6 Scientific American, August 2020LETTERS
[email protected]STARS ON THE MOVE
In “New View of the Milky Way,” Mark J.
Reid and Xing-Wu Zheng state that they
“find that the sun circles the Milky Way ev-
ery 212 million years. To put this in per-
spective, the last time our solar system was
in this part of the Milky Way, dinosaurs
roamed the planet.” But because the rest of
the stars in our galaxy are also moving in
the same direction about the center,
shouldn’t we “always” be in the same place
with respect to them?
Daniel Pankratz
Huntington Beach, Calif.The spiral of the Milky Way has persisted
for billions of years—which means its out-
ermost stars must be moving faster! Since
Isaac Newton, we have known that outer
objects move more slowly. How do you ex-
plain the persistent spiral?
Mark Dormann Palm Coast, Fla.THE AUTHORS REPLY: Pankratz is con-
ceptually right. The analogy we gave was
simply to put the orbital period into per-
spective. To address his question in more
detail: most stars orbit the Milky Way with
a circular speed within about 10 percent of
that of the sun. Because the circumference
of the sun’s galactic orbit is about 50,
parsecs, or nearly 170,000 light-years, af-
ter one galactic orbit, a typical star would
be about 5,000 parsecs ahead of, or behind,
the sun. So after a 212-million-year orbit,
we would be in the company of totally dif-
ferent neighbors.
Dormann raises a question that puz-
zled astronomers long ago. We now know
that because of dark matter, which ex-
tends well beyond where most stars are,
the outermost stars are actually orbiting
at about the same speed as the sun.
That said, the orbital circumference is
larger farther from the center, so the out-
ermost stars have longer orbital periods
than those closer to it. This arrangement
could lead to spiral patterns winding
tighter over time. The answer to the
“winding problem” is controversial, but it
probably involves patterns rotating slow-
er than the stars or patterns that are
short-lived and re-form continuously.WOMEN IN SURGERY
Chethan Sathya’s observations on the chal-
lenges of both discrimination and harass-
ment faced by women surgeons in “Stand
Up for Female Surgeons” [Forum] are note-
worthy. Behavioral change is critical if we
are to address workplace cultures that al-
low gender and other forms of inequality
to persist.
Now more than ever, the need for ev-
ery physician in every health system to be
fully engaged, valued and productive is
obvious. Patients around the world need
all of us working at the top of our game
and collaborating with one another to de-
liver the care that they require today. More
important, society needs the diverse views
that each one of us brings to the urgent
work of redesigning our system of health
care delivery to adapt to our rapidly
changing world.
Our experience shows that systemati-cally addressing barriers to recruitment,
retention and leadership participation is
an essential starting point and that more
can be done to improve well-being in the
workplace for surgeons and their families.
But teamwork is integral to our business.
For generations, women surgeons have
valued the same goals as men: delivering
patient-centered care, experiencing the
challenges and joys of operative surgery,
and undertaking the lifelong pursuit of
aca demic inquiry.
It’s time for all of us to work together to
build a better health service where every-
one’s contribution is valued.
Deborah McNamara National Clinical
Program in Surgery, Royal College
of Surgeons in IrelandREDEFINING RISK
In “Who’s Rational about Risk?” [Observa-
tory], Naomi Oreskes notes that white men
and scientists are less concerned than oth-
ers about the risks of technology.
Viewing the issue with an awareness of
the pervasive racism and sexism in Amer-
ican society might help our understand-
ing. Because I check every box of privilege,
I have been free to live less cautiously than
friends who are not white or male or het-
erosexual. Now it is a deep-seated habit.
My duty to the common good, however, is
to listen more carefully and hear others
more fully.
Jim Eychaner Sacramento, Calif.Although it was not her principal purpose
in the piece, Oreskes makes a very good
case for openness in decision-making
about risks in general. What she does not
do is to discuss the analytical methods used
in risk assessment.
I spent much of my career as an econ-
omist for the British government. One of
the topics in which I had quite a lot of in-
volvement was the economics of flood risk
management (FRM). In England, signifi-
cant FRM projects are routinely subject to
cost-benefit analysis (CBA), in which flood
risks, and how they might be expected to
change following the introduction of a
project, are quantified. Perhaps more im-
portant, the business cases for FRM proj-
ects are subject to judicial review and
thereby to public scrutiny.
One notable component of this kind of“Because I check
every box of privilege,
I have been free
to live less cautiously.
My duty is to listen
more carefully
and hear others
mor e f u l ly.”
jim eychaner sacramento, calif.April 2020
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