can light be bent by electromagnetic fields?

Hi, thank you for bringing your question to Google Answers.

Can light be bent by electromagnetic (EM) fields? The short answer is
no, ?but? with an explanation.

EM fields bend the path of moving particles such as in the Solar Wind,
or simply in a TV tube which uses EM fields to deflect (bend) electron
paths.

Since light is both a wave and a particle at the same time, you might
think that this would cause light to be bent if only you had a strong
enough field.

After all, light is bent by gravity, so what?s the difference?

The reason EM fields can bend the path of many particles is because
those particles are carrying an electrical charge ? the EM field is
actually affecting the charge associated with the particle.

Photons (light) have spin (1) but do not have an electrical charge so
they aren?t affected by even very strong magnetic fields.

One simple demonstration I?ve heard, and which makes complete sense,
is that since radio and TV transmitters produce very powerful EM
fields at the antenna, if light were bent by an EM field you would
expect there to be some visual blurring, but there is none which isn?t
accounted for by heat on hot days.

That, of course, isn?t proof in any real sense, but it does agree with
all the major accepted theoretical explanations so it makes practical
sense.

Now for the ?but? in the explanation. 

http://www.wonderquest.com/extinctions-safetyglass-magnetslasers.htm#magnetslasers

At the quantum level, an effect known as Delbruck scattering can occur
where it is thought that an extremely powerful EM wave can break a
photon down into an electron and a positron, both of which do carry a
charge and can therefore have their paths altered by an EM field.

This effect is extremely difficult to observe and probably too small
to measure given the nature of such things and the Heisenberg
Uncertainty Principal, but there can be a scattering effect where the
particle and anti-particle annihilate each other and form two
lower-energy photons which then travel in different directions.

Technically in most instances this would produce a splitting rather
than a bending, but it does describe one way that EM fields can
interact with a light beam even though the photon technically is not a
photon during the only time interaction can occur (between the
splitting into electron and positron and the rejoining - i.e.
annihilation.) The field only effects the electron and positron.

http://www.phys.unsw.edu.au/SCHOOL_INFORMATION/COLLOQUIA/2001/september_13th.html

And, here is a good lay explanation of light bending by gravity:
http://cassfos02.ucsd.edu/public/tutorial/GR.html

There is an excellent description of light, including an animation of
an EM field, at
http://www.astronomynotes.com/light/s3.htm

Maxwell?s equations, which I can?t reproduce here due to graphics
limitations, are the governing laws for any electromagnetic field
(including light) at anything larger than quantum dimensions, except
for gravitational effects which you must turn to Einstein for (don?t
blame Maxwell, as with many advances in science, Maxwell didn?t
address any gravitational effects, leaving that for Einstein.)

http://hyperphysics.phy-astr.gsu.edu/hbase/electric/maxeq.html

http://galileo.phys.virginia.edu/classes/109N/more_stuff/Maxwell_Eq.html

In fact, Maxwell?s field theory of EM stands up very well until you
get to very short distances where String Theory attempts to explain
things. Unfortunately, String Theory describes things so small that it
doesn?t appear to be possible to make any testable predictions based
on String Theory which is why many scientists reject that it is really
a ?theory? in the tradition of scientific method. You have to be able
to predict and test the predictions to have a valid "theory".

Magnetic Fields and Light
http://van.hep.uiuc.edu/van/qa/section/Electricity_and_Magnets/Magnets/20040825174745.htm

Google Search Term:

can an electromagnetic field bend light
Quantum electrodynamic
Delbruck scattering
Bremsstrahlung
Brensstrahlung


Einstein?s 1911 paper, ?On the influence of gravitation on the
Propagation of Light,? and more technical information on bending light
beams is available at:
http://www.mathpages.com/rr/s6-03/6-03.htm

A quick intro to String Theory:
http://theory.tifr.res.in/~mukhi/Physics/string2.html

I hope this provided the answer you were seeking along with lots of
reference links to follow. The bottom line is that while gravity (on
the order of magnitude of that near a star?s surface) can be shown to
bend light, there has never been an experiment which demonstrated
bending a beam of light using any combination of EM fields and/or
magnets.

There are some theories which may, if proven true, leave open some
possibility of bending light but there has never been any evidence of
this except for the side issue of scattering due to some rare quantum
effects I described, effects which are virtually too small to measure
in most instances.

While quantum mechanics says that photons are constantly splitting up
into positron and electron pairs, then quickly recombining, you can
affect the path of individual photons by scattering some, but this
isn?t something you can control to bend a stream of photons (beam of
light).

EM still doesn't affect individual photons when they are photons and
you won?t be able shine a pointer LASER beam past an electromagnet of
any arbitrary strength and see it bend.

One reason we feel that we understand EM well enough to say it can?t
bend light is because taking EM theory as it now stands, it neatly
explains all of chemistry and biology as well as power generation, TV,
radio, and such.

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Clarification of Answer by siliconsamurai-ga on 07 Jan 2006 13:16 PST

Thanks for the nice rating, the price was fine by me.

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Request for Answer Clarification by gubernacullum-ga on 08 Jan 2006 18:36 PST

i am slightly confused.

light is bent because it is attracted/absorbed/deflected by the
electron right? the electron creates an electromagnetic field right?
so when light bends around the corner of a slit or a star, it is the
em field of its electrons which is causing this bending and not
gravity or some other force.

thnx

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Clarification of Answer by siliconsamurai-ga on 09 Jan 2006 04:52 PST

Join scientists (GRIN), who are often confused ? Einstein, for
example, never really came to grips with quantum mechanics.

If your question regards kottekoe?s comments, please address your
questions to that individual, I?m not at all clear what parts of that
comment means myself, especially when it talks about polarizing a
vacuum or that ?Thus, light can be bent.?

Although people are free to add comments, I think those particular
comments only serve to confuse you.

The light particle (remember that light sometimes acts like a wave and
sometimes like a particle) can?t be affected by any electromagnetic
field, or an electron which has an electrical charge.

In wave form light also can?t be affected.

The extremely rare and tiny variations I described only occur because
the photon turns into something else. As I explained in detail, what
happens at the quantum mechanical level is that the photon actually
breaks up into an electron and a positron, both of which do carry an
electrical charge and can therefore be affected by a magnetic field.

Those ARE ?bent? or are at least affected by an EM field, but they
aren?t light (photons) during the extremely brief period when they are
interacting with the EM field, they are an electron and a positron
pair which usually recombine (although possibly not the same ones
since the EM field moves them in different directions) and become a
photon (light) again and, because they were diverted from their
original path by the EM field while they were charged particles, the
final photon (which isn?t actually identical with the original one
anyway) will probably be moving in a different path.

(My point about electrons not interacting with light doesn?t count the
quantum reaction where light quanta are absorbed and raise an electron
to a higher orbit or where an orbit decays and emits a photon ? that
has nothing to do with bending anything any more than using a piece of
black paper to block a light beam.)

I know this can be confusing (I used to have long discussions about
things such as QM and magnetic monopoles with a friend, Dr. Van Vleck,
who helped develop quantum mechanics and it really isn?t easy to
understand such abstract mathematical concepts in language even if you
are a relatively advanced physics student) but just bear in mind that,
under all currently accepted and seriously proposed theories, light
itself, which is made up of a stream of photons/an EM field, has no
charge and therefore can?t be directly affected by a magnetic field of
any sort while it is still light.

As for kottekoe?s statement, they may make sense in some context but
you really need to address a comment to that person to learn what they
are talking about since that would be a different question.

I hope that clears things up, if not, please follow some of the links
I provided for detailed explanations of various concepts raised by my
answer.

Thank you for bringing your question to Google Answers.

great answer! i didn't know at what price to set the question at but
certainly the 'but' part of the answer was most enlightening.

I'd like to add two small comments to Silicon Samurai's excellent
answer. Electromagnetism is almost perfectly linear, meaning the
propagation of light or any other purely electromagnetic phenomenon is
unaffected by other electromagnetic fields. They simply superpose
without affecting each other.

1) However, as the answer mentioned, there are deviations from
linearity. These can be calculated very accurately in quantum
electrodynamics (QED), perhaps the most accurate, tested, and accepted
of any scientific theory. The fundamental source of this non-linearity
is the one pointed out above, namely that photons are continually
dissociating into "virtual" electron-hole pairs, which recombine to
yield photons again. Since the electrons and holes are charged, they
do respond to electrostatic or magnetic fields. Thus, light can be
"bent" by electromagnetic fields, the theory can accurately calculate
it, but the effects are small and don't have any practical effect on
the macroscopic scale.

One goal for high power lasers is to reach power densities that are so
high that the electric field is high enough to "polarize the vacuum",
i.e. create electron-hole pairs. I've lost track of how far this is
from the state-of-the-art, but if it can be achieved, the
non-linearity of electromagnetism will be manifest in a very dramatic
way!

2) Another way in which electromagnetism is non-linear is that, as
with any type of energy, electromagnetic fields have mass and thus
produce a gravitational field, which can then deflect light. This
would require enormous concentrations of electromagnetic fields to
produce any measurable effect. As far as I know, there is nothing
postulated in the entire universe with such fields, but who knows?

Please substitute "electron-positron" for "elecctron-hole" in the above comment.

Too much time thinking about semicondutors!

"Please substitute "electron-positron" for "elecctron-hole" in the above comment."

   Oh... alright. >:)

I won't go into detail unless kotteoke or someone poses an actual
question, but if I understand the comment "electromagnetic fields have
mass" correctly, does that mean kotteoke says that photons also have
mass? If so, how can they, by definition, move at the speed of light?
If EMF has mass, just how fast does it move? Certainly it can't move
as fast as light if it does.

Saying that mass can be converted into energy isn't the same thing as
saying that energy necessarily HAS mass.

Photons don?t have any mass, what they have is energy which can be
converted into mass. But when that happens they are no longer photons
and no longer move at the speed of light.

Samurai,

I certainly didn't mean to confuse things, just to add some additional
perspective to your excellent answer.

First let me address the easy part of your questions. Photons
definitely have mass. What they lack is "rest mass". That is why they
have to move at the speed of light if they are to have any energy at
all. Energy and mass are different names for the same thing. It is a
common misconception that E=mc^2 means that you can convert matter
into energy or vice versa. In fact they are the same thing, just
measured in different units and c^2 is the conversion factor between
those units. For example, you know that when you speed something up,
it gains kinetic energy. That is exactly the same as the relativistic
mass increase divided by c^2, as a simple calculation will show. The
mass of a photon depends on its frequency (or wavelength) and is given
by hf/c^2 where h is Planck's constant, f is the frequency, and c is
the speed of light.

Yes, electromagnetic fields have mass. The energy density of a
magnetic field, for example, is proportional B^2, where B is the
magnetic field strength. Putting in the correct units and integrating
over a volume of space gives us the total energy, which according to
Einstein, determines its mass by m=E/c^2. Since c^2 is so large in
conventional units, it takes a LOT of field to account for very much
mass. Also, according to Einstein, the curvature of spacetime is
generated by the "stress energy tensor". All forms of energy are
equally good at curving spacetime, i.e. producing gravity, which can
bend light as Einstein predicted.

Two other points. 

1) Electrons are absolutely affected by light, since electrons have
electric charge and thus experience electric and (if moving) magnetic
forces due to the progating electromagnetic fields of light.

2) I understand your point that in the quantum theory of
electromagnetism it is only the virtual electrons and positrons that
are affected by the electric and magnetic fields. In the quantum field
theory view, though, you cannot divorce the photons from the endless
appearance and disappearance of virtual electrons, positrons, and
photons. This is the way the theory works. You can take your view that
it was not the photons that were affected, but the practical result is
that light CAN be affected, as can be measured in experiments
involving the very high fields in close proximity to the nucleus of an
atom.

Thanks for stimulating an interesting conversation.

I would only add that physicists don't really know what mass is - it
will come as a major surprise to many lay people to learn that even in
the widely accepted Standard Model, mass is mostly understood only as
a part of a mathematical function (Lagrangian) and something known as
The Higgs field.

In The Standard Model, Photons and Gluons are defined as massless boson particles.

In addition, Quantum electrodynamics would be violated if a photon had
a ?rest mass? which was non-zero, it would loose what is known as
?gauge invariance.?

A non-zero ?rest mass? would also cause a problem with Coulomb?s law
related to electrostatic because it would add another factor to the
inverse square rule.

BTW, rest mass for a particle which can?t be at rest is rather
meaningless, especially since this should actually be described as the
invariant length of a particle?s four-momentum. See the June 1989
issue of Physics Today for a relatively non mathematical introduction
to the subject.

Finally, E=mc*c is NOT precisely correct, you need to add another
factor related to momentum.

But you still can't bend light with a magnet.

Samurai,

Thanks for some additional interesting points, but I beg to differ.
E=mc^2 is absolutely precise, where m is the relativistic mass, which
increases as the particle speeds up. You can also write this as:

E = sqrt(p^2*c^2 + Eo^2),

where p is the momentum and Eo is the rest energy, given, naturally, by

Eo = Mo*c^2,

where Mo is the rest mass. It is the total mass that gives rise to the
gravitational force.

Since mass and energy are two names for the same thing, physicists
know exactly as much about mass as they do about energy. Again, your
comments about the mystery of mass are about rest mass (or rest
energy, choose your favorite units). In the standard model, the rest
mass of each of the fundamental particles (like electrons and quarks)
has to be put in as a constant that cannot be derived from the theory.
The Higgs mechanism is the theoretical justification, but we don't
have a complete enough theory to calculate the rest mass of the
fundamental particles from basic principles.