fabric of space

[allo4]

With the idea of the fabic of time and space they always describe it as a marble(mass)on a sheet(time and space), the marble bends the sheet like the earth or gallaxy bends space to cause gravity or bend time.

Anyway imagine as the marble travels over the sheet it pulls up a wave in the sheet which eventually catches up and gives a slight accelleration to the marble before it slows down again. if this could apply to a gallexy travelling through space it could explain why the expansion of the universe is accellerating.

I was thinking this the other day and already don't think this at all a possibility just wanted to check what other people thought

[IM Egdall]

I don't think so. I've read that the motion of galaxies is actually pretty small. The expansion of the space between galaxies is a far greater effect.

[DrRocket]

With the idea of the fabic of time and space they always describe it as a marble(mass)on a sheet(time and space), the marble bends the sheet like the earth or gallaxy bends space to cause gravity or bend time.

Anyway imagine as the marble travels over the sheet it pulls up a wave in the sheet which eventually catches up and gives a slight accelleration to the marble before it slows down again. if this could apply to a gallexy travelling through space it could explain why the expansion of the universe is accellerating.

I was thinking this the other day and already don't think this at all a possibility just wanted to check what other people thought

 

The "wave" that you are describing would not explain why space itself is expanding and expanding uniformly in all directions.

 

Space is not a fabric. The analogy to which you refer is not aqccurate -- it is meant only to give a very rough idea of the notion of curvature. It probably generates as much confusion as enlightenment.

Edited March 28, 2011 by DrRocket

[ajb]

It probably generates as much confusion as enlightenment.

 

This I concur with. Almost all misconceptions about general relativity found on this forum have their origin in the "bowling ball on a trampoline" analogy.

[lemur]

The "wave" that you are describing would not explain why space itself is expanding and expanding uniformly in all directions.

 

Space is not a fabric. The analogy to which you refer is not aqccurate -- it is meant only to give a very rough idea of the notion of curvature. It probably generates as much confusion as enlightenment.

Idk, since length contracts due to motion, it doesn't seem entirely implausible to me that the gravity fields of orbiting bodies could be slightly extended in the direction perpendicular to the line of motion and that this could make each orbiting system a weak gravity-wave generator. I know this is radically speculative, so sorry; I'm just thinking with the OP.

 

This I concur with. Almost all misconceptions about general relativity found on this forum have their origin in the "bowling ball on a trampoline" analogy.

Probably some bodily injuries have been caused by experimenting with this analogy using actual bowling balls and trampolines as well.

 

 

[csmyth3025]

Idk, since length contracts due to motion, it doesn't seem entirely implausible to me that the gravity fields of orbiting bodies could be slightly extended in the direction perpendicular to the line of motion and that this could make each orbiting system a weak gravity-wave generator. I know this is radically speculative, so sorry; I'm just thinking with the OP.

Although this phenomenom doesn't have anything to do with length contraction, your idea isn't radically speculative. If a massive body is accelerating - in this case changing direction due to orbiting another body - it will produce gravitational waves:

 

Gravitational waves carry energy away from their sources and, in the case of orbiting bodies, this is associated with an inspiral or decrease in orbit. Imagine for example a simple system of two masses — such as the Earth-Sun system — moving slowly compared to the speed of light in circular orbits. Assume that these two masses orbit each other in a circular orbit in the x-y plane. To a good approximation, the masses follow simple Keplerian orbits. However, such an orbit represents a changing quadrupole moment. That is, the system will give off gravitational waves.

 

Suppose that the two masses are m₁ and m₂, and they are separated by a distance r. The power given off (radiated) by this system is:

 

,^[7]where G is the gravitational constant, c is the speed of light in vacuum and where the negative sign means that power is being given off by the system, rather than received. For a system like the Sun and Earth, r is about 1.5×10¹¹ m and m₁ and m₂ are about 2×10³⁰ and 6×10²⁴ kg respectively. In this case, the power is about 200 watts. This is truly tiny compared to the total electromagnetic radiation given off by the Sun (roughly 3.86×10²⁶ watts).

 

 

In the case of two neutron stars orbiting each other, the amount of energy carried off by gravitational waves can be quite large:

 

A more dramatic example of radiated gravitational energy is represented by two solar mass neutron stars orbiting each other at a distance of 189×10⁶ m (0.63 light-seconds). Plugging their masses into the above equation shows that the gravitational radiation from them would be 1.38×10²⁸ watts, which is about 100 times more than the Sun's electromagnetic radiation.

 

(ref. http://en.wikipedia....orbiting_bodies )

 

PS - The energy carried off by gravitational waves in these systems comes from a loss of their angular momentum. In simple terms, they're spiralling in towards each other. In the case of the Earth, it will take about 10^13 times the age of the universe for Earth's orbit to decay to the point where the Earth will merge with the Sun. In the case of the binary pulsars with the closest known orbital separation (PSR J0737-3039), they're expected to merge in about 85 million years.

 

Chris

 

Edited to add PS

Edited March 29, 2011 by csmyth3025

[ajb]

Probably some bodily injuries have been caused by experimenting with this analogy using actual bowling balls and trampolines as well.

 

Relativists are glutton* for punishment and adore pain!

 

 

* Corrected spelling!

Edited March 29, 2011 by ajb

[J.C.MacSwell]

Relativists are gluten for punishment and adore pain!

 

I'll knead to add them to my latest French Bread recipe.

[ajb]

I'll knead to add them to my latest French Bread recipe.

 

LOL, corrected spelling.