http://www.smbc-comics.com/index.php?db=comics&id=2195 -Thomas C On Sat, Mar 26, 2011 at 6:34 PM, Veit Elser <ve10@cornell.edu> wrote:
Physics teaches us that at a sufficiently fundamental level the laws of motion are invariant upon reversing the direction of time. In classical mechanics the equations of motion are differential equations whose form is unchanged when t is replaced by -t. The same applies to quantum mechanics: time reversal combined with complex conjugation preserves the form of the Schroedinger equation (physicists refer to the field automorphism i -> -i as "charge conjugation" or "C symmetry").
Phenomena that appear at odds with time-reversal symmetry, such as friction and causation, are really just manifestations of the quirky configurations of matter in which we find ourselves -- i.e. in the aftermath of the big bang. A gas freely expanding into a vacuum does not do so as the result of a time asymmetry in the collision processes but because the distribution of positions and velocities is peculiar (low entropy).
It used to bother me that although the laws of physics didn't have a preferred direction of time it sure felt that I was always "moving" in one direction, i.e. toward the future. But "over time" I've come to realize that the complex biochemical/neurological processes that underlie the perception of my transit through time are just as vulnerable to second-law-of-thermodynamics asymmetry as a freely expanding gas.
So I don't agree at all that modern physics is forcing us to revise our cherished belief in causality, since that notion was never supported even by the old physics of Newton and Maxwell. Causality is a casualty of our world being highly out-of-equilibrium. How it got that way is the real mystery.
Veit
On Mar 26, 2011, at 4:26 PM, Henry Baker wrote:
Some modern physicists have already started to give up on "causality", as a result of EPR experiments showing that "spooky action at a distance" does indeed happen.
So "causality" may indeed be an illusion that results from our (vastly imperfect) "memory" system. This is essentially a version of the anthropic principle: we see what our minds & memories allow us to see.
http://en.wikipedia.org/wiki/Anthropic_principle
Szilard/Maxwell/Bennett found that the baseball umpire's rule is true: there aren't any balls or strikes until the umpire calls them. Translation: there is a large energy cost to nailing down a memory; the cost may not show up, however, until you _clear_ the memory to zeros.
http://en.wikipedia.org/wiki/Entropy_in_thermodynamics_and_information_theor...
At 12:00 PM 3/26/2011, Bill Gosper wrote:
In freshman Humanities, we had to read Hume's
1. *An Enquiry Concerning Human Understanding*<http://www.infidels.org/library/historical/david_hume/human_understanding.html>
**wherein he concluded causality was essentially illusory. Or so I gathered. In his gedanken mechanics, the terminology was so muddled and in conflict with modern terminology that I boggled. --rwg
_______________________________________________ math-fun mailing list math-fun@mailman.xmission.com http://mailman.xmission.com/cgi-bin/mailman/listinfo/math-fun
_______________________________________________ math-fun mailing list math-fun@mailman.xmission.com http://mailman.xmission.com/cgi-bin/mailman/listinfo/math-fun