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Relativity and Photon Acceleration
Name: Alan
Status: other
Age: N/A
Location: N/A
Country: N/A
Date: N/A
Question:
I have noted a question posed by Mike T and
answered by Alcir Grohmann, Vince Calder, and Ken Mellendorf.
(http://www.newton.dep.anl.gov/webpages/askasci/phy00/phy00391.htm)
Mike T's question is, "How do emitted photons instantaneously
travel at the speed of light since they were not accelerated? At
one instant there is no photon, and at the next instant, it
miraculously is already travelling at the speed of light."
I have noted sections of Alcir Grohmann's answer "...When the
photon appears it behaves like all EM waves. It does not need to
be accelerated. ...", and of Ken Mellendorf's answer, "...We do
not know whether it requires any time at all." ('It' refers to a
change to or from a photon.)
I have recently read Einstein's Theories of Relativity, and it
seems to me that the primary impetus of the Special Theory is "The
Apparent Incompatibility of the Law of Propagation of Light with
the Principle of Relativity", specifically the incompatibility in
regard to "The Theorem of the Addition of Velocities Employed in
Classical Mechanics."
Velocity is distance per unit of time. If the unit of time
measured is zero, the only rational value for velocity is also zero.
Here is my problem. If a) EM waves do not require acceleration or
if b) 'it' does not require any time at all, and instantaneous
velocity of any object is zero, emitted light cannot inherit the
velocity of the object transmitting the light.
OK, here is my question. Does the obvious effectiveness of the
Lorentz transformation mean that light is NOT instantaneously
propagated and thus can inherit the velocity of the object
emitting the light - in other words, 'the change' DOES require time?
Replies:
You have put your finger on a "technical issue" that is usually
neglected in introductions to the interaction of light and matter --
and the reason for the neglect is that the "answer" is buried in the
"details" which become both conceptionally and mathematically
challenging. The first issue is that quantum mechanics -- the
mechanics that apply to atoms, molecules, and smaller -- does not
lend itself to our macroscopic intuition. Consequently, we have to
follow "the math" and see where it leads. The downside of that is a
description that is not intuitively "satisfying". But that is the
tradeoff. Given the major "audience" of NEWTON sometimes you have to
trade rigor for comprehension. In fact "transitions" are not
instantaneous, but to dig into the details requires a degree of
mathematical sophistication that the 'audience' usually does not
have. For those who care to get into the 'real' reasons, you can
start with:
http://jchemed.chem.wisc.edu/JCEWWW/Articles/DynaPub/DynaPub.html
The issue is: How many of us have the sophistication to get into the
"explanation"?
Vince Calder
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Update: June 2012
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