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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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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1answer
93 views

Black hole merger orbital speed

If a ship is close to a black hole and we see it getting slower to the point if could see them not for red shift would almost stop moving. Then how fast is the little black hole moving in this video? ...
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50 views

See behind the black hole

Why in this video does the 2nd black hole appears to change size and appear larger the farther away it gets? How can you see behind it? http://www.youtube.com/watch?v=ENd8Sz0AFOk
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39 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
37 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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1answer
46 views

Acceleration in Space

Lets assume a body with a certain mass is in a region of space that has zero $g$ (or pretty close to zero $g$). Would acceleration in a straight line produce $g$-forces? Would that mass acquire ...
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0answers
32 views

Is there a fundamental frequency of time? [duplicate]

Our eyes and brains can only perceive frequencies as individual frames up to some limit, after which we perceive the motion to be "continuous." Is there such a frequency of time? Along the same ...
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2answers
63 views

Relative motion of an arbitrary volume of space ( is space static or dynamic?) [closed]

Do physicists consider space as being "static" or "dynamic" ? Hi I asked a question about whether space can move, and from the answer, I realized I was not precise enough and did not actually ask ...
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2answers
66 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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0answers
28 views

Is there any reason (other than convenience) to assume the universe is paracompact?

In this discussion on MathOverflow, it is mentioned that the universe, being a Riemannian manifold, must be paracompact. But is there any reason to assume the universe is globally 'small enough'? In ...
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4answers
157 views

What allows us to assume spacetime is flat when no normal matter is present?

Dark matter causes a bend in spacetime. We see this through gravitational lensing. But what allows us to assume spacetime is flat when no normal matter is present? Why can't we say that dark matter ...
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3answers
98 views

Is time created by movement through a higher dimensional object? [closed]

In a comment I read on this page, someone mentions a theory where time is created by moving through and slicing "moments" of a higher dimensional object. For analogy, a 2-D creature living on a plane ...
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1answer
130 views

What is the deep reason of length contractions and time dilations? [duplicate]

In the theory of relativity, a spacetime can have length contractions or length expansions and time can have time dilations or expansions. In theory of special relativity, any physical object with ...
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0answers
27 views

Length Contraction and Acceleration [duplicate]

Say that I have a spaceship that needs to travel 490 lightyears to the exoplanet Kepler 186f. Half the way of the trip the spaceship accelerates with a constant acceleration of 1G and on the other ...
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2answers
104 views

What is the basic concept of four-dimensions in physics?

I have been reading a few books lately and browsing the internet for an explanation on the concept of "four-dimensional" space (or, space-time, as some of them have been calling it). But, what those ...
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0answers
78 views

What determines time flow? (arrow of time) [closed]

I've been reading up on the arrow of time and there is one thing that is being omitted from every explanation that I've found: time flow. I am rewording this question to make it clearer. From the ...
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0answers
39 views

Special Relativity and Space travel [closed]

I'm doing a science project on space travel where I have to include a part about special relativity and how time acts when you're traveling in space with high speed. I'm not really sure where to start ...
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1answer
81 views

Why quantum fluctuation existed before big bang?

I read somewhere that quantum fluctuation can give rise to a big bang and thus the creation of a universe which we know today, where do these quantum fluctuations come from if space is only created ...
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1answer
95 views

do we live in 3.5 dimension? [closed]

After watching interstellar movie i came to know that time is 4th dimension and watch some videos and read articles which says there is there is around 10 dimension(11 also). As x,y,z are 3 dimension ...
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0answers
134 views

If spacetime is discrete: what would space expansion mean? [closed]

How is space expansion explained in physical theories where spacetime is quantized? Discrete spacetime is claimed in some candidate theories of quantum gravity like loop quantum gravity and algebraic ...
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1answer
120 views

F=ma is true in an accelerating coordinate system [closed]

There are plenty of similar topics about the physical or intuitive meaning of the equivalence principle or statement such as ''laws of physics are true in every frame of reference''. Usually answers ...
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1answer
93 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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0answers
41 views

Looking out from the inside of an Alcubierre bubble

Disregarding the difficulties in achieving a warp "bubble" as per Alcubierre's theoretical warp drive, as far as I understand it the geometry of the spacetime that arises is mathematically sound. ...
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1answer
72 views

Do small objects really exert a gravitional force? [duplicate]

StackExchange articles such as "What is gravity and what causes objects to act against it" seem to state that the gravitational force is only exerted by very large celestial objects that bend the ...
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7answers
253 views

If space is “expanding” in itself - why then is there redshift?

The "kid's" way of understanding the expanding universe is that: "space" is totally "ordinary", and all the galaxies are expanding through it (like an explosion). Of course, that's wrong. The usual ...
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0answers
49 views

Size of the universe from CMB?

The CMB is almost 13.8 billion light years away in every direction so the diameter of the visible universe as we actually observe it is 27.6 billion light years, twice the distance light traveled over ...
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4answers
119 views

What does “the fabric of space and time” actually mean? [closed]

I've heard the term "the fabric of space and time" in both physics and science fiction, and although I know it has something to do with general relativity, I don't understand what, specifically, ...
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0answers
19 views

Question about Gravitational Deflection of Light

I was wondering if deflecting light around two black holes or more would cause light to come back to the original spot. Such as if light from today traveled near a black hole so it was deflected 50° ...
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1answer
63 views

Gravity: Why Do things fall to Earth? [duplicate]

If gravity is in reality spacetime geometry why when I drop an object on the surface of the Earth does it fall to the ground? Does spacetime push it?
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5answers
939 views

How does “curved space” explain gravitational attraction? [duplicate]

They say that gravity is technically not a real force and that it's caused by objects traveling a straight path through curved space, and that space becomes curved by mass, giving the illusion of a ...
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4answers
136 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
39 views

What would be seen when a ship is accelerated to relativistic speeds and back down? [duplicate]

Consider this scenario: Two identical space ships, the SS Observer and the SS Accelerator. Each ship is indestructible and contains an indestructible clock. They begin positioned 1 light-day away ...
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0answers
48 views

Questions arising from the presentation of “Schild's ladder” in “Gravitation” (Misner, Thorne, Wheeler)

MTW, p. 248, presents a description of "Schild's ladder" construction which I quote here extensively enough for referencing some subsequent questions. A. Transport any sufficiently short stretch ...
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1answer
96 views

Spacetime curvature effect on chemistry

Do current chemistry / astrophysics / stellar chemistry calculations include the effects of the curvature of spacetime on chemical reactions? For example, the heat transfer from a point closer to the ...
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1answer
92 views

Relativistic explanation of Radiation

I ask this question again in a simpler, shorter form. Maxwell's equations can be derived with Special relativity starting from the Coulomb's law. Therefore all the phenomena of classical ...
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0answers
28 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
26 views

What would be seen if a firing laser is accelerated to relativistic speeds then back?

Consider this scenario: Two identical space ships, the SS Observer and the SS Accelerator. Each ship is spherical with a band of mirrored material around the outside and contains a green laser. They ...
55
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8answers
5k views

Turbulent spacetime from Einstein equation?

It is well known that the fluid equations (Euler equation, Navier-Stokes, ...), being non-linear, may have highly turbulent solutions. Of course, these solutions are non-analytical. The laminar flow ...
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1answer
80 views

Geodesic equation (free particle)

How to find a coordinate system whose geodesic equation does not have the "Christoffel symbol" term? (i.e. free particle - generalized Newton's second law.)
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2answers
62 views

Minkowski geometry definition

The general relativity is based on Minkowski geometry definition with its special properties. The general relativity cant be approved wihout Minkowski geometry definition. Why Minkowski geometry is ...
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1answer
81 views

Does limiting to infinity violate laws of physics?

It is noteworthy that one cannot simply divide any length more than the Planck-length. If so, one cannot simply divide any volume more than the $(Planck-length)^3$. So if I want to find the limit of ...
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0answers
34 views

Why is it useful to study spatially inhomogeneous spacetimes? [closed]

There are many scholars who have dedicated their efforts towards finding solutions to the Einstein Field Equations that are spatially inhomogeneous. Current cosmological observations indicate that on ...
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4answers
82 views

How does curved spacetime cause motion revisited

There was a previous question titled "Why would spacetime curvature cause gravity?" asked March 10, 2014. The answer given was essentially that since the time component of an object in curved space ...
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2answers
193 views

Is the popular explanation given for gravity in General Relativity misleading? [duplicate]

In most popular explanations of General Relativity, both in print and film/television, gravity is demonstrated using an example of a 2 dimensional plane being flat, then when putting a heavy object in ...
2
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1answer
331 views

Do multiple dimensions exist? [duplicate]

I came up with this line somewhere: To properly experience $n$ dimensions the retina of the organism should be at least of $n-1$ dimensions. And human eye has $2$ dimensional retina, so we ...
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0answers
53 views

Is spacetime elastic or inelastic [closed]

If spacetime is nonelastic and the zero mass curvature is zero than local perturbations of spacetime by mass describable as circumference -2r(pi)is less than zero must be balanced by areas of ...
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2answers
78 views

Are there continuous spacetime events?

What is the formal definition of an event? According to Wikipedia, "an event is a point in spacetime (that is, a specific place and time) and the physical situation or occurrence associated with it." ...
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1answer
68 views

Numerical relativity in causally pathological spacetimes

To perform numerical relativity simulations one almost universally adopts the so called "3+1" approach: spacetime is divided up into spacelike slices, each representing a "moment in time". After some ...
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1answer
58 views

Can blue light encounter slower clock time over red?

I am aware that matter with mass experiences dilation and photon is massless. there is no inertial frame where photon is at rest. However, wave form of light has momentum and energy. Blue light wave ...
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0answers
27 views

Are only measurements registered as events?

When we measure an electron or some other system behaving quantum mechanically, we observe something. Now, this can be called as an event in relativity terms meaning if we live in 1-D spacetime, only ...