Questions tagged [speed-of-light]
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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Can the speed of light be measured only in a local inertial frame of reference?
Whether the speed of light can only be measured at the observer's place, in his local inertial frame of reference, that is, where the measurement is made. It is about the fact that the observer (that ...
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Confusion regarding recessional velocity and Lorentz transformation
Consider that you are receding at a velocity faster than the cosmic speed limit (say, $2c$ with respect to $A$) due to the expansion of our universe. According to me, $A$ is moving at $2c$ and thus ...
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If light cannot change speed, how can it be absorbed or reflected? [duplicate]
Consider a simple model:
A single photon of light in a vacuum travels from (-1,0) to (0,0) , where it hits a reflective point at the origin at time T.
CASE 1: Suppose the velocity of light follows a ...
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Local speed of light and accelerated observers in general relativity
Background:
By the equivalence principle, an observer (time-like geodesic + orthonormal frame (3 spacelike, 1 timelike) which serves as their measurement standard) in gravitational free fall sees ...
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Relative speed between two photons [duplicate]
Is it possible to fix an inertial frame to a photon moving in vacuum?
If yes, what is the speed of another photon moving in vacuum with respect to this frame?
What is the proper time measured by the ...
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Falling/accelerating close to the speed of light
In classical physics velocity and acceleration follow: $v = at$, so an object falling at a constant $10 m/s^2$ for 50 seconds would wind up having a velocity of $500 m/s$.
However, according to this ...
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Max value of I in a circuit
I am a EE student.I have been taught Ohm's law which says $I = \frac{V}{R}$.In the limit of$R \rightarrow 0,I \rightarrow \infty$.But I have also taken the course "Electromagnetism II" where ...
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What is the cause of the constancy of the speed of light in vacuum?
According to the general theory of relativity, every observer will measure the same speed of light $c$ in vacuum, if they measure in their local inertial reference frame.
I assume that this statement ...
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Finding mass of photon with de Broglie wavelength
The de Broglie wavelength equation is given by:
$$\lambda = \frac{h}{mv}$$
Even though this is used to find the wavelength of the matter (matter waves) , I was curious to find the mass of photon ...
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Does Special Relativity apply to waves or particles?
I know that Special Relativity is a classical theory, so perhaps it applies to light waves, but I'm not too sure. The question I want to ask is, does Special Relativity set a bound on particle ...
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Are the non-standard one-way speed of light conventions just transformations of coordinates?
There are a lot of posts and confusion regarding the fact that different standards of simultaneity result in different one-way speeds of light (OWSOL) (that may be non-isotropic). Of course, the ...
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What are light years? like you know how people measure some things in light years? what is light years [closed]
so basically you know how scientists measure how far things are but in space and they measure in light years well what are light years and how long are light years?
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Would everything we see be delayed if light slowed down to 1ms?
I don't know much about physics, though it certainly interests me. so I apologize if this is a dumb question, but if we somehow slowed down the speed of light around us. (like we somehow made air have ...
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Stuck on thought experiment about light [duplicate]
Say we have a very long fluid pipe with the width of a few astronomical units, and that this pipe is perfectly resistant to sustain the stress of a perfectly incompressible fluid going through it ...
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Does Special Relativity assume a finite $c$?
Does SR explicitly assume $c$ to be finite?
If so, by what statement in Einstein's original paper is this implied?
If not, what to make of equations containing $c$? (e.g., $E = mc^2$)
Formulating the ...
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Would an object travelling close to the speed of light gather a lot of energy?
Quick disclaimer: I don't know much about physics, so I don't really know what I'm talking about.
The idea
The idea is that an object traveling fast enough in space will be receiving more radiation ...
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Question on the value of speed of light, non-inertial frames and equivalence principle
One of the axioms of special relativity concerns on the value of speed of light measuread by a family of inertial observers. They must measure $c$.
Now, the global inertial frame is lost if the ...
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Can a rotating body see it's own reflection?
So my question is this: Say I'm able to get close to, but not achieve the speed of light. I want to look at the back of my head in the mirror, would it be possible to turn around before the light from ...
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Can a beam splitter be used to measure Earth's absolute motion through space?
Let say the Earth is not moving through space...Then a beam splitter that refracts the beam into 2 new created beams at an angle of 90° towards reflectors which will reflect the beams at 180° again ...
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How can a camera capture the movement of light (in slow motion) if the electronics operate below the speed of light?
A while back I saw the MIT produced video where they show their camera capturing 1-trillion frames per second and show the light moving around a coke bottle in slow motion.
https://www.youtube.com/...
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What is the necessary speed to travel 1 light-year in 1 year (for the traveler)?
I am stationary and I want to travel to a destination that is 1 light-year away. This journey needs to last 1 year for me. What is the average speed that my rocket must travel to achieve this?
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Does gravity change local space and time units?
Gravity is the curvature of spacetime. Therefore, gravity affects spatial and temporal dimensions in some parts of space. We know that measuring the speed of light in the observer's local inertial ...
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Does the postulate of special relativity say that speed of light in vacuum is the greatest speed? [duplicate]
The postulate of relativity says that the speed of light in a vacuum is the same for all inertial observers. But does it also say that this speed is the greatest achievable speed?
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If the speed of light is independent of motion of its emitter then what is it constant in relation to? [duplicate]
If the speed of light is independent of motion of its emitter then that would be the same as saying that the speed of light is not constant relative to its emitter which, presumably, could move ...
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Relativistic Mass Relative to a Stationary Observer
I know what you’re thinking, “Not another question on Relativistic Mass.” I’ve spent the better part of a day going down the general and special relativity rabbit holes, and I can not find where this ...
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In the early universe (quark-gluon plasma), was there such a thing as a gluon wave like an EM wave and gravitational wave?
I have read this question:
Participating in strong interactions between the quarks, they are "trapped" within a very tiny region of spacetime that we call "hadron". We don't see ...
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Why does relative speed of light when in a non-inertial frame does not increase when viewed from an inertial frame [duplicate]
I mean to ask if I have a moving object and I turn on a bulb in that moving object, when viewed from an inertial frame, we usually add the speed of the moving object with the object's velocity to get ...
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Question about theory of relativity [duplicate]
If you were running at a constant speed towards a light that is coming towards you and an other light was following you, from your perspective how is it possible that both lights go at the same speed....
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How to include the effect of cosmological expansion in the close to speed of light calculations of a relativistic rocket?
I calculated time ago as undergraduated and post it at my blog the calculations for traveling through the Universe in a (special) relativist way. At what level and how should we include the effect of ...
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Why is the speed of light constant in all frames of reference and why is its speed the certain value recorded?
Lorenz transform equations (LTEs) are invoked to preserve the principle of relativity by resolving paradoxes arising therefrom due to the invariance of light-speed in all frames of reference. Said ...
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Length contraction for Gamow's cyclists
In the 1939 book Mr Tompkins in Wonderland, the physicist George Gamow described a hypothetical world in which the speed of light is only 10 km/h. His intention was to provide some intuition of how ...
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Will it reach the speed of Light? [duplicate]
So, I was just wondering if in an isolated environment where there is no external force acting on the body and the body (with any mass) is pushed with a force such that it has a constant acceleration, ...
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Can a ray of light deviate passing from a rarer to a denser medium deviate beyond the normal?
Is this allowed? Technically, if the difference in the refractive indexes is big enough, and the ray of light has a low wavelength (violet), it should be able to deviate beyond the normal.
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How does SR explain constant light speed where the distance between observer and light source is increasing?
Given are two cases of relative motion between an observer and a light source:
the speed of light is always observed to be the same regardless whether the light source is approaching the observer or ...
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If a photon travelled in the opposite direction of another photon [duplicate]
If a photon travels in the opposite direction as another photon, then what is the speed of the second photon relative to the first. Is it 2 times the speed of light? Also what if two photons travelled ...
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Moving in the same direction as a photon
If you were to move in the same direction as a photon moving at the speed of light, what would the speed of the photon be in respect to you? Would it be the speed of light minus your speed or just the ...
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Why the Cauchy Stress Tensor & the Stress-Energy-Momentum Tensor have the same SI units?
Shouldn't adding time as a dimension changes the Stress-Energy-Momentum Tensor's units? What math operation(s) (if any) would transform the 3D Cauchy Tensor into the 4D Energy Momentum Tensor of GR?
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How to rule out that the speed of light was different in the past?
The constancy of the speed of light is a fundamental principle in modern physics, and it is supported by a wide range of current experimental evidence.
There is no evidence to suggest that the speed ...
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What speed of light means? [closed]
speed of light means moving through space with the same speed you move through time?
or to move "only" through space and not through time?
Does this mean that you exist in two (or more) ...
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Question about a paper on "Aberration and the Speed of Gravity"
I found a paper online by S. Carlip (https://arxiv.org/abs/gr-qc/9909087 Aberration and the Speed of Gravity) that looks pretty good, except I can’t get past his metric equation [2.1]! He says it is ...
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Why is light always used as an example while glorifying a black hole?
In almost any article, video, books on a black hole that I have come across, this is the common sentence I have read or heard:
"Nothin can escape a black hole, not even light."
But no one ...
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Counterintuitive effect between event horizons of a 'binary black hole system'
I recently posted a question on my 'mobile phone profile' where I cannot post images and videos so I am trying to use this profile to solve my incomprehension of a gravitational-tidal effect that ...
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Why does refractive index increase with concentration of the medium?
I learnt that lights decrease velocity in a medium during absorbance and emission of its energy in the charged particles in the medium. From the Beer's law, I read that absorbance is directly ...
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How much time does it take for the gravitons generated by a black hole singularity to travel before exerting gravity forces on other celestial bodies?
It is known to all that the travelling speed of gravitons (the propagation speed of gravitational field) is not instant. So for black holes, the gravitons (the gravitational field) generated by the ...
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When travelling through a material, does light bend around the atoms, or does it travel slower in a straight line?
When comparing the speed of light through a material medium as opposed to through a vacuum, the speed through the material (e.g. glass or air) will be slower.
Is this because:
The light has to bend ...
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Why is the phase velocity in a transmission line not affected by its geometry?
When deriving the speed of light in vacuum, one usually starts from Maxwell's equations, does some calculus and finds a wave solution with the phase velocity $c = 1/\sqrt{\mu_0 \varepsilon_0}$. This ...
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Why is the speed of gravity the same as the speed of light? [duplicate]
Why is speed of gravity the same as the speed of light, can anyone explain in simple terms?
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Does only the space region movement due universe expansion affect the possibility of viewing a star?
My question is maybe simple and easy to answer because the intrinsic speed of the star affects only the final frequency of observed light but are there any tricks about the combination of object ...
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What is the velocity of propagation of the interaction, why is there a "maximum value" of it and how can we calculate this value? [duplicate]
I just started reading Landau's Classical Theory of Fields and it starts by mentioning how the change in one particle will affect another particle interacting with the first one after some non zero ...
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The Ricci scalar in FRW, where am I getting wrong?
I'm trying to derive Ricci scalar with FRW metric, but additional $c^2$ makes me confused.
The book by D. Baumann says
\begin{align}
R &= g^{\mu\nu}R_{\mu\nu} \\
&= -R_{00}+\frac{1}{a^2}R_{...
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