How can I understand Light as a Wave?

[nikokapo]

I don't have speaker boxes to do that, but my guess is is that depending on where I'm standing the sound will change in intensity. In some places the sound will constructively interfere, correct?

Try to get ahold of any speaker box and do that, you'll be able to see it for yourself. They don't need to be B&W speakers, you can do it with cheap ones. Even your computer speakers can do it (if you own a 5.1 system in a box you can just swap polarities, they'll probably be passive speakers).

 

[nikokapo]

Sure. That's how sound suppression technologies work, like noise-cancelling headphones.

Play the 'inverse' of the noise and you've got silence.

These 'active noise control' techniques have a lot of uses, such as quieting a car engine:
Active noise control - Wikipedia, the free encyclopedia
Toyota develops noise-cancelling system for cars - MotorAuthority

The idea was to have him see for himself.

 

[ossumguywill]

The car one is cool-the problem is it doesn't actually eliminate noise... it just causes more noise somewhere else. So that's only good for the driver lol...

@niko-if I can get some tiny speakers I can do the same thing with my arduino. I'll just make a square wave sound or something, alternating from speaker to speaker.

 

[Benm]

The car one is cool-the problem is it doesn't actually eliminate noise... it just causes more noise somewhere else. So that's only good for the driver lol...

Since he's likely to be the one to purchase the system in the first place, it seems like a fine idea to me.

The concept doesnt work in practical application for light though: Sound can be measured, the cancelling sound calculated and emitted fast enough to hide/cancel a noise at some point in space.

With light the problem is that there is nothing that can go faster. You could build a similar system to cancel emitted light from a source - so no cloaking device yet

 

[rathat]

This is a great thread.

 

[RoDnSuE]

This is really a wonderful discussion. Very good reading and easier to understand than alot of others I have read on the subject.

One interesting point I have is, light cancelling devices might someday be in our future since a Harvard Physicist has managed to slow, and even STOP, a pulse of laser light in something called a Bose-Einstein condensate.

Link----Harvard Gazette: Researchers now able to stop, restart light


I don't even presume to understand all this physics talk, but I do enjoy reading and learning about it.

 

[dasraiser]

cool thread, great read.

without having the necessary equipment to try this myself , i was wondering if the double slit experiment would work if one slit was covered with a vertical aligned polarizing filter and the other with a horizontal aligned one.
my thought being that the photon travels causing a forward wake in the em field that is orientated to the photons axis and with the slits being at a smaller distance than the amplitude of this (um) wake that its causing the photon to steer via pressure drag on one side.

really sry if this makes no sense. :tinfoil:

 

[Bluefan]

I can make some sense out of it, but photons causing a wake in the EM field? Either you go quantum mechanical and there is no such thing as a EM field or the light IS the EM field. Do photons have an axis? (do they carry one around?) I think you mean the polarisation, and even with the slits so close that the EM fields overlap, they will just superimpose. Only with high powers in a nonlinear medium you will see nonlinear effects instead of just superposition. The closest you can get is a nonlinear refractive index, this can steer light by changing the medium with another high power laser.

 

[dasraiser]

my problems arise when i try to figure the transverse wave nature of light. as its transverse it has orientation (polarization) with its amplitude along that axis which is also perpendicular to the vector its travel along. (my heads hurting now)

so i guess what i meant in a sense was a polarized wave front of sorts that interacts with the slits, and placing the polarization filters over the slits with a 90' angle between them.

ok i can understand that waves in the EM band may not exist at the quantum level, but im sure other fields must exist at some level and photon interaction with electrons prove to some extent that there must be a bridge of sorts.

i guess the thing that may make sense to my understanding and maybe somewhat odd questions is that i see the universe as having infinite resolution making its size irrelevant, aka the "bigbang" created the universe at T0 in its entirety.

the rest of what ur saying is over my head back to google for some insight.

 

[xStatiCa]

But a device like "light-canceling sunglasses" in the same vein as noise-canceling headphones would be very difficult, because of many physics problems, such as working around the speed of light. The light is always moving at c/n (essentially c in air), but you have to detect the light, analyze it, and then emit new light, all while the original wave hasn't passed by yet, and yet none of your signals can travel faster than light. Easier with sound, which moves slow allowing electronic signals to move faster, so you can "get ahead" of the sound wave. Make sense?

You just need to slow the incoming light down after it is read enough to give you time to process it so that you don't need to process it faster than light. Interestingly if it could be done the effect would look kinda like the predators movie because the light that gets manipulated would be slightly delayed.

 

[Cyparagon]

While we're here, how do noise-canceling headphones not violate the law of conservation of energy?

 

[Bluefan]

They're not allowed to, it's the law after all.

But if the sound interferes destructively where your ears are, it will interfere contructively somewhere else. Interference redistributes where the energy goes, it doesn't add or takes away energy.

Another nice problem: if you have two point sources like this:

You see an inteference pattern around. This also works when you have then oscillating out of phase, the pattern only changes slightly.
But when you bring them close to eachother, much closer than the wavelength, you have two source emitting in opposite phase at practically the same location, so there's destructive interference everywhere around. Now why is the light field suddenly gone? take any one of the sources away and there's light, but adding two sources out of phase close enough takes away the light everywhere.

It took my teacher a while to answer this one

 

[HIMNL9]

The real problem trying to understand photons is, imho, that they are "undecided" beings ..... they acts sometimes as waves and sometimes as particles (and this is still confusing some of the big phisic experts ) ..... and that, sometimes, they acts also more weird than so .....

Like in the experiment of the two slits generating interferences (that is the one that demonstrates that they act as waves) ..... some scentists then had the idea to shoot SINGLE photons against the screen with the slits, for see if and when a single photon choose one or the other of the slits, and in what condition this happens ..... and they ended discovering that SINGLE photons shooted to the screen STILL PRODUCE INTERFERENCE SCHEMES, same as if they was passing contemporarily through both the slits (try to explain this without use quantum indetermination equations )

 

[Bluefan]

No they're just virtual force carrier particles (just to add to the confusion )

 

[Cyparagon]

But if the sound interferes destructively where your ears are, it will interfere contructively somewhere else.

So one's ears are always conveniently in the destructive area?

 

[HIMNL9]

^ Yes, if you're in a rave party (as "destructive FOR the ears" area )

@Bluefan: but they are virtual photons .....