Premature Nobel Prize decision?

The awarding of the 2011 Nobel Prize in Physics “for the discovery of the accelerating expansion of the universe” (see PHYSICS TODAY, December 2011, page 14 ) ventures into model-dependent speculation based on the observations of highly redshifted supernovae. The interpretation of the just 13-year-old discovery that the light from distant type Ia supernovae appears to be fainter than expected remains a matter of current astrophysics research.

In mainstream cosmology, type Ia supernovae are treated as calibratable standard candles, and since the more distant ones are apparently increasingly fainter than expected, the usual conclusion is that the universe is expanding at an accelerating rate. But the methodologies that allow the proper calibration of peak luminosities of the type Ia’s—and thus their use in cosmological studies—are empirically based and may introduce systematic errors that give the false impression of an accelerating universe.

The intrinsic peak luminosities of type Ia supernovae depend on the nickel-56 yield of the explosions and vary by a factor of approximately three, whereas the supernova searches have found that distant type Ia’s are only about 25% less luminous than expected after empirical corrections are made. But in 2011, new corrections based on masses of the host galaxies introduced new luminosity recalibrations ¹ on the order of 10%. The field is clearly still evolving; other systematic corrections may need to be made in the future.

Various alternatives to an accelerating universe have also been proposed. ² Whether such alternatives are viable remains to be seen, but the Nobel Committee for Physics has perhaps acted somewhat prematurely by selecting a preferred interpretation of the supernova projects’ data. The effect, intentional or not, is to bully the skeptics into silence, self-censorship, or ridicule, whereas good science proceeds with a healthy dose of skepticism and with open minds.

It may turn out that the universe is indeed expanding at an accelerating rate; however, the scientific issue of the fate of the universe is too important to be settled by Nobel committee fiat. The case is not yet closed, the 2011 Nobel Prize notwithstanding.