Tagged Questions

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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Did space and time exist before the Big Bang? [duplicate]

I accept the Big Bang theory. What I can't understand is how there can be a where or when to the Big Bang if space time did not exist prior to it. Did space and time exist prior to the Big Bang?
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Can the fuzzball conjecture be applied to microscopically explain the entropy of a region beyond the gravitational observer horizon?

In this article discussing this and related papers, it is explained among other things, how the neighborhood of an observer's worldline can be approximated by a region of Minkowsky spacetime. If I ...
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Calculating the speed of an object moving relative to another moving Object (Frame of reference) [duplicate]

Possible Duplicate: How to deduce the theorem of addition of velocities? Let's say that you are in a rocket speeding at 90% the speed of light away from Earth. Now fire a bullet inside the ...
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Confusion regarding geodesic of thrown ball - curved or Cartesian coordinates?

I'm confused trying to understand what's happening in terms of spacetime geodesics when a ball is thrown and its trajectory plotted, height against time to give a parabola. I read (from more than ...
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If the Big Bang theory suggests that the Universe is “expanding” then what is it expanding INTO? [duplicate]

I am a software engineer and not an astrophysicist but I want to know if anyone is working on sorting out what exists outside the universe? So what about outside spacetime? what is there? or shall I ...
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Function to model deformed spacetime in 2D visualization of an Alcubierre drive

In the Wikipedia article on Alcubierre drive there is a top image. It is 2D visualization of an Alcubierre drive, showing the opposing regions of expanding and contracting space-time that displace the ...
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Questions about how the curvature of universe is described with a single number

I often read of physics talking about "the" curvature of the universe, giving it some letter $K$, and claiming that we have seen that $K = 0$ within such and such certainty. I have three questions: ...
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Is it possible to travel faster than the speed of light under extreme warping of spacetime?

The event horizon of a black-hole is defined as the point at which light itself cannot escape, supposedly due to a black-hole's immense gravity and effect on spacetime. However, would this not require ...
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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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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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Gravity vs. Velocity time-dilation [duplicate]

Is there any difference in effects from time dilation of that due to gravity vs. that due to velocity?
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Difference between Distance and Space

So I take particle A and place it in space, then I place particle B 1,000,000 light years away from particle A. I strike a line between the two, and measure that line as having a length of 1,000,000 ...
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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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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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Can gravitational waves carry momentum, and if so what mass/energy produces it, and is space-time capable of vortex formation?

This question is about gravitational waves postulated by Einstein. Is gravitational radiation a form of mass/energy that can form momentum? If it causes ripples in space-time, would space-time ...
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Understand the relation of time and the space dimensions of spacetime?

I assume the relation of the three spacial dimensions and the time dimension is handled purely in the mathematical domain, usually. But is there any intuitive description of this relationship, how ...
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What does “simultaneously” mean in relation to a detonation shockwave?

I understand that the difference between a deflagration and a detonation is that the reaction front of a detonation moves faster than the speed of sound in the material, which means that the pressure ...
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Spacetime in Loop quantum gravity

In LQG, does spacetime consist of interconnected loops? Are those loops real? If spacetime does not consist of the aforementioned loops, what it consists of? The definition of real would be: they ...
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Can a point in empty space be motionless with respect to light?

Being that the speed of light is constant throughout the universe, can a point in empty space be motionless with respect to light?
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Why does the thought experiment of a photon bouncing of a mirror imply anything for other objects?

Okay, so I am reading a book, "The Elegant Universe" by Brian Greene, which talks about motion and its effect on time. Greene makes the point that time changes with motion by saying that if you have ...
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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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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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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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Gravitational force of several massive bodies, from the viewpoint of general relativity

According to Wald's GR, "absolute gravitation force has no meaning". The text goes on to describe two cases: one where a gravitational force can be defined, and one in which it cannot. I'd like to ...
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Is there an absolute center of mass exist in the universe? [duplicate]

By the "absolute center of mass" I mean the center of all the matter that exists in a given moment. My friend asserted that today and it intrigued us very much but since we only have a CS degree and ...
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The universe appears to have a lower bound in the time dimension, why not an upper bound?

The Big Bang looks like a lower bound to the "size" of the universe in the time dimension. Could it also have an upper bound, some furthest point in time from the Big Bang?
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Analogues of mass, space, or time? [closed]

I began wondering about this when working through this question: is there anything analogous to spacetime or matter? Both spacetime (note: most of what I know of about the concept of spacetime comes ...
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Can special relativity be extended such that the frame of a photon makes sense?

Suppose I want to know what the universe looks like from the perspective of a frame of reference moving at $c$ relative to my current frame. As discussed at length in various other questions on this ...
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If gravity bends space time, could gravity be manipulated to freeze time? [closed]

You age at a different rate depending on the force of gravity. Astronauts age fractions of fractions of fractions of a second less than earthlings. If you took a sphere of equal masses, separated by ...
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Knots and singularities

Can space-time singularities be treated as mathematical knots occurring in dimensions greater than four? I just drew an analogy with knots in one-dimensional strings. When a rubber-band is looped over ...
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Is cosmic background radiation absolute [duplicate]

Now that we don't have permeating Ether anymore, why don't we consider the omnipresent Cosmic background radiation in place of it? and measure Speeds with respect to the CMBR? In that way an object ...
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Questions about MTW's “thousand” tests of the Einstein principle

In Misner, Thorne, Wheeler (henceforth written as "MTW"), "Gravitation", Box 16.4, there's an experimental setup construction (or method) presented by which "Each geodesic clock is constructed and ...
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How is Momenergy frame independent?

momenergy = mass * spacetime displacement/proper time for that displacement What I dont understand is how can the momenergy be frame independent? The unit-4 vector always points in the direction of ...
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Best way to check for anisotropy given a metric tensor

Carroll gives the definition of isotropy at a point as given vector $V$ and $W$ in $T_{p}M$, there is some isometry that can push $V$ forward such that it ends up parallel to $W$. I understand what ...
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In which direction do gravitons travel? Do they originate from mass or are they collected by masses?

This is a kind of silly question, that mostly goes unanswered: are gravitons detatched from the objects they act on, like photons in free space. Maybe gravity or gravitons are collected by mass ...
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Can the vanishing of the Riemann tensor be determined from causal relations?

Given a Lorentzian manifold and metric tensor, "$( M, g )$", the corresponding causal relations between its elements (events) may be derived; i.e. for every pair (in general) of distinct events in set ...
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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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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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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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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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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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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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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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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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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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Does curved spacetime arise from inhomogeneity of gravitational field?

In general relativity textbooks such as Sean Carroll's Spacetime and Geometry, there is often a line of reasoning that goes like this: Strong equivalence principle states that free falling frames ...
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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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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 ...