Where can I get more information on this?

[garote]

Here's something that's been bothering me for a little while:

Light is said to act as both a particle and a wave, because it can transmit energy by "hitting" objects at particular points, and it can also interfere with itself like waves on an ocean. For light to interfere with itself, it must be a spreading entity - an ever expanding phenomenon that can occupy and potentially affect a large area, in a very un-particle-like way.

I understand that the two-slit experiment is one where single photons of light are shot at a pair of slits, and though each photon seems to choose a single place to land, the predicted range of landing places suggests that each single photon is interfering with itself as it moves along.

So at some point, the area that the light acts upon, as a wave, is 'collapsed'. All the energy spread out over that wave ends up arriving in a single place.

Here's my question: Is this collapse instantaneous? If it is, it's breaking the laws of nature, because it's affecting a change -- making the wave vanish from everywhere else -- instantly. To stay within the presently understood laws of nature, the collapse would have to occur some time during the propagation of the wave, before it gets where it's going and actually hits something.

How does this happen?

Comments

[zeroheretic.livejournal.com]

As far as your question, I got nothin, but how can a photon interfere with itself? Doesn't interference intrinsically mean that it's being affected by an outside force?

This is interesting stuff. Any physicists on your friends list? Otherwise, I'd say there's a forum somewhere where eggheads quibble about these things.. Google away.

[shinkagakusha.livejournal.com]

So, I'm a bit rusty, but IAAFSSC (Slashdot-ese for I Am A Former Solid State Chemist... har har har). I think that in the two-slit experiment, _two_ photons are sent out, one through each slit. Once they diffract through the slits, then they interfere constructively or destructively with each other.

As for your statement about light being a spreading entity, think of a light bulb outdoors. Here you have a something that is releasing a set amount of energy (photons) over time. Up close to the light it seems very bright, but as you move away, it seems dimmer, as fewer photons reach you. The way I think of it, the bulb is surrounded by a sphere of photons it has emitted. As you move farther away, the area of the sphere greatly increases, but the number of photons stays the same.

Hope this helps. E-mail me if you think I am the poo.

urgh

[garote]

Way back in high school I remember my physics teacher explaining that a photon of light was not actually a particle at all, but a series of interlocking magnetic impulses, leapfrogging over each other across the fabric of spacetime. So it's like a particle in that it goes in a straight line, and hits things, but it actually has no solid physical presence at any point along its journey.

But whether we're talking about one photon or two, I'm still stumped: As these chains interfere with each other, their energy is directed at a destination area, impacting it in a specific pattern. That pattern is mathematically similar to the pattern of interfering ocean waves impacting on a surface. But in the case of ocean waves, the wave is a result of an elastic exchange of energy between particles, in opposition to their preferred state relative to one another. Energy could be said to flow along with the wave, but the particles themselves generally stay next to their neighbors.

A single photon of light however, as one of these self-perpetuating chains, travels in a straight line, taking energy with it, and continues in that direction until it hits matter.How can photons interfere with photons?

I think I got it.

[garote]

I think I figured it out, just now. The photons don't actually interfere with each other at all -- they travel in the straight lines they always have. However, their presence creates a slight distortion in space-time around them, and when two photons pass over each other, their mutual patterns of distortion combine, and affect each photon's journey.

It helps to think of it like this:

Picture space-time as a flat rubber sheet -- like the kind used to demonstrate gravity distortion for Einstein's theories. Think of a photon as a little man, jogging along. Left foot, right foot, et cetera. Each time his foot goes down, he distorts the rubber sheet. His foot also rebounds up at him, and when he puts the other foot down, he compensates for this, so that he travels in a straight line.

Suppose two of these jogging photons are running along at a sharp angle to one another, so they will eventually collide. The men can't directly affect each other, so Instead of impacting, they'll pass through each other ... but as they stomp their feet down, they bend the rubber sheet. Depending on how their feet come down as they pass, they could send each other off in a range of directions. The closer their feet get, the greater the distortion - and the broader the range.

That describes the way that photons would "interfere" with each other without any physical contact, but there are two unanswered questions I still have:

1. A laser is a massive pile of photons with the same wavelength, traveling in the same direction -- right? What happens when two lasers interfere with each other? What kind of distortion, if any, results - and why?

2. The two-slit experiment, as I understand it, is all about photons interfering with photons. But is my understanding incomplete? Doesn't the two-slit experiment work just as well, if the firing device emits ONE photon at the two slits? That is, isn't the real mystery of the two-slit experiment that ONE photon can interfere with ITSELF, when offered multiple pathways to the same destination?