Way to go, Scotland. You friggin' broke physics!

[bhsup]

So if light suddenly goes slower in a vacuum, is it going slower than the speed of light?! But it's light, so the the speed it is going must be whatever it is going!! GAH!

Scientists slow the speed of light

A team of Scottish scientists has made light travel slower than the speed of light.

They sent photons - individual particles of light - through a special mask. It changed the photons' shape - and slowed them to less than light speed.

The photons remained travelling at the lower speed even when they returned to free space.

The experiment is likely to alter how science looks at light.

The collaborators - from Glasgow and Heriot-Watt universities - are members of the Scottish Universities Physics Alliance. They have published their results in the journal Science Express.

The speed of light is regarded as an absolute. It is 186,282 miles per second in free space.

Light propagates more slowly when passing through materials like water or glass but goes back to its higher velocity as soon as it returns to free space again.

Or at least it did until now. <<< See?! They broke it! >>>

^ more to article at link...

 

[Kyriakos]

Cool. Besides, why should light have the same speed no-matter* what in the first place.

*cwhatididthere

 

[uppi]

I am a bit annoyed by the 'they slowed the speed of light' story the press is running with. They did not do anything special. They point out and showed experimentally that in common situations light pulses are slower than the speed of light. If you think about it, it's obvious, but apparently nobody thought about it before.

As a side note, they did not measure the slowdown in vacuum, but in air, where light is slowed down anyway. Regarding their effect there is not much of a difference, though.

 

[Terxpahseyton]

I am a bit annoyed by the 'they slowed the speed of light' story the press is running with. They did not do anything special. They point out and showed experimentally that in common situations light pulses are slower than the speed of light. If you think about it, it's obvious, but apparently nobody thought about it before.

That is not what the article said. The article is pretty clear about how they had showed that they could alter the speed of light itself, by changing the photons. I am not sure what you even mean by "common situations".

 

[uppi]

That is not what the article said. The article is pretty clear about how they had showed that they could alter the speed of light itself, by changing the photons.

Exactly. That is why I am annoyed by the article.

I am not sure what you even mean by "common situations".

Situations like putting light through a lens - not exactly a new technique in the field of optics.

The experiment is pretty neat, but claims like "The experiment is likely to alter how science looks at light." are way too much exaggerated.

 

[Kyriakos]

Speaking of optics, and experiments: Uppi (or anyone else knowing) is there any info about any notable effect of light if it entered a perfect ellipsoid through one of its focal points as a single ray? (i had heard some time ago that supposedly it would exist as a single ray through the other focal point, and cause an illusionary effect for an observer at specific position in that space).

 

[uppi]

Speaking of optics, and experiments: Uppi (or anyone else knowing) is there any info about any notable effect of light if it entered a perfect ellipsoid through one of its focal points as a single ray? (i had heard some time ago that supposedly it would exist as a single ray through the other focal point, and cause an illusionary effect for an observer at specific position in that space).

A single ray (if such a thing would exist) would do nothing special. It would go through the other focal point, but nothing would happen with the ray. With multiple rays going into different directions you could get an effect, because they all meet again at the other focal point. You could probably create an optical illusion with that.

The effect is sometimes used in acoustics: if you have an elliptic room and you stand at one focal point you can clearly hear quiet sounds made at the other point.

 

[Kyriakos]

^Might be interesting in a setting where a given optical event (ie an image/mirage/spectre) is calculated to be the result of merely some particular repetition of rays shooting through one focal point to the other. Cool as a sort of pseudo-isomorphic event, so to speak.

 

[bhavv]

This one time I used to understand physics really well.

Then it got complicated.

 

[BenitoChavez]

Complicated? Oh yes. Which is why the researchers say it might help to think of a bicycle race.

The peloton - the main bunch of riders - may be moving at a constant speed. But within the bunch an individual rider may be moving more slowly, dropping back for a rest or a drink.

Meanwhile other riders in the bunch are moving faster to get to the front.

The bunch is a beam of light, travelling at - yes - the speed of light. The riders are photons, travelling at their individual speeds.

So if I'm reading this right and we take this analogy literally, then that means some photons can travel faster than light as well? Because if some photons slow down, then to keep the average speed of the group constant some photons would have to speed up.

 

[uppi]

So if I'm reading this right and we take this analogy literally, then that means some photons can travel faster than light as well? Because if some photons slow down, then to keep the average speed of the group constant some photons would have to speed up.

Although the article does its best to suggest otherwise, the average speed of the group does slow down:

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.

so, no there is no speeding up of photons to superluminal speed. That would be a very different claim and in that case the hype generated by this paper would be justfied.

In fact, the effect they describe in their paper is what is needed to avoid superluminal photons: Imagine a large lens, that focuses a beam of light to a small spot. You can think of the beam as a triangle (It's not, but you can get close enough) with two vertices at the edge of the lens and the third vertex at the focus. Now imagine a slice of the beam going through the lens to the focus. If the slice was travelling at the speed of light in the center of the beam, it would have to go faster than light at the edges, because the edges of a triangle are always longer than the height of the triangle. Instead the light slows down a bit and physics as we know it is safe (despite claims to the contrary).

 

[Midnight-Blue766]

I think I remember reading something like this in the Guiness Book of World Records. Ten years ago.