Does a controversy still exist ?

[jtbell]

AND what's wrong with things on the web?

In addition to the points that Zz made, I'd like to add:

4. What you find on the Web, even if it's correct, is likely to be in "bits and pieces" scattered on various Web sites, and not organized in a coherent way, such as you find in a good textbook. If you want to really learn a subject, you need to do it systematically, and do exercises along the way to test your knowledge. Textbooks are (at least ideally) orgainzed to make this possible.

Many professors put lecture notes on the web, and some of them are very good. But these are also "bits and pieces", they may have mistakes because they haven't been reviewed and proofread the way a textbook would have been, and they are usually meant as a supplement to a textbook, not as a replacement for one.

While I'm at it, I have a completely off-topic question for you. :) Why do you put spaces both before and after punctuation marks such as periods, commas and question marks? It sometimes causes a punctuation mark to appear by itself at the beginning of a line in my browser, which looks strange. Remember that everyone's browser will re-wrap your text according to the width of the window that they are using.

 

[alfredblase]

I reaaallly don't want to be a pain or anything but my question is in danger of being relegated to a previous page so I have to restate it. If I am being irritating, foolish or ignorant in making it three times please tell me and I will cease, no hard feelings. It just seems people are very touchy in this thread so I'm not sure what posting guidelines apply...

Anyway the question is:

Would it be right to say that a Quantum Mechanical object, be it light or any other, is a point particle, with a time dependant probablity distribution for its position, energy, interaction with other objects, and so on and so forth? Yes or no would do please although more would be nicer. Thanks.

One thing I would say though ZapperZ is that I have done three or more modules on QM. Ok so I didn't get the basics down too good (as I demonstrated in one of my posts), but nevertheless if after a good MPhys degree I am still not sure abouthow to concieve a QM object then there are some serious conceptual shortcomings, perhaps not with the theory itself, but atleast with those who undertake to be our mentors in the subject. And no I don't think its my fault because so many people ask the same question, how do we concieve a QM object and no-one as far as I know has ever given a clear answer, even to people who know a lot of QM maths! (though perhaps still very little relatively, but FGS hwo much maths do you need to forcefeed yourself before a bit of enlightenment comes your way? And no being able to solve/rearrange lots of equations does not necesarily mean you understand physics, it means you understand maths, an important though not stand alone part of physics)

Oh and its all very well saying look in a textbook jtbell but some of us don't have convinient access to a decent library nor have the money to buy the textbooks we need. The internet therefore becomes our only source of information other than the few textbooks and notes that we already have. One of the reasons I love PF, if you can't find it on the net you can ask here hopefully, and perhaps even contribute a little.

Anyway the real point of my post is that someone should kindly answer my question: Would it be right to say that a Quantum Mechanical object, be it light or any other, is a point particle, with a time dependant probablity distribution for its position, energy, interaction with other objects, and so on and so forth?

 

[jtbell]

Would it be right to say that a Quantum Mechanical object, be it light or any other, is a point particle, with a time dependant probablity distribution for its position, energy, interaction with other objects, and so on and so forth?

Yes, with the addition that the probability distribution is not the fundamental "thing" that QM deals with in its equations. Instead, the fundamental "thing" is the complex probability amplitude \psi(x,y,z,t). This is what the Schrödinger equation actually determines. The position probability distribution is P(x,y,z,t) = \psi^\star \psi. We can also calculate probability distributions for other physical quantities, from \psi, but it's more complicated.

 

[alfredblase]

Thank you very kindly indeed, everyone I have read a post by here seems really nice btw =) Ok so everyone trained in the subject sufficiently, (not necessarily a great deal) can concieve what light is. Why is there so much mystery attached to QM still then, why have there been 104 posts in this thread?? I mean if people in the know have the simple enough explanation confirmed by jtbell, why don't they just give it every time they are asked what is light: a wave or a particle? If they get stuck on the probabilty bit just tell em to play with a coin for a while heh, and interactions... just say what's the chance I'm going to hit you? and position well just say, errm that's another story hehehe :P but check up on a conceptual explation of Heisenbergs uncertainty principle its rather interesting... and if you know it and have the patience, why not give it yourself? The actual mechanics of the thing.. do the maths xDDD

 

[Ro69]

no it would not

 

[alfredblase]

now we have a contradiction, Ro69 says nay, jtbell says yay. I tend to trust jtbell's answer more as he is a science advisor and he agrees with me, and he put some details in too.

 

[McQueen]

now we have a contradiction, Ro69 says nay, jtbell says yay. I tend to trust jtbell's answer more as he is a science advisor and he agrees with me, and he put some details in too.

But then we would have to go into what P(x,y,z,t) = \psi^\star \psi stands for , which leads to the disassociation of light and so on. Even on the question of the transition of light there are many explanations , with the classical wave explanation and the QED explanation.

 

[alfredblase]

Like Hurkyl first said all those posts ago, according to QM, light is neither a classical particle nor a classical wave.

Light (according to QM) is a quantum mechanical dimensionless particle with a probability density function for all its properties.

And QM is the most widely accepted theory and with good reason.

 

[Physics Monkey]

As Julian Schwinger noted in his excellent text on Quantum Mechanics, the classical world can be divided into two camps, the discrete and the continuous. A tension exists between these two extremes within classical physics and this tension led the early founders of quantum theory to talk at great length about the mysterious wave particle duality. As we grew in understanding it became clear that this silly classical duality is simply our attempt to force a classical interpretation on what is really a quantum unity. The photon is a quanta, neither classical wave nor classical particle. This is why practicing physicists don't talk or worry about some sort of silly wave particle duality. In my opinion, people who insist on talking about the wave particle duality are people who refuse to give up their classical notions (and of course those who are honestly learning). For these people, everything must be a classical wave or a classical particle, but nature has said otherwise.