So...if electrons and photons are both particles and they pass the two slits, why do they create an interference pattern as if they were waves? Now from what I've read, it's because of the superposition of an electron and since an electron is in every possible state until observed, it is going through both slits and interferes with itself and that's why, if not observed, the double slit experiment will show that interference pattern.  Now my question is: how can that electron propagate as a wave if it interferes with itself? Shouldn't the outcome of the experiment be the same with or without an observer? I mean...that's just so very extremely counter-intuitive that I can't grasp it...an observation changing the outcome. Why does the observation of the slits change the outcome and not the observation of the screen? Why do we get wave interference even with one slit?  Please correct me if I'm mistaken about how this double slit experiment works cause I've also seen interpretations about the wave nature of electrons and photons and it just made things more complicated for me.
121205
According to various sources on the web, it seems like the general concensus is that there isn't actually any wave-particle duality with quantum particles. For example,  implies that diffraction patterns in  were interpreted as wave interference due to apparatus limitation at the time they were first performed.  Does this mean that all those sources and animations showing two waves interfering are simply incorrect, classical conclusions which don't have anything to do with (quantum) reality?  What's actually the most confusing is that most sites which state that it is now possible to pass individual photons through these slits, also claim that these individual photons somehow interfere with themselves resulting in the observed patterns. That seems like a rather thin explanation, doesn't it?  So, is there actually any need to use wave interference to explain the phenomena, or can we simply state that the pattern is probabilistic in a certain way, without involving the "spooky" explanations?
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.
19301
I don't understand how quantum mechanics (and therefore also quantum computers) can work  given that while we work with quantum states, particles that this quantum state consist of cannot be observed, which is the most fundamental requirement.  If I am not mistaken, by "observed" we mean interaction with any other particle (photon, gluon, electron or whatever else). So my very important questions:   Aren't the particles this quantum state consists of interacting with each other? Why doesn't that cause the state to collapse? Aren't all particles in the universe interacting with Higgs field and gravitons etc? Why doesn't that cause every quantum state to collapse?   I feel there is something very fundamental in quantum mechanics that I am not aware of, hence I would be very pleased to have these questions answered.
88235
As I navigate through physics stackexchange, I noticed .  Electrons radiate light when revolving around nucleus? Why is it so obvious?  Note that I do not know anything about quantum mechanics - and I just want classical stories.
98227
Although I've read answers to similar questions, they did not answer my doubt:  If a photon has an energy less than that required to move an electron from one energy level to another, then what happens when the electron and photon collide? Is the photon absorbed, or does it by some mysterious method, just pass through the electron?
101320
When light (photon) is reflected the the original photon is absorbed by an electron and then emitted again. Does this "new" photon have the same wavelength, frequency etc. as the original?
5273
In one of the first lectures on QM we are always taught about Young's experiment and how particles behave either as waves or as particles depending on whether or not they are being observed. I want to know what about observation causes this change?
102265
The electromagnet spectrum looks to be continuous, yet energy is discrete. Shouldn't one see evidence of the electron's "quantum leap"? What's going on?     Moderator, please size my photo. Thank you.
47641
I'm just starting to learn physics and I have a question (that is probably stupid.)  I learned that energy levels that the bound electron can have are discrete. I also learned that when an electron transitions from one level to another, a photon with a specific wavelength (energy) is created and released into the wild.  My question is this: are there holes in the electromagnetic spectrum, values of frequency that the created photon can't possibly have?
61192
In the double-slit experiment, quantum mechanics states that if you try to determine which slit the photon goes through, you won't have a resulting wave pattern.  But, knowing the time it took for the photon to go from the source to the observing screen, can you deduct the distance of the photon path and so which slit it passes through (except if the photon impacts the exact middle of the observing screen)?
104556
I sometimes hear statements like:     Quantum-mechanically, an interference pattern occurs due to quantum interference of the wavefunction of a photon. The wavefunction of a single photon only interferes with itself. Different photons (for example from different atoms) do not interfere.   First of all -- is this correct?   If it is correct -- how do we explain basic classical interference, when we don't care about where the plane waves came from?   I heard that there are experiments with interference of two different lasers -- is this considered as a refutation of the statement? If it is -- how should one formally describe such a process of interference of different photons?  Finally -- such statements are usually attributed to Dirac. Did Dirac really say something like that?
80915
Almost in every book on physics we can find a statement like "diffraction gets stronger when the size of the slit is comparable to the wavelength". Let's say we have a wall in a bathtub with a slit in it. When water waves reach the slit, the books usually come up with the Huygens' principle to explain that the points on the wavefront which are near the edges interfere in some fancy way so that the water waves spread out radially. However I do not see any connection between the size of a slit and the wavelength. I do understand that if we have a really tiny slit, there are very few points on the wavefront which produce radial waves, and if the slit gets bigger, there are more points that produce the same secondary waves which eventually interfere in an interesting way. But what it has to do with the wavelength? If we have a tiny slit and even more tiny wavelength, how does this change the game?  So for example, if we have a big wavelength, the diffraction would be:    But if the wavelength gets smaller while the slit remains the same, I'd expect the very same diffraction with the only difference that the resultant wave will have a shorter wavelength:
117021
I have recently been reading about Quantum Electrodynamics which I found very interesting, but even more confusing.  I understand photons mediate the electromagnetic force and interactions between charges can be described by virtual photon exchange. And that in Quantum Mechanics particles paths can be evaluated by sum over all paths...  An electron travelling from one point to another will take all paths, emitting and reabsorbing virtual photons. Does the electrons take all paths including those that involve faster than light velocities?  Is this question null, Does it mean anything to ask about properties of virtual particles?  Do I have the wrong idea about what virtual particles are?
39213
In double slit experiment only small sized particles were used. however if we use large objects such as a tennis ball, the expected pattern is not observed.   Why the wave nature is not visible for large objects in double slit experiment ? How do I then prove that large objects also have wave nature?
27927
I can't seem to understand the dual nature of matter completely.   If electrons have a wave nature, then if two electrons were to collide, wouldn't they undergo interference and form an electron wave of larger or smaller amplitude? Does that mean the electrons merge and turn into a "bigger" electron?  Then again, this would mean that the electrons would have a phase difference, so what determines the phase of matter?  Also, if we were to consider two photons colliding, would they also undergo interference and form a "bigger" photon?  Why don't normal everyday objects undergo interference? Just because the wavelength (according to the de Broglie equation) of something is small doesn't mean that it doesn't undergo interference (take for example gamma rays which have a very small wavelength but are the most powerful form of radiation).
37234
Maybe an illegal question. Sorry.  Having read that a photon has both wave and a light characteristics it is natural for a novice like myself to wonder "what is the amplitude? "  Naturally I have looked on wiki and other sources and there are a number of answers some of which appear not so much to contradict one another of varying opinions of which is the most meaningful in physics.   I seem to get a higher number of physics sources saying the amplitude depends on how many photons you have and if you have one the question has no meaning.  Of course I have not idea if this is accurate or how one would even test this.   Maybe there are some physics teachers in the audience that can give me a layman's intuition with a little math tossed in.
79481
There are a lot of questions about this topic on this site, none of them answer my question specifically. I have read this question:   I think of the emitted photon as a point particle (but with a polarization vector) traveling in a straight line from the atom to the measuring device.    For some people, a photon is a dimensionless point traveling on a world line (Eugene Wigner's definition of a particle).    The photons do not have a well defined trajectory. The diagram shows them as if they were little balls travelling along a well defined path, however the photons are delocalised and don't have a specific position or direction of motion.    because photons take all paths, but since their underlying physics is &quot;wavey&quot; different paths can &quot;interfere.    This calculation assumes that light simultaneously travels over all possible paths. To what extent this is just a calculational device and to what extent it reflects an underlying physical reality is a matter of opinion.    Indeed, nothing in nature moves around on all possible paths, in reality it's a field that permeates the vacuum which has quantized solutions.  There are mainly two thoughts:  the photon travels in a straight line, and that explains why it only interacts with a certain atom, meaning, that the photon can only be detected once, and the photon will not interact with the other atoms because they are out of its trajectory  the photon takes all paths, and that is why it truly goes through all possible avenues, explaining experiments like interference     Now these lead to two different propagation pictures. On the top, you can see the photon (EM wavepacket) spreading spherically in all directions. On the bottom, you can see a photon traveling from A to B, taking all possible paths. But which picture could be experimentally proven to be correct? The picture on the top cannot explain why the photon misses all the other atoms, that is, why it is not interacting with other atoms, because all atoms are in its way basically (it spreads spherically). The picture on the bottom cannot explain diffraction, because the photons is shown not to spread like a wave (cannot interfere), but just like a billiard ball on different paths. After the question was closed, I am editing to clarify (to reopen), that (as I understand), the question was closed due to the word &quot;really&quot; and what it physically means for the photon to take all paths, or whether the picture on the top (spherical spread) physically describes what is happening. I now revise these words, and the &quot;physically&quot; is meant here to say &quot;experimentally provable&quot;. Question:  Do photons take all paths or not?