My Professor used to ask this question in oral exams: What happens if
an elektron falls off from a table? Usual answer: The elektron is an
accelerated charge and so it radiates elektromagnetic waves.
I argued that an elektron would not radiate when accelerated by an
gravitational field. The picture that guides me is the following: An
elektron usually radiates because some elektromagnetic force from
outside couples to the charge of an elektron but not to the
elektromagnetic field generated by that elektron. The field tries to
follow the charge and in order to do that it radiates. An infinite
homogeneous gravitational field would accelerate the free falling
elektron in the same way as it would accelerate the elektromagnetic
field of the charge because gravitation does not couple to charge but
energy (field- and massenergy), so an free falling elektron in an
infinite homogenous gravitational field would not radiate.

Another argument is, if an elektron which is accelerated by such a
field would radiate for an observer on earth (let the grav. field of
the earth be an infinite homogenous field in good approximation) then
it would loose some Energy and the observed acceleration would be
less. For a free falling observer the electron would not radiate
(Imagine the observer and the elektron are locked in some dark box -
then there is now way to detect the gravitational field). Then we
arrive at the following paradox. The elektron would radiate in a way
that the free falling observer could not see the radiation, but the
observer on earth would see it (difficult to imagine if the two
observers have the same time and space coordinates) and for the
observer on earth the elektron falls slower then the free falling
observer on the other hand for the free falling observer the position
realtiv to the elektron would not change.
So I am quite sure, that an accelerated elektron in a field discribed
above would not radiate.
Whats your opinion about this

Subject: Radiation of an accelerated elektron
From: (Bastian)
Date: 9/5/2003 7:36 PM US Mountain Standard Time
Message-id:

My Professor used to ask this question in oral exams: What happens if
an elektron falls off from a table? Usual answer: The elektron is an
accelerated charge and so it radiates elektromagnetic waves.
I argued that an elektron would not radiate when accelerated by an
gravitational field. The picture that guides me is the following: An
elektron usually radiates because some elektromagnetic force from
outside couples to the charge of an elektron but not to the
elektromagnetic field generated by that elektron. The field tries to
follow the charge and in order to do that it radiates. An infinite
homogeneous gravitational field would accelerate the free falling
elektron in the same way as it would accelerate the elektromagnetic
field of the charge because gravitation does not couple to charge but
energy (field- and massenergy), so an free falling elektron in an
infinite homogenous gravitational field would not radiate.

Another argument is, if an elektron which is accelerated by such a
field would radiate for an observer on earth (let the grav. field of
the earth be an infinite homogenous field in good approximation) then
it would loose some Energy and the observed acceleration would be
less. For a free falling observer the electron would not radiate
(Imagine the observer and the elektron are locked in some dark box -
then there is now way to detect the gravitational field). Then we
arrive at the following paradox. The elektron would radiate in a way
that the free falling observer could not see the radiation, but the
observer on earth would see it (difficult to imagine if the two
observers have the same time and space coordinates) and for the
observer on earth the elektron falls slower then the free falling
observer on the other hand for the free falling observer the position
realtiv to the elektron would not change.
So I am quite sure, that an accelerated elektron in a field discribed
above would not radiate.
Whats your opinion about this


See section 2 of chapter 7 at
http://www.geocities.com/zcphysicsms/chap7.htm#BM7_2

"WaiteDavid137" wrote in message ...
Subject: Radiation of an accelerated elektron
From: (Bastian)
Date: 9/5/2003 7:36 PM US Mountain Standard Time
Message-id:

My Professor used to ask this question in oral exams: What happens if
an elektron falls off from a table? Usual answer: The elektron is an
accelerated charge and so it radiates elektromagnetic waves.
I argued that an elektron would not radiate when accelerated by an
gravitational field. The picture that guides me is the following: An
elektron usually radiates because some elektromagnetic force from
outside couples to the charge of an elektron but not to the
elektromagnetic field generated by that elektron. The field tries to
follow the charge and in order to do that it radiates. An infinite
homogeneous gravitational field would accelerate the free falling
elektron in the same way as it would accelerate the elektromagnetic
field of the charge because gravitation does not couple to charge but
energy (field- and massenergy), so an free falling elektron in an
infinite homogenous gravitational field would not radiate.

Another argument is, if an elektron which is accelerated by such a
field would radiate for an observer on earth (let the grav. field of
the earth be an infinite homogenous field in good approximation) then
it would loose some Energy and the observed acceleration would be
less. For a free falling observer the electron would not radiate
(Imagine the observer and the elektron are locked in some dark box -
then there is now way to detect the gravitational field). Then we
arrive at the following paradox. The elektron would radiate in a way
that the free falling observer could not see the radiation, but the
observer on earth would see it (difficult to imagine if the two
observers have the same time and space coordinates) and for the
observer on earth the elektron falls slower then the free falling
observer on the other hand for the free falling observer the position
realtiv to the elektron would not change.
So I am quite sure, that an accelerated elektron in a field discribed
above would not radiate.
Whats your opinion about this


I am not an expert on the subject but I believe that this
is a very difficult question. You might try a web
search including the name Parrot for more information.

Martin Hogbin

"Bastian" wrote in message
m...
My Professor used to ask this question in oral exams: What happens if
an elektron falls off from a table? Usual answer: The elektron is an
accelerated charge and so it radiates elektromagnetic waves.
I argued that an elektron would not radiate when accelerated by an
gravitational field.

Actually it will radiate. When there is a relative acceleration of charge
and detector/observer, radation will be detected.

Another argument is, if an elektron which is accelerated by such a
field would radiate for an observer on earth (let the grav. field of
the earth be an infinite homogenous field in good approximation) then
it would loose some Energy and the observed acceleration would be
less.

That's the radiation reaction that you're refering to (aka self force).
However for a constant acceleration there is no radiation reaction.

For a free falling observer the electron would not radiate
(Imagine the observer and the elektron are locked in some dark box -
then there is now way to detect the gravitational field). Then we
arrive at the following paradox. The elektron would radiate in a way
that the free falling observer could not see the radiation, but the
observer on earth would see it (difficult to imagine if the two
observers have the same time and space coordinates) and for the
observer on earth the elektron falls slower then the free falling
observer on the other hand for the free falling observer the position
realtiv to the elektron would not change.

The detection of the radiation is observer dependant.


So I am quite sure, that an accelerated elektron in a field discribed
above would not radiate.
Whats your opinion about this

This has been studied in detail in the physics literature. You can see a
summary from these various papers here

http://www.geocities.com/physics_wor...ing_charge.htm

Referances are included.

Pmb

"Martin Hogbin" wrote in message ...

"WaiteDavid137" wrote in message ...

My previous posting was intended as a response to the OP (Bastian)
rather than David Waite.

Martin Hogbin

"Pmb" wrote in message ...

"Bastian" wrote in message
om...
My Professor used to ask this question in oral exams: What happens if
an elektron falls off from a table? Usual answer: The elektron is an
accelerated charge and so it radiates elektromagnetic waves.
I argued that an elektron would not radiate when accelerated by an
gravitational field.

I agree with you, (but I also agree with Pmb as he reconditioned
the set-up). An electron accelerated by a g-field alone and in a
zero electrostatic and magnetic field will not radiate.

In classical terms, Maxwell's radiation equation in a vacuum
is given by the tensor equation,

qF_uv,w + qF_vw,u + qF_wu,v =0

where F_uv etc. are the components of the Electric and
Magnetic fields, and the comma is the partial diff, and
q is electronic charge.

Any radiation emission or absorption would require the
charge q to be subject to a varying EM field given by the
components F_uv,w etc. that are relatively varying quantities.

Naturally, when all the EM field components (F_uv) are
zero or constant, no radiation can occur.
(questions on these equations, ask).

Actually it will radiate. When there is a relative acceleration of charge
and detector/observer, radation will be detected.
Pmb

Agreed
[snip]

Regards Ken S. Tucker

On Sun, 07 Sep 2003 10:48:46 -0700, Ken S. Tucker wrote:

"Pmb" wrote in message ...

"Bastian" wrote in message
. com...
My Professor used to ask this question in oral exams: What happens if
an elektron falls off from a table? Usual answer: The elektron is an
accelerated charge and so it radiates elektromagnetic waves.
I argued that an elektron would not radiate when accelerated by an
gravitational field.

I agree with you, (but I also agree with Pmb as he reconditioned
the set-up). An electron accelerated by a g-field alone and in a
zero electrostatic and magnetic field will not radiate.

In classical terms, Maxwell's radiation equation in a vacuum
is given by the tensor equation,

qF_uv,w + qF_vw,u + qF_wu,v =0

where F_uv etc. are the components of the Electric and
Magnetic fields, and the comma is the partial diff, and
q is electronic charge.

Any radiation emission or absorption would require the
charge q to be subject to a varying EM field given by the
components F_uv,w etc. that are relatively varying quantities.

Naturally, when all the EM field components (F_uv) are
zero or constant, no radiation can occur.
(questions on these equations, ask).

Actually it will radiate. When there is a relative acceleration of charge
and detector/observer, radation will be detected.
Pmb

Agreed
[snip]

Regards Ken S. Tucker

Can I ask what "relative acceleration" means? I thought in relativity that
accelerations were absolute.

"Titan Point" wrote in message
news
On Sun, 07 Sep 2003 10:48:46 -0700, Ken S. Tucker wrote:

"Pmb" wrote in message
...

"Bastian" wrote in message
. com...
My Professor used to ask this question in oral exams: What happens if
an elektron falls off from a table? Usual answer: The elektron is an
accelerated charge and so it radiates elektromagnetic waves.
I argued that an elektron would not radiate when accelerated by an
gravitational field.

I agree with you, (but I also agree with Pmb as he reconditioned
the set-up). An electron accelerated by a g-field alone and in a
zero electrostatic and magnetic field will not radiate.

In classical terms, Maxwell's radiation equation in a vacuum
is given by the tensor equation,

qF_uv,w + qF_vw,u + qF_wu,v =0

where F_uv etc. are the components of the Electric and
Magnetic fields, and the comma is the partial diff, and
q is electronic charge.

Any radiation emission or absorption would require the
charge q to be subject to a varying EM field given by the
components F_uv,w etc. that are relatively varying quantities.

Naturally, when all the EM field components (F_uv) are
zero or constant, no radiation can occur.
(questions on these equations, ask).

Actually it will radiate. When there is a relative acceleration of
charge
and detector/observer, radation will be detected.
Pmb

Agreed
[snip]

Regards Ken S. Tucker

Can I ask what "relative acceleration" means? I thought in relativity that
accelerations were absolute.

If you and I are both in a cabin of a rocket ship and strapped in our seats
and the rocket is accelerating then there is no relative motion between you
and I and thus no relative acceleration. However there is a relative
acceleration between us and observers on the ground and between us and
someone if free-fall

Pmb

"Pmb" wrote in message ...

"Titan Point" wrote in message
news
[snip]
Can I ask what "relative acceleration" means? I thought in relativity that
accelerations were absolute.

If you and I are both in a cabin of a rocket ship and strapped in our seats
and the rocket is accelerating then there is no relative motion between you
and I and thus no relative acceleration. However there is a relative
acceleration between us and observers on the ground and between us and
someone in free-fall
Pmb

I agree completely with Pmb, however the geodesics describing this
take a bit more work, and create detail.
Ken S. Tucker

On 5 Sep 2003 19:36:47 -0700, (Bastian) wrote:

My Professor used to ask this question in oral exams: What happens if
an elektron falls off from a table? Usual answer: The elektron is an
accelerated charge and so it radiates elektromagnetic waves.
I argued that an elektron would not radiate when accelerated by an
gravitational field. The picture that guides me is the following: An
elektron usually radiates because some elektromagnetic force from
outside couples to the charge of an elektron but not to the
elektromagnetic field generated by that elektron. The field tries to
follow the charge and in order to do that it radiates. An infinite
homogeneous gravitational field would accelerate the free falling
elektron in the same way as it would accelerate the elektromagnetic
field of the charge because gravitation does not couple to charge but
energy (field- and massenergy), so an free falling elektron in an
infinite homogenous gravitational field would not radiate.

Another argument is, if an elektron which is accelerated by such a
field would radiate for an observer on earth (let the grav. field of
the earth be an infinite homogenous field in good approximation) then
it would loose some Energy and the observed acceleration would be
less. For a free falling observer the electron would not radiate
(Imagine the observer and the elektron are locked in some dark box -
then there is now way to detect the gravitational field). Then we
arrive at the following paradox. The elektron would radiate in a way
that the free falling observer could not see the radiation, but the
observer on earth would see it (difficult to imagine if the two
observers have the same time and space coordinates) and for the
observer on earth the elektron falls slower then the free falling
observer on the other hand for the free falling observer the position
realtiv to the elektron would not change.
So I am quite sure, that an accelerated elektron in a field discribed
above would not radiate.
Whats your opinion about this

No, it would not radiate. Since it's a point particle falling in a
gravitational field, it is travelling on a geodesic in GR. This puts
its situation on par with the same electron traveling at a constant
speed in a straight line, and it certainly would not radiate in that
case.