Re: [Phys-l] Arrow of Time Issue

[carmelo@pacific.net.sg]

Denis Evans from Australian National University measured changes in  
the entropy of latex beads, each a few micrometres in size and  
suspended in water. By using a precise laser beam, the team measured  
the movement of the beads very frequently, and hence repeatedly  
calculate the entropy of the system at short time intervals. They  
found that the change in entropy can be negative over time intervals  
of a few tenths of a second. In a sense, entropy can be violated in  
isolated system…


Alphonsus

Quoting John Mallinckrodt <ajm@csupomona.edu>:

> Another way of saying the same thing.  The second law of   
> thermodynamics says that the entropy of isolated systems "does not   
> decrease with time."  If we discovered in experiments that the   
> entropy of isolated systems "decreases with time," it would mean   
> that the second law of thermodynamics is wrong, NOT that time is   
> running backwards.
>
> John Mallinckrodt
> Cal Poly Pomona
>
> On Mar 7, 2012, at 7:27 PM, Jack Uretsky wrote:
>
> > I don't understand you.  Let me try to explain why in two ways:
> > 	"If time is increasing" suggests that "time" is defined in such a
> > way that it could be non increasing.  "Time" is not so defined.  We define
> > "time" by findng a periodic phenomenum, and then counting periods.  The
> > count always increases - by definition.  "If time is increasing" is
> > logically like saying "if four is greater than three".  But four is
> > defined as three plus one.  So the "if" in the statement is surplusage;
> > there is no laternate possibility.  Same with "time".  We define it so
> > that there is no alternate possibility.
> > 				Regards,
> > 					Jack
> >
> > "Trust me.  I have a lot of experience at this."
> > 		General Custer's unremembered message to his men,
> > 		just before leading them into the Little Big Horn Valley
> >
> >
> >
> >
> > On Wed, 7 Mar 2012, Bennett Sessa wrote:
> >
> > > That is my understanding. If time is increasing then entropy must   
> > > always increase. If time decreases Clausius equality and the   
> > > entropy equation show that entropy should decrease, but we know   
> > > this to be impossible, therefore time cannot decrease. CPT   
> > > symmetry shows that time is however reversible.