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Wave - Particle Duality





Dennise
Quantum physics tells us that particles can exhibit wave properties, and conversely, light waves can exhibit particle properties. The famous double slit experiment (Young?) I think reveals both properties.

Because the wave-particle duality is nearly always discussed in a quantum context, my question is this:
Can wave-particle duality (E = hv) be extended to the general case? For example, what are the wave properties of an automobile, and what are the particle properties of a 60 Hz wave? Does E = hv always hold?

One article on gamma radiation is most confusing. It states "Gamma radiation is one of the three types of natural radioactivity. Gamma rays are electromagnetic radiation, like X-rays. The other two types of natural radioactivity are alpha and beta radiation, which are in the form of particles."

Now if wave-particle duality is indeed a general theory, the above is nonsense because alpha, beta and gamma rays in their wave 'guise' are all forms of EM radiation differing only in frequency. In their particle guise, they are all particles differing only their (kinetic?) energy.[/url]

Can someone please comment on this dilemma?
codegeek
I think that although all waves are moving particles and all moving particles are waves, it is not always evident because the wavelength is too long or too short, which has an effect on the frequency.
kelseymh
Dennise wrote:
Quantum physics tells us that particles can exhibit wave properties, and conversely, light waves can exhibit particle properties. The famous double slit experiment (Young?) I think reveals both properties.


Hi, Dennise. The classical double-slit experiment does not exhibit quantum complementarity (also called "duality"). Rather, it's a conclusive demonstration of the wave nature of light, and (classically!) a refutation of Newtion's theory that light was made of particles.

You can do the double-slit experiment with light, with sound, even with water waves! You just have to make sure that the "slits" in each case are small, comparable in size to the wavelengths you're dealing with. In all cases, with waves you'll see a pattern of "bright" and "dark" stripes on the other side, caused by the waves from each slit interfering constructively and destructively.

The quantum double-slit experiment is where you pass quanta (like photons, or electrons, or even molecules) one by one through the apparatus, and record the position where each one hits on the far side. In that case, since you're treating the quanta like "particles" (one by one, hitting in a particular place), you would not expect interference. But, if you wait long enough, the pattern you see will have interference stripes!

This is an experiment you can do yourself, at home. I've written up instructions for it, if you're interested: http://www.instructables.com/id/Double-slit-Interference-Experiment/.

Quote:
Because the wave-particle duality is nearly always discussed in a quantum context, my question is this: Can wave-particle duality (E = hv) be extended to the general case? For example, what are the wave properties of an automobile, and what are the particle properties of a 60 Hz wave? Does E = hv always hold?


To answer your last question first, yes. All electromagnetic radiation, from radio waves all the way up to gamma radiation, are quantized, with E = hf (the symbol for frequency is the Greek lower-case nu, which resembles an English "v").

But E=hf isn't really a statement of wave-particle duality. It's a statement about the quantization of EM radiation. Wave particle duality is better expressed in the form of Heisenberg's uncertainty principle: delta-p * delta-x >= h/4pi. That is, the spread in momentum of a wavefunction is related to the spread in position. This relationship is nothing more than the regular old Fourier transformation relationship between wavelength/frequency and position, but with the quantum-mechanical addition that wavelength and momentum are equivalent.

Now, back to your second question. Yes, a car has a quantum wave nature. However, because its mass is so huge, the wavelength (de Broglie wavelength) is infinitesimally small. For example, the de Broglie wavelength of a caesium atom is about 10^-25 m. Since a car contains about 10^30 atoms (5000 moles or so), it's wavelength would be something like 10^-55 m!

Quote:
One article on gamma radiation is most confusing. It states "Gamma radiation is one of the three types of natural radioactivity. Gamma rays are electromagnetic radiation, like X-rays. The other two types of natural radioactivity are alpha and beta radiation, which are in the form of particles."
Now if wave-particle duality is indeed a general theory, the above is nonsense because alpha, beta and gamma rays in their wave 'guise' are all forms of EM radiation differing only in frequency. In their particle guise, they are all particles differing only their (kinetic?) energy.[/url]


Alpha particles are not electromagnetic radiation. They are the nuclei of helium atoms, consisting of two protons and two neutrons in a bound state.

Beta particles are not electromagnetic radiation. They are high-energy electrons.

You can do experiments (which I alluded to above), to demonstrate that electrons and alpha particles have wave-like quantum properties. But that does not in any way make them electromagnetic radiation.
metalfreek
Quantum objects are neither wave nor particles. That's what I have learned so far. Very Happy
kelseymh
metalfreek wrote:
Quantum objects are neither wave nor particles. That's what I have learned so far. Very Happy


They are neither, and they are both. The best word to describe them is quanta.
Dennise
Thanks kelseymh for your informative reply and corrective comments about the double slit. However, you said:

Quote:
Alpha particles are not electromagnetic radiation. They are the nuclei of helium atoms, consisting of two protons and two neutrons in a bound state.


But what about this statement:

When Uranium-238 decays into Thorium-234, an alpha particle is produced in the form of alpha radiation.

Yes an alpha particle is a helium nucleus as you said, but can it also be manifested as EM radiation waves? Isn't this an example of wave - particle duality?
_AVG_
Dennise wrote:
Thanks kelseymh for your informative reply and corrective comments about the double slit. However, you said:

Quote:
Alpha particles are not electromagnetic radiation. They are the nuclei of helium atoms, consisting of two protons and two neutrons in a bound state.


But what about this statement:

When Uranium-238 decays into Thorium-234, an alpha particle is produced in the form of alpha radiation.

Yes an alpha particle is a helium nucleus as you said, but can it also be manifested as EM radiation waves? Isn't this an example of wave - particle duality?


I think it may manifest as a wave or a particle, or neither, or both but in the case it does manifest as a wave, it wouldn't be an EM wave. An EM wave's particle equivalent is a photon.
You could have an EM wave form though if the mass of the fast-traveling helium nucleus (which constitutes the alpha ray) is converted to energy (but this would require a lot of quantities to be conserved, most likely an anti-alpha ray would be needed to do this). I'm not sure, I may be wrong about this.
kelseymh
Dennise wrote:
Thanks kelseymh for your informative reply and corrective comments about the double slit. However, you said:

Quote:
Alpha particles are not electromagnetic radiation. They are the nuclei of helium atoms, consisting of two protons and two neutrons in a bound state.


But what about this statement:

When Uranium-238 decays into Thorium-234, an alpha particle is produced in the form of alpha radiation.

Yes an alpha particle is a helium nucleus as you said, but can it also be manifested as EM radiation waves? Isn't this an example of wave - particle duality?


No. An alpha particle, which is also called, for historical reasons, "alpha radiation", is a helium nucleus. Period. It is not electromagnetic. It is a bound state of two protons and two neutrons, with an electric charge of +2.

The word "radiation" does not have to mean electromagnetism. It refers to any kind of invisible influence which can zap you and cause damage. Oh, yes, and it is only used in that way by (a) non-scientists who don't know what they're talking about, or (b) by science writers who think their audience is too stupid to understand properly used terminology.
Dennise
Ahh semantics and language limitations ..... especially in the quantum world.

Would you say Wikipedia is correct on 'radiation'?

Perhaps I'm trying too hard for a generalized macro understanding of particle wave duality. Is it correct to conclude that electromagnetic waves are only generated by an accelerating electric charge, and that particle waves are a completely different beast restricted to the quantum world?
kelseymh
Dennise wrote:
Ahh semantics and language limitations ..... especially in the quantum world.

Would you say Wikipedia is correct on 'radiation'?


They provide the correct definition of "radiation" as used in occupation health physics, nuclear engineering, and similar fields. Notice that they carefully distinguish between electromagnetism and particles, and make it clear that they are entirely different things.

Perhaps I'm trying too hard for a generalized macro understanding of particle wave duality. Is it correct to conclude that electromagnetic waves are only generated by an accelerating electric charge, and that particle waves are a completely different beast restricted to the quantum world?
[/quote]

Yes, that is exactly right. EM waves are generated by electric or magnetic fields which vary in time, such as a moving charge, moving magnet, or changing electric current. "Particle waves" (or "de Broglie waves") are a representation of the quantum mechanical wavefunction of an entity, and are not electromagnetic.
Dennise
Kelseymh, I think you've nailed it nicely.

Thanks.
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