Text 3632, 85 rader
Skriven 2005-04-12 13:55:58 av Rich Gauszka (1:379/45)
   Kommentar till text 3628 av Gary Britt (1:379/45)
Ärende: Re: Speed of light?
===========================
From: "Rich Gauszka" <gauszka@hotmail.com>

 It's only constant traveling through a vacuum.

http://www.physlink.com/Education/AskExperts/ae23.cfm

If, indeed, the speed of light is constant,why is it usually listed for a
vacuum?

 Answer

In a medium other than a vacuum, light propagates by a cascade of interactions
with the molecules or atoms that make up the medium. Photons, the 'particles'
of light, are absorbed and re-radiated (by atoms or molecules), absorbed again
and re-radiated again, and over-and-over as they pass through the medium.

Since each absorption and re-radiation interaction takes time, though it be
very little, the cascade cannot travel as fast through a material medium as
light can in a vacuum. Light travelling in a vacuum does not have to 'waste
time' being repeatedly absorbed and re-radiated. For this reason, the speed of
light in a material medium is generally less than c, and will exhibit a
specific value that depends upon the characteristics of the medium.


 "Gary Britt" <zotu@nospamforme.com> wrote in message
news:425bf16d@w3.nls.net...
> <g>  At absolute zero?
>
> Gary
>
> "Adam" <acompletemystery@somewhere.org> wrote in message
> news:425bedc2$1@w3.nls.net...
>> Gary Britt wrote:
>> > I'm with you on that one.  Didn't Einstein say light's speed was a
> constant
>> > and couldn't be changed?
>> >
>>
>> I wonder if a nuke in the cold only goes.....pssssssssssssttt & gets a
>> bit warm.
>>
>> <G>
>>
>>
>> Adam
>>
>> > Gary
>> >
>> > "Adam" <acompletemystery@somewhere.org> wrote in message
>> > news:425bbd54$1@w3.nls.net...
>> >
>> >>http://www.theregister.co.uk/2005/04/12/frozen_light/
>> >>
>> >>"Hau has discovered, in her work on slow light, that a BEC can preserve
>> >>the phase and amplitude of a light pulse. In normal matter, these
>> >>properties would be smeared out, destroying any information content. If
>> >>a device can be built that preserves that information, Hau argues, it
>> >>could be developed into the CPU of an optical computer.
>> >>
>> >>In 2003 Hau's research group slowed light from 186,000 miles per second
>> >>to around the speed of a bicycle. Later, they froze light altogether,
>> >>using a cloud of ultra-cold sodium atoms. Dr. Hau argues that frozen
>> >>light could also have applications for memory storage on optical
>> >
>> > computers"
>> >
>> >>
>> >>Slow light?
>> >>
>> >>Adam
>> >
>> >
>> >
>
>


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