User talk:SpookyMulder

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[edit] Physics questions

Hi,

I was going to put the answers where you asked the questions, but I would probably get ripped apart (justifiably, if I'm wrong). I was about to delete what I wrote and then decided that if nobody else responds the following stuff may be a little useful.

OK some other basic questions


Hopefully this isn't common knowledge.
1) How do the detectors that can be set up at either slit work?

They work by causing some change that persists and can be observed. In order for such a change to be produced, a photon has to be absorbed, an electron is moved up in orbit, a chemical or other change is caused, and the electron falls to a lower orbit, emitting a photon. It's not the same photon, and it is emitted from the detector in one slit or the other, so no interference can result.

2) What happens if you have 3 slits in a line? in a triangle shape? unevenly spaced? what if they are round pinholes rather than slits? I've never seen these variations mentioned. I assume that a different pattern appears on the screen for each arrangement of slits/holes.

If you have a laser pointer and a small sewing needle you could easily do the three pinhole experiment yourself.

3) Water waves sent through small gaps make a moving pattern on a screen as the waves move. Does the electron/photon pattern vary over time, or is it static? I don't remember from class, it's been a while!

I think this point is one where the model or the analogy breaks down. The crests of water waves move up and down as the waves move toward the far wall. Light waves are not exactly analogous to water waves. Except for polarized light, the "peaks" of light waves could be going in any direction in a circle--assuming that they could be seen. But each photon is observed only as a consequence of a definite amount of energy being delivered to some object in the path of the light. For instance, a sensitive molecule (or molecules) in photographic film will be changed in chemical structure by the delivery of energy. So it's a little like looking at the entry wound of an arrowhead and expecting to see a record of which part of the arrowhead hit first. All you actually have is a hole. In other words, we cannot hope to observe the wave nature of light by looking at direct manifestations analogous to different water levels contacting a wall. We have to do things like looking at Newton's rings and theorizing from there.
If you are looking at a burst of light from, e.g., a laser whose switch was flicked for a short interval of time, then you are looking at a huge number of impacts. If things are slowed down by making the experimental apparatus emit only an electron or a photon at a time, then the pattern slowly builds up. (One of the footnoted sites has a good series of pictures of the actual build-up of such a pattern over time.)

4) If you gradually increase the separation of the slits, does there come a time where the photons/electrons no longer pass through both? Does each particle pass through both anyway? If not, then how, if you send them through 1 at a time, does a particle which passes through 1 slit only know the other slit is there?

I think the more basic question is why a photon goes through one slit or the other in the first place. Ordinary world experience would suggest that most of the light directed by a laser or other source of photons or electrons should hit the area surrounding the slits and be absorbed or reflected. Simple observation of a homemade two-slit experiment using a pointer laser reveals that the screen that holds the two slits is brightly illuminated. There is no magical concentration of the laser light solely on the two slits. So if only one electron is being emitted at a time, then one would anticipate that many of them would be absorbed or reflected in the same way. But until an electron or a photon actually interacts with something there is no actual location for that entity. It has a probabilistic location, i.e., a curve that predicts its likelihood of coming into interaction with the physical apparatus at various positions. So there must be a certain probabilistic expression that predicts equal opportunities for manifestation at the locations of the two slits if a certain photon or electron encountered a target there. A laster that is designed to approximate a point source and send photons in a narrow beam toward a distant target would presumably give its photons high probabilities for hitting the exact center of the apparatus between the two slits. Depending on the actual probabilities of the "manifestation" of a photon on a screen at various distances from the center of the target, one would expect that, in general, the lowest probabilities of impact would be at the greatest distance from the target center. If I've got all of the above correct, then it ought to explain how the wider the separation of slits the less the chance of transmits an electron or photon.
I dont know whether the math favors any particular slit distances.

5) If detectors on both slits detect 1 photon, I assume they slow it down but don't stop it, which makes it not coherant with say, another photon sent through the other slit at the same time? But the article says that the light doesn't have to be coherent for the diffraction pattern to show up.??

One of the problems in thinking about this stuff is that sometimes people are looking at (i.e., imagining that they are looking at) one or two photons, and sometimes they are imagining that they are looking at continuous streams of photons. In the real world people are looking at darkened photographic film, sensitive electronic sensors, or bands of light reflected from a white screen.
It is tempting to say that the detectors slow "it" down, but that is not actually what is going on. (Heisenberg actually says this with much more economy than I could ever muster. If I had a photographic memory I could probably find his words quickly.) In a double-slit experiment with open slits, a photon is emitted at one end and a physical interaction occurs at the detector. That sequence counts as one event. We can be reasonably sure that we know where the photon came from because we can test our apparatus by leaving it unpowered for a long time and seeing no light flashes on the detector screen. (We become convinced there are no light leaks or other possible sources of light.) Then when we supply current to the emitter for a very short time we get a flash very shortly thereafter. Between times there is nothing to detect. If we put a detector in the middle somewhere and a flash occurs there, then we have, in effect, just moved the detector screen closer to the source. If we put detector devices in the double slits, we will get a flash somewhere on the central wall. The high probability places for hits are at the center where the two slits are. If we get a flash in one of the detector elements tht we've placed in the two slits, then we have just observed an event--from emitter to detector. Then, if we have used a detector device that does not use all of the energy delivered by the photon, a new event occurs. To the casual observer it looks like the same event, but in fact a new photon is sent off by the detector screen. Since energy has been used to effect a change in the detector, the frequency of the second photon must be lowered. Anyway, there is now an event originating at a slit in the central screen and proceeding to the detector screen on the far wall.
Interference at the detector screen really means superposition of probability "waves" arriving from two or more sources, and their working out by the actual appearance of a "hit." (The movie of the build-up of an interference pattern over time that appears in one of the external links to the double-slit article (?) shows this build-up very nicely.)
When we are looking for interference phenomena a few photons at a time, then the importance of the exact time of arrival becomes clear. If one photon arrives 1/1000 of a second after the first photon gets to the screen, it's already all over. The first photon has shown up whetever its own probability wave and a toss of the dice determined, so it can't interfere with the second photon.
I think that the conditions for interference must be extremely tight. Consider this thought experiment: Simply put a tiny monochromatic lights in each of the slits and leave the main laser switched off. If the two lights were emitting photons continuously, then there should be probability waves arriving from two points simultaneously, and they should cancel as before. But two flashlight beams illuminating the same burglar do not cancel out and leave the burglar in darkness. If they were made monochromatic and reduced to point sources would one then notice the same interference phenomena? I think someone would have noticed by now if this effect is observable. If I had two laser pointers I could try it. But it takes time for lasers to cycle, and the likelihood that (a) they are firing in synch and (b) that they stay in synch for any appreciable length of time seem small to me.
If you think of every photon going through both slits, then every photon will "meet itself at the wall." The two versions of the probability wave are in superposition all the way along. It is only when light hits a detector that its likelihood of boosting an electron up increases to an almost certainty. (Greene says that a photon may "tunnel" and show up somehwere beyond the apparatus that is intended to contain it, but the chances for its doing so are extremely remote.)
Uh oh. I'm sorry I got into this. The probability waves are going to hit different parts of the wall at different times depending on how far the wall is from the slits. Just depending on my poor abilities to visualize, it seems that they will meet simultaneously at one point, next we will see two points (where two spherical wave fronts and the target wall meet).
Is it too simple to say that things take finite amounts of time? I think I want to find my compass and protractor. P0M 12:17, 15 October 2006 (UTC)
It just occurred to me that before lasers were available they used sunlight and a pinhole in order to get parallel wave fronts. I guess I don't know how to think about the front of a probability wave of a single photon. P0M 04:19, 16 October 2006 (UTC)

[edit] Re: Lepanto galley number

Well, nobody is really sure how many ships there were, as different sources give different numbers and combinations. There was a big discussion on comparing the sources a while back, but I'm not sure if it came to any real conclusion. Kirill Lokshin 04:35, 25 December 2006 (UTC)

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[edit] Dates

... in the text of an article should have the format [[Month DD]], [[YYYY]] or [[DD Month]] [[YYYY]] but not [[Month DD]] [[YYYY]]. Wikipedia:Manual of Style (dates and numbers) has more detail. :) Gazpacho 20:30, 3 January 2007 (UTC)

[edit] dates in naval battle list

You will see that having gone back to the wikilinked dates, I have been sorting the appearance of the list so that the year is clearly seen. I think it willb e finished ina day or so and then we will have both an easily read list by year and functioning date preferences. On a separate note; "dude" is not an accepted form of address. GraemeLeggett 13:57, 18 January 2007 (UTC)

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[edit] AFD

The article Action of 16 April 1695 has been nominated for deletion due to lack of sources demonstrating notability. Since you are an editor in good standing and continue to be interested in naval historical articles, I assume this is a workable stub, but it might help if you could expand the article or add sources showing why the battle is important, and come to AFD to resolve an apparent date problem. --Dhartung | Talk 22:17, 25 January 2007 (UTC)

[edit] "Once more" (List of naval battles)

Re: List of naval battles (note lack of caps) There is nothing wrong with the links off the article. Those with action of are followed to the article (I just tried it) and clicking on a red link takes you to edit a new article. I think you are getting me confused with the editor that put all the dates including those that were part of an article name into datelink format. May I point out (again) that messages to me belong on my talk page not my user page. Otherwise I won't get "You have new messages" flagged up. GraemeLeggett 09:19, 26 January 2007 (UTC)

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[edit] Niels Juel

Very long ago, you posted a question about the proper spelling of Niels Juel's name. I've posted a reply on the talk page. Happy editing. Valentinian T / C 21:59, 10 February 2007 (UTC)

I've posted a new reply same place. Cheers. Valentinian T / C 10:46, 11 February 2007 (UTC)

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[edit] Please provide edit summaries

Hi, I recently looked over your edits of Black Death. Although you marked the edits as minor, the change log showed the edits to be significant: [1]. It took me a second look to see that you were mostly changing spacing. It would have been very helpful if you had provided an edit summary, and then I would have rested assured at first glance that you weren't a vandal. Just a note for the future. Thanks and best regards, Icemuon 13:00, 6 March 2007 (UTC)

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