# Wavesor particles?

1. Jun 4, 2009

### peeyush_ali

waves..or particles..??

I didnt really get when people say that electrons are "waves" .. when we say like "shape of an "s" orbital is spherical...and shape of "p" orbital is a dumbbell and so on.." we actually wanted to show that the surface of an s orbital some how describes the the trajectory of an electron..
well i know electrostatics..so can I conclude that those surfaces are "equipotential surfaces" for they have a constant magnitude of energy ...??
well..i'm really dumbstruck when my friends argue about the electrons that they re sometimes waves and sometimes particles...
I wonder if an electron were a particle like how they teach in classical physics, will it have dimensions..like if someone says a "particle" the immediate figure that comes in our mind is of a "spherical billiard ball" which is very much a sphere with some radius..

If we take a piece of a metal and we zoom a part of it with a highly powerful microscope, then can we see electrons ..?
what is quantum physics all about..?
and what does it has to do with these things..? like Heisenberg principle..
HOW can a particle on very high velocity have wave nature..?????

Last edited: Jun 4, 2009
2. Jun 4, 2009

### Born2bwire

Re: waves..or particles..??

The orbitals are found using quantum mechanics. In posing the problem, we still assume that the electron is a point charge and we solve for the orbitals using a wave equation called the Schroedinger equation. Electrons are particles with wave-like properties that arise from Schroedinger's equation. But the orbitals represent a probability density of finding the electron in a volume in space when measured. So the orbitals do not represent a smearing of the electron or a cloud, they just represent the likely positions that we will find the electron.

3. Jun 5, 2009

### Naty1

Re: waves..or particles..??

rightly so,....it is not something thats makes "sense" in the classical way of thinking. "No one understand quantum mechanics" I believe Feynman said.

But is has a very useful set of tools for predicting subatomic behavior that matches experimental observations remarkably well..

If you really want to blow your mind, read about positrons, the antiparticle of the electron: how can THAT be?? And how can they pop into existence from NOTHING? It's a crazy subatomic world!!

Interesting question.
An electron microscope might be the finest detail instrument we have....is that still correct??
If so, it's not so easy to detect one electron with another even if it were "visible"...I guess scattering is the basic tool we still rely upon?? One of the 'difficulties' with QM is that the observations you make and the measurements you choose determine the outcome of what you may find....even if you were to "observe" an electron at a pinpoint location a moment later it will be in a different state and likely a different location.

4. Jun 5, 2009

5. Jun 5, 2009

### ZapperZ

Staff Emeritus
Re: waves..or particles..??

Atomic force microscope could be the instrument with the finest detail.

Back to the topic, please note that in QM, there are no "wave-particle duality" in describing these things. We don't switch pictures from wave to particle, and back, when we describe light, electrons, etc. There's one, consistent description, no duality.

Zz.

6. Jun 5, 2009

### peeyush_ali

Re: waves..or particles..??

Are the orbitals "equipotential surfaces" due to electrostatic interactions between protons and electrons..??

7. Jun 6, 2009

### diazona

Re: waves..or particles..??

Well, equipotential surfaces would be a good analogy, but they're really more like "equiprobable surfaces" (not a technical term) - that is, surfaces on which the probability per unit volume of finding the electron is constant.

I assume you're familiar with the electric potential field around, say, a proton. In an electric potential field, of course, each point in space has a certain value that represents the potential energy of a unit charge at that point. The wavefunction in quantum mechanics is also a field; each point in space has a certain value that represents the "amplitude" of finding the electron at that point. The amplitude is a complex number, and the square of its magnitude represents the probability per unit volume of finding the electron at that point. The greater the wavefunction's magnitude in a region, the more likely you are to find the electron in that region.

When they say that an s orbital has a spherical "shape," it really means that the corresponding wavefunction is spherically symmetric. So surfaces of constant wavefunction magnitude would be spheres. In contrast, a p orbital has a dumbbell shape, which means that the surfaces of constant wavefunction magnitude would be dumbbells. P orbital wavefunctions are not spherically symmetric, of course. All these shapes come from mathematical functions called spherical harmonics, which are part of the solution of the Schrödinger equation in a central potential (like that of a proton or atomic nucleus).

8. Jun 6, 2009

### peeyush_ali

Re: waves..or particles..??

thanks alot.. I'm a +2 student..we ve been taught classical physics...can u tell me when will i be learning about what all u hav mentioned such as amplitude..and probability of finding electrons and all... i mean at which level..??

9. Jun 6, 2009

### Staff: Mentor

Re: waves..or particles..??

It depends on how the educational system works where you live. (I don't know what a "+2 student" is.) In the USA, students usually start studying this stuff seriously in the second year of university.

10. Jun 6, 2009

### math_04

Re: waves..or particles..??

Code (Text):
Back to the topic, please note that in QM, there are no "wave-particle duality" in describing these things. We don't switch pictures from wave to particle, and back, when we describe light, electrons, etc. There's one, consistent description, no duality.

hmmm, what do u mean when u say there is no 'wave particle duality'? Light behaves as a wave and as a particle, so do electrons and other particles. Are you referring to the fact that an experiment with light will churn out either a wave or particle description but not both?

11. Jun 6, 2009

### Phrak

Re: waves..or particles..??

What are you talking about? I'm very confused by this statement.

12. Jun 6, 2009

### malawi_glenn

Re: waves..or particles..??

in QM we have the wavefunction, which is the only entity you" need". We neven go from particle to wave and vice versa in the realm of QM.

13. Jun 6, 2009

### Born2bwire

Re: waves..or particles..??

My guess to what he is saying is that when people think of dual wave-particle, they sometimes imagine it as an either/or characteristic. Light behaves like a particle since it is a photon but when it comes to diffraction and interference, then it behaves like a wave. In quantum mechanics, there is no distinction, the behavior is always the same, it is just that in some situations it will behave like a macroscopic particle and in others a macroscopic wave.

EDIT: Ahhh.. malawi beat me to it.

14. Jun 6, 2009

### peeyush_ali

Re: waves..or particles..??

what is meant by a "wave function"?? and "only entity" ??

Last edited: Jun 6, 2009
15. Jun 6, 2009

### malawi_glenn

16. Jun 6, 2009

### peeyush_ali

Re: waves..or particles..??

Are entities like "electrostatics" not allowed in QM ??

17. Jun 6, 2009

### malawi_glenn

Re: waves..or particles..??

I would not call electrostatic an entity...

but the question is not what is allowed or not, the question is if it makes sense.. and electrostatics does not make sense in QM.

What I suggest, is that you pick up a text book on QM, a really easy one, like

Quantum Physics For Dummies

The Quantum World: Quantum Physics for Everyone

The Quantum World: Quantum Physics for Everyone

HFGL

18. Jun 6, 2009

### peeyush_ali

Re: waves..or particles..??

thanks for suggesting..

19. Jun 6, 2009

### malawi_glenn

Re: waves..or particles..??

Almost all questions on "how/why do particles behaves as waves" etc have already been asked and answered 1000 000 times. If you are a physics student, you will eventually have formal quantum mechanics classes.

cheers

20. Jun 6, 2009

### zenith8

Re: waves..or particles..??

I know I keep banging on about it (the Lord forgive me) but the only way to actually make sense of the wave-particle duality stuff is to assume that there are particles and waves (de Broglie-Bohm view).

Now of course you are not morally obliged to assume this (and the officially sanctioned pigheadedness says that you mustn't - no! - but for no really good reason that would stand up in court). However if you don't want to then you mustn't ask for QM to make sense, because it can't and doesn't. It just gives a probabilistic summary of the results without any clear idea of what is going on - and that is fine for all practical purposes.

Now it is usually claimed/implied that quantum mechanics proves that a reasonable understanding of the world in this sense is impossible, and that it is impossible to write down the laws of nature in terms of a clear ontology. The existence of de Broglie-Bohm theory proves that such claims are false, even embarassingly false, because de Broglie-Bohm theory is an utterly straightforward completion of quantum mechanics. Indeed, if you study the theory closely, one sees that it is just is quantum mechanics. Nothing added, nothing taken away.

Just that when you use the word 'particle', you have to mean it.

21. Jun 6, 2009

### Hootenanny

Staff Emeritus
Re: waves..or particles..??

For those unfamiliar with the terminology, zenith8's de Broglie-Bohm theory is more commonly know as the Bohm interpretation.

22. Jun 6, 2009

### math_04

Re: waves..or particles..??

It would not make any sense if there are particles and waves. It leads to a whole heap of new questions. How is this Broglie Bohm theory different from the accepted version? I admit I have some deep misgivings about the accepted Copenhagen interpretation but it has met with a lot of success. Anyone wishing to cough up a new interpretation has a lot to prove.

23. Jun 6, 2009

### zenith8

Re: waves..or particles..??

Oh God. Sometimes you lose the will to live.

It's not a new theory - it's existed in almost its entirety since 1927 (before Copenhagen, note). The only reason it wasn't adopted at the time was for political reasons and the prevailing positivistic philosophy in the 1920s. The history of why it hasn't been adopted since is a fascinating study in the psychology of groups and misplaced hero-worship.

It gives exactly the same results as the standard theory - the only difference being that everything now makes sense and you don't have to have these endless discussions of 'what does the double slit experiment/tunnelling/Heisenberg uncertainty etc. etc. mean. So before you say 'it would not make any sense if there are particles and waves' then please think and tell us why not.

Though it superficially looks like you have to add extra maths and so on, that is just not the case. The only difference is as I said - when you say 'particle' mean it. i.e. the square of the wave function is the probability that the electron actually is at a certain point, rather than the probability of being found there in a suitable measurement. Everything else follows (the electron trajectories travelling along the streamlines of the probability current given by the standard theory etc.).

My favourite reference is this http://www.tcm.phy.cam.ac.uk/~mdt26/pilot_waves.html" [Broken] which is reasonably comprehensible to the novice and (at times) very amusing.

Indeed, or sometimes the pilot-wave theory,or Bohmian mechanics, or the causal interpretation, or the ontological interpretation, or..

Last edited by a moderator: May 4, 2017
24. Jun 6, 2009

### ZapperZ

Staff Emeritus
Re: waves..or particles..??

People, once again, I will point out to you the Marcella paper that I've cited numerous times on here (do a search if you don't believe me). In there, using QM and light as photons, one can get ALL of the wave behavior, such as diffraction and interference, without having to switch gears from "particle" to "wave". There is no "duality" in QM as far as both descriptions are concerned, unlike in classical mechanics where they are not compatible with each other.

There aren't two separate descriptions for photons, electrons, etc.. in QM. There's only ONE. It is this one description that produces ALL of the known observations for all these particles.

Zz.

25. Jun 7, 2009

### muppet

Re: waves..or particles..??

The version I heard was that at the time the pilot-wave theory wasn't sophisticated enough to deal with many-body problems particularly well, and Pauli tore it to strips such that even De Broglie himself adopted the CI, at least for a period of time. I'd be fairly sceptical as to whether or not Einstein and Schrodinger would lose a battle of "hero worship" quite so easily.