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Author Topic: Space-time curvature and antimatter  (Read 1897 times)

Offline McKay

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Space-time curvature and antimatter
« on: 27/05/2014 20:01:51 »
When people talk about how mass is curving the space-time and the geometry of it pretty much accounts for gravity, does the curvature actually means what it is usually represented as - a curve in a higher dimension (from plane to a 3D space)? In our 3D space case it would be a curve in 4th spacial dimension?

If that is the case and it really has such a meaning, doesn't it mean that the curvature can be both "up" and "down" from a 2D plane (not sure if two or more directions for 3D ..) and gravity from both would behave exactly the same?

Curvature to the "up", instead of the usual "down", would NOT have a "negative mass" (well, depends what we mean by that, doesn't it?) or "anti-gravity" properties or something like that, BUT - what would happen if those two came together? They would cancel out, wouldn't they? Would holding a chunk of this oppositely curved mass in my spaceship cancel out some of the mass and make it lighter?

Can anti-matter be thought as simply a space-time curvature in the opposite direction?


 

Offline yor_on

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Re: Space-time curvature and antimatter
« Reply #1 on: 16/06/2014 16:57:55 »
We use dimensions to describe paths in. We have four, and you looking at light can calculate a path for that light assuming it propagates. Doing so you find that it 'bends' around the sun, and now you have to explain why. Assuming that light does not lose 'energy' due to sheer propagation, ignoring the expansions redshift, it must be so that the path taken by light is the 'shortest' 'energy efficient' etc etc path it can find. But according to your observation it did 'bend'? So, in which dimension(s) can this be described geometrically as a straight path?

On the other tentacle, consider it a field, not as a propagation. Let the field be ruled by constants. Make it possible to observe and measure on and let it interact under a arrow of time, locally definable to a same constant as 'c'.
 

Offline yor_on

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Re: Space-time curvature and antimatter
« Reply #2 on: 16/06/2014 17:14:37 »
To further define it. All constants are local. When we call them universal we just mean that they are equivalent all through our observable universe. They have to be to be called 'constant'. So there is a subtlety to constants that most miss. They only exist locally.
 

Offline PmbPhy

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Re: Space-time curvature and antimatter
« Reply #3 on: 17/06/2014 09:43:00 »
Quote from: McKay
When people talk about how mass is curving the space-time and the geometry of it pretty much accounts for gravity, does the curvature actually means what it is usually represented as - a curve in a higher dimension (from plane to a 3D space)? In our 3D space case it would be a curve in 4th spacial dimension?
No. What you’re thinking of is called extrinsic curvature. General relativity is a theory about how matter manipulates intrinsic curvature. See

http://mathworld.wolfram.com/ExtrinsicCurvature.html
http://mathworld.wolfram.com/IntrinsicCurvature.html

Think of a piece of paper. If we think of the paper has having zero thickness then the paper is a two dimensional object. Now roll the paper up into a cylinder. The intrinsic curvature of the sheet remains the same but the extrinsic geometry changes. The intrinsic geometry is determined by measurements made within the sheet while the extrinsic geometry is determined by how the sheet finds its way into three dimensions.

The physics is explained here
http://www.eftaylor.com/exploringblackholes/Curving140610v1.pdf

By the way, antimatter is merely matter which is composed of particles which have the opposite charge and spin of their counter parts. E.g. the antiparticle of a proton is a particle of the same charge and mass but is negatively charged and has the opposite spin. But its impossible to tell whether any substance is matter or antimatter by what it does to spacetime since the only thing that effects spacetime is matter’s energy density, momentum density and stress. None of the parameters that describe those quantities can tell you whether a substance is composed of matter or antimatter. In fact there is nothing about a particle that makes it matter rather than antimatter other than a certain convention. If that convention was changed then so too would the declaration of whether a substance was matter or antimatter.
 

Offline jeffreyH

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Re: Space-time curvature and antimatter
« Reply #4 on: 03/07/2014 23:16:45 »
Quote from: McKay
When people talk about how mass is curving the space-time and the geometry of it pretty much accounts for gravity, does the curvature actually means what it is usually represented as - a curve in a higher dimension (from plane to a 3D space)? In our 3D space case it would be a curve in 4th spacial dimension?
No. What you’re thinking of is called extrinsic curvature. General relativity is a theory about how matter manipulates intrinsic curvature. See

http://mathworld.wolfram.com/ExtrinsicCurvature.html
http://mathworld.wolfram.com/IntrinsicCurvature.html

Think of a piece of paper. If we think of the paper has having zero thickness then the paper is a two dimensional object. Now roll the paper up into a cylinder. The intrinsic curvature of the sheet remains the same but the extrinsic geometry changes. The intrinsic geometry is determined by measurements made within the sheet while the extrinsic geometry is determined by how the sheet finds its way into three dimensions.

The physics is explained here
http://www.eftaylor.com/exploringblackholes/Curving140610v1.pdf

By the way, antimatter is merely matter which is composed of particles which have the opposite charge and spin of their counter parts. E.g. the antiparticle of a proton is a particle of the same charge and mass but is negatively charged and has the opposite spin. But its impossible to tell whether any substance is matter or antimatter by what it does to spacetime since the only thing that effects spacetime is matter’s energy density, momentum density and stress. None of the parameters that describe those quantities can tell you whether a substance is composed of matter or antimatter. In fact there is nothing about a particle that makes it matter rather than antimatter other than a certain convention. If that convention was changed then so too would the declaration of whether a substance was matter or antimatter.

I really get a lot of insight from various members on this forum. Sometimes it just clicks suddenly. I sometimes wish people would stop, take a breath, read the response and ponder. No one has to take an answer as gospel but at least should give it due consideration. Don't stop trying Pete. I know it frustrates you but its not your loss. :-)
 

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Re: Space-time curvature and antimatter
« Reply #4 on: 03/07/2014 23:16:45 »

 

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