# Wave - particle - duality

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1. Feb 13, 2016

### Brian E

If my girlfriend shouts something at me, the sound travels through the room before i hear it. The sound is a wave, I know that. But the message seems to me to be the particlepart. Can this in any way be what happens in subatomic systems as well, like we recive a wave, and reads the massage...

2. Feb 13, 2016

### Staff: Mentor

I'm sorry but I can't see any connection between wave-particle duality and what you've described.

3. Feb 13, 2016

### sophiecentaur

What is your basis for that statement?

4. Feb 13, 2016

### ZapperZ

Staff Emeritus
Before you attempt to offer an explanation to what's going on in the "subatomic systems", maybe you should read this first:

Zz.

5. Feb 13, 2016

### Brian E

Thanks to all for your replies :-)

I'm not making a claim to have discovered anything new and I know that this is not a philosophyforum. My basis for asking this question is something like this.

If a soundwave is emitted and reaches me, I see it as beeing both a wave and a message. If I hear it with my ears and brain, I don't hear or feel any waves. It is my ability to understand the wavepattern as a message that makes it "real", and in my perspective, it manifests itself as a message instantly. on the other hand, if I were an oscilloscope I would treat the message as a wavepattern.
When I read about wave/particle duality, it seems to me, that the particlebehaviour only manifests when measured or observed.
physicists asks the nature questions all the time. To my best knowledge some of these mesurements, have no known explanation, in some manner it does not exist as something meaningful to us yet.

i could explain further, but I guess I have made my point. If answering this is a waste of your time, or if this post violates the rules, im sorry

6. Feb 14, 2016

### sophiecentaur

How do you 'know' that? Your consciousness has no idea how the nerve endings in your ears get their input stimuli. You are describing a model that you have constructed in your mind, to explain the phenomenon of hearing. Phonons (the quanta /particles that are involved in some models of sound transmission) can be applied usefully when discussing how substances interact with incoming energy etc. but it is usually the case that a more straightforward Wave Approach works best.
It's not an 'either or', here; it's a 'what's best for each situation'.
But your assertion that, because you are aware of something, it must involve your ears being battered with particles, is not particularly valid. It's just a subjective interpretation.

7. Feb 14, 2016

### blue_leaf77

The wave contained in the statement of wave-particle duality actually is the wavefunction of the particle / group of particles. In other words, this "wave" satisfies the Schrodinger equation, moreover a wavefunction is not an observable quantity.
In the case of sound waves, as well as water waves or waves on string, the quantity which exhibits the waving behavior is a physically observable quantity. From this point alone, one should be able to distinguish between this type of wave and the wave meant in the wave-particle duality principle. Therefore, to answer your question, no, sound wave cannot be associated with the wave-particle duality phenomenon.
In terms of math, you can see that even in a free potential situation, the free particle wavefuntion cannot be written as a travelling wave $\psi(x,t) = A_0\sin(kx-\omega t)$, as a sound wave can be. Indeed, Schrodinger equation is not a wave equation.

8. Feb 14, 2016

### Staff: Mentor

9. Feb 14, 2016

### blue_leaf77

Well, a wave equation has a second order derivative with respect to time.

10. Feb 14, 2016

### Staff: Mentor

I'm guessing that means that the schrodinger equation doesn't.

11. Feb 14, 2016

### blue_leaf77

Yes, it does not.

12. Feb 14, 2016

### Brian E

Thanks again to you all. I see the difference now. Not that I understand all of your arguments, but I understand that soundwaves are both a wavepattern and a message. Also i think I understand, that if my reasoning were correct, smell, any form of communication and probably much more could be described as beeing either a wave or a particle. I guess I can see the difference now....

13. Feb 15, 2016

### blue_leaf77

Smell is not wave, it's just molecules in gas phase and it propagates with the help of wind.

14. Feb 15, 2016

### nasu

Well, it can be written as

Isn't this a travelling wave?
I agree that Schrodinge equation is not the standard "wave equation". But the solution is still called a wave. Maybe not by mathematicians. :)

15. Feb 16, 2016

### blue_leaf77

That's a complex quantity and thus cannot be visualized as a real occurrence in nature. It's a travelling wave in a mathematical sense but in post #7, the kind of travelling wave I was talking about is that which is real, because a mechanical wave must always be expressed as a real displacement. On the other hand, the (complex) travelling wave exhibited by quantum particle cannot be reduced to the same real expression as is a mechanical wave.

16. Feb 16, 2016

### nasu

Sound waves and EM waves can be represented by a complex quantity as well. Of course, the things that can be measured (wave intensity) will be given by the magnitude squared of this complex quantity. Same as the probability distributions for quantum particles are given by the magnitude squared of the wavefunction.
I don't think your distinction (complex versus real) is relevant in this sense.
But indeed the wavefunction above does not describe a moving particle. You need a wave-packet for this.

17. Feb 16, 2016

### blue_leaf77

Accompanied by the complex conjugate to make the entire expression real.
The fundamental difference between physical waves with that of a wavefunction is the time dependency. In the former case, the time dependency can always be expressed in terms of sine or cosine, while for the latter the time dependency is strictly given by $e^{-iHt/\hbar}$, at least for time-independent Hamiltonian.
The particle moves, with momentum $\hbar k$, in this case the momentum is single valued. A wave packet is merely a wavefunction with a form such that the particle does not have a definite momentum.

Last edited: Feb 16, 2016