Space time Definition and 162 Threads

Interested in Banks' HST these days, for discussion,here are some abstract and an email from L.Smolin. A recent conclusive paper as well https://arxiv.org/abs/2201.06988 The formalism of Holographic Space-time (HST) is a translation of the principles of Lorentzian geometry into the language...

By definition of the vector potential we may write \nabla \times A =B at least in flat space. Does this relation hold in curved space? I am particularly interested if we can still write this in a spatially flat Friedmann-Robertson-Walker background with metric ds^2=dt^2-a^2(dx^2+dy^2+dz^2) and...

It is said that: It is not possible to write a position vector in a curved space time. What is the reason? How can one describe a general vector in a curved space time? Can you please suggest a good textbook or an article which explains this aspect?

My hypothesis: A sequence with the gravitational waves detected, sent by modulating radio waves, could be received and used by other intelligent beings to find the corresponding sequence within their records and then compare it to calculate our spacetime position in relation to theirs. As...

Presume we look at a two-dimensional view of space time, with no local masses, and we draw a grid of equidistance spaced lines. The intent is to look at space but not time. As we begin, we look in all directions and the grid lines are evenly spaced. Begin adding mass to the center of the grid...

probably a daft question asked before, but. if space is expanding at an accelerating rate would that mean time is accelerating too?. after all Einstein* claims and the maths seems to say that space and time are the same thing, ie space-time. so if space is expanding faster and faster shouldn't...

Sorry if the question has been already answered, but I didn't manage to find it. Let's go back to ligo detection of gravitational waves, my question is the following: if space time changes its texture due to a gravitational effect, all the rulers (and clocks) in that spot will be affected, so...

Our 4-D space is ##x^1,x^2,x^3 ,t##. Our sub-manifold is defined by ##(x^1,x^2,x^3)## Therefore for this sub-manifold to be maximally symmetric and for which the tangent vector ##\frac{∂}{∂t}(\hat t)## orthogonal to this sub-manifold The metric becomes...

{Moderator's note: Moved to Cosmology forum.] Dark matter and the fabric of space time, Can someone with a real knowledge base of physics and the current accepted theories, please explain why the fabric of space is not the candidate for the elusive dark matter? Having read extensively about...

This has been bothering me for some time, and would like to get a physicist's view of it. If my understanding or contention is in error, please correct me (gently). I only have under grad physics from 1970, and was a microbiologist, though am interested in quantum physics, cosmology. My...

To explain the concept of curved space time, we often use analogy of rubber sheet. If we put a heavy ball at the centre of sheet then it creates a depression and now a smaller ball will fall towards that heavy ball because of depression. But in this analogy smaller ball is falling down the slope...

If space time (the universe) is infinitely expanding what happens when it rips? Have we observed Virtual particles in an area and counted them? Does the expansion of space time affect the amount of Virtual particles in a particular area? Is it theoretically possible to expand space time to a...

Hello Maybe my question is dumb but is the bent of space time instant due to gravity? If a mass pops into existence will space time be bent instantly ? Intercations between forces are light speed but gravity is and is not a force depending on pov

Hello. I was thinking about gravity and how matter bends the ST (space time) creating gravity.which lead on to singularities. I wondered how much mass it would take to either make a hole in spacetime, or how much it would take to make a black hole. So I googled it. This is where my confusion...

Can it be said that time is directly related to movement? That is to say, on a quantum level, if all motion were to cease, would that not bring about the cessation of time?

I was thinking about the age of the universe which is said to be 13.8 billion years approximately. I read that this is derived from two sources , calculating the life of the oldest stars in the observable universe and from extrapolating backwards the distance which is radius from Earth to all...

Is there a way to explain Lorentz contraction on space-time diagrams ? I cannot find a way by myself. Your teaching will be appreciated.

Based on classical physics all things attract one another due to their own gravity pull, so theoretically the Earth is drawn closer to a tennis ball even if its impossible to detect. Knowing this and Einsteins theory of relativity of spacetime could I not assume then that every physical body...

Why does an object is attracted towards Earth according to Einstein?? I only know that celestial objects are attracted due to curve made by another massive object but what happens in case of objects attached to Earth??[emoji26] [emoji26]

What if the LHC produced a mini black hole and as a result a micro singularity was produced. If you were using Euclidean space time what equations and factors do you think would be most relevant?

I have been doing some reading and from what i inderstand of relativity(wich isn't much granted) it states that space and time can be viewed as a single entity that mass bends warps and affects in various ways. We have a pretty good understanding of how mass affects space in 3 dimensions. For...

Does length contraction means the contraction of space time?

Dear PF Forum, I have a confusion about gravity. And frankly I don't know if this question belongs to this sub forum (cosmology, general physic?). Gravity attracts object - Newton Gravity curves space time - Einstein. Why we revolve around a massive object? Because that massive object curves...

Hey, can the Space Time Fabric be ripped or broken? The answer could help find the state of the universe on some aspects.

Reading about gravity waves got me back to thinking about relativity. And I am left with two questions to which I don't know the answer... Question 1. Gravity waves ripple through the entire universe. They will not cause any macro scale effects because local changes to space-time are very...

ok, sorry if i sound daft, but this one has been keeping me awake and i need a better physics brain to tell me why this is b'locks So, there was a recent study in aus that said Aliens don't exist, or rather that we can't find any evidence, because the conditions for life to evolve require...

I've been wondering, space time is supposed to be consists of one dimensional string as described in the string theory, but how exactly does space time looks like since it is invisible to us. Is it possible to get a sketch of such one dimensional strings?

I think we all know what an Alcubierre drive is, well this is similar in principle. Is it possible to conduct faster than light communication through the acceleration of a bubble of space time? is it even possible to do this without a ship, and just send it out as a warp bubble from a point like...

In this thread, ramparts asked how integration by parts could be used in general relativity. suppose you have ##\int_M (\nabla^a \nabla_a f) g .Vol## Can it be written like ##\int_M (\nabla^a \nabla_a g) f .Vol## plus a boundary integration term (by integrating twice by parts)? I think thay it...

If gravity is not a force, rather the curvature of space time influenced by a body's mass, then why do we perceive an acceleration due to gravity, as though there was a force? In my mind, it would make sense for the bend in space to only cause a massive object to change direction. I suppose if...

I have some questions related to this video: In the Einstein view of gravity, time is warped. Is this warped time same as the gravitational time dilation? In other words, is the curved time axis due to different clock speeds at different height in a gravitational field? Further, can the tidal...

There exist evidence that space time fabric can be curved arround massive objects?

I am having a tough time getting my head around this. I get that traveling faster then c in itself has an effect on the the flow of time from the reference of external observation and the person doing it (isn't actual FTL velocity causing backwards time?). But in a "warp bubble" for lack of a...

I was trying to draw a space-time diagram representing two objects traveling through spacetime, me and the planet Earth. At first I thought I would just draw two straight lines heading upwards some distance, x, apart, seeing as my position relative to the center of the Earth would not be...

Sorry... This question may be very basic. As a self taught, I understand that the mass will bend the space around it such that any other mass entering the bent space will immediately be pushed towards the center because of the bent space. Higher the mass, higher will be the bent (if that is the...

is magnetic repulsion and attraction is due to the bending of curvature of spacetime?

I started a thread previously (https://www.physicsforums.com/threads/time-dilation-happens-on-moving-frame-but-which-one.814622/) around this concept but it got closed by one of the staff after helpfully pointing me to...

Not kidding http://mysteriousuniverse.org/2015/04/nasa-may-have-accidentally-developed-a-warp-drive/ Astounding, is it true?

I was reading about zeno's paradox (arrow), Is it like Quantized Spacetime? that we just move from one 'NOW' to the next? Does zeno paradox can be fully solved?

Did space time be created at the Big Bang, if it did, then theoretically, gravity would not be a fundamental force associated with the Big Bang and any events before the Big Bang would be undefined?

Hello! This is my first post, so I should make a small introduction. I am not a science expert in anyway shape or form, but I am a keen enthusiast who regularly keeps up to date with science news through popular websites such as IFLS, Space, BBC etc. I have been wondering about this particular...

I recently watched Susskind video on general relativity. I am unsure why the commutator of the covariant derivative of the vectors is nonzero when there is curvature. E.g. DrDsVm-DsDrVm In flat space, that difference is zero. But why is it non zero in curved space? Someone please enlightened...

How do we explains space-time through Riemann Calculus?

A large body like the Earth warps space time in its vicinity. This explains the appearance of gravity from the body. But why does a mass bend space time? What is the connection. What is the thing that mass has that makes space time want to warp around it? There must be some communication...

Hello all I just joined this forum so forgive me for jumping right in but I have a question about Gravity and the curvature of space time that I can't get answer with a Google search. My question: though I understand that an object remains in orbit because of the curvature of space time and it...

Is Space time having a actual reality or is it just a mathematical concept to calculate the coordinates of a point in space?

Since the medium in which light propagates is space time, would light be able to exist if spacetime did not exist? Is this like one of those chicken/egg problems, or can light be thought of as a legitimately independent entity?

Does both space & time vibrate when objects move or when they vibrate when objects accelerate? So, what happens of these vibrations? How are they converted back into matter to maintain a cycle?Do these vibrations affect the motion of other moving objects (although negligible)?

Homework Statement Frames S and S' are moving relative to each other along the x and x' axes. They set their clocks to t = t'=0 when their origins coincide. In frame S, Event A occurs at xA = 1 yr and tA = 1 yr, while event B occurs at xB = 2 yr and tB = 0.5 yr. These events occur...

As far as I have the knowledge of GTR that a mass bends the space time around it.But why does this bend occur?The example from real life that when a mass is placed on a net then the net bends but it us very difficult for me to visualise the situation of bending of spacetime due to a mass.What is...