Page 16 - Astronomy - October 2017 USA

FORYOURCONSIDERATION

B Y J E FF H E S T E R

Entropy’s rainbow

The statistically likely path to complexity.

he early universe disorder increases with time.” logarithm of the number of Nope. The molecules are
was remarkably To this very day, that statement microstates corresponding to indeed more localized in both
uniform. Today’s remains de rigueur in class- the same macrostate.) space and momentum, so their
universe is anything rooms (and blogs) any time the Rather than “disorder entropy is clearly lower than it
Tbut. What gives? subject crops up. But it is an increases,” what the Second Law started out. But what about the
The details of how we got from oversimplification that does of Thermodynamics actually photons that were radiated
there to here form one of the more harm than good. says is that random changes away? There are all sorts of
grand themes of science. But Identifying entropy with tend to move things toward sta- possible ways for those photons
viewed from 30,000 feet, the “disorder” is a lot like equating tistically more likely configura- to be arranged, meaning that
transformation can be summed energy with “bombast.” It may tions. What happens along the there are lots and lots of pos-
up in one word — entropy. well be that adding energy often way can be really amazing. sible configurations for the
“Hold on a minute,” you say. makes things more bombastic. Imagine watching a giant system as a whole. The
“Entropy doesn’t build stuff. Talking about bombastic events cloud of interstellar gas as it starts increased entropy of the pho-
Entropy tears stuff down!” might even help someone visu- to collapse under its own weight. tons is more than enough to
That is certainly the common alize what can happen when As the cloud gets smaller, it sure make up for the decreased
impression people have lots of energy is dissipated at looks like things are getting more entropy of the cloud itself.
about the Second Law of one time. But there is no such “ordered,” so perhaps you com- As energy (and entropy) is
Thermodynamics. It’s also thing as “conservation of bom- plain about the seeming violation radiated away, the cloud loses
dead wrong. bast.” Trying to apply such a of the Second Law. pressure support and collapses
Rewind the clock to the mid- further. Eventually that col-
dle of the 19th century. In one lapsing cloud settles into a
of the all-time greatest advances disk. Stuff in the disk clumps
in the history of science, up. The gas at the center gets so
Ludwig Boltzmann has just hot and dense that a fusion
used the statistics of how mol- reaction kicks in. Where once
ecules move to explain why heat there was a big, spread out,
always flows from hot things to “disordered” clump of inter-
cold things. It is a beautiful, stellar gas, now there is a
elegant piece of work. It is also young star surrounded by
counterintuitive to a generation The tombstone of Ludwig Boltzmann (1844–1906), who defined entropy, carries planets. So much for tearing
of scientists who are only begin- the equation for the Boltzmann constant. MICHIGAN STATE UNIVERSITY things down!
ning to get used to the atomic As it goes with the forma-
theory of matter. notion to the physical world What you don’t see is that the tion of a planetary system from
Boltzmann has trouble would lead to all sorts of collapsing cloud is also getting an interstellar cloud, so it goes
explaining what he is on about, absurdity. hotter, meaning that the mol- for everything beginning with
until he starts talking about In like fashion, it is wrong, ecules in the gas have the energy that early uniform universe,
entropy as “disorder.” A low even nonsensical, to identify to move faster. The wider range right up to you sitting there
entropy state, says Boltzmann, entropy with disorder. of velocities (more correctly reading this article. The glori-
is more ordered. A high entropy “Increasing disorder” is not a momentum states) that mol- ous, complex, awe-inspiring
state is more disordered. It’s physical law. It can’t be. ecules can take on more than structure that surrounds us is a
easier to jumble things up than Disorder isn’t even a physical makes up for the decrease in byproduct of increasing
to go the other direction, which quantity. Rather than a measure places the molecules can be. entropy, the blind, unguided,
is why entropy always increases. of disorder, entropy is actually a Entropy increases as it must. inexorable march of the uni-
It is a simple, visually compel- quantitative measure of how But that hot molecular gas verse toward ever-more statisti-
ling explanation that people can many different ways you can gives off radiation, which takes cally likely states.
sink their teeth into. The idea of rearrange the components of energy away from the mole-
entropy as disorder sticks. And something without changing its cules, reducing the available Jeff Hester is a keynote speaker,
sticks. And sticks . . . bulk properties. (If you want momentum states. OK, surely coach, and astrophysicist.
“The Second Law of that in more formal terms, this is a violation of the Second Follow his thoughts at
Thermodynamics says that entropy is a constant times the Law! jeff-hester.com.
BROWSE THE “FOR YOUR CONSIDERATION” ARCHIVE AT www.Astronomy.com/Hester.

16 ASTRONOMY • OCTOBER 2017