Tagged Questions

1
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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 ...
3
votes
3answers
158 views

How does relativity explain gravity, without assuming gravity [duplicate]

I have seen the "objects pull down on space-time" explanations, but they assume a "pull down" force themselves. Could anyone explain the space-time explanation without assuming gravity in the first ...
0
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1answer
76 views

Spacetime and Timelike Intervals

The difference between a “timelike” spacetime interval and a “spacelike” spacetime interval can be understood in the following way: If the spacetime interval between two events is timelike, there ...
3
votes
1answer
97 views

How much time has passed for Voyager I since it left the Earth, 34 years ago?

34 years have passed since Voyager I took off and it's just crossing the solar system, being approximately at 16.4 light-hours away. How much time have passed for itself, though?
1
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1answer
77 views

Could light travel more slowly than the “universal speed limit”? Could this imply quantization of spacetime?

One description of relativistic effects that I've heard/read goes something like this: Everything moves through spacetime at a constant speed. An object's direction of travel through spacetime can ...
-1
votes
1answer
122 views

How do photons experience time? [duplicate]

I know that as velocity approaches the speed of light the time dilation shoots to infinity as shown below. 1)So I want to know how time is perceived from the point of view of the photon? 2)Since ...
3
votes
3answers
315 views

Why do clocks measure arc-length?

Apologies in advance for the long question. My understanding is that in GR, massive observers move along timelike curves $x^\mu(\lambda)$, and if an observer moves from point $x^\mu(\lambda_a)$ to ...
1
vote
1answer
58 views

Are branes in 4D-spacetime moving, or are they static?

Given that a worldline, worldsheet, worldvolume, are representation in a 4D-spacetime of a point particle, a string or a brane, respectively, I was wondering if those objects necessarily have to be ...
-9
votes
1answer
213 views

Why are we talking about space curvature as if we know what space is? [closed]

1) Why are we talking about space curvature as if we know what space is? Every question about gravity seems to evoke an answer involving "space curvature" which seems like an undefined placeholder ...
0
votes
0answers
56 views

Space-time & solar mass

Does the space-time curvature described by Einstein have any affect on the accuracy of our determination in the age of a star or globular cluster? How does this affect our interpretion of how old we ...
2
votes
4answers
328 views

Reducing General Relativity to Special Relativity in limiting case

I understand that general relativity is applicable to gravitational fields and special relativity is applicable to case when there is no gravity. But is there a derivation on how to reduce General ...
2
votes
2answers
425 views

Nature of spacetime 4-vector and tangent space?

An entry level confusion about spacetime. I understand that a 4-vector describes a point or event in spacetime. But I've also read (Bertschinger, 1999) that re spacetime "we are discussing tangent ...
0
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0answers
237 views

How to formulate Lorentz invariance without the temporal dimension? [closed]

The role of "time" in fundamental physics has changed a lot in recent decades. Some physcists believe time is an emergent property rather than a most fundamental parameter of nature laws. However, ...