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
2answers
174 views
What equations do I use to do basic time dilation problems?
I understand the concepts of relativity, but I don't know where to go to set up equations to do any actual calculations. For example, what equations would I use to find out the following:
A ship ...
2
votes
1answer
205 views
What bends fabric of space-time?
I know that mass can bend fabric of space-time, which causes gravity by making an object curve around a planet or star but is there anything else that can bend it?
Other energy sources, forces ...
1
vote
1answer
129 views
Symmetries of spacetime and objects over it
I guess according to mathematical didactic, we first think of spacetime as a set and we reason about elements of its topology and then it's furthermore equipped with a metric. Appearently it is this ...
5
votes
0answers
156 views
Penrose Conformal diagram for flat 2-dim Lorentz space-time
I have the following metric
$$ds^2 ~=~ Tdv^2 + 2dTdv,$$
defined for
$$(v,T)~\in~ S^1\times \mathbb{R},$$
e.g. $v$ is periodic.
This is the according Penrose diagram:
Question 1) Is the ...
3
votes
2answers
228 views
The order of seeing event in different spacetimes
Assume this question:
Three events A, B, C are seen by observer O to occur in the order ABC. Another observer O$^\prime$ sees the events to occur in the order CBA. Is it possible that a third ...
0
votes
0answers
92 views
QFT on fixed Robertson-Walker background spacetime [closed]
What's known about QFT (or even QM) on fixed, but non-Minkowski spacetimes such as the cosmological Robertson-Walker background defined by:
$ ds^2 = c^2 dt^2 - a(t)^2 * (dx^2 + dy^2 + dz^2) $
By ...
-3
votes
1answer
73 views
Is it fabric of space or fabric of space-time?
Very quick question, in the general relativity is it fabric of space, fabric of space-time or both mentioned?
5
votes
2answers
253 views
What really is Spacetime?
What is a good definition on Space, Time and the most specific topic "Spacetime"? Because someone told me that spacetime is the foundation of the entire universe?
And also, Is it possible to create ...
15
votes
3answers
741 views
What is the length of 1 second in meters
If time is treated as a fourth dimension of spacetime, what is relation between length and time units?
Or in other words, how can I convert time units to length units, for instance seconds to meters?
...
1
vote
1answer
209 views
What is the general relativistic calculation of travel time to Proxima Centauri?
It has already been asked here how fast a probe would have to travel to reach Alpha Centauri within 60 years. NASA has done some research into a probe that would take 100 years to make the trip. But ...
1
vote
1answer
123 views
Is time the rate at which one moves through space
I'll start out with the cliche attempt in a protective shield of my dignity. I am a young highschool kid just eager to learn and understand. If I'm way off or this is already a known idea, or maybe ...
2
votes
1answer
62 views
Why is that the space-time associated with the Earth is not shrinking?
If we apply the Friedmann Lemaître equation to the Universe, we find a critical density $\rho_c$ : if the actual density $\rho$ is under it, the Universe will continue to expand, if it is higher than ...
9
votes
5answers
468 views
Is it possible for one black hole to pull an object out of another black hole?
Suppose we have a spacecraft just inside the event horizon of a black hole, struggling to escape, but slowly receding into it. Another (bigger) black hole expands until its event horizon includes the ...
-9
votes
1answer
202 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 ...
2
votes
3answers
173 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 ...
4
votes
1answer
121 views
Limit on space-time dimension from susy
I read an argument saying that it would be impossible to write down a super-symmetric theory in more than 11 dimensions, this limit coming from the dimension of the Clifford algebra that goes as ...
0
votes
3answers
143 views
The radius of the universe and time
Ok - fair warning - Non-physicist asking dumb-assed questions here again.
I've been reading a lot of Einstein, Feynmann, Ferris etc. I'm just loving this stuff.
But I suddenly found myself looking at ...
1
vote
1answer
117 views
Is it possible to describe the entire universe with the behavior of an $\mathbb{R}^n$ field?
Suppose every phenomena in this universe (of course most are reducible to some particular general ideal ones - basically I'm talking about those!) could be described as ...
1
vote
2answers
300 views
Light speed in space-time. is it really constant?
I am by no means an expert in this field, however something puzzles me about the speed of light and the relativity of time and space (space-time).
Is is universally acknowledged that the speed of ...
3
votes
2answers
419 views
Do we live in a world with 4 or more dimension?
A NOVA show have told the audience that we are live in 3 dimensional world, the world we lived in is compose by 3 element: the energy, matter, space. By the time Einstein have invented the ...
0
votes
0answers
55 views
Space-time & solar mass
Does the space-time curvature described by Einstein have any affect on the accuracy of our determination in the age of a star or globular cluster? How does this affect our interpretion of how old we ...
0
votes
1answer
56 views
Proper notation when working with three Euclidean spatial coordinates in a setting with a time parameter
The How does the Euclidean metric is the symmetry group of Euclidean space. It includes rotations and translations.
Say I consider an Euclidean space and a time parameter. How does the Euclidean ...
0
votes
2answers
128 views
Is it possible to change the path of a single photon?
In other words, if a photon is emitted from source, is it possible to change its course en route either by introducing a gravitational lensing or some sort to change the road it travels (spacetime) ...
2
votes
1answer
246 views
Does electric charge affect space time fabric?
I am confused with this question. Does electric charge affect the space time fabric? If so, why? Also if electric charge does not affect the space time fabric, how can we interpret the origin of the ...
3
votes
1answer
150 views
How would be tv reception in a spaceship travelling close to speed of light?
My little brother has made me a tough question (specially for a computer science engineer).
Imagine that there is a spaceship orbiting earth close at nearly speed of light (say 99%).
Someone in earth ...
1
vote
1answer
71 views
Is it best to look at light as a particle when trying to understand special relativity?
So my course about special relativity explains time dilation using a moving train, where one sends up (i.e. perpendicular to the direction of movement) a light pulse which gets reflected etc. (a ...
-4
votes
1answer
96 views
Can project LISA will bring us closer to time travel? [closed]
After looking at the current discovery of Higgs Boson and the next long term plans of NASA and ESA(European Space Agency), I can't stop myself asking about the possibilities in near future.
According ...
5
votes
0answers
146 views
Energy balance of closed timelike curves in Gödel's universe
I recently read Palle Yourgrau's book "A World Without Time" about Gödel's contribution to the nature of time in general relativity.
Gödel published his discovery of closed timelike curves in 1949. ...
2
votes
4answers
347 views
Why are objects at rest in motion through spacetime at the speed of light?
I read that an object at rest has such a stupendous amount of energy, $E=mc^2$ because it's effectively in motion through space-time at the speed of light and it's traveling through the time dimension ...
-3
votes
1answer
168 views
If the universe is infinite, shouldn't I already have been contacted by a time and space travelling doppelgänger?
If the universe is infinite, by virtue of chance it means that every possible configuration of matter must exist somewhere (according to this documentary).
Therefore, if we accept that the universe ...
0
votes
1answer
72 views
Is the spacetime interval between the Big Bang and a given event dependent only on the time component?
My thinking is this - at the time closest to the Big Bang when physics doesn't break down, the universe would have had a volume that was still very close to zero. If that were so, wouldn't the space ...
4
votes
2answers
301 views
Does String theory say that spacetime is not fundamental but should be considered an emergent phenomenon?
Does String theory say that spacetime is not fundamental but should be considered an emergent phenomenon?
If so, can quantum mechanics describe the universe at high energies where there is no ...
4
votes
4answers
863 views
Is spacetime discrete or continuous?
Is the spacetime continuous or discrete?
Or better, is the 4-dimensional spacetime of general-relativity discrete or continuous? What if we consider additional dimensions like string theory ...
13
votes
3answers
507 views
Can light exists in $2+1$ or $1+1$ spacetime dimensions?
Spacetime of special relativity is frequently illustrated with its spatial part reduced to one or two spatial dimension (with light sector or cone, respectively). Taken literally, is it possible for ...
-1
votes
1answer
132 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 ...
7
votes
4answers
349 views
Hamiltonian and the space-time structure
I'm reading Arnold's "Mathematical Methods of Classical Mechanics" but I failed to find rigorous development for the allowed forms of Hamiltonian.
Space-time structure dictates the form of ...
3
votes
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
2answers
602 views
Why does string theory require 9 dimensions of space and one dimension of time?
String theorists say that there are many more dimensions out there, but they are too small to be detected.
However, I do not understand why there are ten dimensions and not just any other number?
...
-6
votes
1answer
198 views
Speed of light is not fixed?
In my research, I found that the speed of light is not fixed. IS it true?
Namely, We know that light refracts when the medium it travels through changes. Actually, light travels in the same medium ...
3
votes
1answer
88 views
Is GPS time measuring the proper time on the mean sea level or the GPS station itself?
LeapSecond.com states:
Global Positioning System time is the atomic time scale implemented by the atomic clocks in the GPS ground control stations and the GPS satellites themselves.
Does GPS ...
3
votes
4answers
157 views
Can a huge gravitational force cause visible distortions on an object
In space, would it be possible to have an object generating such a huge gravitational force so it would be possible for an observer (not affected directly by gravitational force and the space time ...
2
votes
0answers
279 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
111 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
111 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
353 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
184 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
131 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
146 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 ...
