|
| If this is your first visit, be sure to check out the FAQ by clicking the link above. You may have to register before you can post: click the register link above to proceed. To start viewing messages, select the forum that you want to visit from the selection below. |
|
|||||||
| Register | FAQ | Members List | Calendar | Mark Forums Read |
![]() |
|
|
LinkBack | Thread Tools | Display Modes |
|
|||
|
Quote:
|
|
|||
|
Quote:
You have a flat manifold. By the model, this means you have Euclidean spacetime. But you still have spacetime.
__________________
Some try to tell me, thoughts they cannot defend,... - Moody Blues. |
|
|||||
|
Quote:
" if " space does in fact expand it is not because of " space " but because of the matter in space what properties does space have in and of its self , by itself , alone ? you don't curve space you curve the matter in that space space is nothing , since it is a consequence of , rather than an impetus Quote:
energy/ matter so gravity is not based on space but on the energy/matter IN a particular place in space Quote:
Quote:
this concept that space can be curved is a mathematical concept and is not derived from reality Quote:
and a null expansion in the end |
|
|||
|
Quote:
OK but what is the metric? |
|
|||
|
Hmmmm ... I think I disagree with most of this.
I agree that space acts as the room. However, I believe that it is more than that. Light passing through curved space curves. I can see your point that the light is what is curving ... but I think that this is where we disagree. I look as space-time as being the rails that guides matter. Lets look at gravity and a black hole. Why does gravity escape from a black hole but light doesnt? I believe the answer to be that space is curved ... but while light is effected by the curvature of space-time gravity is not and can thusly escape. Also time is curved along with space. So as the flow of time relatively changes near a gravitational source so does any measurement of space change in proportionately in that area. Space has properties ... the amount of energy that is in its space + the fields that it is in ... gravitational, magnetic etc ... Quote:
|
|
|||
|
Quote:
look at light passing through water , the light curves because the Nature of water inotherwords there is a form of matter which " causes " the curvature of light in space not empty space in and of its self |
|
|||
|
Per your definition of space how does it expand? Things are just moving apart from each other?
Do all points in empty space allow light to pass through it in the exact same way? Does a point in space have a temperature? gravitational field? magnetic field? |
|
|||
|
Quote:
the light does not " appear to be bend " light does bend |
|
||||
|
Well it is more correctly put that light follows the geodesics (the shape) of space because light is a mass-less energy. It is incapable of determining the vector it will travel because that is decided by the direction of emission from the light source and as such light must follow the curvature of space.
Light may be absorbed and re-emitted which would lead to scattering which is the equivalent of 'light noise' or general light wash when looking at an individual image. It may have the speed determined by the medium in which it is travelling and that is why it is measured as light speed in a vacuum. In a diamond light travels at about 40% the speed of light because of the effect of the material in a diamond. Just a small point which is why tensor equations are used to calculate curvature but the curvature is not of the light.
__________________
"Nature is obliged to let reality determine its laws, whereas mathematics is under no such constraint." |
|
|||
|
The metric tells you how to measure distance (for each coordinate) on a manifold. Which is quite handy in GR, as most of the time, the manifold, which represents spacetime, is warped. The metric provides you with a way to measure distance and time on a particular manifold. Remember, the manifold represents spacetime. For a discussion of metrics, go here
__________________
Some try to tell me, thoughts they cannot defend,... - Moody Blues. |
|
|||
|
Quote:
|
|
|||
|
By using the manifold you get when you solve the Einstein Field Equations. The metric tensor comes from the tangent spaces of the manifold. Mathematically, it drops out as a matrix, once you decide what coordinate system you want to use (remember, GR is coordinate free, it allows you to use any arbitrary set of coordinates). It was explained in the link in my original answer.
__________________
Some try to tell me, thoughts they cannot defend,... - Moody Blues. |
|
|||
|
Sorry article is a little over my head. I may have asked the question wrong.
What I want to ask is when energy = 0 on one side of GR equation you have a flat manifold. Right? What does that mean? Uggg ... I realize all that I do not know right now because I dont know the terms of the question I want to ask. Can you please show the equation again when energy is equal to 0 and all zero'd stuff removed? Quote:
|
|
|||
|
Quote:
Quote:
__________________
Some try to tell me, thoughts they cannot defend,... - Moody Blues. Last edited by Jim : 14-May-2008 at 05:02 PM. Reason: fixed quote tag placement... I think |
|
|||
|
Using:
( taken from another thread ) Rij - (gij*R)/2 + L*gij = -8*pi*G/c2 * Tij Rij = Ricci tensor R= curvature scalar gij = metric tensor L = cosmological constant G = Newtonian gravitational constant c = speed of light Tij = energy - momentum tensor (sometimes called stress energy tensor pi = 3.14159265358979323846… If the right side goes to 0 Rij - (gij*R)/2 + L*gij = 0 then Rij + L*gij = - (gij*R)/2 right? But what does that mean? Quote:
|