If you have 2 mirrors over for each other placed exactly so they face each other perfectly, and then use a laser light pen as the source into one of the mirrors so it bounces to the other mirror and back again:   Would the laser light line continue to exist between the 2 mirrors if the source of the laser stopped? If so, how long could the laser light continue to be between the mirrors without a source? Would it just continue existing between the mirrors using itself as the source or is this not possible for light?   Note: It doesn't have to be only 2 mirrors. It could be any amount of mirrors if that would change the outcome.
112329
As written in the title it's a somewhat rhetoric question, so let me be more clear.  Let's say I have two mirrors facing each other. They are perfectly aligned and perfectly reflective. I'm looking through one of them (using the one-sided mirror effect) and see what seems to be infinite reflections.  If I look closely at the vanishing point, I obviously can't see very well what goes on there, because the reflections are too small. My question is, are there other limitations?  a) If I look close enough to the vanishing point, is there a point at which the light would have to travel too much distance to reach me that no photon would actually make it?  b) If I start looking immediately after turning on the light, it should take a tiny amount of time until all the reflections are created, i.e., it takes time for light to do all the back and forth trips it takes to create the very small images. How good a microscope (telescope?) would I need to be able to see the image being created? That is, to look at a spot and see nothing, and then some epsilon of time later see an image appear.
24386
This is not a contradiction and I know it is impossible but still consider a thought experiment by me and point out if something is wrong. See the following picture and then the explanation follows.    Rest frames are easy to understand. They are just for clarification. Lets move on to the moving frames. The velocity of the box is $0.1\ c$. Now a photon is emitted (I am not taking a light ray to avoid complication in discussion). After emission the box also moves a certain distance ahead. So the photon takes more than one second to reach the wall. But even the source moves that much distance ahead. When the light is reflected back, the source and the wall again move forward as the box is moving. But after reflection the wall has no role to play. We are concerned about the source. The source moves a certain distance ahead and therefore light takes less than one second to reach back. But the difference of the first case and the second case is not the same. To explain, I will give some equations.  Moving frame 1:  Velocity of the box: $0.1\ c = 30,000km/s$  Time taken by light to reach the wall $=\frac{330,000\ \text{km}}{300,000\ \text{kms}^{-1}}= 1.1s$  Distance moved ahead by the box from original position: $30,000\ \text{km}$  Moving frame 2:  distance moved ahead by the box from original position  $&gt;30,000\ \text{km}$ as the box also moves ahead after reflection.  let $d$ be the distance moved ahead by the box after reflection.  Time taken by light to reach the source: $\frac{270,000\ \text{km}\ -\ d}{300,000\ \text{kms}^{-1}} &lt;0.9s$  Therefore we see that this could possibly determine the absolute motion.  So in total we see that the light will take lesser time to reach the source. Please correct me if I am wrong and give your opinion why is it so.  EDIT 2 for clarification  The box is the compartment in space in which you are moving and I am calculating the time the light takes to reach back the source. I am not even adding velocities. Please correct me and tell me where did I add velocities. For clarification just let me give a simple example. Suppose person A is standing still and B is running towards a light source. Obviously he will see the light before person A even though the speed would be the same. So, what I am doing over here is not increasing the speed of light, but instead decreasing the distance to be covered by it.
113131
Would be possible to create a light saber using photons or plasma, like the ones in the Star Wars movies? If not what forbids it? What is the physics behind these sabers?
110992
Pardon me if this has been asked before. I was just thinking about how light from a source like the sun is unpolarized. I have two questions:   Is unpolarized light from the sun 100% random? Meaning all wavelengths in the visible spectrum, polarized in all directions? (please correct me if "polarized" is not the right term here) If that's the case, how do the random waves not cancel each other out, rendering the sun invisible to us when we look at it?   Of course my thinking is flawed, so I'm just wondering what I'm missing. The analogy I could come up with is that waves in the ocean are random (I assume?), yet they still occur. Thanks in advance to anyone who can fix my brain.
26571
I'm a newbie with physics but I'm wondering how a ray of light can essentially be represented. I have always known that a ray of light proceeds in a straight line until it encounters another object (or material) that refracts/reflects it. But a light ray should be part of an electro-magnetic wave, is this correct? If it is so, it should obey to the  and this doesn't seem to me to describe a straight line ray.  I'm having problems visualizing how light is emitted and how it relates with the wave equation. Can someone with a clear understanding of the problem explain it to me in simple terms?
116244
In the double slit experiment we have something like this     Light waves from two sources interfere at screen to give us this pattern. To reach the middle (that is a point on the perpendicular bisector) of measurement screen waves will travel equal distances (at sources they are in phase because of the same main source) and hence will be in phase at the middle of the screen and hence a constructive interference will occur.    We can write things a little more mathematically, if at time $t$ the crest of the light wave is at the sources (secondary) then at time $t+nT$ ($T$ is the time period) crests will be at the middle of the measurement screen and hence a maximum will occur. Here, I have assumed, for simplicity, that distance between the source $S_1$ and the middle point M is $n\lambda$.    Now, my question is when there was a crest at $S_1$ and $S_2$ then we had a maximum at $M$, but when there is no disturbance at sources (I mean $E(t)=0$ and $B(t)=0$) then there should be no disturbance at M too and therefore we should obtain a dark fringe (no light) for this particular interference. Why does the interference pattern remains static? The bright fringes should be turning on and off periodically.    My question comes down to normal light also, why do we see the light even when the electric field and magnetic field components reach their zero position periodically? We should see light as being turning on and off, off when $E(t)$ and $B(t)$ becomes zero and on for every other time.    P.S. :- My $M$ in the figure doesn't coincide with the maximum but by $M$ I meant the middle of the screen where the first maximum gonna occur.
50617
The question pretty much sums up what I need to know. Why is it that light only gets dispersed into a spectrum when travelling through two non-parallel sides(like a prism) and not through something like a glass slide with parallel slides.  And how does this experiment(an experiment conducted by Newton) explain this? Because this is what is in my school textbook.
56669
So I've been reading a bit and watching some videos about the double slit experiment, and therefore the wave particle duality; I've also read this "implies" that a particle can be in two places at the same time. Can you clarify this, and how could that be possible?
71719
There are several techniques to do a 3 point lighting system.   How do you properly light a scene while using mesh planes as emission light sources?   I'm following , however despite setting up planes to act a lighting sources, the scene is still very dark.      Actual Blender file here:
73896
If you emit a single photon, wait an interval, emit a second photon, wait the same interval, and keep repeating, is the resultant stream of photons describable by the frequency at which you emitted each one? Or does each photon have its own "frequency", independent of the rate of emission? I thought the former description explained the Doppler effect.
106650
I have found that light always produces heat. The only cases I think heat is absent with light is  and  (maybe because they emit low energy but maybe the heat is still present?). So my question is: Is heat energy always present when light is emitted, specially for bright light(more energy)?    If some example or any links can be provided, then it will be very helpful.
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? :)
12376
We have two sets: set No.1 and set No.2 as in this picture:   The observer is fixed to set No.1 . He sees set No.1 motionless and observes set No. 2 approaching with velocity 100,000 m/s.   Each set has one lamp and two, so called, touchers. Each set is designed so that if both touchers are touched simultaneously the lamp is turned on otherwise it remains off.  Set No. 2 is approaching set No. 1 so that each toucher in each set will be touched twice by the touchers of the other set.  The observer on set No. 1 observes the distance between touchers in each set 10 meters. He thinks the lamps on set No. 1 will be turned on because touchers in it will be touched simultaneously.  My question: Will the lamp on set No. 2 be turned on? How if an electrical current flowing from one toucher in a set to the other proves simultaneous touching?
2134
Yesterday I read that we can affect the path and the 'form' (particle or wave) of a photon after the fact ().  Part of what is puzzling me is the beam-splitter. Are the individual photons actually being split into two new photons of lesser energy?  This  implies that you cannot split a photon but it seems that beam splitters do exactly that.
60837
Everyone have seen and knows how lightning occurs. But then I realized that lightning never occurs in straight lines but it follows branching. But Why is that so? Why can't lightning goes in straight line rather than generating multiple branches just likes in this picture ?
115536
How would I go a about making volume light beams?  I have have tried  various tutorials, but they must be for a older version. as applying them does seemingly nothing.  A link to a functioning tutorial would be greatly appreciated as well.  I don't have a picture or .blend to show, as my problem with atmospheric lighting does not pertain to any specific scene.
40920
The HUDF used to be the deepest image of the universe ever taken by the Hubble telescope, the furthest star in this image is 59000 light years away.  The star in question:   Now Imagine a light emitting object like a star and an observer like a telescope, 59000 light years apart. I represented everything in 2D, but in 3D I suppose it would be the same but with spheres:    Now picture the photons that the object is emitting, in particle form. They will all have one direction and they will go towards this direction at C, given that there are no massive objects in between their paths:    Notice how the photons have separate paths, because they have different directions, now obviously there should be a lot more photons but for simplicity I drew it like that. My point is, given enough distance shouldn't the probability of hitting a photon be so small that seeing an object becomes nearly impossible? Like so:    Here the observer can detect the photons, but if it was slightly off it wouldn't:    So how can we detect objects so far away? Is there something about light's wave form that I'm not considering, is this how light is emitted at all?  Update:  Looking at other duplicates questions I've seen two answers:  1- There are just too many photons being emitted that the "gaps" are just too small to make any difference.  2- This isn't really how photons are emitted, instead a quantum field is spread out radially and we only detect the photon when we interact with the field.  Does this mean that there are objects that we can't see, even if given enough time for the light to reach us (presumably outside of the current observable universe)?  Or do the gaps not exist at all because of answer number 2?