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 spaghettification really happen with conditions found close to a black hole?

This website tries to explain why the term spaghettification doesn't actually occur when something gets close to a black hole. The argument of the author is that the equations we use to predict the ...
3
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1answer
37 views

Charged versus rotating black holes as different kinds of wormholes

I've heard that a maximally extended charged black hole can be a traversable wormhole to the same universe whereas a maximally extended uncharged rotating black hole can only be a wormhole to ...
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2answers
92 views

The Twin Paradox using reference frame following the ship

The Twin Paradox is undoubtedly one of the most discussed things in special relativity and have a tendency to confuse most of us. Classically, it's resolved by either stick to one of the three ...
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1answer
29 views

What is the meaning of t=infinity at the black hole horizon?

Looking at the Kruskal diagram for black holes, it seems to me that at the horizon, all free falling objects cross the horizon at the same coordinate radius and time. Does this not mean that all ...
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5answers
129 views

Why isn't time just a function of the speed of light being finite

Time is generally referred to as the fourth dimension and seems frequently to be treated as an equivalent to the 3 spatial dimensions. But then people seem to get tied in knots as to why time has an ...
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27 views

what is the real physical sense of moving only in time? is that actual question for today? [on hold]

Best regards, I'm not physicist, but knoweledge that you possess as specialists, is very inspiring for me. My question: It's simple... But possible answer could be interesting. Einstein's theory ...
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1answer
61 views

If space and time are woven into one fabric do I still exist yesterday? [on hold]

First timer, and not more than an avid layman, so forgive if the question is naive. If space and time are woven into one fabric, and when looking into a telescope at light emanating from the centre ...
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3answers
125 views

Is it possible to express various nonlinear motions as straight lines in transformed spacetime?

I am trying to understand simple examples of space-time curvature. Assume for the moment that $c$ is infinite (classical curvature due to Newton's laws). Also, I will only consider 1+1-dimensional ...
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2answers
70 views

Is there anything else than spacetime? [on hold]

Can we say that the only thing that exists is the spacetime and everything in it is expressed as curvature?
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0answers
48 views

About the entanglement and space time construction [on hold]

It seems lots of people now believe that spacetime geometry is emergent from entanglement. But according to papers, usually they only talk about how the geometry of 'space' is related with ...
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3answers
285 views

What is the exact meaning of homogeneity in cosmology?

I understand that, in general, homogeneity is the physical attribute of being uniform in composition (" of the same form at every point"), but I'm slightly confused when it is used in cosmology as ...
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1answer
22 views

Does the Relative Velocity Time Dilation of an object multiply the Gravitational Time Dilation of the object?

A moving object in free space would experience time dilation from relative velocity. A stationary object inside the gravity well of a black hole would experience time dilation from gravity. A moving ...
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2answers
128 views

What are the photon/electron consequences of matter in a gravitational time dilation?

So I saw the movie Interstellar, and it got me thinking. I won't even mention all the plot holes, but I wanted to ask about a planet orbiting a black hole. I always thought you had to travel near the ...
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1answer
42 views

Traveling Back in Time at the End of the Universe [closed]

I apologize if this question may seem fantastical. Since the heat death of universe is said to be inevitable, is it possible to travel back in time to a younger universe when the time comes? Is that ...
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1answer
118 views

If a black hole is just warped spacetime, then where is the electric charge?

I've heard Kip Thorne repeatedly state that matter is destroyed when a black hole is created, that all you are left with is distorted spacetime. "The idea that black holes are made from very ...
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0answers
8 views

Order Dimension resulting in Delayed Choice Quantum Eraser [closed]

Computers handle video (h.264) similar to how data is transmitted over the internet using TCP/IP. Data flows in packets; data chunked into smaller units. Part of the TCP/IP (and h.264) protocol states ...
2
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2answers
236 views

Is space stretched with no limits by a black hole?

Some depictions of black holes show space being warped into a singularity, with no end, e.g. as pictured below. Moreover, in Cosmos, Neil Tyson speculates with the possibility that Black Holes contain ...
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2answers
54 views

Is there a proof that space expanding produces observers at all points that see what we see?

I know that galaxies are moving away from us, and so can see that it's intuitive that if space was expanding, then the astronomical observations from Earth would be the same as at all other points in ...
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1answer
374 views

2D space-time curvature

Actually, why is the space-time curvature considered 2D plane. As 2-D dimensional space-time curve is used to explain why moon revolves around the earth stating because the massive objects wraps the ...
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2answers
90 views

How do we know the expansion of the universe is “of space” and not “in space” or “into space” or another less intuitive arrangement?

How do we know the expansion of the universe is "of space" and not "in space" or "into space" or another less intuitive arrangement? For example, what implicit and explicit assumptions underlie the ...
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1answer
52 views

Since space expands (and can theoretically contract) faster than light, does that mean that in a big crunch information could travel FTL?

Layperson here. In a theoretical big crunch with space contracting faster than the speed of light, would information be travelling faster than speed of light? Because the points A and B themselves ...
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2answers
91 views

How do we know the speed of light is constant and spacetime dilates rather than vice versa?

Some conspiracy nut was telling me that Einstein was BS and there's a giant conspiracy that he's wrong but scientists would loose all their jobs if they admitted it. Of course this is all baloney, ...
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1answer
33 views

How to calculate spacetime intervals on a spacetime diagram?

In SR, the spacetime interval is given by the metric: $ds^2=-dt^2+dx^2$ (where I set $c=1$). To calculate $ds^2$ of a worldline on a spacetime diagram, I measure $dt$ and $dx$ of the line of ...
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0answers
40 views

Time, space and matter? Apart from these what else could be in Universe?

After reading many articles and watching scientific videos, many of theories concluded that Universe is of Nth dimension. This Nth number varies some scientist said Universe is of 10th dimension and ...
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0answers
44 views

Highest symmetric non-maximally symmetric spacetime

What is the highest number of symmetries (Killing vectors) that a (4-dimensional) spacetime can have without being maximally symmetric? From what I can see, it seems to be 7 (which includes the ...
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0answers
59 views

Black Hole - Between event horizon and singularity

Dear Physics Board Users What is between the singularity and the event horizon? If the gravitation gets bigger and bigger coming nearer to a black hole, is then the gravition inside even bigger that ...
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2answers
356 views

Can light exist without spacetime?

Since the medium in which light propagates is spacetime, would light be able to exist if spacetime did not exist? Is this like one of those chicken/egg problems, or can light be thought of as a ...
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0answers
18 views

Rotating object influence on space time [closed]

We know that an object with a big mass curls the space time, but if an object starts rotating, so the experienced gravity reduces, will this make the space time curl less?
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3answers
94 views

Do gravitational waves exist at the quantum level?

Do gravitational waves exist at quantum level produced by electrons or by atoms or by molecules? If yes, which particle produces them and how are they produced? Spacetime exists at a quantum level ...
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1answer
59 views

Does spacetime exists inside matter? [closed]

Does spacetime exits inside matter like in the atom or molecule? If yes,my other question would be as electron moves inside atom, can it create gravitational waves(I know they will be very small in ...
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2answers
64 views

Does calculus work on the quantum scale [duplicate]

I have read somewhere that Leibniz championed the idea that the world is continuous as this was needed for his (or maybe Newtons) new invention (or discovery?) of calculus. But if I am not mistaken a ...
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2answers
44 views

If light travels along null-like geodesics, does that mean it remains at the same point on a spacetime manifold? [duplicate]

I know my question doesn't make sense all ready. Suppose I have points $(0,0,0,0)$ and $(1,1,0,0)$. The distance traveled is zero since $ds^2 = 0$ in this case. And light has moved from one point to ...
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1answer
39 views

If there is a point in a past set, does its chronological future interset a future set?

This post concerns the causality of spacetime $\mathcal M$. A future set $F$ is defined to be the chronological future of some set $S\in \mathcal M$, ie., $F=I^+[S]$. Similiarly, a past set ...
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23 views

How does space-time behaves between opposite gravitational pulls? [duplicate]

this is my first question in physics.stackexchange. I'll try to be more specific. I have a very basic understanding that time flows (is there a better word?) differently depending on the gravity ...
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5answers
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Why is gravitation force always attractive?

Why is the gravitational force always attractive? Is there another way to explain this without the curvature of space time? PS: If the simple answer to this question is that mass makes space-time ...
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3answers
162 views

General relativity without energy?

I am kind of new to GR but I have been familiar with the concepts for a long time, I am getting used to the mathematics just now. My question is, what would GR predict if we would have an empty ...
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9answers
5k views

If an event happens 10 light years away and we observe it here, did it actually happen 10 years ago?

I'm sorry if this question has been answered a squillion times; I need someone with smarts to explain it to me. If an event happens at a distance of 10 light years away, and we observe it here, at a ...
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2answers
104 views

Is it plausible for spacetime to be shaped something like a torus? [duplicate]

I have heard three theories for how space-time is shaped, flat, sphere-like, or saddle-like. Flat is the most likely, as all our measurements implies that space time has curvature close to 0. Is it ...
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2answers
322 views

Is the assumption that space-time has to be a continuum just a matter of mathematical taste?

Is the assumption that space-time has to be a continuum just a matter of mathematical taste? Isn't there any physical significance associated with it?
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0answers
39 views

Does quantum chromodynamics imply continuous space? [duplicate]

I am thinking it does. That's because a pillar of quantum chromodynamics is renormalization, which is itself due to the assumption that electrons are point particles (having no extent). A point ...
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0answers
40 views

Complex Space Time - Mathematical Foundations [duplicate]

I am really curious as to what the current research is in complex space time. Because in "The theory of Everything". Stephen Hawking does talk about imaginary time. Is there any mathematical ...
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2answers
1k 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 ...
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4answers
2k views

Minkowski spacetime: Is there a signature (+,+,+,+)?

In history there was an attempt to reach (+, +, +, +) by replacing "ct" with "ict", still employed today in form of the "Wick rotation". Wick rotation supposes that time is imaginary. I wonder if ...
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1answer
31 views

If an object's motion through space-time at speed $c$ corresponds to ageing, would cooling it down to slow ageing mean it doesn't move at $c$?

I get that all objects must move at the speed of light (c) in their reference frame because of the 2-part vector of space-time. For a case where the vector is pointing directly at time (because it is ...
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1answer
127 views

Physical interpretation of distances

Suppose we have a universe with only two distinguishable particles, neglecting gravitation. These particles start off next to each-other, ostensibly "touching" each-other and at rest. If it takes ...
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2answers
30 views

On a graph, can the compositions of both the x and y variables involve the unit time?

Time seems to be so fundamental to the calculations that we make, that it seems to be at the core of everything we do. Indeed, this is not just philosophically true, time is very often the x axis, by ...
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1answer
90 views

Is this statement correct or incorrect: Moving objects undergo length contraction because they appear in space-time cross-section

Why or why not? This is closely related to another question I posited here, Does it make sense to say that objects moving at relativistic velocities appear in space-time cross-section? What I mean ...
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3answers
82 views

Does it make sense to say that objects moving at relativistic velocities appear in space-time cross-section?

Let object A move at relativistic velocity relative to a frame O. In 4D space-time (Minkowski diagram) the space view of O at any given moment of its own time is a space-like hypersurface (hyperplane, ...
4
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3answers
283 views

What are the technical obstructions that prevent scale relativity from being a viable theory of quantum-gravity? [closed]

This post has been imported on physicsoverflow, see here. The astrophysicist Laurent Nottale develops since 1984 the scale relativity, which aims to unify quantum physics and relativity theory, ...
2
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2answers
93 views

Watching a LIVE stream in spaceship traveling away from earth close to speed of light

My name is Dennis. This might sound just straight up ignorant of basic concepts of physics. I was having a conversation with my friend in regards to streaming a LIVE event on earth to a spaceship ...