Time's arrow, or what universal property is asymmetric, anyway?

[gendou2]

Troubles of categorization aside, do we have any laws that predict the arrow of time?
All known laws are time-symmetric, right?
The arrow of time does appear in experiments, right?
(Example: Waiting for a broken egg to piece itself back together and hop up onto a table -- a very boring experiment).
To me this seems to imply that there is a law missing, one that predicts the arrow of time.
Does anyone get the same impression?

 

[ZapperZ]

Troubles of categorization aside, do we have any laws that predict the arrow of time?
All known laws are time-symmetric, right?
The arrow of time does appear in experiments, right?
(Example: Waiting for a broken egg to piece itself back together and hop up onto a table -- a very boring experiment).
To me this seems to imply that there is a law missing, one that predicts the arrow of time.
Does anyone get the same impression?

But there are many phenomena that have a broken time reversal symmetry[1,2]. In fact, the CP violating events in kaon decays indirectly implies a broken T symmetry in such decays.

Zz.

[1] Covington et al. PRL 79, 277 (1997).
[2] Kaminski et al. Nature, 416, 610 (2002).

 

[Chrisc]

Troubles of categorization aside, do we have any laws that predict the arrow of time?
All known laws are time-symmetric, right?
The arrow of time does appear in experiments, right?
(Example: Waiting for a broken egg to piece itself back together and hop up onto a table -- a very boring experiment).
To me this seems to imply that there is a law missing, one that predicts the arrow of time.
Does anyone get the same impression?

I certainly do.
That's what my posts refuting Phrak's comments are about.
What's missing is the Principle of General Relativity applied to our "qualification" of fundamental
dimension instead of as it is now, just a quantification of measure. This is the reason the constant
debate over as you put it, the "categorization" of time continues.
It is also why such dimensional equivalences expressed by E=mc^2 are falsifiable and incredibly accurate "quantitatively".
If you're interested, I have submitted a model of time that predicts the second law of thermodynamics
in the FQXI.org contest.
"The Heuristic Significance of the Principle of General Relativity on the Nature of Time"
It is probably too absurd for most to appreciate, but might help you understand the dilemma.

As for your question of the time symmetry of the laws of physics, you will find all the laws are
and always will be time symmetric as long as the operational definition of time remains the accepted
definition of time in physics.
Any argument against such a kinematical-mathematical operation is futile as it amounts to disputing
the axioms of mathematics. Without any concern for the identities, kinematic and dynamic the math
represents, this operational definition of time cannot fail. This is the gist of Phrak's argument above.

So as long as we ignore the evidence of the second law (the most pervasive empirical evidence in
the history of the universe) and as long as we do not care about the few exceptions such as ZapperZ
pointed out, we can keep our heads in the sand and look for more comfortable solutions.

 

[Dale]

All known laws are time-symmetric, right?
The arrow of time does appear in experiments, right?
(Example: Waiting for a broken egg to piece itself back together and hop up onto a table -- a very boring experiment).

No, as mentioned above not all known laws are time-symmetric. The "boringness" of the broken egg experiment is governed by the time asymmetric 2nd law of thermo: dS/dt >= 0.

 

[ThomasT]

Troubles of categorization aside, do we have any laws that predict the arrow of time?
All known laws are time-symmetric, right?
The arrow of time does appear in experiments, right?
(Example: Waiting for a broken egg to piece itself back together and hop up onto a table -- a very boring experiment).
To me this seems to imply that there is a law missing, one that predicts the arrow of time.
Does anyone get the same impression?

The second law of thermodynamics is the thermodynamic arrow of time.

The basic equations of motion are time-independent.

The arrow of time does appear in experiments.

The universe is expanding. Since this is the source of all motion, maybe it can be used as the basis for some new fundamental law of physics.

The source of the expansion is an unsolvable problem.

 

[DB Katzin]

That's what some people think, but I really don't believe it at all. Time is something humans invented, just like any measurement system.

I think there is a distinction between a "measuring system" and the object the system is measuring. When one is describing the physical characteristic of an object the system: meters vs. yards, pounds vs. Kg is certainly arbitrary and invented but the object and quality being measured is something we all sense more or less in common: how big it is, how heavy it is, etc. Time it seems is different. When describing something when we ask how old is it we are not talking about an intrinsic quality you can rub up against like size or weight, even color or smell. Yet we all know what is being asked even if our measuring system differs: hours, days vs. moons since the great fire, etc. But I think you mean something different when you say "time is invented." Don't you mean something like this. We live in a world where we are aware of change. We change, the seasons change, the weather changes, the world changes. But not at the same rate. We need things like 2 o'clock so we can coordinate activities--something we do a lot of in complex society. So we count up a bunch of changes--sunrises, quartz crystal vibrations, etc and we standardize it so we know when to do stuff in relation to other stuff. But you don't find time anywhere. Even though you can spend time, you can't buy much with it, and even though you can save time, you can't put it in the back and get interest.