Naked Science Forum
Non Life Sciences => Physics, Astronomy & Cosmology => Topic started by: neilep on 21/08/2009 11:44:19
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Dearest Awe Makers Of Me !
As a sheepy I of course use torches !...It's difficult to find the right hole at night !!
Torches are like ..well great..they are lasers but not so strong yes ?
So shouldn't colliding light cancel itself out ?
As a firm believer in empirical study I took an image of a torch and saved it then rotated it and added it to the original image. As ewe can see they are now facing each other !..but the light has not cancelled out !!...eh ?
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Light Not Cancelling Out A Minute Ago
What happens when light collides then ?...Does it scatter ?...I don't know....despite my laboratory conditional experimentation I have no answer !
what about sound ?
hugs & shmishes !
neil
Help me know and free this plight
About the nature of colliding light !
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Aha - I think I've spotted what the problem is in your experiment.
Perhaps it's best explained in the form of another experiment...
Go around to your neighbour's house in the middle of a bright and sunny day and open all the curtains/blinds in his living room. Perhaps, to ensure that the blinds/curtains aren't stopping any light from getting in, you'd better just pull them down completely. Then make a bonfire in the middle of his living room floor and observe how it doesn't seem to make your neighbour's living room much brighter. Next, wait until it's the middle of the night, go back to your neighbour's living room and start another bonfire. Now observe how the fire seems to make your neighbour's living room much brighter when it's dark.
So, where you've gone wrong in your experiment is to paste the two torches on a white background when what you should have done is to paste them on a black background. If you paste them on a black background and the light from the two torches cancel out then the background will stay black but if they don't then the background will get lighter.
HTH
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Although I have no personal experience of 6*10^15 Hz electromagnetic waves cancelling out It certainly happens at the lower frequency of 909 KHz in two places in my town which is served by two synchronised radio five transmitters operating at this frequency.
May I suggest Neilep tries using two lasers instead of torches when he will find the effect more apparent.
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Aha - I think I've spotted what the problem is in your experiment.
Perhaps it's best explained in the form of another experiment...
Go around to your neighbour's house in the middle of a bright and sunny day and open all the curtains/blinds in his living room. Perhaps, to ensure that the blinds/curtains aren't stopping any light from getting in, you'd better just pull them down completely. Then make a bonfire in the middle of his living room floor and observe how it doesn't seem to make your neighbour's living room much brighter. Next, wait until it's the middle of the night, go back to your neighbour's living room and start another bonfire. Now observe how the fire seems to make your neighbour's living room much brighter when it's dark.
So, where you've gone wrong in your experiment is to paste the two torches on a white background when what you should have done is to paste them on a black background. If you paste them on a black background and the light from the two torches cancel out then the background will stay black but if they don't then the background will get lighter.
HTH
LOL....*le that made me laugh*
I couldn't do that to my neighbour !..................oh..OK !!
I guess I should also complain to the originator of the torch piccy who should have known that I would one day want to empirically experiment with it and thus should have made for a more contrasting background !..sheesh !
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Although I have no personal experience of 6*10^15 Hz electromagnetic waves cancelling out It certainly happens at the lower frequency of 909 KHz in two places in my town which is served by two synchronised radio five transmitters operating at this frequency.
May I suggest Neilep tries using two lasers instead of torches when he will find the effect more apparent.
Thank ewe syhprum Good old radio 5. That's my favourite radio station !
If I used two of those hand held lighty pointy things...would that work...?..I'm fresh out of lasers !...tch ! [:)]
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In order to interfere, the waves coming out of the two light sources have to be "out of phase." That means when one is waving up, the other is waving down. When you add them together, you get up+down=0.
The light from your torches is going to be a really messy wave that has a lot of randomness in it. Getting it to match up and cancel out another really messy wave is going to be impossible. Lasers have very little randomness and give a nice clean wave. If you use lasers and adjust your system properly, I think you should be able to see the light canceling out in spots. The easiest way to see this is to just use one laser, chop the beam in half (you can use a mirror that reflects half the light to do this) and then use mirrors to direct the laser beams back together. Since you know both beams come from the same laser, they both have the same wave structure, and by adjusting distances between mirrors in your setup, you could make the light interfere and cancel out at points.
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What happens to the energy of the cancelled out waves?
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Newton's rings are an example of constructive and destructive interference of (monochromatic) light ...
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http://en.wikipedia.org/wiki/Newton%27s_rings
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What happens to the energy of the cancelled out waves?
Good question
It turns up in the bright bits; they are 4 times brigther than they would be with just one light source (as oposed to twice as bright as youo might expect)
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Newton's rings are an example of constructive and destructive interference of (monochromatic) light ...
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http://en.wikipedia.org/wiki/Newton%27s_rings
that's just newton's fingerprint! we see through your lies, dead man! [:D]
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What happens to the energy of the cancelled out waves?
Good question
It turns up in the bright bits; they are 4 times brigther than they would be with just one light source (as oposed to twice as bright as youo might expect)
Now i'm even more confused :p Why 4 times?
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With 2 lights shining on the surface you would expect it to be twice as bright- and, on average, it is. But, in order to make the average right the bright bits have to be 4 times brighter.
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If light has no mass, how can it be affected by gravity?
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Think in terms of electricity. If the volts add up to zero, the power is zero. If they add up to twice the voltage, the power (volts squared) will be 4 times. Total power over all space is still the same ( i.e. twice).
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Ah yes I get what you mean now.
If light has no mass, how can it be affected by gravity?
Gravity is a warping of space-time, light travels in a straight line, but it's the straight line itself that gets warped by gravity.
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In order to interfere, the waves coming out of the two light sources have to be "out of phase." That means when one is waving up, the other is waving down. When you add them together, you get up+down=0.
The light from your torches is going to be a really messy wave that has a lot of randomness in it. Getting it to match up and cancel out another really messy wave is going to be impossible. Lasers have very little randomness and give a nice clean wave. If you use lasers and adjust your system properly, I think you should be able to see the light canceling out in spots. The easiest way to see this is to just use one laser, chop the beam in half (you can use a mirror that reflects half the light to do this) and then use mirrors to direct the laser beams back together. Since you know both beams come from the same laser, they both have the same wave structure, and by adjusting distances between mirrors in your setup, you could make the light interfere and cancel out at points.
I think you just described a very basic hologram, jp.
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If two light beams heat each other at an angle, do they scatter? Or do they continue on the same path?
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Actually colliding light has been used to create an electron anti-electron pair at the Stanford linear accelerator in 1996.
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In vacuo?
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http://prola.aps.org/abstract/PRA/v62/i4/e043817
You can at least read the abstract. I've heard a couple of physicists mention the theoretical high-energy photon-photon interactions that could occur because of nonlinear effects of QED at high energies. I think there might even be a little bit of experimental evidence for it.
Also, since an electron-positron pair can annihilate into two photons, this process should be reversible. The chance of it happening when you fire two photons at each other must be tiny, though.
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In other words, for two normal light sources, you wouldn't see these effects. You need absurdly powerful lasers very precisely aimed.
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If two light beams heat each other at an angle, do they scatter? Or do they continue on the same path?
The second (unless you talk about the extremely little effect that jpetruccelli mentioned).
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Wouldn't these photons need to be gamma energies?
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I'm not sure. I would guess that to get any significant probability of it occurring you'd need gamma-energy photons. I don't know if it's impossible at lower energies, or just incredibly improbable.
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Wouldn't these photons need to be gamma energies?
I think that Heisenberg principle of ind. allows virtual fermions to be produced and coupled with photons even at lower energies and so photon-photon scattering should occur even for visible light (at incredibly smaller percentages).
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In vacuo?
They claimed the effect was the same as in vacuo, however they used high energy electrons in the process.