Speed of light Definition and 1000 Threads

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...

So, according to my understanding, if we leave Earth and travel close to speed of light and then come back we may have time dilation (there will be one year for us, but 10 years for the people on Earth). But how does this work as long as there is no frame of reference? Why can't we consider...

hello, my name is Zachary. i have little to no experience in astrophysics but i must say it is the most intriguing subject of discussion for me. what i believe i have worked out is the amount of nuclear energy (MeV) in megaelctronvolts, to propel a space shuttle (for a general number for M) at...

According to some physicist and cosmologist observation the speed of light is not a constant depending on region of the universe they observe and according to Einstein theory gravity move at the speed of light now my question is if gravity move at speed of light than gravity should move faster...

"Breaking Light" My friend tried explaining to me that you can "break" the speed of light. He showed me a youtube video, "minutephysics" saying that if you could point a laser at the moon, by flicking your wrist, the image/spot of the laser on the moon would be moving faster than light. Is he...

Someone said that entire theory of relativity hinges on the assumption that the speed of light is constant in a one way direction between any two points and that this cannot be proven scientifically; it must be assumed. A response to this was: constancy of the speed of light through a given...

OK, so I am not a physics major, but I think that I understand that matter or energy cannot travel faster than the speed of light. Today I was using a laser pointer, and I noticed that it traveled rather fast, and it traveled faster as it went farther away from me. So if you imagined the laser...

If Einstein's theories are correct, specifically about objects approaching the speed of light and their mass approaching infinity, how is it that a photon (and object with mass or mostly energy) is able to remain nearly massless? Why doesn't an electron fired through a particle accelerator...

As far as I know all light speed measurements done using light sources that utilized electrons. The nominal light speed measurement used laser which is actually exited electrons. The speed of X-ray radiation from synchrotron used accelerated electrons. The speed of gamma radiation also involved...

Picture a perfectly aligned row of pool balls all touching each other that was 200,000 miles long. If the first ball was struck with enough force at the exact center of the ball, would the movement of the last ball occur before a laser beam could move from the beginning to the end of the balls...

Can a body exceed 3/4 the speed of light in water.

Here is a question which can seem stupid to a lot but it has stuck it my mind and i can not move forward. There are two points to it. 1 - The speed of light is same in all inertial frame of references. So if an observer is moving with a relative velocity 'v' withrespect to another stationary...

Hi! Need some help with this that's been plaguing my brain. :smile: Hypothetically, if an object's speed were to be increased so as to reach the speed of light and let it gain maximum momentum, what would we perceive as happening to the object?

Hi I'm new and an idiot so please don't burn me, I wouldn't have come to a specialist forum if I could have found the answer in a more mainstream place. Anyway, can somebody please explain to me in layman's terms why, if one could travel faster than the speed of light, they'd go back in time...

Hi, Before I phrase my question, I'll just go through what I know so no unnecessary comments happen. I've read that the speed of light slows down in a medium because when a photon hits an electron the electron absorbs the energy of the photon and re-emits another photon. I also know...

I am a beginner in this field. I have read Special theory of relativity by Einstein, but the one written for beginners, not the technical. I have also read couple of undergraduate books which had STR. From my understanding, STR is a theory about transformation from one frame to another, both...

Speed of light broken?? I do not know if there is a topic on this but has anyone heard about the findings of how physicists have found neutrinos that traveled faster than light speed? Here is the link, I'm interested in what the PF community has to say! I think it is just systematic error but...

I've been looking into the history of the speed of light values and when the last accepted value was set at. This value we use today was set in 1983. In interest of the Cern experiment and the technology advances today compared to technology that is over 30 years old, Has anyone used todays...

say you are in a car traveling at 60 mph, and another car beside you is traveling at 80 mph about to overtake..If a third really fast car was to zoom past at 200 mph (in a third lane), to me he is effectively traveling at 140 mph and to the overtaker 120 mph.. But the speed of light would be...

How do Maxwell's equations predict that the speed of light is constant? I found different answers and some people even said that they don't. I'm still confused...

There has been so much interest lately in objects going faster than the speed of light, I though I would propose a little thought experiment. An observer is standing stationary relative to Object A, which is 1x10E10 meters away. Since there is no relativistic limit on acceleration, suppose...

Has anybody heard of this? http://www.telegraph.co.uk/science/science-news/8783011/Speed-of-light-broken-by-scientists.html

"Speed-of-light experiments yield baffling result at LHC" - 22nd Sept News Article?! http://www.bbc.co.uk/news/science-environment-15017484 Came here to get some further information and I can't find a thread. If there already is one about this, sorry I should delete it. Very interesting...

i am just a beginner in studying SPTOR..dunno whether thr question is trivial... as per the second postulate of SPTOR the speed of light is constant for all observers but why did einstein while stating this postulate refer to the speed of light in vacuum to be constant and not anything...

Referring to: http://en.wikipedia.org/wiki/One-way_speed_of_light I am about to quote 2 sentences that obviously have different meanings. The problem is that I don't understand, why they have different meanings, and yet at the same time they appear to be understood as not negating each...

Hi All, I can not get my head around this. If nothing can go near the speed of light then why can the below happen? electrons travel near c proton beams around the LHC travel at near c as far as i know they both have mass and therefore should not be able to do this?? also if...

He everybody :) I guess I am not the only one who cannot comprehend the idea that the light has same speed for all observers, regardless of the velocity between the source and the observer. In an attempt to get a picture of the idea, I constructed a thought experiment which I think could be...

If you could fire a piece of lead at the Earth that was 1cm3, at close to the speed of light, what would be the amount of energy released? What would be the effect on the planet with and without an atmosphere? thanks guys GRB

is the speed of light any faster in low density space than in high density space?

This is my first post here, Consider the typical simultaneity scenario: An observer `O' right in the middle of two light signal sources `A' & `B', all three has their clocks synchronized to each other. Now, A & B both emit a light signal simultaneously and then again one second later...

Is the accuracy of atomic clocks in any way dependent on the speed of light? For example, if the speed of light were to speed up slightly, would that somehow speed up the frequency of oscillations of caesium used in an atomic clock? ...or would those 9 billion (or so) oscillations occur at...

I was reading about dentist drills, and I discovered an amazing piece of trivia about them: modern dentist drills spin at 400,000 revolutions per minute (over 6666 times per second!). So I thought, if this was spinning a large wheel, whose outer rim would rotate at a rate progressively faster...

why isn't it like infinity or something.

if the cars are moving towards each other.

Lets say we have a frame of reference moving at, say, 10% speed of light. In it is a nuclear reactor (fusion or fission etc) that can be used to convert tiny amounts of mass into energy. Since the reactor is moving at, say, 10% the speed of light, the mass of the nuclear material would...

If you were infinitely close to the speed of light, and you attempted to take a picture of yourself, would it work? Would there be any way to make it work using relative velocities?

Suppose a rocket is traveling almost at the speed of light...but relativity says he will still measure the speed of light 3*10^8...if a beam of light is sent at the time the rocket started...if the beam of light and the rocket both travel the same distance, let 2 light minutes, then what will...

i know this might be a dumb question but it was in my head and i would love to hear an answer, so the famous E=mc2..e obviously energy, m mass, c is the speed of light, but what speed of light? we all know that c is constant at vacuum but it changes when it goes through another medium like...

I understand that the Speed of light is the universal speed limit (I do not believe this is in question). However, I watched Steven Hawking's show this weekend on TV where they stated "10 minutes after the big bang the universe was thousands of light years across." How is this possible if...

Does that mean the spaceship has become bigger or denser up to the subatomic level? Or is it just more atoms have stuck to the spaceship? What happens when it slows down? The added mass just 'evaporates'?

if train moves at speed of light the passenger will do any work with very less speed as time becomes slow. why this happens?

If light scatters when propagating through (example) water then why does it appear to travel in straight lines. Yes, i know pencils appear broken but the overall impression is of straight line focused light propagation, and that does not make sense to me from a 'scattering' point of view. If...

I am not a physicist, so apologies if this is something that has been discussed before and is well understood. I, sort of, understand why it has been theorized that light (or mass) has a maximum speed that can't be exceeded. Also that experiments have shown it to be 299,792, 458 m/s in a vacuum...

How do we know the speed of light "exists"? If we "know" that it can't be reached, how do we know it exists? Like I am looking at this from a math view. So okay, "infinity" is not a number, it is a concept. It took me about a year of convincing to settle it down. So is the speed of light...

When the an object is accelerated and when the velocity approaches the speed of light, its mass increases exponentially the force required to accelerate the object increases exponentially. So it cannot be done. Fine. But what if I travel in a spaceship with A LOT of fuel and the spaceship is...