# Faster than light

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It would take infinite energy for us to travel at light speed because we have rest mass, and the mass of objects with rest mass increases to infinity as c is approached.

Light can travel at light speed because it has NO rest mass.

Look in the Lorenz Transforms that are posted in this board.

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Originally posted by KHinfcube22

Just so I know, for I don't want to go all over the place, why can't we travel at c? And please don't say "

Because one needs inf. energy to travel ay c." If one needed inf energy, then how does LIGHT do it? Can't we jusst find out how fast light moves, how much light ways, and make up some equation to find out fast it would need for us to go?

some equations? those would be the Lorentz transforms, and I have mentioned them many times. they are in an announcement in this section.

Light doesn't have mass, that is how it travels at c

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If one needed inf energy, then how does LIGHT do it?

No mass, no problem. Not to mention that when light is created it is already traveling at c, it does not accelerate to c. I don't know what that means, but it seemed relevant to type.

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Originally posted by KHinfcube22

Just so I know, for I don't want to go all over the place, why can't we travel at c? And please don't say "

Because one needs inf. energy to travel ay c." If one needed inf energy, then how does LIGHT do it? Can't we jusst find out how fast light moves, how much light ways, and make up some equation to find out fast it would need for us to go?

The reason that we say that we need infinite energy to travel at c is because we need to accelerate to that speed, and to do that we need to put in an infinite amount of work because as your speed approaches c, the mass tends to infinity. I don't think anyone knows why light travels at c.

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Originally posted by MrL_JaKiri

It would take infinite energy for us to travel at light speed because we have rest mass, and the mass of objects with rest mass increases to infinity as c is approached.

Light can travel at light speed because it has NO rest mass.

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LIGHT HAS MASS!!! It has been proven that light DOES have mass. Its made up of some type of subatomic particles, THAT HAVE MASS!!!!!

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Originally posted by KHinfcube22

LIGHT HAS MASS!!! It has been proven that light DOES have mass. Its made up of some type of subatomic particles, THAT HAVE MASS!!!!!

It has not been proven, because light does not have mass. there aren't even any theoretical suggestions that light has mass.

furthermore, I assume you are talking about photons. you have to be really careful here because of wave-particle duality. you cannot say that a photon is really a particle, because it has both particle like and wave like properties. In reality a photon is an excitation of the electric field. I suggest you read (at the very least the forword )Principles of Quantum Optics by Rodney Loudon, he explains it rather well, though I believe his explanation was borrowed from Lamb.

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Originally posted by KHinfcube22

LIGHT HAS MASS!!! It has been proven that light DOES have mass. Its made up of some type of subatomic particles, THAT HAVE MASS!!!!!

Sometimes I wonders if this kid isn't jerkin' our chain with his "knowledge".

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My teacher (woodshop), who is a physics hobbyist insists that superluminal travel is possible with the use of magnetism. He says that if we could use the magnetic pole of the earth, we could somehow get enough force to launch a ship and get it to travel c+.

I am a complete skeptic of his hypothesis, for obvious reasons. But I can't seem to convince him superluminal travel is impossible.

Okay, I feel guilty that I think it is impossible, and I'm rejecting it for that reason. Remember Nicola Tesla; he did everything that was theoretically impossible in his time. Why not superluminal travel?

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Originally posted by MajinVegeta

My teacher (woodshop), who is a physics hobbyist insists that superluminal travel is possible with the use of magnetism. He says that if we could use the magnetic pole of the earth, we could somehow get enough force to launch a ship and get it to travel c+.

tell him to carry on cutting wood.

Tesla did things that people thought were impossible, but were not theoretically impossible. should the speed of light be constant (locally) then ftl travel would be able to be used to create paradoxes, like sending you a message telling you you have broken your leg before you break it, hence allowing you to not break your leg.

I will type up the paradox tomorrow.

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It's not "theoretically impossible" to travel faster than light, it's just theoretically impossible to accelerate to that speed, which is why tachyons have not been ruled out, particularly in brane theory.

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oh, I should clarify a bit: the main issue with ftl is that of information transfer.

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If time stops at c, how does light move?

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Originally posted by fafalone

If time stops at c, how does light move?

you're in a different rest frame.

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It's actually quite useful to have time stopping at c, as it removes the possibility of something I don't think many people, when contemplating QP, have considered; that of the decay of exchange particles. Fortunately, there is no time so this can't happen.

Be glad we've only got the uncertainty principle to worry about, and not about forces randomly changing into other forces.

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Originally posted by KHinfcube22

LIGHT HAS MASS!!! It has been proven that light DOES have mass. Its made up of some type of subatomic particles, THAT HAVE MASS!!!!!

Light doesn't have a rest mass. It has momentum though (De B's :lclambda: equation)

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I can't be bothered typing it out. Get the Emperor's new mind, and read p273

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If the computer crashes while I am editing this post I will be really annoyed.

I have a spare computer hahahahahaha

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• 1 month later...

whoever fafalone aws trying to make look stupid was right (that velocity across the 4 dimensions x,y,z,t always equals c).

Think of it this way (idea taken from "the elegant universe") - a car is placed on a race track going 100mph. The race track is quite wide- lets just say 10 times the width of the car. Let's say that if the car travels in a straight line from the start of the race track to the end of the race track, it will take 7 seconds. This is if the car went in a perfectly straight line moving in only one dimension (forward in the x dimension). Now, since we said the track is much wider than teh car, the car can also move sideways (in the y dimension). If the car, still going 100mph, travels in a diagnal line (e.g. it drifts sideways) from the start of the racetrack to the end of the track, it will take longer to do so, say 8 seconds. Why? The car was still going at 100mph...

Its cause the cars speed was now split between two dimensions - x (moving forward) and y (becaause it was drifting sideways). The cars speed is constant, but it was split between two dimensions.

Einstein argued the saem thing. That is, our speed is always constant - C. its just the way we split it between the four dimensions that chagnes.

Shit late for class, ill finish later

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Many questions come to mind. When we speak of the speed of light are we speaking of gamma rays travelling at 186,000 miles/second through a vacuum? What if the electromagnetic spectrum goes beyond gamma rays and we just haven't discovered or observed this yet? This may be entirely possible and who is to say that the properties of light that could exist beyond gamma rays, in the electomagnetic spectrum, can't have properties vastly different than those of the types of light we have observed thus far!

I submit the following for review just because I found it interesting:

" In one experiment performed by researchers at the NEC Research Institute in Princeton, N.J., a pulse of light was sent through a transparent chamber filled with specially prepared cesium gas and was pushed to travel at speeds of 300 times the normal speed of light. The light travels so fast that the main part of the light pulse exits the chamber even before it enters. Theoretically, this means that you could see a moment in time before it actually takes place."

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Next question...We know that a wave in water isn't actually water moving but energy moving through water. In a light wave, are the electrons/photons actually moving or is the energy just transferring through stationary electrons/photons?

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Originally posted by Star-struck

Many questions come to mind. When we speak of the speed of light are we speaking of gamma rays travelling at 186,000 miles/second through a vacuum? What if the electromagnetic spectrum goes beyond gamma rays and we just haven't discovered or observed this yet? This may be entirely possible and who is to say that the properties of light that could exist beyond gamma rays, in the electomagnetic spectrum, can't have properties vastly different than those of the types of light we have observed thus far!

We're talking of any of the spectrum of the electromagnetic wave packets ('photons'). These travel at 299792458ms^-1 in a vacuum, and their interactions are entirely predictable.

Originally posted by Star-struck

In one experiment performed by researchers at the NEC Research Institute in Princeton, N.J., a pulse of light was sent through a transparent chamber filled with specially prepared cesium gas and was pushed to travel at speeds of 300 times the normal speed of light. The light travels so fast that the main part of the light pulse exits the chamber even before it enters. Theoretically, this means that you could see a moment in time before it actually takes place

I don't believe that exists. It would invalidate SR for a start, and something of that magnitude would be international news, not just a small aside somewhere.

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The article goes on to say that NEC won't publicly comment on the experiment until it is reviewed by Nature, a weekly peer-reviewed science journal. Great thing about the truth; It is true whether or not anyone believes it!

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The people who carried out the experiment have a webpage webpage located here

One bit of information from their page that should be noted:

"Our experiment is not at odds with Einstein’s special relativity. The experiment can be well explained using existing physics theories that are consistent with Relativity. In fact, the experiment was designed based on calculations using existing physics theories.

However, our experiment does show that the generally held misconception "nothing can move faster than the speed of light" is wrong. The statement only applies to objects with a rest mass. Light can be viewed as waves and has no mass. Therefore, it is not limited by its speed inside a vacuum.

Information coded using a light pulse cannot be transmitted faster than c using this effect. Hence, it is still true to say that "Information carried by a light pulse cannot be transmitted faster than c." The detailed reasons are very complex and are still under debate. "

Here is the abstract of the experiment...

Gain-assisted superluminal light propagation

L. J. WANG, A. KUZMICH & A. DOGARIU

NEC Research Institute, 4 Independence Way, Princeton, New Jersey 08540, USA

Correspondence and requests for materials should be addressed to L.J.W. (e-mail: Lwan@research.nj.nec.com).

Einstein's theory of special relativity and the principle of causality imply that the speed of any moving object cannot exceed that of light in a vacuum ©. Nevertheless, there exist various proposals for observing faster-than- c propagation of light pulses, using anomalous dispersion near an absorption line, nonlinear and linear gain lines, or tunnelling barriers. However, in all previous experimental demonstrations, the light pulses experienced either very large absorption or severe reshaping, resulting in controversies over the interpretation. Here we use gain-assisted linear anomalous dispersion to demonstrate superluminal light propagation in atomic caesium gas. The group velocity of a laser pulse in this region exceeds c and can even become negative, while the shape of the pulse is preserved. We measure a group-velocity index of ng = -310(5); in practice, this means that a light pulse propagating through the atomic vapour cell appears at the exit side so much earlier than if it had propagated the same distance in a vacuum that the peak of the pulse appears to leave the cell before entering it. The observed superluminal light pulse propagation is not at odds with causality, being a direct consequence of classical interference between its different frequency components in an anomalous dispersion region.

Also, it was published in nature about 2 years ago.

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Also, another note from their page:

It has been mistakenly reported that we have observed a light pulse’s group velocity exceeding c by a factor of 300. This is erroneous. In the experiment, the light pulse emerges on the far side of the atomic cell sooner than if it had traveled through the same thickness in vacuum by a time difference that is 310 folds of the vacuum transit time.

In our experiment, a smooth light pulse of about 3-microsecond duration propagates through a specially prepared cesium atomic chamber of 6-cm length. It takes 0.2 nanosecond for a light pulse to traverse a 6-cm length in vacuum. In our experiment, we measured that the light pulse traversing through the specially-prepared atomic cell emerges 62 nanosecond sooner than if it propagate through the same thickness in vacuum. In other words, the net effect can be viewed as that the time it takes a light pulse to traverse through the specially prepared atomic medium is a negative one. This negative delay, or a pulse advance, is 310 times the "vacuum transit time" (time it takes light to traverse the 6-cm length in vacuum).

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