Linked Questions

16
votes
6answers
6k views

Are we really moving at the speed of light in the time dimension? [duplicate]

I have seen a vector explanation of time dilation that our net velocity in space-time is the speed of light. Most of that velocity for slow spatial speeds is in the time dimension. As you go faster ...
10
votes
3answers
3k views

Is the speed of light the only speed that exists? [duplicate]

Well, it seems to me that if I move faster in space I move slower in the dimension of time which is orthogonal to the dimension of space. All speeds are then equal. Is this statement correct?
6
votes
3answers
2k views

If something is not moving in space, is it moving on the time axis at the speed of light? [duplicate]

I heard this theory yesterday: If something is not moving in space, then it is moving on the time axis at the speed of light. I realize that in essence there is no object which can be considered as "...
4
votes
1answer
4k views

Are we traveling through time at the speed of light? [duplicate]

In the image below the y axis represents time and x represent velocity. Point D represents velocity c, point E represents 1 second per stationary observers second. What this chart is showing is as you ...
2
votes
2answers
2k views

Stanford: "Objects in spacetime all move at constant speed $c$." Are they right? [duplicate]

In this Stanford University lecture on Relativity, it is stated: Likewise, objects in spacetime all move at constant speed c in spacetime but if you change its direction, say by moving at speed v in ...
3
votes
2answers
1k views

Can someone explain to me what the phrase "Everything moves through space-time at the same speed" means? [duplicate]

It's a statement I've seen thrown around here and there. Essentially, under relativity, everything can be said to move at c, some part of it is motion through space, some of it through time, and when ...
2
votes
1answer
273 views

Are we all moving at $c$? [duplicate]

Is it true to say that all matter in the universe is travelling with velocity c through spacetime, but that for baryonic matter most of that velocity is through the time dimensions rather than the XYZ ...
38
votes
4answers
6k views

How do we know that gravity is spacetime and not a field on spacetime?

How do we know that gravity is the curvature of spacetime as opposed to a field, which couples equally to all objects, on spacetime?
21
votes
5answers
2k views

What are some ways to justify the Einstein field equations?

Since they are a postulate of general relativity, it is not really possible to "derive" the Einstein field equations $$R_{ab} + \left(\Lambda - \frac{1}{2}R\right)g_{ab} = -8\pi T_{ab}$$ in any very ...
12
votes
4answers
3k views

Isn't LIGO basically measuring the luminiferous aether?

I am bit confused about this one. I am not very acknowledgeable about gravitational waves and LIGO. But if it is basically a Michelson interferometer and can detect shifts in vacuum, doesn't this ...
26
votes
2answers
2k views

Do light waves precisely follow null geodesic paths in General Relativity?

In special relativity one may show that a plane wave solution of Maxwell's equations (in a vacuum), of the form $A^a=C^a\mathrm{e}^{\mathrm{i}\psi}$ has the following properties: The normal $k:=\...
28
votes
3answers
1k views

Do any quantum gravity theories deal with closed timelike curves?

As far as I'm aware, there are no quantum gravity theories that deal directly with closed timelike curves. Some of them (like canonical quantum gravity, causal dynamical triangulation and loop quantum ...
4
votes
3answers
251 views

If gravity is simply a curvature of space, why does it accelerate objects? [duplicate]

I understand how an object moving through space would be affected if gravity were a curvature of space as opposed to being a force. However, I do not understand why this creates a "pull" on ...
3
votes
3answers
1k views

Does a massive object contract space-time or expand it?

Before asking, I must say that I am not a physicist of any sort, but I do have a strong interest in Relativity that has led me to question my layman’s understanding. So please stay with me on this “...
-2
votes
1answer
1k views

How far does a photon move in the 4th dimension when it travels one light second? [closed]

In one second a photon moves 3x10^8 meters through the three spatial dimensions. Light's velocity is 3x10^8 m/s. If the photon moved at all in the fourth dimension, it's velocity would no longer be ...

15 30 50 per page