Wave-particle duality is a correct theory of reality

Ostronomos

Do share your thoughts on this statement.

Mark M

Of course. We observe that light can be thought of a wave in the double slit experiment, refraction, and the fact that it emerges from Maxwell's electrodynamics as an electromagnetic wave. But we also see that light has particle-like properties. The photoelectric effect and quantum electrodynamics, in which light is represented by the photon.

Similarly, electrons, neutrons, protons, quarks, and other matter particles exhibit wave-like properties along with their obvious particle-like properties. This is observed in Thompson's double slit experiment.

ZapperZ

Please start by reading the FAQ subforums in the general physics forum.

Zz.

Ostronomos

Can you possibly point me to the FAQ? I can't seem to find it.

Mark M

Zz is referring to this FAQ:

http://www.physicsforums.com/showthread.php?t=511178

Ostronomos

Thank you.

bhobba

The wave particle duality is a crock. It is neither particle or wave - sometimes it is LIKE a classical particle in that it can have a definite position and sometimes LIKE a wave in that the theoretical solutions in certain physical situations such as being in an eigenstate of momentum is wave like - but in reality it is neither.

Thanks
Bill

Ostronomos

So if light is neither a wave or a particle then what could it be? The simplest answer is usually the most correct one so what could it be if it's neither as you say?

phinds

I take it you did not actually READ the FAQ that you were pointed to, and still think it would be meaningful to give a classical name to something that doesn't have one. From the FAQ:

Call it a quantum element or even a quantum particle, but whatever you call it, get away from any notion of definition outside of quantum mechanics.

jtbell

It is what it is. "Wave versus particle" is a false dichotomy in quantum mechanics.

vanhees71

It is really important to note that wave-particle duality is not considered a theory of reality since 1925 anymore. This has been a quite short-lived model from about 1900-1925, the socalled "old quantum theory" and it referred mostly to electromagnetic radiation (including light). In fact the old quantum theory has been discovered by Max Planck in 1900 when analysing the empirical found law about the black-body spectrum as measured by Rubens and Kurlbaum at the Technische Reichsanstalt (by the way with the very practical goal to find a technical standard for the luminsity of light bulbs, which where a pretty new invention in those days). Since Young light has been considered a wave phenomenon and since Maxwell it has been identified as an electromagnetic wave. Then Einstein in one of his famous papers in 1905 interpreted Planck's Law as a particle nature of electromagnetic waves.

After the famous interlude of the Bohr-Sommerfeld quantization conditions for the motion of electrons (particle picture!) to explain the patterns of atomic spectra, de Broglie came up with another brillant idea to describe this motion of electrons, namely the wave description, which later has been formalized by Schrödinger in his famous formulation of modern quantum mechanics as an eigenvalue problem.

In 1925 also the modern interpretation of wave mechanics and the equivalent formulations in terms of matrix mechanics (Heisenberg) and the general abstract formulation in terms of abstract Hilbert-space theory (Dirac, von Neumann) by Born has been given: The (modulus squared) wave function describes the probability distribution to find the particle at a given place. There is no wave-particle duality left in this interpretation, because the wave function doesn't refer to a physical entity like a classical field but only to the probability for the outcome of measurements on a system prepared to be in a state represented by this wave function.

bhobba

In terms of classical pictures its not anything. Mathematically its an element of a Hilbert space as implied by the fundamental principle of QM - the superposition principle which is the rock bottom essence of quantum weirdness. If a particle can be in two states (say for example be in two definite positions) then it can partly be in both states simultaneously (which means in some sense in the case of position in two positions at the same time). That is what quantum objects are - something very weird and totally unvisualisable classically.

Thanks
Bill

HallsofIvy

How is saying it is 'sometimes like a classical paricle and sometimes like a wave" NOT "wave-particle" duality. "Wave particle duality" does NOT say electrons and other thing sometimes are waves and then magically change into particles. It says that at the particle scale there is no such thing as particles or waves but objects that have properties of both.

Naty1

The modern idea of quantum field theory is that quantum fields are the basic ingredients of the universe, and 'particles' are just bundles of energy and momentum of the fields.

So for example, you can think of an electron as a wave....when it's in free space the wave is everywhere, it extends all over the place. But when attracted by a proton in a nucleus, for example, that wave is now localized...it's energy is constrained and so its different from the free space case. It's very unlikely for the electron to be found between allowed energy levels. It is now 'localized'.

Think of a violin string as an analogy: the ends are constrained, so it can have only certain tones...certain vibrational patterns and associated energies. It's energy levels are constained to certain values...it's degrees of freedom are limited. Same kind of thing happens to bound electrons...in atoms, lattices, etc. Funny thing is, the behavior of the electron can also change!!

In contrast, a free electron can take on any energy level. But when it is part of an atom or a larger structure, it's constrained...it's degrees of freedom are determined and limited by the whole structure. So an electron's energy levels and degrees of freedom are determined by the numbers of protons in the nucleus as as well as the particular structure of a lattice, as examples. The Schrodinger wave equation describes these.

A good 'particle' discussion and research paper are these:

What is a particle
http://www.physicsforums.com/showthread.php?t=386051

Rovelli:
http://arxiv.org/abs/gr-qc/0409054

bhobba

Saying it is LIKE a particle in that measurements can give a definite position and LIKE a wave in that the wavefunction can have wavelike solutions is not endorsing the wave-particle duality which is basically a load of rubbish - it is neither particle or wave but sometimes has 'aspects' (I have chosen that word with care) LIKE a particle or wave. This is very clear when considering the wavefunction, the exact nature of which is very interpretation dependent. In many interpretations it is simply a device for calculating probabilities and doesn't have any real existence - that's how they get around the wavefunction collapse issue - nothing actually collapses.

To be specific the wave particle duality says quantum objects exhibit wave and particle properties. Certainly it has a particle like property when having an exact position but its wave aspect is only what you could reasonably call a property in some interpretations such as BM - in say the ensemble interpretation it is nothing concrete at all - which is why I used the word aspect.

I also appreciate you picking up my lack of clarity - much appreciated.

Thanks
Bill