The arrow of time

[Aki]

Time as we know, only goes forward, but not backwards. What determines the direction of the arrow of time?

[maddog]

Depends. Antiparticles can be thought as having time-reverse orientation.

Maybe there is more to time (as Qfwfq said elsewhere -- hidden variables) and we

don't yet know why this is different.

 

Maddog

[Queso]

i believe there are actually 3 arrows of time, i forget what they were though.

[Qfwfq]

Maybe, if we could find the bow, we could shoot the arrow the way we like!

 

If time were going "the opposite way", we'd call that forward and "this way" backward.

 

Maybe there is more to time (as Qfwfq said elsewhere -- hidden variables)

Surely you don't mean the Kaluza-Klein stuff?

[UncleAl]

"Entropy indicates the arrow of time" is the classical answer, but it is a weak arrow. Entropy is only statistical. Small ensembles will give you large fluctuations including spontaneous reversals. It's much worse than that! Energetic systems with positive feedback will spontaneously order over large scales and long times - Belousov-Zhabotinsky reaction, and life for that matter.

 

Angular momentum is a better arrow of time. Consider a broad flat motion picture film can. Weld one port normal to its center, weld one port tangent to its edge, seal the halves together. Make a video of water being vigorously pumped in the middle and out the edge - no problem. Reverse the movie - NO WAY. It's one-way valve, a hydraulic diode, with no moving parts other than the water.

 

Time flies like an arrow; fruit flies like a banana.

[Aki]

Surely you don't mean the Kaluza-Klein stuff?

 

What's the "Kaluza-Klein stuff"?

[maddog]

Surely you don't mean the Kaluza-Klein stuff?

I wonder if Kaluza and Klein had something to their idea. I don't think this alone would

do. There is the Weak and Strong force to handle.

 

For Aki, the Kaluza-Klien model is a method to unify Gravitation (GR) and the EM force.

This is done in 5-dimensions, with the last dimension "rolled-up" very small. How small

determines the fine structure constant. Kaluza first thought it after reading Einstein's

paper on GR. Einstein conversed with and thought Kaluza's theory had merit. I have

come across the original paper Kaluza wrote and read it (got a translation from

German). Klien later uptated it with some generalization about 1925. You should be

able to find a Sci Am article on it in the last five years or so.

 

Back to Qfwfq: I do think like Einstein that a Unification would require some kind

Geometrization. I do think QM <all forms> needs to be incorporated to be the working

final theory. Of course I do have a day job. So I have to mediate studying all this with

working for a living. ;)

 

Maddog

[UncleAl]

Nobody has ever been able to make Kaluza-Klein treatments work to unify EM and gravitation by adding a fifth dimension. One problem is that Einstein's gravitation fundamentally does not look like EM interaction - but it can! There are two observationally indistinguishable yet very different ways to formulate gravitation.

 

Einstein postulated the Equivalence Principle - that all local masses fall identically in vacuum regardless of composition or geometry. One then gets spacetime curvature and metric gravitation (General Relativity). The math is parity-even tensors. EM interactions are vector cross products of current, field, and acceleration. Spacetime curvature looks nothing like that.

 

Weitzenböck/Weitzenboeck ignored the Equivalence Principle. One then gets spacetime torsion and affine gravitation (teleparallel gravitation). The math is parity-odd pseudotensors. EM interactions are vector cross products of current, field, and acceleration. Spacetime torsion looks exactly like that. General Relativity is wholly contained within affine gravitation. Perhaps folks have been looking in the wrong place.

 

If you find two lumps that fall differently in vacuum, Einstein was wrong. It is as simple as that. Folks have been looking at different chemical compositions drop since Galileo Galilei and Simon Stevin in the 16th century. (Modern experiments are much more clever than merely dropping lumps.) All chemical compostions fall identically to one part in ten trillion difference/average. That includes oppositely spinning fused silica balls and oppositely spinning superconductive shells inside Gravity Probe B. What else could there possibly be?

 

Geometry, obviously. Does a left hand fall identically to a right hand? Optically right-handed quartz and amorphous fused silica did not fall identically, though the difference was not statistically significant. The full parity Eotvos experiment, left-handed vs. right-handed quartz, is being set up in China. Results by the end of 2005. qz.pdf in signature block, below.

 

Drop a shiny silver dollar in the middle of a long dark block in the dead of a moonless night. You won't find it at the corner just because there is a nice bright streetlight located there - even if you use a metal detector.

[Qfwfq]

Consider a broad flat motion picture film can. Weld one port normal to its center, weld one port tangent to its edge, seal the halves together. Make a video of water being vigorously pumped in the middle and out the edge - no problem. Reverse the movie - NO WAY.

What's the difference between reversing that movie, and reversing the momenta after two gasses have mixed, or after hot and cold have exchanged heat?

[Qfwfq]

I know there is one difference:

 

Even classically, reversing the momenta of individual molecules would be far harder than for the drops of water. Further, Heisenberg objects far more strongly in the case of the molecules.