The speed of light is a fundamental universal constant that marks the maximum speed at which energy and information can propagate. Its value is $299792458\frac{\mathrm{m}}{\mathrm{s}}$.

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Speed of gravitational waves vs speed of light

I own an educational YouTube channel on physics and astronomy. I am currently working on a gravitational waves video extension to my "How Fast Is It" video book on relativity theory. I have a question ...
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63 views

Photons when passing through matter

I am wondering whether there is a simple—or complicated—way to explain from a purely quantum mechanics (or QFT) viewpoint what happens to the photons when they go through some material whose index of ...
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2answers
87 views

What particles travel near the speed of a photon? [closed]

I know photons travel at the speed of light. How does the size of a particle determine its maximum velocity? Phonons, Preons, Electron ect. Is there a scale in from the smallest particle's maximum ...
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2answers
95 views

Why does Special Relativity apply to more than just light?

It is my understanding that time dilation is derived from the constancy of the speed of light in vacuum. I would assume this implies that the quirky consequences would therefore apply only to light. ...
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4answers
2k views

Am I just some energy traveled at light speed? [closed]

I don't understand $E=mc^2$ very well, and here is my question: Does this equation mean masses are just condensed energy? And does this mean that the extra energy an object has when traveling at ...
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0answers
24 views

Why are black holes black? [duplicate]

If heard two explanations for this. One explanation is that the gravity is so strong that space is being stretched inward faster than the speed of light and thus no photons could possibly escape. The ...
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1answer
76 views

Where is the mistake in the following rationament [duplicate]

Well... kind of hard to translate in English so bare with me :). Let's consider a wheel that spins in the void. Each point of the wheel has the speed $v = ω r$. That means that for any $ω$, there is ...
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2answers
55 views

Does the constancy of the speed of light in vacuum hold for any observer in GR as well?

From SR, we know that the speed of light in a vacuum is the same for all observers, regardless of the motion of the light source. But in GR, does it still hold for all observers? I mean the constancy ...
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1answer
36 views

How are the frequency and wavelength of electromagnetic waves affected within an event horizon?

I apologize if this has been asked previously or if my thinking is way off base, but I am inexperienced with relativity (and this is my first question on the site). I am wondering; as one (not ...
3
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3answers
175 views

Relative velocity of light beams

Assume two light beams moving in the same direction i want to use the relativistic velocity transformation equation to find the relative velocity with each other, Note : i let $C$=1 $V_{ab}$=$\frac{...
-2
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1answer
128 views

How far does a photon move in the 4th dimension when it travels one light second? [closed]

In one second a photon moves 3x10^8 meters through the three spatial dimensions. Light's velocity is 3x10^8 m/s. If the photon moved at all in the fourth dimension, it's velocity would no longer be ...
0
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1answer
80 views

At what speeds does time dilations start to occur?

My question is, is it possible for time dilation to occur at a speed less than that of speed of light?
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1answer
110 views

What happens to a ball spinning with peripheral speed near to the speed of light?

I can't imagine such phenomenon. Would it becomes an ellipsoid, or maybe a straight line?
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0answers
29 views

How much time will for the observer last sound of thunder? [closed]

We have height of the cloud 5 km. The observer stands 20 km away. The speed of sound depends only on the temperature. $C=a\times\sqrt T$ Temperature on 5 km is $-33^o C$ and on the ground $7^oC$. ...
2
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2answers
404 views

Stanford: “Objects in spacetime all move at constant speed $c$.” Are they right? [duplicate]

In this Stanford University lecture on Relativity, it is stated: Likewise, objects in spacetime all move at constant speed c in spacetime but if you change its direction, say by moving at speed v in ...
0
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1answer
86 views

Why is the speed of light being invariant and finite in all inertial reference frames?

I understand the basics of Lorentz transformation and Riemann Geometry but I still cannot understand why the speed of light is the same in all inertial references. Has anyone ever researched about ...
0
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1answer
95 views

Do Gravitational Waves disprove superluminal Alcubierre drive?

I am not a physicist. But... does the rate at which gravitational waves travel set an upper limit to the "speed" of a ship propelled with Alcubierre drive? Or does it present a relativistic trick (...
32
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2answers
3k views

Were the Michelson-Morley results a surprise?

How unexpected were the Michelson-Morley experiment results? Did physicists have theoretical reasons to predict that the speed of light would result to be invariant?
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1answer
62 views

How time and speed of light are related? [closed]

I want to know how speed and light and time are related? How will motion with highspeed effect time? I am not a physics student. I want an answer which is free of mathematical relations. I want an ...
5
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3answers
500 views

How did we realize that light travels at a finite speed?

We all know that light travels at a finite speed of nearly $3\times10^8\mathrm{m\,s^{-1}}$. But how did we come to think that light has a finite speed? Why did the scientists try to calculate the ...
0
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0answers
60 views

Cherenkov Luminescence Imaging, Cherenkov radiation,

Is it possible to see glowing from Thin Layer chromatography (TLC silica gel on Aluminium) when we image it by IVIS spectrum (no radioactive source)?
6
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3answers
162 views

What's the problem with light traveling at speed higher than $c$?

I'm trying to understand how Einstein concluded that time is relative based on thought experiments such as a torch attached to the end of a rocket. Based on answers to questions like this one, this ...
0
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1answer
31 views

Multiple Objects at Constant Speed

Imagine 1 million objects travelling in space, at a constant speed, along an imaginary line. They don't deviate from that line for the sake of this argument. Now, object 1 has a velocity of $v_{1}=1$ ...
0
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1answer
57 views

Can something go faster than the speed of light in a medium? [duplicate]

Since some mediums have an index of refraction more than 1, light goes slower than in a vacuum. Does this mean it is possible for particles to go faster than the speed of light in these mediums? If so,...
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1answer
98 views

Does massive particle really move at speed of light? [closed]

According to this answer I understood that particles with mass also move at speed of light but interaction with higgs field make this movement zigzag. So average speed is below speed of light. But I ...
0
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3answers
168 views

Why did Einstein took speed of light unit or constant in his equation of relativity?

We can find that no object can have speed more than light from Einstein's equation of relativity because if anything have speed more than light then we get -ve value within square root. But why did ...
0
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2answers
377 views

How to achieve speeds faster than light? [duplicate]

So, I heard that all speed is relative. And that nothing can travel faster than light. Then I guess it is OK for a spaceship to leave Earth at 0.6c constant speed. And what if an other spaceship were ...
0
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1answer
80 views

Does a black hole really slow down time?

When an object gets pulled into a black hole it seems to slow and stop, but could it be possibly be because the speed of light that hit the object and came back was slowing down as the object got ...
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1answer
65 views

What would happen if space were considered a medium?

Space is not empty they say, is it a new idea or has it always been like that? Can you explain what is the (current) real meaning of vacuum, which is just the Latin for empty Can you also explain ...
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1answer
42 views

Speed of light in vacuum in special relativity

In special relativity, the speed of visible light is defined as a constant. But visible light is only a small part of the electromagnetism field. So why?
-2
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1answer
64 views

Can information be sent faster than speed of light [duplicate]

I just had this idea one day and I decided upon a thought experiment to verify it. Imagine 2 people A & B sitting on two sides of a pipe which is stretched to a length of 3x10^8 m. The pipe is ...
1
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1answer
52 views

Stacked motors thought experiment

first of all, I'm not a mathematician, just curious about something that came up to my mind and maybe you can help me out. Scenario: I have a motor that spins let's say at 20K revolutions per minutes....
4
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2answers
267 views

Is there a limit to how hot an object can get?

If heat is the measure of how fast the atoms are moving in an object, than isn't there a limit to how hot that object can get as nothing can go as faster than the speed of light. So because the atoms ...
0
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1answer
121 views

Maximum wavelength of a photon/electromagnetic radiation?

This asked; What is the minimum wavelength of electromagnetic radiation? And also this; What is the maximum possible frequency and wavelength? The second question is contradictory; maximum ...
0
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1answer
32 views

Incomprehensible substance: information traveling faster than light? [duplicate]

Say I'm holding a rod composed of an incomprehensible solid, and this solid rod is 1 light second long. Then say I poke you with the rod and at the same time I flash a light on you. If light is the ...
0
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1answer
53 views

Does slowing light violate relativity?

Last year Scottish scientists managed to slow down photons in vacuum by changing their shape. Does this violate the special theory of relativity?
22
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3answers
5k views

How can muons travel faster than light through ice?

When a neutrino traveling through ice hits and interacts with an oxygen atom, muons are created. Cherenkov radiation can be created when muons travel through ice faster than light and create a ...
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4answers
207 views

Could the Heisenberg uncertainty principle be derived from the speed of light limit? [closed]

Background: As I was thinking about an alternative approach to the question: "why is there a finite speed of light, and why its magnitude corresponds to c?" –ultimately, I was trying to understand ...
0
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1answer
68 views

how long will take for an astronal travel in near lightspeed in his point of view

I always had a question about relativity. Suppose an astronaut in orbit Saturn just must reach earth fast as possible. Your ship can travel at any speed between 0 and the speed of light. the distance ...
2
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2answers
150 views

Can the constancy of the speed of light in vacuum be derived from a deeper theory?

Einstein's second postulate of special relativity is: The speed of light in vacuum takes the same value ($c$) for any observer in an inertial frame of reference. I know there is a lot of ...
0
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1answer
34 views

Speed of light and sound

Speed of light is universally constant so in denser media its collision increases so effective speed will decrease so how we distinguish this effective speed and $3\times10^8$ m/s. But why sound ...
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0answers
15 views

A Question about Time Dilation and different observers [duplicate]

This is a question about time dilation and different observers. Say you had two observers. One on earth and the other one traveling around 20% of the speed of light. The observer on earth will age ...
0
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1answer
75 views

Would forcing a photon to travel under $c$ even after it leaves a medium break Relativity? [duplicate]

So, I stumbled onto this article which really blew my mind (http://www.bbc.com/news/uk-scotland-glasgow-west-30944584). To sum it up, these researchers set up some kind of material that slowed a ...
0
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1answer
55 views

Does light always travel at *c* even when moving through a medium?

The title of the question is a bit misleading, but with limited space it was all I could think of. So, I know that light travels at fractions of c when traveling through a medium; however, as I ...
0
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1answer
55 views

3 points in space, relative motion, and the speed of light

I'm new to thinking about relativity, as well as phenomena related to the speed of light, time dilation, length contraction, simultaneity, etc. I am pondering a paradox. Assumptions: Motion is ...
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2answers
78 views

Is the speed limit as light speed just based on what we see? [duplicate]

I know, the title makes no sense, generally. Let me explain. I am just asking a question for which I found an answer nowhere (not even here). i think similar questions has been asked before and, no ...
2
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3answers
168 views

Why is speed of light a constant while distance in space is not?

Disclaimer: I asked this at Astronomy.SE, but got no answer whatsoever, so I am trying my luck here. As you probably know current state-of-the art physics (i.e. gravitational waves, cosmic expansion) ...
8
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3answers
2k views

Is there a maximum energy for a relativistic particle?

So I was told today that the Standard Model breaks down at really, really high energies. The lecturer mentioned particles such as electrons hypothetically having energies equivalent to that of entire ...
3
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2answers
103 views

Can we watch the light travelling in slow motion?

If light travels 3 lac km in 1 second we cannot see it moving and it seems to be continuous. Everything in our lives are far slower than this. Like we cannot differentiate between the different ...
0
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1answer
48 views

Motion in space

Does a space shuttle travelling in space experience any resistance to its motion? If a body in space is applied constant force, does it attain speed of light after sufficient time?