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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0answers
175 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
619 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 ...
0
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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.
2
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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 ...
2
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3answers
418 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
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 ...
4
votes
2answers
391 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 ...
4
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5answers
528 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 ...
2
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1answer
202 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 ...
2
votes
2answers
367 views
Does space have to be filled with charged particles to carry electromagnetic waves?
I'm a newbie here so have mercy.
I'm studying electromagnetic waves. This is the propagation of energy via the vibration of charged particles, as I understand it.
A charged particle could be like ...
1
vote
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
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0answers
89 views
Confusion with infinity and time [closed]
I have some confusion between with resolving the following situation.
I know that no measurable quantity can have a value of infinity. For example, I just wrote something out, but clearly this ...
0
votes
1answer
175 views
Can a vortex be self-sustaining? [closed]
Can vortices be self-sustaining?
I suppose vortices in water are not self sustaining, since they need constant supply of water at speed i.e. kinetic energy. But is the same case applicable to space ...
2
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1answer
286 views
Orientability of spacetime
In many theoretical setups it is implicitly assumed that the underlying manifold (i.e. spacetime) is orientable. Then our analysis depends on this implicit assumption. For example, Stokes' theorem ...
4
votes
2answers
337 views
Can a black hole be formed by radiation?
I'm trying to find out if black holes could be created by focusing enough light into a small enough volume.
So far I have found (any or all may be incorrect):
Maxwell's equations are linear, ...
-1
votes
1answer
200 views
How to bend 3d space embededd in a 4d enviornment? [duplicate]
Possible Duplicate:
Calculating position in space assuming general relativity
I recently started to program a 4 dimensional visualization program.
I have the 4 dimension space perspectively ...
4
votes
2answers
367 views
Why is time special?
In Special Relativity, the spacetime interval between two events is $s^2 = -(c{\Delta}t)^2+({\Delta}x)^2+({\Delta}y)^2+({\Delta}z)^2$ giving the Minkowski metric $\eta_{\mu\nu}=\text{diag}(-1, 1, 1, ...
5
votes
1answer
227 views
What does scalar phi represent in spacetime?
Trying to understand one-forms and vectors via Schutz's A First Course In General Relativity.
His example uses a spacetime diagram, a scalar field phi, a curve (worldline) parametrized using proper ...
-4
votes
1answer
147 views
If an apple that is rotten transports back in time will it become fresh again? [closed]
I was wondering about organics that traveling back in time. for example. I'm standing on main street where there is a an apple tree about 30 years old. I pick a rotten apple from it, I go back in time ...
1
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0answers
111 views
Einstein's postulates <==> Minkowski space. In layman's terms [duplicate]
Possible Duplicate:
Einstein's postulates <==> Minkowski space. (In layman's terms)
In the spirit of Einstein's arguments using flashes of light, moving trains and mirrors;
...
16
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4answers
2k views
Einstein's postulates <==> Minkowski space. (In layman's terms)
What's the cleanest/quickest way to go between Einstein's postulates [1] of
Relativity: Physical laws are the same in all inertial reference frames.
Constant speed of light: "... light is always ...
3
votes
3answers
402 views
Rotations in space-time
In Landau's Classical Theory of Fields, one finds the statement:
Every rotation in the four-dimensional space can be resolved into six
rotations, in the planes $xy,zy,xz,tx,ty,tz$ (just as every ...
1
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3answers
219 views
Could we enable ourselves to send messages to and receive messages from the future?
Based on John Isaacks' question, "If you view the Earth from far enough away can you observe its past?" and the responses, it appears that we could use mirrors to see into the past. Using Vintage's ...
3
votes
2answers
250 views
How is the complexification of spacetime justified?
As always the caveat is that I am a mathematician with very little knowledge of physics. I've started my quest for knowledge in this field, but am very very far from having a good grasp.
General ...
8
votes
2answers
399 views
Is spacetime simply connected?
As I've stated in a prior question of mine, I am a mathematician with very little knowledge of Physics, and I ask here things I'm curious about/things that will help me learn.
This falls into the ...
73
votes
7answers
25k views
If you view the Earth from far enough away can you observe its past?
From my understanding of light, you are always looking into the past based on how much time it takes the light to reach you from what you are observing.
For example when you see a star burn out, if ...
2
votes
2answers
176 views
Is the assumption of space time to be a continuum is just a matter of mathematical taste?
Is the assumption of space time to be a continuum is just a matter of mathematical taste ? Isn't there any physical significance associated with it.
8
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5answers
1k views
Why is gravitation force always attractive?
Why is the gravitation force always attractive? Is there a way to explain this other than the curvature of space time?
PS: If the simple answer to this question is that mass makes space-time curve ...
1
vote
1answer
339 views
Does spacetime really exist in quantum gravity?
If there are no localized observables in quantum gravity, does spacetime really exist, or might spacetime really be an illusion?
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1answer
118 views
the search for calabicles
Pop-sci ST books say, "At every point of space, there is a Calabi-Yau space..." or similar. But uncertainty p. and noncommgeom say, no points in space, only planckons (not my coinage). Is 'point of ...
2
votes
2answers
426 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 ...
12
votes
3answers
115 views
What is meant when it is said that the universe is homogeneous and isotropic?
It is sometimes said that the universe is homogeneous and isotropic. What is meant by each of these descriptions? Are they mutually exclusive, or does one require the other? And what implications rise ...
26
votes
5answers
1k views
Is 3+1 spacetime as privileged as is claimed?
I've often heard the argument that having 3 spatial dimensions is very special. Such arguments are invariably based on certain assumptions that do not appear to be justifiable at all, at least to me. ...
8
votes
7answers
1k views
Why are extra dimensions necessary?
Some theories have more than 4 dimensions of spacetime. But we only observe 4 spacetime dimensions in the real world, cf. e.g. this Phys.SE post.
Why are the theories (e.g. string theory) that ...
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 ...
-2
votes
1answer
191 views
future light cones and light paths
I understand that an event, in a four dimensional space-time, produces a light cone. As time increases the cones gets larger on either side of the event (past and future). For example the if the sun ...
3
votes
3answers
799 views
Gravitational time dilation at the earth's center
I would like to know what happens with time dilation (relative to surface) at earth's center .
There is a way to calculate it?
Is time going faster at center of earth?
I've made other questions ...
-3
votes
1answer
186 views
Gravitational time dilation and intelligent life [closed]
Thinking in the posibility of extraterrestrial life,
I think that gravity could be a fundamental factor for evolution,
I mean, in darkest zones of universe,
where is dust, little mass accumulation, ...
3
votes
1answer
658 views
Voyager local time dilation (caused by gravity)
Voyager I, as an example, taking account gravity
and setting aside effects of speed as cause of time dilation.
If it is very far away from earth and sun,
so then there must be a difference in the ...
0
votes
1answer
181 views
Is relativistic motion equivalent to fluctuating gravitational fields?
The theory of relativity makes very precise predictions about how an object's motion through space-time affects the passage of time for both the object and observers in other frames of reference.
I ...
7
votes
2answers
1k views
Is reality discrete at the quantum level? (…and what does it imply not only mathematically?)
On a quantum scale the smallest unit is the Planck scale, which is a discrete measure.
There several question that come to mind:
Does that mean that particles can only live in a discrete grid-like ...
-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 ..
2
votes
1answer
142 views
Does the recent Gravity Probe - B mission mean both the mass of an object and the spin of an object affect time?
I'm a non-engineer interested in the recent GP-B mission results: http://www.engadget.com/2011/05/06/nasa-concludes-gravity-probe-b-space-time-experiment-proves-e/#disqus_thread
Is it correct that ...
15
votes
7answers
1k views
Does Quantum Mechanics assume space and time are continuous?
I was confused when I was listening to a Quantum Mechanics lecture online. Are space and time assumed to be continuous or discrete in Quantum Mechanics?
I can see the question is vague, but this is ...
8
votes
2answers
606 views
Can a non-euclidean space be descripted through an euclidean of higher dimension? so why use non-euclidean?
If you draw a big triangle in earth 2D surface you will have an aproximated spherical triangle, this will be a non euclidean geometry.
but from a 3D perspective, for example the same triangle from ...
9
votes
2answers
780 views
Invariant spacetime - distance - Circular Motion
I understand that the closer something travels to the speed of light, that time will stretch by a factor, and distance will compress by the same factor.
My question is, if something travels in a ...
-1
votes
1answer
319 views
2
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3answers
278 views
If the Big Bang theory suggests that the Universe is “expanding” then what is it expanding INTO? [duplicate]
Possible Duplicate:
origins of the universe questions.
i am a software engineer and not an astrophysicist but i want to know if anyone is working on sorting out what exists outside the ...
7
votes
2answers
2k views
Why does Venus rotate the opposite direction as other planets?
Given: Law of Conservation of Angular Momentum.
Reverse spinning with dense atmosphere (92 times > Earth & CO2 dominant sulphur based).
Surface same degree of aging all over.
Theoretical large ...
5
votes
2answers
669 views
Space-like Killing vector of Robertson-Walker metric?
In the book "Kinetic theory in the expanding Universe" (J. Bernstein, 1988, Camb. Univ. Press), it was stated that
"for nonstationary Robertson-Walker
matrixes [sic] there is no spacelike
...
