Light speed Definition and 318 Threads

This may not be the correct Forum to post this Thread, but i thought i might as well. I was just wondering: if the matter in the Universe is assumed to be 13.75 billions years old, why is it that we can witness things over 13.75 billion light years away? I came across this Wikipedia article on...

First off, I'm new here so if this is in the wrong section I apologize. Now to the question: As dumb as this may sound to people that know more about physics then me (I'm a med student but I find myself reading about physics time to time) it makes perfect sense in my head (due to lack of...

why does the object shrink in size when they travel close to the speed of light?

humans traveling at light speed? just a little thought experiment. we know it is ludicrous to suggest that humans can travel at "c" because we have mass and it takes infinite energy to travel at c if you have mass. however, does this work for relative velocities: let us assume you are in a...

I am not a scientist just an observer and enthusiast. We have 3 spatial dimensions and one dimension of time. What I have been wondering is... could time have more than one dimension? I mean we percieve time as a continuous line, but can time move in other ways that we cannot percieve, like...

Hi, I know the speed of light is the highest in vacuum. And in any other mediums is a bit slower. I just want to know... ...if a light passes through a medium (water let's say) and comes out in vacuum, will it retain the same speed as it had in the water, or will it increase back to its...

This is probably the stupidest question I have ever asked, but it is bugging me and I am looking for an illuminating answer - not one that simply tells me I have the wrong idea, but one that explains in what way I have the wrong idea. I can, based upon some knowledge of initial conditions and...

My brother-in-law proposed the following thought experiment: Suppose a person was sitting on the nose of a spaceship traveling at the speed of light through outer space. Now suppose that person pushed off against the spaceship launching himself ahead of it. Is it the case that that person will...

I understand that the speed of light is always constant for the observer, but I keep coming across references that suggest it varies in different situations. What situations, and what frame of reference? I saw an interesting documentary many years ago. They talked about light moving at...

From http://en.wikipedia.org/wiki/Frame-dragging" : "Under the Lense–Thirring effect, the frame of reference in which a clock ticks the fastest is one which is rotating around the object as viewed by a distant observer. This also means that light traveling in the direction of rotation of the...

Amateur with questions ;) It seems possible (probable even?) that some galaxies are moving away from us faster than light, which means we'll never get to observe them. That may only be a relative speed (like 2 cars doing 60mph in opposite directions, meaning 120mph relative to each other)...

I have two spacecraft originating from the same point each at velocity .9c in opposite directions. One spacecraft has a chord attached to it rigidly. The other has a spindle attached that can freely unwind the chord with no friction. We can measure the speed of the chord unwinding on this...

Since I began studying relativity, there has been a lot of talk about treating time on equal footing with space. Then there is the space-time. I have been pondering this a little while and I came across a (what I find) curious pair of situations. They are somewhat modified versions of the...

I have to start by saying that I don't have any formal training in this space (no pun intended). Still, I had a thought and I hope someone here might be able to tell me if it is valid. I read an article on Physorg about an experiment which showed that two atomic clocks showed different times...

If you were in a spaceship that was going JUST under light speed & you ran forward... If you were in a spaceship that was traveling JUST under light speed & you ran forward towards the front of the Spaceship, what would happen? I'm talking literally JUST under c, like 0.999999999999999999999...

im having trouble understanding why the speed of light is a speed limit for space crafts light has an origin. and from what i understand, the doppler effect only changes the wavelength, not the speed of the wave but Earth is spinning very fast and traveling very fast through space and our...

I was reading about the VSL theory as an alternative solution to inflation that solves the horizon problem. My question is, wouldn't special relativity still hold true, just to a different value of c in the early universe? As in, if we have a varying value of c, wouldn't it still hold true that...

Hey y'all, I've been lurking for a little bit and just reading since I'm not as knowledgeable as many of y'all. I'm a university student preparing for web design/database administration but consider studying physics/cosmology my (only) hobby. My question is about the requirements for light...

Just joined today, so, hi everyone! And please, forgive me and point me in the right direction if this has been answered/discussed etc... I'm pretty much an armchair physics kinda guy, and understand the whole concept of speed of light.. But what I can't really find an explanation for...

For the MMX, the speed of light is measured isotropically at c in free space regardless of the frame, so gives a null result. To another frame of observation, light still travels isotropically at c while the apparatus is length contracted by sqrt(1 - (v/c)^2) in the line of motion, whereby a...

According to the special relativity, an object that has a mass cannot travel at the speed of light. So nothing in this universe can travel faster than the light, especially our spacecraft which has mass. Then would it be ever possible for us to visit far off heavenly bodies in a finite (less...

assume if enough fuel is there is it possible to achieve near light speed? what are the factors preventing this? how we can link relativistic mass to the thrust of rocket at near light speed? assume mass of spacecraft is constant and enough fuel is there then can chemical rockets can reach...

Imagine this scenario: An "airplane" that runs on some type of fuel, let's say, liquid, reaches 90% of the speed of light. Once it achieves this speed, will the ship require less fuel due to time dilation, the same amount of fuel due to time dilation, or more fuel to maintain a constant...

http://physicsworld.com/cws/article/news/2810 Can anyone provide some clarification on this experiment? Is this just a case of 'phase velocity' surpassing group velocity? If so, why does the last paragraph in the article seem to point to FTL? "There is no widespread agreement among...

I recently came across an article relating to Gliese 581 g and some theoretical information about getting there. It said something along the lines of "while it is 20.3 light years from Earth, passengers aboard a vessel traveling at nearly the speed of light would perceive the journey as nearly...

Earlier today a friend and myself were having a discussion about a vehicle going the speed of light and what it would look like if someone was to witness this event happen. (The discussion started because we were watching Star Wars) First off my understanding of an object reaching the speed...

This was probably asked some time ago. It involves a paradox of relativity and I hope someone can answer it for me: Imagine a solid cylinder (call this the plunger) with a bar welded to one end making a T. The plunger fits just perfectly into a hollowed cylinder of the same length, and the...

1) Consider that one way light speed is anisotropic. 2) Use the Einstein method to synchronize all the watches by the watch located at (x,y,z)=(0,0,0). Now, all the watches are synchronized by the watch at (0,0,0) but they are not necessarily synchronized with each-other (Consider watches...

I first pondered this a number of years ago but I've never formally studied physics or known anyone who has, so I've had no one to ask and it falls into the back of my mind for years at a time before I revisit the thought. I'm sure this is a question physics students deal with in some form...

Hello, I know I'm just full of silly ideas, but afterall this is the physics forums, and I happen to have lots of questions :P. So, basically what I'm interested in, as the topic suggests, light speed internet. Now now, I know many of you would respond with, "its been done --fiber optics!"...

I've noticed that when driving down a road, cars passing in the opposite direction appear to be going much faster than if viewed from a stationary position. I asked my friend how you could calculate how fast the other car appeared to be going and he said you just add your speed and the other...

Hello, I'm new here and not too bright so go easy please.. My question is something that has bugged me for years; The setup - A light speed (or nearly light speed) craft is orbiting Earth or at least circum-navigating it at a distance and at speeds close to the SOL. A cable runs from the...

According to Einstein, if you could ride a beam of light and look at your surroundings it would seem as if everything around you has stopped. Even time. If this is the case how come there is a time delay from the suns rays reaching earth? 8 minutes I believe. From the photons point of view...

If galaxies aer expanding fast than the speed of light how are we able to see them. At the moment this expansion surpassed the speed of light shouldn't these galaxies dissappear or remain unchanged visually?

Hey guys, this is my first post. I posted here a few time a while ago, but forgot my logins :) I am no physics expert, just really enjoy learning about it when I can. Ok, what I need help understanding is the theory that for example if I leave Earth traveling at the speed of light, and I...

Help me out please. I need a definitive comment for a book I'm writing. Hypothetically - if Usain Bolt were to approach (c) in a 100m sprint - his mass would become infinite right? basic E=Mc2. At inifinite mass - space-time would warp (correct?). And light would bend (right?) Can I say...

I just want to make sure I understand this clearly. Light travels at 186 000 miles/second right? So if something was 10 light years away would that mean that it would take 10 years going at the speed of light to get there? Wouldnt it be possible to make a probe go even half that speed? I don't...

First off, I'd like to point out that I am by no means an expert in this area, and I am only doing some casual research as a personal interest topic, and have some further unanswered questions that I'm unable to find reasonable answers for. These questions are all inter-related, so I'll post...

Why photons can't afford more than light speed? They are not limited by E=mc^2.

This solution is from my notes about twenty years ago and the integration by form was made by a friend. We worked on this interesting question together. Many others have surely gone down this same road. I am not a physicist, nor have I had University Physics since 1968. It should be...

I've heard that future spaceships traveling at near the speed of light will have to deal with massive amounts of radiation due to interstellar gas. I think these spaceships might also have to deal with radiation from star light being blue shifted. How close to the speed of light would one have...

I'm trying to get my head around an idea that i had and i was wondering if you people here could clarify for me i am sure some of my basic assumptions are wrong so here goes 1 objects cannot go faster than the speed of light, it take more and more energy to accelerate an object as it...

"Absolute" light speed or velocity or both? Consider an inverse of Einstein's light clock. On a cartesian plane in a vacuum, a beam of light emanates from the origin at 45 degrees with velocity c. Is it OK that the x and y component velocities are each less than c (i.e. c divided by sqrt 2)...

The speed of light in a gravitational field is not a scalar quantity because at any given coordinate its speed is a function of its direction. Does general relativity treat time in a gravitational field as a scalar quantity?

Hi everyone - I am having trouble getting my brother to wrap his head around why you cannot move faster than the speed of light. My little brother has said that he believes eventually we will have technology that will allow FTL travel - I agree with this but I told him that IF it happens it...

I've read the Fomalont and Kopeikin's experiment, and though very interesting and supposedly proves the speed of gravity, I feel there may be a very "simple" experiment that will make a comparison of the speeds, with an event that occurs every day, and may be tried by many groups with the...

Since I've only heard of light traveling at light speed, then I'd assume that the force carriers that are not photons probably do have mass. I was wondering how these other field interactions propagate...do they displace themselves at a certain speed?

Does the principle of invariant light speed still hold in a non Inertial frame of reference? Thank you!

Hypothetical question: Imagine that a massive object large enough to observe with a powerful telescope was ejected from the sun and began traveling toward earth. It would take about 8.3 minutes for the light from the sun to reach Earth so we could observe the initial event. Let's imagine...

If e=mc^2, then (e/m)1/2= either +c or -c. What is the physical meaning of minus c?