gib65

Disclaimer: I am absolutely not a QM-expert. I've tried reading your text but stopped after about 1/4th of the text because it became too time-consuming.

At least you read some of it. I owe you for that.

Thanks for the comments. I'll respond to a few of them. Those that I don't respond to I'm just taking as they are.

- You are saying "it's written by a non-expert for non-experts" but on your HP you say "there are two papers in this website that the reader will not get through without a thorough understanding of quantum mechanics". Sounds like some contradiction to me.

Maybe I should replace the word "thorough" with "rough".

- Explicitely not mentioning what a "mode" is leads to the information content of the whole "quantized energy" section to be zero (at least I didn't understand it).

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- Orbital. Just like "mode"' date=' except now you even have an unexplained picture using the term.

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This is a difficult thing for me. It's *partly* because my understanding of these concepts (modes and orbitals) don't stretch much beyond what I've written, but I suppose I could elaborate on it. Alternatively, I could simply drop any mention of modes or orbitals all together. On the section for orbitals, I could simply say "The reason why the pattern is unique for each element has to do with the unique structure of the atoms composing each element." and leave it at that. As for "modes", I could just say that the formula that lead to the ultraviolet catastrophe calculated the energy (not modes) of radiation at a specific frequency. This is one way I've heard the problem put, but I'm not sure if this is fully accurate (and I wondering if it matters). I have to strike a balance between thoroughness and brevity. I don't want this paper to be too long since it's only meant to be a brief rundown of quantum mechanics, but I don't want my readers to be lost in the wake either. Maybe what I should do is add a paragraph near the beginning stating that this overview is brief and may contain too much information in too little space - maybe provide some links for more in-depth reading on the subject.

 

- Chosing an appropriate f and natural n' date=' I can still get any amount of energy E=nhf. Unless there is some reason that fixes f or n, E=nhf does not quantize energy.

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n is fixed to the positive non-zero integers. That's the whole gist of Planck's hypothesis. He didn't give a reason. Einstein did though: energy comes in fundamental/indivisible particles called "photons".

 

- Mayhaps the high energy photon in the animated picture shouldn't be emitted (especially not in the direction of the outgoing electron). Picture seems pretty nice otherwise (perhaps a bit too fast).

 

As in' date=' get rid of the photon once the electron is knocked out of its orbit? That might actually be better.

 

- I am not sure that a big-bang model was widely accepted at the time atomic spectra were explained.

 

So get rid of "shortly after the Big Bang"?

 

- Not explaining orbitals => no fix on f => no quantization of energy => you didn't really show why atoms are stable. Or in other words' date=' the answer to "The reader can see how useful the quantization of energy really was to the scientific community" is "no, they can't".

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I hope that after making the above fixes, it becomes more clear.

 

- "When the amplitude doubles' date=' the light becomes twice as bright." I am not exactly sure how brightness is defined (probably something like "log(|A|²)" but you might want to look it up yourself), but I think that statement is wrong.

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You know what, I think you're right. I vaguely remember reading somewhere that the intensity/brightness of the light quadruples with the doubling of the amplitude. I'll have to look that up.

 

- "the larger the object' date=' the more narrow the region this wave covers,". Ok, you didn't explain what a wave is so there is some interpretational degree of freedom. But it's misleading, at least. For me, a baseball almost always has a wave function that is more widely spread out around the position than that of an electron (due to the internal structure).

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By "internal structure", do you mean the fact that the baseball is bigger, and therefore its wave must span at least the width of the baseball which is so much wider than the width of an electron? What if I said "the larger the object, the more narrow, in proportion to the size of the object, the region this wave covers" or something like that?

 

- Superposition is not unqiue to QM. You have superposition of gravitational fields in Newtonian gravity' date=' superposition of electrical fields in electrostatics, ... .

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Would it be better if I said superposition of position, momentum, spin, etc. is unique to quantum mechanics?

 

I stopped reading at this point; it became too time-consuming for me and I understood little. Some general comments:

 

I appreciate the reading you did do.

 

You seem to put relatively little information into a lot of words.

 

My feeling is that I'm trying to cram too much information into too few words, and some of that information is getting lost. I think it might come across as too little information because of this loss, and too many words because the lost information resides in those extra words.

 

But I do appreciate your comments, and I take most of them to heart.

 

One thing I might note: as it stands right now, most of the links don't work. That includes some of the icons in the left margin, but not all. I have these links in the left margin at key points where I feel a ton more could be said on the subject. For example, where I talk about orbitals, I have a link to the left that takes you to the wikipedia article on orbitals. The link works on my end. Mabye it doesn't for you (if not, would you please let me know?) I'm hoping this helps alleviate the difficulties with information not being clear as the reader can click on these links for further information.

The experts say to get your energy from proper diet and exercise, as well as regular sleep patterns.

I eat well and exercise regularly. As for sleep, I usually get between 7-8 hours every night, but I've got a busy schedule and it's hard.

After that, you can take all the uppers and downers you want until you die like Elvis did shitting on the toilet.

So is that a no - as in, no there's no difference in health effects between coffee and caffein pills?

Hello QM experts,

I've just written a paper on quantum mechanics, and I need some expert criticism. Basically, I want to know if I've got it right. Keep in mind it's written by a non-expert for non-experts.

The paper is written in three parts. The first part covers the basic facts of quantum mechanics, the second part covers the major interpretations in the field, and the third is my own personal take on these interpretations. Mostly, I need criticism on the first two parts. You can criticize the third part as well, but I'd appreciate if you kept your criticisms to an assessment of my understanding of the subject - not whether or not you agree with the positions I take (you can criticize my positions if you want, but that's not what I'm centrally concerned with).

I guess I should also say that this paper is part of a larger collection of papers that makes up my website. Right now, the QM paper is the only one up there, which means that a lot of the links don't work. This also means there might be some confusion over references to "my theory", so just FYI, the theme of the website is a philosophy of mine concerning the problem of consciousness (i.e. it's a theory of what consciousness is). Also note that I haven't tested it out in Mozilla (let me know if anything doesn't work in Mozilla).

Lastly, I hope it's acceptable posting a link to my website and asking people to visit it. I know this is sometimes taken as spamming or flogging, but I hope this can be taken as a special case since I'm asking for an evaluation on my understanding of quantum mechanics (consider it one enormous question that I had to create a whole new website in order to post it).

Anyway, here's the link: http://www.shahspace.com/mm-theory/qm/qm.htm

EDIT: I almost forgot to mention - I hope no one gets offended if I ask for sources in response to your comments. I know it seems contradictory to ask for criticism and then ask for proof once it's delivered, but on the internet, one never knows who the other person is. Anyone could post a criticism claiming to be an expert even though he/she is just some dilettante crackpot who thinks they know it all. I wouldn't know them from the real experts, so if I don't know who you are or if your comments seem suspicious, I might ask for sources. So don't take it as confrontational, it's just that I want to be sure I'm getting the goods.

Hi,

Are caffein pills more dangerous for you than a cup of coffee? I'm wondering because, on occasion, I take caffein pills. I know caffein in general can do damage to your kidneys over the longhaul (by increasing your blood pressure), but can the same amount of caffein in pill form do worse or other damaging things? The only thing I can think of is that caffein pills hit your system faster than a cup of coffee (more caffein consumed at higher concentration) and your body may not be prepared for the impact. In fact, I used to take a couple caffein pills first thing in the morning before I even got out of bed (I'd take them, and half an hour more of snoozing, I'd be wide awake). I've stopped doing this because I was afraid that going from an intensely sedated and groggy state to one of full awakeness in such a short period of time might be too much for my system.

What do the experts say?

Crazy!!!

Without the "borrowing" it would be as Magic.

What you call "Magic", others simply call "indeterminacy" - as in, the particle's position is not determined, and so could very well turn out to be on the other side of the barrier. The weirdest it gets, IMHO, is when one measures the particle's position and it turns up on the one side of the barrier, and then measures it again a short while after and it turns up on the other side. Then, we know that it somehow got from one side to the other. I guess some feel that this "somehow" can't be explained unless we bring in the concept of "borrowing" energy. I feel that quantum indeterminacy does the job just as well, but I'm no expert.

Does anyone know about that 3-box experiment?

No, please tell us.

My understanding of the phenomenon of quantum tunneling is that a particle surrounded by a barrier may be detected outside that barrier due to the fact that its wavefunction spans across the barrier (i.e. there's a small portion of the particle's wave that reaches beyond the barrier). Therefore, there's a small chance the particle will be found outside the barrier when measured.

What I don't understand is why some physicists feel this has to be accounted for by the particle "borrowing" energy from a parallel universe. As I see it, the idea that a particle exists as a probability wave means that we don't need any sort of energy-borrowing account. I can see that we would in the context of classical mechanics - in that case, the particles needs extra energy in order to penetrate the barrier. But by the standards of quantum mechanics, there is no "penetrating". There is only the probability that the particle will turn up outside the barrier.

So why the theory of "borrowing"?

There's this sentence from the wikipedia article on dispersion:

"refractive index n decreases with increasing wavelength λ. In this case, the medium is said to have normal dispersion. Whereas, if the index increases with increasing wavelength the medium has anomalous dispersion."

I'm not sure if I was following this correctly, but are they saying that different colors of light will refract more than other colors depending on the medium. That is, for some media, red refracts more than blue, but in other media, blue refracts more than red?

I want to follow this thread up with my latest chemically induced insight. I had this "vision" of my motabolism slowing down almost to a halt. It looked so sickly, like it had collapsed and was just hanging there. My heart had to do all that it could to keep the rest of me alive. It had to pump blood through my veins with enough force to compensate for the temporary impotence my motabolism had succumb to.

I know this is greatly exaggerated, but is this generally how it works - pot slowing the motabolism and the heart rate increasing to compensate?

Because you will shift the wavelength of the photon and it will scatter at some angle. Since energy and momentum will be conserved, this can give you the initial momentum of the electron.

Ah, thank you swansont. I finally feel enlightened . The shift in wavelength is the crucial piece of information carried by the photon that experimenters use to deduce momentum. That's exactly what I was looking for. thanks.

Scattering a photon off of a particle can tell you about the position and the momentum. But when you maximize the precision of one measurement, you maximize the uncertainty of the other.

Okay, but how? How does scattering a photon off a particle give you a measure of its momentum?

Well, since no one seems to be able to answer my question, I'll venture a guess. I'm going to say that, concerning our current technology, momentum of a particle can't be measured. The HUP is true, first and foremost, mathematically - that is, it can be shown mathematically that as one increases the precision with which one measures position, the precision with which one measures momentum decreases in proportion - and visa-versa. This tells us that, if we were to fire long wavelength photons at it (thereby degrading our position readings), the particle to be measured can gain in momentum in virtue of collapsing in the frequency domain (as D H put it). But this effect is only inferred by the math. As for verifying this collapsed frequency observationally, we don't have the means to do so technologically. But the math tells us that it's there, waiting to be measured, and if the day ever came where we would be able to measure a particle's momentum, we would find that it can only be done at the cost of precise position readings.

I would really like for someone to challenge me on this.

The HUP is inherent in the system, and really isn't about how you observe. The position and momentum operators don't commute, so there will always be an uncertainty. As D H has already said, there is a problem in trying to extrapolate from the classical world down to the quantum world.

I understand this. But how does one do a momentum reading? I understand that one fires a long wavelength photon at the particle to be measured, and I assume that it returns (with degraded position reading, of course). How does the experimenter deduce the particle's momentum from this photon?

One way to look at this is using a photography analogy. If I took a picture of an explosion, if my shutter speed was too slow, I would get motion blur. We don't exactly know the position of any fragment due to the blur. But based on the blur one can know we have momentum. If we use a shutter speed, that stops the motion, so we can know the exact position, the object looks like it is not moving.

This analogy I get - but is that the way it is in particle experiments? I mean, when you fire a long wavelength photon at an electron, say, attempting to get its momentum, does the photon come back bearing a "smeared out image" of the electron (the smearing representing the displacement of the electron)?

I'm thinking of the Heisenberg Uncertainty Principle here. I understand why an increase in the precision of position measurements results in a degradation of the precision of momentum measurements, but I don't quite understand how the reverse works - that is, getting precise measurements of momentum even though your position measurements are more uncertain. I mean, the only way I know of for getting momentum measurements is to get two position measurements, and using the amount of time between them, deriving the velocity. Multiplying that by the mass gives you momentum. But how are you supposed to get the two positions if the measurements you take of them are degraded? Is it a matter of taking many such measurements and deriving the average?

A system at an energy of nhf will go, for example, to (n-1)hf (n being an integer) and would emit a photon of hf.

Oh, I see. So a particle vibrating at, say, 3hf can emit three photons, each carrying E=1hf, right?

Thanks to the last two replies. They show a good understanding of my question and answer it accordingly. Sorry to the first two replies; I could have used better terms and ideas.

A particle, vibrating at a certain frequency, can only have descrete amounts of energy determined by E=hf. I'm told that you can have integer multiples of this basic energy amount but not fractional multiples. But what happens to the light given off by this particle if it's a multiple of E=hf? It couldn't increase its frequency because that has to stay the same as f. It couldn't increase its amplitude because that corresponds to a greater number of photons, not the amount of energy carried by each one. So in what way would the light carry more energy if E was a multiple of hf?

I'm thinking of the fact that time dilates to a halt relative to an observer at rest as you approach the speed of light. That means that no time passes for those inside the space ship that's traveling at the speed of light. All their displacement in spacetime is through space. As the space ship slows to a halt, no displacement in space occurs but displacement in time dilates to its usual rest rate (relative to an observer also at rest, of course). But what is this "usual rate"? Wouldn't it just be the same rate of displacement as that through space which the spaceship traveled when going at the speed of light? That is, when at rest, do we travel through time at the speed of light? I might be getting my terms mixed up, but isn't this what Lorentz invariance is all about?

Basically, the question is: Do we pass through time at the speed of light?

no, the filings group into lines because they themselves become magnetised. there is still a magnetic field within the gaps.

 

to have an electric field you would need to apply a charge to the magnet.

Hhm... I'm trying to find the right kind of visualization of this phenomenon. I'm taking the "leap-frog" image of magnetic waves creating electric waves creating magnetic waves... and there you have the propagation of electromagnetic waves through space. Do the magnetic and electric fields correspond to the crests and troughs of the waves? I thought the example of the iron bar might suggest they exist as a standing wave, but I guess not. Light moves, obviously, so the crests and troughs must also move through space, right?

Pretty much, it's described as boot strapping.

Okay, so let's take this image as an example:

We see that the iron filings have alinged themselves along those archs which I'm assuming are the magnetic fields. Would the electric fields be the areas in between (i.e. the white archs where no iron filings seem to exist)? If I took a bucket full of protons () and dumped them onto this magnetic bar, would they settle along the white archs between the iron filings?

Very interesting.

Now I've heard that the relation between electric charge and magnetism goes both ways - that is, that a moving electric charge creates a magnetic field, and a moving magnetic field creates an electric charge. I also heard that Maxwell proposed that this is what accounts for the propagation of electromagnetic waves through space - that is, a moving electric charge creates a magnetic field surrounding it, and since this field would have to be moving with the electric charge, it in turn creates more electric charge surrounding it, which in turn is also moving and therefore creates another magnetic field surrounding it, and that in turn creates an electric charge, and so on.

Is this how it works?

A valence electron is going to have a magnetic moment from the spin and orbital angular momentum.

So then what determines the polarity of the magnet? Is it the direction of spin or angular momentum?

Yes. Normally the effects cancel out, but not in a magnet.

Oh, of course, the electrons orbit their nuclei; I never thought of this until you put it the way you did. So what's unique about the motion of electrons in a magnet? Do they have more of a uniform pattern of motion (like most in the same direction)?

Magnetism is created by moving electrical charges.

So does that mean that the magnets on my refridgerator have electrons moving about inside (or something else eminating electric charge)?