Space-time Definition and 406 Threads

Space-time is a single entity. Space does not flow. How can time flow?

A photon may be considered as an excitation of the electromagnetic (ER) field. ER is thought to be omnipresent/ubiquitous in time-space (?) Is it possible to construct a region in space-time (say a "black" box):1. That contains no ER fields? 2. that contains no photons? i.e. no...

Does entanglement means that space-time is not a continuum after all?

Homework Statement Hi guys! I must show by brute force that ##\Delta s^2=-c^2\Delta t^2+\Delta x^2+\Delta y^2+\Delta z^2## is invariant under Lorentz transforms. Homework Equations Lorentz transforms: ##\Delta t' = \gamma \left ( \Delta t -\frac{\vec v \cdot \Delta \vec x}{c^2} \right...

Is there a reason why light ( electromagnetic waves) is the only thing that can move that fast through space-time? I understand that light doesn't have mass and it is affected by the geometry of space-time, but could there be a specific reason?

This was just posted http://arxiv.org/abs/1308.2206 Energetic Causal Sets Marina Cortês, Lee Smolin (Submitted on 9 Aug 2013) We propose an approach to quantum theory based on the energetic causal sets, introduced in Cortês and Smolin (2013). Fundamental processes are causal sets whose...

Is it fair to state "mass distorts space-time" I thought it was. Here's the response I'm getting, I think time is a constant and space is undistortable (gravity's influence on mass can be mistaken. You're talking about gravity fields and their impact on the space/time continuum but nothing...

hello, I would like to check that, ie if the tangent spacetime of schwarzschild can be linked to minkowski spacetime via a lorentz transformation. But i have a problem from the onset since the tangent space seems to me to exist only in exterior geometry. For example the tangent plane to a...

I apologize for my ignorance but I've looked around a decent bit and still don't quite understand. I understand its no longer a force as Newton described it, but then the bowling ball on a trampoline analogy is useless without a force such as gravity to accelerate objects in the metaphorical...

I have had a physics related question buzzing around my head for some time now, but have not been able to find the answer to it. I should state that have no training in physics, but have an interest in science and the universe. The question; if space is accelerating, what are the...

Can one show that strict charge conservation ##\nabla_{a}J^{a} = 0## follows directly from ##\nabla_{a}F^{ab} = 4\pi J^{b}## alone? Also, how does ##d^{\star}F = 4\pi ^{\star}J## follow directly from that same equation where ##\star## is the Hodge dual operator?

I was reading a paper by Geroch and I was confused by the following: given a scalar field ##\omega## satisfying ##\nabla_{a}\omega = \omega_{a} = \epsilon_{abcd}\xi^{b}\nabla^{c}\xi^{d}## and the scalar ##\lambda = \xi^{a}\xi_{a}##, where ##\xi^{a}## is a killing vector field, can someone prove...

Are "small" extra space-time dimensions represented correctly? This is my first post, I searched briefly but I apologize if this is a commonly covered topic! The following is written in the spirit of the "aether" -- that, being an overcomplication with no evidence. One of my biggest...

Hi all! Fields associated with a particle affect other particles and their fields and that's ok. But why would a particle affect the space-time (which is not a particle) making it expand? Thank you in advance!

in a 4D space time, ¿what is de descomposition of de distribution: \delta^{(4)} (P_x+P_y-P_z-P_t) ? i think that is equal to \delta^{(4)} (P_x+P_y-P_z-P_t)=\delta(P_x) \delta(P_y)\delta(-P_z)\delta(-P_t), but, i don't understand...

Hello there Ladies and Gents! This question is (mostly) related to problem 10.2 in Wald which is to show that the source-free Maxwell's equations have a well posed initial value formulation in curved space-times. We start off with a globally hyperbolic space-time ##(M,g_{ab})## and a spacelike...

my knowledge of time-space is limited, so my question might be poorly/wrongly constructed/verbalized: Do we have two sets of co-ordinate systems when space-time is bent (by say, mass)? in one system the circle becomes, say, an ellipsoid while in other it remains a circle? in one...

Imagine we have a perfect fluid with zero pressure (dust), which generates a solution to Einstein's equations. Show that the metric can be static only if the fluid four-velocity is parallel to the time-like (and hypersurface orthogonal) Killing vector characterizing the static metric. So, I...

Is there a way to know one way or another? If smallest possible scale is Planck scale, does it mean that space-time is discrete where smallest possible step is Planck's length (PL) and smallest possible time is Planck's time (PT)? If I move my hand from point A to point B, say 1m exactly in...

what changes will take place in maxwell's equations if the space-time was curved?

If gravity rises from the fact that mass bends space-time and stuff falls in because it actually follows a straight line in a curved space as it moves by a gravitating object - doesn't that mean that a relatively stationary particle would not fall in the the claws of gravity as it would NOT be...

There are 2 phenomena which I understand are more or less received wisdom (when seen from my pop science standpoint anyway). Firstly :space-time is ever expanding. Secondly:in a quantum "vacuum" matter/energy is continuously being created ( and disappearing) out of "nothing". Could...

Proper length is given by $$ L = \sqrt{\Delta x^2 + \Delta y^2 + \Delta z^2 - c^2\Delta t^2 }$$ So, when $$ \Delta x = \Delta y = \Delta z = 0 $$ there is no motion and $$ L = ic\Delta t $$ What does that mean, if anything?

If light is both a partial and a wave; and the speed of light is an absolute; and a partial traveling at the speed of light experiences zero passage of time (I think that’s what Einstein was on about)how can light move at all through space time? Or is that what we experience as matter?

I wonder if there's a connection and it's a requirement or it's a completely different matter and space(time) warps anyway.

Hello all . My questions are : Space/time are any meaning without matter or energy ? Space/time are exist without matter or energy ? We can image space/time without any matter or energy ? These terms are any meaning in physics ?

Space-Time Curvature Question! Hi Guys, A question about the curvture of space-time by mass. Where is the point of maximum curvature?? Is it at the centre of mass (i.e.. the middle of the body) The reason I ask, is that when space-time curvature is shown visually it makes out like it is a...

Black holes can pull photons in although they move at the speed of light. So, does this means that black holes pull space-time in faster than light and if so, why can space-time "travel" faster than light?

According to GR is space actually supposed to be bending around mass, or is the concept of "curvature" just abstract and purely mathematical idea?

Hi, so I was going over my lectures notes and I was looking at the Invariance, S2 for space time. I was just wondering why they call it time-like for S2<0 and space-like for S2>0 because, S2>0 says that there is an inertial frame where events occur at the same time (this has to do with...

Good day! I am quite blur with the Space-time concept proposed by Einstein. Can anyone explain briefly on what he meant by that term(Space-time)? 3-D space+1-D time? :confused:

If someone were able to travel back in time and change an event in history which resulted in a divergent timeline from the one you came from would both timelines be part of the same space-time continuum? I suspected they could be because part of their timelines are shared and connected to...

Feynman checkerboard as a model of discrete space-time Back in 2006 Ed Hanna posted an interesting thread about this topic and I would really like to discuss it with him. Are you out there Ed - or does anyone know how to contact him? Thanks, John Wellings

in an empty infinite space time, there lies the possibility that something came from nothing, since infinity encompasses everything. yes? no? i assume that the matter that appear out of thin air, without any external intervention in my belief. was Hydrogen. the simplest element in the table...

Can someone please explain to me how space-time works? Is space-time a graph? If so how does it actually work? I just don't understand the idea of how it works. Is time treated as a constant so time is the same? Because if time wasn't the same I don't quite understand how you can relate space...

In particle physics, quantum field theories such as the Standard Model describe nature in terms of fields. Each field has a complementary description as the set of particles of a particular type. Does any field, other than gravity, bend (or have any noticeable interaction with) space-time?

Why does it seem that modern physicists have thrown out Einstein's theory of gravity warping space-time for the idea that the force of gravity is caused by a specific particle? Has Einstein's theory been discredited or is it just simpler for the Unification of the four forces for gravity to be...

I am not sure if this belongs in General Relativity or Quantum Theory or just General -but here goes. First , I have to say that I do assume Space-Time to be quantized (since anything else seems too difficult!) and this is my question. I have often read that physicists have peered back...

Do theories of quantum gravity require that space-time is a lattice instead of a continuum? I guess this question has been addressed elsewhere, but I would appreciate hearing different points of view. Please dummy down the responses so a philosopher can understand it.

New thread continuing a topic raised in https://www.physicsforums.com/newreply.php?do=newreply&p=3865854 Okay, so I saw on wikipedia that you can have a 'flat torus' --- at least a 2 dimensional torus inbedded in 4-space. So you can also have a 3-torus, that's flat? And would time just be...

I have no idea about it, as my understanding,that Mr.Einstein depicted that what actually happening in space are above on a plane and flat Space-time fabric.Is this telling us that the Earth around is nothing ?What i trying to say is the surrounding of a mass might not exist only a plane of...

The classical expression of a plane electromagnetic wave (electric part) \bar{E}(t,\bar{x})=\bar{E}_{0}e^{i(\bar{k}\cdot \bar{x}-\omega t)} looks a lot like the basis function of the Fourier decomposition in Minkowski space-time...

To talk about differentiable vector fields in Galilean space-time, one needs to define convergence. Galilean space-time is an affine space and its associated vector space is a real 4-dimensional vector space which has a 3-dimensional subspace isomorphic to Euclidean vector space. There is no...

Hello everyone I'm fairly new to the world of Astrophysics and as such have come upon an odd question. Is there any material possible that you could assemble on Earth that would have any significant Frame-Dragging or space-time distortion effects? Let's say we are able to extract, pressurize...

Hello, I am new to the forum and have a question that has been bugging me for some time that I hope someone can help me with. In the following image is a typical example used in documentary's to try to show how Einstein's theory of relativity explains how mass effects time. Uselly they will...

Hi, Just a quick question I can't get my head around... Say I have a big planet sitting in intergalactic space and I place myself somewhere in the vicinity, relatively stationary to it. So I am not moving, the planet is not moving, how do I then 'follow' a curve in space-time? Am I assumed to...

Hi there. This is my first posting to this forum, and in fact to any forum in many years, so please excuse me if I have not followed the rules correctly or chosen the correct forum. I have been watching a lot of Neil DeGrasse Tyson-related videos and it has lead me to a line of thinking...

Time variable of space-time at the end of universe... As universe is continuously expanding at the accelerating speed...expansion of the universe causes Redshift...the whole universe is made up of the tiny particles and the material. Because of this all the material particles of the universe...

Can someone direct me to the solution to the space-time metric, ds^2 = -dt^2 + dx^2 + dy^2 + dt^2? Thanks.

Are spinors needed in modern theoretical physics as opposed to tensors? I have come across Penrose's book "Spinors and space-time". Does anybody know what mathematical prerequisites are needed to actually understand it? (at least volume 1) Can I manage to go through it with a good knowledge of...