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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Does the actual curvature of spacetime hold energy?

My understanding of GR is that curvature of spacetime reflects the density of energy-matter. Does the curvature itself have energy? Or if energy is assigned to curvature it simply reflects the energy ...
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2answers
438 views

Excluding big bang itself, does spacetime have a boundary?

My understanding of big bang cosmology and General Relativity is that both matter and spacetime emerged together (I'm not considering time zero where there was a singularity). Does this mean that ...
9
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1answer
310 views

Our Universe Can't be Looped? [duplicate]

With reference to the Twin-Paradox (I am new with this), now information of who has actually aged comes from the fact that one of the twins felt some acceleration. So if universe was like a loop, and ...
3
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0answers
144 views

Curvature and spacetime

Suppose that it is given that the Riemann curvature tensor in a special kind of spacetime of dimension $d\geq2$ can be written as $$R_{abcd}=k(x^a)(g_{ac}g_{bd}-g_{ad}g_{bc})$$ where $x^a$ is a ...
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0answers
60 views

metric extension outside the light cone

Could anyone explain what "extending the solution" beyond the past light cone means? Say, for example, if I have a metric (no coordinate singularities), how can I extend it to the outside of the past ...
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2answers
186 views

Limit on velocity in Minkowski Spacetime geometry

Let A be a rocket moving with velocity v. Then the slope of its worldline in a spacetime diagram is given by c/v. Since it is a slope, c/v = tan(theta) for some theta > 45 and theta < 90. Does ...
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2answers
975 views

Are all points in the universe connected?

Is it true that every point in the universe is connected or could be so theoretically? If so how is this mediated? Is it through the quantum nature of the fabric of space or is it through the ...
3
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1answer
383 views

The most general form of the metric for a homogeneous, isotropic and static space-time

What is the most general form of the metric for a homogeneous, isotropic and static space-time? For the first 2 criteria, the Robertson-Walker metric springs to mind. (I shall adopt the (-+++) ...
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1answer
793 views

Spacetime and Timelike Intervals

The difference between a “timelike” spacetime interval and a “spacelike” spacetime interval can be understood in the following way: If the spacetime interval between two events is timelike, there ...
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0answers
54 views

Has Time in the Universe been found to be Discrete or Continuous? [duplicate]

I have a question, has the Universe been found to come in Discrete Quantum, like Quantum Physics or is it Continuous in Nature? I was wondering if time was like a Continuum, like the fluid in a soft ...
2
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0answers
192 views

Do we expect that the universe is simply-connected? [duplicate]

I heard recently that the universe is expected to be essentially flat. If this is true, I believe this means (by the 3d Poincare conjecture) that the universe cannot be simply-connected, since the ...
4
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1answer
523 views

Questions about angular momentum and 3-dimensional(3D) space?

Q1: As we know, in classical mechanics(CM), according to Noether's theorem, there is always one conserved quantity corresponding to one particular symmetry. Now consider a classical system in a $n$ ...
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3answers
213 views

What is the cause the light is affected by gravity? [duplicate]

I know that photons have no mass and that a photons exist only moving at the speed of light. So what is the cause that a massive astronomical object can bend a ray of light? I have two thoughts, but I ...
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0answers
75 views

What were Feynman's objection(s) to a cubic lattice universe? [duplicate]

In this video of Feynman discussing the scientific method, starting at around eight minutes and 30 seconds, Feynman describes the proposition that space consists of a cubic lattice of points (as ...
6
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1answer
227 views

A Game Of The Number Of Space-Time Dimensions

Holger Bech Nielsen, one of the founders of string theory, has apparently just played some sort of game between different potential dimensions for space-time and reached the conclusion that D4 wins in ...
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1answer
366 views

Multiverse theory and infinite individuals

I read an article about possibility of existence of multiverse and came up with a conflicting view with one of the sentences written in the article which goes as follows: "If space-time goes on ...
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1answer
2k views

Did space and time exist before the Big Bang? [duplicate]

I accept the Big Bang theory. What I can't understand is how there can be a where or when to the Big Bang if space time did not exist prior to it. Did space and time exist prior to the Big Bang?
3
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1answer
238 views

Space time a function of itself, objects in it, or both?

Is spacetime a function of itself, objects within it, or both? I am struggling to understand just what is spacetime without objects in it (or theoretical reference points) and thus no frame of ...
2
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3answers
265 views

Why are black holes special?

A black hole is where it's mass is great enough that light can't escape at a radius above the surface of the mass? I've been told that strange things happen inside the event horizon such as ...
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0answers
81 views

When is spacetime homogenous and isotropic?

When is spacetime homogenous and isotropic? For example, some metric $g_{\mu \nu}$ is homogeneous and isotropic. We now construct effective metric $$n_{\mu \nu} ~\rightarrow~ g_{\mu \nu} + ...
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0answers
135 views

Naked singularity and null coordinates

I'm trying to understand the notion of a naked singularity on a more mathematical level (intuitively, it's a singularity "one can see and poke with a stick", but I'm having troubles on how to actually ...
2
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0answers
75 views

Naked singularity and extendable geodesics [duplicate]

I'm currently trying to understand the notion of a naked singularity. After consulting books by Wald and Choquet-Bruhat, it seems that for a naked singularity one must have that the causal curves can ...
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0answers
74 views

When spacetime expands to the point where galaxy clusters are not observable, will there by any interaction?

It's my understanding that in a few billion years, clusters of galaxies won't be able to directly observe one another due to the expansion of spacetime overcoming gravity between those clusters. ...
2
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1answer
137 views

At the smallest level, how do things move?

When we see something moving on a screen it's usually just pixels being turned off at one location and turned on at another. For example: This would render a dot moving from A to C. Turn on pixel ...
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4answers
623 views

Time inside a Black hole

If time stops inside a black hole, due to gravitational time dilation, how can it's life end after a very long time? If time doesn't pass inside a black hole, then an event to occur inside a black ...
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1answer
246 views

Space time curvature real or theoretical (mathematical)?

Assuming one were in a capsule of some kind, with no window or instruments, and you swung into the gravitational field of a massive object (planet). Assuming no atmosphere to provide friction, could ...
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2answers
437 views

Einstein's theory tells us that gravity is a curve in space and time but how does that causes attraction in mass? [duplicate]

The sun is incredibly massive object and it causes the space around it to bend. This causes the planets to pulled to the sun or the planets move in an elliptical path around the sun. But I don't ...
3
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4answers
279 views

About gravity through space time curvature

Is it possible to produce virtual gravity? I mean gravity without the help of mass by curving spacetime with other effects like fast rotating objects?
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1answer
98 views

Can the fuzzball conjecture be applied to microscopically explain the entropy of a region beyond the gravitational observer horizon?

In this article discussing this and related papers, it is explained among other things, how the neighborhood of an observer's worldline can be approximated by a region of Minkowsky spacetime. If I ...
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2answers
272 views

If inherent randomness exist in quantum mechanics, what then of eternalism implied by relativity?

I am nothing but a curious layman so don't go too technical on me. First of all, I am well aware that a lot of people consider the question of determinism vs indeterminism to be unsolved and others ...
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2answers
1k views

If the universe is 3D, how is space-time like a “fabric”? [duplicate]

I have been taught that space-time should be viewed as a fabric and that objects with a large gravitational influence indent that fabric. My question is, if the singularity of a black-hole punctures ...
5
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2answers
728 views

How do Doppler Effect and Time Dilation differ?

Above, I have drawn a diagram showing Doppler Effect (here we are using space-time but in a non-relativistic sense. Time and distance are the same for A and B). Edit: I am adding a relativistic ...
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2answers
196 views

How to find a curvature of the space-time by having $g^{\alpha \beta}$ in the following case without cumbersome calculations?

The metric tensor for Fock-Lorentz space-time, $$ \mathbf r_{||}{'} = \frac{\gamma (u)(\mathbf r_{||} - \mathbf u t)}{\lambda \gamma (u) (\mathbf u \cdot \mathbf r) + \lambda c^{2} (1 - \gamma (u))t + ...
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3answers
287 views

How do we know for certain that space is expanding?

How do we know for certain that space is expanding? Let's say that in the year 1950, we observe that galaxy 1 is 5 billion light years away from us and galaxy 2 is 10 billion light years away from ...
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2answers
1k views

Spacetime around a Black Hole

If we consider the sun, then space-time is curve around it. My question is that what is the kind of curvature of space and time around the black hole. Is that space and time more curved around the ...
4
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1answer
671 views

How much time has passed for Voyager I since it left the Earth, 34 years ago?

34 years have passed since Voyager I took off and it's just crossing the solar system, being approximately at 16.4 light-hours away. How much time have passed for itself, though?
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2answers
171 views

What is the link between the metric signature of spacetime and fundamental field equations?

The signature of Minkowski spacetime is 2, as is explained here: metric signature explanation. The signature is related to the form the fundamental equations take, but I'm not totally clear on the ...
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1answer
149 views

Could light travel more slowly than the “universal speed limit”? Could this imply quantization of spacetime?

One description of relativistic effects that I've heard/read goes something like this: Everything moves through spacetime at a constant speed. An object's direction of travel through spacetime can ...
4
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1answer
214 views

Does the curvature of space-time cause objects to look smaller than they really are?

What's the difference between looking at a star from a black hole and looking at it from empty space? My guess is that the curvature of space-time distorts the wavelength of light thus changing the ...
1
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1answer
103 views

What is the age of universe? [closed]

As we know at the time of big bang as mentioned by the scientist the universe expanded faster than the speed of light. So does it mean that at that time all the particles present travelled in the time ...
0
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1answer
108 views

How much energy is needed to curve the space so the Sun will come 1 meter closer to our planet? [closed]

How much energy/work will it take if our planet is: 5.9736×1024 kg or 3.0×10−6 Suns to move Sun and Earth 1 meter closer ...
2
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2answers
187 views

Why can certain functions be absorbed into the Schwarzschild metric, while others can't?

Another question about the Schwarzschild solution of General Relativity: In the derivation (shown below) of the Schwarzschild metric from the vacuum Einstein Equation, at the step marked "HERE," we ...
2
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3answers
254 views

Vacuum-ether and spacetime

In the past you could not give an explanation for various phenomena in which there was an action at a distance, like magnetism or gravity, that occurred in a vacuum; For this reason, ether was ...
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1answer
573 views

How do photons experience time? [duplicate]

I know that as velocity approaches the speed of light the time dilation shoots to infinity as shown below. 1)So I want to know how time is perceived from the point of view of the photon? 2)Since ...
-1
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1answer
151 views

How would time duration and space distance change when we move in the speed of light? [closed]

It is possible to figure out how time duration and space distance change when we are close to the speed of light - but I am not sure what happens to them if we travel in the speed of light.
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2answers
294 views

Is this a great flaw in big bang theory? [duplicate]

Einstein said that, Time & Space cannot exists without one another. Big bang says, time didn't exist before the big bang. So the Primordial ball referred in the Big Bang theory didn't had any ...
6
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7answers
2k views

Surely space-time Curvature does not explain gravity, it just describe its effects?

In special relativity co-moving objects see the other's 4-velocity as being only temporal. When they move relative to each other they see the other's 4-velocity has rotated so that it points less in ...
2
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1answer
456 views

Is Space-Time Quantisation necessary or even meaningful?

It is believed among people working on Quantum Gravity, that space-time must be quantised at the Planck scale. Although it is very hard to verify such proposition, it is interesting from a ...
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2answers
265 views

about the 1D singularity of black hole

I saw some responses here saying that the singularity into the black hole is one dimension object so my question is : is it possible that the singularity is simply a merger of the 4 dimensions of the ...
5
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2answers
665 views

Does gravitational redshift imply gravitation time dilation?

The EEP is used to justify that if an observer on the ground shoots a beam of light towards a tower, then when the light reaches the tower, it will be red shifted. This is because of what happens in ...