As a consequence of the Lorentz transformations, time and space transform into each other when changing reference frame. This calls for a unified description: Minkowski spacetime.
3
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7answers
1k views
According to General Relativity, Does The Past “Exist”?
I'm curious about just what is meant by time being another dimension, like the three (observable) spatial dimensions. Does this imply, according to General Relativity, that the past and the future ...
3
votes
1answer
142 views
Hamiltonians and Lagrangians, Euclidean and Hyperbolic: Are they related?
The Lagrangian of a system is the difference between its kinetic energy $T$ and potential energy $V$, and is relativistically invariant:
$L = T - V$
The Hamiltonian of the same system is the sum ...
2
votes
1answer
128 views
Questions about angular momentum and 3-dimensional(3D) space?
Q1: As we know, in classical mechanics(CM), according to Noether's theorem, there is always one conserved quantity corresponding to one particular symmetry. Now consider a classical system in a $n$ ...
2
votes
3answers
175 views
In a very small static universe with only a particle, does it make sense to talk about time?
I am sorry if this question is silly; it′s just one of those things I wished I asked before leaving university.
If there were a static universe only as big as the size of two particles, say ...
2
votes
3answers
505 views
Does the Opera result hint to a discrete spacetime?
Could the Opera result be interpreted as some kind of hint to a discrete spacetime that is only seen for high enough energy neutrinos?
I think I`ve read (some time ago) something like this in a ...
2
votes
1answer
407 views
Introductions to discrete space-time
It's comparatively easy (cum grano salis) to grasp the following concepts:
Euclidean space-time (continous space and continuous time)
classical mechanics (discretely distributed matter in continous ...
1
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3answers
225 views
Is there a single metric for a given system?
Let imagine a tunnel that connect two distant places at the globe (eastern-western or north-south)
There are a lot of posible "distances" or metrics, defined by maps, routes, "as the crow flies", ...
1
vote
1answer
343 views
Universe Expansion as an absolute time reference
Why we call "constant" to the Hubble constant?,
if the universe were really expanding then the Hubble "constant" should change, being variable, smaller and smaller..with "time".
Other example/view ...
0
votes
0answers
121 views
Is it mathematically possible or topologically allowable for cutouts, or cavities, to exist in a 3-manifold?
A few weeks back, I posted a related question, Could metric expansion create holes, or cavities in the fabric of spacetime?, asking if metric stretching could create cutouts in the spacetime manifold. ...
7
votes
4answers
543 views
Does the “Andromeda Paradox” (Rietdijk–Putnam-Penrose) imply a completely deterministic universe?
Wikipedia article: http://en.wikipedia.org/wiki/Rietdijk–Putnam_argument
Abstract of 1966 Rietdijk paper:
A proof is given that there does not exist an event, that is not already in the past for ...
5
votes
2answers
397 views
What's the difference between space and time?
I'm having a hard time understanding how changing space means changing time. In books I've read people are saying "space and time" or "space-time" but never explain what the difference is between the ...
4
votes
1answer
145 views
Does the curvature of space-time cause objects to look smaller than they really are?
What's the difference between looking at a star from a black hole and looking at it from empty space?
My guess is that the curvature of space-time distorts the wavelength of light thus changing the ...
4
votes
3answers
248 views
Can spacetime exist in the absence of matter and energy?
I'm pretty sure Ernst Mach would have said that spacetime cannot exist without matter in it.
But I'm also pretty sure that a black hole can be described as a self-sustaining gravitational field, ...
4
votes
2answers
777 views
What does “foliation” mean in the context of a “foliation of spacetime?”
I've seen foliation used in the context of "foliation of spacetime" here and elsewhere in papers and such. Generally defined in reference to a "sequence of spatial hypersurfaces." But I don't know ...
3
votes
2answers
196 views
About space-time and its four dimensions
I explained to someone I know about General Relativity (as much as I know).
He said that he didn't see how it could be correct.
He argued:
How is 4-dimensional space-time space different to ...
3
votes
1answer
387 views
Is the universe finite and discrete?
Is the universe finite, both in the sense of being a closed spacetime manifold, as viewed from the macro level, but also in the sense of being fully discrete and finite in all of its intricate quantum ...
3
votes
3answers
2k views
Example of space-like intervals in spacetime
From wikipedia:
When a space-like interval separates
two events, not enough time passes
between their occurrences for there to
exist a causal relationship crossing
the spatial distance ...
2
votes
0answers
65 views
Naked singularity and extendable geodesics [duplicate]
I'm currently trying to understand the notion of a naked singularity. After consulting books by Wald and Choquet-Bruhat, it seems that for a naked singularity one must have that the causal curves can ...
1
vote
2answers
139 views
How to find a curvature of the space-time by having $g^{\alpha \beta}$ in the following case without cumbersome calculations?
The metric tensor for Fock-Lorentz space-time,
$$
\mathbf r_{||}{'} = \frac{\gamma (u)(\mathbf r_{||} - \mathbf u t)}{\lambda \gamma (u) (\mathbf u \cdot \mathbf r) + \lambda c^{2} (1 - \gamma (u))t + ...
1
vote
1answer
468 views
What is the 4th dimension? [closed]
I have heard before that the 4th dimension is time, however, another theory makes a lot more sense to me. This is that the 4th dimension is the third dimension stacked on top of each other in a ...
0
votes
1answer
147 views
Did space and time exist before the Big Bang? [duplicate]
I accept the Big Bang theory. What I can't understand is how there can be a where or when to the Big Bang if space time did not exist prior to it. Did space and time exist prior to the Big Bang?
0
votes
1answer
177 views
The real meaning of time dilation
Is this true or false: If A and B have clocks and are traveling at relative velocity to each other, then to B it APPEARS that A's clock moving slower, but A sees his own clock moving at normal speed.
...
-1
votes
1answer
136 views
The expansion of space time (EST)..and the one directional flow of time?
Time flows one way...cause creates effect.
Could the expansion of the universe also cause an expansion of space time in a similar fashion?...and if so, would this phenomenon explain the one way ...
-1
votes
2answers
413 views
Space-time hospitality
Are there any reasons to assume that organic processes cannot arise in relatively flat spacetime environments?.. An argument for the existence of a critial value or window ..
-5
votes
1answer
215 views
What do scientists believe about existence in dimensions? [closed]
I couldn't really think of a suitable question title, I'm not sure if it's completely related or not.
But this is as far as I know (well, I thought it all up last night and it seemed extremely ...
-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 ...
