
What is the Bell spaceship paradox, and how is it resolved?
Bell describes two spaceships that start out at rest...

Mar1114 10:20 AM
bcrowell

0 
5,510 
FAQ: How fast do changes in the gravitational field propagate?
General relativity predicts that disturbances in the...

Sep1012 10:09 AM
bcrowell

0 
9,592 
Why is the speed of light the same in all frames of reference?
The first thing to worry about here is that when you...

Aug412 07:19 PM
bcrowell

2 
10,351 
Can I send a signal faster than light by pushing a rigid rod?
One common proposal for achieving faster than light...

Oct311 02:07 PM
DaleSpam

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11,066 
How can light have momentum if it has zero mass?
The relativistic expression for the momentum of a massive particle...

Jul711 10:52 AM
bcrowell

0 
8,663 
Why does c have a particular value, and can it change?
Short answer:
Because c has units, its value is what it...

Jul211 12:29 PM
bcrowell

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6,525 
I've read that in relativity the concept of the rest frame of a photon doesn't make sense. Why is that?
A rest...

Jan2611 08:11 AM
D H

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9,287 
In general relativity, gravitation is a manifestation of the curvature of spacetime. The motion of all objects is...

Aug2108 11:42 PM
jtbell

0 
7,704 
Do photons have mass?
The quick answer: NO.
However, this is where it gets a bit confusing for most people. This...

Mar2707 10:14 AM
ZapperZ

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18,849 
Definition/Summary
Time dilation is the factor by which an inertial observer measures another observer's clock as...

Jul2414 09:06 AM
Greg Bernhardt

0 
840 
Definition/Summary
The metric tensor g_{\mu\nu} is a 4x4 matrix that is determined by the curvature and coordinate...

Jul2414 09:05 AM
Greg Bernhardt

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251 
Definition/Summary
A Lorentz transformation is the relation between the coordinates of two inertial observers who...

Jul2414 09:04 AM
Greg Bernhardt

0 
244 
Definition/Summary
Where two particles very close together have the same velocities, their two geodesics are...

Jul2414 09:03 AM
Greg Bernhardt

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229 
Definition/Summary
The Einstein Field Equations are a set of ten differential equations which express the general...

Jul2414 09:01 AM
Greg Bernhardt

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228 
Definition/Summary
e = mc² is the formula relating mass to the total energy which could theoretically be produced...

Jul2414 09:00 AM
Greg Bernhardt

0 
228 