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Scientists Slow the Speed of Light
lightbox32 sends news that scientists have found a way to slow individual photons within a beam of light. Their work was published today in Science Express (abstract, pre-print). The researchers liken a light beam to a team of cyclists — while the group as a whole moves at a constant speed, individual riders may occasionally drop back or move forward. They decided to focus on the individual photons, rather than measuring the beam as a whole. The researchers imposed a particular pattern on a photon, then raced it against another photon, and found that the two arrived at their destination at slightly different times.
The work demonstrates that, after passing the light beam through a mask, photons move more slowly through space. Crucially, this is very different to the slowing effect of passing light through a medium such as glass or water, where the light is only slowed during the time it is passing through the material—it returns to the speed of light after it comes out the other side. The effect of passing the light through the mask is to limit the top speed at which the photons can travel.
I don't think it does.
The Lorentz equations use the constant c, which happens to be the same as the maximum speed of light in a vacuum. Tricking some light into going slower doesn't change the constant, and it isn't a big deal to go faster than some particular light (see Cherenkov Radiation), but it would be a big deal to go faster than c.
See that "Preview" button?
no, c is the top speed of your paceman - in fact, c is the only speed of your paceman. Every other rider can only travel at the same speed or *slower*. Switching pacemen means that your current paceman must drop back (ie slow down) rather than the column speeding up to overtake (thus breaking c). The average speed of the entire column must necessarily be less than c at all times, the guy at the front (doesn't matter who it is) is always the fastest man on the field unless he is dropping back to let the column overtake him - without the column having to speed up.
In cycling, the pace rider may travel at a certain speed (let's call it 40km/h), that may be the designated pace for the event. His replacement may do a short burst at 41km/h to assume the pace position. This breaks the model.
Political debates have me rolling my eyes so much I think I got optical whiplash. I should sue. - Foamy The Squirrel
You read, but you did not comprehend. Yes, their experimental setup accounted for this.
The short form is that they played with the wave. Think of it as giving a (planar) sine wave a sideways tug. At any given moment it's still traveling at c, but it's taking a curvier path to get there.
“Our work highlights that, even in free space, the invariance of the speed of light only applies to plane waves. Introducing spatial structure to an optical beam, even for a single photon, reduces the group velocity of the
light by a readily measurable amount.”
How they made their light fly in curlicues is definitely interesting, but as for the results, I can only say: Go home, photons, you're drunk.