Superluminial speeds, huh? Just where would that be?

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Offline yor_on

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Photons Do Not Exceed the Speed of Light.

"According to Du, the scientific community got all excited about time travel several years ago with the discovery of "superluminal propagation of optical pulses," which basically said that a group of optical pulses could move faster than the speed of the light. Du, however, said this was only a visual effect and could not actually be used to transmit real information. People then focused on a single photon moving faster than the speed of light, but  "because of lack of experimental evidence of single photon velocity, this is also an open debate among physicists," Du said.

As a result, Du's team measured the maximum speed of a single photon, which showed that it obeys the universe's speed limit and "confirms Einstein's causality; that is, an effect cannot occur before its cause," researchers said.

In their tests, researchers managed to separate the optical precursor, a wave-like structure at the front of an optical pulse, from the rest of the photon wave packet. To accomplish this, Du's team created a pair of photons and passed one of them through a group of laser-cooled rubidium atoms, which allowed them to observe optical precursors for the first time.

The team found that, as the fastest part of a single photon, the precursor wave front always travels at the speed of light in vacuum," researchers said. "The main wave packet of the single photon travels no faster than the speed of light in vacuum in any dispersive medium, and can be delayed up to 500 nanoseconds in a slow light medium. Even in a superluminal medium where the group velocity (of an optical pulse peak) is faster than the speed of light in vacuum, the main part of the single photon has no possibility to travel faster than its precursor."

So, until someone came come up with something that travels faster than the speed of light, it looks like time travel will be confined to movies and TV."
« Last Edit: 02/08/2011 10:45:09 by yor_on »
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Offline Phractality

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Superluminial speeds, huh? Just where would that be?
« Reply #1 on: 02/08/2011 11:19:57 »
It remains to be seen whether so called "quantum teleportation" is instantaneous across a distance. Even if it cannot be used to communicate faster than light, it still may prove the existence of a substantive immovable æther. It only needs to be verified after the fact, via light-speed communication, that an effect was simultaneous with its cause across a significant distance.

Of course, the effect cannot be instantaneous in every reference frame without implying time paradoxes, but there is no paradox if the effect is instantaneous only in the reference frame of the æther. A good guess is that the æther is motionless relative to the CMB. The blueshift of the CMB in the direction of Virgo indicates that our solar system is moving in that direction at about 627 km/s. That corresponds to a relativistic gamma of .0000022 and a time shift of about 9 ns/km. In other words, in the reference frame of the CMB, Earth clocks closer to Virgo are that much ahead of Earth clocks farther from Virgo. So an effect that is instantaneously sent toward Virgo, in the reference frame of the æther, would arrive before it is sent according to Earth clocks. This is not paradoxical because an effect sent in the opposite direction would be delayed by the same amount, and a two-way communication would be instantaneous. You could not send an effect into your own past.   

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Offline imatfaal

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Superluminial speeds, huh? Just where would that be?
« Reply #2 on: 02/08/2011 13:47:08 »
Phract - you know the rules, please keep ether and non-mainstream speculation to the New Theories board.  There is a world of difference between the results of a tight peer reviewed paper and a discussion of the ether.
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