# How to reverse irreversible changes LO24398

From: Winfried Dressler (winfried.dressler@voith.de)
Date: 04/19/00

Replying to LO24373 --

At de Lange stated:
>Students believe that the chemical reaction is reversible.
and suggested a title for a LO-dialogue:
>How to reverse irreversible changes.

That it is not only possible to reverse irreversible changes, but that we
do it all the time may be the reason, why students believe that chemical
reactions are reversible.

Nothing is crazy about breathing, drinking, eating or repairing what is
broken. Only in those moments, when this is not possible, we become aware
of the basic irreversibility, the arrow of time.

In my first contribution to this thread in LO24201, I have introduced a
diagramm:

>Diagram 1:
>state 1 --(learning)--> state 2 --(unlearning)--> state 3

as a possible evolution of time (arrow of time is from left to right) in
contrast to the impossible:

>Diagram 2:
>state 1 <--(unlearning)-- state 2

A reverse change would be:

state 1 --(change)--> state 2
state 1 <--(reverse change)-- state 2

which includes a forbidden arrow back in time.

Now, what is a reverse irreversible change?

state 1 --(irreversible change)--> state 2 --(reverse irr. change)--> state 1

Is this possible? If yes and if this is all, the word 'irreversible'
becomes meaningless. Irreversible does mean that state 1 is gone forever.
So this one is not possible too.

Then, what IS possible?

state 1 --(irreversible change 1)--> state 2 --(irreversible change 2)-->
state 3

Now we want this 'irreversible change 2' to be a 'reverse irreversible
change' with respect to 'irreversible change 1' and this naming should
make sense.

I have stated in the beginning, that we are doing reverse irreversible
changes all the time and used breathing, drinking, eating and repairing as
examples.

What we want when we think of reversing something is

state 3 = state 1

but this is not possible due to irreversibilty, which means (hoping that
you are slowly getting familiar with this '>' :-) ):

state 3 > state 1

This one can be written as

state 3 = state 1 + ACE

(ACE: Additional Changes in the Environment) Now we have what we want:

state 1 --(irreversible change)--> state 2 --(reverse irr. change)-->
state 1 + ACE

So these ACE are the clue to revese irreversible change.

For example, breathing reverses some irreversible changes in our body,
which would otherwise lead to death. The ACE is a decrease in
concentration of oxygene and an increase in concentration of carbondioxide
in the environment.

This was the easy part. I am not going to get into the difficult part,
which depend from the change which should be reversed: How to skillfully
apply entropic forces and connect the system with it's environment, so
that in the end the system show state 1 again, and how to care for those
ACE which inevitably will occur as a consequence of the irreversible
nature of the changes.

I am looking forward to read about your experiences and examples.

Liebe Gruesse,

Winfried

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