I'm not sure what you mean by "sensible" but, to me, there are many
many more operations that we can use sensibly. One such irreversible
(in the sense of lacking a strict inverse function) operation is
squaring. If someone told you that they squared a number and got 9,
you do not know whether the number they squared is 3 or -3. You do
know its one of those two, but you cannot reverse the process only
with the information "I squared some number and got 9". There are
much worse examples.
For instance if someone told you they took the sine function of a
number and got 0, there are infinitely many possible numbers they
could have applied sine to. Typically, irreversibility in nature is
justified mathematically (entropy has a mathematical justification,
for example, though it is statistical in nature).
Hugh
You might want to x-post to sci.physics. They love this topic. I think
irreversibility in nature is the offspring of quantum mechanics
(built-in probability), statistical mechanics (entropy) and chaos
theory ("it's all downhill from here").
-mark