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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203 views

How does LIGO account for curvature of Earth?

Using an earth curvature calculator, I found that at a distance of 4 km (the length of LIGO's arms), more 1.26 m is hidden by the horizon. When constructing LIGO, did they account for the curvature of ...
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48 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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1answer
370 views

How is it that distortions in space can be measured as distances? [duplicate]

Imagine yourself and anything you're able to perceive to be drawn onto a rubber band. Any means of determining distances would be affected by the stretching/contracting of the rubber band. The ...
3
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1answer
62 views

Is all energy quantised?

I'm wondering if all energy is quantized? Can a particle with kinetic energy have any value of kinetic energy or is kinetic energy also quantized? My reason for asking this is that if a particle is ...
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1answer
55 views

Does gravitational time dilation have a direction?

I understand that higher the gravitational potential, "slower" time runs. So a clock on international space station will run "faster" than a clock at sea level. However does it matter where the ...
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1answer
79 views

Meaning of $R=0$, $R_{ab}=0$. $R_{abcd}=0$

First let me state some definition The Einstein tensor is given by \begin{align} G_{\mu\nu} = R_{\mu\nu} - \frac{1}{2} g_{\mu\nu} R \end{align} and note that \begin{align} G^{\mu}_{\phantom{\mu} \...
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120 views

Does gravity have two directions?

Imagine a particle that interacts strongly with gravity, but not with any of the other forces, and does not interact with normal matter (this may be analogous to the description of dark matter, I'm ...
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1answer
55 views

Is there any description of a mechanism of curving of space-time fabric

Most of us know about famous line - "mass tells space how to curve and space tells mass how to move". There is quantitative description of the curving and its effects in Einstein's theory. Mass and ...
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49 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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2answers
73 views

If black holes warp space-time infinitely, does that mean space-time goes on infinitely in all directions?

My thoughts are if a black hole warps space-time infinitely then does that mean space-time goes on in all directions infinitely? Maybe (probably) my understanding of space-time is not great, if ...
3
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40 views

Why do some stars actually produce “Gamma ray bursts”?

I looked it up but I haven't found any explanation as to why some stars produce them, I understand that collapsing and merging stars produce them, but my question is why is the energy concentrated in ...
3
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1answer
95 views

What am I doing wrong while proving time dilation using Minkowski space-time diagram?

Consider two events A and C. They have same value of x' and time interval between them is $\triangle \tau$. This is the proper time interval between the events. The ...
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32 views

How can you find the $u$ using time dilation if you only know $\Delta t_o$? [closed]

I've come across two problems dealing with time dilation now that ask how fast should an astronaut go in order to travel EG: 400 LYears in 10 Years. What I can not wrap my head around is how this is ...
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1answer
114 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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0answers
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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1answer
122 views

Why does time stop its flow? [duplicate]

According to the "list verse" time gets to a pause when someone or something travels at the speed of light. But a question still lies in my mind, if time always travels forward and does not stop at ...
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90 views

Is it known what the necessary and sufficient conditions are for the existence of a “3+1 split” (by means of a foliation) of a (Lorentzian) manifold?

When trying to do physics on a more general pseudo-Riemannian manifold we want to require that there is a foliation of this manifold into three-dimensional subspaces. By this I mean we would like to ...
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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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2answers
75 views

Space-time and gravitational fields

I am reading a book by Carlo Rovelli, Seven Brief Lessons On Physics, and would like to check if I have understood something. Apologies if my question is badly phrased, feel free to edit where ...
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1answer
99 views

Evaporating black hole Penrose diagram

The context for this is the diagram from From where (in space-time) does Hawking radiation originate? - the more I think of it, the less it makes any sense ) This particular question is about ...
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1answer
49 views

What if--the universe is closed and very small? [duplicate]

Closed--you can come back to where you started by going all the way in one direction. Very small--the expansion of the universe, if inevitable, will not be able to prohibit this kind of round-about ...
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2answers
136 views

Does time have a minimum 'speed'?

Sorry if this is an ignorant question, but I've been having some trouble grasping some concepts related to time dilation. So far, my understanding of the concept says that if I am in a certain frame ...
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0answers
59 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
104 views

Big Bang Quarks Travelling at Light Speed [closed]

When I think of an explosion it lasts a fraction of second. When the entire mass of the universe explodes how much time passes before the perfect sphere slows from traveling at/near the speed of light ...
3
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1answer
101 views

Universe vs Multiverse. Time and Space

Wikipedia defines a multiverse as a hypothetical set of finite and infinite possible universes. Similarly, it defines the Universe is as "all of time and space and its contents". On the surface, ...
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1answer
197 views

What is the meaning of the particle horizon in conformal diagrams?

I'm reading "Physical Foundations of Cosmology" (Mukhanov) and in Chapter 2.3 conformal diagrams get introduced. They seem to be a (graphical) tool to understand the causal structure of the universe. ...
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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 horizon,...
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1answer
77 views

Most efficient speed to travel at, considering the effects of time dilation; according to Special Relativity

I understand that this question has recently been asked, and yet not answered to the greatest and most understandable extent, but I was wondering whether travelling at the speed of light is really the ...
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1answer
62 views

How is Zeno's Dichotomy Paradox resolved according to physics? [duplicate]

I always thought of quantum space and quantum time as a solution, but then i figured out that "quantum space-time" is not actually true(yet). I've also heard of the calculus approach and limits, but i ...
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1answer
39 views

Why do we look at non-flat geometries in Cosmology?

In Cosmology we use the Robertson-Walker-Metric which follows from the cosmological principle & mathematics. This metric leaves three cases for a possible curvature (or geometry) of space (not ...
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1answer
83 views

Mass and time relativity [duplicate]

In the space between galaxies in the absence of matter, would time run faster than inside a galaxy? A black hole can slow time. Is there a cosmic opposite of that effect on time? Like the following ...
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1answer
56 views

Do wormholes only allow FTL travel in “folded” spacetime?

Faster than light wormhole travel depicted in science fiction and in popular science articles seems to assume that rather than being flat (with dimples centered around large masses), spacetime is ...
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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 ...
2
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1answer
78 views

Gravity is Instant [duplicate]

Without being able to manipulate gravity. How do we know that gravity is restricted to the speed of light? or gravitational effects from an exploding star would be felt (if we were near) before we ...
1
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1answer
114 views

Theoretical implications of multidimensional Time [duplicate]

While the idea of extra spatial dimensions has been around for quite a while now, is there a possibility or any theory which proposes extra time dimensions? If so, what could be theoretical ...
3
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1answer
59 views

Why mass can distort spacetime? [duplicate]

Ok I knew nothing about the definition of mass but I do know that mass can be converted into energy and vice versa. And I read that anything that have stress, energy and momentum will bend ...
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1answer
79 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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1answer
118 views

Gravitational Time Dilation vs Acceleration Time Dilation

I might be a little dense to this subject, but I would like to ask a question relating to this one ( Is gravitational time dilation different from other forms of time dilation? ) but asking if this ...
2
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0answers
43 views

Does entropy flatten spacetime?

Forgive me if this is a non-question, but I could not find anything regarding this. I only know parts of GR, and I am not familiar with the math. Since energy and matter density curve spacetime, ...
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0answers
151 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
92 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. ...
3
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2answers
185 views

Why time slows only for moving object and not stationary observer? How the “stationary” & “moving” are decided? [duplicate]

Explanation for the questions in the title: According to the the (special theory of) Relativity, if an observer is stationary and sees a fast moving object then time runs faster for the observer ...
0
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1answer
57 views

Using wormholes to see out of the visible universe

As is commonly known, using our telescopes, we can only see so much of the universe because of its faster than light expansion. However, although under normal circumstances it is impossible to see ...
5
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2answers
91 views

Is space expanding equally in every direction?

Does space expand equally in every direction, so that it draws a perfect sphere or is expansion asymmetric, so it creates "bubbles" (when seen from the outside)?
0
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1answer
94 views

Geometry of spacetime and spinor bilinears

In this paper (http://arxiv.org/abs/0704.0247) p.20, the author says in the section titled Geometry of spacetime the following: In order to obtain the spacetime geometry, we consider the spinor ...
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0answers
43 views

Direction of Gravity [duplicate]

I ran into a pde that has a parameter in it that can be either $+1$ or $-1$. They say the $+1$ case corresponds to gravity pointing upwards, whereas the $-1$ case applies to gravity pointing downwards....
0
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1answer
95 views

Bigger Galaxies = Faster Clocks [closed]

There are in all about 100 known galaxies with blueshifts out of the billions of galaxies in the observable universe. We have Blue-shifted galaxies are in our own local group, and are all bound to ...
1
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3answers
292 views

Time Dilation Equals Red Shift looking in or blue shift looking out

We can see the center of our galaxy. With more density near the center of our galaxy is red shifting observed from our perspective? From the center of the galaxy looking at us would a blue shift be ...
0
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1answer
66 views

Is an event formally a 4-vector? [duplicate]

An event is a 4D point in spacetime. At every point in spacetime there is a tangent space. 4-vectors live in the tangent space. One can contract two events using a metric tensor. Is there a process ...
0
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1answer
51 views

Empty space and velocity

If there was a universe without anything in it except you in a space rocket how you would you know what your velocity if you kept the engine on?