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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Which wins the race, the neutrino or the photon? [closed]
You have an emitter at A and a reciever at B. Exactly half way between them is a star. The emitter simultaneously emits a burst of photons as well as a burst of moderatly high-energy neutrinos. The ...
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Is it possible to explain how electromagnetic waves propagate through a vacuum solely using classical physics? [closed]
I'm struggling to understand how electromagnetic waves are able to sustain through a vacuum without thinking of them as photons instead of waves.
Am I right in thinking of the situation as the wave ...
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Why does light travel at 45 degrees in spacetime diagrams?
When trying to visualize the movement of matter in Relativity a spacetime diagram is often used, where in one or two spatial axes are removed and an axis added in for time. The standard way to ...
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What is gravity near speed of light due to contraction?
observing a box traveling close to $c$ i would see the box shrink in the direction of travel. so the mass in the front approaches the mass of the back getting arbitrarily close as the box approaches $...
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What is velocity of light in Schwarzschild metric at distance $𝑟$ for observer that is infinitely far away?
This is a generalization of the question which more specifically asks for radial and tangential velocity only.
Given a point at distance $r>r_s$ from a mass ($r_s$ the Schwarzschild radius), what ...
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Time derivative of electric field associated with moving charge
The electric field intensity at a given point in a lab frame will vary in time if the point's position relative to a charge varies in time. If the position of the point from the charge's reference ...
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Wavelength and Energy relation [closed]
Wavelength $\lambda$ formula:
$$\tag1\lambda=\frac h{mv}$$
Put here value of $h$ as
$$\tag2h=\frac Ef$$
Then formula becomes:
$$\tag3\lambda=\frac E{fmv}$$
In this formula, wavelength is directly ...
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Matter density right after the decoupling
Once photons decoupled from matter, they traveled freely through the universe without interacting with matter and constitute what is observed today as cosmic microwave background radiation (in that ...
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Historical justification for assuming terrestrial light speed equals ether frame speed in Michelson-Morley experiment [closed]
I'm trying to understand the historical reasoning behind a key assumption in the Michelson-Morley experiment (1887).
The assumption: Michelson and Morley assumed that the speed of light they measured ...
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Has the speed of gravitational waves been verified beyond GW-170817?
To my knowledge GW170817 is still the one and only GR+EW signal detected by LIGO. Are there other experimental results confirming that gravitational waves propagate at the speed of light?
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Mathematical process for path of light in a perfectly gradual thickening medium
Preface:
I do know: Algebra, Basic Calculus, Basic Refraction of light.
I do not know: Riemannian geometry (just began to study), Matrices, General Relativity.
I enjoy studying physics and math as a ...
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Should a moving star show a Shapiro drag?
The Shapiro timelag effect (1964) describes one physical consequence of a gravity-well containing more space (positive curvature), and less time (gravitational time dilation) than the region's ...
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Would a Newtonian theory of gravity with finite propagation speed already predict gravitomagnetic effects?
In General Relativity, moving/rotating sources lead to gravitomagnetic effects, such as frame dragging. These arise naturally from the off-diagonal components of the metric in the weak-field limit, ...
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What's faster: phase velocity or group velocity?
On page 423 of the 4th edition of Introduction to Electrodynamics by David J. Griffiths, he says the phase velocity is twice the group velocity. He defines the phase velocity as
$$v_{\text{phase}} = \...
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Why is space itself not regarded as a medium?
The idea of a hypothetical medium filling space, enabling the motion of light, was a central concept in physics in the centuries after Newton. Finally, with Einstein's theory of relativity, the "...
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Relativity in an isotropic and homogeneous system filed with medium
In the vacuum, it is well known that every inertial frame, regardless of speed, observe the same speed of light. However, we also know that in the medium, like gas, the speed of light will be lower ...
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If speed of different frequencies of light differ in glass; of which frequency of light does the expression from the maxwell equation gives speed of
I recently asked a question on the Stack Exchange: why does the speed of different frequencies of light differ in glass [or any other optically dense medium other than a vacuum]
I got the answer, but ...
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Questions about light speed [duplicate]
First off I am not a physicist and I do not know how to do the math involved. But I like knowing what the math means.
The speed of light is constant in a vacuum regardless of the motion of the ...
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Can a symmetric vertical Michelson interferometer reveal gravitational anisotropy in light speed without being confounded by mechanical distortion?
I'm exploring whether a vertical Michelson–Morley–type experiment can detect directional anisotropy in the speed of light due to gravity, and whether a specific symmetrically mounted setup can cancel ...
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Ideas to measure speed of light in a lab setting [duplicate]
I’m teaching an undergraduate experimental physics course next year. Instead of giving students fixed and legacy experiments, I want to give them an open-ended task, like “measure the speed of light”, ...
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Why do speed of different colours of light vary in glass but are the same in vacuum? [duplicate]
Light is an electromagnetic wave and therefore it follows the wave equation.
$\frac{\partial^2 \psi}{\partial t^2}= v^2 \frac{\partial^2 \psi}{\partial x^2}$
Now with some maths, the wave equation can ...
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In light cone, why is it a cone and not a sphere, given that light travels in all directions in space-time? Is it a projection of slice of 4D sphere?
The light cone concept says that whenever a flash of light is tracked from a point in space-time, its path becomes a cone in 3d. The explanation I found is that you stack up the circle that it tracks ...
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Speed Time Dilation and travelling 90% of $c$
If a spaceship travelled away from Earth at 90% of the Speed of Light over a distance of 10 light years, then I read that an atomic clock would record a "time taken" of less than 5 years (...
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GR and SR time dilation of light
I'm wondering about GR and SR time dilation and light.
First, we put a mirror on Mercury and flash a laser at it. The return time to Earth is 10:00 minutes. Now we dig a big tunnel right through ...
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Taylor and Wheeler Definition of Inertial Frame
In Spacetime Pysyics, Taylor and Wheeler define an inertial frame as:
A reference frame is said to be an “inertial” or “free-float” or “Lorentz”
reference frame in a certain region of space and time ...
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