Spacetime Definition and 1000 Threads

Hello, Is there a way to find the lorentz factor of a point particle in a curved spacetime in terms of metric elements(diagonal) More specifically I was trying to write energy of a point particle in a curved space. thanks

On page 36 of these notes: http://arxiv.org/PS_cache/gr-qc/pdf/9707/9707012v1.pdf we are given a proof of the claim at the bottom of p35. However, this proof doesn't actually seem to do anything! All he does in the proof is shows what the acceleration is - he doesn't make any connection with...

I know that the spacetime interval is the same in coordinate system moving wrt each other at constant speed. But is it true that the spacetime interval is invariant under rotations? If so can you suggest a proof or post a link to one?

Could someone clarify, and/or point me to some reference on: Lorentz metric is not really a metric in the sense of metric spaces of a topology course since it admits negative values. If I use it to define the usual open sphere about a point, that sphere includes the entire light-cone through...

"Spacetime has No Time Dimension" http://www.dailygalaxy.com/my_weblog/2011/04/spacetime-has-no-time-dimension-new-theory-claims-that-time-is-not-the-4th-dimension.html#more

http://www.dailygalaxy.com/my_weblog/2011/04/spacetime-has-no-time-dimension-new-theory-claims-that-time-is-not-the-4th-dimension.html I'm sorry for being so clueless, but isn't that article basically saying exactly what special relativity said in the first place? That there is no absolute...

Alright, my first thread with this title got locked down. Let's see how long this one lasts ;-) Actually, this time I have a specific queston. It is often stated there is no test that can determine if space time curvature is truly real. What about LIGO? As I understand it, with the...

Hi, Amateur here. I think Sheldon has reignited my long dormant interest in physics. ;) Trying to understand just how rigid the spacetime equation is. Is there a way to create interference? Add a variable, the same way adding a proton to a molecule changes the element? I'm thinking that if you...

Hi there, Physics lovers! I've got some questions for you! Denoting by (1) ds^{2}=g_{\mu\nu}dx^{\mu}dx^{\nu}=c^{2}d\tau^{2} the interval (and \tau the proper time) and using the signature (+---), we have that the equations of motion for a free particle are: (2)...

So I'm new to the forum and to relativity as well and I am confused as to how the equation for an invariant distance between two points in spacetime is derived, specifically where subtraction comes from s^2=srqrt[((ct)^2)-x^2)] i understand most of that but just not why its subtraction...

Given the Lorentz-Fitzgerald contraction equation: t = \sqrt{1-\frac{v^{2}}{c^{2}}} 'c' can be understood as the maximum allowable occupation of spacetime. I've seen it written on these boards that black holes are calculated by Einstein's equations as infinitely dense points, which is...

It is my understanding that all things travel through spacetime at the same speed. Additionally , I am told we are moving through space at some velocity. My question is this: If an object were made to travel in a direction opposite to our direction of motion , would that object not then be...

Branes are confusing subject. Branes are objects. Yet Branes are also Spacetime. But how could that be. General Relativity says geometry is not physical, but just math relationship. Now how could Branes itself be spacetime when Branes are objects like strings...

I can accept that spacetime has no substantial aspect to it because for General Covariance (Diffeomorphism Invariance) to be true, spacetime "points" can't be real or else General Covariance won't work. Now question. How does Inflaton Field and the Cosmological Constants for example interact...

If wormholes connect two areas in spacetime, wouldn't that require 5 dimensions? (an extra dimension past 4d spacetime.)

Having studied GR as far as Einstein's tensor equation and a bit beyond, I'm just doing a bit of a double-take wondering what we mean when we talk about spacetime. Frequently it is referred to as if it is a thing that exists, like mass and energy. For example, we say that spacetime is curved...

I don't see how the bending of spacetime can be a proper way of explaining to people gravity. Why would bending of space-time imply movement?, (or acceleration.) The analogy with a ball on a bed sheet can only go so far. (which isn't very far.) Is this lame analogy used only because, there...

Expansion of spacetime stretches wavelengths and produces the red shift. Does it also stretch the amplitude of the wave, and make distant stars look brighter and therefor nearer?

Hi, I'm new to this forum so maybe this topic has been addressed ad nauseum at some point before, so I apologize if so. But, as the title suggests, do you feel the spacetime curvature is a reality, or is it just a mathematical convenience for making predictions? dm4b

When Einstein conceived GR he added the cosmological constant in an attempt to create a static universe model. The problem with this was that it was unstable. I've recently read about static spacetime (static spacetime admits a global, non-vanishing, timelike Killing vector field K which is...

Special Relativity is just a special case where spacetime is flat and fixed. Meaning it is not really a correct picture of reality because nature chooses curved spacetime that is background independent. So quantum particles shouldn't be occurring in a flat fixed background but a dynamic...

I was wondering if such could be possible in the future, to travel from one spacetime to another (if other spacetimes exist)?

Are there any indications in different theories or approaches to QG explaining what could possibly single out 4-dim. spacetime? Is there an idea why string theory favours compactification of 6 dimensions? Is there an idea why purely algebraic spin networks (w/o any dependence on...

Homework Statement Two events occur 5 s apart in time and 3 s apart in space. A clock traveling at a speed of .6 can be present at both these events. What time interval will such a clock measure between the events? A. 8 s B. 5.8 s C. 5 s D. 4 s E. 2 s F. Other Homework Equations...

Apologies in advance if this has been asked and answered somewhere else, I searched but could not find anything. I just wanted to verify if my intuitive understanding of why space time (if it is to be physically plausible) can not be compact. According to Hawking and Ellis (and others)...

Hi. If Newtons theory of gravity was changed - so that gravity is considered to propagate at the speed of light AND not only masses but all energy feels and radiates gravitational attraction - would the predictions then be identical to the ones of Einsteins generel relativity?' Thanks, Henrik

We know that the laws of physics are unique to our universe, that is they only hold true in our spacetime. My question is about logic and if logic holds true outside our universe unlike the laws of physics. For example, if we say that x>y and z>x then we can conclude that z>y is true by logic...

This might be a stupid question.. Why does curved spacetime cause objects with mass to accelerate towards each other? If I placed a massive particle next to a larger massive object, at rest with respect to the large object, shouldn't the particle stay at rest?

Hello, I understand light can be accelerated in a gravitational field, because it follows the curves in the spacetimecontinuum. Now I was wondering: does light itself also create a distortion in spacetime and thus attract other things? And are there experiments to confirm this? (E.g. two...

This thread is in case discussion of the following paper is wished. http://arxiv.org/abs/1102.0954 The Holst Action by the Spectral Action Principle Frank Pfaeffle, Christoph A. Stephan 11 pages (Submitted on 4 Feb 2011) "We investigate the Holst action for closed Riemannian 4-manifolds with...

Does anyone know if there exist a formulation of QED in curved spacetime. If yes could you give me some references to papers in which solution to these problem is described?

Hi, I am new to this forum so hello to everybody. I have this problem to solve: Homework Statement Q is moving away from P at speed 4/5 c. After 3 years (in Q's frame of reference) he turns around (assuming that turning takes no time) and is moving back to P at speed 4/5 c. What are spacetime...

In early 2010 I attended this inaugural lecture by string theorist- Prof. Mavromatos entitled 'MAGIC strings'. In it he proposes that some string theory models may violate Lorentz symmetry at the Planck scale resulting in a kind-of foamy spacetime that could be observed by differing arrival...

if the 3 spatial dimensions are represented on a 3 axis graph. would time be a straight line through the origin? if not could your direct me to some reading that i may find answers? I'm uncertain whether space-time can be represented using euclidean geometry.

What is k-Minkowski spacetime, and... In http://www.physorg.com/news157203574.html, k-Minkowski spacetime, which decreases down towards zero at small scales, is mentioned as a possible tool in a theory of quantum gravity and spacetime. But it is very, very vague. First, how is k-Minkowski...

Someone told me that spacetime is a matter. I know that matter must be a mass or energy. Is spacetime a matter (mass or energy) , and if it is a mass. why can't we see it? Is it due to the presence of dark matter? If it is an energy. what is its source? The sun?? If it is not mass or...

Homework Statement A3. Show that the Lorentz transformations on a spacetime 4-vector can be written as x'μ = (Lμν)*(χν) . Find the matrix L. Prove that (in matrix notation) Lτ gL = g where g is the Minkowski spacetime metric.Homework Equations Any help suggesting at least equations will be...

Hi, Is Spacetime inside the Quantum Vacuum or is the Quantum Vacuum inside or fill up Spacetime?

Below is a spacetime diagram which depicts the movement of a rod, four units long, relative to another rod of equal length. The red lines are the "moving" rod; the purple lines are the "stationary" rod. The gray lines are the world lines of the unit marks (0, 1, 2, 3, 4) on each rod. As I...

Homework Statement Two rockets are sent off at t=0, one from x=0 and the other at x=4. The rocket leaving from x=0 is moving at .8c and the rocket leaving x=4 is moving at .2c. When the paths of the two rockets meet, they send a light signal to x=0. Read off the coordinates in the S frame...

Hi all, Alright so while reading through some stuff, I came across something peciluar, string/M-theory state that rips in spacetime are a natural phenomenon and happen all the time. "Edward Witten showed that strings, which have spatial extant, can travel while encircling the tear as it...

Lets say I have a very low energy photon moving through space and I want to visualize how space-time is effected by the motion of the photon thru space. Photons are supposed to be quantized.. If it were possible to build a machine to measure the "gravitational" effect of a single photon would...

In Big Bang theory, Spacetime itself expands from Planck size to the universe today. This means there is no existing space before the bang. But what if we assume space and time already existed in the universe and the Big Bang was an explosion of just matter. Is there no cosmology theory or...

In flat space time the Lagrangian for the EM potential is (neglecting the source term) \mathcal{L}_{flat}=-\frac{1}{16\pi}(\partial^{\mu}A^{\nu}-\partial^{\nu}A^{\mu})(\partial_{\mu}A_{\nu}-\partial_{\nu}A_{\mu}) which is a scalar for flat spacetime. I would have expected the...

I understand that Spacetime is expanding, as demonstrated by the increase in red-shift with distance. And I also understand that light travels *through* spacetime which itself is expanding. It seems rational to me that one may compare the rate of spacetime expansion to the speed of light...

Consider the spacetime metric ds^2=-(1+r)dt^2+\frac{dr^2}{(1+r)} + r^2 ( d \theta^2 + \sin^2{\theta} d \phi^2) where \theta, \phi are polar coordinates on the sphere and r \geq 0. Consider an observer whose worldline is r=0. He has two identical clocks, A and B. He keeps clock A with...

hi, I have a very simple question: why is there really a need for more than 4 spacetime dimensions? are there any concepts for which 4 dimensions are not sufficient? thank you!

How can matter change the geometry of spacetime?

Do planets follow the curvature of spacetime as they orbit, or what is their path considered to be?

While posting a reply in another thread, I had an inspiration for a device to measure spacetime curvature. It is well know that we can measure this curvature by measuring the angles of a large triangle or comparing the circumference of a circle to its radius, but his device may may be simpler or...