Sсiеntifiс Аmеricаn (2019-06)

(Antfer) #1
6 Scientific American, June 2019

LETTERS
[email protected]

VIRTUAL HEALING
Thank you for “The Promise of Virtual Re­
ality” [The Science of Health], Claudia
Wallis’s excellent piece on the uses of the
technology in medicine. I would like to in­
sert “medical education” as another po­
tential tool for VR. My colleagues and I
have published some research on using im ­
mers ive VR to teach cardiac anatomy to
medical students in the March issue of
Clinical Anatomy. We found that they not
only scored 24  percent higher on quizzes
than non­VR students but also said they
had “fun”! Fun should not be a dirty word
in medical education.
Hillel S. Maresky University of Toronto


Wallis is excited about the completion of a
randomized controlled trial on the use of
VR to treat post­traumatic stress disorder.
The problem is that you can’t truly single­
blind a VR trial and have the trial’s sub­
jects unaware whether they are receiving
the treatment or a placebo, and the bias of
knowing thus cannot be filtered. Stat ing
that VR “will help make mental health
care cheaper and more accessible” risks
overselling an intervention that can not be
robustly validated.
Douglas Berger Tokyo

GEOSCIENCE GEOMETRY
“Is Antarctica Collapsing?” by Richard  B.
Alley, claims that a complete collapse of
the Thwaites Glacier in West Antarctica

could lead to a sea­level rise of 11 feet. I am
puzzled because I cannot make the arith­
metic work out.
Let’s call Alley’s figure 3.5 meters. For
simplicity, let’s also say a kilometer is
1/10,000 the distance from the pole to the
equator, as it was originally defined. So the
earth’s circumference is 40,000 km, and its
radius is about 6,400 km, giving a surface
area of about 510 million square km. But
the ocean is only about 70  percent of the
earth’s surface, or about 360 million  km^2.
(When I had a chance, I Googled it and
con firmed my number.)
From the map, the glacier appears to
be approximately a right triangle with
each side measuring about 600  km. So its
area is about 180,000  km^2. I assume only
the portion above sea level matters. The
article says the glacier rises up to a mile
(1.6  km) above sea level, but clearly it is
not that high everywhere, such as the
coast, so let’s guess 1.5  km on average. My
rough estimate of the volume of the gla­
cier above sea level is therefore 270,
km^3. Ignoring the additional water ne^ c­
essary to shrink the coastlines as sea level
rises, that is only enough water to raise
sea level by, at most, about 0.7  meter.
I didn’t expect my computation to be
exact, but that results appears to be off by
a factor of five. Did I do something wrong?
Dan Graifer via e-mail

ALLEY REPLIES: Graifer’s math is pretty
good. But West Antarctica is now drained
by ice that flows in other directions, into
the Ross and Filchner-Ronne ice shelves,
as well as Thwaites, with so-called con-
tinental divides along the highest parts
of the Antarctic Ice Sheet separating the
different drainages. If Thwaites degla-
ciated to the divides and stopped there, it
would leave mile-high cliffs that would
not be stable. Both our physical under-
standing and our models show that degla -
ciating any of the main drainages of
West Antarctica would tap into ice that

now goes out the other drainages, degla-
ciating the marine basins of all of them.
The total is usually taken to give us 3.
meters, or 11 feet, of global sea-level rise
without too much uncertainty.

PLANETARY PARITY
“The Exoplanet Next Door,” by M.  Darby
Dyar, Suzanne  E. Smrekar and Ste ­
phen  R. Kane, states that Venus has no
magnetic field and yet has an atmo­
sphere of extreme density and depth.
Mars, on the other hand, has almost no
atmo sphere. The explanation for the lat­
ter’s thin atmosphere that I am most fa­
miliar with is that because the planet
lost a strong magnetic field, the solar
wind from the sun stripped it of a previ­
ously much thicker atmosphere.
I would think that Venus, being much
closer to the sun, should have expe ri­
enced a much greater solar wind effect.
The two planets were created around the
same time, so the atmospheric difference
seems to defy common sense. What am I
missing here?
Chris Scholfield via e-mail

THE AUTHORS REPLY: The key to answer-
ing this question is that Venus has a negli-
gible magnetic field at the present epoch.
We must not fall into the trap of thinking
that this situation has persisted for the
past four billion years. Assuming a com-
position and core size similar to Earth,
models of the Venusian magnetic field
through time show that the planet most
likely had a field comparable to Earth’s up
until about one billion years ago. Crucial-
ly, this would have protected the Venusian
atmosphere when the sun was younger
and much more active. Additionally, Ve-
nus’s atmosphere is much thicker and has
a higher mean molecular weight than
Earth’s, which makes it generally more re-
sistant to at mospheric escape degradation.
But exactly how magnetic fields shield
atmospheres is apparently more compli-
cated than once thought. For example, re-
cent measurements suggest that oxygen
is currently being lost from Earth, Mars
and Venus at similar rates! This is a very
puzzling result, given the idea that mass,
magnetic field and distance from the sun
are the main factors in atmospheric loss,
as Scholfield notes.

February 2019

“Fun should not


be a dirty word


in medical education.”
hillel s. maresky university of toronto
Free download pdf