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.
1
vote
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
171 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
votes
1answer
282 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
329 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
198 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 ...
3
votes
2answers
359 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
222 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
146 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
vote
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;
...
15
votes
4answers
1k 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
400 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
vote
3answers
217 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
245 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
393 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 ...
71
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
votes
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
318 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?
-1
votes
1answer
117 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
418 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
104 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 ...
22
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. ...
7
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
337 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
185 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
732 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
182 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
632 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
412 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
140 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
592 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
766 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
313 views
2
votes
3answers
276 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
657 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
...
3
votes
5answers
777 views
How does the curvature of spacetime induce gravitational attraction?
I don't know how to ask this more clearly than in the title.
6
votes
3answers
697 views
Does the curvature of spacetime theory assume gravity?
Whenever I read about the curvature of spacetime as an explanation for gravity, I see pictures of a sheet (spacetime) with various masses indenting the sheet to form "gravity wells." Objects which are ...
4
votes
2answers
532 views
How do I develop an intuitive model of spacetime?
I am your nightmare poster - a layman trying to learn special relativity. (I'm also a refugee from stackoverflow.com: trust me, it's only going to get worse). Apologies in advance if my question is ...
0
votes
6answers
3k views
Does vacuum (empty space) exist? [closed]
Added: 5 times down vote for now! Down voter is this religion or physics, please try to explain your decision.
I'm confused about this.
In physics we know for a vacuum, but I think that there is a ...
0
votes
1answer
546 views
Light years in terms of actual time space [closed]
What actually is 1 light year? What is the equivalent time in Earth time space?
5
votes
4answers
816 views
Did spacetime start with the Big bang?
Did spacetime start with the Big Bang? I mean, was there any presence of this spacetime we are experiencing now before big bang? And could there be a presence/existence of any other space-time before ...
7
votes
3answers
478 views
Is anyone studying how the topology of space arises from more fundamental notions?
Stephen Wolfram in his book "A New Kind of Science" touches on a model of space itself based on automata theory. That it, he makes some suggestions about modelling not only the behaviour of matter ...
1
vote
1answer
444 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 ...
3
votes
3answers
522 views
How could spacetime become discretised at the Planck scale?
I didn't have much luck getting a response to this question before so I have tried to reword and expand it a little:
In early 2010 I attended this inaugural lecture by string theorist- Prof. ...
4
votes
1answer
236 views
What are the current (popular(ish)) approaches to modelling the quantum nature of spacetime at the Planck scale?
My guess at a list of them would be: spin foams, casual sets, non-commutative geometry, Machian theories, twistor theory or strings and membranes existing in some higher-dimensional geometry...
...
8
votes
6answers
1k views
Experimental evidence of a fourth spatial dimension?
As human beings, we observe the world in which we live in three dimensions. However, it is certainly theoretically possible that more dimensions exist.
Is there any direct or indirect evidence ...
