A Fear of heights, Microscopic Reversibility and King Cnut 


Hovione, Sete casas, Loures, Portugal
Member of Chimica Oggi – Chemistry Today’s Scientific Advisory Board

I’m sure we all have had, or witnessed, a few close calls in the laboratory. As scientists we try to make nature do what we want her to, but sometimes we do not have that deep understanding necessary to accomplish the feat – that is - we are still ignorant of the many of rules that Mother Nature has lain out and follows. Sometimes the situation can be comical but at other times there can be really serious consequences. One of the things that concerns me (not to say frightens me) is the irreversibility of some reactions once they get underway. This irreversibility is also behind my acrophobia, a fear of heights. Once you fall over the cliff there is no way to you can get back up and save yourself from that long drop.

As chemists we are taught the Principle of Microscopic Reversibility. Reactions at the microscopic level are reversible due to the microscopic equations of motion that are symmetric with inversion of time. However, statistically the reverse reaction is only as likely as the forward reaction at equilibrium. So it’s a long way down once you go over the cliff till you reach equilibrium. The longer the fall the more energy needs to be dissipated ...