Correction Offered to Science and History of Cosmic Acceleration
As a member of the High-Z Supernova Search Team (HZT), I think it is worthwhile to correct both the science and the history that were described in “This Month in Physics History”
that appeared in the January APS News
On the science, Type Ia supernovae are not standard candles: their luminosities vary by a factor of 3. Sorting the bright from the dim by the shape of their light curves to get precise distances was introduced by HZT member Mark Phillips in 1993.
Similarly, absorption by interstellar dust can mimic dimming that is due to accelerated expansion. Riess, Press, and Kirshner developed a solution to this problem, published in 1996, which was essential to the analysis of distant supernovae submitted by Riess and HZT to the Astronomical Journal
on March 13, 1998. This paper was accepted on May 6, and published in September 1998. The Supernova Cosmology Project also developed an effective way to measure dust absorption to individual supernovae, but not until 2003. Their article on cosmic acceleration was submitted to the Astrophysical Journa
l on September 8, 1998 and appeared in the June 1999 issue.
On the history, the January 1998 AAS meeting was not the time and place where the world learned we live in an accelerating universe. At the AAS press briefing, 5 speakers, including Peter Garnavich from HZT, concurred that we live in a low density universe that would expand forever. In that public setting, no one claimed that the universe was accelerating [see, e.g. John Noble Wilford, The New York Times
, Jan 9, 1998 “New Data Suggest Universe Will Expand Forever”.] The first clear public statement that evidence from supernovae indicated cosmic acceleration took place in February 1998, at the Dark Matter meeting in Marina Del Rey. Alex Filippenko of HZT said “the dimness of the supernovae–pointing to unexpectedly large distances–implies that cosmic expansion has actually sped up in the years since the stars exploded.” This triggered a flood of public attention, including an interview of HZT member Adam Riess on The News Hour. Cosmic acceleration seemed like news to the world in February. Not January.
In March 1998, Saul Perlmutter was asked by The New York Times
to explain his reluctance to assert cosmic acceleration at the AAS in January. According to the Times
, “Describing their results in January, Dr. Perlmutter acknowledged that the evidence strongly suggested a cosmological constant, but went no further. ‘We were trying to be very conservative until we had more observations’.” Nobody claimed to have announced cosmic acceleration in January 1998. I think we should mark the dates of scientific discoveries from the submission of refereed publications, not commemorate the extrapolations of reporters who get ahead of prudent scientists in drawing reliable conclusions. I say we should have the anniversary on March 13! On this basis, I look forward eagerly to the next “This Month in Physics History.”
References to the articles mentioned above can be conveniently found at http://www.cfa.harvard.edu/~rkirshner/whowhatwhen/Thoughts.htm Robert P. Kirshner Cambridge, MA