# Urgent, About the relationship of uncertainty principle and wave particle duality

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1. Nov 16, 2014

### RQwtq

Which of them comes first,(I mean the concept or the theory)? Did Heisenberg come up with the idea of uncertainty principle because of the discover of the wave particle duality?

Thanks for paying attention~

2. Nov 16, 2014

### atyy

What do you mean by "wave-particle" duality? It's usually a heuristic, rather than a specific technical term. Do you mean $[x,p]=i\hbar$?

3. Nov 16, 2014

### RQwtq

Is it true that waves sometimes behave like particles and particles sometime behave like waves? If it's true, that is what I meant......

4. Nov 17, 2014

### bhobba

The wave particle duality is actually incorrect - its neither wave nor particle - its quantum stuff. Concepts like that were part of the ideas prior to the full birth of QM that happened in December 1926 when Dirac came up with his transformation theory that basically goes by the name QM today.

The uncertainty principle follows from that fully developed theory - its a theorem about non-commuting observables.

Historically Heisenberg came up with the uncertainty principle 1925-1927. The wave particle duality probably dates from De-Broglies Phd thesis in 1924 - so it likely came first. But I want to emphasise its incorrect.

Thanks
Bill

Last edited: Nov 17, 2014
5. Nov 17, 2014

### RQwtq

I'm working on a chemistry video for homework. I want to say that it is wave-particle duality that led Heisenberg to come up with the idea. But, really, I'm not sure about it, so I'm here to ask......Now I'm even more confused

6. Nov 17, 2014

### bhobba

It wasn't.

It followed from the matrix mechanics he developed about that time.

The wave particle idea led to Schroedinger's equation and wave mechanics.

They were two different versions of QM.

It was suspected they were in fact the same theory.

Dirac succeeded in showing that in December 1926:

There were a couple of mathematical technicalities that needed elaboration due to what's called the Dirac Delta function. Von-Neumann fixed that issue in 1932 when he published his famous Mathematical Foundations of Quantum Mechanics.

Thanks
Bill

Last edited: Nov 17, 2014
7. Nov 17, 2014

### RQwtq

Ok, that's much easier to be understood. Thank you

8. Nov 17, 2014

### bhobba

Yes that's true - but its not a generally applicable principle because there are many circumstances where its neither.

Thanks
Bill

Last edited: Nov 17, 2014
9. Nov 17, 2014

thanks