STARDUST and Niels Bohr

STARDUST is based on a graphic novel by Neil Gaiman. A star (Claire Danes) falls to Earth in human form and can't return to the sky. Along the way she encounters lovestruck Tristan Thorne (Charlie Cox) and pirate Captain Shakespeare (Robert DeNiro), who captures lightning in his airship. She is pursued by Prince Septemus (Mark Strong) and a wicked witch (Michelle Pfeiffer). The villains wish to cut out the star's glowing heart to gain her secret of eternal life.

The eternal life of stars has been a mystery that life on Earth's surface depends on. According to standard models, life should not have evolved here at all because when the Solar System was forming the Sun was only 75% as bright. Earth's average temperature would have been 15 degrees below zero Celsius, frozen solid. This can't be true, for geology and the fossil record say that Earth had liquid water and life when models say it was frozen solid. This conflict with observations is the Faint Young Sun paradox.

Niels Bohr is best known for describing the heart of an atom, but he also turned his attention toward stars. Bohr's atomic model is based upon a miniature Solar System. In the early part of the 20th century many old ideas of science were questioned. Bohr would say that "Your theory is crazy, but it's not crazy enough to be true." In work that was never published, Bohr hypothesised that a star's heart is made of an unknown material radiating at a constant temperature To.

The region surrounding this core would be composed of a hot plasma. At the boundary, particles of the plasma would have energies given by:

E = (3/2)nkT

If To of the core were greater than T of the plasma boundary, an equilibrium would be reached. The star would maintain a constant luminosity.

Bohr's hypothesis required a material radiating at a constant temperature, something unknown in the 1930's. Though Black Holes are predicted by Relativity, even Einstein himself didn't believe they exist. In 1974 Stephen Hawking reached the amazing conclusion that they radiate at a temperature depending upon their mass. For many Black Holes this temperature would be nearly constant. Connecting Bohr with Hawking, a Black Hole at a star's heart would be just the thing to maintain a constant luminosity.

Recently astronomers have discovered that the outer Solar System contains many objects with temperatures suitable for liquid water. These distant bodies are now considered possible abodes of life. They are far too distant for the Sun to warm them, and must depend on an internal source of heat. Presence of Black Holes may create conditions for life on these dark worlds too.

The history of science is full of great unpublished work. Account of Bohr's theory came from friend George Gamow. In 240 BC most people thought that the Sun circled Earth and stars were fixed to an immense sphere. Aristarchus, librarian of Alexandria, wrote "On the Distances to Stars and Planets," with estimates that were remarkably accurate for the time. Those distances were estimated from the Earth, fitting an Earth-centred cosmology. The enormous distances may have started Aristarchus thinking about alternatives. He wrote another book that is now lost and only known through citations of contemporaries like Archimedes.

The second book introduced a cosmology where the stars were immeasurably distant and that Earth circled the Sun as a planet! The book caused great argument, with another contemporary writing that Aristarchus should have been put on trial! (Did he write nasty comments in blogs?) If Aristarchus' model had been widely disseminated, the world might have been saved 1500 years of Ptolemy. Alternative cosmologies need to be considered, or science will again be wound up in epicycles.

In fantasies from Harry Potter to STARDUST, heroes overcome many trials. New theories are almost inevitably hounded by the jealous lords and wicked witches of science. Bohr also said that "An expert is a person who has made all the mistakes that can be made in a very narrow field." Heroes are often aided by some lost knowledge or ancient wisdom. It is very pleasing that truth always wins in the end.