Reviews

A beautifully told story with colorful characters out of epic tradition, a tight and complex plot, and solid pacing. -- Booklist, starred review of On the Razor's Edge

Great writing, vivid scenarios, and thoughtful commentary ... the stories will linger after the last page is turned. -- Publisher's Weekly, on Captive Dreams

Saturday, September 4, 2010

The Adventures of Dark Energy and Lithium Abundance

Sounds like good names for a pair of super-heroes....

1. The Mystery of Dark Energy
Scientists say that the expansion of the universe is accelerating.  The evidence for this is that the most distant supernovas are dimmer (thus, farther away) than they should be, absent acceleration. 

The usual epicycle to explain this away is the mysterious Dark Energy. 

However, Dark Energy apparently violates conservation of energy, which is considered a major faux pas.  Also the usual calculations for vacuum energy are way smaller than that which Dark Energy must have.  Way smaller.  Like 120 times smaller, which is bad. 

2. The Missing Lithium
Big Bang models predict how much Stuff was produced by the Bang.  Hydrogen, deuterium and helium-4 pretty much match these predictions, which is good. 

But there is only about a third the amount of lithium as there "should" be, which is bad. 

Now on the face of it, this "falsifies" the Big Bang, which is not only bad, but worse. 

Fortunately, as Pierre Duhem pointed out, there are always multiple hypotheses being tested and when a prediction doesn't happen like it should, it's not always clear which of the many assumptions have been falsified.  (A classic example is the way heliocentrism was falsified by the lack of stellar parallax.  Turned out, the lack of parallax falsified the distance to the stars, which had been based on apparent relative brightness and diameter.  Seems they are farther than 70 million miles away!  Which is good.) 

3. A Mark of a Promising Theory
A new theory in physics looks promising when it not only explains the problem it was developed to solve, but also solves another problem in some unrelated area. 

Two Cape Town physicists -- Marco Regis and Chris Clarkson -- came up with an explanation for the lithium shortage.  Turns out, it also explains why the farthest supernovas look too dim.  If it pans out, we can explain the latter without any "accelerated expansion" or "dark energy" at all.  Which is good. 

Prof. Regis is the Marco of the promising theory.  You knew I couldn't pass that by. 

But the solution has a problem of its own, which is bad. 

4. Farewell, Nick
To wit: we abandon the Copernican Principle, an a priori metaphysical assumption that states that the universe is the same everywhere and on all scales; i.e., no "privileged place." 

Abandoning this metaphysic makes the supernovae easy to explain: The universe is not homogeneous at the largest scale and the earth is "sitting at the centre of some kind of giant void in a much larger universe." 

By the same token, lithium is not evenly distributed and our "bubble" happens to be a Lithium Desert.

And why should Stuff be evenly distributed?  It's only a metaphysical assumption. Right?  But metaphysical assumptions are harder to abandon than a mere physical theory!  The Big Bang will go on the ash heap of history before we give up Ockham's Razor!  And the Copernican principle is most devoutly held by moderns. 

That stuff is not evenly distributed is one thing.  Big deal.  But that the earth really is at the center of the world is much more difficult to accept.  Modern a priori commitments make it hard to shake the Earth-is-not-special meme. 

No comments:

Post a Comment