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.
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256 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?
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2answers
122 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?
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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".
...
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1answer
205 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 ...
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3answers
201 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 ...
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1answer
165 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 ...
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1answer
116 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 ...
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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 ...
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1answer
318 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 ...
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2answers
194 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
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1answer
334 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
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3answers
235 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 ...
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2answers
243 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 ...
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1answer
376 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 ...
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2answers
193 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 ...
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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
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2answers
402 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
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3answers
439 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 ...
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2answers
214 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 ...
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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 ...
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1answer
282 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
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1answer
368 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
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2answers
112 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
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1answer
350 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 ...
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3answers
244 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 ...
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3answers
568 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 ...
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4answers
508 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 ...
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1answer
82 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 ...
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5answers
517 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 ...
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2answers
248 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?
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2answers
190 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 ...
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2answers
279 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 ...
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1answer
84 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
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2answers
472 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 ...
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2answers
366 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
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2answers
635 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
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2answers
84 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 ...
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4answers
314 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 ...
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2answers
180 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 ...
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6answers
424 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
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2answers
138 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 ...
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0answers
174 views
The structure of space-time
I came across this paper recently called The Small Scale Structure of Spacetime and the following idea occured to me:
To uninformed humans the universe appears Euclidean but we know from GR that on a ...
5
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4answers
606 views
Alternate layman's metaphors for illustrating curved space-time
The metaphor of a surface (typically a pool table or a trampoline) distorted by a massive object is commonly used as a metaphor for illustrating gravitationally induced space-time curvature. But as ...
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2answers
78 views
Resources for current thought on time/spacetime?
Are any of the big-name physicists associated with the time in the same way that Hawking and Penrose are associated with black holes? I'm interested in some good books that focus on the topic.
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0answers
91 views
Does Spacetime have a “This Side Up” arrow? [duplicate]
Possible Duplicate:
Does the curvature of spacetime theory assume gravity?
Forgive my naivete as I am not schooled in Physics or Mathematics.
I was watching NOVA's "The Fabric of the ...
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3answers
408 views
Defining a Riemannian manifold - made easy?
In the context of GTR spacetime, I'm trying to get the basic idea of a Riemannian manifold clear in my mind. Apologies for the longwindedness.
Question 1. Is this a reasonable, simplified summary of ...
2
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3answers
504 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 ...
4
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2answers
374 views
Can an “absolute” frame of reference be determined by measuring the compression of light?
General relativity tells us that there is no absolute frame of reference (actually, it tells us that all frames are relative, which is close but not the same as there is no absolute frame).
Special ...
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5answers
500 views
What is the extent of the universe?
Is there any realistic, understandable, provable (even in some extent) explanation/model for the extent of the universe?
What is its shape? and Why? I mean physical explanations not philosophical ...
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1answer
201 views
Spacetime assumptions at OPERA
I would like to know what are the assumptions about the spacetime metric between the neutrinos emiter and detector, I mean, perhaps (just a stab in the dark) could be a mistake to asume the metric of ...
