Speed of light Definition and 1000 Threads

Why is speed of light constant in all frames of reference. I don't understand.

Hi I understand that accelerating you get closer and closer to the speed of light wrt anything in an asymptotic way, but would acceleration still act the same way as non relativistic speeds (inertia, gyroscope, etc?) even if the speed won't increase almost at all (for example at 0.9999 c) Thank you

According to my physics book light changes speed in different mediums such as water. Doesn't the speed of light have to remain constant? Thanks in advance

Hi everybody. I had a discussion on another (engineers') forum about the "lower than c" speed of light inside a transparent material (e.g. glass). The explanation that I gave is that the reduction of the light's speed inside such a material is only "apparent" and not "real". The incident photons...

Homework Statement A harmonic EM-wave is propagating in glass in the +x-direction. The refractive index of the glass ##n = 1.4##. The wave number of the wave ##k = 30 \ rad/m##. The magnetic portion of the wave is parallel to the y-axis and its amplitude ##H_0 = 0.10A/m##. At ##t=0## and ##x =...

Usually we measure the speed of light using light generated here on Earth or coming from the Sun or other stars, but have we ever tried to measure the speed of the light coming from distant galaxies? As in directing that light into an apparatus and measure its average velocity over a round-trip...

For example, if photons were the size of galaxies, would they still move at the speed of light?

Theoretically you can travel back in time by moving faster than the speed of light, or the universal speed limit. Is there a minimum speed? 0. But with gravity you would be moving, so if you move against gravity relative to yourself you are moving. So if there was a place in the universe free of...

In Brian Greene's book, Fabric of the Cosmos, he mentions that not enough time has passed for light from some parts of the universe to reach us. (I'm paraphrasing, but I think this is pretty much what he said, and I've heard similar statements from others). How is this possible if the universe...

I've always wondered this. Let's say we're not limited by the type of vibration, e.g. if choppy vibration doesn't constitute continuous movement, then some sort of oscillating vibration.

Let's say a mother ship is traveling at the speed of light. If you shoot a pod out of the mothership at the speed of light(and that pod is already traveling at the speed of light), then wouldn't that pod be traveling at twice the speed of light? And if you have a second pod speeding away from...

Constancy of the Speed of light (I am not a physicist, but somehow interested to understand some aspects of relativity) The constancy of the speed of light in vacuo is an important postulate on which the Special theory of Relativity is based. The speed of ordinary objects depend upon the...

In an electromagnetic wave like light,both wavelength and frequency changes but it's speed always remains constant.Why?

As I understand it an object moves through time and space and the faster it moves through space the slower it moves through time. So say somehow an object was accelerated to the speed of light (I know this isn't possible) it would theoretically stop moving through time but my question is that if...

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...

Dear friends: Put a big disk in the space which can rotate at a speed. for example, if the radius of the disk is 10000km, and it rotates at a speed of 30 rad/s, then the speed at the disk boundary is 30,0000km/s. am i right?

Hi! Yes, I know that faster-than-light travel is impossible. But please stay with me for a while to help me understand this. Let's imagine we take some unobtainium and build a 12-km-radius propeller, attached to an engine able to accelerate it up to 250,000 rpm (like a turbocharger, or not a few...

I've been attempting to learn special relativity, but I've encountered a stumbling block. I understand that the speed of light is independent of the speed of the source of the light (similar to how sound waves travel at a speed that is independent of the speed of the energy source of those...

I'm trying to understand why the speed of light is the same for all observers. I have found different answers on-line. This page claims that it relates to time dilation. But consider the following thought experiment: two ships flying at 98% c. Ship A is moving toward the sun, and ship B is...

Hi all, I was trying to figure out the following: Say I am standing right in front of a movie playing on a screen. Then, at time t0, I immediately am traveling at the speed of light away from this non-moving screen. Say I looked back while traveling away. Would I see an image (the frame the...

My questions is about the conversion of a range of wavelengths in Hz, such as for an optical filter, in a medium different from air. Since the refractive index n is higher than 1, (let's say n=1.5) and than the value of c is almost 2x108 m/s, also the equation in the link below has to be...

I'm curious about one thing. What happens after exceeding the speed of light? What are you opinions about this? What does it mean as the formula m=\frac{m_0}{\sqrt{1-\frac{v^2}{c^2}}} goes after subsitute to equation example mass to m_0 and speed higher than speed of light to v negative mass...

I have a couple of questions regarding the new detection of signals believed to be gravitational waves at LIGO 1. Two similar signals were detected at both facilities. Why does the Livingston signal appear to be weaker than the Hanford signal? 2. The signal in Livingston was reported to have...

Homework Statement For a modern physics class, has to do with relativity In a lab experiment a muon is observed to travel 800 m before disintegrating. The mean lifetime of a muon is Tau = 2E-6 s A muon's travel distance at the speed of light is x = tc = 0.66 km Earth's atmosphere is x = 100 km...

Is my following summary correct : An observer will see that time has stopped for a photon as it is traveling at c. From the photon's perspective time is "normal" but this implies that the photon "sees" time for the rest of the universe as moving at infinite speed. i.e. could see the beginning...

You perform a double slit experiment, detecting the photons at the slit, and storing, but not observing, that data on a memory stick. The pattern on the screen is also stored, but not observed. Person A travels with the memory stick to New Zealand and person B travels to London with the...

What is the need to find the speed of light in a specific medium ? How will knowing that light travels at 0.723c in gelatin going to help us ? not just gelatin but any medium in general

It has been made clear to me that any velocity can be seen as rest mass, meaning that if I observe someone else experiencing time more slowly than me due to general relativity, so long as they do not change velocities, they will see me as experiencing time more slowly than them. I have also...

I don't know if this kind of thought experiment is authorized here, but let's give it a try. Let's assume that we had managed to build a spaceship able to travel at the speed of light. Since relativity forbids to accelerate until reaching such speed, the spaceship would have to reach it...

Mentor note: this discussion was split out of a different thread. The speed of light in a vacuum is constant, but what I would like some information regarding is Black Holes. Does a Black Hole increase the speed of a light photon as it is being pulled into the Event Horizon?

It seems to me, and so I'm really just checking to see if I understand it all correctly, that there are four phenomena in nature that are indistinguishable from one another: (1) crossing beyond an observer's cosmic horizon, (2) crossing the event horizon of a black hole, (3) accelerating toward...

How can Gluon travel at speed of light when it is bound inside a proton or neutron?

I was reminded that the speed of light in water is ~75% of the speed of light in a vacuum and I wondered if the speed of light around the time of the BB, when the Universe was more dense needs to be taken into account in calculating various characteristics related to the CMBR? For example does...

What would happen if you were to fly a starship traveling near the speed of light directly into a black hole? Would it stay in tact because it cannot be accelerating any faster? Or would it split because it's being accelerated in all directions simultaneously?

can someone reduce the speed of light?

klotza submitted a new PF Insights post The Speed of Light and Galilean Relativity Continue reading the Original PF Insights Post.

Homework Statement Name several ways in which our life would be different if the speed of light is 20 m/s rather than its actual value. Homework Equations Does it also affect our biological clock? The Attempt at a Solution I believe that if your would travel any vehicle at opposite...

I have always felt that the inflationary period immediately following the 'big bang' is a contrived theory, and this leads me to ask if the speed of light has always been the same figure. The reason I ask this is that to explain the initial rapid expansion, I wondered if the speed of light...

Just wondering if the speed of light in vacuum has always been constant since the big bang. Is there any evidence (theoretical or experimental) that the speed of light could have been faster or slower in the early universe or just after the big bang? How about at the big bang itself? Was the...

I've built a rod 186K miles long, of ultra-light, ultra-rigid material. I am on one end of the rod, and an observer is at the other end (we're both in the near vacuum of space). I want to send a signal to the observer on the other end of the rod signaling whether the Packers have won the...

[Mentor's note: Split off from this thread] Distinguished members I am not a physicist, so I cannot make a comment. I can only put my doubts and views. In most of the explanations or examples of time dilation given on internet, the source of light and the ray of light emitted from it travel in...

Hey Friends, In Einstein's special relativity I find "Twin Paradox", where Dick and Jack, two twins . one of them went to space at a speed of 0.80c to a star 20 light year away (where c is the speed of light) and other remains on earth. When Jane returned to Earth his age was...

I have been thinking about light and i have read that the universe expanded faster than speed of light. So , then why people say that the speed of light is the fastest thing known if people know that the universe expanded faster than speed of light . Also , if the universe could have expanded...

I've heard that nothing can travel faster than the speed of light. Is that actually held to be a scientific truth, and if so what is the basis for that? The reason I ask, I was watching a video on relativity, and it illustrated a straight-line light beam traveling through space. Superimposed...

Good day, I'm a high schooler so my knowledge of physics is futile and still expanding. Please correct me when I'm wrong, I love physics. Now to my question. I'm still a bit fuzzy on this theory of time dilation and the speed of light etc. But if time dilation happens at the speed of light can...

If two guys, each sitting on a different Earth-like habitable planet, fly in the opposite directions, each at the speed of light, which guy would age slower? And slower compared to what? My own understanding is that they both age normally. Because Special Relativity doesn't describe...

Hi I want to create a thought experiment involving waves of any kind. I am going to create a thought experiment I am on a boat that is at rest in the ocean. I am standing on the boat measuring the size of the waves and the frequency. So I measure the wave along the side of my boat to have a...

Light, amount other things, have no mass, and therefore is able to attain the highest speed possible in this universe. Yet for some reason this speed is not infinite, as would what intuition dictate, but has a finite value. Would it be fair to say that the fact light, something that "should" be...

What limits the speed of light to 3x10^8ms^-1? I was referred to Maxwells equations and have studied them but am not sure if this is the full answer and am unsure where Maxwell's relate anyway, the lectures I watched were unclear apart from relating to Ampere's Law. As much maths as possible...

Say my spacecraft is traveling c, and I'm walking .5 m/s towards the front of the spacecraft . Would that not mean I am traveling faster than light? I'm sure everyone has seen movie where a ship is traveling at the speed of light, while someone is moving about the cabin. I know only photons...