Speed of light Definition and 1000 Threads

I'm sure this has been asked a million times but a quick search didn't give me quite definitive answers so here it goes: Imagine a spaceship traveling away from the Earth at 0.99c. For argument's sake, let's ignore the acceleration and deceleration stages of the ship (is that valid?). Simply...

I recently watched a documentary on Albert Einstein that said the inspiration (or epiphany I guess) for the slowing of time as speed increases occurred to him while he was on a bus. It said that one of Einstein's day dreams, was that he would imagine himself riding on a beam of light. Well...

Homework Statement Write the momentum four vector of a particle that has: Rest mass = 80 Gev/c^2 Energy = 100 Gev and moves along the z axis.What is its speed as a fraction of the speed of light. Homework Equations E^2 = p^2c^2 + m^2C^4 The Attempt at a Solution...

Hello Everyone. This is my first post started on this site. Please, please, please excuse my ignorance but I couldn't seem to find the answer to my question online (although I'm sure it is). If the size of the know universe has a diameter of 93 billion lightyears with a radius in accordance to...

Relativity says that the speed of light is constant for all observers regardless of their state of motion. So does that mean even if you are heading towards a light beam at a constant velocity that the light beam would take the same amount of time to reach you as when you are at rest relative...

First, i want to state that i am very interested in physics, but i have not done any education on this subject, except for science class, which only covered the tip of the iceberg of information we now have. Second, i want to excuse myself for possible faults in data, I'm happy if you correct...

I'm not sure if this is the correct area to post this question, but I don't know where else it could go. If it is incorrect, can someone please move it to the correct area if that is possible. This is a purely hypothetical question, and I am by no means good at physics (just starting out)...

Is speed of light relative to "eather" flow? If 2 rockets fly from Earth in opposite directions. Both end up flying at 60% the speed of light. Does that mean they flay faster then the speed of light, compared to each other? Or is it relative to spacetime or eather or whatever?

So relativity is defined about the speed of light. The speed of light is what it is because the photon is massless. What if, sometime in the future, it's discovered that the photon has a small mass so that it travels a little less than the speed of light. What does that do to relativity?

I have a question (thought experiment) that pertains to the speed of light and point of reference. I'm just interested in thinking about this subject and I can't quite get my head around this. I'm sure the answer is probably simple. Thank you for your help. By the way, if the answer involves...

Let's say there is a football field with a mirror set up in one of the end zones. If I am standing at the 50 yard line with a laser, and I point it at the mirror (facing me) in the end zone and shoot of a single blast of the laser and then record it's velocity as it bounces back and hits a...

I have a fog in my brain as I am trying to wrap my head around a problem and I am not sure how to word it so I will do my best. If object A is moving near the speed of light but without acceleration then it could be said to be at rest. Measuring a beam of light that passes its position...

Is there any other object except photon which moves at the speed of light? Why can't an object moving at the speed of light be taken as reference frame? Can we use the equation m=m(0)/sqrt(1-v^2/c^2) for an object moving with speed of light?

I honestly can't make any sense of this. I've been told traveling even one time faster the speed of light, the mass becomes infinite; therefore, infinite energy is required. However, traveling just one time above speed of light isn't an infinite speed. The object isn't constantly increasing...

Let's say you have a spaceship with an observer on it who has an experiment set up on the ship to measure the speed of light from a laser beam that is directed at the ship from behind. This experiment consists of two mirrors, one half silvered to only reflect part of the beam, that reflect the...

Why is it constant regardless of how fast the observer or the source was moving.. can anyone explain it to me or give me a good site that explains it? Thanks in advance

suppose we have a moving frame and a rest frame..we know time dilution and length contraction had occurred in moving frame wrt rest frame,this is to make sure that speed of light is same in any frame..but this is not the case..consider measurement of speed of light in moving frame wrt rest frame...

Not a physicist or a mathematician, but reading about cosmology whenever I have a chance. Alfa Centauri is 4.37 light-years away, so I conclude that it takes 4.37 x 2 traveling at 1/2 the speed of light. However, I am assuming that 4.37 x 2 is measured here on Earth. How much time has elapsed...

If I were to watch a ship reach the speed of light from earth, I would eventually see the ships engine slowing down as well as the crew and the ship itself, but with the ships engine slowing down from my perspective how would the ship continue to accelerate to near the speed of light? Since the...

Let's ignore the impossibility of it and assume you are in a spaceship going at the speed of light. If you shine a light from the spaceship how would an observer see it? Just light? What if the observer is shinning light parallel to the spaceship.. How would you see it?

As I've understood it, Einstein developed SR in an attempt to explain why the speed of light would be observed as a constant law from any point of reference, but it seems more like he only asserts this and goes on. How does he actually explain it? Does he ever explain why light speed velocities...

I can't post a link so just bing or google the topic. I have heard a little bit about this phenomenon and was wondering if anyone knows more about it or can give me a reference. If galaxies farther away from the milky-way are moving faster as they get more distant, then should galaxies...

is it possible to make one particle move with the same velocity with the speed of light ( c ) ?

Those "moving near speed of light simulation" videos Lowly undergrad here. Have you people seen these relativity simulation videos? http://youtu.be/bYdohPiFF6Y for example. My question is, what causes this spherical distortion effect? I know about length contraction and time dilation, but...

is the value of c is constant , although the light through other media , like glasses or water or vacuum ?

I've read that time and space dilate under acceleration to ensure the constant speed of light. I'm having trouble visualizing a scenario that illustrates this concept. Could someone please explain this to me? Thanks.

Hello, I would be interrested in building a list of things moving close to the speed of light. This list would contain these information: name of the experiment/observation date nature of the object nearing the speed of light method used to create the fast object method used to...

if a disc was spinning faster then the speed of light... would you be able to see it? and would it make a sonic boom when it past the speed of sound?

Your opinion on"exceeding the speed of light means the ability to return to the past" I personally think this assertion is absurd, so I'm wondering why so many people(including physicists) think this is true.

Picture yourself accelerating to 3/4 the speed of light, taking your girlfriend with you, and leaving your best mate behind, back on Earth (with no speed!). At this speed you stop accelerating and continue to travel through space at 0.75c. From this position, you see light traveling at the...

Has the one way speed of light been measured? All the measurements of the speed of light that I am aware of are two way or round trip measurements.

Hello, this has been bugging me for a bit, so some clarification would be greatly appreciated. Say I'm located on a planet 30x10^8 m away. And assuming light to be 3x10^8 m/s for easy calculation, it would take light 10s to travel to Earth, where you'd be able to see me, as I was 10 seconds ago...

I have a question about physics theory pertaining to the singularity beginning our particular universe. The laws physics may be thought of as “A logical explanation of the workings of our particular universe”. If you are going to accept that our universe is one of many others, how can you...

For example, as well known the period of the pendulum is (in linear approximation): T \approx 2\pi \sqrt\frac{L}{g} \,. So, no speed of light appears explicitly. What I'm wondering however is if and how it might be implicit? In the sense that after all the tension in the rod depends from...

So, I'm certainly not a physicist but I think I've just about started to grasp the concept of relativity and spacetime - maybe. A little bit. Hopefully. Anyway, I've always felt the concept of time travel is ridiculous, or at least backwards time travel, and I was trying to prove this to myself...

i don't know this question goes at the right place but i would like to know why speed of light remains constant what i mean is simple suppose you throw a ball and then consider you are throwing the ball by running yourself the ball acquires more speed in the 2nd case i would like to...

Hi just a quick question, why do they choose to collide the ions at just under the speed of light? what would happen if they were shot at the speed of light or higher?

See attachment for my text's explanation's on the permittivity and permeability of free space, if you want but it's not necessary. Anyway, after reading those explanations of the p & p of free space I'm having a very difficult time understanding why taking the inverse square root of the product...

Homework Statement The distance from Planet X to a nearby star is 12 Light-Years (a light year is the distance light travels in 1 year as measured in the rest frame of Planet X). (A) How fast must a spaceship travel from Planet X to the star in order to reach the star in 7 years...

So I've had many wonders about the whole unbreakable speed of light and what an army of scientists at CERN did. I already know they said it was a broken fiber optic cable or something else which caused that, but let's assume that what they were saying was true, then my questions arises...

I don't want to beat a dead horse with anyone fixed on dogma, but I do understand the theory of relativity and the part on time dilation, I don't yet believe. Who knows of evidence that time dilation really does occur and that traveling faster than the speed of light really is and always will...

Homework Statement A large cube of glass has a metal reflector on one face and water on an adjoining face (the figure). A light beam strikes the reflector, as shown. You observe that as you gradually increase the angle of the light beam, if Theta is greater than 58.7 no light enters the water...

In e=Mc2 Does c have to be exactly the speed of light? Can it not be a slightly bigger or smaller number? Or does C squared simply represent an enormous number?

If we have light, any particle, and maybe car, the particles travel at 0.98c and car let say 50m/s. Let them start moving at the same time to the given point let say 300 metres away. The difference between times of arrival of light and particle will be small compared to that between light and...

Its been noted through the Doppler Effect (or red shift maybe? not 100% sure atm) that some of the farthest galaxies seem to be moving away from us faster than the speed of light (c+). Since there is no axis point to measure the speed of these galaxies from, other than the milky way, could it...

I am not an expert on Physics and have for the past year been engulfed in work, so I am very rusty. I read a comment online recently that essentially said the laws of physics simply prevent any object from accelerating to the speed of light (infinite energy required?), but do not say that an...

I do not know a lot about physics, however, I was wondering if anyone would know, now that they think something can travel faster than the speed of light, would that solve the entanglement issue in quantum mechanics or at least the problem Einstein had with it? Or how two particles would be...

Hello all, Having read many threads and posts about light, it’s speed c, SR etc, the particular issue of not being able to measure the one way speed of light has always stood out and kept me very interested, so, after pondering about it for a while, I would like to propose an experimental...

Why can't we go any faster? If the speed of light is measured, why can't we go 1 mph faster? What's the theoretical barrier that makes it so unbreakable? why all this respect for this speed limit? Who's giving the tickets?

I was just reading on inflation and the book was saying that since the universe is expanding, the light we see from stars are now ALOT farther away from us now. This seems to my noob mind to be contradictory to relativity. If you on a train going 500mph at a beam of light the beam of light...