The speed of light is fundamental universal constant that marks the maximum speed at which information can propagate. Its value is $299792458\frac{\mathrm{m}}{\mathrm{s}}$.
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How did the scientific community receive this measurement of speed of gravity
This link and this one concern a recent measurement, by Chinese scientists, of the speed of gravity using Earth tides. They find it is consistent with a speed equal with the speed of light, with an ...
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2answers
41 views
reflection at speed of light when both mirror and viewer is travelling at the speed of light [duplicate]
consider me sitting on the top of a train which is travelling close to the speed of light, will I be able to see my image on a mirror which I'm holding in my hand??
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4answers
48 views
How does light behave within a black hole's event horizon?
If the event horizon of a black hole is the distance from the center from within which light cannot escape, imagine a person with a flashlight falls into the black hole.
He points his flashlight in a ...
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1answer
46 views
Use something that slower than light in Michelson–Morley experiment
Follow by the Michelson–Morley experiment, What happen if we use something that has a speed lower than light instead of light in Michelson–Morley experiment? How about the result?
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66 views
Speed of Light Question and Einstein [closed]
Einstein's clock experiment. What would happen if you were to travel at the speed of light or faster than the speed of light towards the clock? Can we translate this into traveling large distances ...
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1answer
55 views
Simple Question: Speed of Electromagnetic Waves in a Medium
If the speed of an electromagnetic wave in a particular medium is such that $v = c$, the speed of light, does this mean that the permeability $\mu = \mu_0$, i.e. that of a vacuum and the index of ...
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55 views
When A moves away from B and C moves away from B in the same direction, how fast is C moving away from A? [duplicate]
When A moves away from B at 0.9c and C moves away from B at 0.9c in the opposite direction , how fast is C moving away from A?
When we'd be talking about A, B, C being cars and much lower speeds, I'd ...
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4answers
158 views
Is velocity of light constant?
There is a difference between the concept of the speed of light and the velocity of light.
are both of them constant ($dc=0$ and $dv_c=0$)? if yes, why?
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1answer
115 views
What exactly is implied by Einstein's insight in this scene from the NOVA series “$E=mc^2$ Einstein's Big Idea?” [closed]
In the documentary movie "$E=mc^2$ Einstein's Big Idea?", the narrator says "Einstein had a monumental insight", when Einstein and his close friend were looking at the clock towers in the city. ...
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0answers
43 views
Where the speed of light is constant how big bang evolve per time? [closed]
I mean where the $\frac{dc}{dt}=0$ how could world evolve by time during big bang?
How is time evolution of energy possible where the velocity of light doesn't vary by time?
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2answers
75 views
Relative to the speed of light
Einstein's relativity tells us that light always travels at the speed of light relative to me, no matter how fast I'm going. Right? This really confuses me though. If light travels from A to B in one ...
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1answer
51 views
Can a pushed plank beat light and break the laws of physics? [duplicate]
Imagine you are one lightyear away from a photon sensitive (light sensitive) switch. So it is obvious that light would take one year to reach to the switch. Now I have a one lightyear long plank. I ...
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2answers
88 views
What is the time component of velocity of a light ray?
If we have a light ray $x^\mu$ with velocity $c$, what is $c^0$ (the time component)?
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1answer
66 views
Is it possible to make a light beam act like a stream of water from a spining hose? [closed]
If we had the ability to make an actuator that could turn around at or past the speed of light and I attached a high miliwatt laser to it, then spun the laser around on the actuator at the speed of ...
3
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1answer
86 views
The Speed of Light [duplicate]
I know that the speed of light is constant for some reason.
But why is it that when shining light from a spacecraft that is moving at (almost) the speed of this light, the speed of this light ...
2
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1answer
61 views
Quantum Mechanical Effects of an object accelerating near speed of light $c$?
Consider a space ship, undergoing constant acceleration (which for our purposes means that the same amount of energy is being used per second to increase its speed). According to special relativity ...
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2answers
87 views
Points in Spacetime
Assume there are two points in spacetime $a=(t,x,y,z)$ and $a'=(t',x',y',z')$. Let's say that the first one is in the origin of spacetime i.e. $a=(0,0,0,0)$. The point $a'$ has two possibilities
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3answers
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Does the expansion of the universe soon after the Big Bang affect the amount of time that light takes to reach us?
If faster than light travel is impossible, how is it that light emitted from matter so close together in the time soon after the Big Bang is only now just reaching us? I would assume that there would ...
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0answers
38 views
Solar sail area going to Proxima Centari [closed]
I have a physics question that I need some help with:
"Proxima Centauri is a star in the Alpha Centauri solar system, it’s the
nearest star to our sun (4.24light−years) ...
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0answers
25 views
Black hole and photons [duplicate]
I've read in a book that even light can't escape the gravitational pull of a black hole after a certain distance. But this seemed impossible to me.
Imagine a photon, moving directly in the opposite ...
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1answer
64 views
Does the magnitude of a mass affect the velocity?
Imagine that I shrink my entire mass to fit within the volume of a light particle. If I was then 'hit' by another light particle would my greater mass affect my gain in velocity from this collision ...
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3answers
105 views
What causes the permittivity and permeability of vacuum?
When light travels through a material, it gets "slowed down" (at least its net speed decreases). The atoms in the material "disturb" the light in some way which causes it to make stops on its path. ...
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2answers
109 views
Superluminal particles with causality
What kind of CLASSICAL theories would allow to true (non-apparent) superluminal particles (beyond speed of light, BSOL) agreeing with causality to exist? I mean, are causal superluminal classical ...
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1answer
37 views
Relation of color and frequency for the visible spectrum
In this question the OP is looking for a way to see light that is outside of the visible spectrum without using electronic sensors. This got me wondering about the visible spectrum itself. Typically ...
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1answer
82 views
Describing physical constants in alternate wording; c = there can only be 671million miles of space for every second of time [closed]
This spawns from part of an answer to a question I asked.
All sorts of things go to 0 and/or ∞ if you start boosting at c, and
so you cannot boost into and out of a photon's frame.
It ...
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1answer
53 views
Zero uncertainty constant and a unit change
So, we know the speed of light with zero uncertainty. We also know that values of $\epsilon_0$ (electric constant) and $\mu_0$ (magnetic constant) are known with zero uncertainty.
My questions are ...
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1answer
103 views
Neutrinos and Speed of light
Einstein's Special Theory of relativity postulates that the speed of light is same for all frames.
Suppose a neutrino is there moving at the speed of light. Then will that neutrino also be flowing ...
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0answers
70 views
Is there any proof that the speed of gravity is limited? [duplicate]
I must warn that though I'm argumenting with black holes I'm not asking how does gravity escape the black hole!. I want to know if the absolute speed of gravity waves were proven bu an experiment.
We ...
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1answer
135 views
Why does Lorentz factor not hold for relativistic mass when we apply it to photons? [duplicate]
We know that the photon itself is massless particle $m_0=0$. But we also know, that the mass of the objects does increase with their energy. And we know that under certain circumstances (gravity, ...
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1answer
95 views
Could the shadow move with faster-than-light speed? [duplicate]
If I make a huge laser with a figure for shadow in front of the laser, and I shine it on to the moon, will I see the light from the laser AND the shadow moving the same speed? (I read somewhere the ...
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1answer
116 views
Could entropy explain dark energy?
This was 3rd beer idea, so please bear with me. What if the universe was not actually expanding but the speed of light was slowing? Wouldn't that be indistinguishable to our observations? Either way ...
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3answers
105 views
Reaching the speed of light via quantum mechanical uncertainty?
Suppose you accelerate a body to very near the speed of light $c$ where $v = c - \epsilon$. Although this would take an enormous energy, is it possible the last arbitrarily small velocity needed -- ...
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1answer
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Is the speed of light related to the mass of the universe?
If the mass of the universe were cut in half, would it affect the speed of light?
Would it be twice as fast?
Would it stay the same?
Do we have instruments that are sensitive enough to measure the ...
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1answer
53 views
Live feed from a Rocket traveling near the speed of light?
Okay, odd question popped up in my physics class today. If a rocket ship is traveling at .99c for 1 year, and is streaming a video at 30 frames/sec to earth, how would the earth feed be affected? ...
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0answers
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How does this paper relate to standard QED?
This paper proposes a microscopic mechanism for generating the values of $c, \epsilon_0, \mu_0$. They state that their vacuum is assumed to contain ephemeral (meaning existing within the limits of ...
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3answers
118 views
Stuff can't go at the speed of light - in relation to what? [duplicate]
We all know that stuff can't go faster than the speed of light - it's length becomes negative and all kinds of weird stuff happens.
However, this is in relation to what? If two objects, each moving ...
2
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2answers
112 views
Is Earth's orbit around the sun affected by the ~8 minutes light delay?
Gravitational change occurs at the speed of light. As a consequence, we experience on Earth the gravitational attraction of the sun based on its position relative to us ~8 minutes ago. How does this ...
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1answer
109 views
Michelson–Morley @ Home
The Michelson-Morley experiment seems to have taken many years, resources and a nervous breakdown to complete.
Is it possible to recreate a variation of this experiment at home for say, under $1000, ...
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1answer
64 views
Magnets and speed of light
I am in no way a physicist but I do have a fascination with physics. My question is if magnets are being explored / studied as a potential source to achieve the speed of light and if that is even ...
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3answers
75 views
What is the cause the light is affected by gravity? [duplicate]
I know that photons have no mass and that a photons exist only moving at the speed of light. So what is the cause that a massive astronomical object can bend a ray of light?
I have two thoughts, but I ...
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1answer
58 views
Rømer's determination of the speed of light
I am trying to understand Rømer's determination of the speed of light ($c$). The geometry of the situation is shown in the image below. The determination involves measuring apparent fluctuations in ...
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1answer
29 views
If there's a light ray and it's turned to a new location by a certain angle
Imagine that there's a light ray, with source at point A, and it's directed towards point B (which is very far from point A) and it continues for a huge distance.
How will an observer at point B ...
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2answers
110 views
What is the mass of a photon moving at the speed of light? [duplicate]
What is the mass of a photon moving at the speed of light?
And if it does not have mass, how is it affected by gravity?
Also why does Einstein's general relativity support that a gravitational wave ...
2
votes
3answers
132 views
Why are black holes special?
A black hole is where it's mass is great enough that light can't escape at a radius above the surface of the mass?
I've been told that strange things happen inside the event horizon such as ...
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2answers
63 views
Speed and transparency of light
I have been puzzled with a fact that as an object moves faster, it ceases its property of opacity. I mean to say that as an object moves faster we can see right through it (more clearly than in a ...
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3answers
167 views
Is there absolute proof that an object cannot exceed the speed of light?
Have any known experiments ruled out travelling faster than the speed of light?
Or is this just a widely accepted theory?
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1answer
64 views
How do we know that light is massless? [duplicate]
Almost everybody knows that light is massless. But where this come from and how it can be proven (experimentally or theoretically)? I actually found this article which explains and calculates the mass ...
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1answer
239 views
How is it possible the speed of light is not constant?
I was reading this article recently, which summarizes a couple of new studies into the speed of light.
In one paper, Marcel Urban from the University of Paris-Sud, located in Orsay, France and his ...
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2answers
41 views
About hubble observatory and distant galaxies [duplicate]
According to Hubble observatory, the age of universe is 14 billion years. But, the distant galaxies are about 40 billion light years. How could that simply be possible? That means the information that ...
4
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2answers
306 views
Why cosmic background radiation is not ether?
why cosmic background radiation is not ether? I mean it's everywhere and it' a radiation then we can measure Doppler effect by moving with a velocity.
