Speed of light Definition and 1000 Threads

I'm debating whether this should go in the GR & SR section, but anyways, I heard both claims and both of them are supported by calculations and observations. The ∞ mass is proved by equations from SR (and the fact that a certain amount of energy pushing an object to c will always be converted to...

If light from a moving away object, such as a star, would appear red-shifted (and blue in case of approaching object), why don't we conclude that the speed of light is affected from that. Doesn't it mean that since light from a moving away object appear red, then the speed of light with respect...

I beg my pardon in advance for the stupidity of my question. Is there any "Behind the standard model" paper, document, crazzy theory, essay... exploring a universe where the speed of the light would have several upper limit: c, 2c, 3c, ... N. c? (with c = 3. 108 meter/second) That is.

Ok. I got this today from looking at a crane spinning around. What if you had an extremely long pole, huge order of magnitude, and you spin it. As you go outward, the velocity of the particles of the pole increase. As this velocity nears c, what happens to the pole as you keep going further...

Ok I have a question regarding black holes and light. If a photon is traveling directly towards the centre of a black hole, when it comes within its gravitational pull, theoretically it is being given GPE therefore it must go faster than the speed of light because a black hole has enough energy...

I understand that the speed of light can be slowed down when it passes through different mediums. I also understand that general relativity describes how space time is cured and this curvature depends on the mass of local objects and that it can influence the direction of light. So my...

Evidence has surfaced that the speed of light is not c in deep space. Is it true? <<unacceptable link removed>>

I'm not talking about relativistic effects, just solid state physics. I'm wondering what determines the size of objects at the particle, atomic and molecular level, and especially how the constant c enters the equations? I suppose it depends from the strength of the molecular bonds which...

Einstein theorized that if you were to go the speed of light or even faster then the light around you would become paralyzed. But if you're going that fast then the light wouldn't be able to catch up to you, so technically wouldn't the light around you would become black because the light...

Lets pretend I am in a spaceship and I am moving at the speed of light. There is a light bulb at the center of the ship. I understand that velocities don't simply add together, and the formula is v_{3}=\frac{v_{1}+v_{2}}{1+\frac{v_{1}v_{2}}{c_{2}}}. So the light would not be moving in your frame...

Everyone knows that if a light come in a material will change speed(will become less),and from wikipedia I read that light wants to go from his faster way. So when material 'eat' from light some speed,then light as more 'clever',goes from a sooner way.(that what we call "refraction."). So my...

I have red only about a few experiments conducted to detect the speed of light using interference pattern. but i need to know whether there have been any experiment conducted by MOVING LIGHT SPEED DETECTOR (INTERFERENCE DEVICE) & keeping the source of light and mirrors in rest? If there...

Hi, I have been pondering a special relativity question about the concept of simultaneity when moving at speed of light. Say for instance I took a round trip to Alpha Centauri 4 light years away, traveling at the speed of light both out and home (using negligible time to turn around). Then...

Speed of light through vacuum is 299 792 458 m / s, but is slower through a denser medium like glass or water. We now know vacuum is not empty as previously thought, but has all kinds of new material in them like dark matter. Has any experiments been done to determine how fast light can be...

Hello everyone, One of the conclusions of relativity is that no massive object can move at v ≥ c, but with respect to what, I don't understand? Let me try making my question clearer with an example: Suppose there are two bodies both moving side by side at v=0.9c relative to earth. The relative...

after watching minutephysics video on breaking the speed of light with a laser pointer (kinda a cheat though, as you are not actually making anything move faster than light.) I came to wonder, what if instead of using beam a light and the image it creates to appear faster. you instead used an...

The Lorentz's transform: ##x' = k(x - vt), t' = k(t - vx)\ k = \gamma,\ and\ c = 1## I. The speed composition derivation: ##w' = dx'/dt' = \frac{dx - vdt}{dt - vdx}## and we divide everything by dt, and: ##w' = \frac{dx/dt - v}{1 - vdx/dt}## now we assume the dx/dt is some speed u, and the...

What would happen to a neutron star (on the cusp of becoming a black hole) if it were sped up to near the speed of light? Or more easily done, if I sped up to near the speed of light. Would the additional mass from the near light speed cause the neutron star to collapse in on itself and form a...

While reading Special Theory of Relativity from Feynman Lectures, I fell into the confusion about invariant speed of light. What I'm asking for is an explanation about this. No matter whether physical explanation or mathematical. So my question is Why the speed of light is same for a person...

I have read that the speed of light is 299,792,458 m/s in a vacum, and is the Max speed of light. But if the speed of light can be reduced once it is removed from that vacum, and we now propose that Dark energy and Dark matter may exisist. If Dark mater and energy are everywhere that humans...

Can you explain please! thank you.

Hi I am in a debate with some creationists. They are claiming that the speed of light changes in strong gravitational fields and can be slower or faster. My view is there can be time dilation effects. For example light towards the centre ( a black hole ) will be red shifted, and away from...

Homework Statement Let's assume that the classical ideas of space and time are correct, so that there could only be one frame, "ether", in which light traveled with same speed in all directions. Assume that the Earth's speed relative to the ether frame is our orbital speed around the sun...

Why photons can't go any slower than the speed of light, in vacuum? Or if they could, then why they don't?

Consider two equal and opposite charges moving in the same direction and velocity v0, and are separated a distance R. There will always be an attractive electromagnetic force Fel=q2/(4πεR2), but when they are moving, they will produce a magnetic field B=μqv/(4πR2), and thus a repulsive magnetic...

Considering that speed of light is constant and finite, then why are the time dilatation and length contraction infinite to a frame of reference moving at the speed of light? We know that a moving frame of reference experiments time dilatation and length contraction from the point of view of a...

Hi all, I've recently learned some details about refractive indices in different media that I never knew about before. Up until now, I was aware that the speed light travels in a certain medium is dependent on the wavelength of light used. However I wasn't aware that for different kinds of...

So, I will try to explain this as best as possible. I am literally on the first chapter of a classical mechanics book. The chapter is discussing all the basic SI units...the meter, the second, etc. It's these units that I am having such a hard time understanding. They seem so easy but my...

Hi, I would be really grateful if someone could help me with two questions I have, both have puzzled me on and off for years. I have read what I can regarding these points, but a lot of it I don't understand (the maths specifically). I would love it is someone who understands this more than...

Starting at the beginning and have been having some difficulty explaining the implications of the constancy of the speed of light. Seeking confirmation that I at least have it right. For all scenarios below the observer is Bob standing in the middle of a train car moving at speed v. Bob has a...

Assume observer is located on the surface of the Earth with a small amount of time dilation due to gravity. There are two beams of light moving approximately parallel to the surface of the Earth at some moment in time and the reflection of the beam off some objects back to the observer is being...

Greetings PF. I've got an idea for a demonstration of the speed of light utilizing a pulsed electromagnetic coil and ferrofluid. I'm concerned with the feasibility of this project as it may push the limits of semiconductor technology. I would appreciate any insight on the difficulties of...

I've gone though a lot of google searches and couldn't find the reason why one way speed of light is undefined. All i know is that it is about synchronizing clocks. So i made my own thought experiment Imagine two clocks A & B. Both are not active I keep A with me and keep B at 1 light...

Imagine a system with a laser and a receiver with the ability to detect when light from the laser reaches it. There is also a console equidistant from both the receiver and the laser which sends a signal to each instrument, making the laser turn on and the receiver start a timer. The distance...

Hello guys, I just had to ask a quick question about the nature of light. In different synchronization parameters regarding inertial frames (other than 1/2) light can take value between c/2 and infinity. So far, so good for inertial frames. But considering non-inertial frames, what are the...

Sorry if I mess up some terms, I am not a physics guru in any way. To my understanding, the universe inflates like a balloon being filled with air. So.. Q1) Which is correct to say, that everything is being pulled away from the each other at different speeds from 0 to C, the further away 2...

The symbol, c, represents both the speed of light and the speed of sound in most scientific reference texts. Can the speed of sound be substituted for the speed of light in the Michelson-Morley (MM) formula: T = [L / (c - v)] + [L / (c + v)]? Consider an observer on a train of length, L. It...

If the speed of light is changing, does this mean that the permattivity and/or permeability are dynamically changing quantities? are these "constants" derivable yet or are they still only experimentally measured quantities?

Constant for all observers? I have heard that maxwell showed that the speed of light is constant for all observers even before Einstein did. Is that true? If not, then how can we say maxwells equation shows the speed of light is constant?

hy, there is nothing in Maxwells equations that would limit the speed of light. the only way one can get light speed, is to assume that em waves solve Maxwells equations and then one gets c as the square root of something out from Maxwells equations. the same goes for gravity waves, only...

Hey guys, I was recently thinking about theoretical ways to accelerate objects ( spacecraft ) and I had the idea that seems feasible and could potentially reach the speed of light in a reasonable time period. In order for this to work, we would need to develop an artificial gravity generator...

So, if I travel in a ship at light speed in a line from Earth to space for 10 minutes. Than turn around and travel back at light speed for 10 minutes. To Earth time, I would be gone 20 minutes... But everywhere I read people are saying that Earth will be in the future by the time I come back...

It is very important for me to know how scientists detect the speed of light in details...because there is something confuses me ...einstein concluded the dilatation of time on basis of that the speed of light is constant even if it comes from a mobile source ... but this fact is supposed to be...

In, BBC - Wonders of Universe, Professor Brian Cox explains that universe is stretching and the space that we live in is stretched from the early universe. If space is stretched as a result of Big Bang, and space is stretched at the speed of 74 km per second / megaparsec. is the speed of light...

Let us have an observer moving at some velocity v. And let our observer have 2 mirrors, one on either side of their vehicle, that they will use to measure time. In this situation, our observer is using a single photon (or ray, it really doesn't matter) to measure time. A ray of light...

So this has been really bugging me over the past few days (and forgive me if the answer is so simple). Let's say we're observing the Sombrero galaxy. It is about 29 million ly away and 50 thousand ly in diameter. So we should be observing the "front" of it at what it looked like 29 million years...

This from a page of notes on MIT's Relativity course 8.033: http://ocw.mit.edu/courses/physics/8-033-relativity-fall-2006/ Can someone please explain a bit what's going on in the last two bullet points? I'm not sure where they come from.

It is a postulate of SR that the speed of light in an inertial frame is always c, no matter what inertial frame is in question. But clealry, as I've understood, the Earth is not an inertial system and our bodies cannot be considered to travel inertially. So my question is, what is the speed of...

I'm a high school student and I don't know much about this stuff e.g. the Higgs Field but i know that the Higgs field gives mass to some particles. I also learned that the mass of an object is relative to its speed. So my question is, what happens to the Higgs field at those near light speeds to...

As far as I understood the relativity: 1. Massless particles travel at the speed of light. 2. As the speed increases, so does the mass of the moving body. It goes to infinite as the speed gets close to that of light. My questions: Why would particles with infinite mass (theoretically)...