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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385 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
2k 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 ...
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2answers
212 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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2answers
375 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 ...
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1answer
82 views

Are branes in 4D-spacetime moving, or are they static?

Given that a worldline, worldsheet, worldvolume, are representation in a 4D-spacetime of a point particle, a string or a brane, respectively, I was wondering if those objects necessarily have to be ...
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1answer
430 views

Time contraction

This is my first time posting on this site. I am a computer programmer that stumbled across a physics text book and have a question on special relativity. So firstly, I understand that there is no ...
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1answer
156 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 ...
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1answer
137 views

Classical black holes?

How big should the black hole be so we can consider it to be classical? When they claim that we can not probe shorter distances than the Planck length, can it be true? The argument says that, ...
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2answers
359 views

How to concile flat spacetime and big bang?

After reading How do we resolve a flat spacetime and the cosmological principle? I still remain perplex. Please excuse my ignorance and try explaining to me : I thought that basically, when we ...
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0answers
76 views

The path that a light beam takes in empty space

First excuse me if this question is very simple for you but for me and for my friend is not. Recently we were discussing what path a light beam will follow in a box moving at a constant velocity in ...
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1answer
80 views

Spacetime surgery - why are there unglueable points?

In The time travel paradox by S. Krasnikov (2002), Deutsch-Politzer spacetime is constructed by making two cuts and rejoining the manifold by gluing opposite "banks" of the cuts... omitting the ...
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27 views

A point on a disc travelling at the speed of light [duplicate]

This might be a duplicate of this. I had an interesting thought experiment: suppose that you have a disc of a 1 m radius, where a point P2 inside the disc travels at the speed of light. You have a ...
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66 views

Zeroth component of 4-momentum and relativistic energy-momentum relation

As I understand it one is forced to use 4-vectors since we require objects that transform as vectors under application of Lorentz transformations and 3-vectors do not (technically they do under ...
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1answer
33 views

How are the frequency and wavelength of electromagnetic waves affected within an event horizon?

I apologize if this has been asked previously or if my thinking is way off base, but I am inexperienced with relativity (and this is my first question on the site). I am wondering; as one (not ...
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0answers
32 views

Curisioty about universe [duplicate]

I am a bachelor student and I have a question going round my mind about the universe. Every one says that the universe is ever expanding and it is also said that the vast possible space is also the ...
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0answers
39 views

What is the space-time medium? [closed]

What is the space-time medium? According to this answer: "... fields are a fundamental part of the universe." Then why do we describe a gravity as being depressions in space-time? And why don't we ...
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0answers
29 views

Why doesn't electricity and magnetism distort space as well? [duplicate]

I think Kaluza/Klein was partly worked on to find additional dimensions to account for electric and magnetic fields. I am confused why the gravity field gets the privileged spot of distorting ...
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3answers
107 views

How/why does gravity affect spacetime? [duplicate]

I've always heard that gravity warpes spacetime, but I've never understood why and/or how. I'm only 12 so please keep it simple if possible.
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1answer
43 views

Could the rest mass be somehow considered as a very exotic kind of kinetic energy?

In its rest frame a free system of invariant mass $m$ has energy $E=mc^{2}$. That frame is moving in spacetime with a four-velocity whose magnitude is $c$. Inside my brain something asks: Would ...
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0answers
96 views

What is the justification for continuing to model space-time as a manifold in string theory?

Background The question I have arises from taking seriously the idea that, in a physical theory, one should first define all physical quantities via (thought) experiment. Justification and ...
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0answers
22 views

Time in the early universe [duplicate]

When it is said, for example, that grand unification took place "Between 10−43 second and 10−36 second after the Big Bang", how are these figures of time derived? Moreover, do these figures have any ...
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0answers
38 views

Do relativistic frames imply different realities? [duplicate]

From Einstein's principle of relativity space-time and mass are relative to the frame from which they are being observed. Now would that mean a ball moving at the speed of light wrt to earth would ...
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2answers
89 views

Is Time Dilation in GR Simply a Consequence of Curved Space?

My understanding of time dilation in General Relativity is that it is the consequence of particles traveling at the speed of causality following longer, curved paths. Since it takes longer for two ...
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0answers
41 views

Measuring distance in a spaceship moving with 0.5c [closed]

If there are a spaceship moving at a speed of 0.5c that sent a photon when an asteroid was exactly $3\times 10^8$ m away, will the distance between the spaceship and the asteroid when the photon hits ...
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1answer
57 views

Turbulence in gravitational waves

I want to understand physical meaning and possible implications of few terms often used in physics specially with regards to gravitational waves / space-time fabric Space-time fabric is disturbed by ...
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0answers
47 views

Can a photon be captured in a grid space representation at a fractional Planck position?

Consider a photon, positioned in space in a finite portion of a grid. Any point of the grid is vertically or horizontally aligned, each distanced by a Planck unit. $l_P = 1.616 199(97) × 10−35 m$ ...
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48 views

What is conformal symmetry physically?

I'm reading a paper by t'Hooft http://arxiv.org/abs/1410.6675. There is an argument in the paper that I could not understand: "Now that system, described by Maxwell’s equations, does have conformal ...
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1answer
111 views

How can space and time occur spontaneously? [closed]

In the book: "A universe from nothing" by the theoretical physicist Lawrence Krauss he mentions that space and time can occur spontaneously. Unfortunately he does not explain how. So my question is, ...
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35 views

Relativity Mapmaking in spacetime [closed]

The problem as stated: I do not know how I am supposed to map this. The instructions don't make sense to me and the textbook is really un-helpful. This is the map that I have to draw this on. I ...
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0answers
43 views

Could time consistently flow in reverse?

Could time consistently flow in reverse? Here is an article about the subject of quantum asymmetry of time and space. Thoughts?
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58 views

Could a perfect vacuum exist at the boundary of the universe?

Space is not truly a vacuum because of our observation of quantum foam, but if causality does not exist outside our universe, could that mean that quantum foam cannot exist outside our observable ...
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1answer
44 views

light in black holes and space time

I watched videos, read articles, learned a lot about black holes and got confused: Lets say that a light is doing its way inside a black hole toward the singularity. If it's inside the event ...
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0answers
47 views

If black hole is equivalent to a planet of same mass for a distant observer, then why does 'excess radius formula' require uniform mass density?

I understand that the spacetime curvature of a non-rotating, uncharged black hole is identical to that of a planet with same mass/energy for an observer at a distance farther than the radius of the ...
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1answer
71 views

What is the physical significance of taking derivative with respect to proper time?

I would like to know if there is any physical significance associated with the derivative of a quantity with respect to proper time or is it just a mathematical trick. Since proper time is measured in ...
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0answers
149 views

If gravity is due to curvature, how does gravity work in situations with no curvature?

The strength of the gravitational field falls off as the inverse square of the distance from a spherical source. It only falls off as the inverse of the distance from an extended cylindrical or line ...
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1answer
91 views

Why do we introduce the idea of manifold in GR books

After reading Timaeus answer here: http://math.stackexchange.com/questions/1302672/compound-map-in-manifolds, I got an idea that spacetime we usually talk about in GR can be described as a manifold. ...
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2answers
51 views

Time dilation and freefall (follow up and simplification) [closed]

A person is four miles up in the atmosphere, and freefalls towards earth. Another person is standing on earth, watching them come down. During this period of freefall, which person experiences more ...
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3answers
274 views

How can the past, the present and the future coexist at the same time? [closed]

We all heard it many times, the theory of Time suggest it is parallel rather than being linear. This leaves the door opened for alternate realities and well, immortality. However, even after reading ...
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0answers
44 views

Spacetime as a coset of a symmetry group

In the introduction to his nice PNAS paper on symmetry, David Gross said Einstein’s great advance in 1905 was to put symmetry first, to regard the symmetry principle as the primary feature of ...
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0answers
46 views

Proper time and asymptotic flatness

I'm trying to understand the concept of asymptotic flatness in general relativity, and came up with the following question: If the proper time $\tau$ is infinite for a timelike geodesic, does it mean ...
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0answers
75 views

How does bending in space-time caused by mass energy translate into acceleration of object? [duplicate]

Let say we have 2 similar apples separated by a distance apart, just their mass energy alone is sufficient to cause bending in the space-time. I think it is this bending in the space-time that cause ...
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1answer
121 views

Can you shine a laser on an object that has fallen into a black hole? [duplicate]

I've been having a small back and forth on another website about the nature of objects that fall into black holes. I know that they never reach the event horizon from the perspective of a distant ...
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4answers
162 views

Which tensor describes curvature in 4D spacetime?

I heard these two statements which don't work together (in my mind): In 4D spacetime the curvature is encoded within the Riemann tensor. He holds all the information about curvature in spacetime. ...
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0answers
29 views

Fixed background theories which feature lorentz invariance?

Are there fixed background theories that also display lorentz invariance? Could be with lorentz invariance being true only approximately at some limit... Realized we can still arrive at time-dilation ...
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0answers
25 views

Do all black holes have the same mass density? [duplicate]

I have been reading about black holes in Stephan Hawking's 'A Brief History of Time'. Then I was reading more about it on Wikipedia; I am making a school project on it. I do not really remember what ...
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63 views

Is there a model of the universe with the transfinite (space)time?

In mathematics there is a concept of ordinal numbers where one can count to infinity and beyond. For example the least number that is greater than all the finite numbers is denoted by $\omega$. Such ...
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0answers
22 views

Is the position of matter discrete in universe? [duplicate]

In computer, for example, if we use integer to represent position of objects, position can be (0,0) , (3,5), but not in (1.5,3.5). In real world, there are something that is discrete, such as atomic ...
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1answer
55 views

Describing the shape of a singularity

Hawking and Ellis write about the difficulty of describing the shape of a singularity when presented with a manifold that has curves of finite length that don't reach a point in the manifold. ...
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1answer
54 views

According to some theories space is constantly expanding but at what granularity? [duplicate]

One idea from cosmology is that galaxies are all moving away from each other. Naively this could be taken to mean that they are expanding into something. Popularly this could be seen as them moving ...
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1answer
139 views

Is there a minimum distance?

I would imagine there is no limit to how small space can get. Is this correct? I am aware of planck's constant, but cannot objects be closer than Planck's constant is short? Perhaps this question is ...