October 2013 is a great month for physics fans

Of course the month began with the announcement of the Nobel Prizes in physics, chemistry, and medicine. The conversation about the physics prize in particular, discussed earlier on this blog, has been lively. Meanwhile, here in the U.S., Physics Today offered its usual bounty in this month's issue, including an article on “Measuring the Hubble Constant” by prominent astrophysicists Mario Livio and Adam Reiss, the latter a Nobel Laureate. (More on this article below.) Meanwhile, the 50^th anniversary issue of the New York Review of Books features an essay on the last 50 years or so of the development of particle physics and cosmology by Nobelist Steven Weinberg (Nov. 7, 2013 issue). Both fields, though in states of disunity and confusion in the early 1960s, gradually came to develop their own highly successful and unifying 'standard models'. The two fields also converged. Weinberg manages to tell the story without naming a single physicist, including himself.

In the U.K., it gets even better. Physics World celebrates its 25^th anniversary by publishing a spectacular special issue, which is available for free download (volume 26, number 10, October 2013). And last weekend the Financial Times' FT Weekend Magazine offered its first special issue devoted to a single science, physics (Oct. 18, 2013 issue). (Unfortunately there doesn't seem to be a single link that compiles all the online articles. Here is the lead editorial.) Finally, even The Economist covers physics in an article about the possibility of particle accelerators made of glass, which would allow them to be smaller (Oct. 19, 2013 issue).

Returning to the article by Livio and Reiss, I note with particular interest a discussion of comparing the Hubble constant H0 based on global methods, such as those made by the Planck satellite, with measurements based on local objects.

Local measurements of H0 are complementary to other, higher-redshift probes. Indeed, we'd be remiss if we did not note an apparent tension, at the 3 sigma level, between current measurements of H0 based on local objects and its deduced value based on the standard cosmological model and new Planck results for the cosmic microwave background. That tension may be the harbinger of new physics, but past experience indicates that discrepancies below 3 sigma disappear when more data are available.

Indeed, the threshold for discovery in physics is often five sigma, which was the threshold used in the discovery of the Higgs boson. As a physicist who has strayed into the life sciences, two aspects are particularly striking. First, I admire physicists' relentless skepticism of 3 sigma results (2 sigma is routinely considered 'statistically significant' in the life and behavioral sciences) and willingness to collect more data. The epidemic of non-reproducible research in the life and behavioral sciences betrays the precise opposite tendency in those fields. Second, in physics when we talk about measuring universal constants, there are often many independent procedures for measuring the same universal phenomena. This has been true throughout the history of physics. In the clinical sciences, there is usually exactly one clinically meaningful endpoint, and other substitutes (biomarkers, surrogate endpoints) may provide compelling evidence, but never sufficient in a true outcomes study. If you want to prevent a remission of cancer, you must measure the time to remission. If you want to prevent a heart attack, measure the time to the next one.

References

The Economist, 2013: Small really is beautiful. The Economist, vol. 469, no. 8858, pp. 83-84.

Mario Livio and Adam G. Reiss, 2013: Measuring the Hubble constant. Physics Today, 66 (10), 41-47.

Steven Weinberg, 2013: Physics: what we do and don't know. The New York Review of Books, vol. LX, no. 17, pp. 86-88.