# OFFTOPIC: physics question

jim bell jdb10987 at yahoo.com
Mon May 13 12:07:58 PDT 2019

The speed of light in a vacuum is fixed, and is called 'c', about 299,272 kilometers per second.The speed of light (including radio waves, and all other frequencies) in a vacuum does not vary with wavelength.One way that astronomers know this to be true is displayed by the flash of a supernova, which can be seen billions of light-years away.  If the speed of different colors of light through a vacuum varied by frequency, then that flash would relatively quickly appear to change color over a period of minutes, hours, or days.It doesn't, showing that all the frequencies of light travel as the same speed in a vacuum.
The speed of light in gases is slightly slower:  It is about 0.05% lower in air at sea level.
The speed of light in typical glass is about 2/3's of 'c'.
In typical glass, the speed of light varies a bit with wavelength.https://en.wikipedia.org/wiki/Prism

For many decades, diffraction gratings have been used to separate colors of light.
https://en.wikipedia.org/wiki/Diffraction_grating

The shiny surface of a CDROM or DVD approximates that of a diffraction grating,You can aim the beam from a laser at a CDROM or DVD to see different reflections.If you start with a light beam generated with a LED (Light Emitting Diode; which has a much wider spectrum than a laser) you could see the spectrum it possesses.
Jim BellFrom that Wikipedia article on 'c']
"The speed of light in vacuum, commonly denoted c, is a universal physical constant important in many areas of physics. Its exact value is 299,792,458 metres per second (approximately 300,000 km/s (186,000 mi/s)[Note 3]). It is exact because by international agreement a metre is defined as the length of the path travelled by light in vacuum during a time interval of 1/299792458 second.[Note 4][3] According to special relativity, c is the maximum speed at which all conventional matter and hence all known forms of information in the universe can travel. Though this speed is most commonly associated with light, it is in fact the speed at which all massless particles and changes of the associated fields travel in vacuum (including electromagnetic radiation and gravitational waves). Such particles and waves travel at c regardless of the motion of the source or the inertial reference frame of the observer. In the special and general theories of relativity, c interrelates space and time, and also appears in the famous equation of mass–energy equivalence E = mc2.[4]

On Sunday, May 12, 2019, 7:00:36 PM PDT, \0xDynamite <dreamingforward at gmail.com> wrote:

Sorry for this little diversion, but it has occurred to me that
physics has a bit of a logical contradiction and I think highly of the
group's rational faculties here to help me sort this out.

If light travels at a. different speed for different colors in order
to account for the rainbow of a prism, how fast is the. speed of light
then?  Is there real physics to optics?  How can light know what
direction to bend after it leaves the lens?

Am I the first to discover these discrepancies?  I know everyone tends
to bow to the priesthood on these topics, but I believe the
Establishment has failed to deliver us a secular revolution.

Cheers,

Marcos

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