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ToSeek
2003-Apr-01, 05:15 PM
Not April Fool's:

Ultra-simple Desktop Device Slows Light to a Crawl (http://www.spacedaily.com/news/lightspeed-03a.html)

I'm putting in my order for "slow glass" today.

Laser Jock
2003-Apr-01, 05:54 PM
I was wondering if this would pop up here. It's not really astronomy, so I wasn't going to say anything when my research started showing up on sites all over the web. But since ToSeek brought it up ... :D

If you want a copy of the PRL that explains it a lot better, go here:

http://www.optics.rochester.edu/workgroups/boyd/nonlinear.html

click on "Published Papers," then click "View Papers by Date," and it's the only paper from our group in 2003.

tvelocity
2003-Apr-01, 06:33 PM
Very interesting. Sounds to me like such technology could be used in optical computers. But the other article on the same page was even more intriguing, not to mention related to astronomy:

http://www.spacedaily.com/news/lightspeed-01b.html

SeanF
2003-Apr-01, 07:38 PM
I have a technicality question (or maybe this is actually a grammar question) tangentially related to this article. About half way down the page, it says this:

Light passing through a window is 1.5 times slower while moving through the glass . . .

Can someone explain to me what "1.5 times slower" actually means? I can only assume they mean it's travelling at about .667c, but is this really correct usage of words like "times" and "slower"? :)

JS Princeton
2003-Apr-01, 08:12 PM
It's utter laziness. The reason they used this funny nomenclature is because the common measurement for such things is to use the index of refraction which for glass is about 1.5. One of the interpretations of this number is the ratio of the speed of light in the vacuum to that of the material. Lazy writers might say it's "1.5 times slower". Sometimes science writing can be bad in terms of syntax as opposed to science.

Laser Jock
2003-Apr-01, 08:17 PM
Light passing through a window is 1.5 times slower while moving through the glass . . .

Can someone explain to me what "1.5 times slower" actually means? I can only assume they mean it's travelling at about .667c, but is this really correct usage of words like "times" and "slower"? :)

You are correct that light travels at about 0.667c in glass. It's trying to explain the index of refraction without actually using those words, and the result is a little awkward. If a car was going 30 kph and another car was going 60 kph, we would say that the second is going twice as fast. Would we then say that the first car is going twice as slow? Perhaps it would be better if the article said "1.5 times slower than light in a vacuum." Or maybe just say refractive index of 1.5 and hope the reader has a clue.

russ_watters
2003-Apr-01, 08:23 PM

Iain Lambert
2003-Apr-03, 10:30 AM
Speed of light = 127 mph

Thats what you get for storing your speed in a signed integer :D

Mainframes
2003-Apr-03, 11:56 AM
Light passing through a window is 1.5 times slower while moving through the glass . . .

Can someone explain to me what "1.5 times slower" actually means? I can only assume they mean it's travelling at about .667c, but is this really correct usage of words like "times" and "slower"? :)

You are correct that light travels at about 0.667c in glass. It's trying to explain the index of refraction without actually using those words, and the result is a little awkward.

I may have got this totally wrong in my head but here goes - the light isn't actually travelling at 0.667c but in fact takes 1.5 times as long to pass through the glass because it is travelling further due to interactions with the material within the glass?

Moose
2003-Apr-03, 01:22 PM
Speed of light = 127 mph

Thats what you get for storing your speed in a signed integer :D

Dang. You beat me to it. :-?

Reacher
2003-Apr-03, 02:34 PM
Well, thats interesting... however, they mentioned a controlled condition at a temperature that causes all attoms to act together, and it sounds to me like they're talking abaout producing absolute zero( 0 kalvins, or 1 kalvin... no, im pretty sure its 0), and so far as i know, thats unproduceable. totally impossible. someone, please prove me wrong.

Iain Lambert
2003-Apr-03, 02:43 PM
That sounds to me like a Bose-Einsein condensate, which actually happens a little bit above 0 degrees K. Basically, as you cool the atom the wave spreads out a bit, and this happens when the waves start overlapping. Here is a natty little transcript on the stuff (http://physics.nist.gov/Pubs/Bec/j4cornel.pdf).

Laser Jock
2003-Apr-03, 02:57 PM
I may have got this totally wrong in my head but here goes - the light isn't actually travelling at 0.667c but in fact takes 1.5 times as long to pass through the glass because it is travelling further due to interactions with the material within the glass?

But if it takes 1.5 times longer to get through an eqivalent distance of glass, isn't that the same as slowing it down? Yes, the slowing is caused by the interaction with the atoms, but the light itself is slow. That is why when you send a particle through glass (or water) at .9c, it produces Cherenkov(sp?) radiation.

Mainframes
2003-Apr-03, 03:04 PM
What i mean is that the light is travelling further because of the interactions, ie it is changing direction more often. Sort of like going from the east coast of the US to the West coast but visiting loads of different cities along the way. In essence you've travlled x miles (don't know distance from coast to coast) but in reality you've actually travelled x+y miles....

ToSeek
2003-Apr-03, 03:29 PM
What is intriguing is the notion that even the speed of light in a vacuum is retarded through interactions with virtual particles. If those particles could somehow be suppressed, as with the Casimir Effect (I think that's what it's called), then light might actually go faster.

JS Princeton
2003-Apr-03, 06:06 PM
and it sounds to me like they're talking abaout producing absolute zero( 0 kalvins, or 1 kalvin... no, im pretty sure its 0), and so far as i know, thats unproduceable. totally impossible. someone, please prove me wrong.

0 Kelvin is indeed impossible to reach. This is because of a little thing called zero-point energy fluctuations. Even if one could remove all the abient energy from the system, the Heisenberg Uncertainty Principle says you are not going to be able to determine both the position and the momentum of a particle. The effect of this is that your particle which should stay in one place has to move around a bit. Sine it's moving, you can measure a temperature and you are no longer at 0 K.

Bose-Einstein condensates get very close to 0 K but never reach it.

tracer
2003-Apr-04, 03:21 PM
Lazy writers might say it's "1.5 times slower".
Pedantic-but-obfuscating writers might say it's "1.5 divided-by faster."

kilopi
2003-Apr-04, 04:11 PM
Lazy writers might say it's "1.5 times slower".
Pedantic-but-obfuscating writers might say it's "1.5 divided-by faster."
Would "two-thirds slower" be better understood than "1.5 times slower"? I think I've seen it that way a lot of times.

What i mean is that the light is travelling further because of the interactions, ie it is changing direction more often. Sort of like going from the east coast of the US to the West coast but visiting loads of different cities along the way. In essence you've travlled x miles (don't know distance from coast to coast) but in reality you've actually travelled x+y miles....
We talked a bit about that in this thread (http://www.badastronomy.com/phpBB/viewtopic.php?p=62471&highlight=atmosphere#62471). It is not a simple case of the photon just traveling farther.

SeanF
2003-Apr-04, 05:09 PM
Lazy writers might say it's "1.5 times slower".
Pedantic-but-obfuscating writers might say it's "1.5 divided-by faster."
Would "two-thirds slower" be better understood than "1.5 times slower"? I think I've seen it that way a lot of times.

Nope, I don't like that, either (and, of course, this is all about what I like!), though "two-thirds as fast" would be just fine.

I guess my problem with this terminology is where the baseline is. .5c is "half as fast" as c because it's half as far from zero as c is. 2c is "two times as fast" because it's two times as far from zero.

If we say .5c is "two times as slow" as c, we're saying it's two times what from what? The only thing that's twice the distance from .5 as it is from 1 is 1.5, and I don't think that's our baseline . . .

And, of course, "two times faster" is faster than "two times as fast", so do we mean "1.5 times slower" or "1.5 times as slow"? :)

tracer
2003-Apr-04, 05:17 PM
Would "two-thirds slower" be better understood than "1.5 times slower"?
No, because "two-thirds slower" means the same as "one-third as fast", which is wrong here. "One-third slower" -- or, for that matter, "33% slower" -- would work, however.

kilopi
2003-Apr-04, 05:39 PM
And, of course, "two times faster" is faster than "two times as fast", so do we mean "1.5 times slower" or "1.5 times as slow"? :)
In which case, thn I guess 1.5 times slower would be a negative .5c. Is that an imaginary velocity, or is it in the opposite direction?

ToSeek
2003-May-22, 05:14 PM
Further developments (http://www.sciencedaily.com/releases/2003/05/030522082709.htm), courtesy of NASA

russ_watters
2003-May-23, 03:50 PM
I may have got this totally wrong in my head but here goes - the light isn't actually travelling at 0.667c but in fact takes 1.5 times as long to pass through the glass because it is travelling further due to interactions with the material within the glass?

But if it takes 1.5 times longer to get through an eqivalent distance of glass, isn't that the same as slowing it down? Yes, the slowing is caused by the interaction with the atoms, but the light itself is slow. No. If you drive 60 miles on a highway at 60 miles an hour for one hour to reach a destination 60 miles away, how fast were you driving? If you go to the same location at 60 miles an hour on a different highway thats 120 miles long (its curved) how fast were you driving? 30 miles an hour? No. Still 60 miles an hour. You just took a longer road.

Thats how light works.