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actually because it interacts with the mask before continuing back on its normal speed, causing it to arrive at the "finish line" a tad after the unaffected photon?
originally posted by: MarioOnTheFly
a reply to: alldaylong
but but but...all the scientific guru guys are telling me the light speed is a constant...all our formulas depend on it.
The article like many articles about science doesn't do a very good job of explaining what is going on.
originally posted by: alldaylong
Exactly what the title says. I didn't know this was possible.
I am not that clued up on the science but here is the article
Their paper on page 7 implies the effect matches their theoretical predictions, so I don't expect much re-writing of textbooks:
One sentence summary: The group velocity of light in free space is reduced by controlling the transverse spatial structure of the light beam.
the delays we measure can only result from the transverse structure of the beam and indeed are consistent with our theoretical predictions.
So we can make the group velocity of light travel faster or slower than the speed of light.
The group velocity of a wave (e.g., a light beam) may also exceed c in some circumstances. In such cases, which typically at the same time involve rapid attenuation of the intensity, the maximum of the envelope of a pulse may travel with a velocity above c. However, even this situation does not imply the propagation of signals with a velocity above c, even though one may be tempted to associate pulse maxima with signals. The latter association has been shown to be misleading, basically because the information on the arrival of a pulse can be obtained before the pulse maximum arrives. For example, if some mechanism allows the full transmission of the leading part of a pulse while strongly attenuating the pulse maximum and everything behind (distortion), the pulse maximum is effectively shifted forward in time, while the information on the pulse does not come faster than c without this effect.
The effect can be derived from a simple geometric argument, which is also supported by a rigorous calculation of the harmonic average of the group velocity. Beyond light, the effect observed will have applications to any wave theory, including sound waves and, potentially, gravitational waves.
"So we measure the speed of a single photon as it propagates.
"And we find it's actually being slowed below the speed of light."