Photon's can't interact

[vikneshraj]

Is there is any light ray(some invisible photons) which can act as an obstacle to the ordinary white light?

 

what do i mean is that can a light ray act as an obstacle for the other light ray?......

 

If we are able to find such a light ray it would find applications like,screen for a projector ray and many more applications ........please do reply me......

 

.................thank you................

[CraigD]

Is there is any light ray(some invisible photons) which can act as an obstacle to the ordinary white light?

 

what do i mean is that can a light ray act as an obstacle for the other light ray?......

In short, no. What vikneshraj describes – photons reflecting off of one another - is theoretically (nearly) impossible.

 

Photons are bosons. They interact with fermions, such as electrons, but not with one another (with the exception of a very small effect involving gravity).

 

Experimentally, this is pretty easy to test. Direct a beam of ordinary light (eg: a flashlight) or laser light (eg: a laser pointer) at a photodetector (eg: a camera light meter). Intersect the beam with other EM radiation sources – a flashlight, large laser, microwave emitter, etc, and check the photodetector reading. Alternately, do the experiment in long dark box, then repeat it, admitting sunlight into the center of the box.

 

Note that photons can interfere, producing patterns of light and dark bands, but that this is an example of their wave-like quality, not of photons “blocking” or reflecting one another.

[LaurieAG]

Hi Craig,

 

In short, no. What vikneshraj describes – photons reflecting off of one another - is theoretically (nearly) impossible.

...

Note that photons can interfere, producing patterns of light and dark bands, but that this is an example of their wave-like quality, not of photons “blocking” or reflecting one another.

 

The photons might not reflect but they can do the (nearly) impossible with the help of an intermediary.

 

http://hypography.com/forums/technology-news/12638-photon-transistors-supercomputers-future.html

 

What he wants to do with the light is non-linear optics. That means that the photons in the light collide with each other and can affect each other. This is very difficult to do in practice. Photons are so small that one could never hit one with the other. Unless one can control them – and it is this Anders Sørensen has developed a theory about.

 

Light collisions at the quantum level

Instead of shooting two photons at each other from different directions and trying to get them to hit each other, he wants to use an atom as an intermediary. The atom can only absorb one photon (such are the laws of physics). If you now direct two photons towards the atom it happens that they will collide on the atom. It is exactly what he wants.

[Qfwfq]

In short, no. What vikneshraj describes – photons reflecting off of one another - is theoretically (nearly) impossible.

 

Photons are bosons. They interact with fermions, such as electrons, but not with one another (with the exception of a very small effect involving gravity).

Actually the simplest indirect photon-photon interaction is via fermion-antifermion pair. Certainly the cross section is tiny, but non zero. In the vacuum, the electromagnetic field is linear to prctical purposes, whereas in a transparent material it isn't too hard to reach the dielectric rigidity (although that's cheating, it's not the same thing as in vacuo pair production).

[CraigD]

Actually the simplest indirect photon-photon interaction is via fermion-antifermion pair.

Interesting point. Though, as a practical solution (vikneshraj’s question is directed, essentially, toward making a movie screen out of EM radiation) I don’t think it holds much promise. Though the calculations are more than I can manage off the top of my head, I suspect you’d need whole stars worth of energy or tame black holes to make the desired movie screen – just a bit impractical. :)

Certainly the cross section is tiny, but non zero. In the vacuum, the electromagnetic field is linear to prctical purposes, whereas in a transparent material it isn't too hard to reach the dielectric rigidity (although that's cheating, it's not the same thing as in vacuo pair production).

I’m not sure what you’re getting at here, Qfwfq. :) However, even without quite following, it brings to mind an important point: vikneshraj’s proposed movie screen wouldn’t be erected in a vacuum, but in fermion-dense ordinary surface-level Earth atmosphere. On a good summer, night, I’ve seen a pretty good movie screen effect produced by fog rising off of a lake with no artificial prodding, and as anyone who’s seen a good laser light show can attest, with the right equipment (including a smoke/fog generating machine), the effects possible are arguably better than a movie screen, being capable of producing moving 3-dimensional images.

 

Though there are some hypotheses (such as controversial physicist Henrik Svensmark‘s) suggesting that cosmic (very high gamma frequency) radiation causes small particles around which clouds slowly form (cloud condensation nuclei), I can’t imagine a practical way to make ordinary air opaque using EM radiation. I can’t say, however, that it’s theoretically impossible.

[snoopy]

Interesting point. Though, as a practical solution (vikneshraj’s question is directed, essentially, toward making a movie screen out of EM radiation) I don’t think it holds much promise. quote]

 

 

Yes I know no star trek style force fields either or holo decks ah well.....:)

[Qfwfq]

I don’t think it holds much promise.

Of course!!!

 

I was only nitpicking on the fact that gravity is hardly the main source of non-linearity in EM...

I’m not sure what you’re getting at here, Qfwfq.

Only at the reason why it holds no practical promise!

 

Now a screen of fog is doing none else than scattering the incident light, which is the same thing the good old flat white surface of a movie screen does, and better to the end of image quality. The 3-D effects a fog may give are arguably no more than special effects, rather than a faithful and better reproduction.

 

I can’t imagine a practical way to make ordinary air opaque using EM radiation. I can’t say, however, that it’s theoretically impossible.

An intensity sufficient to keep a layer of air highly ionized could have the effect of making it like a metallic surface! For long enough waves, at least, and it might even be quite opaque, but certainly not a good movie screen.

 

Now obviously the air makes it more feasible to have non-linearity than in the vacuum. I've heard of labs in which they focused a laser beam onto a point in mid air with an intensity that surpassed dielectric rigidity, causing a fizzly crackling of sparks at that point. It is not impossible, at a great energy expense that would make those big plasma screens seem eco-friendly, to get a crude image in a layer of air in front of the projector. It would be crucial to get polarization and phases right, and adjust the "screen" to just miss dielectric breakdown. It would not in any case be a high-quality Technicolor image.