If a narrow slit makes monochromatic light coherent, why is light required to pass through the single slit before the double slits in Young's experiment? Wouldn't the double slits individually make light coherent if narrow enough and then form an interference pattern without a single slit?
36516
In , a home experiment is presented which appears to produce a very good double-slit interference pattern with normal sunlight.  The experiment is an empty cardboard box with a visor and a placeholder for a microscope slide with two slits on one side. This is arranged with the slits and visor facing the Sun, so the interference forms on the bottom of the box.    They claim to observe a good interference pattern from the two slits:    Discussions of interference in optics textbooks often stress that coherent light is needed to produce such patterns, and that sunlight and other thermal sources of light do not have such coherence. How, then, is this possible?
56054
My question is a little silly I know, but I'm curious to know if a particle of light can be theoretically trapped between two reflective screens.   For example once the particle of light has left it's source, and is reflected against a mirror (assuming there is no loss of energy) and you immediately replace the source of light with another mirror. Would the light beam bounce in between the sheets endlessly?
118354
I was wondering why a laser beam diverges. If all the photons are in the same direction, I would imagine that it would stay that way over a long distance. I am aware that a perfectly collimated beam with no divergence cannot be created due to diffraction, but I am looking for an explanation based on  photons rather than wave physics.
6863
So light travels slower in glass (for example) than in a vacuum. What causes light to slow down? Or: How does it slow down? If light passes through the medium, is it not essentially traveling in the "vacuum" between the atoms?
78347
Whilst going through 'A brief history of time', I faced difficulty in understanding the . How can an individual electron cause fringes on screen? I was unable to understand it? Please explain it simply.
11714
The assumptions are:    Alice and Bob have perfectly synchronized clocks Alice and Bob have successfully exchanged a pair of entangled photons   The idea is simply to have Alice and Bob perform the Quantum Eraser Experiment (doesn't need to be the delayed choice).   Alice and Bob agree on a specific time when Bob's photon will be between the "path marker" (which is usually just after the slits) and the detector.  If Alice acts collpasing the wave-function on her photon, the interference pattern will disappear. If not it won't.  Alice and Bob can be spatially separated...  What am I misunderstanding?   The only meaningful difference from this spatially separated quantum eraser experiment to one done on tabletop is that you won't be able to use a coincidence detector, but that is not impeditive to identifying the interference pattern, just will make errors more probable. Which we should be able to deal with a appropriate protocol...  There is a experimental paper with a small amount of citations pointing out to the breaking of complementarity in a very similar setup:
104212
I remember sitting in on a conference talk by a person (possibly Rainer Blatt) doing research with trapped ions (or single atoms strongly coupled to light in an optical cavity), and the person showed a photo of the trap with dots of light from the fluorescence of the single atoms/ions. I thought the person mentioned you could see this with the naked eye b/c the optical coupling to the ion in the trap was so strong, but thinking about it now I'm not sure if this can be true and I can't seem to find any (obvious) reference to this in the literature.    So my question: Is it possible to see light from a strongly coupled single atom or ion with the naked eye? If so can you point me to a reference (and hopefully an image of this as well)?    Note: The best I can find is the image below from the  taken with a CCD (). However it is not at all obvious that this would be visible to the naked eye, or if the exposure was just set very high on the camera.
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This is a thought experiment where I have made a &quot;C&quot; shaped hole inside diamond. The refractive index $(\mu)$ of diamond is 2.45. Say we shine a laser from top of the &quot;C&quot; as shown. My calculations show that light reaching A can reach B in the least possible time if gone through the &quot;C&quot;. but I'm pretty sure the perpendicular laser beam travels undeflected and straight down. Though I don't have experimental evidence, I see something wrong either with my intuition or with the theory. It would be great if someone could clarify. *       'a' in the diagram is the thickness of the cutout and all comparable distances can be taken 'a'.
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I understand that assuming light is quantized implies that if a lower energy interacts with  metal, it is possible that that quanta will not have enough energy to eject the electron. What prevents two quanta from interacting with the electron at the same time, though, and summing to have enough energy to release the particle. Indeed, what if two separate light rays of the same frequency impact the electron, why can't that free it?
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I'm curious about QM and spent the last 3 days thinking about Delayed Choice Quantum Eraser (DCQE) experiment, but I couldn't solve this issue:   Assume we do the DCQE experiment so that for the whole experiment (let's say, 1000 particles) finishes before the first particle reaches the detectors 1-4 (using the notation from ). Assume also we're using a switch to control if the idler particle goes to which-way-detector or to the eraser.  shows what we should see in D0, even though we don't know yet R01-04 Now, knowing D0, use the switch to send the 100 particles that reached the most-left side of D0 to the eraser detectors (D1 and D2). It seems much more likely that they reach D2 than D1, because it's on peak on D2 (and on rest on D1) even though it's going through a half-silvered mirror. This looks like a contradiction to me.   So, am I missing something or QM is just that weird?
107894
Why there can not be a monochromatic pulse? My physics professor told us that we can't generate a monochromatic light pulse and I was wondering what are the physical limitations causing this.
84847
My teacher told me that in an atom (assume hydrogen), as soon as the single electron absorbs a photon with the right amount of energy, it jumps up to another energy level, and instantly falls back down to the initial one, releasing a photon with the same wavelength as the one it absorbed. So, if I place a source of white light, and in front of it a sample of hydrogen, and then a prism, according to what I have read so far, the screen should show an absorption spectrum, but why would it? Since the electrons are falling back down in all the hydrogen atoms almost instantaneously, they should give out the specific wavelengths of light which form the emission spectrum, which, I think, would combine with the previous one (absorption spectrum) to give a continuous spectrum? TL;DR: If a sample of hydrogen atoms is excited by white light, why don't the electrons getting excited and coming down instantly give absorption and emission spectrums respectively, which would combine to give a continuous spectrum? **NOTE:**I would have the same question regarding emission spectrums, but I assume all the atoms in the discharge tube would be excited (so no room for further absorption and production of an absorption spectrum), which would give out just the emission spectrum of hydrogen.
33481
I have a quick question about the refraction of light, and I'm sorry if it seems a bit simplistic or even stupid, but I'm still learning.  We know that when light passes through a denser medium, it slows down. However, is there a limit to that slowing down? If no, wouldn't it be possible, with some type of medium we make ourselves (like a crystal), to decrease the light's speed down to a point where we would be able to "see the photons moving forwards"?  I know it is way more complicated than that and that you can't see light unless some other light bounces off it, what I mean is slowing down light to an extreme and unusual speed). That sounds completely absurd but I can't seem to find what is wrong. Can anyone can explain it to me? :)
79807
Let's say we are doing the double slit experiment with electrons. We get an interference pattern, and if we put detectors at slits, then we get two piles pattern because we measure electrons' positions when going through slits. But an electron interacts with other particles in a lot of different ways, e.g. electric field, gravity. Seems like the whole universe is receiving information about the electron's position. Why is it not the case and the electron goes through slits "unmeasured"?  Bonus question: in real experiments do we face the problem of not "shielding" particles from "measurement" good enough and thus getting a mix of both patterns on the screen?
85264
How exactly does  about the propagation of wavefronts account for interference?
16766
How is the following classical optics phenomenon explained in quantum electrodynamics?   Reflection and Refraction   Are they simply due to photons being absorbed and re-emitted? How do we get to Snell's law, for example, in that case?  Split by request: See the other part of this question .
84827
While trying to understand polarization in quantum field theory, I wondered how a single photon could go through a linear polarizer. I found a  which asked "Is a single photon always circularly polarized?"   This paper proposes an experiment to determine if a single photon can be linearly polarized, or if only pairs of photons can be linearly polarized.  It suggests that there may be non-trivial consequences regarding all Bell experiments with a "linearly polarized single photon" (because such thing may not exist).  The paper is from 2014 and the experiment seems simple if you have the right equipment, so do we have the result of the experiment yet?