Can free electrons absorb photons?

[Kirk Gregory Czuhai]

The photon easily changes the atom's internal state but can't so easily change that of the free electron. This is the crux of the difference. Without changing the internal state of the electron it can't be "really" absorbed, a photon must be emitted just about immediately otherwise energy-momentum couldn't be conserved.

 

In practice, the photon may be scattered by the free electron but not actually absorbed by it.

 

how does one change the internal state of an electron? At least the undressed, bare particle is thought to have no internal structure and therefore no dimensions, i.e. a point correct?

and as i think just how much we understand about the vacuum state and its causing dressed particle states i get lost and realize even then whatever represention is given them that it is an approximation at best.

 

looked at from the wave nature of those under discussion:

the photon travels at the speed of c via an electromagnetic wave. NOW would anyone say that if this wave nears a free electron that it would not influence the free electron's position? After all the electromagnetic force has an infinite range because its force carrier is the photon and the photon is thought to have zero mass.

 

and intuitively we are stretching things a bit by thinking that the photon could not possibly have an energy loss just by having tranversed a great deal of the distance of the universe by interaction with the virtual particles of the vaccum state or something else like the dark energy or dark mass which constitutes our universe or at least we figure 95% of it that we have no consensus as to what these even are.

 

so to me at least i am not convinced that the shift in the spectra with distance traveled is only due to the universe's expansion.

 

thank you for your kind responses so far but some things are easier to accept on faith than others.

:cup:

[Qfwfq]

how does one change the internal state of an electron? At least the undressed, bare particle is thought to have no internal structure and therefore no dimensions, i.e. a point correct?

That was the point. No change of its internal state, therefore it can't absorb a photon.

 

When an electron is accelerated by an electric field, this may be seen as it absorbing virtual photons but the energy-momentum of these isn't a null 4-vector as it is for a real photon.

[Kirk Gregory Czuhai]

That was the point. No change of its internal state, therefore it can't absorb a photon.

 

When an electron is accelerated by an electric field, this may be seen as it absorbing virtual photons but the energy-momentum of these isn't a null 4-vector as it is for a real photon.

That was the point. No change of its internal state, therefore it can't absorb a photon.

 

When an electron is accelerated by an electric field, this may be seen as it absorbing virtual photons but the energy-momentum of these isn't a null 4-vector as it is for a real photon.

 

first i would like to say that i do not hate science as i feel the miracles of science have touched my life and the ones i love more than once in very

beneficial ways; life and death actually.

 

but here we are and photons travel via electromagnetic waves, with speeds and electrical and magnetic component amplitudes dependending on the medium through which the wave travels. AND IN THE CASE of a vaccum the physics DEFINE the value for the speed of the wave.

 

the energy of a photon = E = h * f where energy could be in Joules or electron volts or some other energy unit and h is Planck's constant suitably expressed, and f is the frequency of the wave in hertz, cylces per second.

 

but as described above and i can not with certainty recall what a null four vector is now but by a null four vector are you just implying that the photon's velocity is expressed by them since particles without mass travel such velocity vectors or do not exist BUT when energy of a photon is particaly taken the photon

does not slow down but its frequency of its associated electromagnetic field is just reduced so this four vector discussion

is fog to what we are trying to figure out. when a photon gives up enegy it frequency is redshifted so are you saying you agree with me, any energy taken from a photon redshifs it. So if it causes any change in a passing particle its redshifted right?

but as you say the electron could change its velocity in a continuous way as well from the em wave with the action of virtual particles produced by both the wave and i presume the travelilng photons, what loses energy so that energy is conserved? would not a photon or more be lowered in frequency as soon as the increase in electon momentum was achieved to do this ==>

a redshift?

 

if not from the photon or photons where does the energy from these virtual photons/electron come from to give to the free electron increased energy so that the original causes of the situation do not lose enegy and become red-shifted!?

 

the conservation of energy go awol? :eek:

 

peace and love,

and,

love and peace,

(kirk) kirk gregory czuhai :singer: :) :girl_hug: :love:

o

[Qfwfq]

It isn't essential to consider redshift, if you imagine the photon as a non-quantum "little ball" that just happens to be massless and apply only SR dynamics.

 

What is essential is that the energy-momentum vectors must be conserved, so the change in that of the electron must be equal to that of the incoming photon. But, as the latter is a null 4-vector, this can't be without a change in the electron's mass. It's easy to do by choosing coordinates such that the electron is initially at rest (using natural units, c = 1):

 

[math]m_e^2 = E^2 - p^2 = E^2[/math] (p = 0 at rest)

 

[math]\Delta E^2 - \Delta p^2 = 0[/math] (change is a null vector)

 

[math]m_e^2 = (E + \Delta E)^2 - \Delta p^2 = E^2 + 0 + 2E\Delta p[/math]

 

Unless, of course, the photon's momentum vanishes.

[Aireal]

Kirk Gregory Czuhai

 

I am not sure if this will help. An electron that is accelerated by an electric field is not an accurate compairsion to a free electron hit by a photon.

 

Electromagnetic fields are not the same as the scalar fields of particles in free space in their interactions. More on this point I can not add.

 

The electron is a real particle and has mass, the photon is a virtual particle, and as Qfwfq pointed out, can considered massless with only SR synamics. Gfwfq lost me at the null 4-vector point also, as my math is not what it should be, but I think it ties in with the above point. Hope this tidbit helped.

[Kirk Gregory Czuhai]

Kirk Gregory Czuhai

 

I am not sure if this will help. An electron that is accelerated by an electric field is not an accurate compairsion to a free electron hit by a photon.

 

Electromagnetic fields are not the same as the scalar fields of particles in free space in their interactions. More on this point I can not add.

 

The electron is a real particle and has mass, the photon is a virtual particle, and as Qfwfq pointed out, can considered massless with only SR synamics. Gfwfq lost me at the null 4-vector point also, as my math is not what it should be, but I think it ties in with the above point. Hope this tidbit helped.

and this is why Physics is not the reality but just various curve fits or mathematical models to small portions of the what is there is not of what appears.

and i contend that during the travel across billions of light-years of distance the photons could very well lose energy in a continuous over all fashion that would be similiar to gravitational red shift thus supplementing its effect or even the cause replacing it! its time to realize that our cosmological physics is still in its infancy at best and i wonder how less than ten pounds of gray matter will ever under stand the rest of the matter anyway.

too much thinking and too little drinking~ :beer:

chow