gib65

We do need to watch out for how much value we place on "proof". Don't get me wrong - obviously we need good solid proof that global warming is real and we are the primary cause, but we shouldn't place more importance on this than on solving the problem itself.

Thank you.

The official report on global warming was announced today. Scientists made a formal statement saying that global warming is real, it is escalating at a dangerously fast rate and will make life unbearable within a few decades, and it is due to human emissions of CO2.

Is the 'De Young' experiment any different from the ones I've heard of? The ones I've heard involve single electrons (or photons) being fired at a double slitted wall and observing the interference pattern building up after a while.

I've heard of two ways to interpret the concept of "superposition": 1) particles existing in more than one place at a time, and 2) particles existing in more than one universe at a time. Is there any scientific reason to choose one interpretation over the other, or is this just a matter of philosophical speculation?

Wow, if only everyone had insights that deep when they used positive think:-)

The most general definition I can think of is "thinking happy thoughts" - at least, this is the way I've always interpreted it. Some people say that if they're in a foul mood, all they have to do is think about the good and the mood goes away. This has never worked for me. Whenever I'm depressed or angry, I'll dwell over how much "life sucks" and although I'll trying thinking "Life doesn't suck. Life is great!" it doesn't make me feel any better. I think fredrik got it right when he said it works differently for each person. For me, positive thinking works only when I can really believe in the positive thoughts. In the above example, if I told myself "Life doesn't suck. Life is great!" my mind would immediately retort with "Oh yeah? Why is life so great?" If I don't have a good rational answer for this, it will be powerless to improve my mood. It has to be something for which I can say "Hey, I've never thought of it like that before. That makes sense!" Anyway, I just wanted to know if I was the only one who really had to work hard at crafting just the right kinds of positive thoughts in order for them to work. In other words, I wanted to know if, by and large, people could think things as simple as "Life doesn't suck. Life is great!" to get themselves out of their miseries. Are there any studies that shed some light on this?

This is a question I've always wondered about. Sometimes I've tried using positive thinking to bring myself out of a miserable mood - sometimes it works, sometimes it doesn't. I think I'm one of those people whose thoughts are more burdened by emotions than the other way around. My first question: are there any studies that show that positive thinking can alleviate bad moods to a higher degree than would be expected from a placebo effect? Second question: are there any studies that show a causal relationship (thoughts effecting mood) rather than just a correlation?

Use it or lose it, eh?

From what I understand, when the brain develops, neurons grow in random directions and form random connections with each other. The more functional or effective wiring schemes are then selected for based on whether or not they help the organism accomplish certain tasks (such as recognizing food, getting past barriers, satisfying urges, etc.) What is the feedback mechanism that lets these neural circuits know that they're useful and should be preserved or improved upon?

What does it mean to say that it's wasteful to transform? Does this mean it creates waste or that it's not worth it? Also, the risk of explosion upon launch is only a danger if there are people or other life near by. But what if it was done in a relatively uninhabited area like a desert or the center of Antartica. If there is life that we're worried about in these regions, couldn't we seal the area off by some means and use it for the sole purpose of launching?

Why can't radioactive waste be launched into space? Yes, it would probably cost a lot of money and require tons of energy, but if nuclear fission supposedly creates so much energy to begin with, why not use some of that and sell some of that?

I hope I'm posting this in the right section. This was inspired by this other thread, but I think it needs to be its own thread since the course that other thread seems to be going is away from my question. What are the current problems surrounding nuclear fusion and fission as alternate energy sources? From what I understand (and I forget how I understand this), fission is messy as it leaves a lot of toxic waste behind. The problem with fusion, as I understand it (which, again, isn't saying much) is that there's no practically efficient technology to implement it. How true are these assumptions and how promising does road to solutions look? What other problems are there?

The version of the experiment I've heard involves electrons. But if Dehmelt et al. only figured out how to do it in 1973, that puts the first double-slit experiment using electrons after 1973. I thought this experiment was done in the early half of the 20th century. Thanks for the link, snail, but it doesn't explain how they did it.

How does one isolate a single electron? For example, the double-slit experiment requires that a gun fire a single electron at the slits. How do you get just one electron?

I think you might be misunderstanding what the wave actually is. It's not an "energy" wave as you called it. The electron doesn't become the wave and visa-versa. The wave is a representation of the probable locations of where the electron is. The best way to think of it is as a conceptual or mathematical tool that tells us where we can expect to find the electron when we try to measure its location. It's not actually there like a mechanical wave. What this means is that the electron has no definite location before the collapse of the wave. We call this "superposition". It's important to note that, although you'll hear superposition being defined as "being in more than one place at the same time", the most accurate way of understand it is "having equal probabilities of being measured in one place versus other places" (and even then, the probabilities aren't always equal). So, to answer your question, the bulge of the wave does not always determine where the electron will strike the plate. Even though it hits the plate first, there isn't really a "something" that's hitting it. If you look at the diagram, you'll see that the bulge is just as much a wave peek as other points along its circumference. This tells you that the electron has equal chances of being at the bulge as all the other points. Just because the bulge hits the plate first (conceptually/mathematically) means nothing insofar as where the electron will ultimate be found when measured. However, where the two waves interfere, the probability augments, and so you get double the probability of the electron being found at those points - hence, the interference pattern.

Well, they are interacting with the target screen, and this brings about the collapse. If this results in something observable, then you could call it a measurement. From what I understand, all measurement is a form of interaction, so all measurement brings about the collapse, but I'm not so sure that measurement (human observation) is the only condition under which things collapse.

I was thinking about this some more and came to some very strange conclusions. So the electron is localized when it hits the plate. Is it also localized when it hits the wall with the slits? Obviously, it doesn't hit the wall every time - at least a few times, it has to go through the slits. But when it does this, what do we say about the collapse of the wave function? Did it "partially" collapse? I mean, before it reaches the slits, I'm assuming the probability of measuring its location anywhere in front of the wall is evenly distributed over the whole area (well, tapering off as you approach the edges of the wall). Once it goes through the slits however, this distribution cannot be the same. It definitely did not hit the wall and there is an equal probability of the electron being in either of the two slits. Therefore, the electron going through the slits represents a change in the probability distribution, but not a change that is decisive in localizing the electron to one point. Does this constitute "half" a collapse, so to speak?

Really? I misunderstood the results of the experiment then. I still see how it is possible to get an interference pattern though.

As a metaphore, yes this works. But the uncertainty of a coin toss is an example of classical uncertain - that is, it is uncertain only because we haven't measured exactly the initial state of the coin toss, and we haven't done the necessarily physics and math to figure out exactly what side it's going to land on. In principle, however, this could be done and we could figure out which side it will land on. In QM, it's a whole different ball game. When we talk about the uncertainty of an electron's spin or momentum or position or whatever, we really mean that it has no definite spin, momentum, position, or whatever - at least, when it's not measured. The double slit experiment is decisive in clarifying how to interpret this uncertainty. Did you read swansont's post about this? You should read up on this. This double slit experiment shows that the only logical interpretation of its results is that a single electron is sometimes in two places at once - not that we don't know which of the two places it's in, but that it is in those two places at the same time.

Of position. Yes, there are other states (spin, for example) which may or may not collapse due to binding/absorption (AFAIK). Only over the whole area of the interference pattern, but not at a single point.

I had an insight and I want to see if more knowledgeable scientists think there is something to this. It concerned the "collapse of the wave function" of quantum mechanics and what exactly causes it. I'm going with an assumption I made in a previous thread - namely, that a photon travels as a wave for the same reason an electron travels as a wave (a-la-double-slit-experiment). I'm calling this a "probability wave" for obvious reasons. To get to the point: 1) photons are emitted and absorbed by electrons. An electron in a high energy state will drop to a low energy state while emitting a photon. It will rise to a high energy state when absorbing a photon. 2) An electron will bind itself to an atom if there is an empty orbital available to it. An electron will be "torn away" from an atom with enough energy. 3) A single electron which is not bound to an atom will travel in a state of superposition whereby it will exhibit wave properties much like that of photons. 4) The "probability wave" that describes the superposition state of an electron does not "collapse" simply by "making contact" or "colliding" with other particles or atoms. This is evinced by the double slit experiment whereby the electron doesn't "hit" the wall with the slits in it in any one definite spot, nor does it "hit" the electron-sensitive plate in any one definite spot. Conclusion: It is possible that the binding of an electron to an atom is exactly the same phenomenon as a photon being absorbed by an electron. Likewise for an electron being "ripped" from an atom and a photon being emitted from an electron. That is, the term "absorption" and "binding" are two words for the same thing. Same with "emitting" and "ripping away". In our models, we use the mental imagery of electrons "orbiting" the nucleus of an atom, and photons being "absorbed" by an electron like a spunge, but really we could think of photons "orbiting" electrons or electrons being "absorbed" by the nuclei of atoms. Furthermore, whatever this "absorption/bind" phenomenon is, it is responsible for the "collapse of the wave function" as they say. That is, an electron or a photon is in a state of superposition until it is "absorbed by/bound to" an atom's nucleus or an electron. At that point, it is definitely there wherever the atom or electron might be. This "absorption/binding" phenomenon is obvious more than just an electron or photon making contact with something (as point #4 above points out). It is a very specific phenomenon. If we could figure out exactly what it is, this might be a step in the right direction towards figuring out what brings about the "collapse of the wave function".

Can somebody comment on this? If light is a probability wave, how would this be explained?

1) I know that light exhibits wave/particle duality. 2) I know that pretty much all fundamental particles exhibit the same kind of duality where the "wave" is a region of probability where the particle might exist. Conclusion: the "wave" property of light is the same region of probability for the photon. Not exactly a deductive argument, but am I right?

How do we measure the electron's momentum?