From: SFPhysics@aol.com
Date: Tue Oct 17 2000 - 03:36:38 PDT
From: SFPhysics@aol.com Message-ID: <b7.7a6034f.271d85b6@aol.com> Date: Tue, 17 Oct 2000 06:36:38 EDT Subject: Re: Questions about light
> From: "David Lauter" <dyakov@ix.netcom.com>
Question 1:
> "How is it possible to determine the frequency or the wavelength of light?
> (I know you must use Planck's constant, so I suppose a good answer would be
> to explain how Planck figured out his constant. )"
Question 2:
> "If all light in empty space travels at the same speed what happens when
> light falls into a black hole? Doesn't it go faster and faster?"
> And finally,
> "But the light can't come out of a black hole so it must stop. Does light
> stop in a black hole?"
> David Lauter
> Washington High
>>
Hello David:
Here are my answers to the best of my understanding:
1) Early experimental measurements of the wavelengths of light were done with
an instrument called an "interferometer." The interferometer split a light
beam in two then put it back together again with one of the beams being phase
adjustable. A micrometer adjustment allowed the phasing to be measured. So,
if a red spectrum line from a sodium vapor lamp was used, the micrometer
moving the phasing mirror would go half of the wavelength (6700Å) to cancel
out the light beam. The micrometer would have shown a movement of 335nm.
Used in conjunction with spectrometers the interferometer calibrated the
spectrometers then the prism in the spectrometers could separate out the
color lines and the angles of refraction indicated the wavelength. Today we
use diffraction gratings as well as prisms to give us refraction angles that
tell what the wavelength of an unknown ray might be.
2) Imagine an object that is so massive that the gravitational acceleration
at some point exceeds 3x10^8m/s (the velocity of light in a vacuum). That is
a black hole gravity well. Traveling toward a black hole you would reach the
point at which the gravity acceleration is faster than the velocity of light
and this is called an "event horizon." Below the event horizon the universe
ceases to be. Time and space don't really exist there. Inside you have a
"singularity" or point of no physical size. The massive star that created
the black hole is no longer in existence. All that is left is the hole where
it dropped out of this space/time continuum and left this universe. To
answer your question then, below the event horizon there is no light and
light going into the gravitational pull of a black hole does not change its
velocity which is always the same while it is in this universe and it ceases
to exist when it crosses the event horizon. However, it is not a simple as
that and there is a gravity induced time dilation thing in conjunction with
the velocity of light that will give one a headache for sure, so I'll quit
here. Lastly, a black hole may best be summed up as the ultimate, "There is
no there there!"
Al Sefl
always willing to help confuse the issue and guaranteed to be correct 50% of
the time..................
Now if Dr. Doherty will correct my misconceptions and
misstatements.............
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