Speed of light

[mfgoode]

Slowing down light used to be considered a
neat trick for physics wonks. But researchers in New York now say
[0]they've pushed light into reverse. And as if to defy common sense,
the
backward-moving light travels faster than light." While there's not
much
use to come of it yet, it will be interesting if Einstein himself is
proved wrong.
This strenghtens my belief that the speed of light is infinite, but the limiting speed of interaction is 'c'

http://www.scienceblog.com/cms/light...rds-10590.html

Mally

These things have been theorized for awhile I thought.
While a particle cannot travel faster than the speed of light, it can bump other particles ahead of it's own path, so that the observer sees this illusion as faster than c travel.

Einstein said information can't travel faster than light, and in this case, as with all fast-light experiments, no information is truly moving faster than light," says Boyd. "The pulse of light is shaped like a hump with a peak and long leading and trailing edges. The leading edge carries with it all the information about the pulse and enters the fiber first. By the time the peak enters the fiber, the leading edge is already well ahead, exiting. From the information in that leading edge, the fiber essentially 'reconstructs' the pulse at the far end, sending one version out the fiber, and another backward toward the beginning of the fiber."

Mozart was the first faster than light transmission, through a brass medium.

[Xyzzy]

If I am in a car travelling at the speed of light, and I turn my headlights on, what happens?

[biwema]

Originally Posted by Xyzzy

If I am in a car travelling at the speed of light, and I turn my headlights on, what happens?

you cannot drive at the speed of light.
if you drive at speed of light - 1km/h, the light from your headlights travels 1 km/h relative to the car. Due to the speed of the car your time runs so slow that you have the feeling that the light from your headlights has the speed of light.

[biwema]

thoughts...

- I assume that the light has not speed of light but epsilon (very very small amount) less than that speed where the kinetic energy of a mass reaches infinte.

- Black holes are not that black. Light always can exit but its frequency goes asymptotic to zero when the mass of the black hole increases. A mass falling into the black hole will not rech the speed of light, either. The frequency is so close to zero that nothing can be observed, but still there is no blackshield horizon or so.

[jinydu]

Originally Posted by biwema

if you drive at speed of light - 1km/h, the light from your headlights travels 1 km/h relative to the car. Due to the speed of the car your time runs so slow that you have the feeling that the light from your headlights has the speed of light.

Not true. From your frame of reference, the light from your headlights still travels at 299,792,458 m/s. It is a postulate of special relativity (and a consequence of Maxwell's equations) that the speed of light is the same in all inertial frames of reference.

And also, time does not run slow for you in your frame of reference. After all, in your frame of reference, you are at rest.

In any case, the phrase "If I am in a car travelling near the speed of light" is misleading because all speeds are necessarily measured in a particular frame of reference, and there is no universal frame of reference.

Originally Posted by biwema

- I assume that the light has not speed of light but epsilon (very very small amount) less than that speed where the kinetic energy of a mass reaches infinte.

That is impossible. c is by definition the speed of light; and as pointed out earlier, special relativity postulates that this speed is always the same in every frame of reference. Furthermore, it can be shown that the speed at which the kinetic energy of a massive particle approaches infinity is exactly c.

All these conclusions (except the constancy of c, which must be either accepted as an axiom or derived from Maxwell's equations) can be derived mathematically; they are not just vague, qualitative, speculative ideas.

[philmoore]

Originally Posted by jinydu

Not true. From your frame of reference, the light from your headlights still travels at 299,792,458 m/s. It is a postulate of special relativity (and a consequence of Maxwell's equations) that the speed of light is the same in all inertial frames of reference.

And also, time does not run slow for you in your frame of reference. After all, in your frame of reference, you are at rest.

Biwema was correctly describing what would be observed in a frame of reference with respect to which the car moves at slightly less than the speed of light. Obviously the existence of such a frame is implied by the original question. Jinydu is also correct in pointing out that the difference in velocity being 1 km/s and the time dilation are not what the passenger in the car sees, but what is observed in the frame in which the observations are made. There really is no contradiction here.

[mfgoode]

Originally Posted by Xyzzy

If I am in a car travelling at the speed of light, and I turn my headlights on, what happens?

A good question Mike and requires an equally good answer.

I tried to explain this phenomena but it is much too long to write it out.

First of all one must understand the theorem of the addition of velocities.
In Newtonian physics this is simply to add the two velocities. In Relativist physics the added velocities will always be less than the speed of light.
At slow speeds the effect cannot be noticed but at subliminal velocities the effect is appreciable.
No amount of explanations can cover this topic. The only resource is math equations which as you will see are not so difficult to follow and are quite elementary.
I give this URL as a first step to your question. From there on, there are several links to go onto.

http://www.bartleby.com/173/13.html

Mally
P.S. Read down till Equation A and Eqn.B and follow thru.

[alpertron]

There are other problems here:

* An actual passenger will need a year accelerating at 1g in order to reach relativistic speeds (and more years to reach (c - 1km/h)).

* From the speed the elemental particles in space crashes into your vehicle, you will see that it will be destroyed, much like the Columbia Space Shuttle on February 1st, 2003 when it converted into flames over Texas at an altitude of 63 km and a speed of 5.6 km/s (20000 km/h).

[mfgoode]

Originally Posted by biwema

you cannot drive at the speed of light.
if you drive at speed of light - 1km/h, the light from your headlights travels 1 km/h relative to the car. Due to the speed of the car your time runs so slow that you have the feeling that the light from your headlights has the speed of light.

:surprised
Speed of light-1km/hr.? Alpertron uses the same value.
Am I missing something ?
Mally

[alpertron]

The speed of light is (by definition) 299792458 m/s.

1 km/h = 0.27777.. m/s

So c - 1 km/h = 299792457.72222 m/s = 1079252847.8 km/h

Where is the problem?