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Subject: Re: You use different lenses underwater because the speed of light is different




"Xiaoding" wrote in message
news:1146231182.698875.302260@j33g2000cwa.googlegroups.com...
> "In their laboratory, Hau and her colleagues have been able to slow a
> pulse
> of light, and even stop it, for several-thousandths of a second.
> They've
> also created a roadblock for light, where they can shorten a light
> pulse by
> factors of a billion.
>
>
> "This could open up a whole new way to use light, doing things we could
> only
> imagine before," Hau said. "Until now, many technologies have been
> limited
> by the speed at which light travels."
>
>
> The speed of light is approximately 186,000 miles per second (670
> million
> miles per hour). Some substances, like water and diamonds, can slow
> light to
> a limited extent. More drastic techniques are needed to dramatically
> reduce
> the speed of light. Hau's team accomplished "light magic" by
> laser-cooling a
> cigar-shaped cloud of sodium atoms to one-billionth of a degree above
> absolute zero, the point where scientists believe no further cooling
> can
> occur. Using a powerful electromagnet, the researchers suspended the
> cloud
> in an ultra-high vacuum chamber, until it formed a frigid, swamp-like
> goop
> of atoms "
>
> A perfect example of a reporter not having a clue, and then people
> mis-understand what exactly is going on.
>
> This article refers to the "slowing down" of a PULSE of light, not THE
> SPEED OF LIGHT.
> They are two very different things. The reporter is unquallified to
> wrie on this subject.
>

The speed of light is the measurement of how fast what travels?
Light, correct? Whether as a pulse, continuous beam, etc.

Can we agree on that?
I sure hope so.
Light travels at c in a vaccuum.
It is slowed by air, water, or other media.
Can we agree on that?

http://www.physics.upenn.edu/balloon/cerenkov_radiation.html

The blue glow that emanates from the water in which highly radioactive
nuclear reactor fuel rods are stored is caused by the Cerenkov effect. For
fuel rods, much of the radiation they emit is in the form of high energy
electrons. The electrons travel through the water at a velocity greater than
that of light in water and hence cause the characteristic ``Cerenkov glow''.

Or are these folks wrong, also?

The point to which I ws responmding was the person who wrote:
> Honestly, I thought you guys are all joking.
> To sumurise theory of relativity, the speed of light is the universal
> constant, it never changes, through vacuum, air or water. It refracts,
> just no speed bumps...

here's anotehr item:
http://acept.la.asu.edu/PiN/rdg/refraction/refraction.shtml
"The change of direction of light as it passes from one medium to another is
associated with a change in velocity and wavelength. The energy of the light
is unchanged as it passes from one media to another. When visible light in
air enters a medium such as glass, the velocity of light decreases to 75% of
its velocity in air and in other materials the decrease can be even more
substantial."

Let me guess, theyre wrong too, claiming that the velocity of light
decreases to 75% of what it is in air?

To reiterate, the point to which I was replying was
> Honestly, I thought you guys are all joking.
> To sumurise theory of relativity, the speed of light is the universal
> constant, it never changes, through VACUUM, AIR or WATER. It refracts,
> just no speed bumps...

This is incorrect, as I think I've shown.

I hope I'm clear on this

Dennis



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