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Questions tagged [spacetime]

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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If spacetime is emergent, are strings and branes in String/M-Theory also emergent?

Many physicists including string theorists say that spacetime is emergent from something more fundamental. String theory says strings and branes are fundamental, or in the case of M-Theory, membranes ...
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What is the farthest Time Zone location ever known to man [on hold]

What place in the world that has the most farthest time zone known to man, I heard it was Kiritimati but then I searched that Apia (Samoa) is further, so is there anyplace that is the farthest in time ...
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As space expands does the density of matter remain same or increase? [duplicate]

I learned that space is always expanding. Even between sun and earth, it's just gravity is stronger. Imagine space as graph paper and there is a square object that fills it. Space expands, 1x1 cell ...
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Nature of motion between comoving observers; What is the common time that they agree on?

This is a set of follow-up questions regarding this post. The following four queries are very closely related and needed to asked at the same place. Question 1 Is it really possible to regard the ...
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Is it 4-D or 11-D Universe? [closed]

I know these are just theories, but I wish to know which of the two are the most used right now to speculate how many dimensions of space and time our universe has. I heard that in the standard ...
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Relativity Confusion

In the time dilation formula $\Delta t=\gamma\Delta t_0$, I am confused about what $\Delta t$ and $\Delta t_0$ measure. If we have two people, Tom and Bob, moving at constant velocity relative to ...
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Does charge affect space-time?

Okay suppose there is an hypothetical particle called Nelectron which has mass = mass of electron but is electrically neutral. It has same spin and other quantum mechanical properties. Even the same ...
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Is it possible relativity could have been discovered much earlier? [closed]

Special relativity is a creation of Einstein. Mathematically unlike general relativity it is elementary. Is it conceivable Newton missed it? Or is it the case that it had to wait till the $20$th ...
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Doubt about energy conditions: the Time-like Convergence Condition

First of all, consider a congruence of smooth time-like geodesics parametrized by proper time $\tau$. So, a tangent vector to a time-like geodesic is indeed a four-velocity up to a factor constant; ...
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Can we consider speed of light as escape velocity? [closed]

Consider following hypothetical scenario: A space ship starts to accelerate from planet Earth towards Alpha Centaury at a very pleasant 9,8m/s2.The astronauts onboard the ship keeps the acceleration ...
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How is time “homogeneous”?

My book$^1$ states: Let's consider a clock moving freely over a curve such as: \begin{equation} \frac{dx^i}{dt}=\text{const} \tag{1.20} \end{equation} We define the proper time $\tau$ as the ...
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Implication of the Jacobian map for the structure of the Euclidean space-time

I'm listening to Alain Connes "On the Fine-Structure of Space-Time" around minute 23 saying that it was disappoing that the solution Y to the equation $$ <Y[D,Y]^{2m} >= \gamma $$ with $D$ a ...
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How gravity really works in 3D and how and massive object attracts another object? [duplicate]

space is 3d then how an massive object creates curvature in 3d an how another object falls into that 3d curvature also if you are answering plese show an image of it.
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Pridictions and Observational evidences of No Boundary Condition of S.Hawking

Reference: http://www.hawking.org.uk/the-beginning-of-time.html Predictions of No Boundary Condition proposal: 1) Irregularities in the current universe same as the Big Bang theory predicts and it ...
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Imaginary time concept in S.Hawking's No Boundary proposal, extra-time dimensions and the Big Bang

In this post I will be refering to S.Hawking's lecture: http://www.hawking.org.uk/the-beginning-of-time.html I have a couple of questions regarding the Imaginary time and the Big Bang. In the ...
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How similarly are light and matter affected by gravity?

For a path of travel in a shape that is straight before it curves, if the curvature of the path is attributable to gravitational force, what additional information (if any) would be capable of ...
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Question about position dependence of time dilation?

I found this picture from a physics stack exchange question on time dilation: Time dilation all messed up! I am now returning to it a few weeks later and was wondering if I am correctly interpreting ...
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Can space be considered as a grid of cubes of planck length, or is it continuous? [duplicate]

I don't know how to describe it exactly, please try to understand. The question is if space is continuous or gridded. Consider a particle of planck length (or whatever is the smallest possible ...
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Train and lightning bolts: why the time difference does not depend on the position of the moving person?

So imagine two lightning bolts hit the ground, simultaneously to a stationary observer. There is also a person on a train traveling to the right at a constant velocity. I know that if he started in ...
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4answers
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Is there a frame of reference in which I was born before I was conceived?

I'm struggling to understand the relativity of simultaneity and position. If my conception and birth are separated by time but not space, a frame of reference in which my birth and conception are ...
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What would be the time dilation standing on a neutron star in comparison to earth?

What would be the combined gravitational and velocity time dilation one would experience if they stood on the surface of a neutron star in comparison to standing on the earth's surface? Specifically, ...
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The Special Relativity springs from the space-time nature? [duplicate]

Suppose we have 2 clocks in the same reference system which are synchronized. These two clocks exchange signals every second. Now suppose that one of the two starts to move away (instantly with $||v||=...
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Is there only one vacuum solution of the Einstein equations?

I am thinking about this: A vacuum solution means vanishing Ricci tensor. The Ricci tensor is a contraction of the Riemann, which itself involves contains second derivatives of the metric. Thus they ...
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The universe, as a whole? [duplicate]

If the current visible universe looks the same no matter which direction you look, how can it be described as flat? Since the big bang is the current theory of the beginning of the universe, there is ...
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Does theoretical physics suggest that gravity is the exchange of gravitons or deformation/bending of spacetime?

Throughout my life, I have always been taught that gravity is a simple force, however now I struggle to see that being strictly true. Hence I wanted to ask what modern theoretical physics suggests ...
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Meaning of $n+1$ dimensions

Is there anything mathematically significant about studying a theory in $n$ dimensions or $m+1$ dimensions if $n=m+1$? For instance in the context of general relativity I hear people talk about the ...
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Solving the biharmonic equation $\square^2f(\vec{x}) =0$ on a curved space

How to solve the biharmonic equation $\square^2f(\vec{x}) =0$ on a curved space (e.g. $d$ dimensional sphere or hyperboloid)? I was thinking in the following line : I know how to solve $\square f(\...
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1answer
65 views

What was Newton's idea of absolute space and time?

When one says that Newton believed in the concept of "absolute space" and "absolute time" does it simply mean that the length interval between two points in space and time interval between two events ...
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Spacetime curvature and measurements

From a programming perspective, I've always thought of gravitational influence as a kind of vector field, (crudely drawn) which seems to attribute to the motions of bodies through the field ...
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When is the value of spacetime interval $ds$ negative?

The spacetime interval in special relativity, $ds$, is defined as $$ ds^2=c^2dt^2-dx^2-dy^2-dz^2 $$ with the $(+,-,-,-)$ Minkowski sign convention. The value of $ds^2$ can be positive, zero, or ...
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Question about the geometric structure of Newtonian mechanics

My point here is about the mathematical structure of Classical pre-relativistic physics and general relativity (GR). It became more clearly, after GR, about the fact that pseudo-riemannian are a nice ...
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Spatial and temporal dimensions orthogonality

It seems that the spatial dimensions are orthogonal: a particle can move along one axis without changing its position in relation to other two axes. It seems that the temporal dimension is somewhat ...
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Boundary conditions of temporal progress [duplicate]

If one wanted to assume time as a sequence of smallest units, what would be their physically possible sizes ?
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One Electron Universe - Bumping particles back in time? [closed]

I understand that John Wheeler's 'One Electron Universe' proposal is not generally accepted, but it's obvious that in disproving such a proposal, or at least discrediting it, we can gain insights to ...
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Minkowski diagram of two frames in rest with respect to each other

I'm starting to study Minkowski diagrams, but I can't figure out how should the axis of a $S'$ system look if it is in rest with respect to the frame $S$. I've seen that in all diagrams the origin ...
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Would any continuous model of the universe have/be based on hypercomputational laws?

I've read that when Turing-Church thesis is applied to the universe and physics, one of the three interpretations that we can use and is defended by some important physicists is that: "The universe ...
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Time difference between all particles and waves [closed]

Since all elementary particles and waves were created simultaneously in the big-bang (t0) would there be any time difference between any interacting elementary particles and/or waves after t0? I'm ...
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Experimental proof of length elongation due to gravitational field?

In general relativity we see that length around a massive object is elongated due to its effect on the geometry of spacetime which elongates the length due to stretched space time. Is there any ...
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How Can the Universe Be Bigger Than It is Old? [duplicate]

My question is this: If we can look back to roughly 500m years after the big bang and have estimated the age of the universe at 13.7B years, why is the galaxy we are looking at not a part of the non-...
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1answer
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Solution to invariance equation when deriving Lorentz transformation

Requiring that the spacetime interval (1 spatial dimension) between the origin and an event $(t,\, x)$ stays constant under a transformation between reference frames: $$c^2t^2-x^2= c^2t'^2- x'^2$$ we ...
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Chart(s) of space-time as a smooth manifold

So we all know that space-time in general relativity is modeled as a smooth (pseudoRiemannian) manifold. Each point (event) on space-time is labeled with a unique coordinate $(t,x,y,z)$ in a specific ...
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Could gravitational waves give an illusion of an expanding universe? [closed]

‪Could the effect of “expanding” gravity (gravitational waves spreading at the speed of light) as it travels through space (and therefore becomes less local) red-shift all EM waves and thus give us ...
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1answer
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How much does time-dilation effect our observance of the most massive objects in our solar system?

Disclaimer: I'm kind of a newb, so I apologize if this question is not well formed. Please comment if anything is unclear, and I will do my best to make corrections. Reading this post about time ...
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Biconformal space and curvature

I've found very few contributions about the so called Biconformal Space, "a curved phase space". I was sure that in general phase spaces are cotangent bundles naturally equipped with a symplectic 2-...
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Would CTCs in wormholes change physical laws?

A wormhole is a speculative structure linking disparate points in spacetime, and is based on a special solution of the Einstein field equations solved using a Jacobian matrix and determinant. (https:...
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Friedmann equations and dependence on each other

I have quick question regarding Friedmann (for FLRW cosmology) and dependence of 00 th component and ii-th component (space-space). Are they equivalent? For example authors of https://arxiv.org/abs/...
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Meaning of time and distance in general relativity?

I have just started studying cosmology and I have realised that certain statements (that made perfect sense before I studied GR) no longer make sense: -The universe is 13.2 billion years old. What ...
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Respect to What Time is Calculated in Space

This may be the silly and stupid question but I have read that time appears to move slower near massive objects because the object's gravitational force bends space-time and the phenomenon is called ...
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Would non-hyperbolic space times have different laws?

Would a non-hyperbolic model of our universe have fundamentally different laws than our universe? For example, in Gödel's metric, its laws would be described by general relativity. But if the Gödel ...
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If a Black Hole Singularity is a 1 Dimensional Object, How Does it Affect 4 Dimensional Space

If the center of a black hole is an one-dimensional point, gravitational singularity, where density and gravity become infinite and space-time curves infinitely, then / why: If spacetime is warped ...