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Author Topic: How can light behave as a particle AND a wave?  (Read 4887 times)

@DavidWorley94

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How can light behave as a particle AND a wave?
« on: 05/11/2010 17:30:03 »
@DavidWorley94 asked the Naked Scientists:
   
How can light behave as a particle AND a wave? cheers :)

What do you think?
« Last Edit: 05/11/2010 17:30:03 by _system »


 

Offline lightarrow

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How can light behave as a particle AND a wave?
« Reply #1 on: 05/11/2010 18:13:35 »
Because for microscopic, quantum systems, "behave as" is equivalent to "which kind of measurement apparatus + quantum system to measure, we are using". If the measurement apparatus is able to precisely register the position of the quantum system, then the quantum system (light, in this case) behaves as particle; if it doesn't, the quantum system behaves as wave (this over simplifying a lot).
As you see, it doesn't depend on the quantum system *only*, but on the measurement apparatus too.
Let's make a metaphor: if you ask to a person which film he/she saw at cinema, he/she probably won't have problems in telling you the truth; if you ask him/her if he/she has made a crime, it won'y probably tell you the truth (in case he/she has). The person's behaviour depends on the asker's question.
« Last Edit: 05/11/2010 18:15:53 by lightarrow »
 

Offline Soul Surfer

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How can light behave as a particle AND a wave?
« Reply #2 on: 05/11/2010 18:29:53 »
There is an alternative and less expected question How can an electron or a proton (or even a buckyball) behave as a wave and a particle!

The basic answer is because they do! it is a fundamental property of everything in the universe that it can behave as both a wave and a particle that applies whether or not it has mass.

Let me try to get over what is happening.  Firstly let me discuss electromagnetic radiation or light.

Electromagnetic radiation always comes in defined lumps called quanta which have a total energy of Planck's constant times the frequency of the radiation.  So you can think of a packet of waves consisting of a few cycles of the frequency which you can visualise as a particle.  The particle like behaviour is much more apparent as the energy gets greater  i.e. the frequency is higher.

Now let us think about a particle like an electron.  The wavelength of a particle has been found experimentally to be Planck's constant divided by the momentum (mass times velocity)  of that particle so the faster the particle is moving the shorter is its wavelength.  This means that the slower a particle is moving the more "fuzzy" it becomes and the less precise its location.  These wavelike properties can be observed using diffraction of an electron beam or interference using a two slit experiment  (classic wave analysis experiments). Quantum mechanics tells us that every particle and every wave in the universe exists everywhere in the universe at all times.  The fact that particles and waves can be localised with a high probability does not mean that the probability is absolutely zero everywhere else it is just very low indeed.  So a single electron wave striking a two slit pattern can interfere with itself to produce an interference pattern.
This may be counterintuitive but it IS the way the universe works and cannot be disputed!

 

Offline Bill S

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How can light behave as a particle AND a wave?
« Reply #3 on: 05/11/2010 19:12:13 »
Quote from: S S
So a single electron wave striking a two slit pattern can interfere with itself to produce an interference pattern.
This may be counterintuitive but it IS the way the universe works and cannot be disputed!
Unless, of course, you subscribe to the multiverse view; in which case trillions of shadow electrons and trillions of double slits combine to throw the whole set up into confusion. [B)]
 

Offline Soul Surfer

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How can light behave as a particle AND a wave?
« Reply #4 on: 05/11/2010 19:21:52 »
Whatever the process the results are observed and I tend to prefer simple solutions.  remember the short wavelength of the particle only applies in the direction it is travelling in other directions the particle is in effect much larger.
 

Offline sciconoclast

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How can light behave as a particle AND a wave?
« Reply #5 on: 11/11/2010 23:48:31 »
Bohr's Principle of Complementarity:   " A quantum mechanical system consisting of a boson or fermion can either behave as a particle or as a wave, but never simultaneously as both. "

www.wordig.com/definition/Principle_of_Complementarity   
 

Offline QuantumClue

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How can light behave as a particle AND a wave?
« Reply #6 on: 15/11/2010 09:12:16 »
I saw someone said the Complimentarity Principle. Yes, this is true from a Copenhagen Interpretation.

However, the root reason is the wave function. The wave function manages to spread a system over many possibilities. These possibilities become probabilistic with what is called a density of probability. This density represents what is called the collapse of the wave function, and the collapse is equivalent to finding a particle state rather than a wave form.
 

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How can light behave as a particle AND a wave?
« Reply #6 on: 15/11/2010 09:12:16 »

 

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