Light Definition and 1000 Threads

Hello, I came to this site, with a question in mind. The speed of light. Nothing travels faster than the speed of light. This is a phrase, most of us are familiar with, to some extent. The word "Nothing" has two syllables, "No" & "Thing". There is no thing, that can, travel faster than the...

In Einstein's famous equation, why did he use the speed of light squared? Why not some other constant?

Photons do not have mass, so why stop at 299700 km/s??

How should we deal with the fact that GR predicts light not scaping from a BH while QM states BHs radiate?

Please, moderator, just delete this question if it is too silly. I am wondering what is happening in anyone point in the SpaceTime field. That's what it is called, I think? Because my simple understanding is that we see colours/light because of propagated electromagnetic radiation at...

Hi. Reading some recent threads I have found basic questions about light, fields, etc. For example, why something like light, associated with the electric and magnetic fields, can exist in a vacuum. And I noticed that every time I've been asked that kind of question, I answered "how" the...

Hi. When we see a laser ray, it seems that part of the ray are brighter than the other parts and they seem like they’re vibrating and moving. It also seems there are fractures in its path. I want to know why do we see like this? For example see this picture (it is from wikipedia). I circled...

Why are sounds louder at night than during the day?

Dear Physicists, My understanding of physics is at the utmost basic level. Let me apologise in advance for what is probably a dumb question. What I do know (I think): When white light hits a prism, it comes through the other side, showing the colours of the rainbow. It is my udnerstand that...

Hi guys I know we feel infrared light as heat but my question is that is infrared a kind of light or just heat ? Thank you

Homework Statement (Is the image read-able now? ) The fig 1 shows the relationship between voltage and current when voltage is applied to a certain light bulb. Next, in fig 2, the bulb is connected in series with a 12-V battery and a 5 ohm resistor. Question : what is the amount of power...

If you were to connect a string from one star to another (assuming everything remains still), and then you were to pull one side of the string towards you, the other would be pulled immediately, thus the "communication" between the two edges is technically faster than the speed of light? Does...

dear sir, light travels with constant speed of 3 x 10^8 m/s. does that mean light is in absolute motion irrespective of the its source?

Yet the neutron degeneracy pressure is unknown correct? Said size of neutron is a variable? What if we view the pressure as a volume knob, why could not a BH be viewed as a NS with the volume turned up from higher pressure?

The universe seems to be expanding since the farther away an object is, the faster it is moving. However, because of the finite speed of light, the farther away we look in distance, the further back in time we look. Does that mean that galaxies were moving faster in the past and are now slowing...

Homework Statement Prove that snell's law ## {n_1}*{sin(\theta_1)} ={n_2}*{sin(\theta_2)} ## is derived from using euler-lagrange equations for the time functionals that describe the light's propagation, As described in the picture below. Given data: the light travels in two mediums , one is...

In his second lecture of the QED series (see below), Prof. Richard Feynman explains the phenomenon of reflection from a plane mirror, and then the working of a diffraction grating with his theory of arrows (probability amplitudes), and we see that how the new theory, which is much moved from the...

If a photon doesn't travel through time (if there is no internal change by one definition of time) then I would expect a photon not to have a changing phase as that seems to count as a timeable internal change. Is this the case?

Good Day, all! Currently having a semi-half-mid-life crisis xD I am currently enrolled at the Open University (UK) nearly finished with first year (120credits), though this is distance learning and I would prefer to go to Birkbeck University of London which will be evening classes. Now...

Like the title says, bending light by means of a strong field.. And before you say "it's electromagnetic field by itself and therefore can't be changed by such.." A strong gravitc field (also an electromagnetic field) can in fact change photons to never escape it (in effect bending the light...

Hi everyone, I have a few questions about the composition of light: First, what is it? Is white light the result of all color wavelengths present in an area? Second, if so, then why is there no interference in waves of light (or is there)? Third, if photons all travel at the same speed, then...

Homework Statement A study found that children with light-coloured eyes are likely to have parents with light-coloured eyes. On this basis, can we say anything about whether the light eye colour trait is dominant or recessive? Why or why not? Homework Equations Not Any The Attempt at a Solution...

Hi! I would like to wrap my head around a relatively simple issue. Lets say that you have an excited atom, which rests in your refernce frame. When it emits light, the atom will have a backreaction, and it will "gain momentum" with the opposite direction as the photon. Of course, without...

:smile::smile::smile::smile:Have you ever observe in night a source ( spherical) emitting light in strange fashion. If not then observe today. I saw that it was more towards the corner making plus sign or cross sign which can be seen through our eyes . Is there is something which is attracting...

A particle without mass is supposed to travel at speed of light. But isn't it that a photon has no mass but has relativistic energy.. therefore why does it travel at speed of light.. or perhaps if a photon had no relativistic energy.. it would travel a bit faster than the current lightspeed?

Has the spectrum of light that is reflected off planet Earth ever been measured from outer space? (In the same sense that we measure spectra of the light emitted/reflected from other celestial bodies in astronomy). If so, would it be possible that there could be dips in the spectrum resulting...

I want to make a wire grid surface that transmits no light. For that I wanted to use quarter-circular arc wires. My question is what dimensions would I need to apply to the wires, would an arc with radius = wavelength of incident light be sufficient (since then it is the size of a wavelength in...

I can't get my head around stimulated emission.Why does a photon traveling towards an atom stimulate emission? The best way I could answer is that a photon has an electro magnetic field and this causes an excited atom to oscillate.This induces an excited electrons to fall down an orbital. But...

Lets consider an index matching antireflective coating on a conducting substrate (i.e. salisbury screen). The waves reflected destructively interfere in the direction of specular reflection. However, the energy has to be conserved, and since it is not transmitted, it most me reflected in a...

If the moon were a light bulb how many watts would it be.

Hi, I'm studying GR these days. But then I got to thinking about something about SR and got kinda stuck. I know that if a light clock is moving in the x direction(from left to right), the light beam has to traverse more space and then you will see this person's clock running slower in the...

I know that only light with polarization in the plane of the "stripe" gets reflected. What i need to know is if a single metal stripe could reflect such polarised light at ONLY the angle equal to the angle of incidence or do only a whole array of stripes produce specular reflections? Sources...

This is my first (well second if we exclude introduction forums) topic here. I just want to make clear that I am not professional nor involved in field in any way. I am just regular Joe who wants to know more about nature. I could say that I understand fact that mass distorts space but there is...

Hi I am wondering if it is possible to see the full distance of a 600m beam from a 500lm torch with an infrared filter and infrared goggles?

Hello. I have been thinking on faster than light things. I thought about: chemical engines, lasers, wormholes... All that kind of cool, advanced physics. But, I stumbled on faster than light mechanical actions. I thought about a lever: first class, if you wish, if you apply a force to one side...

I'm trying to understand the time delay induced on each photon when several individual photons travel in an open space from a sender to a receiver for example in the application of Quantum Key Distribution. So what I understand so far is light(photon) travel around 299,792 km (186,282 miles) per...

10 seconds somewhere can be one on Earth due to time dilation, right? So In the case of distance wouldn't light have traveled more than 186,282 MPS since it had 10 seconds to travel relative to the 1 second on earth. So if light traveled at 186,282MPS for 10 seconds it would have traveled...

Homework Statement [/B] A box is traveling with a certain velocity in space. Inside the box is a light bulb, which is capable of releasing one photon of light. The light bulb harnesses the energy from the box; it does not require an outside power source but instead uses the energy on the...

I came across this YouTube video describing some of the "science" behind light sabers, and what it would be like to be hit with one. I thought it was worth sharing.

The question: If the max speed I can go in the universe is the speed of light measured from? Background: If there are three rocks in a vacuum along a line (the x axis), one is stationary (rock 1), one is moving 5 m/s in the x direction (rock 2) and one is move -5 m/s in the x...

Hi Guys, I have attempted to solve the following question and was hoping someone can have a look and give some feedback. Any help will be greatly appreciated. Thanks! 1. Homework Statement Angler fish emit light through bioluminescence. An angler fish is swimming in a fish tank that has a...

Why does combustion emit light? For heat, for excited electrons or for other reasons?

How is it possible for different parts of a single rectangular wavefront to produce different intensity at particular point(P) despite the fact that wavefront is something which has all the particles at same phase?

Homework Statement Two thin lenses are placed 5 cm apart along the same axis and illuminated with a beam of light parallel to that axis, The first lens in the path of the beam is a converging lens of focal length 10 cm whereas the second is a diverging lens of focal length 5 cm. If the second...

If the concept of a wormhole is like folding a piece of space-time like a piece of paper, for near instantaneous travel faster than light, what is keeping us back right now? I am aware that it's really complicated and far beyond my scope of understanding right now, however I am fascinated by...

Other than relativity is there any theory, proof, experiment, etc. that tells us a photon has no mass? i.e. Is the concept of zero mass solely derived from relativity

Homework Statement Four identical wave sources (s1,s2, s3,s4 ) are located at the corners of a square. We know the phase at three sources: 0 at s1, π/4 at s2, π/2 at s3. Whet is the phase we have to give to s4 in order to have a maximun of intensity at the center of the square? Homework...

Hi everybody, I'm a curious worker and passionate student, I haven't got the possibility to study at the university but my passion for SSL lighting and light phenomena in general started some years ago, has helped me to start a long journey, trying to understand a little more day by day of what...

In school, I was taught that the position of an electron relative to the nucleus is only an approximation. It is very likely that the electron will be close to the nucleus and where it is 'expected' to be, but it may in fact be anywhere in the universe. Is this correct? And does this allow...

I have heard that LED light is not as good for growing plants as incandescent or fluorescent, can someone explain this? And what is the best color or wavelength to keep seedlings from getting all tall and falling over...? or is it the intensity?