Scientists slow down the speed of light travelling in free space

This is weirdly interesting.

Scientists slow down the speed of light travelling in free space

Quote :

The researchers found that one photon reached the finish line as predicted, but the structured photon which had been reshaped by the mask arrived later, meaning it was travelling more slowly in free space. Over a distance of one metre, the team measured a slowing of up to 20 wavelengths, many times greater than the measurement precision.

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.

The description makes no sense -- if "traveling through he mask" slows them down as they traverse the "mask" -- whatever that is -- there's no explanation here for why the photons don't resume the SOL afterward.

Maybe the article writer was as baffled as me.

I would like to know what they mean by "mask." Is it an electromagnetic interference? I can't think of another type of mask the could affect a proton. It would also be nice if they knew, and if so describe, what causes the slowdown. They did say, "...the effect has a solid theoretical foundation" but they don't say what that foundation is. Bummer.

It's been a very long time since I have delved into physics, but unless the science has changed, or I am remembering incorrectly, a proton is always traveling at c. The time elapsed between the creation of the proton and the proton attaining c is zero. And that speed is constant for all the time that the proton is in open space.

However, the writer says, "The effect of passing the light through the mask is to limit the top speed at which the photons can travel." That would indicate that what I have been taught, that the speed of a proton is created and maintained by the inherent quantum properties of the proton, is incorrect.

Or else the "structured proton" as they call it, has been modified into something else.

Or -- real possibility here -- the writer didn't know shit from shinola.

I wouldn't make that statement just yet, but I do believe the article is incomplete and would be much more interesting, to me at least, if it contained what I think is required supporting material.

Here's the abstract from Science Express. Full article requires a subscription.

Quote :

Abstract

That the speed of light in free space is constant is a cornerstone of modern physics. However, light beams have finite transverse size, which leads to a modification of their wavevectors resulting in a change to their phase and group velocities. We study the group velocity of single photons by measuring a change in their arrival time that results from changing the beam’s transverse spatial structure. Using time-correlated photon pairs we show a reduction of the group velocity of photons in both a Bessel beam and photons in a focused Gaussian beam. In both cases, the delay is several micrometers over a propagation distance of the order of 1 m. Our work highlights that, even in free space, the invariance of the speed of light only applies to plane waves.

If I understand all of this, then the title of the article is misleading. They didn't slow down the speed of light, only the speed of some photons within a beam of light.

Way over my head, chief.

In addition to LLS scientists have also apparently achieved FTL.
http://www.sciencedaily.com/releases/2010/01/100126175921.htm

Much easier to understand, and more likely as the photons only achieve a faster speed within the material. Very reasonable.

Quantum physics makes my brain ache.

You should see the incredibly tiny wrenches that quantum mechanics use.

Metric I can see, but tiny?