Speed of light Definition and 1000 Threads

Romer measured speed of light using moon's of Jupiter but he got value with a error of 26%. Is anyone did same experiment in modern era? And what value they got?

It is commonly said that the speed of light when traveling inside materials is lower than that of light in vacuum, but I don't understand how this can be true. It is the same light traveling, so how can it act differently? Does light appear to be slower in materials because it is not following a...

Play from 3:00 It states that we will age slower if we were traveling at the speed of light compared to being on Earth. Would we not age the same but just be further away hypothetically? Next it states that if we travel away from a clock at the speed of light at 12:00, we would always see...

Homework Statement In the Fizeau's Experiment to determine the speed of light, let the gear have N teeth, the frequency of the rotating gear being f, the distance traveled by the light beam/ray L (distance b/w the gear and the mirror) and let there be n eclipses(blocking of the light beam)...

Hi, The speed of light is given c=1/√(ε0μ0) where ε0 is permittivity of vacuum and μ0 is vacuum permeability. The permittivity and permeability of a material is given as ε=εrε0 and μ=μr)μ0 respectively where ε is absolute permittivity of the material and εr is relative permittivity of the...

My question is about the speed of light. Our current understanding of light says that light is constant for all observers, and uses time dilation to explain this. Have we proven this? The speed of light emitted from a stationary object is equal to C. The speed of light emitted from a moving...

I know that special relativity is based on the postulate that an object that travels at the speed of light with respect to one inertial observer must travel with the speed of light with respect to all inertial observers. This postulate implies that no two inertial frames can differ by a relative...

Is the average nonlocal speed of light the same for travel out from the Sun and travel back to the Sun over the distances the Voyagers are now located?

I was curious, is the speed of light in a vacuum really constant to all observers no matter their speed or movement? Is it possible for someone to somehow see light travel slower?

I keep hearing that the relative speed of light remains constant because time and lengths change with speed, what I believe is called the Lorentz factor. At slow speeds the Lorentz factor is extremely small, so what do people believe accounts for the rest of the change? If I travel...

The Lorentz factor shows how fast one frame will judge speeds in another frame to be taking into account the relative motion between the two frames. The speed of light is a factor in the Lorentz factor but I have heard that this is not because the speed of light is fundamental to it. So...

If the speed of light would change in the universe without any other natural constant changing, would all clocks be affected in the same way by this? This is implied by Einstein in this paper on page 368 http://myweb.rz.uni-augsburg.de/~eckern/adp/history/einstein-papers/1912_38_355-369.pdf...

I have seen thought problems with an observer on a train or in a station, etc., but I have not seen ones with the observer traveling at relativistic speeds. It seems to me that at sufficient speed he would observe himself exceeding the speed of light due to the slowing of time. This seems like...

Hello. Today I've thinking about limit velocity and speed of ligth. We know that material particles can't achieve that speed, also when the speed of particles increases your own clock walks slowly. In the particular case of ligth your speed don't move anything. This it a explanation of why...

I am trying to get a better understanding about the constancy of the speed of light which is a well-established axiom of current day physics. for the start i want to understand how it is experimentally established and how these results are interpreted. My difficulty here is that this seems to be...

Hi people! May be this could be an historical question. Before Einstein, it is suppoused that speed of light in ether is always the same, I´m right? I mean, if observer O is at rest respect ether and observer O´ is moving respect ether and O´ send a photon to O, the speed at which that photon...

How fast would the light travel for a SuperBig observer... immagine his head is the size of the Sun, and he is sitting in a room, then he decides to turn on the light in the room... if he is so big, would he have to wait some seconds until the light reaches his eyes? Would it mean that for this...

Drive two 15m long optical fibers extended in opposite directions with a 1GHz pulse generator. The recievers at the end of each fiber are now syncronised sources of 1GHz pulses. Connect them to pulse counters, one of which provides a signal whenever a pulse train is present. Connect this...

Why is the speed of light a constant?

Can we truly have a rest frame or should it be a close to rest frame? Even if I'm stationary and sitting on my porch and the observer in the car passing is moving, I'm still not at 0 velocity. The Earth is moving at 67,000 mph and the galaxy is moving at 250,000 mph. I'm never in a single...

By Uncertainty Principle speed of a particle cannot be constant. then speed of a single photon not?

This is a question I was looking at based on Relativity and John Wheeler's one-electron universe theory. https://en.wikipedia.org/wiki/One-electron_universe My question is this. The faster you move towards the speed of light, wouldn't everything in the universe contract to a single particle...

if speed of light were not 3*10 ^8 m/s and something else would it affect the reality ?

Homework Statement The problem I have been working with recently has been deriving the speed of light using maxwells equations, however in order to do this I must make two assumptions; there is no net charge or displacement currents in the space in which I am attemptin to derive the speed of...

The speed of light from a moving source of light is usually recognized indirectly, based on various explanations of phenomena. The speed of light is fairly simple directly measurable on the basis of autonomous and separate measurements of the frequency and wavelength of the light. Is a similar...

Let us imagine a photon circling around a black hole, as the picture shows. The gravity of the black hole curves the movement path of the photon into the shape of a circle. From point 0, geometric points A and B appear simultaneously with the photon, each in its own direction. The points travel...

Suppose for the sake of argument someone said the outward speed of light is infinite and the return speed is c/2, creating a two-way speed of c. Wouldn't this violate the conservation of momentum? p = E/c. That means on the way out, the momentum of light would be zero, but on the way back it...

Does anyone know the speed of light in dark matter?

I'm reading Special Relativity by TM Helliwell and in it he describes the second postulate and the fact that moving with respect to air changes the speed of sound, and that because light doesn't need a medium it's speed is constant. I remember my physics teacher saying that light itself(EM...

I recently saw this question on a forum thread on The Guardian's website but was unable to follow it up. Question: Why is the speed of light what it is? Could it have been another velocity?

Hi all I have struggled with the assumptions that the speed of light is absolute and constant. I have some logic to this which is based on the common assumptions that light behaves both as a wave and a particle. It is also based on light having mass, the effects of heat and vacuum environments...

If a car drives on the highway at a speed of 100 ft per seconds and a gun in the car shoots a bullet forward at the speed of 1000 ft per second the total speed of the bullet will be 1000 + 100 = 1100 ft per second. If a car travels at the speed of light when you turn on the head lights will...

Hello everyone, I'll go straight to the question. The gravitational time dilation is equal to tearth = tspace*sqrt(1 - rs/r), with rs = 2GM/c2. However, the formula for speed of light in gravitational field is equal to v = c(1 - rs/r). My intuition tells me that these two formulas must be the...

Are there any relationships between the speed of light and the virtual particles in the vacuum? I mean that, Can I call it as a medium of propagation of a light beam?

As a neophyte when it comes to the relativity solutions I have been surfing the web. I came across something in Science Forums. <speculative link deleted> I have now become interested in what gravity does to light. My understanding of the post above is that the reference frame for light...

I decided to read up on the chapters we didn’t cover in first year Physics from my textbook, and decided to start with general relativity since it was in the same section of the textbook as the last topic we covered (that topic was physical optics - not lenses- photons and the double slit...

Using Newton's 2nd law F=ma, If you provide a constant force of 1mil Newtons then an object will accelerate at 100m/s. Using V = U + AT I can say that (speed of light) 299,792,458 = 0 + 100T thus T = 2997924.58 seconds or I can achieve speed of light in 35 days or so. Why is this not...

Just wondering how a photon reacts when it is affected by gravity of an object in space like a star. Does the gravity actually bend the light/photons? Say you have a series of photons in a perfect line, all travelling, well, at the speed of light toward a massive object(x). The photons in the...

Any one please tell,all experiment attempt to find speed of light

I've been told that when a photon of light is created it instantly achieves the speed of light without having to 'speed up". How is this possible?

Hello, If the speed of light is the maximum speed limit in our universe, how was the big bang event possible because surely the expansion would have been constrained by the speed of light?

Hello - I'm posting this here because of a discussion I got into on another forum following the recent death of Stephen Hawking. I should stress that I am by no stretch of the imagination a physicist (though I did do modules on special relativity and quantum mechanics as part of my maths degree...

A rocket is in constant velocity. The velocity of the rocket is 150Mm/s (or 0.5 of the speed light, or 150 million meters per second) relative to us (we as observer). We observe two lights, one moving in parallell with the rocket, another is moving in the opposite direction. Below I have made...

Does the speed of light change in different substances, or does it seem to change because it gets absorbed and emitted by all the particles?

Respected physicists and members (I am not a physicist) I have a little doubt that i want to clarify. If I am sitting in a stationary train, having a ball in my hand, the ball will remain stationary relative to my hand and plateform. Now if the train starts moving, again the ball is stationary...

Is it possible that the speed of light exists because we cannot move faster than our particles? I.e. the speed of electrons that create the electromagnetic force that hold matter together.

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?

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...

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...