Light speed Definition and 317 Threads

Hi. Say a positive charge is at (x,y,z)=(0,0,0) at t<0 then (1,0,0) at t>0. Electric field at (x,y,z)=(l,0,0) is (a,0,0) at t<l/c then (b,0,0) at t>l/c thus a<b. With time delay of l/c, what propagates from (x,y,z)=(0,0,0) to (l,0,0) ? I do not think it is electromagnetic wave because it is...

Hi, Are anyone here familiar with this? It shows a camera that can capture 1 trillion frames per second, and the camera can be used to record the speed of light. The other day, I saw an article when I was searching something on Google and it said a 4 trillion camera were created by Japanese...

Definitions: Astronaut is A Person on Earth is B A travels to a star far away at near light speed, A would see B's time dilate. B would also see A's time dilate Twin paradox revived: What would happen if A returns to B at a very slow speed? Then both frames of reference would see each others'...

As speed of the sounding source approaches speed of sound, sonic boom is heard... Can it happen in terms of light too.. ?

Hello community, First of all I want to apologize if what I'm about to post is a complete nonsense, I have to admit that my knowledge in physics and futhermore astrophysics is close to NULL, but from a few years back I've been wondering some things but I didn't have the chance to discuss about...

So, I've been wondering: how would time dilation affect communications? For the sake of visualisation, imagine the Flash is running at 99% the speed of light in a circle around a fixed position. There's a building in this position, and inside this building are his friends. Due to time dilation...

I've been told contradicting ideas about this. I've been told that light doesn't travel at a constant speed everywhere (i.e. light slowing down in speed after entering a more dense medium). However, I've also read that light speed is constant everywhere (i.e. if you could travel close to the...

Hello all, I was thinking about the speed of light and why it's constant and it brought me to the principle of the LIGO experiment for which I have an assumption that I want to verify. I'm a novice at this so please bear with me. From what I know, the LIGO experiment splits an emitting light...

Hello ! A few days ago, I came across this article http://www.bbc.com/news/uk-scotland-glasgow-west-30944584 And I was wondering if it has any consequences with the relativity ? I mean, in my mind, light velocity is supposed to be constant in vaccum, c0 = 3e08 [m/s] approximatively... What...

Big masses like planets and stars have gravitational fields. Gravitational fields curve space around them. So in theory a particle having mass moving at fixed speed, from its own perspective, will accelerate when moving closer to such a planet. It'll be moving at fixed speed in a curved space...

According to Einsteins Theory of relativity if an object traveled at the speed of light, it's mass would become infinite, time would seem to stop relative to others and it length would become absolute zero. The same conditions were thought of at the Big Bang, when time didn't seem to have...

My first question on your forum. I just found you last week and have spent a whole lot of time reading. My question: Not actually a question, but a supposition seeking confirmation. Were it possible to travel faster than light, could we "catch" the light from prehistoric Earth and see...

The thought experiment used to prove Lorentz transform uses a light signal as an assumption. What if there was something other than the light signal then Lorentz transformation would have totally different term in place of 'c'(speed of light).

Hello everybody. I am an spanish student of a bsc in Chemical Engineering, so as you can imagine, all this questions are going to be purely curiosity. First of all, sorry for any english language mistake I can commit. I have always been curious of the spacetime issues, and how the world really...

(I think) I know that massless particles can only exist traveling at c, but I find it somehow counter-intuitive (like many other real things... :D ) Would anyone please be so kind to confirm that, for instance, a gamma photon generated by the radioactive decay of a stationary isotope is already...

How long/what distance would it take a spaceship (with a hypothetical propellant-less engine) to accelerate to near light speed, and secondly, how low long/what distance would it take to decelerate back to zero again?

Forgive my ignorance?.. If we can see 13.8-ish billion light years away how can the universe be the same age? Matter cannot travel at the speed of light, so how are we as far away (in light years) as the universe is old?

I watched a BBC documentary that said that the observable universe is about 46 billion light years in size. How can this be if the age of the universe is 13.7 billion years (and nothing travels faster than the speed of light)?

If particles at the LHC are traveling very near the speed of light, are they affected by the slowness of time? Also, how can they travel near the speed of light when the planet is rotating around the sun and the solar system is traveling around the galaxy and the galaxy is moving through space...

Dear PF Forum, There's one thing still bothering me. The speed of light. Supposed two observer, A and B A is from the west, B from the east. Separated by 100 lys. B sends a signal, say, B1 to A. So B1 will be received by A in 100 years, right? Now, supposed B travels at 0.8c and at the distance...

Ok Little background knowledge I am a huge scifi nerd I know some about modern physics mostly conceptual not mathematical The limit of my mathematics is the rocket equation. Anyway as most good ideas this one came to me in my sleep. I understand that the general convention is travel to the speed...

i think it is possible but its too complicated to write down in english so i think comunication faster than light is possible without anything acctualy moving faster than light. If you had a big stick between Earth and the sun and you push the stick towards the sun for 1 inch it will instantly...

Two spaceships pass by each other. Both are traveling at near the speed of light. How will each spaceship percieve each other speed and time? Besides how do you do it mathematically?

Hello PF, A question on special relativity I've not found an answer to,I tried to google it but no luck, so here is it : If you were to observe a moving body whose speed is very near to the speed of light, will you see it slowly due to time dilation, or you'll observe it as it really is, very...

Riddle me this. If it was possible to vibrate at near the speed of light, would that still create the effect of time passing faster for you but your surrounding passing through time at the same rate? Just wondering. I am aware that A) Time travel backwards would not function, due to the...

wiki says "Experiments that attempted to directly probe the one-way speed of light independent of synchronization have been proposed, but none has succeeded in doing so" Here's a proposed experiment which I could not find any evidence of this being performed before.. Central light source...

Hi all, this my first forum ever. I'm a self taught physicist. So pardon my ignorance. I pose this question. If speed :s = distance :d ÷ by time :t Then how can we possibly measure our cosmos accurately with a measure of speed aka "Light Speed". The problem I see with this is TIME is a variable...

While the main problems of a functioning starship are commonly known such as energy requirements and radiation I have realized another problem when near the speed of light. The dynamic Casimir effect occurs when a reflecting object reaches relativistic velocities. Therefore a starship with a...

If velocity is relative and dependent on an observer then how does an isolated object "approach the speed of light"? Approaching the speed of light relative to what? Does the ubiquitous constant velocity/closed compartment analogy break down at relativistic speeds? If one were traveling "near...

Hi, I am currently plotting a piece of writing and wonder if anyone could give me some feedback on the following: - Space craft 1 is a beam/ sail craft with constant acceleration of 1 G to a speed of 0.2c. It travels along a straight line between Tau Ceti and Sol (circa 12 ly). Ship time...

Hi there. Just wondering if the speed of light is wrong for a 3 dimensional universe. As each photon of light traverses space its velocity is 299 792 458 m/s. And since each photon has a wavelength and amplitude, then the actual distance that each photon travels, depending on its wavelength and...

I'm fairly new to the concepts provided by special and general relativity, and was wondering if someone could provide an answer to a thought exercise I came across regarding time dilation on an object going near light speed. Say a spaceship were connected by a live video feed to a monitor on...

everyone knows that if an electron travels close to light speed, they gain mass, but how about the wave side of things? since gravity and electromagnetism are 2 completely different things (is gravity and magnetism both waves?) would the electron wave traveling close to light speed be not...

Is it true that if time stood still it would violate the uncertainty principle. therefor if you traveled at the speed of light time stands still and you would violate the uncertainty principle. if this is true does that sugest that QFT sets a lower max speed that matter can travel at than what...

Homework Statement In terms of the energy involved (using formulas provided), explain why accelerating a spacecraft to the speed of light is impossible. Homework Equations time, mass and length dilation formulas, and a few astrophysics formulas, E = Ek + mc2, projectile motion formulas The...

What would happen to a neutron star (on the cusp of becoming a black hole) if it were sped up to near the speed of light? Or more easily done, if I sped up to near the speed of light. Would the additional mass from the near light speed cause the neutron star to collapse in on itself and form a...

While reading Special Theory of Relativity from Feynman Lectures, I fell into the confusion about invariant speed of light. What I'm asking for is an explanation about this. No matter whether physical explanation or mathematical. So my question is Why the speed of light is same for a person...

Considering that speed of light is constant and finite, then why are the time dilatation and length contraction infinite to a frame of reference moving at the speed of light? We know that a moving frame of reference experiments time dilatation and length contraction from the point of view of a...

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...

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...

Hi everyone, First I want to say that I hardly know anything about advanced physics, and I'm just looking to ask something that I've been thinking about for a while. So I'd also appreciate if you kept the explanation somewhat understandable :P Anyway, here's my question: If light from...

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...

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...

Homework Statement If a 0.505m long wire is excited into its lowest electrical resonance by a 2.2E7 Hz electrical oscillator, what is the ratio of the speed of the electrical current to that of light? Assume that the wire is like a tube with both ends closed. f=2.2E7 L=0.505 v=...

Einstein theorized that if you were to go the speed of light or even faster then the light around you would become paralyzed. But if you're going that fast then the light wouldn't be able to catch up to you, so technically wouldn't the light around you would become black because the light...

Everyone knows that if a light come in a material will change speed(will become less),and from wikipedia I read that light wants to go from his faster way. So when material 'eat' from light some speed,then light as more 'clever',goes from a sooner way.(that what we call "refraction."). So my...

ok, light isn't relative, or is it? Its said that galaxy far across the universe appear to be moving away from us at beyond light speed; as since the universe is expanding all around us. So, does that mean light within these distant galaxies moves around relative to within its own local...

Someone published a simple computation of the relativistic shift in Mercury's perihelion (over and above classical, ie. the small correction over the classical-mechanical shift) by more or less using the principle of relativity. I believe it was a she and she computed how far mercury travels...

all objects travel at a speed .when we come to light , the speed is approximately 3 * 108 . i am confused about how can it travel with such a speed . i have surfed in the internet but it only says that it is not yet proved . i wish to know the answer . this could help me to study optics more...

Hi all, I am wondering if time has any control over light or is it vice versa? For instance, is light speed controlled by time? I have read that it is impossible for anything to travel faster than light and time slows down the closer you get to light speed. Is this because of time being in...