Why is light not affected by magnetic fields?

[logy]

Moderation note: the first 5 post of this thread were moved from 17768, because they are more of an in-depth discussion of physics than a simple question & answer

 

in my humble oppinion:

 

light is not affected by magneting or static electrical fields because it has no mass and it's speed is constant !

magnets and static electricity creat a force field which can accelerate objects that have mass and gain gain or loose kinetic energy and momentum, like say other magnets or an electrically chared charged piece of metal, but light itself travels at the speed of light, had no "rest mass" which means no mass for the purpose of this discussion and therefore will travel in a streight line unless one of the following happens.

1.it hits a reflecting or refracting surface

2. it enters a gravitational field, in which case, the curve in space itself will make it "curve".

 

simply put, since light had no mass and cannot be accelerated (as acceleration shanges speed), it will not react to a force.

[Moontanman]

in my hombel oppinion:

 

light is not affected by magneting or static electrical fields because it has no mass and it's speed is constant !

magnets and static electricity creat a force field which can accelerate objects that have mass and gain gain or loose kinetic energy and momentum, like say other magnets or an electrically chared charged piece of metal, but light itself travels at the speed of light, had no "rest mass" which means no mass for the purpose of this discussion and therefore will travel in a streight line unless one of the following happens.

1.it hits a reflecting or refracting surface

2. it enters a gravitational field, in which case, the curve in space itself will make it "curve".

 

simply put, since light had no mass and cannot be accelerated (as acceleration shanges speed), it will not react to a force.

 

 

While what you say may have some bearing on the process the fact that Photons have no charge is the main reason magnetic fields to not affect them. Massive particles with charge are affected as are less massive particles with charge. I know of no massless particles with charge but if they had charge a magnetic field would affect them. Particles with no charge are not affected no matter how massive they are.

[logy]

While what you say may have some bearing on the process the fact that Photons have no charge is the main reason magnetic fields to not affect them. Massive particles with charge are affected as are less massive particles with charge. I know of no massless particles with charge but if they had charge a magnetic field would affect them. Particles with no charge are not affected no matter how massive they are.

 

the question asked was how come EM waves are not affected by EM force fields, and yes, EM waves don't have a constant charge, but they do have an alternating electical/magnetic field and as a result some of the time they do exist as a static electrical field or as a magnetic field, so why are they not affected by by a magnet? the answer IMHO lies in the fact that they are only fields and the interaction between two charged particles relies on they mass, distance and charge according to the formula

force = (KxQ1xQ2)/R^2

acceleration = (force x distance)/mass

 

where K is the electric constant

Q1 and Q2 are the charge of the particles in columbs

R is the distance in meters between the 2 particles

 

if there where massless partiles with a constant charge, the math will not work as the acceleration is inversly proportional to the mass and therefore any force would accelerate such a particle to infinite speed (division by zero since the mass is zero) the natural conclusion is that massless particles with a 'charge' cannot be acclerated. my argument is that massless particles cannot have their speed affected by force fields due to the division by zero problem.

 

in my understanding, it is the fact that force will accelerate massive particles, but has no effect on EM waves as they are an alrernating static/magnetic force fields with no mass. the concept of charge, is simply saying that a massive particle has a constant EM force field. if i where to create a system that has mass and has an alternating electrical/magnetic field it will be affected by a magnet, accelerating, decelerating or changing direction depending on it's configuration.

 

am i wrong?

[Moontanman]

the question asked was how come EM waves are not affected by EM force fields, and yes, EM waves don't have a constant charge, but they do have an alternating electical/magnetic field and as a result some of the time they do exist as a static electrical field or as a magnetic field, so why are they not affected by by a magnet? the answer IMHO lies in the fact that they are only fields and the interaction between two charged particles relies on they mass, distance and charge according to the formula

force = (KxQ1xQ2)/R^2

acceleration = (force x distance)/mass

 

where K is the electric constant

Q1 and Q2 are the charge of the particles in columbs

R is the distance in meters between the 2 particles

 

if there where massless partiles with a constant charge, the math will not work as the acceleration is inversly proportional to the mass and therefore any force would accelerate such a particle to infinite speed (division by zero since the mass is zero) the natural conclusion is that massless particles with a 'charge' cannot be acclerated. my argument is that massless particles cannot have their speed affected by force fields due to the division by zero problem.

 

in my understanding, it is the fact that force will accelerate massive particles, but has no effect on EM waves as they are an alrernating static/magnetic force fields with no mass. the concept of charge, is simply saying that a massive particle has a constant EM force field. if i where to create a system that has mass and has an alternating electrical/magnetic field it will be affected by a magnet, accelerating, decelerating or changing direction depending on it's configuration.

 

am i wrong?

 

You are far beyond my level of expertise, the original question was is light affected by a magnetic field, it is not, i honest do not know why except that photons are not charged. If indeed massless particles were charged I would expect them to be affected but as far as I know there are no massless charged particles. Your take is interesting but will require someone who is above me on the food chain.

[CraigD]

the question asked was how come EM waves are not affected by EM force fields, and yes, EM waves don't have a constant charge, but they do have an alternating electical/magnetic field and as a result some of the time they do exist as a static electrical field or as a magnetic field, so why are they not affected by by a magnet?

I think I’m wandering onto semantically difficult ground, but I’d explain this by noting that magnetic fields aren’t affected by magnetic fields, rather changes in the position and velocity of charged particles result in differences in their associated magnetic fields. Magnetic field are really just descriptions of how a hypothetical, arbitrarily low mass and change test body’s momentum would change at points within them.

the answer IMHO lies in the fact that they are only fields and the interaction between two charged particles relies on they mass, distance and charge according to the formula

force = (KxQ1xQ2)/R^2

acceleration = (force x distance)/mass

…

I think what you’re saying here is that particles with zero invariant (“rest”) mass ([math]m_0[/math]) can’t be meaningfully considered to be subject to force or acceleration.

 

A problem with this limitation is that such particles (eg: photons) behave in many ways as if they have non-zero masses when their speed is, as it always is, the speed of light in vacuum ©. They appear to be subject to gravity, and to transfer momentum (mass x velocity) when they collide with other particles.

 

Though formal purists cringe at it, an easy solution to this problem is to consider photons and other such particles to have “relativistic” (dialated) mass [math]m_1 = \frac{E}{c^2} = \frac{h f}{c^2}[/math], where [math]f[/math] is the photon’s frequency, and [math]h[/math] is Planck’s constant.

 

One of the reasons purists cringe at this is that it implies some arithmetic absurdities. For example, the usual equation for mass dilation is [math]m_1 = \frac{m_0}{\sqrt{1 - \left( \frac{v}{c}\right)^2 }}[/math]. [math]m_1[/math] being defined for a body with speed [math]v=c[/math] implies a nonsensical [math]m_1 = \frac{m_0}{0}[/math].

 

However, if you’re careful not to use it inappropriately, the concept of photons with non-zero relativistic masses is useful and convenient.

 

Justification and objections to this approach can be found in many texts and websites, including the wikipedia articles “mass in special relativity” and “photon”.

[GAHD]

Light *IS* affected by magnetic feilds: they cause polarization of the waves. Faraday noted this effect and it is used quite extensively in solid state polorization controllers.

 

minor semantics, but there IS interaction between the two.

[CraigD]

Light *IS* affected by magnetic feilds: they cause polarization of the waves. Faraday noted this effect and it is used quite extensively in solid state polorization controllers.

 

minor semantics, but there IS interaction between the two.

Just the sort of semantic we’re here to discuss! :thumbs_up

 

As far as I know – and I could well know wrongly - the Faraday effect can only occur when light passes through a non-vacuum medium – that is, a volume with non-zero rest mass particles in it. I don’t believe a beam of polarized light has its polarization rotated if it passes through a magnetic field in vacuum.

 

So it’s not an example photons interacting with other photons – which I understand is forbidden – but magnetic interaction photons interacting with fermions (usually electrons), which interact with EM radiation photons. In practical terms, true vacuums don’t exist enough to worry about – interstellar space, for example, has at least 2000 electrons/m[math]^3[/math], so magneto-optical effects like the Faraday effect happen effectively everywhere - but for understanding fundamental interactions, the distinction is, I think, critical.

 

I don’t know how to describe light polarization effects – Faraday or others – in terms of photon-fermion interactions. If someone can, I’d greatly appreciate it – it’s puzzled me for a long time. :confused:

[logy]

Just the sort of semantic we’re here to discuss! :thumbs_up

 

As far as I know – and I could well know wrongly - the Faraday effect can only occur when light passes through a non-vacuum medium – that is, a volume with non-zero rest mass particles in it. I don’t believe a beam of polarized light has its polarization rotated if it passes through a magnetic field in vacuum.

 

So it’s not an example photons interacting with other photons – which I understand is forbidden – but magnetic interaction photons interacting with fermions (usually electrons), which interact with EM radiation photons. In practical terms, true vacuums don’t exist enough to worry about – interstellar space, for example, has at least 2000 electrons/m[math]^3[/math], so magneto-optical effects like the Faraday effect happen effectively everywhere - but for understanding fundamental interactions, the distinction is, I think, critical.

 

I don’t know how to describe light polarization effects – Faraday or others – in terms of photon-fermion interactions. If someone can, I’d greatly appreciate it – it’s puzzled me for a long time. :confused:

 

thank you craig, i think it is important to note that the farady effect is a result of the magnetic field acting on an electron, and not on a photon.

 

i don't fully understand the way fermoins work but i do know that they all have half integer spin so if an electron absorbs a photon, then rotates around their its axis due to the spin of the fermion, and then re-emit a photon, that photon's plane of polatization will move in a clock wize or anty clock wize direction.

 

what 'spin' really is, is something that i am still learning about but it can be considered to be an actual spin of the electron according to wiki.

"spins obey the same mathematical laws as do quantized angular momenta."

...i can't post links yet :(, it's the wiki page titled "Spin_(physics)"

 

the above mentioned page from wiki about the farady effect has a good diagram that shows how it works. it's important to remmember that the vector of a magnetic field point to the north pole, while it's spin is around the south-north axis !

 

i hope this will shed some light on the topic. i think that in order to properly understand the whole magnet thing i will have no choice but to study maxwell's equations... hmm :eek2:

[Little Bang]

If there have been experiments that confirm magnetic fields have no effect what so ever on light please point them out. Since EMR has both electric and magnetic components how do we know that a magnet field doesn't cause something like rotation of the wave?

[logy]

If there have been experiments that confirm magnetic fields have no effect what so ever on light please point them out. Since EMR has both electric and magnetic components how do we know that a magnet field doesn't cause something like rotation of the wave?

 

light is an alternating electromagnetic field, and when you have 2 light waves in the same spot you get constructive or destructive interference. if light was affected by electromagnetic fields, it would show very clearly in such experiments. the rules of physics are that fields generate forces and forces move objects, but fields do not move fields, they just interfere with fields that are similar. usually fields are generated by objects (particles with mass) like magnets and electrons and then, if you move the object, you move the field that is generated by that object, but light has no (rest)mass and cannot be accelerated.

 

the experiments you are talking about have been done in mechanics, and it has been discovered that moving an object with rest mass requires a force, which a massless object cannot be moved as such, it will always go in a straight line and have the same polar plane. one exception to that is gravity, since according to general relativity, space itself is curved and therefore a "straight line" is not really straight when it goes through such a curve.

[Little Bang]

So if we pass a beam of light through a moving magnetic field experiment has shown that the light is not polarized?

[CraigD]

Since EMR has both electric and magnetic components how do we know that a magnet field doesn't cause something like rotation of the wave?

We know that if a medium containing electrons (eg: glass or interstellar gas) is subjected to a magnetic field, polarized light that interacts with that medium (ie: passes through it) has its plane of polarization rotated. This is the Faraday effect. It depends on the wavelength of the light, the density and molecular structure of the medium, and the orientation and strength, but not the direction, of the magnetic field. Different materials can rotate the plane in a positive or negative direction, and if the magnetic field is oriented perpendicular to the light beam, zero rotation occurs.

 

According to theory, as the density of electrons in the medium is reduced, so is the rotation. Visible light in one of the most effective Faraday rotator mediums, terbium gallium garnet, has a Verdet constant of -40 rad/T/m, glass around 1.8e-7, typical interstellar gas about 2e-20. (from data and links from the preceding wikipedia link, and some simple calculations)

If there have been experiments that confirm magnetic fields have no effect what so ever on light please point them out.

This “proving a negative” would be pretty tough. The best experiments can show, I think, is that as a medium approaches a perfect vacuum, its Verdet constant approaches zero. To measure a Verdet constant of absolute zero, you’d need to have a vacuum better than found in deep space stretching for many light years and subjected to a strong magnetic field, and even then, you’d not be sure that your experiment was not sufficiently sensitive to detect some tiny effect not predicted by theory.

 

Most measurements of very small Verdet constants (usually called “rotation measure”, and with an additional unit to allow multiplication of the square of the light’s wavelength) are made in combination with other measurements to determine the density of matter in interstellar space. Given that theory predicts a zero Verdet constant for absolute vacuum, and all experimental data supports it, I doubt many experimental resources will be spent attempting to support the theory greater certainty.

So if we pass a beam of light through a moving magnetic field experiment has shown that the light is not polarized?

It’s important to note that the Faraday effect doesn’t itself polarize light, but rotates the plane of polarization of previously polarized light. Un-polarized (randomly polarized) light will still be randomly polarized after its many planes are rotated by the Faraday effect.

 

The Faraday effect doesn’t require a changing/moving magnetic field. Change in the strength and orientation of the field is averaged to determine the total rotation of the material.

[Jonthegreat]

After reading up on the extensive information posted specifically on a design for a 'light accelerator' that was plaguing my head, I have a question.

 

Understanding that light waves cannot be affected by EM or EMR (as photons have neither charge nor resting mass) and that fields cannot be 'bent' by other fields I have arrived at my next proposal.

 

What about the field interference on an oscillating, polarized, and accelerated fashion with staggered strengths of interference? Would, in effect, the field itself be accelerated?

 

As light travels through such an accelerated field, is it possible to accelerate such motion beyond the constants of light?

 

Perhaps I am grasping at straws here...

 

PS... This is not referring to the above rotating situation, rather linear acceleration. Also the medium would be of the gaseous type. The threads I was attempting to comment on also seemed to disappear after posting. This is more under the umbrella, DOES light bend under the effects of magnetism.

[logy]

After reading up on the extensive information posted specifically on a design for a 'light accelerator' that was plaguing my head, I have a question.

 

Understanding that light waves cannot be affected by EM or EMR (as photons have neither charge nor resting mass) and that fields cannot be 'bent' by other fields I have arrived at my next proposal.

 

What about the field interference on an oscillating, polarized, and accelerated fashion with staggered strengths of interference? Would, in effect, the field itself be accelerated?

 

As light travels through such an accelerated field, is it possible to accelerate such motion beyond the constants of light?

 

Perhaps I am grasping at straws here...

 

PS... This is not referring to the above rotating situation, rather linear acceleration. Also the medium would be of the gaseous type. The threads I was attempting to comment on also seemed to disappear after posting. This is more under the umbrella, DOES light bend under the effects of magnetism.

 

According to Einstein, the speed of light in vacuum is constant and never changes. If anyone where to discover an experiment that demonstrates otherwise, the theory of relativity will fall apart. BUT that does not mean that you can't get light move slower, or for something to like it's moving faster then the speed of light. if you shine a light through a transparent material (say glass) it will look like it's traveling at a slower speed, but that is only because the light photons are absorbed and then re-emitted by the glass. the phtons of light coming out of the glass are not the same ones that entered the glass. According to wikipedia scientists have managed to completely halt light boze-einstein condensate. I don't fully understand that phenomenon but I think that it is quite amazing !!! :).

 

If you wish to make something move faster then the speed of light using interference patterns, I don't see why it won't work. And I will elaborate;

Let’s say that Johnny has a strong laser torch and he is pointing it on a very distant object. On that object, you will get a dot of light from the laser beam. now if Johnny where to move the laser torch fast enough, that dot will move faster then the speed of light, since the laser only has to move a couple centimeters in order for the dot to move thousands of meters. but for both dots to be illuminated it will require for the light to travel from the laser to the distant planet. The light can reach the second dot within a tiny fraction of a second (say 1/300,000,000 of a second, approximately the time it takes light to travel one meter) of reaching the first dot, and the dots can be thousands of meters away from each other.

 

The key thing to note is that nothing actually moves from dot A to dot B, rather, light is moving from the laser to both dots. And I see no reason that this cannot be done with interference patterns so that within an area that is illuminated by lasers, you will have a dark spot (due to interference) that 'moves' faster then the speed of light.

[Jonthegreat]

Okay. Fair enough. Back to the situation of alternating field interference - can a wavelength be.. 'accelerated'.. to a wavelength of higher intensity without changing the output of the source, such as a beam from a laser? My thoughts, to put it simply, are to construct a resonance device that compounds so that a weak wavelength (such as radio &/or laser pointer) would end up an intense wave out the other end. I understand E's determination that light is as fast as light can go. Thank you for reminding me.

 

This may seem pointless, however, due to the fact that the energy required to do so may far exceed both the source and the product combined. The thoughts are of using such resonance to harness such energies found in nature *ie Sun*

 

Am I a hopeless dreamer? or could there be light at the end of the tunnel, no pun intended.

 

I am somewhat familiar with how photovoltaic cells work -- this is unrelated. More of a refocusing/amplification of a weak source to a strong product.

 

If this sounds unfocused or inconclusive I guess sum me up as asking "What if?"

 

: ( Could be the 101.2F fever I got going on too...

[logy]

Okay. Fair enough. Back to the situation of alternating field interference - can a wavelength be.. 'accelerated'.. to a wavelength of higher intensity without changing the output of the source, such as a beam from a laser? My thoughts, to put it simply, are to construct a resonance device using placed induction of current producing EMR so that a weak wavelength (such as radio &/or laser pointer) would end up an intense wave out the other end.

 

This may seem pointless, however, due to the fact that the energy required to do so may far exceed both the source and the product combined. The thoughts are of using such resonance to harness such energies found in nature *ie Sun*

 

Am I a hopeless dreamer? or could there be light at the end of the tunnel, no pun intended.

 

I am somewhat familiar with how photovoltaic cells work -- this is unrelated. More of a refocusing/amplification of a weak source to a strong product.

 

Jonthegreat, I don’t think that you’re not a hopeless dreamer, far from it. In fact your ideas are in the cutting edge of scientific research in more the one area !

 

First of all, intensity in this context usually refers to the amount of energy produced by a specific light source, i.e. the number of photons, which cannot be changed without 'creating' more photons.

 

In regards to changing the amount of energy per photon, that would mean changing it's wave length, and that happens all the time. one example is Red shift in astronomy which is a result of the Doppler effect.

an example that is closer to what you motioned is lazer cooling , where essentially they use laser beans that have slightly less energy then what is required in order to excite an atom. since heat is essentially movement (or 'vibration' in solids) of atoms, if the atom is moving *towards* the light , then the light will appear to have a higher frequency from the atoms perspective and will be absorbed, slowing down the atom by 'taking' kinetic energy and momentum from it. Then, it will be re-emitted in a random direction with a slightly higher average frequency.

 

If you where to build a machine that generates EMR, it will emit photons all on it's own, which if i understand correctly, is how radio's and mobile phones work. So your idea is being used by billions of people already !

 

In regards to harnessing energy from the sun, it depends, if you are talking about sunlight, that's what solar panels do, convert the light energy into electrical energy.

since you cannot create energy from nothing, the sun itself has to get its energy from somewhere and that comes from nuclear fusion , something that scientists have been trying to duplicate for decades, but are having trouble containing the hydrogen because fusion requires very high temperatures, in excess of 100 million degrees Kelvin, while any known material will vaporize before it reaches 10,000 degrees.

[Little Bang]

Jon, haven't you figured out yet that no one on this planet can explain electromagnetic radiation? Just like gravity and charge they give their interpretation of theory. But 99% of the scientific community will agree with them.