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.
2
votes
0answers
292 views
de Sitter and anti de Sitter metric
Is the following correct for the distance $d$ from the origin $(0,0)$ to point $(t,x)$ in the 2-dimensional
de-Sitter and anti de-Sitter spaces? Here, $t$ is time and the distance may be called the ...
4
votes
1answer
112 views
How should one interpret the de Sitter slicings?
When 'constructing' the usual de Sitter space in $\mathcal{M^5}$ by invoking the contraint $-X^{2}_{0} +X^{2}_{1} +X^{2}_{2} +X^{2}_{3} + X^{2}_{4} = \alpha^2$ we quickly see that we end up with a ...
2
votes
4answers
1k views
If gravity is a bend in Space-time then what is magnetism?
Einstein postulated that gravity bends the geometry of space-time then what does magnetism do in to the geometry of space-time, or is there even a correlation between space-time geometry and ...
0
votes
1answer
114 views
weak bosons and feynman-stueckelberg interpretation
from Wiki "The W bosons have a positive and negative electric charge of 1 elementary charge respectively and are each other's antiparticle."
Q:If each is the other's antiparticle then which is ...
1
vote
1answer
375 views
How is traveling back in time possible in theory according to some scientists? [duplicate]
Possible Duplicate:
Is it possible to go back in time?
Is time travel possible?
I get the idea of traveling to the future and it makes perfect sense as we'd be somehow trapped in a ...
5
votes
2answers
186 views
Do objects with mass “suck in” spacetime?
I don't really understand the general theory of relativity (GTR) really deeply, but according to my understanding, the GTR say that gravitation is caused by the curvature of spacetime by objects with ...
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 ...
6
votes
1answer
147 views
If a fundamental theory exibits e.g. a mirror symmetry, in what sense it the underlying geometry real?
Are the more recently discovered symmetries in string theory such that the theories based on mirroring geometries are absolutely the same from an observable point of view?
I have mirror symmetry ...
1
vote
1answer
78 views
Two definitions: 'semi-classical space-time' and 'supersymmetric Minkowski space'
By reading articles I ran several times into two terms, never being defined so I assume they must have well established definitions somewhere.
The first is semi-classical space-time. If I where to ...
1
vote
3answers
265 views
Is spacetime moving in general relativity?
Is spacetime moving in general relativity?
If not, how does spacetime retain its past, while moving toward future?
0
votes
2answers
124 views
How is spacetime depicted in quantum field theory?
How is spacetime depicted in quantum field theory?
Is space and time completely separate, and time is just nature of law as in Newtonian mechanics?
0
votes
0answers
25 views
How can we know the size of a dimension? [duplicate]
Possible Duplicate:
Measuring extra-dimensions
I was watching a layman's documentary and it said:
"The 11th dimension is incredibly small, like a long tube about $10^-30m$ in diameter".
...
-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 ...
1
vote
3answers
210 views
The metric expansion of space and Hawking
In a Wikipedia article I read that the "Metric Expansion of Space" exceeds the speed of light.
If this is true then we must be being disconnected from very remote parts of the universe since gravity ...
-1
votes
1answer
172 views
Time dilation at the speed of light
Does a massless particle travelling at the speed on light in a vacuum (c) experience an infinite time dilation effect?
i.e. Would the time dilation extend from the perspective of the massless ...
1
vote
1answer
126 views
A question about multiverse
I have a question that I would like to ask here since I'm not an expert or any near to that.
Actually I just came up with this question when I was watching The fabric of cosmos.
I couldn't find where ...
0
votes
1answer
84 views
Is it possible to mould _ruptures_ in Space-time?
In one of the documentaries hosted by Morgan Freeman, a reference was made that just like an ordinary three-dimensional object like a ruler has scratches and cracks, in the same way there might be ...
2
votes
1answer
341 views
is space infinitely divisible?
As a child I remember hearing the popular paradox presented by Zeno proposing that Achilles could never catch a tortoise in a race since he would have to traverse the infinite space between himself ...
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 ...
2
votes
1answer
345 views
$\pi$ and the Curvature of Space
If one draws a circle on a sphere and measures the ratio of the diameter to the circumference, that value varies depending on the diameter of the circle compared to the diameter of the sphere it is ...
2
votes
3answers
240 views
How to distinguish 4D and 3D vectors in handwriting?
Usually vectors are denoted with bold font in printbooks and with arrows above in handwriting.
In Thorn's e al. Gravitation, 4D vectors are denoted with bold and 3D vectors with bold italic. How to ...
4
votes
2answers
252 views
Does the current acceleration of universe imply that our universe is open?
Does the current acceleration of universe imply that our universe is open?
If the universe is closed, from the Friedmann's equation, the acceleration of universe wouldn't be possible, would it be? (Of ...
3
votes
1answer
391 views
Is the Portal feasible in real life?
Firstly, I assume prior knowledge/experience with the game Portal.
Should it be possible that two openings (circles/unidentified-constructions) would work as interchangeable gates? With one opening ...
1
vote
2answers
199 views
Confusion regarding geodesic of thrown ball - curved or Cartesian coordinates?
I'm confused trying to understand what's happening in terms of spacetime geodesics when a ball is thrown and its trajectory plotted, height against time to give a parabola.
I read (from more than ...
1
vote
1answer
109 views
Classical black holes?
How big should the black hole be so we can consider it to be classical?
When they claim that we can not probe shorter distances than the Planck length, can it be true?
The argument says that, ...
5
votes
2answers
422 views
Why do objects follow geodesics in spacetime?
Trying to teach myself general relativity. I sort of understand the derivation of the geodesic equation ...
10
votes
3answers
449 views
Space-time in String Theory
I would like to understand how Physicists think of space-time in the context of String Theory. I understand that there are $3$ large space dimensions, a time dimension, and $6$ or $7$ (or $22$) extra ...
1
vote
2answers
215 views
How does gravitation propagate along curved spacetime?
In this wikipedia article it is described how a beam of light, with its locally constant speed, can travel "faster than light". That is to say it travels a distance, which, from a special relativistic ...
0
votes
1answer
133 views
“Conceptualizing” neutrinos
Layman here. EE and BS physics. I am "content" in viewing photons/electromagnetic radiation as an "emergent" property of spacetime? due to the electrons ("particles..?") and all their activity jumping ...
6
votes
1answer
295 views
Do spacelike junctions in the Thin-Shell Formalism imply energy nonconservation and counterintuitive wormholes?
The Thin Shell Formalism (MTW 1973 p.551ff) is used to properly paste together different vacuum solutions to the Einstein equations. At the junction of the two solutions is a hypersurface of matter – ...
3
votes
1answer
389 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 ...
5
votes
2answers
118 views
Why does the homogeneity of the universe require inflation?
They say inflation must have occured because the universe is very homogeneous. Otherwise, how could one part of the universe reach the same temperature as another when the distance between the parts ...
4
votes
1answer
354 views
The nature of time, according to quantum field theory
I will try my best to ask the question that best fits something I have been pondering on for a few days.
Are virtual particles really constantly popping in and out of
existence? Or are they ...
1
vote
3answers
248 views
Evidence that “space exists rather than just particles”
What is (theoretical) evidence that you need to define all of space with properties rather than just stating where all particles are? I mean, does every single coordinate x, y, z have a meaning or ...
4
votes
3answers
588 views
Why are there 4 Dimensions and 4 Fundamental Forces?
Is it a coincidence that there are four fundamental forces and four spacetime dimensions ? Does a universe with three spacetime dimension contain four fundamental forces? Can magnetism be realized in ...
7
votes
4answers
544 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 ...
0
votes
1answer
87 views
Wormhole related experiments? [closed]
Are there any simple "experiments" that can be done in a high school science lab that could demonstrate some sort of basic principals of wormholes or spacetime? Or sort of proving how long something ...
3
votes
5answers
542 views
Can you use a wormhole to travel through space not time?
I want to know if you could theoretically travel from your house to work via a wormhole but stay in the present day...without changing time. Kind of like teleportation but harnessing the energy of a ...
1
vote
2answers
252 views
What does a closed time-like curve look like?
I want to see a plot of closed time-like curve in $(t,x)$.
$t$ - vertical axis
$x$ horizontal axis
(the usual setting just neglect $y$ and $z$ components of $(t,x,y,z)$).
What does it look like?
1
vote
2answers
191 views
How to concile flat spacetime and big bang?
After reading How do we resolve a flat spacetime and the cosmological principle? I still remain perplex.
Please excuse my ignorance and try explaining to me :
I thought that basically, when we ...
0
votes
2answers
294 views
Can the expansion space time reverse itself and contract the same way?
If there's a mechanism for space-time expanding faster than the speed of light, is there an example of It contracting in the same manner? If whatever mechanism is causing it to expand, can the ...
0
votes
1answer
85 views
spacetime or only space? [closed]
I was thinking one day, if time doesn't exist and there is only space. I was trying to think about what other measurementunit could be instead of speed(m/s) and acceleration(m/s2) and I came to ...
14
votes
2answers
485 views
Has the concept of non-integer $(n+m)$-dimensional spacetime ever been investigated by theoretical physicists?
The following image serves to aid the reader in understanding the "privileged character" of $3+1$-spacetime.
The wikipedia article on spacetime, and the sub-article "The priveleged character of ...
6
votes
2answers
370 views
Some questions regarding $n+m$-dimensional spacetime [duplicate]
Possible Duplicate:
Has the concept of non-integer $(n+m)$-dimensional spacetime ever been investigated by theoretical physicists?
The following image:
serves to aid the reader in ...
2
votes
2answers
659 views
Proof that Energy Momentum Tensor of Scalar Field Theory satisfies Weak Energy Condition
It's a question on Sean Carroll's Spacetime and Geometry, where we are supposed to prove that the energy momentum tensor of scalar field theory satisfies Weak Energy Condition (WEC). The energy ...
3
votes
2answers
126 views
How can I vizualize and understand curved spaces in general relativity?
I'm taking a basic physics class and the teacher described space with a special table that has curves and black holes etc. He would throw a metal ball down onto it and the class would watch it circle ...
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 ...
0
votes
2answers
192 views
Is this alternate theory of gravity as cause instead of effect plausible?
I came across this video today on YouTube that presents an interesting alternate theory of Gravity and the "missing" matter in the Universe that Dark Matter/Energy theories try to account for.
If I ...
4
votes
5answers
490 views
ALL “forces” as manifestations of properties of space-time
I apologize if this seems like a quack question, but I need some insights by those who know much more than me in Physics.
Anyway, the gravitational "force" (not really a force) is a manifestation of ...
4
votes
2answers
144 views
Plausible explanations for 3 local space dimensions
Every now and then I see accounts of models that claim to explain why we experience only 3 space dimensions (locally, i.e. within cosmic horizons and outside black hole horizons).
One such of course ...
