Speed of light Definition and 1000 Threads

What experiments have been done to prove that the speed of light is constant among all frames of reference? Discounting the aehter, wouldn't the Michelson Morley experiment only be confusing if they already new about it's "constant-ness?"

Greetings, Sometimes I read that the speed of light is constant, and sometimes I read that it is always measured to be the same. Is it: A - The speed of light is actually constant. or B - It is not constant, but is always measured to be the same due the effect of something such as time...

I was reading that a meter is the length of the path traveled by light in a vacuum in 1⁄299,792,458 of a second. So the speed of light is exactly 299,792,458 m/s. I am wondering what is the uncertainty in our most accurate measurement of the speed of light. For example say I had a machine...

First off, please do not direct me to: https://www.physicsforums.com/showthread.php?t=104715 topic number 4 because i have read, read again, and then read once more and i am getting nowhere with that. Can you please just address these points: Does light slow down because of the...

Hi, I'm reading up on special relativity and it is pointed out that the galilean transformation dictates that if a light source were moving at velocity v wrt to an observer in another inertial frame of reference, then this observer would calculate the speed of light to be either (c-v) or...

i have been pondering why is max speed 3x10^8m/s and what govern that speed. why can't it be like 4x10^8m/s or smth?

Hey guys, If something with mass comes close to the speed of light, the laws will adjust and slow down time in order to prevent the mass from passing the speed of light. Is that correct? So, would the object start to gain mass as it gets close to the speed if light? Where does this...

Greetings, I read in a relativity paper or book (I think one of Einsteins. I am trying to find it again.) that c is actually represents the speed limit of the universe, and because light has no mass it travels at that speed. That c was arrived at independently from the speed of light. I think...

Hi, I am in my sophomore year and taking a class of intro modern physics.. I read Methuen's Monographs on Physical Subjects - The Special Theory of Relativity by Herbert Dingle..as a reference The author claims several times that the limit of possible velocities, even in vacuum, the speed...

Alright, I have a noddle scratcher..at least for me. I understand light can slow down and speed up as it moves through different materials. I know light cannot exceed the speed of light (c). I know at the speed of light time is instantaneous or stops - same difference. So my question is...

Has anyone ever done an experiment with an entangled pair (say a pair of photons of opposite spin) where both are measured at the same time (or at least a time less than the separation, d, of the two particles divided by the speed of light, d/c)? Less than d/c and more than d/c seem to be...

Everyone know speed of light is nearly 1079252848.8 km/hr . Assume that I am driving car at 40 km/hr. then I turn on the light. so why speed of light doesn't goes +40 km/hr. Why it will still nearly 1079252848.8 km/hr . I think you will understand what I am trying to say. Help soon...

Let A and B be two points that are at rest relative to an inertial frame S. Let's say the distance between them is 1·109 m. In the beginning you are at rest relative to S, but during exactly 1 second (counted by your wristwatch), you have managed to accelerate up to the velocity v=0.99c. Let's...

Homework Statement Question Given that the speed of light in a vacuum is 3.0 x 10^8 ms^-1, calculate the speed of light in a diamond of refractive index 2.4. Homework Equations - 3. Attempt So if the refractive index is 2.4, which means 2.4 = sin i / sin r, how can I solve this question...

guys, i got a simple question i'll make it in parts after stating what i think is well known... a) speed of light decreases in a medium...that is it decreases when it movers through matter b) there is dark matter present throughout the entire galaxy and so is present on Earth as well c)...

We all know the constant which stands for the speed of light in a vacuum. However the speed of light is not constant, we can slow its speed to near zero right here on Earth (Scientific American). My question is, if the speed of light can be slowed, can it not also be increased? Supposed we...

If we were to measure the speed of light as the scientists in the 1800s did (such as Foucault and Fizeau), without knowing the relationship between speed of light and its wavelength and frequency, would it be possible to do so using only simple apparatuses like mirrors and low powered motors and...

I'm a high school physics teacher, but unfortunately I do not have a lot of experience with physics outside of a few courses I took in university - none of which dealt with relativity or quantum physics. As a result, I'm at a bit of a disadvantage when trying to teach concepts I'm not entirely...

Why does light or anything have a finite speed? In E=mc2, it gives the constant of the speed of light but I don't understand why light has a maximum speed. Is there something that slows down light?

An observer (in zero gravity) witnesses two parallel but widely separated beams of light that are transmited at the same time. One of the beams experiences zero gravity. The other beam travels between two massive objects with a very strong gravitational field, but arranged so that the beam...

Well the other day I was thinking about the speed of light and how physics says that nothing can go above the speed of light and that you need infinite energy to go at the speed of light. But take this example: Imagine this example, you're on a train going at 99% the speed of light (therefore...

Homework Statement Two parties (A and B) are signing a treaty at opposite ends of a 40.0meter table. The two parties and very suspicious so it is important for the two to sign the documents at the same time. This is arranged when the light from a light bulb at the center of the table reaches...

Can you explain for me what part of general relativity says that gravity must go outward from the body at the speed of light, rather than instantly? I realize that Einstein believed nothing could go faster than the speed of light, but is there evidence that this must be so in the case of...

Can anyone please tell me what does SPEED OF LIGHT WITH RESPECT TO AN OBSERVER mean? Some explain it like this: If there are two poles 10km apart, in front of an observer and he sees a ray of light passing past them, then he would see that the light would cross the poles in time 10/c. Is it...

Speed of light and momentum? Hi all, I have just started reading about quantum physics as my uncles cousin was the late John Bell (Bells Theorem), so got interested in the subject, purely as a hobby! My question is probably very simple, but I have only started reding about this last...

Hi everybody, I would like to begin with apologizing for anything stupid I might say or ask because I am not a qualified physicist. I'd like some minutes of your time because i have a question that's been on my mind far too long and i would really like some help with this. Am I correct when I...

Alright guys here's the challenge. Take this seriously because I don't understand how he got the speed of light, so is someone capable of explaining this thing step by step? My friend is a muslim, an excellent student and he claims that the speed of light is predicted in the Quran. Now he's...

I thought that the idea that the speed of light is a constant in every reference frame came from the Michelson-Morely experiment. But a friend of mine was saying that Einstein supposed that if one could catch up to a light beam then it would no longer be moving and would then not be an...

It is often stated that the one way speed of light cannot be measured and that the isotropic speed of light is just an assumption based on two way measurements and clock synchronisation conventions. Here is a proposal for measuring the one way speed of light. It is not entirely original as it...

What makes light travel so fast?

Assume that both light and an observer are traveling through water with a refractive index of 1.33. Without getting my calculator out, I think this means that the light would be traveling at about 0.75c. The observer is traveling in the opposite direction at about 0.25c (it is only a thought...

So I have been wondering about something, this is completely theoretical obviously you cannot sit on a photon but think about this and let's see what you think... We have a Photon traveling at the speed of light from one point to another. The origination point, a light source 1000 light years...

In QED calculations are made with variable c. But Duff says that c does not exists, because it is only a transformation factor. So if we put c=1 how QED is changed at small distances?

hello all, I know that it is impossible for something to have a speed greater than c, is it possible however to accelerate faster than c? For example, would it be possible to accelerate something at 4c/s for 1/8 of a second, resulting in a speed of 1/2c?

Hi! Consider a high-speed camera set up to record an explosion and the resulting shockwave emanating from the explosion. In the same frame you can see the shock wave as well as people in the distance. Is it true that the people in the distance wouldn't hear the sound of the explosion until...

and you flew in a spaceship going the opposite direction, also at 51% the speed of light... Would each of us be breaking the light barrier, relative to the other? If not, why not?

Hi, how is the speed of light measured in objects such as water, glass, diamond etc ? what are the tools and techniques used. thanks in advance !

Is it possible to go faster than the speed of light? And why do some scientists say you can't? Thanks -_-!

As per the theory of general relativity nothing can travell faster than the speed of light. Therefore we would always be in the past light cone of a distant celestial body, say planet X in another solar system, that is 100 light years away. A minimum of 100 years would have to lapse before an...

I have puzzled over a couple of things relating to the speed of light as a constant to all observers. I fully recognize that it has been demonstrated to be so, and that those demonstrations have been confirmed by facts such as the existence and workability of GPS; however, these go much more to...

I got this doubt while solving a problem. Suppose an electron starts moving from rest in a region of very high electric field of the order or 106V/m along its direction. Its acceleration is given by a=Eq/m, which is 1.758 x 1017m/s2 on substitution. We can ignore 'g' here. The time taken...

How is it possible for the rate of universe expansion to surpass the speed of light? (According to the Big Bang theory, and according to the model of an accelerating universe, hasn't/won't the universe surpass the speed of light?)

Has the speed of light always been the same since the beginning of the universe? The reason i ask is i work with a guy who is a strict creationist and he said that despite the universe appearing to be 13 billion years old, the speed of light may of been billions of times faster just after the...

hmmmm, let's say I'm floating about in space, and all of a sudden a giant star magically zaps into existence a few thousand light seconds away. Do I feel the gravity then and there? Or do I have to wait few thousand light seconds for the gravity to "get to me?" Are the effects of gravity limited...

It has been stated that as something approaches the speed of light, time slows down for that object. Since light photons are traveling at the speed of light, does that make them even older?

The LHC is acccelerating particles to 99.9% the speed of light, but don't objects approaching the speed of light theoretically also attain infinite mass? So my question is, how would the accelerator keep those particles "roped in"?

While listening to "Science Friday" on NPR today, I heard a Swiss physicist explaining that scientists can now produce Ant-Matter in a process based on Eintein's formula E=MC^2 whereby energy is converted into matter. Given that "C" in the formula is the speed of light and knowing that the speed...

In my opinion the key to dealing with the current cosmological problems require applying some of the ancient spiritual Philosophies like buddhism. As I understand the big bang: Nothing can travel faster than light. Light travels at 2.998E^8m/s. The universe is accelerating at an increasing...

Lets say we manage to build a spaceship 30miles wide and long that is capable of reaching to 99.99% the speed of light. Now inside this massive spaceship we have a particle accelerator. The spaceship is now traveling just a fraction under the speed of light when we decide to fire up the particle...

Can someone help me with speed relative to different objects! Nearly everything in everything in everyday life is relative to the earth, however if i was traveling a little be slower than the speed of light, relative to the earth, why am i not traveling faster than the speed of light relative...