63 votes

If a photon truly goes through both slits (at the same time), then why can't we detect it at both slits (at the same time)?

Think of it this way: A photon is the detection event. When there is only one photon, there is only one detection event. The probability distribution of detection events is associated with the ...
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  • 24.1k
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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61 votes
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Double slit experiment at home failed

In order to see the interference fringes, four conditions must be fulfilled: Your light source either has to be point-like or very far away from the slits, Your light source must be monochromatic* (i....
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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
47 votes

If light propagates like waves, why can't I see around corners?

The bending of waves around corners is known as “diffraction,” and its natural length scale is the wavelength of the diffracted wave. So if you want to block the sound from a speaker playing a middle ...
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  • 74k
44 votes
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Practically, how does an 'observer' collapse a wave function?

The other answers here, while technically correct, might not be presented at a level appropriate to your apparent background. When the electron interacts with any other system in such a way that the ...
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44 votes
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When will a wave function collapse if the observer was only a camera and the video was watched later in time?

The collapse of the wave function happens whenever the quantum system initially described by the wave function becomes entangled with environment — the part of the Universe that wasn't tracked by the ...
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  • 26.6k
41 votes

What's the problem with my Young slits experiment?

The angle between maxima in the double-slit pattern is $$ \theta \approx \frac\lambda d $$ for wavelength $\lambda$ and slit separation $d$. I wild-guess that the slits in your photograph are about 5 ...
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  • 74k
33 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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32 votes
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If a photon truly goes through both slits (at the same time), then why can't we detect it at both slits (at the same time)?

If the photon truly goes through both slits (at the same time), then why can't we detect it at both slits (at the same time)? Alright, let's play some word games: This isn't a well-defined question. ...
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  • 108k
30 votes

Why is the shape of the fringes in Young's double slit experiment hyperbolic?

I will give you the mathematical details at the last, first just visualize what is going on. I am assuming that slits are like pinholes because if you took into account that they are thin rectangles ...
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30 votes
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Why aren't particles constantly "measured" by the whole universe?

Seems like the whole universe is receiving information about the electron's position. Yes, the influence that an electron exerts on the rest of the universe does depend on the location of the ...
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29 votes

When will a wave function collapse if the observer was only a camera and the video was watched later in time?

I agree with the answers given by Ruslan and Xcheckr. I would like, however, to caution against a common mistake of confusing of what an observer means in physics and philosophy: in philosophy it ...
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25 votes

Why aren't particles constantly "measured" by the whole universe?

There are time-scales related to interactions, or, equivalently, interaction rates. These interaction rates are often calculated in lowest order based on Fermi’s Golden Rule. An experiment that ...
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17 votes
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Is double-slit experiment dependent on rate at which electrons are fired at slit?

Yes, the interference pattern will occur, although you'll have to wait a while to be able to see it. As long as the average arrival time between photons is markedly greater than the travel time from ...
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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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17 votes

Is particle superposition reflected in the particle's gravitational footprint?

The simple answer is that we don't know because we have no theory of quantum gravity. If I interpret your question correctly you're thinking about semiclassical gravity, where matter is quantised and ...
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17 votes

Question on wave interference?

Actually, you're completely right. Most treatments of the double slit have some kind of simplification. The usual idea is that we approximate each slit in the double slit to be a point source, so what ...
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17 votes

Does the particle interfere with itself, or the observer?

The term 'observe' does not mean watching the experiments from a camouflaged hideout so that no one notices you are there. 'Observe' here means 'making a measurement' and hence interacting with the ...
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  • 23k
15 votes
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Differences in Double slit experiment and 2 slit Diffraction

A realistic double-slit has two effects at play: there is single-slit diffraction from each sit (giving rise to the larger envelope) and there is interference between the two beams of light from each ...
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14 votes

How does the light source fire a single photon in the double-slit experiment

A light beam is not like a swarm of photons flying through space - the relationship between light beams and photons is rather more complicated than that. This is discussed in What is the relation ...
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14 votes
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Why does fringe width in double slit experiment remain constant if slits get narrower?

If I'm misunderstanding anything about your question, feel free to tell me. As I derived in this post, the (one-dimensional) formula for the double-slit intensity (in the Fraunhofer regime) is $$ I(\...
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13 votes
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Is a photon always in a state of superposition while traveling through space?

It's tempting to think of the light as a little ball (the photon), and since little balls have a definite position the little ball has to be in a superposition of a state where it goes through one ...
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13 votes

Is particle superposition reflected in the particle's gravitational footprint?

There are several misconceptions here to correct: Double-slit experiments with humans or cars are impossible in any meaningful sense. If you compute the deBroglie wavelength of humans or cars with ...
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  • 108k
13 votes

When will a wave function collapse if the observer was only a camera and the video was watched later in time?

Collapse is not a physical phenomenon! It may be real in a metaphysical sense, but this is a physics website. Collapse is a numerical tool. Here is how we use it: We divide the "universe" ...
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13 votes

If light propagates like waves, why can't I see around corners?

Light traveling in straight lines is an approximation that works very well most of the time. The most common case where it fails is when light travels through a pinhole or slit. Then it bends a little....
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