138 votes

How does light 'choose' between wave and particle behaviour?

In fact, light is not really a wave or a particle. It is what it is; it's this strange thing that we model as a wave or a particle in order to make sense of its behaviour, depending on the scenario of ...
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  • 1,639
68 votes
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What do we see while watching light? Waves or particles?

You are seeing particles. However there's more to this than meets the eye so I need to explain exactly what I mean by this. Light is neither a particle nor a wave. Instead it is a quantum field. As a ...
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62 votes
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In the double-slit experiment, why is it never shown that particles may hit the space between or outside the slits?

"Is it because they are just simplified illustrations?" you ask. The answer is simply: yes it is because they are simplified illustrations. Furthermore, not only can the particle hit the barrier ...
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52 votes

Is it wrong to say that an electron can be a wave?

What is a wave? From sound and water waves we come to an association with sine and cosine variational behavior. Wave equations are differential equations whose elementary solutions are sinusoidal . In ...
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  • 223k
52 votes
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Did I get hit by a car this morning?

Asher's comment written above is simply wrong, and the reason is rather fundamental in quantum mechanics. "The car slightly hits you" isn't how it works in quantum mechanics. The reason is that weak ...
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43 votes

What's the significance of the nickel crystal in the Davisson and Germer experiment?

They were looking at the scattering of electrons from samples of nickel out of general interest, and because their nickel target was polycrystalline the electrons came off pretty much in all ...
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  • 9,357
43 votes

What actually is white light?

There is some confusion of terms in the question. A photon is an elementary particle in the standard model of particle physics, see table. Its mass is equal to zero, it is a point particle, and its ...
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  • 223k
34 votes
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How does the light source fire a single photon in the double-slit experiment

I think there's a bit of confusion here. The double-slit experiment was not performed with "single photons" - it's very hard to even consider what that would mean. At its heart, it is a thought ...
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  • 5,992
33 votes
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Heisenberg's Uncertainty Principle

From the comments, you seem to want the minimum possible math. There are 4 things you have to know first: First, what you have to know is that a basic quantum wavefunction can be imagined as exactly ...
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33 votes

How can an electron be a point particle but also a wavefunction?

A point particle is a point in space of a fixed co-ordinate That is not what a point particle is in modern physics. A point particle is a particle with no structure as measured by scattering ...
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  • 69.2k
32 votes
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Why do photons follow specific path after reflection from a mirror surface if they can be emitted in any direction by electrons of mirror surface?

Although a single photon can only be absorbed and emitted by a single electron, it leaves that electron in exactly its original state. There is no record, and no way of knowing, which electron ...
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30 votes
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Why is the force exerted by a light beam on a spherical object independent of the amount of light reflected or absorbed?

Consider a photon that strikes the center and is reflected straight back on itself. That photon gives the sphere twice its momentum. Consider a photon that strike the edge at a glancing angle and is ...
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  • 27.8k
29 votes
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Why did Feynman say the double slit experiment "contains the only mystery" of quantum mechanics?

I think what he was getting at is that we don't yet have a single agreed interpretation of what is 'really' happening at a quantum level, and the two-slits experiment typifies the nature of the ...
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  • 20.2k
26 votes
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Why would Pilot-Wave be wrong?

Let me first say that I'm a fan of this theory, so whilst I'm giving what I believe to be a neutral response, bare in-mind that I'm pro-Bohmian which is in many fields an atypical viewpoint. To ...
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26 votes

'Why' is the Schrödinger equation non-relativistic?

In non-relativistic Quantum Mechanics (NRQM), the dynamics of a particle is described by the time-evolution of its associated wave-function $\psi(t, \vec{x})$ with respect to the non-relativistic ...
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25 votes
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Is the Uncertainty Principle valid for information about the past?

The uncertainty principle should be understood as follows: The position and momentum of a particle are not well-defined at the same time. Quantum mechanically, this is expressed through the fact that ...
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  • 15.8k
24 votes
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Why doesn't De Broglie's wave equation work for photons?

What you have there isn't actually de Broglie's equation for wavelength. The equation you should be using is $$\lambda = \frac{h}{p}$$ And although photons have zero mass, they do have nonzero ...
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  • 74.1k
24 votes

What is an example of an electron acting as a particle?

In an old-school TV picture tube, electrons were shot into one end of it, accelerated, steered into specific directions, and then collided with a thin phosphor coating on the inside of the picture end ...
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21 votes

Example where photon acts only as a wave

It is not true to say that a photon acts in some circumstances as a classical particle and in other circumstances as a classical wave. Rather, it acts in all circumstances like a quantum thing, which ...
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21 votes

Can particles be in a superposition of times as well as positions?

I don't think this question has an exciting answer. Strictly speaking, superposition refers to a wavefunction occupying multiple states at a particular time, so the question you've asked is "why ...
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  • 9,227
21 votes
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If particles are also waves cant we invert them by making it reflect off a fixed boundary?

Here is a simulation of the Schrödinger equation I made a while ago: In the gif you see the Schrödinger equation for a single, one-dimensional particle. The particle moves on the left-to-right axis ...
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20 votes
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What actually is white light?

It is very important to understand that white is not a spectral color, but a perceived color. Why? White is not a spectral color. It's a perceived color. The human eye has three kinds of color ...
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20 votes

What is an example of an electron acting as a particle?

Some examples of electrons behaving like a particle: The photoelectric effect : As beautifully described by Einstein, electromagnetic radiation hits a material which leads to the emission of ...
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  • 4,408
20 votes
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Example where photon acts only as a wave

There is a misconception in the question, a photon by axiomatic definition in the standard model of particle physics, where it is defined in the table is always a point particle, and its kinematics is ...
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  • 223k
19 votes

'Why' is the Schrödinger equation non-relativistic?

To do relativistic quantum mechanics you have to abandon single-particle quantum mechanics and take up quantum field theory. The Schrödinger equation is an essential ingredient in quantum field theory....
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19 votes

If photons have also particle properties why should they not collide with each other?

Having particle properties does not mean that a photon is a small sphere traveling at the speed of light. Collisions in quantum mechanics mean that particles interact and modify their free-particle ...
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  • 25.1k
18 votes

How does light 'choose' between wave and particle behaviour?

How does light 'choose' where to be a wave and where to be a particle? It doesn't, YOU do. That's really the entire "weirdness" of quantum right there. It's not entirely crazy. If you measure a car ...
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17 votes

Is it wrong to say that an electron can be a wave?

Yes. No! Both! Neither? The electron is an excitation of the QED quantum field, which is not quite compatible with the classical notion of either fields or particles. All you can do is draw analogies ...
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