s4cnnd1imema9

(Marcin) #1
4 Scientific American, April 2019

LETTERS
[email protected]

TALES OF ENTANGLEMENT
“Spooky Action,” by Ronald Hanson and
Krister Shalm, discusses quantum entan-
glement, in which two particles exhibit a
“spooky” connection regardless of distance.
The authors do not explain why some-
thing as nonspooky as the following can’t
be going on: Suppose I hide a pair of gloves
in two different envelopes and send one
(without knowing which) to my friend on
Mars, with a note to open it on receipt. The
envelopes are now “entangled” because if
my friend finds a left glove, then I will find
a right glove, and vice versa—before a light
signal has had time to travel to Earth.
Gordon B. Hazen Professor emeritus
of industrial engineering and manage-
ment sciences, Northwestern University

The article made this old sci-fi fan’s imag-
ination run wild. Do we know that entan-
gled particles are “monogamous”? If an
electron can be entangled with one part-
ner, why not multiple partners simultane-
ously? Could entanglement be a relation-
ship among a large number of particles
independent of location? And if so, could
manipulating allow for truly instant mes-
saging across interstellar distances?
Bob Morrison Asheboro, N.C.

THE AUTHORS REPLY: Regarding Ha-
zen’s suggestion: Just as “correlation does
not imply causation,” it does not always
imply entanglement. The nonspooky cor-


relation of the two gloves is determined
the moment they are placed in their enve-
lopes and is an example of a “hidden vari-
able theory.” John Bell showed that any
such theory will not have correlations that
are as rich as those allowed by quantum
entanglement. In our experiments, once
our particles are sent to their distant loca-
tions, they are randomly measured in one
of two ways. Because the particles do not
know in advance how we are measuring
them, they cannot agree ahead of time how
to correlate their outcomes. It appears as if
measuring one particle randomly and in-
stantaneously influences its distant part-
ner, which is the spookiness that Albert
Einstein referred to.
In answer to Morrison: It is possible to
entangle many different particles with
one another, and this is an active area of
research—for instance, for building quan-
tum computers. But if two particles are
maximally entangled, there can be no en-
tanglement with any other particles at the
same time. In that sense, entanglement is
indeed monogamous, which ensures a lev-
el of privacy that is unmatched in classi-
cal physics and is at the heart of quantum
applications in secure communication.
Alas, faster-than-light communication
must remain science fiction. With entan-
glement, the outcome is random but corre-
lated. Let’s say you and a distant friend
share entangled electrons and have agreed
that if they are measured to be “up,” that
means “yes,” whereas “down” means “no.”
Your partner will get the same result as you,
so the electrons appear to have somehow
influenced one another faster than the
speed of light. But there is no way to force

your electron to be “up” to send a “yes” re-
sponse. When it is measured, the electron,
not you, will “choose” with a 50  percent
probability of whether it will be up or
down. It is no better than flipping a coin.

WISE TECHNOLOGIES
In “Sacred Groves,” Madhav Gadgil dis-
cusses the ecological benefits of areas of
primeval forest in India protected as the
homes of deities. Gadgil illustrates how
the sacred in traditional cultures can
transmit practical wisdom distilled from
bitter experience, which we need to help
save our planet. Such perspectives make
me less sanguine about the technologies
Scientific American often features. I ap-
preciate the lure of discovery, having had
a 40-year career in the physics of the
earth, but not everything we might create
ought to be created. All technologies must
be evaluated in the current reality that
anything that can be exploited for a profit
probably will, regardless of the dangers.
The greatest service to humanity at the
moment would be rendered not by imple-
menting technical innovations of uncer-
tain benefit but by gaining the emotional
maturity to appreciate and act on the kind
of wisdom portrayed in “Sacred Groves.”
Geoff Davies Retired senior fellow,
Australian National University

OCEAN CONSERVATION
In “The Last of the Ocean Wilderness” [Fo-
rum], Kendall Jones and James Watson
raise the point that we have depleted about
“90  percent of formerly important coastal
species” and that any conservation agree-
ments should set wilderness-retention tar-
gets. But their recommendation does not
go far enough. I think to be successful over
the short and the long term, we must also
spearhead public campaigns that identify
overexploited ocean species, explain what
classifies as pollution and how it can affect
ocean life, and make a list of recommend-
ed actions geared toward the average con-
sumer. And we should monitor overfish-
ing or illegal fishing by enforcing existing
legislation; using nontransferable unique
numbers to tag fishing vessels; encourag-
ing seafood traceability through documen-
tation; and monitoring vessels via inspec-
tion stations, drones and satellites.
Vasilios Vasilounis Brooklyn, N.Y.

December 2018

“All technologies


must be evaluated


in the current reality


that anything that


can be exploited


for a profit probably


will, regardless


of the dangers.”
geoff davies
australian national university
Free download pdf