What is light? And how do we know that light is an electromagnetic wave? I asked my teacher and he said that when you place a compass in light's path, the needle of the compass rotates. Which I think is not a valid answer and thats not what actually happens when we place a compass in path of a light.
120681
I'm trying to understand quantum physics. I'm pretty familiar with it but I can't decide what counts as observing to cause particle behave (at least when it's about lights). So the question is what do we see with our eye-balls?   We point a laser (or any kind of light source) to the wall. We see its way from point A to B. Do I "see" a particle or a wave? Let's see an average object. It pretty much looks like their "pieces" a observing that influences their behave. Does this means while we're watching a light it acts like particle in quantum level?
24153
Consider the question, .  The answers say, "an elementary particle" and not much else. They don't actually answer the question. Moreover, the question is flagged as a duplicate of,  &ndash; the answers there don't tell me what a photon is either. Nor do any of the answers to  mentioned in the comments. When I search on , I can't find anything useful. Questions such as,  look promising, but bear no fruit.  say things like, "the photon is an excitation of the photon field." That tells me  nothing. Nor does the , which says:     The photon is the quantum of the electromagnetic four-potential, and therefore the massless bosonic particle associated with the electromagnetic force, commonly also called the 'particle of light'...   I'd say that's less than helpful because it gives the impression that photons are forever popping into existence and flying back and forth exerting force. This same concept is in the  too - but it isn't true. As , "Virtual particles only exist in the mathematics of the model." So, who can tell me what a real photon is, or refer me to some kind of authoritative informative definition that is accepted and trusted by particle physicists? I say all this because I think it's of paramount importance. If we have no clear idea of what a photon actually is, we lack foundation. It's like what :     Photons seem to be one of the foundation ideas of quantum mechanics, so I am concerned that without a clear definition or set of concrete examples, the basis for understanding quantum experiments is a little fuzzy.   I second that, only more so. How can we understand pair production if we don't understand what the photon is? Or the electron? Or the electromagnetic field? Or everything else? It all starts with the photon.   I will give a 400-point bounty to the least-worst answer to the question. One answer will get the bounty, even if I don't like it. And the question is this:    What exactly is a photon?
81610
I know how you can emit light with an alternating current, running back and forth, creating an electric field in addition to the magnetic field.  But why does an electron emit light when it gets accelerated, there is no positive end to create an electric field.  Further more, as opposed to talking about currents, talking about acceleration seems to be a different beast entirely.
81103
A  suggests that photons can have half-integer spins. This seems to contradict the well understood notion that photons are vector (1-form) fields  What does this mean for the fundamental picture of electromagnetic propagation?
114509
My physics professor explained to me that electromagnetic waves are consisted of two components - electric and magnetic - which cause each other.   Which part of the mirror actually reflects the wave? Which of those two wave components? Both? How come the wave doesn't get heavily distorted in the process?     I guess the actual electrons of atoms of silver play a role, but why isn't every material reflective, then? Because is isn't "perfectly" flat? If I lined up atoms of a non-metal element in a perfect plane (maybe several rows), would it reflect light just as mirrors do?
43688
We know a sound wave is a disturbance that moves through a medium when particles of the medium set neighboring particles in motion. And using the pressure variations we can plot a  pressure/time graph which looks like a 'wave'in the drawing sense.  What do we mean when we say light is a wave and particles? using the above system, can we  say that light is the disturbance that moves through a medium of photons( forgive me that makes no sense). When we draw a light 'wave', what does it mean? a photon goes up and down?  Please keep the answer as 'not complicated math' as possible.
15960
Is there an actual definition of "direction" (that is, spatial direction) in physics, or is it just one of those terms that's left undefined? In physics textbooks it's always just taken for granted that the reader knows what it means (and it is true that just about everyone does indeed have an "intuitive" idea of what it is). But it would be more satisfying to have an concrete definition, if possible.
74677
To be clear here, My question arises from studying Electromagnetic induction and polarisation and photoelectric effect. From here I've gained the knowledge that creation of a photon involves:  Electromagnetic Induction - The fact that a time varying spatial magnetic field which creates a closed loop electric field [Super Confusing as to why universe does that] Polarisation - In the books, they show that light is oscillating electric field vectors and magnetic field vectors Photoelectric Effect - Creation of light has something to do with an electron returning to a lower energy state, not saying that it's the only way.  So how does light get produced? I'm seeking in-depth explanation.  Some Context The question arose when I was talking to my friend about a hypothesis of mine where I was saying that If I released a photon from , say a torch. I could, under some known error margin, say at what instant the photon was created but according to what I've heard multiple times, time stops at light speed. So, any photon at 'c' would basically never had experienced any time. So, from the perspective of the photon, its birth can't be defined. We seem to reach a paradox here, if I observe a time at which the photon was created but the photon has no notion of time, it has no notion of a beginning or an end. Then, I tried to expand the concept of the hypothesis to say that maybe in a similar sense, the universe doesn't hold a concept of beginning or an end. As we experience it's perspective, we can't determine its birth time using our maths which has been cultivate throughout this universe, and we also know that maths do break down when we try to solve equations for the t=0 time of Big Bang. NOTE: This talk was just to have fun, I just like physics and like to talk about the universe, however, I understand that I might have just annoyed someone by ignoring a dozen of laws and theorems that I'm yet to find out about. APOLOGIZES!  I'm expecting a somewhat dumbed down explaination, now don't get too carried away by that. I'm a high school student but I do love a bit of technical mumbo jumbo but I'm just asking to keep in mind that I'm in high school. Example: Say we have an equation: x3+x2-x+44=0 Instead of saying the degree of equation is 3 maybe say the highest power in the equation is 3.
74003
I've heard that light can form a curve if they travel near high-mass stars or even a black hole with strong gravity. Which is according to this   $$\large F_{g}=\dfrac{Gm_1m_2}{r^2}.$$  But I've also heard that photons do not have (rest) mass! So it doesn't fit that equation anymore! But why can photons be pulled by gravities without (rest) mass? Could someone explain that?
85305
In many pieces of literature, light is said to travel like a "wave". Does this mean the light literally propagates through space like a wave as in up and down and so on or does light move linearly through space? Also, if it move linearly, why do we say photons are a wave then?
44038
I've read that light travels in a straight line and has a wavelength of 400nm to 700nm. But I don't understand why does it have a wavelength and what creates its wavelength? I agree with the concept of sound which also has wavelength, thus called sound waves which are created by the vibrational movement in air. I'm not aware of calling light a wave. Does the light vibrate too? If so, then how?
2102
So I have learned in class that light can get red-shifted as it travels through space. As I understand it, space itself expands and stretches out the wavelength of the light. This results in the light having a lower frequency which equates to lowering its energy.  My question is, where does the energy of the light go? Energy must go somewhere!   Does the energy the light had before go into the mechanism that's expanding the space? I'm imagining that light is being stretched out when its being red-shifted. So would this mean that the energy is still there and that it is just spread out over more space?
73549
I understand how one associates the spin of a quantum particle, e.g. of a photon, with intrinsic angular momentum. And in electromagnetism I have always understood the polarization of an EM wave as the oscillations of the E and M field, not necessarily being  aligned with the direction of propagation of the wave.     Questions:   But when one talks about the polarization of a photon in Quantum Mechanics, how does it really differ from its spin?  Are they somehow related and what's the physical idea behind photon polarization in contrast to photon-spin? Feel free to use mathematical reasonings as well if you see it fit!
7269
I was researching sinusoidal functions when I realized that the wave produced by a wave function looks exactly the same as a light wave. Is a light wave a sinusoidal wave, and can a light wave be described as a sinusoidal function?
14578
The origin of spin is some what a puzzle to me, everything spin from galaxies to planets to weather to electrons.  Where has all the angular momentum come from? Why is it so natural?  I was also thinking do photons spin? we always think of the wave as a standard 2d sin wave but could this rotate in 3d? What implications would this have?   And what about spacetime how does all the spinning effect?  This has always been avoided in all lectures and classes I ever went to.
71799
I'm having trouble understanding the diagrams of elctromagnetic waves.  I have no problem with any concept in classical mechanics, and I think this can be answered without any relativity (which I don't know yet). I hope for an answer which is as intuitive as possible but any answer will be good.  So in the common diagram of an electromagnetic wave:     What exactly do the vectors represent? The wave is propagating though an eletromagnetic field. Are the lines just the field created by a particle?  We learned in physics that a charged particle creates a field in all of space, Is this a picture of changes in the field when it moves? And if so, how does it move? does it move up and down with the amplitude of this wave?  Lastly, It's not clear to me why the E-field part is not in the direction of the motion of the wave, because usually an electric field is depicted as so:    i.e it is in a direction "outwards" from the source of the charge.  This is really running through my mind for some time, so thanx for reading this!
55446
As we know light travels in straight line in normal circumstances but when exposed to gravity it bends. But does it actually bends?