# How can the speed of light be 38 MPH??!!!???

I just read something in the paper that’s freaking me out a bit. It seems that a team of scientists at Harvard managed to get within five billionths of a degree of absolute zero (-273.15 degrees Celsius) and thus managed to reduce the speed of light to 38 miles per hour. Would someone PLEASE explain in a manner intelligible to a layman how this is possible to I can get some sleep tonight???!!!??? Why would extreme cold reduce the speed of light to practically nothing???!!!??? Oh, yeah, and how exactly did they achieve that degree of cold?

The sodium they cooled down to that point became something called a Bose-Einstein Condensate. Basically, so far as I understand it,the wave functions of the individual atoms collapsed into a single wave. This rendered the material transparent to light with a wavelength that resonated with this wave function. They shined a laser tuned to that frequency into the sodium, and because of the way the atoms were behaving the light had to take the long way around every atom. Or something like that.

Pretty neat, figuring that sodium is opaque at temperatures above that where a Bose-Einstein Condensate forms.

Anyway, light passing through ANY medium slows down. The “speed of light” so often referenced is the speed of light in a vaccuum.

So how come it takes light only 8 minutes (assuming a normal speed of light of 186,000 miles per second) to get to the earth from the sun, through outer space which is mostly a vacuum? Huh???

The 186,000 miles per second thing is the speed of light in a vacuum … the 38 mph speed is the speed in a super-duper dense medium. (I’m not trying to varify they 38 mph speed, I’m just trying to sum up what Dr. Fi. was saying.)

I don’t want to make people think like me, I want them to think like me of their own free will.

I have found an article about the experiment with the speed of light within a Bose-Einstein condensate, in case anyone is interested in reading it. The speed of light, which is a fundamental constant in a vacuum, is different when it is propagated through any medium. Glass lenses are able to bend light because of the inherent fact that the change in velocity at the interface between glass and air causes the light to bend if the surface is not perpendicular to the direction of the light. Bose-Einstein condensates are simply the most striking example of difference in speed. The speed in a vacuum is the greatest possible speed that in any other medium will be less.

## <P ALIGN=“CENTER”>Tris</P>

Have a place for everything and keep the thing somewhere else. This is not advice, it is custom.
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Um, Dougie… What are you asking exactly? The Sun is about 93,000,000 miles from Earth. The speed of light in a vacuum is 186,000 mps and there are sixty seconds in a minute, so 93,000,000 / 186,000 / 60 = 8.333 minutes. What’s the problem?

Stephen
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If you put a brick in a light’s path, the speed drops to 0. wow

I just read that article that Trisk found, and all I can say is – damn, I’m amazed.

HANDY FOR PRESIDENT.

So that’s how a laser beam can be used to freeze something. And next they’re going to try to slow light down to 120 feet per hour?!

What does a slowed-down light beam look like? It wasn’t clear from the article.

>< DARWIN >
__L___L

*dougie_monty: So how come it takes light only 8 minutes (assuming a normal speed of light of 186,000 miles per second) to get to the earth from the sun, through outer space which is mostly a vacuum? Huh??? *

186,000 mi/sec * 60 sec/min * 8 min = 89,280,000 (mi/sec)*(sec/min)*min
= 89,280,000 miles

That’s about how far we are from the Sun.

oops, sorry Stephen. I guess I should scroll down more before I answer.

Handy: What if it’s got holes in it?

“What does a slowed-down light beam look like? It wasn’t clear from the article.”

look like?

I don’t think anyone has seen a ‘slowed down light beam’. The BEC is glowing brightly to begin with and when the light exits, it resumes normal (for air/glass/etc.) speed. My own WAG is that in the BEC it would look like a little light saber, slowly growing in length, until it reached the other side.

Stephen
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You see “slowed down light beams” all the time. It’s called “refraction.”

In other words, light bends in a lens because it slows down as it passes through glass. The difference in speed isn’t much, but it’s enough to produce noticeable effects.

## I’d guess that if you slowed down light to 38 MPH, the refraction will be even more noticeable.

“East is east and west is west and if you take cranberries and stew them like applesauce they taste much more like prunes than rhubarb does.” – Marx

Read “Sundials” in the new issue of Aboriginal Science Fiction. www.sff.net/people/rothman

Who has seen light anyway? Shucks, few can even define it, but hey, at least we can see it reflecting off things.

Something has been bugging me about this report. The angle of refraction is related to the ratio of the speeds of light in the 2 media involved, for example, air & the Bose-Einstein Condensate. The bigger the slowdown the sharper the refraction angle. With this much slowdown, it seems like you would need an angle if incidence of almost exactly 90 degrees, or the light would get reflected & wouldn’t pass thru.

Of course, I’m tacitly assuming that the B-E Condensate has a suface, which it doesn’t really. More of a fuzz. The location of the individual atoms is severely smeared due to the fact that their momentum is so precisely determined to be near zero, and the Uncertainty Principle.

Can someone shed some light?

I think dougie got distracted by the glare off the vacuum of space/temperatureof space/absolute zero deal,which is a whole nother thread or subeject that cecil addressed. All I know is ,as my grandmammy Light Horse Harper Lee used to say, Light Beer sux.

“Pardon me while I have a strange interlude.”-Marx

The ninety-degree angle referred to in the article is the angle of a laser beam introduced into the B-EC across the path of the beam to be measured. For reasons I barely comprehend, and cannot hope to explain the presence of the first laser is a part of the conditions being examined, which produce the slow speed for the second light.

## <P ALIGN=“CENTER”>Tris</P>

Politicians are the same all over. They promise to build a bridge even where there is no river.
Nikita Khrushchev