My turn to Guess, by Joe Blow Nobody

[Little Bang]

I've had a new thought on (My Guess). So far I have been unable to find any information for or against my new thought. If (My Guess) is in anyway close to the truth then it makes a prediction. I'll post it here and see if the members can prove it wrong. A laser beam will have a minute magnetic field just like current in a wire.

[freeztar]

A laser beam will have a minute magnetic field just like current in a wire.

 

Yes. As it is electromagnetic radiation, it will have both a oscillating magnetic field and an oscillating electric field forming the electromagnetic wave.

[Little Bang]

I know the beam it's self is EMR. I mean the space just outside the beam. Since it is coherent light there should be no effect outside the beam.

[CraigD]

A laser beam will have a minute magnetic field just like current in a wire.

I don’t think so.

 

Laser beams consist of photons, which have no charge. Therefore, whether constant or varied, a laser beam has no classical magnetic field. A charged body will not experience any force due to a laser beam in vacuum (provided the laser beam doesn’t hit it, in which case either a charged or uncharged body will experience a force).

 

Photons do have associated complementary magnetic and electric fields, but to the best of my knowledge can’t exhibit any effects due to them in vacuum. In fermionic media, they can have magnetic effects, from obvious ones such as photoelectrical creating an electric (consisting of electrons, which have charge) current, which has a classical magnetic field and will exert a force on a charged particle, to subtle magneto-optic effects.

 

Magnetic effects involve photons, but only in their role as carriers of magnetic force between particles with charge. A photon can’t emit a photon (if it did, it’d be violating Bose–Einstein statistics, and following Fermi-Dirac statistics, which would make it a fermion, rather than a boson), so can’t have a classical magnetic field without somehow interacting with a fermion to do it.

 

While theory predicts we’ll never experimentally measure a magnetic force on a charged body due to a nearby laser beam, theory predicts that a laser beam has a very small relativistic mass, so should exert a gravitational force on massive body (including photons in another laser beam!)

 

The relativistic mass of even a very high energy stream of high energy photons being so small, however, I doubt it’s within the ability of any experimental technology to detect this effect. So while we see lots of evidence of light being gravitationally deflected by large masses (the Sun, etc.) we don’t have the ability to see a massive object being moved by a nearby beam of light.

 

If someone doesn’t beat me to it, I’ll work out some numbers for experimental predictions to verify my hunch that the gravitational force of a laser beam isn’t practically experimentally detectable.

[Farsight]

A laser beam will have a minute magnetic field just like current in a wire.

It doesn't, Little Bang. Make things simpler and think about a single photon. Then think of yourself as being very very small, standing there with a compass. As the photon passed you, your compass needle might flick one way then the other, but then the photon is gone at the speed of light. The magnetic field was extremely transient, it was in one direction to start off with, and then was equally transient in the other direction. And it all happened so fast that you probably didn't notice much of a flickflick at all. With a whole host of photons, all going past you at the same time, all the opposite transient magnetic fields would cancel each other out and your compass needle wouldn't even twitch.

 

It isn't like a current in a wire. The current in the wire is acting like a drill bit. Get hold of a drill bit, grasp it hard, and push it hard between your fingers. Your fingers are forced to follow the turning of the grooves on the drill bit. That's what a magnetic field is like. That's why a charged particle goes round and round a wire. You can achieve the same sort of thing if you could run along a whole string of electrons, you'd see a deflection of your compass. You don't get this sort of thing with a laser beam. You'd get a bit of a flickflick motion for a passing photon, but it all cancels out when a whole heap of them are streaming by.

[Little Bang]

Both posts were very good and thank you for the response. I'll answer with a story. A young grad student comes up to professor X, head of a laser physics research center, and says, " Professor X, I want to build an extremely sensitive circular detector and shine our laser beam through it to see if there are any forces surrounding it. " Professor X responds, " It won't do any good because you see all forces are carried by mediator particles according to the standard model. Therefore since there are no particles outside the beam there can be no forces. " Grad student asks, " But since we have never found the graviton isn't it possible that the theory could be wrong? " Professor X replies, " The reason we have not found the graviton is because it is to massive even though it must travel at the speed of light with all that mass."

[freeztar]

Both posts were very good and thank you for the response. I'll answer with a story. A young grad student comes up to professor X, head of a laser physics research center, and says, " Professor X, I want to build an extremely sensitive circular detector and shine our laser beam through it to see if there are any forces surrounding it. " Professor X responds, " It won't do any good because you see all forces are carried by mediator particles according to the standard model. Therefore since there are no particles outside the beam there can be no forces. " Grad student asks, " But since we have never found the graviton isn't it possible that the theory could be wrong? " Professor X replies, " The reason we have not found the graviton is because it is to massive even though it must travel at the speed of light with all that mass."

 

What serious professor would say that?

Does the standard model allow for particles with mass traveling at c?

[Little Bang]

My point exactly. No prof would consider anything outside the standard model. No he would not say that. I did not intend to put the last part of that statement in his reply. It was supposed to be mine. The point is that if we can't find it because it's so massive it can't travel at C and it must.

[Little Bang]

I have made a stupid mistake and apologize for it. I had been doing some studies on the higgs and confused it with the graviton. but it still remains that the graviton must be found because if we don't it puts the standard model in jeopardy. Not as long as you can aways find an excuse that something is keeping it hidden.

[freeztar]

I have made a stupid mistake and apologize for it. I had been doing some studies on the higgs and confused it with the graviton. but it still remains that the graviton must be found because if we don't it puts the standard model in jeopardy. Not as long as you can aways find an excuse that something is keeping it hidden.

 

So because the Higgs boson or the graviton have not been discovered, we should toss out the Standard Model?

 

From what I understand, the Higgs boson has a reasonable chance of being found. And while I'm still dubious about the possibility of reconciling gravity with the Standard Model, some other quantum field theories look promising (M-theory). How do you feel about this Little Bang?

[Little Bang]

The problem is that the standard model says all forces are mediated by carrier particles and it may in fact be correct. I don't like the idea but may be wrong in my judgment. How long do we go on looking for the Higgs and graviton, 100 years a 1000? When do we try another way? M-theory, I like it a lot.

[Erasmus00]

The problem is that the standard model says all forces are mediated by carrier particles and it may in fact be correct.

 

The standard model of particle physics is a very specific theory, encompassing ONLY the strong, weak, and electromagnetic interactions. Gravity is not at all part of the standard model, which is unfortunate.

 

The reason we that most particle physicists are fairly certain about the graviton has to do with the general relativity(sometimes called the "classical" theory of gravity). If you take a certain limit(the linear limit, for those playing at home) of general relativity you get a theory that fits very nicely with quantum mechanics. This theory DOES predict spin 2, massless gravitons that weakly interact with particles.

 

From this, many physicists take away two things. First, the graviton probably exists as a force mediator in weak gravitational field. Second, our standard model might only be valid in weak gravitational fields- in this same limit where the graviton is a good description.

 

How long do we go on looking for the Higgs and graviton, 100 years a 1000? When do we try another way?

 

If the higgs exists, and does what physicists think it does it should definately be seen at the LHC. The graviton is a harder problem- its so weakly interacting, how do you build something to detect it?

-Will

[Little Bang]

The standard models dream was to become a gut which means it must include gravity.

[Erasmus00]

The standard models dream was to become a gut which means it must include gravity.

 

A grand unified theory would eventually include gravity. The standard model is not such a theory. In fact, the standard model does not unify the strong force with the electroweak.

 

The problem with adding gravity to the mix is that general relativity is not a theory that is easy to quantize.

-Will