Re: recoiling photons evidence?

"ralph sansbury" <[EMAIL PROTECTED]> wrote in message
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> "George Dishman" <[EMAIL PROTECTED]> wrote in message
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> > "ralph sansbury" <[EMAIL PROTECTED]> wrote in message
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>
>  RS     Baez FAQ says that some people want to change the
> notation of
> E^2=(m_0)^2c^4+p^2c^2  where p=mv=Ev/c^2. Even in the more
>  recent texts the distinction between rest mass and the mass
> increase
>  due to relativity of a mass in motion is made in the description
>  of the formula if not in the notation.

This is part of what it says:

"These days, when physicists talk about mass in their research,
they always mean invariant mass.  The symbol m for invariant
mass is used without the subscript 0. Although the idea of
relativistic mass is not wrong, it often leads to confusion,
...  Using the word "mass" unqualified to mean relativistic
mass is wrong because the word on its own will usually be taken
to mean invariant mass."

I am over 50 and have never known "mass" to mean anything but
invariant mass. I am aware of the old "relativistic mass"
but have alwys known it as a shorthand notation representing

 m_r = m / sqrt(1 - (v/c)^2)

>  GD It is not a split but a change. It will take a long time
>  for old ways to die out but there is no debate about it.
>  As the FAQ pages say, one of the reasons the term
>  "relativistic mass" is being dropped is because of these
>  confusions that it creates.
>
> RS     The  confusion is in the inadequate concept. The rest mass
> of a photon is zero, its mass in motion due to the relativity
> increase
> is infinity so (1/2)mv^2 =(1/2)mc^4 =infinity times c^4 but also
> hf where f is the frequency is equal to the kinetic energy of the
> moving photon (1/2)mv^2. This says
> that infinity is equal to a finite number. Because of such
> confusion in the concept I am questioning conclusions like you're
> here based on its use.

Now try it the conventional way:

 The mass of the photon is zero. If it could be at rest the
 mass would be zero. When it is moving it is zero. The mass
 of any particle is the same whether it is moving or not.
 When a particle is moving, its total energy is the sum of
 its mass (times c^2) and its kinetic energy.

There you are, no confusion at all.

>       Re a solar sail, this involves much stronger magnetic
> forces than the absorption of radiation by a distant spacecraft
> antenna.
>
> GD  I'm not aware of any magnetic effect on solar sails.
>
> RS    I am aware of the light momentum photon energy argument
> "that when light is emitted from a source there is a recoil
> effect".

Right, and the evidence for this is the Compton Effect
and laser manipulation of particles at small scales, lab
radiometers at medium scales and solar sails at large scale.
All rely on the principle that light carries momentum.

>  But I am suggesting that there is no evidence for cases like the
> 8Watt transmitter on a distant spacecraft and that solar sails
> involve much greater Wattage and that light pressure on mirrors
> etc involve oscillations in the source and the receiver/reflector
> acting on each other. That is  the mechanism(see Feynman Lectures
> p34-10), Bvq, on oscillating charge moving up and down at
> velocity v in the direction of the propagation of the fields E
> and B causes a driving pressure in the direction of the light
> beam which is called light pressure.

None of that suggests that light doesn't carry momentum,
it is just a classical description of the mechanism.

>    Do you know any evidence besides the blanket application of
> the momentum argument showing
> such pressure effects in cases where the emission of photons
> occurs in an isolated source like the spacecraft?

Pressure is nothing but the transfer of momentum and
the examples I have suggested all require momentum
transfer. If you want to use classical field theory
to describe it, there should be no problem in principle
but it might be difficult in practice.

I am still not clear what you are looking for. You started
this thread by saying:

>    Instances of light pressure on reflective surfaces and Compton
> like scattering of xrays at lower frequencies with the missing
> energy transformed into the linear movement of the electron
> suggests a recoil of the electron but not of the photon.

That is incorrect since the relationships in the Compton
Effect require both the incoming and outgoing photon to
carry momentum. That is your evidence.

George