# Tag Info

1

Strangely enough, when you do a quantum mechanics experiment, you get a result that says something about what you already know. If you place a detector at one (or both) of the slits, you watch individual particles go through the slits, and you get a particle result from your detector (e.g., no interference pattern). If you don't know which slit the ...

2

No, if you observe which slit they traveled through then there is NOT an interference pattern. The act of observing, or more accurately, the need for the location of the electron to be resolved causes it to take on a definite position and then continue on from that position as a particle. If it is not observed or interacted with in some way that would make ...

2

Atoms do in fact have a sort of wave behavior you might say. Everything with mass does, even you! When the mass is small enough, like that of an electron or an atom, this behavior becomes more important to take into consideration. For example, when we go to look for an atom by shining light of a small wavelength on it, we can only say with a certain ...

2

This is just a short expansion of Ernies comment (answer really) above, same reference, and the only thing I want to add is the size of the molecules, not just atoms but 58- and 114-atom molecules, made of links of carbon, hydrogen and nitrogen. $\mathrm{C}_{60}$ Fullerene Double Slit experiment and Neutron Interference Pattern both provide details of ...

0

There's an important difference between water waves and light waves. Water waves require a medium to travel through (i.e. water). Light waves require no medium. In fact, even postulating they do contradicts special relativity. So when the waves in the water cancel out, the water is left behind, but when the light waves cancel out, nothing is left behind.

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For water waves, the quantity that is subject to interference is the amplitude of the surface disturbance (i.e. the water's height above its undisturbed value). So as you correctly stated at regions of destructive interference the water's height remains at its undisturbed value for all times. For light waves, the quantity that is subject to interference is ...

1

You're missing the very last step: averaging the intensity over time. Since there's a $t$ inside the argument of the sinusoid, the contribution of that term is zero. Averaging over time is always done in these kinds of problems, though often implicitly. For example, if you just have one slit, the electric field might be proportional to $\cos(\omega t)$, in ...

1

Use the pilot-wave metaphor The pilot-wave picture is the best way to somebody (non-physicist) understand the double-slit experiment, as a typical photon scattering experiment. You can see the pattern construction (at @annav's answer) imagining that each photon can go its path-way as particle, after a little (harmonic-randomic) oscillation in the slit. ...

1

Why doesn't the observation of the pattern count as an observation of the photons' paths? That's because knowing the position of a dot on the screen does not allow you to tell which slit the photon passed through. If you, say, used colour film and put filters over the slits, so that you'd have a red dot when the photon went through one slit and a green ...

1

Moving the observation screen as close as possible to the slits, one will observe electrons as particles and never as wave distributions. The explanation that electrons interfere with itself is a interpretation, based on the intensity distribution on the observation screen. This interpretation is saved by the fact, that any measurement of the position of the ...

6

Why doesn't the observation of the pattern count as an observation of the photons' paths? As John says, one photon gives one hit. If one thinks of a classical ball thrown at two slits the slit size of the order of magnitude of the ball size, the balls thrown aiming perpendicular to the slits location, one would get hits on a screen of two types: 1) ...

7

The photon in transit between the light source and the screen is described by a wavefunction. Specifically, the wavefunction describes a photon that is delocalised i.e. it does not have a well defined position. Because the wavefunction is delocalised it encompasses both slits, which is why we say the photon goes through both slits. Whenever you interact ...

1

Lets run a few numbers. Go with electrons. 200keV electrons (like from a standard transmission electron microscope). These have a velocity of just about 2E8 m/sec (yes, relativistic effects need to be taken into account). One nano-ampere is a little more than 6E9 electrons per second. Dividing through, that gives you, on average, 30 electrons per meter of ...

1

Just extending Anna's answer. In order to observe the interference pattern which your probing electron(s) make, its associated de Broglie wavelength has to be several tens of nanometers at least. The wavelength of the electrons consisting the wall is approximately the distance between the atoms of the wall which is at least a few orders of magnitude lower ...

3

To get a wave function one has to solve the quantum mechanical equation for the boundary conditions of the experiment:"electron impinging on two slits". In the usual description one is using approximations : the incoming electron is a plane wave, the effective potential of the electrons in the matter of the slits is high. Then the distance between slits and ...

0

Yes, it is important to take in attention the surface electrons from edges. Electrons, shoot far enough to the edge, as well as photons, interact with their electric field with the electric field of the surface electrons. The difference is, tha the first intensity fringe from electrons makes the real shadow wider. In case of photons the first fringe makes ...

1

Yes, to the notion that it is really interactions between charged particles with quantum natures. The "walls" of the slit are really the outer electrons of the surface atoms of the substance that are either covalently or metallically bonded to each other. Those bound electrons form a potential surface that is not exactly square, but when viewed from the ...

1

Imagine that the sended electron interacts with the surface electrons from the slits edges. Together they form a quantized electric field. This field is not static in the sence that the position of the incoming electron is slightly different and the surface electrons are not standing still. The incoming electrons get deflected from the surface electrons (or ...

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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 slit to detector, the actual rates don't matter - each photon interacts with the slits by itself. This URL shows such an experiment, in which a laser beam was ...

0

Yes, the electron is discribed not by a path, like a macroscopic object, but by a wavefunction. And if an undisturbed electron (we better say an undisturbed wavefuction associated with an electron) goes through the slit it, just like a normal wave, interferes with itself, producing an interference pattern that will become visible if you only wait long ...

3

Yes,you will see the interference pattern,time doesnt matter if the conditions are same. If you send one electron it will hit particular point on the screen,you cannot predict where it will hit,but ofcourse you can predict the probability of hitting a particular point. after many days,most of the electrons will hit the most probable regions and few hit ...

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There's various pictures on the internet of the double-slit experiment with electrons. Some of them are badly misleading because they show the electrons passing through the slits as dots. They aren't dots, because the electron's field is what it is. It's quantum field theory, not quantum point-particle theory. And that field doesn't stop one micron from the ...

-1

The answer is quite simple. the reason is that the first half-silvered mirror reflects the light down and therefore there is no light in the path to Cam2

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A performed in 1940 experiment contradicts the above calculations. H. Boersch get the deflection of 34 ekV-electrons on an edge. The lateral dimension of the beam was 140 Å, the distance to the edge 0,35 mm and the distance to the observation screen was 330 mm and the distance between maxima about 20 μm. Source: Die Naturwissenschaften, Heft 44/45 1940 ...

4

The interference pattern comes from the calculated wavefunction phase difference at a specific position of the detector. Every interaction of a particle along its paths (whether they are real/collapsed or virtual/calculated) would randomly bring a phase difference to the calculated wavefunction, therefore its coherence would be quickly destroyed as the ...

4

I'd like to expand my earlier comment into a little essay on the severe practical difficulties in performing the suggested experiment. I'm going to start my asserting that we don't care if the experiment is a "two-slit" per se. It is sufficient that it is a diffractive scattering experiment of some kind. However, we do care about having spacial ...

-1

As the comments have stated, you cannot do this experiment, because (1) the particle is wavelike when passing thru the slits, and (2) the cloud path only happens because a particle's wavefunc "collapses" the moment it interacts with the junk in the cloud chamber that causes the path to appear in the first place. You might as well ask how to measure the ...

-1

On January 24th, 2013 Mike W. (with help from Lee H) from the University of Illinois at Urbana-Champaign performed a thought experiment in which they sent a particle through a double slit in a bubble chamber. When the bubbles were smaller than the slit, no interference pattern occurred. For closer slits and larger bubbles, the results were inconclusive.

3

Your question touches upon the characteristic features and controversies of quantum mechanics. You want to know whether any theory can predict or explain which slit a photon passed through in a double-slit experiment. With a few caveats, the answer is that there is no such theory. Relativity, quantum field theory, string theory etc say nothing about the ...

1

Photons are elementary particles and as such obey the laws of quantum mechanics. Quantum mechanics is the underlying framework of nature, at the microscopic level ; classical mechanics, classical electrodynamics are macroscopic theories that emerge from the underlying quantum mechanical frame. In contrast to classical mechanics, where the trajectories of ...

3

How do we measure the position of an electron with a light source? Experiments with elementary particles are mostly scattering experiments. One needs the source of the particles and a detector that can identify particles. In this figure we see electrons one by one passing the slits and leaving a point (x,y) on a screen sensitive to electrons (deposition ...

0

From your description, I think you are talking about the diffraction pattern from a pinhole, and that is an Airy Disk. https://en.wikipedia.org/wiki/Airy_disk It shows a central maximum with surrounding rings which decrease in intensity as you get further from the center of the pattern.

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