Faster Then The Speed Of Light?

Question

Need more info on laser light...

From CNN:

http://archives.cnn.com/2000/TECH/space/07/20/speed.of.light.ap/#graph

Scientists have apparently broken the universe's speed limit.

For generations, physicists believed there is nothing faster than light moving through a vacuum -- a speed of 186,000 miles per second.

But in an experiment in Princeton, New Jersey, physicists sent a pulse of laser light through cesium vapor so quickly that it left the chamber before it had even finished entering.

The pulse traveled 310 times the distance it would have covered if the chamber had contained a vacuum.

Wow...too many great answers...thank you...you-all really know your stuff...I think I'll put this on to vote...Thanks

Answer 1

Whoa! All fun and games until someone takes a critical look at the fundamentals behind Einstein's theory and the media hoopla. Let me draw in a deep breath here as I begin my long-winded rant.

The peak of this pulse is simply not the kind of "thing" to which Einstein's famous law applies. Relativity teaches us that if two space-time events are separated so that they cannot be connected by any signal travelling at c or less, then different observers will disagree as to which of the two events came first. Since most physicists still believe that cause needs to precede effect, we conclude that no information can be transmitted faster than the speed of light. This is why the "scientists" (I think they are grad students) are scratching their heads trying to explain the impossible.

Nevertheless, velocities greater than c can be observed. Suppose a lighthouse illuminates a distant shore. The rotating lamp moves quite slowly, but the spot on the opposite shore travels at a far greater velocity. If the shore were far enough away, the spot could even move faster than light. However, this moving spot is not a single "thing". Each point along the coastline receives its own spot of light from the lighthouse, and any information travels from the lighthouse at c, rather than along the path of the moving spot. Such phenomena are described as the "motion of effects", and are not forbidden by relativity.

In contrast, the NEC team creates a region of anomalous dispersion in a nearly transparent medium. Wang and co-workers do this by pumping energy into the caesium vapour to create a kind of optical amplifier. First a laser is used to pump most of the caesium atoms into a particular spin state. Next, two additional pump lasers are used to lend energy to the atoms. These atoms can amplify light from yet another "probe" laser by making an electronic transition in which they absorb "pump" energy and re-emit it into the probe beam. There are two specific frequencies at which such a probe can be amplified in this way. By replacing absorption with amplification, the NEC team can swap the regions of normal and anomalous dispersion. A region halfway between the two amplification lines appears where there is little loss, amplification or distortion. Here the group velocity becomes negative and nearly constant. Indeed, Wang and co-workers measured a group velocity of -c/310. In other words, a pulse travelling a distance, L, is advanced by 310L/c.

What is shocking is that such an effect has been observed for the first time without a great deal of attenuation, amplification or distortion of the pulse. It appears as though energy has, in fact, travelled faster than light.

Of course, this is not the case. The effect observed at NEC only works in the presence of an amplifying medium, i.e. a medium that stores energy. In this case the energy is stored in the pump-laser beams. The caesium atoms are prepared in a state that allows them to transfer energy from these beams to the signal beam. The faster-than-light propagation occurs because the pump beams preferentially amplify the leading edge of the incident pulse, lending power to the signal and being repaid by absorbing some of the energy in its trailing edge. (It is important to note that even the dramatic 60 ns advance is only one fiftieth of the width of the pulse.) This is exactly analogous to the intuitive explanation of normal dispersion, except that in this case the atoms temporarily amplify the light pulse rather than absorb it.

A fascinating suggestion is that this experiment might work even for a pulse composed of only a single photon. However, there has been a good deal of controversy over how to discuss the information transmitted through such a system by a single-photon pulse, and many subtle issues remain.

Answer 2

This experiment is very interesting and has very interestinf implications if it is true. However, they have not been able to reproduce the experiment since and achieve results that reflect what they observed and recorded previously. Their results did seem to be valid though and this is why it deserves further study.

But it still is not proven to have happened as it was supposed to have happened and still it is a theory to explain the results. Also the scientists involved were trying to achieve a faster than light speed. This could mean that there bias has affected the logic. Maybe not though, I don't doubt for a minute that these people are absolutely brilliant. Einstein used only thought experiments in any case and all information gathered to date supports his theory, while this is the only experiment ever to contradict this particular theory. And since the experiment only achieved the results once I am unsure how accurate the experiment was.

Generally the scientific community needs quite definitive proof before dubunking a theory and it is true for this case (at least for now). So perhaps if they perfect the experiment and theory in the future we will see an addition to the laws of physics. It'd be pretty unreal if they could manage to do this.

Answer 3

TM is correct in his analysis, but please give graduate students a little more credit: no one is really "scratching their heads" over this. That is, no one other than some reporters and their readers. Let this be a lesson that the news is best taken as entertainment, and should never be assumed accurate.

(by inaccurate I mean the assertion that "for generations physicists believed their is nothing faster than light moving through a vacuum"-that's just plain wrong)

Answer 4

Faster than the light, Fastest in the universe is Mind

Answer 5

I KNEW IT!! I knew that limit of 186k was a buncha hooey.

Anyway, what do you mean "need more info on laser light". Their laser? Lasers in general? For general laser workings, go to http://howstuffworks.com and type in "lasers".