Speed of light Definition and 1000 Threads

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)...

Hello. So I always hear people say, "If someone flew in a ship at light speed to a far away star and then came back to earth, and it only took him two years to travel (the star being a light year away). When he came back all of his family/friends would have been dead for a long time." My...

Hi, I was wondering if it is possible to compute e.g. bohr radii for a metric system whose correspondence to real units is unknown and only the speed of light is known. Let's say the only thing I know is that lightwaves travel x spaceunits in t timeunits, therefore defining the speed of...

Hey guys, I have what I'm sure is a very simple question that I can't seem to find a simple answer to. I'm wondering what the ratio of time passage is between someone traveling at X times the speed of light versus someone on the surface of a planet. Say for a scenario I was traveling at 10...

Hey all, first I just want to say that I am by no means a physicist - just someone that is very interested in physics, and I have very little understanding of physics, but I am trying to learn. I've been reading this article about anisotropic synchrony convention which mentions that we cannot...

Suppose a black hole travels at something like v = 0.999999999c relative to some observer. Does the black hole's event horizon becomes length contracted, thus appearing to turn into a black disk?

good day , I am not a professional , but I read that in according to laws of physics it is not possible to go faster than speed of light . but I also read that after the big bang in just seconds the universe expanded from a size of an atom to the size of a galaxy . so obviously it expanded...

Please excuse this question from a lay person but if I don't ask I will never know. I know that the speed of light is a constant, that no matter how fast an object travels, light travels away from that object at the same speed. Hence nothing can travel at or faster than the speed of light, time...

Sorry if this turns out to be a colossally stupid question. I'm a newbie. But since light has a constant speed in all inertial frames wouldn't that mean where it would end up would have to be relative? A famous example of relativity for things in inertial frames of reference other than...

Biking at near the speed of light If a biker is going at 0.99c, an observer standing still would notice his clocking moving slower.Fine. But then how would the wheels of the bicycle match the ground? Would the bike hover over the ground? thanks

This is an experiment I'll be undertaking for labs. Given the following equipment: - laser with modulation input - lenses and mirrors - function generator - high-speed photo detectors - oscilloscope and the setup as shown in the picture (the function generator is connected to the...

Just a thought for the constancy of the light speed. Since photons are massless and therefore if they do not add the velocity of the moving light source i.e doesn't follow Newtons first law of inertia. It is only the surrounding that moves wrt the observer. The observer and the point light...

Howdy, This is my first post. Please be gentle. ;-) I have been thinking about the speed of light. Scenario 1: I'm on a train traveling at the speed of light. Everything in the train immediately about me appears normal. The reflection in the windows, looking down at myself, indeed...

If a a object is falling in a gravity field with infinitly long radius. can it eventually travel faster than the speed of light?

Would someone be kind enough to tell me if I'm getting this correct. Problem A A spherical light source is 1 light year away from Point A at point B. It moves at near light speed in a circumference around Point A to Point C for a distance of 1 light year. When the light reaches it's...

i have asked my physics and maths teacher a question which they could not answer, the question follows:- Does the large gravitational pull of Jupiter reduce the speed of light (on jupiter) ? Because what i understand so far that a photon has near no mass however it does a micro mass so it...

Everywhere we see that nothing can go faster than light. Light is the fastest. Is there any accepted law that states that nothing else can be faster than light? Or is it just that humans are unable to perceive things which is faster than light? There might be something faster than light, giving...

why is the phase velocity(c^2/v) greater than c?? since v<c it should be greater than c.. how does this happen?

Speed of light is constant because photon is massless. If this is wrong please correct me. So is it that any massless particle will move at speed of light? Do we know any such particles? There is this analogy that explains how particles get mass. Basically the higgs field gather around heavy...

It is said that the light we see from a star a million light years away is actually what happened a million years ago, that we are not seeing it at it's present state. For example, we see an explosion from a star that is a million light years away, then that means that star in real time had not...

I have a question, my bestfriends dad said that if we were driving at 70 mph and then honked the horn, the sound would go 70 mph + the speed of sound. So the obvious question, if that is true can we go the speed of light? But sound is the vibrations of atoms? Does that mean the atoms would have...

we cannot measure the speed of light in a vacuum only in space, and since we are told that space is expanding it could be that the speed light varies through time.

I had to cut the title short but would anything going the speed of light kill you even though it is impossible? I know that light is going the speed won't kill you but would it count? Because since fermions are transferring forces like photons transfer the electromagnetic force between two...

1) Are there any experiments/measurements of speed of light from distant (redshifted) galaxies? 2) Are there any experiments/measurements of luminosity distance of bodies moving away relative to us? 3) Where can I find type 1A supernova data (redshift and luminosity distance) for low z...

hey guys, I need some tech support for a spaceship in a story that is currently in the works :) Assuming the characters could get their ship up to the speed up light in real space (no hyper drive or warp drives) What would the effects of time dilation be on the crew? Time slows down as you...

Only but few may disagree that the inverse squared law affects speed. For example, not only lengths of far away vehicles shorten, (with increase in distances from obsevation) the moving vehicles generally seem to have "slowed" down; the direction either from right to left or vise versa. Please...

Fast than speed of light... Hi guys & girls, I have a question regarding traveling faster than the speed of light, a small theory, which I am hoping someone can explain to me why this wouldn't work. Note: I'm a total amateur science enthusiast, so please forgive me if this sounds really...

I'm writing a book and in it there is a character who can accelerate objects to extreme speeds in one direction. His weapon of choice is a custom built gun that is similar to a BB gun. It fires 5mm tungsten rounds that weigh 1 gram (for simplicity). Normally the gun is just a non-lethal air...

In Stephane Hawking's book-A Brief History of Time-Stephane says that in the past they used to believe thatthe speed of light is constant only relative to ether and it's variable acc. to the speed of the observer , but now acc. to Enistein: he says that the speed of light is constant whatever...

Why 299,792,458 m/s? Why does light travel at the speed that it does?

Hello! Consider the law of addition of velocities for a particle moving in the x-y plane: u_x=\frac{u'_x+v}{1+u'_xv/c^2},\, u_y=\frac{u'_y}{\gamma(1+u'_xv/c^2)} In the book by Szekeres on mathematical physics on p.238 it is said that if u'=c, then it follows from the above formulae that...

Hi , well we all know that the speed of light in vacuum is measured at c and it slows down when it enters other mediums. Now we always say speed of light is c in vacuum but hence I believe the speed is c there because there is nothing in the way that could slow light down like there is in other...

i was watching sixty symbols today, and i learned about refractive indexes. light travels at 40% of its normal speed c when traveling through glass. after i watched that video i attended my summer class (engineering physics II, covering circuitry, optics and EM waves) and i started asking about...

Who first studied variable speed of light? --- Einstein Variable speed of light is a hypothesis that states that the speed of light, usually denoted by c, may be a function of space and time. Einstein's first mentioned a variable speed of light in 1907, and he reconsidered the idea more...

Is there anyway to figure out the distance at which the universe is expanding (rate of stretching) at a rate that is equal to the speed of light?

Spaceship Alpha is traveling at 0.9c. It shines a light beam. An observer that is stationary observes that the light beam is traveling at c, not 1.9c. Explain. How can I answer this question? I don't want to just say because Einstein said c is the same regardless of frame of reference. Imagine...

I have learned that the universe came from big bang and it's expansion is accelerating...Now let us assume that there is only one universe and that there is no multiverse... According to postulates of relativity, in any frame of reference, no body can travel faster than the speed of light...Let...

Say I am in the middle of two people that are 2 lightseconds (we'll call this unit a distance that speed travels in 1 second) away from me. They are 4 lightseconds away from each other. So these two guys are my friends, and before they moved to 2 lightseconds away from me, I told them, if I am...

Is it possible to travel further in distance (position 2 - position 1) over a unit time more than that of traveling at the speed of light? This is not wormhole, or anything that sort, just change in position. I am coming from the fact that a moving particle can exist on a moving object.

1) On a recent exam, one of the questions asked to find the minimum speed at which you would have to fire two protons head-on if you wanted them to get them within 10^-15m. To make things a bit easier, I treated one proton as being stationary and then found the energy needed to bring the other...

It is often said that although the expansion of the universe may create the illusion of objects in very far regions of the universe to recede from each other at superluminal speed, that does not violate c because locally they never move faster than c. This I can understand. How would things...

Coulomb’s (electric force, electrostatic) constant (symbol κ (kC, ke)) is a proportionality constant, expressed as: κ ≡ kC ≡ ke = 1/(4πε0) = 8987551787.36818 N•m2/C2 (exactly) κ can also be derived from lightspeed squared divided by ten million (c2/107)... Can someone please help me...

This is my first post so let me know if I'm posting this in the wrong section. I read somewhere that if we are ever able to travel faster than the speed of light that fact would automatically enable us to travel back in time. I don't see how those two things are connected. Even if we travel...

can anyone give me some good explanations or experiments about time and the speed of light. my knowledge at this point is kind of limited. I know the concept but can someone explain how its proven in theory or experiment. thanks

For example - When an electron is excited from an inner shell to an outer shell in an atom, it does the quantum jump between the states. Pretty much it disappears from inner state and appears in outer state. Isn't this happening at faster than light? (The velocity is actually infinity for...