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From: Chumley on 25 Jun 2010 12:37

"Luyang Han" <luyang.han(a)gmail.com> wrote in message
news:4c1fcb21(a)news.uni-ulm.de...
> Hello,
>
> One question comes into my mind. Is there any fundamental interaction
> which
> shows a hysteresis or a memory effect?

of course Magnetics

>
> If we consider the framework of Newton,

yes, yes, Newtonian space..........

> the evolution of the system

Evolution means TIME

> just
> depends on the interaction and its state at a certain time, but does not
> depends on how the system reached this state.

that is quite wrong old boy, take a random walk and where you are at
depends on where you have been, right ?

One of your problems is understanding the difference between deterministic
and un-deterministic processes.


>
> Lots of macroscopic phenomena show memory effect. But the memory is only
> due
> to the reason that the microscopic description is ignored

ignored by Who? You ?

then stop ignoring it.


> and a statistical
> macroscopic view is taken. Consider the typical example of a magnet. The
> response of the magnet to the external field depends on its history.

you should clearify that, position, time, fields etc

> But
> here just the magnetization of the material is considered.

too simple, what about hysteresis?

> If we know the
> microscopic configuration of the magnetic moment, the behavior of the
> magnet
> can be predicted without knowing its history.

However that moment, or vector, is a product of what happened in the past.

>
> So the question is, is there any fundamental interaction, whose influence
> to
> the system evolution depends on the history of its interaction?

Yes, a magnet. (you missed it, please get demagnitized)

>
> Is this problem related to the concept of arrow of time in physics?
>

no, that is just a vector direction.


> Han


From: Luyang Han on 26 Jun 2010 18:27
mordent wrote:
>
> Wrong.
> The first computer memory was Magnetic core memory.
> http://en.wikipedia.org/wiki/Magnetic_core_memory
> One cannot predict magnetic behavior without knowing its history.
>
> A good learning lesson for you.

As I have said, if you just know the macroscopic state of the system, here
the magnetism, you cannot predict its behavior without knowing its history.
But If you know all the configuration of the spins, you CAN predict. This is
what people in micromagnetism research is doing every day.

http://en.wikipedia.org/wiki/Micromagnetism
From: Luyang Han on 26 Jun 2010 19:00
Chumley wrote:
> take a random walk and where you are at
> depends on where you have been, right ?
> One of your problems is understanding the difference between
deterministic
>and un-deterministic processes.

OK. So first which system shows truly a random walk behavior? If you are
think the movement of the gas molecules or so, it is not truly random. One
should distinguish the apparent randomness and the intrinsic randomness
here. For example, it is usually believed that the radioactive decay or
collapse of quantum state is the true random process. The question of memory
effect I would like to discuss is just for the fundamental process, not the
macroscopic statistical process.

Even in an un-deterministic processes, the concept of memory effect is still
valid. Take the example of random walk, of course where you are at
depends on where you have been. But more specifically, if you are at a
certain position P, the future, although un-deterministic, we usually
describe as a probability distribution of jumping to other sites. Then the
question is whether this probability distribution depends on how you arrived
at the position P. If not, the system does not show memory effect.

Many true random process does not show memory. The probability of the
nuclear decay (half life) does not depends on how we assemble the atoms in a
defined state.


And Chumley. If you want to discuss, make your idea clear and spare your
disdain.

Han
From: Luyang Han on 26 Jun 2010 19:18
Edward Green wrote:

>
> That's pretty much ruled out by semantics: if the system has a
> "memory", then the memory is part of the current state of the system.
> A better question is, what kinds of "states" do we have in mind when a
> system is said to display memory?
>

OK. More specifically, imaging we have two systems, at a specific time they
are identical, which means ALL the physical description of the system is
identical, but these two systems are obtained in different way, so to say
they arrive in the same state by different path. The question is, in a
physical world will the evolution of the two system be different or not.

some remarks:

1. ALL the physical description
This means every degree of freedom is considered. The idea is the discussion
is about fundamental physical process. I would like to repeat again that
magnetism and ferromagnetic material has NO fundamental memory effect that I
would like to discuss here.

2. (two systems) arrive in the same state by different path
It is interesting to think about whether this is really possible.
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