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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Gravity: Is there curved space besides curved spacetime?

Wikipedia: Curved spaces play an essential role in General Relativity where gravity is often visualized as curved space. Is the Wikipedia article "curved space" talking about curved space or ...
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2answers
126 views

Why isn't the Heisenberg uncertainty principle stated in terms of spacetime?

As I understand it, there are two "versions" of the Heisenberg uncertainty principle: Position-Momentum uncertainty \begin{equation} \sigma_x \sigma_p \geq \frac{\hbar}{2} \end{equation} where ...
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0answers
44 views

What does the phrase 'muons are brought to rest' mean?

I have a physics question in a text sheet. I am currently doing work on relativity where calculations of rest frames and laboratory frames are being completed. The formula: $t(\text{laboratory frame}) ...
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1answer
45 views

Can invisible galaxies exist? [duplicate]

Is it possible that there are newly formed galaxies which are moving so fast that we will can't see them, even though they exist "inside" our visible universe? I've been wondering if this could be a ...
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2answers
231 views

Why do things slow down when you move faster, rather than speed up?

I've been trying to get to grips with SpaceTime. As I understand it, we move at a set rate through spacetime. Any increase in our rate of travel through space results in a decrease in our rate of ...
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1answer
28 views

Is the term “Lagrangian density” specific to spacetime?

Wikipedia talks about Lagrangian densities here. But they never actually say whether they're just applying the concept to spacetime or that Lagrangian density is the analog for Lagrangians but for ...
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1answer
57 views

Is a black hole really a hole in space? [closed]

What if when a supernova occurs, instead of it condensing into a singularity it creates enough force to tear a hole into the fabric of space? Is a black hole just what is sounds like, a hole in space? ...
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1answer
180 views

Are we living in a Universe with 3 time dimensions and 1 spatial dimension? [duplicate]

If I said that we are living in a Universe with 3 time dimensions and 1 spatial dimension, would I be wrong? By that I mean if the spacetime interval was evaluated as ...
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2answers
135 views

Lorentz transformation paradox

I got to solve a simple exercise about special relativity when I kinda came to the conclusion it doesn't stroke with my intuition. The homework-problem The problem was about two people Sam and ...
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1answer
86 views

Space-Time and Entropic gravity [closed]

Gravity warps space-time, and Gravity can be thought of as Entropy. (Entropic gravity) So, as spacetime expands, how is space-time Entropy (or the inverse of gravity) effected? (If this is a noob ...
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0answers
56 views

With the new time cloak technology could it be possible to stop time for everything except one person

So I was just reading up on some new research on national geographic from the Cornell University scientists and it seems that they've managed to bend waves of light around something to hide it from ...
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2answers
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Why isn't the center of the galaxy “younger” than the outer parts?

I understand that time is relative for all but as I understand it, time flows at a slower rate for objects that are either moving faster or objects that are near larger masses than for those that are ...
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1answer
48 views

Does the payload of an Alcubierre drive have to be on board during the preparation phase?

I was thinking about the practical aspect of using an Alcubierre drive, assuming one existed. I'm no expert, but my understanding is that, since the destination has to be in the forward light-cone of ...
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3answers
310 views

How strong must gravity be to stretch time?

I'm not sure if this is true or not but I heard that gravity has the ability to stretch time, and I was wandering if this is true. If so, how intense/powerful does the gravitational force have to be ...
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0answers
88 views

Gravitational time dilation in changing curved space time

Imagine a portion of spacetime which is changing its spacetime curvature because of an object with great mass travelling nearby. For instance, before it was flatter, and after the object passes it ...
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1answer
57 views

Empty Space - Could we exist without it? [closed]

I have been giving empty space much thought. I imagined reaching the edge of the Universe and thought of 2 scenarios(focusing on 1): There is no more empty space 1.1 Would space extend with me if ...
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5answers
85 views

Does spacetime have a “preferred” speed/metric? [duplicate]

I read recently that spacetime has a preferred speed, c, and that all observers would agree on the speed of anything moving at c. In particular, there is nothing unique about light when talking about ...
2
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2answers
154 views

Curvature gravity and a falling apple? [duplicate]

I know very little of physics after Einstein. I am aware of that Einstein's gravity theory says that the existence of matters creates curvature of a space-time, so that our Earth orbits our Sun. I ...
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4answers
129 views

Is light amplitude spacial?

In diagrams I often see light waves depicted as little sine waves that travel through space. And often when describing polarizers, the explainer will angle their hand to show the angle of ...
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6answers
351 views

Mass without Matter?

My cursory studies of general relativity had introduced me to the concept of how gravity is associated with the warping of spacetime and that the presence of matter in space warps space and this ...
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3answers
91 views

How do we expect distance measurements to compare inside and outside the event horizon of a black hole?

I've read that as one approaches the event horizon of a black hole, time is dilated relative to time measured farther away from the event horizon (clocks tick slower near the event horizon). I've ...
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3answers
133 views

Is a metric tensor field the same thing as $ds² = -dt² + dx²+ dy² + dz²$?

I am having trouble understanding the nature of the metric tensor field on spacetime manifolds. In particular, a Riemannian manifold $(M,g)$ is defined as a real smooth manifold $M$ equipped with an ...
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1answer
101 views

Does a spacetime manifold have the structure of a metric space?

My first introduction to spacetime physics was Wheeler and Taylor's book Spacetime Physics. This book gave me an appreciation for how important the spacetime interval was for giving the distortions to ...
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1answer
133 views

General relativity: is curvature of spacetime really required or just a convenient representation?

I'm not really far into the general theory of relativity but already have an important question: are there formulations that can do without spacetime curvature and describe the general theory of ...
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2answers
83 views

Is a non-accelerating object far from a gravity source moving at the speed of light through time?

I'm trying to understand the Minkowski spacetime better. If an object is not undergoing acceleration, and is far from any large mass, does it travel maximally "fast" through time? Can we calculate a ...
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2answers
347 views

Curvature of spacetime as a real thing?

I get the curvature tensor in General Relativity, it is “just” math. Does space-time REALLY curves as a tangible thing, or is Einstein proposing a mathematical abstraction? More naively, please ...
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2answers
628 views

Spacetime geometry around two black holes

For space-time geometry we all know images like he one below. But if I were to take a neutron star and put it right next to but not touching a black hole what effect would that have on the geometry of ...
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1answer
51 views

Expanding possibilities

How does the nature of space-time and how we are able to interact within it relate to the expansion of space? If Space expansion ceased to be a constant would a body of mass still be able to change ...
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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
123 views

Is the surface of a heavy sphere bigger than $4 \pi r^2$ due to general relativity?

I am unfortunately not familiar with the mathematics behind general relativity. However, on a heavy planet (say a sphere) gravity will bend space-time in a way that an object initially in rest, will ...
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1answer
80 views

How do we presently understand time?

How do we presently understand time? Can a second be related directly to physical phenomena? What is a second really? Why are we sure that time is linear?
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1answer
143 views

Time coordinate inside black hole horizon [duplicate]

I am new to physics and was trying to learn more especially about general relativity. The Schwarzschild metric, changes the sign of the time and radial parts of the metric once we cross the event ...
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1answer
135 views

Are a black hole really connecting 2 parallel universe?

What is beyond the point of singularity in a black hole and universe expands in all the 3 $x$, $y$ and $z$ axis? So how can one thing be on top of another when we don't know where the end point of ...
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3answers
419 views

How does a rotating object cause frame dragging?

Frame dragging is a consequence of general relativity. But I don't really understand it. Of course I can find metaphors like the "honey metaphor" where stirring a honey can move the specks even if ...
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2answers
87 views

What logic did Newton give in support of using relative spatial measurements? [closed]

The crux of space-time is that it is one thing to have abstract concepts of absolute space & time,and it is other thing to describe the actual motion of an object in terms of measured changes of ...
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1answer
265 views

If space warps distort moving objects' trajectories, does it mean that static objects are immune to gravity? [closed]

If gravity is just space distortion, which affects trajectories of moving objects, then a static object (not moving, thus no trajectory) will not suffer any type of accelerating force from gravity? ...
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1answer
194 views

What is dimension and how many types of dimensions are there in the universe?

What is dimension and how many types of dimensions are there in the universe? I mean how many total dimensions are there? I have only heard about 2d and 3d. Other than these two, are there any other ...
2
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1answer
49 views

Is measurement of energy also relative? [duplicate]

From SR we know that the measurement of space and time are relative to the specific reference frame of the observer. What about measuring energy content? When an object is accelerated to a near ...
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1answer
134 views

Solving relative velocity without Lorentz transform [closed]

A train with proper length $L$ moves at speed $\frac{5c}{13}$ with respect to the ground. A ball is thrown from the back of the train to the front. The speed of the ball with respect to the ...
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2answers
238 views

Complex numbers in quantum mechanics and in special relativity

Is there a physical relation between the use of complex numbers for the wavefunction in (non-relativistic) quantum mechanics and in special relativity (as formulated in the setting of Minkowski ...
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1answer
76 views

Spacetime Metrics and Quantifying Length of a Spacetime Curve

On page 247 in Gravitation by Misner, Thorne, and Wheeler, they state: "No metric means no way to quantify length; nevertheless, parallel transport gives a way to compare length!" Three questions: ...
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2answers
134 views

Can other fundamental forces bend spacetime?

I was wondering what makes gravity so special that it bends spacetime? and if it is part of the four-fundamental forces, why or why cant the other forces bend the time space continuum?
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2answers
305 views

Visualizing GR spacetime distortion in 1+1D spacetime instead of 2D space

Usually spacetime distortion due to mass in GR is visualized as a rubber sheet distorted under some massive object, like this: source or as shown in this link. But what has always bothered me is ...
2
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0answers
95 views

Kleppner derivation of Lorentz transformation

I am reading Kleppner.(Lorentz transformations) He said,we take the most general transformation relating the coordinates of a given event in the two systems to be of the form $$x'=Ax +Bt, y'=y, z'=z, ...
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2answers
727 views

Visualizing gravity in 3D

We've all seen the depiction of gravity bending space downwards, and so attracting objects into the dent it creates, cf. e.g. this and this Phys.SE posts. That's intuitive and makes a lot of sense, ...
2
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1answer
136 views

Can two distinct events occur at precisely the same moment in time?

I am writing a simulation and am having difficulty resolving the order in which two distinct forces occur. The simulation will give different results if the forces are applied to the state in ...
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1answer
110 views

A Theory of Almost Everything? [closed]

Before I present this theory, I ask that you take the time to read this disclaimer. I do not claim to have an excellent knowledge of physics, it is actually rather limited. Therefore, I am not ...
2
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0answers
82 views

Is time depending on the observer in string theory?

I heard that in the theory of relativity the time of an action is depending on the observer. But in string theory, is the time also depending on the observer? Are strings acting according to the ...
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3answers
431 views

A sees B's clock running slow and B sees A's clock running slow? [duplicate]

This paradox is very common it seems, in which A sees B's clock running slow and B sees A's clock running slow. Here is the question a little more concretely. Let's say B flies by A's spaceship. If ...
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3answers
65 views

Space time curvature bends back

If our perception of space-time curvature is gravitation and Reduced Gravity Plane can reach weightlessness on some point of its trajectory, doesn't that mean that when Reduced Gravity plane reaches ...