction producing greater than light speed relative to the first object. As a result the only limit on the speed of a rocket is the limited energy (and ejectable mass) it carries with it.

6. Feb 1, 2004

Staff Emeritus
Actually if some energy source is already travelling near the speed of light relative to some other object it can still accelerate another mass in the same direction producing greater than light speed relative to the first object. As a result the only limit on the speed of a rocket is the limited energy (and ejectable mass) it carries with it.

Absolutely wrong, and often refuted on these boards. Learn relativity.

7. Feb 2, 2004

### Phobos

Staff Emeritus
- - moving this to the Relativity forum - -

8. Feb 2, 2004

### franznietzsche

Umm...yeah. You can't jsut add velocities straight like that. The correct formula for adding velocities ( don't recall off hand) does not allow for the sum to exceed the speed of light. Just as the speed of light in a vacuum is a constant irrelevant of the motion of the observer, at the same time the sum of two velocities is limited to the speed of light irrelavant of the speed of the observer. This is dictated by the Lorentz transformations which are in turn dictated by the minkowski metric which describes spacetime in the absence of gravity (Special Relativity).

9. Feb 4, 2004

### Nudnik

I gave a physical process for why the mass increase is only apparent. How about you giving a physical process for why velocities can't be added (not just a mathematical speculation). [:>)]

10. Feb 4, 2004

### turin

How about 100 years of experimentation in electromagnetics?

11. Feb 4, 2004

### Nudnik

12. Feb 5, 2004

### Staff: Mentor

A good example is a particle accelerator. They put tons and tons of energy into a proton (or other small particle) and only get it asymptotically closer to C. Einstein's relativity is not just "mathematical speculation."

13. Feb 5, 2004

### Nudnik

You didn't read my first post. Remember that in the accelerated particles rest frame its mass is still rest mass. Where is the increased mass. It only looks to the accelerator (or any observer at rest relative to the accelerator) as if the mass has increased because the particle is tending to outrun the means of energy transfer (or information transfer).

14. Feb 5, 2004

### turin

Electromagnetic energy propagates at speed c away from its source. This is true regardless of how fast the source is moving or how fast the observer is moving.

15. Feb 6, 2004

### Nudnik

Tha manner of that statement shows, beyond any shadow of doubt, that you don't have a clue. The idea of relativity is just that. RELATIVE. {;>)] ~

16. Feb 9, 2004

### turin

By all means, enlighten me. Which part of my last statement of incorrect? I will admit that I have not performed exhaustive experimentation to validate my last statement, but the experiments I have done have demonstrated it. I have also been taught the same thing in all of my academic education. So, I would certainly like to hear why you think that it is incorrect. Has there been an experiment that falsifies the invariance of Maxwell's equations under a Lorentz transformation?

17. Feb 9, 2004

### Peterdevis

Electromagnetic energie propagates at speed c in every inertial system.
When the source is moving with a speed v in te observers systems, lights propagate at speed c for the observer, but the relative velocity between the light and the source isn't c, but c-v (if v is small). The observer who travels with the source, sees that the light is going away from the source with light speed.

18. Feb 9, 2004

### meddyn

I think we are getting a definite maybe on this subject.

Maybe some light shift would help:

Take two observers, one on Earth and one on Earth'. They are two billion light years apart. Exactly halfway between the two planets is a galaxy (8C1435+635). It is .93C red shifted to Earth and blue shifted a like amount to Earth' indicating a movement away from Earth and toward Earth'. Strictly from the perspective of the observers on Earth and Earth', and these observers only, take a simultaneous emission of a beam/wave/photon leaving the exact center of 8C1435+635 at the same instant moving toward these planets. From a number of discussions it appears the .93C red shifted light will arrive at Earth in the same instant the blue shifted light will arrive at Earth'.

No other observers are allowed. We don't care about an observer on 8C1435+635. Assume ideal vacuum along both paths with no intervening mass. Is there general consensus the arrival times would differ or arrival times would be identical?

19. Feb 9, 2004

### meddyn

If they did arrive at the same instant, should the red and blue shift be so pronounced?

20. Feb 10, 2004

### Nudnik

Where does the doppler shift occur, at the source, at the observer, half at the source and half at the observer or gradually along the way?