A theory that describes how matter produces and responds to the geometry of space and time. It was first published by Einstein in 1915 and is currently used to study the structure and evolution of the universe, as well as having practical applications like GPS.

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are pinch-off bubbles valid solutions to general relativity?

are bubbles of spacetime pinching-off allowed solutions to general relativity? With "pinch-off bubble" i really mean a finite 3D volume of space whose 2D boundary decreases until it reaches zero and ...
3
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4answers
580 views

White Holes and Time-Reversed Oppenheimer-Snyder collapse

So, the canned explanation that I always hear about why the white hole solution of the extended Schwarzschild solution is non-physical is that "The matter distribution cuts off the white hole ...
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1answer
2k views

Why is light described by a null geodesic?

I'm trying to wrap my head around how geodesics describe trajectories at the moment. I get that for events to be causally connected, they must be connected by a timelike curve, so free objects must ...
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1answer
308 views

Gravimagnetic monopole and General relativity

Review and hystorical background: Gravitomagnetism (GM), refers to a set of formal analogies between Maxwell's field equations and an approximation, valid under certain conditions, to the Einstein ...
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1answer
228 views

Will a black hole increase the speed of sound above the speed of light in this medium

For the sake of this question we are inside the EH and a sound wave enters from our perspective as the sound moves closer to us at the EH would it speed up. Specifically how would the extreme ...
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3answers
286 views
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1answer
197 views

quantum curvature

If a state can be a superposition of energy states, and mass equals energy (special relativity), and mass curves space-time (general relativity), then could we say that space-time around a quantum ...
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2answers
320 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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2answers
357 views

fourth rank tensor for stress energy

The Weyl tensor equates the Riemann tensor in vacuum $$ C_{\mu \nu \eta \lambda} = R_{\mu \nu \eta \lambda} $$ So it makes me wonder about the tensor $$T_{\mu \nu \eta \lambda} = C_{\mu \nu \eta ...
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7answers
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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 ...
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2answers
294 views

Effect of gravitation on light

Einstein predicted that the gravitational force can act on light. This was verified in one solar eclipse that light from a star near to the sun's disc bent due to Sun's gravity as predicted. Since ...
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2answers
244 views

Are we going to be able to travel trough space deforming the space-time?

I'm not talking about the speed of the spaceship. If we can deform space-time we needn't any type of propulsion. And how can the travel affect to it's pilots? Can they survive?
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1answer
743 views

Is 4-volume element a scalar or a pseudoscalar in special relativity?

In general relativity 4-volume element $\mathrm{d}^4 x = \mathrm{d} x^0\mathrm{d} x^1 \mathrm{d} x^2\mathrm{d} x^3$ is clearly a pseudoscalar (or scalar density) of weight 1 since it transforms as ...
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236 views

How can things at the event horizon slow down and appear to stop to a remote observer?

So they say the remote observer will never see anything fallen to the black hole, because any object will slow down as it gets closer to the event horizon and eventually stop to stay there forever. Am ...
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1answer
114 views

Are there any well-known theories successfully unifying the inertial and gravitational mass?

From what little I know of general relativity, the equality of inertial and gravitational mass is an axiom of the theory. I suspect that this precludes GR from unifying them in the same sense as ...
3
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1answer
145 views

How can a deSitter space have finite size?

a deSitter space is a maximally symmetric solution of Einstein equations, I have some problem picturing one thing: this space is past and future (time) infinite but spatial slices have finite size, ...
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0answers
75 views

Reference request: FLRW with k>0, dust, and positive cosmological constant

The exact solution representing a FLRW universe with $k>0$ and dust (p=0), and $\Lambda=0$, is described by a cycloid. What is the exact solution for dust, in the presence of a positive ...
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5answers
530 views

How important is the cosmic censorship conjecture?

I would like to know how important the cosmic censorship conjecture is? Should a quantum theory of gravity must obey this? It was never rigorously proved in classical GR too. What would be the ...
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1answer
131 views

Why does the cosmic censorship conjecture hold so well?

Why does the cosmic censorship conjecture hold so well? Penrose proposed spacelike singularities and closed timelike curves are always hidden behind event horizons in general relativity. His ...
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1answer
429 views

geometry inside the event horizon

I'm trying to understand intuitively the geometry as it would look to an observer entering the event horizon of a schwarszchild black hole. I would appreciate any insights or corrections to the above. ...
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1answer
1k views

What's next after Higgs Boson discovery? [duplicate]

Possible Duplicate: Practical matter of the Higgs-Mechanism As everybody knows that the Higgs Boson was discovered on July 4th,2012, I am so curious about it. What are the possible ...
2
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0answers
83 views

quadripolar moment in curved space

So, i'm going over the Thorne's derivation of the quadrupolar radiation term, and they write the core term as: $$ \frac{3 r_i r_j - 2 r^2 \delta_{ij}}{4 r^5} $$ But if i try to obtain this term by ...
3
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4answers
240 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 ...
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4answers
360 views

Formulation of general relativity

EDIT: I think I can pinpoint my confusion a bit better. Here comes my updated question (I'm not sure what the standard way of doing things is - please let me know if I should delete the old version). ...
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3answers
307 views

How to connect Einstein's Special Relativity(SR) with General Relativity(GR)?

How Einstein's SR becomes GR? $$ds^2=dr^2-c^2dt^2,$$ $$ds^2=g_{\mu\nu}dx^{\mu}dx^{\nu}.$$ When the $s$ is constant $ds^2=0$, isn't it true? How to connect Einstein's SR with GR? What is the ...
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1answer
72 views

Tower redshift paradox

If photons are emitted at intervals a, from the top of a tower of height $h$, down to earth, is this formula correct for the intervals b in which they are received at earth? $b=a(1-gh/c^2)$ If so, how ...
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2answers
631 views

Where do I start with Non-Euclidean Geometry?

I've been trying to grok General Relativity for a while now, and I've been having some trouble. Many physics textbooks gloss over the subject with an "it's too advanced for this medium", and many ...
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2answers
127 views

What is gravitational speed for a black hole? [duplicate]

Possible Duplicate: What is the escape velocity of a Black Hole? This is gravitational speed for earth: $$v=\sqrt {g_{e}r}.$$ What is gravitational speed for a black hole? I want an ...
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1answer
162 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 ...
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2answers
200 views

what is relation between time and space in general relativity?

there is a relation between time and space in special theory of relativity: $$t^2c^2-L^2=\tau^2.c^2$$ what is relation between time and space in general relativity?
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1answer
163 views

Understanding the E=MC2 for multiple objects

Im actually not a very good at physics, but I was playing with this functions (just for fun and education, so this question might end at the Scifi forum), and would like to know if this logic is ...
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3answers
1k views

Alcubierre Drive - Clarification on relativistic effects

On the Wikipedia article on the Alcubierre drive, it says: Since the ship is not moving within this bubble, but carried along as the region itself moves, conventional relativistic effects such as ...
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0answers
228 views

How is the poincare conjecture(and perelman proof) helpful in studying the properties of the universe?

Can someone tell me how the poincare's famous conjecture or its proof by perelmen can be helpful in deciding some properties like the shape of the universe?
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2answers
327 views

length contraction question

we know from eintein's theory of relativity that lets say, a ruler is travelling to a speed if light, then we can say that the ruler (from our view as observers) has shorten. but why, lets say we have ...
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1answer
136 views

extracting energy from cosmological expansion

This question is a more concrete reincarnation of an old question about energy conservation in GR. Are there mechanisms to extract energy from the cosmic rate of expansion? putting some extremely ...
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1answer
81 views

Space station gains enough mass to lose orbit?

I.S.S is constantly being improved (add-ons). Will the space station need to be moved to a higher orbit at some point?
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1answer
130 views

Can we develop in the future a technology that can send a message to the past? [duplicate]

Possible Duplicate: Is it possible to go back in time? I believe that everything is possible in this world. If that can be done then why aren't we receiving any message from the future.
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1answer
149 views

How do gravitational waves sustain and propagate large scale spacetime curvature?

I understand that gravity in GR is a manifestation spacetime curvature dictated by the field equations by the principle that objects follow the geodesic path in spacetime. And, I get how ...
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3answers
369 views

Theory that gets rid of dark matter/energy

Is there any physics theory that either groups together gravity and dark energy/dark matter or eliminates dark energy/dark matter by modifying standard understanding of gravity or any force? If so, ...
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1answer
150 views

Calculating a Deflection of Light Integral from Einstein's 1907 paper on Gravity and Light

$\frac{1}{c^2}\int_{\theta=-\pi/2}^{\theta=\pi/2} \frac{kM}{r^2}cos\theta ds=2\frac{kM}{c^2\Delta}$ An observation: $\cos\theta=\frac{\Delta}{r}$
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1answer
625 views

Energy conservation and center-of-mass inertial frames

For a given set of fast-moving objects in empty space, the maximum mass-energy that can be extracted by using only interactions between objects in the set (e.g., colliding all of them together) is ...
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2answers
412 views

ergosphere treadmills

suppose you place a number of rotating black holes in linear sequence (rotating around the same axis) between two stars at distance $d$ (assume as tightly packed as practical for purposes of ...
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1answer
392 views

The Strength Of A Black Hole

Does the gravitational strength of a black hole at its singularity change the more it pulls things into it?
2
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1answer
228 views

Can a charged black hole interact via electromagnetism? [duplicate]

Possible Duplicate: Detection of the Electric Charge of a Black Hole Light cannot escape from a black hole. However light is also interpreted as the carrier of the electromagnetic force. So ...
0
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1answer
109 views

Does General Relativity require that Spacetime must be a orientable? [duplicate]

Possible Duplicate: Can spacetime be non-orientable? Apart from the constraints put on the topology of spacetime by QFT (Parity For example), if the global topology of a universe is that of ...
12
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1answer
711 views

Why is there no dynamics in 3D general relativity?

I heard a couple of times that there is no dynamics in 3D (2+1) GR, that it's something like a topological theory. I got the argument in the 2D case (the metric is conformally flat, Einstein equations ...
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4answers
684 views

Why should one expect closed timelike curves to be impossible in quantum gravity?

From the Wikipedia article, it seems that physicists tend to view closed timelike curves as an undesirable attribute of a solution to the Einstein Field Equations. Hawking formulated the Chronology ...
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1answer
1k views

What is the stress energy tensor?

I'm trying to understand the Einstein Field equation equipped only with training in Riemannian geometry. My question is very simple although I cant extract the answer from the wikipedia page: Is the ...
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3answers
199 views

Is the gravity we feel in our everyday life mainly curvature of the time coordinate?

The question is pretty clear I think. I only started learning GR but the results I've seen so far and from some lectures I saw from Leonard Susskind on YouTube I understood that for low energy ...
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1answer
223 views

A Query on the Trapped Null Surface

A a compact, orientable, spacelike surface always has 2 independent forward-in-time pointing, lightlike, normal directions. For example, a (spacelike) sphere in Minkowski space has lightlike ...