Light speed Definition and 318 Threads

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...

Hey folks, My first post. I'm a retired guy who liked physics in college, but couldn't quite get my head around calculus, so I was never able to confirm the things I learned through mathematical equations. I read primary lit., but I don't have the math skills to understand it. Physics became a...

this is my first post so please go easy on me : D My question basically is : how does time dilation work if you are moving towards a source of light ? if i am moving with a speed , 150 km/s and there is a light beam moving in the same direction as i am with a speed of 300km/s , according to...

I had thought about it, and came to this conclusion: In order to accelerate your mass faster and faster, you'll need a higher and higher amount of energy in order to move yourself; this energy (which could be considered mass?) curves space/time and causes time dilation. How off am I?

i think F=ma accounts for the gain in force required to accelerate objects as you go faster and faster but this does not explain how objects cannot reach the speed of light. what equation explains how it takes an infinite amount of energy to get to the speed of light.

This is a question someone asked me today and it's bugging me allot. If the acceleration caused by gravity is greater than the speed of light at a black hole event horizon then does this mean that the matter is falling at faster than light speed?

What do you think of the article published in the "European Physical Journal D" with the title: "The quantum vacuum as the origin of the speed of light" ? http://link.springer.com/article/10.1140%2Fepjd%2Fe2013-30578-7

I've not got much of a background in physics, but this question has bugged me for ages. So I hope you don't mind me asking :) I know that as an object under acceleration approaches the speed of light, it becomes increasingly more difficult to push it further. I imagine it like pushing against...

What would happen if the entire universe would be reduced in size by several orders of magnitude. I mean not just the distances between the galaxies but also the size of every planet, every atom, every nucleus and so on. That also means the strength of all forces would have to become smaller...

If you are traveling .6C away from your point of origin and your friend is traveling .6C away from the same point of origin but in the opposite direction, why are you not traveling 1.2C away from your friend?

string endpoints move at light speed--? In Zweibach's introduction to string theory I encounter the assertion that the endpoints of an open string move at the speed of light. A few other sources on the web agree with this. But nobody bothers to tell me what the heck it means (not even in...

Apologies if this is a really stupid question but I've never seen it satisfactorily explained although that is perhaps because it is a really stupid question! Bill stays on earth, Ted flies off into space traveling randomly at or very near the speed of light. He's back after a few days and...

I heard that light speed is attainable for a spacecraft from Jupiter's magnetic field and by Lorentz force. in this concept electric charge is turned on in a spacecraft orbiting Jupiter and Lorentz force caused by Jupiter's high magnetic field causes spacecraft to rotate around Jupiter faster...

something that has been banging around in my head for a few years. with the development of wonderfully large science devices like the LHC and ISS.. why have we not yet created a centrifuge capable of moving it's test bed at the speed of light? Honestly, with the exception of higher math, we...

Based on special relativity object with speed nearing to speed of light has increased mass and also its gravity pull is increasing. But this is in special relativity calculated for linear moving objects, not for rotating objects. Based on general relativity does increase mass and gravity of...

E=mc2 gives us the cosmological constant, which later was found to be the maximum speed at which light can travel. i also understand that when accelerating particles such as they do at CERN, it requires more and more energy the faster u want to go, the mass/speed issue. so i think i understand...

Hi, If there is really one way to go back the past, must the way be through light speed or not? If the answer is yes, I really do not believe that the human beings or any animals are able to endure light speed technically! Best Regards

Hi All.. I have a basic doubt in time dilation theory. As per time dilation theory, when an object moves with the velocity of light, then relatively its time becomes zero. In that case, light is traveling at 'velocity of light'. So for light, there is no age? Or I misconcepted time dilation...

broadcasting a message at light speed back to earth... if a ship was traveling at 80% speed of light (Cern proved mathmatically this speed is achievable hypothetically using anti-matter) while continually broadcasting the cockpit/crew of the ship 'real time' at light speed back to earth, would...

Hello I'm new to the forums and was wondering, Since time is not a constant, and speed is a function of time, would light have a higher speed when time passes by quicker? It seems kind of obvious but I'm not really sure.

In this thread in another forum, I calculated the coordinate speed of light as measured by a distant observer. As far as I understand it, the length contraction in GR is only in the radial direction, right? None tangent, correct? The time delay of light found, though, trying different examples...

Hello. I'm not very educated in the field of physics but I do like to let my mind wander at times and contemplate the nature of gravity and the speed of light. I had this thought today over morning coffee and thought I would share it with someone who has a much better understanding of these...

Could a person see an object moving away from themselves at lightspeed?

Does anyone know if any work, no matter how speculative, has been done on the following: Assume a ship (or any vessel) travels through space with a Gamma of 10-100. As the ship travels through the interstellar medium, there is a constant barrage of nuclear explosions over the tip of the jet...

Hi all One things that puzzles me is the speed of light. We measure it always the same speed independently if we are moving or still. But here is where i get really confused: if we are moving against a light ray (imagine that I will "bump" with the light ray), the speed that we measure is the...

Hi all, I just want to check my qualitativie understanding of what I would see if a ship approached me at the speed of light. Is the following correct: Let's say a light-radiating ship traveling near "c" a long distance off approaches Earth. The light it emits will travel at "c", so the...

Is it true that massive observers travel with c when passing an event horizion? I know that light cones get tilted at the event horizon. But every observers travels at light speed there? thanks in advance

If light from long dead stars is only just reaching us, does this mean that if I shine a Lazer pointer into space, the light beam will continue long after I have turned of the power .. If this is true would a light beam continue to travel indefinably ?

Hi! Special relativity states that nothing can travel faster than c. But how do we know that c is the speed of light?

Dear Physicists, Do you know why there was a massive fuss made last year about the experiments at CERN which recorded neutrinos traveling faster than light speed? Do these results contradict any previous experiment? I hear a lot of talk about said results conflicting with the equations...

Einstein is riding the beam of light away from the clock tower so the hands of the clock don't move. Suppose the beam of light he is riding on is going from one clock tower and directly to another clock tower. Would he see the hands of the clock that he is traveling toward move?

What will happen in the following scenario? I am standing on the earth. Right next to me, a small rocket containing a clock blasts off and accelerates to 90% of the speed of light almost instantly (within its 1st millimeter of travel). As the rocket passes my head, I look at its clock...

Theres something I don't understand. Assume we have two light particles that approach each other. (obviously with light speed) Logically since each of them are traveling with the speed of light they should approch to each other with 2xC, but according to relativity theory they approach...

Hi, I'm not sure if this is the right sub-forum because i know very little about this kind of stuff :/ But something has been bugging me for a while and it's probably very stupid but like i said, I know very little :) So, from what i understand if we can travel close to the speed of light we...

Hi, I hope this is the appropriate forum.. pls move if not. I've been trying to learn how light "speed" found its way into relativity. Doing a bit of Googling, I found a Wiki reference that says Newton suggested that light and matter are interchangeable. As a layman, I can sort of understand...

The Hubble parameter is defined by: H(t) = a'(t) / a(t) where a is the scale factor which is a function of cosmological time t. This definition is equivalent to the Hubble relation: v(t) = H(t) r(t) where v(t) and r(t) are the proper velocity and distance of an object at...

Hi, I've been listening to a Professor Jim Al-Khalil's scipod on time travel. I think this guy is bloody excellent by the way. http://reader.mac.com/mobile/v1/http%3A%2F%2Fwww.jimal-khalili.com%2Fpodcast%2Fjim.rss Anyway, He said to an observer on the Earth a clock on a...

Hi All! I found discussions on this here while researching the subject to see if anyone else has attempted to explore the subject. I saw that several people asked questions pertaining to this, but the question was never really answered. It seemed unanswerable. While many discussions of...

I saw the recent report where CERN was able to measure something that traveled a tiny bit faster than light. It made me think that only in exceptional circumstances can that speed limit be passed. But it did prompt other questions. If light speed wasn't the limit, how would that affect things...

do all mass less particles travel at the speed of light?

Hey, this is my first post. I am a biology major so I know pretty much nothing about physics, yet sometimes it interests me way more than chromosomes do. So, given that I know nothing about physics, this is probably going to sound like a stupid question. But I've always wondered how it is...

What if you had a laser solar sail and in front of the sail was a small thruster (either chemical or itself a laser)...thrusting constantly at a right angle to the forward direction of the craft so that the sail's trajectory would bring it back towards the first (main/stationary) laser that...

I feel like this is one of those things where they say "oh my god this will change physics forever" but it ends up being being incorrect. Either way it is odd that they would measure faster then light speed at all, I'll give them that. But 60 nanoseconds? Not quite enough to make me convinced...

Just wondering people's opinions if this is true? Is it enough evidence to conclude this (not yet obviously), but do you feel the evidence might be valid? Lastly what would be the implications if it was true? http://www.bbc.co.uk/news/science-environment-15017484 I was also...

a relativistically moving body passes through much more field energy than a slow moving body per unit time. Does all that field energy have anything to do with the slowing of time in the fast moving object?

this is my first post so please be gentile with me what would a wheel or a disc turning at a speed approaching that of light look like my knowledge of the subject it quite small but say the disc was rotating clock wise then looking at it from its right side would the top half look...

note: I will be brief, I previously attempted to post this thread and was logged out while writing a wall of text, I do not have the energy to get it all down again. - Is near light speed space travel theoretically viable due to time dilation (traveler covering light years while potentially...

A gigantic machine that has let's say another 1000 machines inside of it. We start the primary machine to travel at 100 km/h. We send it out to space, then the machine sends the next machine inside of and kicks it to give it a boost for another 100 km/h. Now the kicked machine has an extra 100...

Is it possible to build a vehicle that can accelerate to .99 C? How would we go about doing something like this? If at all possible, how many centuries or millennia is it before this can be accomplished? Could a Bussard scramjet do it? How large would a laser/maser/gaser have to be...

This is something that has always bugged me about relativity... I must be missing something... Lets say you have a space station sitting stationary out in space... a spaceship approaches it from one side at .75c...another ship approaches the station from the other side, also at .75c, still no...