Talk:Interference
From Wikipedia, the free encyclopedia
I'd like to see information here regarding the phenomena of rainbow-like interference patters as created by a continuum light source repeatedly refracting in a thin film, such as soap bubbles or oil on water. If this isn't the right article for the discussion, where would be? --zandperl 01:07, 9 Mar 2004 (UTC)
I suggest that effort should be devoted to the subject of interference at the level of
words
two languages
memory and thinking
intent and expression
etc.
in other words in more lay areas of common experience of living
Apogr 13:43, 30 Aug 2004 (UTC)
[edit] How an interference pattern is produced
In the article it is stated:
- Light beams that can produce interference patterns are called "coherent," and have all of their photons' phases aligned with each other.
This is incorrect. Incoherent light will produce an equally sharp interference pattern. White light will give an unsharp interference pattern, as the different wavelengths have different diffraction.
The famous Michelson-Morley experiment was conducted well before lasers were available. It must have tested the e~xperimentors ingenuity to obtain a lightsource that is both close to monochromous, and sufficiently bright to get a good reading.
According to quantum electrodynamics, each photon interferes only with itself. Laserlight is an exception to that: because of the cascading way they are produced laser photons are mutually connected in deeper ways than light from normal origin. --Cleon Teunissen | Talk 19:51, 22 Mar 2005 (UTC)
[edit] How do you explain this?
The text currently says:
When a single source interferes with itself, the principle of conservation of energy dictates that the energy "missing" from the darkened regions of an interference pattern where destructive interference has taken place will be found in the brightened portions where constructive interference has taken place.
Who says that there has to be a "brightened portion where constructive interference takes place"? Look at the diagram of out-of-phase reflection. If the two surfaces involved are the same distance apart at all points, then if there is destructive interference at one point there must be destructive interference at all points. It the same thing, essentially, as the noise cancellation headphones people use on airplanes. You don't cut sound to nothing at 440 hertz and get blasted by sound at 660 hertz or any other frequency. If two teams are contesting in tug of war and they are evenly matched, the flag tied to the midpoint of the rope doesn't go anywhere, but that does not mean that the energies expended by the two teams have evaporated. They are just balanced. P0M 08:07, 11 January 2006 (UTC)
- Noise cancelation equipment has indeed the property that for every zone with cancelation there must be another with mutual reinforcement. To my knowledge: a noise cancelation headphone for a helicopter pilot would actually increase the noise level in the cockpit as a whole, the technique is to set up the device in such a way that right at the point of the pilot's eardrum there is a zone of cancellation. --Cleonis | Talk 19:06, 11 January 2006 (UTC)
- I suggest that you provide a description of a device in which self-interference of oscillations from a single source is elicited, with only destructive interference. Here is an example of a device that doesn't meet that requirement: a trumpet with a single mouthpiece, but with two tubes. The length of the two tubes is such that the soundwaves that are emitted from the cones are exactly in counter-phase. Let the two cones face each other. Then very little of the acoustic energy will come out, but inside the tubes the two will reinforce each other.
- This is not something that can be covered by a single textbook citation. It is similar to the principle of conservation of energy. Strictly speaking we have no proof that the principle of conservation of energy is universally valid. What we have is that despite looking hard for it, no exceptions to conservation of energy are known. That in itself is strong evidence. --Cleonis | Talk 11:32, 12 January 2006 (UTC)
-
- I can do that, but it's not exactly to the point. You are actually supporting my position, albeit indirectly. If you produce interference as you suggest with the two trumpets, or if you produce Newton's rings with an optical device, or if you produce an interference pattern by making a double-slit device, you will get constructive interference alternated with destructive interference. There is no question about that.
-
- If you make a sound cancellation device of the sort that I've seen described, you generate additional sound with an electronic device that is out of phase with the ambient sound. So in the cockpit of the airplane, or wherever we're talking about, there is more energy being put into sound than there was before. (And it's getting marginally hotter in there too because the additional electronic circuitry being run is warming up.)
-
- All of that is irrelevant to the false statement: "the energy 'missing' from the darkened regions of an interference pattern where destructive interference has taken place will be found in the brightened portions". There is no demon in the double-slit (or other interference-demonstration) device that moves energy from the dark fringes to the bright fringes. Photons do not deviate in pairs from their original course toward the dark fringes and flock to the bright fringes. If it is a double-slit device and you merge the slits you will not find that the places that had bright fringes have now dimmed down by half because half their energy has moved back to where it belongs in the areas that were previously dark.
-
- Think of it in terms of two teams of workers. Each team is divided into two squads. Each squad can either push north or south on their pole, and each of the two poles is attached to a rigid harness on a mule that doesn't particularly want to move.
-
- Team one has its collective head together. They want their mule to go north and both squads push their poles to the north. The mule moves, kicking and braying to the north.
- >>>>>>>>>> /NN^>>>>>>>>>>.
The other team is stuck in tug-of-war mode, and one squad tries to move south while the other squad tries to move north. The mule stands quietly grazing in the middle.
-
- <<<<<<<<<< /NN^>>>>>>>>>>
- Like a book sitting on the table, you don't necessarily realize that there is force acting on the second mule. However, if the harness breaks, or if one of the attachments that holds a pole to the harness breaks, then you will realize that the forces haven't moved over to cooperate moving the mules of other teams. No work is being done because forces are balanced, but the forces haven't gone away, and the teams will get hungry and tired because they are expending energy just to stay where they are. P0M 17:14, 12 January 2006 (UTC)
[edit] Indeed, there is no demon in the double slit
I copy and paste from above
- There is no demon in the double-slit (or other interference-demonstration) device that moves energy from the dark fringes to the bright fringes. P0M 17:14, 12 January 2006 (UTC)
You are quite correct.
The current formulation in the article goes:
- When a single source interferes with itself, the principle of conservation of energy dictates that the energy "missing" from the darkened regions of an interference pattern where destructive interference has taken place will be found in the brightened portions where constructive interference has taken place.
I think I agree with you in criticising the suggestion of direction of causality. The principle of conservation of energy is something that we see around us, but it is in itself not a causative agent. It is plain wrong to suggest that conservation of energy is in a position to dictate anything, so that should be fixed. --Cleonis | Talk 20:14, 13 January 2006 (UTC)