Has any scientist measured the rate of the acceleration of the universe's expansion, as discussed in “The Puzzle of Dark Energy,” by Adam G. Riess and Mario Livio? And were that acceleration turned back nearly 14 billion years, would it conform with the current models of the big bang?

Howell, N.J.

As I recall, our galaxy is bound to merge with Andromeda. Would this be delayed by an expanding universe?

Fullerton, Calif.

RIESS AND LIVIO REPLY: Regarding Hackett's letter: One of us (Riess) has recently measured the rate of the universe's expansion, including the acceleration, with an unprecedented precision (an uncertainty of only 2.4 percent): it is 73.0 kilometers per second per megaparsec. There is some discrepancy between the value of the rate of expansion obtained from measurements of the cosmic microwave background and the more local measurement. It is not known yet whether that discrepancy reflects an underestimate of the potential errors or rather points to some new physics (such as an additional family of neutrinos or a dark energy that changes with time).

Current models of the big bang start with an “inflation,” a stupendous expansion that happened when the universe was a tiny fraction of a second old. That expansion is thought to have been driven in a very similar fashion to the accelerating expansion we see today.

In answer to Menkes's question: The local group of galaxies is gravitationally bound by the matter they contain, so if the dark energy is indeed a cosmological constant, then the acceleration will have no effect on the collision, which will still happen in about four billion years. If it turns out that dark energy's so-called equation of state parameter (the ratio of its pressure to its density) is more negative than −1, then our universe will advance toward a “big rip” in which galaxies, stars, atoms and even nuclei will be ripped apart in succession. But that would likely occur well after our future merger with Andromeda.


In “Anatomy of a Mass Murderer,” by Howard Lee, I noticed on the world map showing the “where and when” of the large areas strewn with volcanic vents called large igneous provinces (LIPs) that the locations of those in the Central Atlantic LIP (except for the one on the upper East Coast of North America) appear like they would “fit” together where North America, South America and Africa were located in that period of time when Pangaea was in existence. Is there a relation between where the Central Atlantic provinces are now located and Pangaea?

via e-mail

LEE REPLIES: The Central Atlantic LIP does indeed mark the “bleeding wound” of Pangaea's dismemberment. Parts of the LIP now separated by the Atlantic Ocean were connected at the time of its eruption, as you deduced. The counterpart to the northeastern U.S. is in northwestern Africa, particularly Morocco.


The discovery of the glymphatic system, the brain's pathway for eliminating waste products, as described by Maiken Nedergaard and Steven A. Goldman [“Brain Drain”], has far-reaching implications. I have always slept short and irregular hours, so it is alarming to read that the brain's flushing of waste matter such as beta-amyloid is accomplished mainly during sleep and that short sleepers are at more risk of dementia. Yet in my 80th year I have at least as much mental energy, and almost as much physical, as when I was 20. I wonder whether it could be that the glymphatic flushing occurs most strongly in the first 90 minutes of deep sleep?

Dorset, England

The link between the brain's disposal system and sleep demonstrates sleep's importance once again. It is not surprising that there is a relation between sleep health and neurological diseases such as Alzheimer's and Parkinson's because both insomnia in the middle-aged and neurological diseases in the elderly affect a high proportion of the population. Wouldn't it be better, then, to start treating insomnia with the gravity that this condition deserves? I am an insomniac frustrated trying to find the cause and solution for my condition; I recently visited a sleep clinic, and the only diagnosis was: “It is not apnea.”

London, Ontario


I cannot think of a scarier educational reform than Michael Shermer's suggested cure in “Left Behind” [Skeptic] for what he sees as a lack of political diversity in American colleges and universities. Given that so many U.S. institutions are explicitly conservative (the military, most government agencies, many of our religious organizations, a growing portion of the media, much of business and industry, and religious-based colleges and universities), higher education has been a lone habitat for liberal and progressive thinking.

Ashford, Conn.

SHERMER REPLIES: My proposal for “viewpoint diversity” includes not only political views but economic, social, religious and ideological perspectives. As for the military, according to a 2012 Time magazine article, troops and veterans are “not the monolithic bloc many believe.” One in three officers opposed the Iraq War, and although officers lean conservative, enlisted soldiers may lean liberal, and they outnumber officers four to one. That could account for political donations from military personnel in the 2012 presidential election, including $678,611 to Barack Obama compared with $398,450 to Mitt Romney. Nationally, according to a 2015 Wall Street Journal/NBC News poll, conservatives are no longer the largest political cohort: 33 percent identify as conservative, down from 37 percent in 2014, whereas 26 percent identify as liberal, up from 23 percent. Moderates are now the plurality at 38 percent. Students need to hear all perspectives, and liberals do not need a safe haven.


“Brain Drain,” by Maiken Nedergaard and Steven A. Goldman, stated that the brain replaces “half a pound of detritus a month and three pounds” a year. It should have given the figures as half a pound each month and nearly six pounds each year.

“Editing the Mushroom,” by Stephen S. Hall, should have said that the oil produced by soybean strains created by the company Calyxt had higher levels of monounsaturated fats than olive and canola oils, not monosaturated fats. Further, it erroneously referred to the removal of developing horns among male Holstein cows. Cows are female by definition, and the practice is performed on male and female Holstein cattle.

In addition, a caption in the box “Genetic Modification by Any Other Name” said when a cell repairs DNA cut by the Cas9 enzyme, it adds several base pairs at the site. In fact, it may add or delete base pairs.