Alan Lightman, in Defense of Disorder

Like Albert Einstein, Clausius was a theoretical physicist – that is, all of his work, including his
seminal work on disorder, consisted of mathematical feats performed with pencil and paper.
Clausius’s great paper on disorder, ‘On the Moving Force of Heat’ (1850), was published the
same year that he became a professor of physics at the Royal Artillery and Engineering School in
Berlin. In that paper, Clausius showed that change in the physical world is associated with the
inevitable movement of order to disorder. Indeed, without the potential of disorder, nothing in
the cosmos would ever change – like a row of upright dominoes held rigidly in place, or like a
completed Buddhist mandala locked in a bank vault, safe from the brooms of the monks of
Namgyal.
‘Heat’ occurs in the title of Clausius’s paper because increasing disorder is often associated with
the transfer of heat from hot bodies to cold – but the concept is more general. In a later paper,
Clausius coined the term entropy as a quantitative measure of disorder. The word comes from the
Greek ἐν (en), meaning ‘in’, and τροπή (tropē), meaning ‘transformation’. It is the increase of
entropy that is linked to transformation, movement, change in the world. The more disorder, the
more entropy. The last two sentences of Clausius’s 1850 paper are:
1. The energy of the Universe is constant

2. The entropy of the Universe tends toward a maximum
Order inevitably yields to disorder, and entropy increases until it cannot increase any further. It is
this movement that drives the world. Clean rooms become dusty. Temples slowly crumble. As
we grow older, bones grow brittle. Stars eventually burn out, emptying their hot energy into the
coldness of space – but while doing so, they provide warmth and life to surrounding planets. We
live off this relentless increase of disorder.
Disorder is also the answer to the profound question: why is there something rather

than nothing?
Even something as fundamental as the direction of time is governed by the movement of order to
disorder. If that seems like a preposterous statement, consider a glass goblet falling off a table
and shattering on the floor – a transformation from order to disorder of the most obvious kind. A
film of the event would look normal to us. But if we saw a movie of scattered shards of glass
jumping off the floor and gathering themselves into a fully formed goblet, perched on the edge of
the table, we would say the movie was being played backwards in time. Why? Because
everything passes from order to disorder as we march towards the future. One might say that the
forward direction of time is the increase in disorder. Indeed, without these changes, we’d have no
way of telling one instant from the next. There would be no clocks, no flights of birds, no leaves
slipping through the air as they dropped from trees, no breathing out and in. The Universe would
be a still photo for all of eternity.
Disorder is also the answer to the profound question: why is there somethingrather than nothing?
(Such questions keep physicists and philosophers up at night.) Why does material of any kind
exist, rather than pure energy? From a scientific perspective, the question relates to the existence
of antiparticles, predicted in 1931 and then discovered in 1932. Every subatomic particle, such as
the electron, has an antiparticle twin – identical to the first, except with opposite electrical charge
and certain other qualities. Which of the pair we call the ‘particle’ and which we call the
‘antiparticle’ is a matter of convention, like the North and South poles. When they meet, particles
and their antiparticles annihilate each other, leaving nothing but pure energy.
If there were an equal number of particles and their antiparticles in the infant Universe, as one
would expect from a completely symmetrical universe, all matter would have been obliterated
billions of years ago, leaving nothing but pure energy. No stars, no planets, no people – or any
other solid material. So why are we here? Why haven’t all the particles disappeared along with
their antiparticle partners?
The answer to this physicists’ conundrum came in 1964. In very delicate experiments at that
time, we discovered that particles and antiparticles do not behave in exactly the same way.
Rather, there is a slight asymmetry in how they interact with other particles, so that immediately
after the creation of the Universe, particles and their antiparticles were not produced and
destroyed in equal numbers. After the mass annihilations of particles with their antiparticle
partners, some particles would remain, like a surplus of boys sitting on the bench at a school
dance. Those remaining particles and the asymmetry that produced them is why we exist.

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Like Albert Einstein, Clausius was a theoretical physicist – that is, all of his work, including his

1. The energy of the Universe is constant

Disorder is also the answer to the profound question: why is there something rather

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