Light Definition and 1000 Threads

Recently saw this video. "Why No One Knows If Photons Really Are Massless: What if they Aren't?" Arvin Ash He says photons need not be massless, but they must be quite light nonetheless. He separates speed of light from speed of causality. Is it true that we can't know its mass below a...

Bear with me this will be long, but everything here I feel is necessary to understand the context. I recently used a crt at varying refresh rates and noticed a few things that has made me question how the brain perceives colors on a display. First, is that my crt appears to have more color...

if matter and anti-matter meet, they annihilate each other. Gravitons are anti-photons and photons are anti-gravitons. They MUST meet in immesurable quantities in our universe. Yet gravity exists, and light exists in our known universe. This denies the annihilation necessity. And annihilation...

Inside a dark room, when light comes through a hole, we see the dust particles as the particles scatter the light. But, when the whole window is open, we don't see the dust particles scattering the light. Why?

A spaceship moves at half the speed of light, what will be the results of measuring the speed of light for it: in relation to the light source it is approaching and in relation to the light source from which it is moving away?

We are attempting to penetrate 1m of water featuring dissolved ions ( assume salinity of sea water) using radio waves. Aside for using wavelengths of very low frequency radio or below, what would be the best frequency for achieving this task?

Hi guys! Is there a simple explanation to describe why light owns the faster speed at the universe ?

The theory of relativity is based on two key principles: the principle of relativity and the constancy of the speed of light. The constancy of the speed of light is one of the fundamental postulates of the theory of relativity. Which statement is wrong?

How are we interacting with light to measure its frequency? And how'd we learn the distance between its crests and troughs? What sort of interactions are giving us such info?

The answer key is the light is directed through one polarising filter then filter is rotated and the light changes intensity. I don't understand how that proves that the light is plane polarised. I think if the light is unpolarised, the intensity will also change when it passes through...

According to Einstein light would be a particle and a wave. So I infer that it propagates in vacuum in form of waves of little bullets (particles). This explanation is very insuficient. So tell me how do waves increase in size since it's made of little bullets (particles)... a wave gets...

Hi. I’m trying to solve an optics problem and really struggling. The problem is best described as follows… Imagine you have a section of a wall that you want to look like a window on a spaceship. So you want to look at this “window” and see through it some “stars” (i.e. pinpoints of light) that...

Hello , I study the principles of optical coherence tomography, where we emit light and by the refraction that we detect we reconstruct and image, but I don't understand why we use low coherence light , if i want to measure the refracted light i would prefer to have coherent light so that the...

I've read that the refraction of light at the boundary of a medium can be described as follows: -a line of connected people marching. one side of the line enters mud, and slows down. This causes the non-mud side to pivot towards the slower side, which then causes the line to change direction...

while browsing for new propulsion methods I found the following interesting: https://en.wikipedia.org/wiki/Radiation_pressure "Radiation pressure (also known as light pressure) is the mechanical pressure exerted upon any surface due to the exchange of momentum between the object and the...

Based on the current understanding of general relativity, it is possible that curving spacetime in the back of a spacecraft would allow for faster-than-light travel. In general relativity, the curvature of spacetime is determined by the universe's distribution of matter and energy. If a...

Sometimes I cannot imagine light as the popular Maxwell's blue and red electric and magnetic wave https://simply.science/images/content/physics/Electromagnetism/em_waves/emv.jpg but I found the image below to be the more accurate representation of how light actually looks like as waves...

You've helped me change a couple bulbs so far, hopefully this is the last one. There's a recessed light on a hinge (a gimbal light maybe?) There are three exterior white rings - the outermost is a trim, the middle is a flat piece, the inner is ridged. Both the middle and inner piece move on...

I'm studying optics in this semester and one of the topic is polarization of light. Please help me. For ease of understanding we only consider the electric field E, right? I'm confused, if light passes through a polarizer then there will only be one field whose direction of vibration is only...

You can see from the picture that the teacher has circled the arrows which shows light coming from image to the eye, and drew it in the opposite direction saying the light goes from the eye to the image. The marking scheme of this paper only says the correct direction does not specify which is...

I asked a similar question on Quora not that long...

Pretty much, I was picturing a 1x1x1 meters cube of a dark colored, mostly uniform material (limited porosity, no crevices) with a small chamber in its interior - exactly where the center of mass should be. In it, a body emitting light is activated with the goal to find the intensity necessary...

This is problem 62 in Cutnell & Johnson's Physics (9th edition): Suppose that the light falling on the polarizer in the figure is partially polarized (average intensity \bar S_P) and partially upolarized (average intensity \bar S_U). The total incident intensity is \bar S_P+ \bar S_U and the...

I'm obsessed with this problem and need some light, I've tried solving it using inequalities but there seems to be an asymmetry that's hard to deal with.

From what I've read, it is not possible to measure the one way speed of light. We must reflect it off a mirror and then divide its travel time by 2, giving us its round trip average speed. Time dilation makes synchronizing two separated clocks impossible. We just assume light goes at C in all...

I don't know if there are some here familiar with "Veritasium", a YouTube video channel dedicated to science and engineering. It was created and is hosted by Dr. Derek Muller. It has over 8 million subscribers and many of its programs have been watched millions of times. Today I was watching an...

Hi. I use Matlab to simulate that two parallel light rays pass near a Kerr BH. The angular momentum of the BH points to the ##z## direction. The ##z## components of the start points of the two rays are ## 1\times 10^3 ~\rm{m}## and ##- 1\times 10^3 ~\rm{m}##, respectively. The result, as shown...

I would appreciate knowing if there is any error in the mechanics illustrated in this animation with respect to phase change in the signal reflections shown at A and B, or in the description accompanying it. I have embedded the description with the animation and included it in this post for...

If emw spectrum is continuous, possible wavelengths should be infinite and there should be fraction of frequencies like 25,2 hertz. Well is there a fractional frequency of light? In high school when we are teaching interference of light we say "only the same wavelength of lights interfere with...

How can a photon of light literally travel across the galaxy? Where does it get the energy to do so and what then keeps it going? Why isn't yhe frequency and energy depleted? Does the coldness of space have anything to do with it?

##\gamma = \theta_1 - \theta_2## where do you get that from? Thank!

data I'm trying to fit

Hello, I have a question linked to gravity and speed of light : According to the Special Theory of Relativity, the speed of light cannot be exceeded because it would need an infinitive energy to accelerate the relativistic mass of a moving objet (a space craft for example) : indeed if the...

Dear PF Forum, It's been a while since I logged in here. And I really do appreciate all the answers that I've been getting here. Now, I wonder. Is there any standardization for 1 light year distance? Is it 10 trillion kilometers, or 299,792,458 * 60 * 60 * 24 * 365.256 = ...

Everything we see is a result of reflected light. True or False We had an all out war over this question. The question is not as easy as it seems. There are many valid arguments. It would be interesting to see any opinion or contribution to this argument.

Hi, I've been struggling for a long time to understand the propagation of light. Here are my key problems: - since a star can be seen from any direction, it means that photons are emitted in all these directions, which are infinite, how is this possible? infinite photons? - in case there are...

In Cosmos: A Spacetime Odyssey episode 5 Hiding in the Light, Neil Degrasse Tyson describes one of William Herschel's experiments with light in the year 1800. The episode shows Herschel's experiment as a cartoon. Herschel put two thermometers under a prism that was in the sunlight. Herschel put...

If the speed of light in the vacuum of empty space is the same for all observers, how can there be a Doppler effect on light? Doesn't the shift of color/frequency indicate a change in speed? Sorry if I posted with the wrong prefix, I'm just a curious senior (as in old guy) :oldconfused:

A light source in uniform motion emits a flash of light. A spherically symmetric wavefront propagates from a central point, the source, or the “origin” of emission. The wave front remains at c relative to the origin as measured by all observers. How fast do these origins move? Am I missing...

The constancy of the speed of light is a fundamental principle in modern physics, and it is supported by a wide range of current experimental evidence. There is no evidence to suggest that the speed of light was different in the past, and the idea that it could have been different is at odds...

1. How much is acceleration of light? 2. Why is speed of light constant if time is relative, to keep speed constant distance must be changed as well? 3.What is time by Einstien? If we state it is not absolute, it is illusion, dont exsit? 4. Can we say ratio between distance and time is...

Elevator (2m height) is accelerate upward, light is at the top pointed toward flor of elevator. Is time t=2m/c to light pass from top to bottom? Bottom moving toward light,so time would be smaller then t=2m/c?

I brought time over to the other side and multiplied to get 686 m/s but that wasn't correct

In the illustration below, a laser beam is emitted, and the time recorded, from the rear of a frame which is 150,000 km long and is moving at velocity 0.5 c to the right. When the beam reaches a half silvered mirror at the front of the frame, the frame being shown as a rectangle and using...

In Feynman's book, QED, The Strange Theory of Light and Matter, page 27 he says, "As long as the photon moves, the stopwatch hand turns (about 36,000 times per inch for red light); when the photon end up at the photomultiplier, we stop the watch." I've been puzzling about the significance of...

Is my understanding correct that if we have a moving vehicle moving to the right at speed v, as above, with a light source in center going in both directions, that (upon emitting the light at time T), a detector at D1 & D2 would both detect light reaching it at T2? (even though in the time it...

Last night I was awoken by what seemed like an extremely bright flash of light. I sat up and saw another bright flash of light just outside my bedroom that seemed to originate just down the hall. I was worried there was an electrical short so I ran out and nothing. I thought maybe I imagined it...

I once read (though I don’t remember where) that in the same way that you talk about a dimensionless ratio between Y and X in ordinary space, you can conceive of c as a dimensionless ratio between T and X in spacetime. Do you know where I can find a reliable treatment of that idea? As...

This is much like the "grain of sand" at near speed of light hiting Earth, but now targeting Jupiter with a needle! What if... Any way, which is the correct way to analyze this kind of scenarios? For example, I think than being the speed of the needle near c, is nonsense to think about the...

I perfectly understand that we cannot, as of our current methods, determine the one-way speed of light - I was, however, wondering if we could determine a relative speed using electrical transmission. the basis of which would be sending a laser light across a field into a sensor, starting a...