Speed of light Definition and 1000 Threads

so what i am about to write is quite possibly wrong, but this is just how i was thinking about why the speed of light is different in a vacuum as it is in glass or water etc. i am writing this to see whether my train of thought is on the right lines, and if it isn't to hopefully get an insight...

How many experiment measured the vertical speed of light? I wonder, how can gravity affect it?

An acquaintance (my boss, actually, so please be nice) has suggested that, if a windmill could be made large enough, the tips of the blades could travel at the speed of light. Notwithstanding the impracticalities (there's no wind up there; the blades would surely strike the planets; where would...

It is my understanding that an astronaut could get from Earth to the far edge of the Milky Way within the length of a human lifetime if she were traveling close enough to the speed of light. From earth’s perspective, time would pass very slowly for her as she moved across the galaxy. From the...

Einstein postulated that the speed of light is the same for all observers. But it seems that this speed limit applies to more than just photons. It also applies to any massless particle. So I have to wonder if there is some way of deriving the speed of light from more general principles that...

Hello, There are two observers. A is stationary and B is on train. Train is moving. B is at middle of train. If B flashes a beam to front and back, and at the both end there are detectors, then what does B measure one way speed of light in both direction? Thanks.

As you will see this is my first post so I apologize if I have chosen the wrong sub-forum. My academic training (maths) was many years ago and it now seems to me that for the last 30 or so years my brain has been in a kind of intellectual limbo from which it is only now beginning to emerge, so...

First please forgive me, if my question is in the wrong board. Dear members. I'm only Junior High School graduated. So I knew nothing about physics /science/math, etc. My friend "teach" me that if a person mr. X move at the speed of light, then time not exist anymore for mr.X or time...

In my class's set up of Foucault's design of the experiment to measure the speed of light, the light beam passes through a beam splitter but there is only one beam spot in the microscope. I'm confused as to why this is. Can someone help explain it to me?

If it is true that when traveling close to the speed of light makes you go forward in time. Then do you go back in time (observed from the destination) as you travel to your destination close to the speed of light? And why don't particles traveling at near light speeds appear to warp time...

I read that the speed of light is constant, that everyone measures the same speed of light from their own reference frame. Yet I have also read that light can't escape from a black hole, because of the gravitational effects. How can you measure it's speed at 'c' and yet at the same time not...

Is there an equation to figure out how much time would pass traveling light speed for 10 years relative to the person traveling? I know its less, but by how much exactly?

Why do gravitons travel slightly slower than photons (99%) and why do neutrinos travel slightly faster than photons (101%)? What is an intuitive interpretation of why a joule is a gram multiplied by the speed of light squared? For a layman like me, this seems very unintuitive - first of all...

So my Cosmology prof (who does research in String Theory) mentioned something during class a few days ago that the driving factor behind Superconductivity is that the speed of light changes. Someone in my class spoke to him after the lecture about it and he rambled on about something to do...

If Earth is here 0 and I go at 90% the speed of light in that direction <--in my spaceship and my friend is going a 90% the speed of light in that direction --> in is spaceship so it look like this. 90% <-- 0 --> 90% relative to people on Earth we each go at 90% the speed of light in oposite...

Is the speed of light what they call the front velocity, the formost part of a beam of light? If this is so the actual path of the electromagnetic wave must travel further than the distant traveled by the beam of light. So any point along the path of the wave must be traveling faster than the...

I know from my physics lessons many years ago that a gravitational field can bend the path of light, but what is the effect of gravity on a photon when it is heading directly at a star. "If" the speed of light cannot be exceeded, what happens ?

Sorry in advance if this is a ridiculous question, but I've always wondered about this. Let's say we could create a wire in space away from any gravitational affects. Make the wire 2 light seconds long, for example. If we pulled on one end, when would the effects be felt on the other end? I'm...

My teachers in school use to say. "the dumbest question is the one not asked", but I might just break that rule with this one. :smile: Here goes... I've been reading a lot of articles today on light travel, the Higgs field, and other fascinating stuff. Lastly, I was just reading an article...

Why is the speed of light slower in certain substances than in a vacuum. Since most of the atoms is empty, shouldn't the speed be the same? Is it because photons bounce off the nucleus, or because they get re-emitted?

Okay, so I'm no physicist, but I just had a random thought. So they say that traveling at the speed of light is impossible because the mass of the engine would have to be constructed infinitely big. But what if the propulsion didn't come from the spacecraft ? I was wondering what you guys...

Curious Why does the equivalence of mass/energy involve the speed of light at all? Is it because Einstein discovered that this was simply the correct multiplier or was there some other reason to connect the speed of light to the relationship?

Does the speed of light vary with different frequencies(or wavelengths) in mediums other than vacuum, or is it constant for all light regardless the frequency?

I have another thread going right now but I don't want you to refer to that thread. I frankly don't understand what is going on in that thread so please answer my question here. Why do you need to measure the speed of light in both directions for an accurate reading? If I am in an inertial...

What is the Temperature of an atom moving at the speed of light? Since absolute zero is the lack of activity and energy and since no physical object can move faster than the speed of light What is the temperature of an atom moving at the speed of light? Light is either a particle...

Had this question in a test today, :). Homework Statement Carbon tetrachloride (n = 1.46) is poured into a container made of crown glass (n = 1.52). What's the speed of light in the liquad? Homework Equations v=c/n The Attempt at a Solution I just multiplied 1.46 by the...

I recently saw a documentary on TV in which Stephen Hawking stated that the universe was 600 lightyears in diameter, 10 minutes after the Big Bang. How can this possibly be true? - the particles and matter making up the outer limits will have had to have traveled at many times the speed of light...

I would like to propose a school task, that may lead to some paradox (to my mind): It is known that light travels from Sun to Earth for about 8 minutes. If light propagates instantaneously will we observe sunrise 8 minutes earlier?

I googled for the slowest record for the speed of light and it came up with just over 40mph or 60kph. I am fairly knowledgeable with Einsteins equations regarding the speed of a massless particle but what were scientists able to do when they were able to do this with light. Heres where I...

Speed of light becomes Infinity and Zero! Hi Guys, I am just new to SR & GR. I learned about Lorentz contraction and time dilation, but they don't make sense when i consider the following situation... Your(Moving non inertial frame) Time runs slow relative to a stationary observer when your...

Thank you in advance for reading this and hopefully answering my questions. I've spent about two hours or so now trying to get my questions organized in a clear way, so that they are direct and to the point. I've drawn an image to help explain what I'm getting at. I'm not much of an artist...

So I remember in basic physics the scenario: If you're driving at the speed of light, and you turn on your headlights, can you see them? I know the standard answer is yes; that it propagates at speed c no matter the reference frame. So how about this: Suppose I'm driving my car...

Hi, I'm kind of a noob when it comes to physics so I just have to ask. Me and my friends are kind of in a pickle, so here it goes: IF you run around a tree at the speed of light, thus bending time (correct me if I'm wrong) is it possible to touch yourself in the back?

Hello all, Would like to get some feed-back on some questions I had about special/general relativity and a thought experiment. In the case of gravitational lensing, an obvious case being the Earth is lined up with the sun which is lined up with a distant star. From Earth the star is seen...

Hi, Now we have the "faster than speed of light" neutrinos, I was wondering the next philosophical question: If we presume it is indeed correct they are faster than speed of light, would all observers of these neutrinos, no matter in what inertial frame of reference they are in, measure...

So I'm new to this, but it's one hobby that fascinates me. I figured I'd come here to listen to your thoughts. I was thinking the other day about an alternative energy and naturally "too bad we can't tap into a quasar" came up. For now I think the thermosphere seems to be the biggest source of...

Just wondering if the two are fundamentally linked ? If the universe is in the shape of a 3 sphere and if it's radius represents time, then does the expansion rate of the radius determine what the speed of light is ? I've also read elsewhere that the passing of time is linked to the...

The speed of light, the term "light year", and reference frames. Hi everyone. This is my first post, and I post out of desperation. A friend of mine and I were casually discussing Time Dilation, interstellar travel, etc. when we came to a point we fundamentally disagreed upon. Neither of us...

Suppose, A is moving with constant speed c/2 and B is stationary. A fires a beam in direction of his travel. A measures the speed of light as c. B also measures the speed of light as c obviously. But when we ask B to claim what is speed measured by A, then what should be B's answer? I guess...

Hello, Surfing the web I came across a question posted by someone. Basically the question asked if I were to have a very, very long rod, say 1000 ly long, and at each end I place an observer. If observer A pushes the rod, would observer B instantly detect the nudge? I do understand that...

Hey, this is my first post of many as I have hundreds of questions! As speed of light is a constant, does it travel from the eye of the observer ? e.g is a stationary person observing light travel away at ≈ 3x108m/s but a person traveling at 1/2 of, c, witnessing it travel 1/2 that speed...

I have recently been watching the series "Into the Universe with Stephen Hawking" and I have a question (commence eye-rolling of anyone reading this). I don't think the series is supposed to be an educational tool necessarily, its more of a horizon expanding view of some high level topics with...

How much experimental evidence is there that the speed of light stays c between a source and target moving wrt to each other?

I have been reading Einsteins Relativity and a simple concept in special relativity is tripping me up. I have heard that an object can never reach the speed of light. To which observer is this speed limit seen by. I know your answer will be "By all observers" but that is what I don't get...

If a spacecraft were traveling at the speed of light (OK, forget the difficulties for now) relative to an observer on Earth then would it appear to an occupant on that ship that they had traveled instantly from one point to another?

Many students interested in knowing if scientists have achieved a greater speed of light for subatomic particles. Any comments please

What is the reason for this?

Hi, I hear that light always seems to travel at c, but I've failed to completely understand what that means, could anyone help out with that? c is measured in m/s, but both seconds and meters seem to be able to change depending on the observer due to time dilation and length contraction. When...

Hi, May be a dumb question; imagine a hypothetical situation of a spaceship in space with no influence of gravity due to Earth or nearby moon. Assuming the spaceship has enough fuel, if it injects the fuels outwards, it will accelerate in the opposite direction. Now, the new velocity will be...

The theory of Relativity uses a constant c which has the approximate value of 3x108 ms-1 The measured speed of light in a vacuum vl has apparently the same value. What is the experimental evidence for this equivalence? As far as I know, the only way to measure c is to measure the speed of...