gib65

Ok, this is going to be a very complex question, so bare with me... I've been delving pretty deep into quantum physics lately, and I'm particularly interested in the Heisenberg Uncertainty Principle. After researching it a bit, I'm starting to get the impression that there's an "early" version of it and a "later" version, and I want to know if I'm onto something here. The early version seems not to break from classical mechanics too much, although there is some "fuzziness" to it, and the later one seems to be in the thick of quantum indeterminism in a more matured and established overview of what quantum mechanics comes down to us as today. The early version comes straight out of Heisenbergs mouth: In order to grasp what Heisenberg means by a change in momentum, one need only imagine particles bumping into each other in the classical sense - changing each other's speeds and directions. I might also add that our good friend and resident physics expert swansont enlightened me about the reason why position is hard to measure if one knows the momentum:

My first thought: there can't "be" nothing. Nothing, by definition, is non-existent.

Thanks swansont. Your answers are invaluable. Something else I was wondering was who came up with the idea of a "probability wave"? I'm not even sure if any one particular person did or if it just evolved as quantum mechanics did. I'm not even sure if "probability wave" is the standard term physicists use. What I mean by "probability wave" is idea that as a particle travels through space in the form of a wave, like in the double-slit experiment, what constitutes the wave isn't really a "something" - that is, it isn't like a wave of energy, or a smearing out of the particle, or anything like that. It's the region of space where one is most likely to find the particle if one tries to measure its position. In a sense, it's really just an abstract/mathematical concept rather than a real thing with substance. The only thing that's real is that the particle's position is undetermined but mostly confined to this region. Anyway, that's my understanding of a "probability wave", and assuming I've got it right (even remotely right), I was just wondering if there's one character in history that we can credit with presenting this model.

The thing that inspired me to start this thread was a series of audio lectures I downloaded from http://www.theteachingcompany.com. The lecture are titled "United States and The Middle East: 1914 to 9/11". If you can afford to fork out a few bucks, it's worth the while to download it. Highly recommended by me. I'm up to the regan years, and in the 80s, the Israelis did some pretty atrocious things to innocent Palestinian civilians, some of which are almost on par with what the Nazis did to them. Not that the Palestinians, or other Arab states, are completely innocent either, but it just goes to shoe there are no saints in that corner of the world.

Yup, it is cool stuff. I'm writing a paper on it right now and I'm mentioning all those things. So it goes through even with the detection device present. How is this detection device setup? I imagine you could have magnets at the edges of the slits, and so if you fire charged particles at the slits, you could detect them by a slight "pull" on the magnets. It would have to be super sensitive though. Is this how they do it?

Concerning the souble-slit experiment with one particle fired at a time... If we put a detection device in one of the slits so that we can detect the presence of the particle or not, can it be setup so that the particle still passes through the slit, or does the detection device essentially block the slit entirely?

How do measurements of a particle's momentum reduce the certainty in its position? I understand how this works the other way around - when you bump a photon off a particle, like an electron, it will change its momentum. In order to have as little effect on the momentum as possible, we need to fire photons of long wavelength since the longer the wavelength, the less they disturb the particle being measured. But the photon still has to bounce back, right? And when it bounces back, you can get the time it took, and thereby figure out the position of the particle being measured just as accurately as you could when the photon had a shorter wavelength. I'm wondering if the uncertainty in position comes from the fact that, with a long wavelength, the position of the photon becomes less certain (it's "spread out" more), and so where and when it collides with the particle being measured is more uncertain. Is this right?

I take it these experiments came before Heisenburg proposed his uncertainty principle, correct? What was it about these experiments that proved randomness in natue. Was it the random scattering of impact points on the screen as the interference pattern built up (like this)?

Here's my next question: What were some of the experiments that lead to the discovery that some outcomes in quantum mechanics are random?

There are too many theories and laws to list them all for you. Although I think your question is phrased a little poorly, I think I know what you're asking for. My recommendation is to look at the sub-forum titles under "physics" on the forum index page here at SFN. Those are the major threads in the fields you seem to be interested in. I would strongly recommend starting with classical mechanics since the rest is extremely hard to understand without a strong background in this.

I've always thought (and my thoughts are very layman-like) that a dimension could be described as having the properties of linearity, continuity, and infinit extension in at least one direction. There's also how it relates to other dimensions of its kind, and that is that whatever the dimension is a scale or measure of (distance, energy, time, etc.), things that find a place on that dimension must be able to sustain or vary that place independently of its sustaining or varying its place on other orthogonal dimensions. For example, if you take one spatial dimension (call it the x-axis) and find a particle to be placed at a specific point on that dimension (say at x=5), that position should stay fixed at 5 or move away from 5 independently of its position on any other spatial dimension (call them the y-axis and z-axis) whether fixed or varying. This understanding of a dimension works just as well with physical phenomena (like space and time) as it does with non-physical or abstract phenomena, such as personality traits. For example, the theory in psychology called "the big-5" theory of personality has it that personality can be broken down into 5 major factors (Neuroticism, Extraversion, Agreeableness, Conscientiousness, and Openness to Experiences). These can be considered dimensions of personality since, theoretically, the personality dispositions of any one random person varies along each of these personality traits independently of any of the other four traits (although I think some studies show the big-5 to be not completely independent of each other, but I'm not sure).

Okay, this is starting to make some sense to me. In any case, it's more than I need to explain the photoelectric effect and atomic line spectra. I think if I delve any deeper than this, I might as well take a university level course that's heavy on the math (*shutter*). Thanks for all your answers... and stay tuned for my next question .

Okay, so the set of possible wavelengths that swansont was referring to (determined by the "universe-well") is a constraint put on electromagnetic waves only, not on energy in general (sorry if this is tedious).

Hmm, so it's a combination of the two views I'm toying with. When an electron in a particular atom (say helium) drops from one energy level to the next one down, the difference in energy need not be considered even close to the fundamental unit of energy of the universe-well (i.e. the smallest amount of energy possible - the difference between successive wavelengths). In other words, there's plenty of room for minor adjustments from one atomic system to another. Is this right?

I'm just going to throw out: the second law of thermodynamics and maybe game theory for economics and skinner's theory of language acquisition for psychology.

I think what you're saying is what I'm saying. What I mean by an "energy particle" is the fundamental unit of energy that Plank postulated and Einstein dubbed the "photon". I call it a "particle" because it's said to be indivisible like a particle of matter. I must apologize for my poor lingo. I'm not in my own waters here so it's difficult for me to be clear in my questions. Please bare with me. Basically, what I'm asking is this: is there any constraints on the amount of energy carried by a single photon? The context from which I ask this is as follows: when I first understood the basic principle from which quantum mechanics stems - namely, that energy comes in discrete packets or "quanta" - I assumed this to mean that the amount of energy one could ever encounter in anything is a multiple of n, where n is the smallest amount of energy possible... period. This puts a constraint on the amount of energy that a given photon can carry. A photon can carry n, 2n, 3n,... but never (3/2)n or (6/5)n and so on. I also understood from the photoelectric effect that as the frequency of the incident elecrtomagnetic radiation increase, the amount of energy carried by the photons absorbed by the electrons increases proportionally. Putting these two (mis?)understandings together, I took this to mean that the frequency likewise comes only in discrete amounts (knHz, 2knHz, 3knHz... where k is some constant). This would have to be the case since a frequency of, say, (3/2)knHz would correspond to a photon of energy (3/2)n which was not possible. But now I'm considering this alternate understanding: that the frequency of electromagnetic radiation and the amount of energy carried by a single photon has no constraints - it can be (3/2)n or whatever amount from the domain of the positive real numbers. What's quantized, or "indivisible", is the photon itself. That is to say, although a single photon can carry any amount of energy, as a photon, that energy cannot be partially removed or divided (or absorbed as you put it, klaynos). For all intents and purposes, it is fundamental and indivisible. It is the fundamental "quanta" that Plank proposed. Is this right? In any case, I think if I understand this stuff, my understanding of the atomic line spectra will follow.

Thanks. I guess what confuses me most is the idea that if energy is quantized, subtle changes in atomic number and repulsion/attraction forces wouldn't have much effect. Take the minor repulsion force of the electron you mentioned as an example. Supposing this force is indeed minor compared to the force with which the electron is pulled from one orbital to the next one down, then the amount of energy carried by the photon emitted in that event would be just slightly less than what it would be if no repulsion force was present (as in the hydrogen atom). Now, I'm assuming that the energy carried by the emitted photon is indivisible (that's what it means to be quantized - right?). So how is it possible to get a photon with such a minute degree less energy due to the presence of a repulsion force? Wouldn't you have to take that minute difference of energy and consider it as a removable fraction of the total energy you would have without the repulsion force? Maybe I'm thinking of these energy particles too much like matter particles. For example, if you had some particle and found that under some conditions, you could get a slightly smaller or less massive particle out of it, you'd assume the original particle was divisible. But tell me if this alternate conception of energy particles is correct: the energy carried by a photon can come in any amount - it is not limited to predefined quantities. But as a photon, no smaller amount can be extracted from it, thus rendering the photon suitable for treatment as though it were fundamental and indivisible. This way, you don't have to think of different frequencies of electromagnetic radiation as coming only in descrete amounts - it can be smooth and continuous. Would this be a better understanding (am I making sense)?

I think I get the general picture (Still a little confusing though ). Thanks. Onto my next question: atomic line spectra. I understand the general theory behind it (electrons dropping to lower energy levels, and the photons emitted carrying the difference in energy between those levels - thus corresponding to a certain frequency of light and to a specific spot and color in the range of spectral lines). What I'd like to understand better is why these spectral lines are unique from one gas to another. For example, between hydrogen and helium. It seems to me that if hydrogen and helium contain electrons in the same orbital (though helium would have 2 in that orbital where hydrogen would only have one), there shouldn't be any difference in the spectral lines. The electrons should be raised and dropped to the same energy levels. The only difference would be that it would be happening twice as often in helium since it's got two electrons, and so the spectral lines for helium would be twice as intense. But this doesn't seem to be the case in the research I've done, and I'm not sure why.

See, this is what I'm having trouble with. If an electron can obsorbe more than one photon, let's say one after the other rather than at the same time, then the energy with which it is emitted should also increase. Why don't we see this with the photoelectric effect?

I'm writing a paper on the "basics" of quantum mechanics, and I'd like to start a thread to ask questions on the subject. First of all, I'm trying to explain how the quantization of energy (and the idea of the photon) explain the photoelectric effect. Based on what I've read, I'm lead to assume that an electron can only obsorbe one photon at a time. I understand that an increase in the frequency of the incident radiation correlates with a greater amount of energy carried by the photons that make up that radiation. I also understand that an increase in the intensity of the radiation correlates with more photons making up that radiation. So, if it's only the frequency of the radiation that causes electrons to be ejected with more force, then the number of photons the electrons are douced with wouldn't be making a difference. Essential, I assume this means electrons can't obsorbe more than one photon at a time, otherwise you'd see the same effect wither by increasing the frequency or by increasing the intensity. Am I right?

How about this: if the US is going to support Israel, why not make it conditional instead of just handing Israel anything they want. Make it conditional on seceding to the one most urgently demanding condition the Palestinians (and the rest of the Arab world) want: repatriation. What the Palestinians want is their land back. But this doesn't mean booting the Jews out of Israel either - it means that it's high time they both learned to live together in the same territory. The US can make their support conditional upon this. If at least Israel agrees to this, the US continues lending support. If both agree to this, and a migration of Palestinians into Israel indeed occurs, the US can continue lending support in the form of peace keeping (i.e. making sure violent outbreaks stay at a minimal level). IMHO, this is the most fair way to go about the situation, and faced with the alternative of losing support, Israel would probably go for it, however reluctantly that might likely be.

I'm not saying it's right, and I'm not saying it's wrong either. I'm just saying it's reality. The arab world is angry at the US for supporting Israel. If the US was to pull out of the region completely (not just in terms of pulling troops out of Iraq, but in terms of any involvement whatsoever), then it would curtail a lot of the animosity you guys are experiencing. You wouldn't be doing what they say, you would just be doing what's in the best interests of your own nation.

Okay, I can understand that the US might benefit from having a foothold, even an ally, in the middle east just in case "something happens", but at what cost? There's tons of American-targeted animosity in the middle east and one of the main motives for it is the support the US gives to Israel. Isn't it at least thinkable that it's causing the US more menace than trategic advantage?

I'm not an American so I know less about the US's motives for support Israel than actual Americans. Please don't take this as a belligerent question. I'd honestly like to know.

I thought they have a fancy way of explaining particle splitting. They would say that a particle, being a vibrating string loop, is able to split itself into two segments with different vibration frequencies each.