Spacetime Definition and 1000 Threads

Michio Kaku stated that current physics does not rule out the possibility of time travel even tho it would take comprimable measures to achieve it, such as the energy of a supernovae, my question is even if you can bend spacetime to that extreme to get to a planet with life on it, how are you...

Homework Statement on a spacetime plot (y-axis) = t (x-axis) = x find the spacetime interval between points (0,0) and (300,700) Homework Equations Interval = (c^2(del t)^2 - (del r)^2)^1/2 The Attempt at a Solution So I can see clearly my del t is 700 (700 - 0 = 700 ) but for the...

After a while of trying to understand this, it's still kind of confusing. I get how the planets orbit around the sun because of the sun's spacetime curve, but if one were to drop something, how does spacetime curvature cause it to fall? How can everything in the universe have a gravitational...

Can spacetime be created ? if yes how if not why ? I understand that spacetime is not physical and more of geometry. Still bec it exist virtualy ,as gravity depends on warping of spacetime. So can we ever create this spacetime , does it existing before big bang ??

I've tried several hours to understand Lorentz transformations(for space and for time)...it simply dosn't make any sense...I've posted here,on math section,because I need a better mathematical view over it... whitout this I can not understand much out of the restricted theory of relativity,thus...

Hi guys, simple question I have: Do particles without a rest mass (including EM radiation) cause spacetime to bend? Or only those with a rest mass have gravity?

What are the facts by which we believe that it's spacetime itself which is expanding since the big bang and not that it's only the matter-energy in the universe which expands in a pre-existing unchanging spacetime canvas?

In a space time with metrics : ds^2=f(t)(-dt^2+dx^2+dy^2+dz^2) which is the unit that measures time t? second?, meter of time?

Homework Statement Draw a clearly labelled “Minkowski spacetime” diagram illustrating two events ((1) a farmer firing his laser gun at his cow, which is sitting along his positive x-direction, and (2) the cow dying) as observed by two observers (S at rest in the farmer’s and cow’s frame...

in this article http://en.wikipedia.org/wiki/General_relativity it says in the first paragraph that the curvature of spacetime is related to the stress energy tensor i.e. the matter in the universe. i.e. the curvature at a particular point depends on the matter present at that point...

Does spacetime could curved in a "square way"? Suppose there is a square mass object in the universe (I know its impossible, but suppose...). Does spacetime will curved in a "square way"? I believe that not as GR is defined on a smooth manifold. Am I right?

Brian Greene describes in The Fabric of the Cosmos how spacetime itself is now thought to be the cause of the inertial effects behind Newton's bucket experiment (rising water, etc.). That is, rather than the "fixed stars" being the cause, as was the commonly held notion before Einstein...

Excercise Exercise 1.6 of Roger Blandford and Kip Thorne's online textbook Applications of Classical Physics: "In Minkowski spacetime, in some inertial reference frame, the vector A and second rank tensor T have as their only nonzero components A0 = 1, A1 = 2, A2 = A3 = 0. T00 = 3, T01 = T10...

Hello I'm looking for diagrams (Kruskal and Penrose diagrams) representing Minkosky spacetime. I found two diagrams at http://nrumiano.free.fr/Estars/int_bh.html (the two first diagrams of the page). Do they represent a Minkowski spacetime ? Thanks, Jeff

Hello, I have had this lingering curiosity for a while. I read through https://www.physicsforums.com/showthread.php?t=5732" thread a second ago and would like to kind of take it a step further on a tangent. I have only read about gravity effects and space-time as such they are...

From my reading of introductory texts on special relativity, I've seen this defined in various ways, and I'm curious about whether any of these definitions are preferable to others, for example because they're more convenient, consistent, logical, clearer, more widely used or more easily...

In Misner, Thorne, Wheeler: "Gravitation" it is stated on that "no one has discovered a way to make an imaginary coordinate work in the general curved spacetime manifold" (p.51). Can anyone elaborate on this? Right now, I don't get why it wouldn't work and nothing more is said in the book.

Hi all! I'm studying black holes and there's a point that I cannot understand. The book I'm reading is Modeling black hole evaporation, by Fabbri and Navarro Salas. The path is the following. After introducing the Schwarzschild metric ds^2 = \left(1 - \frac{2M}{r} \right) \ dt^2 - \left(1 -...

I apologize for the poorly worded title. Let me try to explain my question better. A scientific theory must be predictive to be useful. Since we only know what happened in the past, the global topology of spacetime cannot be an input to the theory. Given space-like slices/"chunk" of the...

Can we think about 2 different "interpretations" of GR: 1. Without embedding: space is curved, that's all 2. With embedding: curved non-euclidean space can be embedded in higher-demensional euclidean space. In another words, spacetime is just curved (1), or it is curved is something (2)...

With one clock stationary at the common origin for 10 time units and the other rocket clock traveling out and back at v=.6c. When both clocks are compared at the origin the elapsed time on the traveling clock will show less time by a factor of (.8) from the Lorentz Transformation. The...

Please clarify / correct my misunderstanding. I'm not a physics pro (just a personal interest). Also, please excuse the complete lack of technical terms! It has been said that to move beyond the speed of light is to move backwards in time? (Though it's also stated that this isn't possible...

Energy Gaps in a Spacetime Crystal L.P. Horwitz, E.Z. Engelberg (Submitted on 14 Oct 2009) This paper presents an analysis of the band structure of a spacetime potential lattice created by a standing electromagnetic wave. We show that there are energy band gaps. We estimate the effect, and...

Mass/energy as a "condition of spacetime" I recently read somewhere (I think here) that mass is not something you "drop into" space, rather it's a condition of space, and that gravity waves are also a "condition of space". a) is this correct? b) If so, is it more generally correct to say...

Homework Statement The Tale: The Klingon home world of Kronos is located at x=0. At time ct=-4 , a wonderful event occurs: Federation emissaries negotiate a peace treatywith the Klingons, bringing many years of warfare to an end! As part of this treaty, the Federation agrees to share its vast...

Homework Statement So, I am working on a question that requires me to prove that s^2 = s'^2 from the Lorentz equations. It seemed like it'd be trivial... and then I ended up here a few hours later, not willing to waste any more time. Homework Equations By definition: s^2 = x^2 - (ct)^2 &...

In the BBC film Einstein and Eddington, Eddington describes the theory of spacetime using a table cloth (space), a loaf of bread (sun) and a piece of fruit (a planet). The Bread is placed in the middle of the table cloth, this forms curves in the cloth. He then takes a piece of fruit and...

Could someone point me in the direction of the relevant differential geometry/topology terminology/definitions/explanation etc. to express the idea that spacetime cannot be "torn". Methinks it's "diffeomorphic invariance" but, even if it is, a few nice words and/or an example (or two...) of...

http://img233.imageshack.us/img233/5816/espaotempoquntico1.th.jpg Two pictures of quantum spacetimes... The theory of quantum gravity (LQG) can perform calculations and predictions on the concrete structure of space and time at the Planck scale. Equations formulas that describe...

I'm curious as to whether parameters like rest mass and mixing angles, half-life for 2nd/3rd gen and other properties change for SM particles like muons in highly curved spacetimes.

Ok, so according to Einstein, the Earth is held in by a "fabric" due the the Sun pulling on said "fabric." So my question, what holds people on Earth if gravity is this "spacetime fabric?"

Rencently, I found myself confused by some fundamental concepts in GR. I hope someone can help me with that. We all know the vacuum Einstein equation (VEE) without the cosmological constant \Lambda is Rab=0. Since I learn GR the words " matters bend the spacetime " been told again and...

Spacetime is 3D + 1T = 4D Is spacetime in string theory 4D as a result of compactification, or 12D, 11D+1T?

I have maintained here several times , amid howls of objection from a few, that spacetime IS something more than a mathematical construct or that at least we should maintain an open mind about that possibility. I have been thinking WHY I have that view and a significant reason is the presence of...

What affect does spacetime have on a rotating planet? (Velocities in the center differ from surface velocities)

Obviously not. But I am confused on this. Newtons laws of gravity did not fit with Einsteins Relativity theories because Newton said that a change in matter of an object would cause a shift to be felt by others in the universe because of the change in gravity. This would mean that the movement/...

Hello, I have what is probably a relatively (no pun intended) simple question pertaining to general relativity. I thought that I had achieved a solid understanding of the theory (and its special counterpart), until this question formed in my mind. My problem is based on the following...

Hi, I have recently been delving into Quantum gravity related material... and I came across a paper by Ted Jacobson "Thermodynamics of Spacetime: The Einstein Equation of State" http://arxiv.org/abs/gr-qc/9504004 and as far as I understand the argument it is very impressive who would have...

In the Einstein's theory of general relativity, the gravitation is an attribute of curved spacetime instead of being due to a force propagated between bodies. But the quest for the famous graviton does not presume that gravitation is due to a force? Is the quantum gravity conflicting with the...

As I understand it a vacuum is space that doesn't contain matter, however is it possible to have space that is a vacuum that also doesn't have any energy?

Is Spacetime Smooth? Smooth: infinitely differentiable If there were a limit to the differentiability of matter's motion through time, I'd assume it would be at the quantum level (where particles are not actually point particles). Example: When I accelerate in my car, the value of my...

Hidden dimensions of string theory "hiding" in 4D spacetime? Could the hidden dimensions of string theory be "hiding" in 4D spacetime? Thank you for any thoughts.

Is anyone interested in going through Hawking and Ellis' book by the title above and posting questions and insights? My interest is in singularities in higher dimensional spacetime, and whether there are other ways to achieve singularities (and their zoology) besides large enough mass. I am...

Hello, I have been reviewing some relativity notes, and I am confused over something. I apologize if this seems like a silly or obvious point, but humor me. When we are talking about Lagrangians in field theory and in regular mechanics, we are often looking at symmetries. Namely, almost...

Hello all I have been at ease with spacetime diagrams of the usual sort where the y and z dimensions are suppressed until I came across this passage from the following book. Problems of Space and Time. A reader edited and with an introduction by J.J.C.Smart. Page 293 of the chapter...

I've read in a few places that the energy and momentum of the electromagnetic field will itself induce a curvature of spacetime, much like the presence of matter. I'm not very familiar with general relativity, but does this imply that particles with mass and zero charge will still be affected...

Okay, here’s the concept. Is it just “empty space” or something else? But since relativity; we know that space cannot, and does not exist without time, And it’s a continuum "spacetime" rather than space and time. So does it means that vacuum is just “empty spacetime” There arises a...

here is my poor effort at teaching newbies how to draw spacetime diagrams (somebody has to do it): first draw your x axis. this represents space. (one dimension of it anyway. one dimension is enough for most thought experiments) the y-axis represents time. imagine there is a stationary...

At one time it was thought(still is?) that we live in a closed universe? So if we live in a closed universe we might try to get a picture of this space by thinking of the space S^3? remember, S^1 surface of a 2 dimensional ball, S^2 surface of a 3 dimensional ball, S^3 surface of a 4...

It’s often asserted that there’s a contradiction between Special Relativity and our experience of living in the present moment. Einstein made a few statements like that, and it seems many physicists assume that if the theory is correct, this very basic feature of our awareness of the world must...