Elevator in a twist
In your article about the space elevator
(5 May, p 24),
why is it that there is no mention of the Coriolis force?
The space elevator will have to transfer angular momentum to the cargo going
up there. Unless this is precisely matched by cargo going down it will result in
a net change of angular momentum of the elevator, which will then begin to drift
out of phase with the Earth. This would ultimately result in a catastrophic
failure as it wraps itself around the equator like a tethered ball around a
pole.
Even if one manages to balance the books for angular momentum in the long run
(with equal downward mass transfer) every carriage is likely to cause lateral
oscillations in the whole structure, which would be hard to manage. It seems
that one would still need to use large amounts of rocket fuel going in both
directions to counter the Coriolis force.
Karl Ziemelis replies: The angular momentum is transferred by the Earth
itself, which slows down as a consequence (but not by very much). Similar
criticisms were levelled against the original proposal, but were long ago shown
to be non-problems.
Letter
I wouldn’t like to be the insurer of the space elevator, in case the cable
broke due to a meteorite or perhaps stray manmade space debris. If it did, we
had better hope it didn’t break near the top, because “all” that would happen
then is that about 40,000 kilometres of cable, plus the space station and maybe
the 30-kilometre tower as well, would crash into the ocean with enough kinetic
energy to create a large tsunami. This would then flood the coast of whichever
poor Third World country was unfortunate enough to be nearest the space
lift.
If the cable broke near the bottom, initially the anchoring meteorite,
trailing a space station and several tens of thousands of kilometres of cable,
would rise away from the Earth. But it would probably not escape the Earth’s
gravity, but go into a hard-to-predict elliptical orbit. At some later point it
could crash back to Earth, hopefully not near a city.
Come to think of it, perhaps the dinosaurs did have a space programme.
Safety and environmental concerns about the scheme are addressed
in detail in the NASA report Space Elevators: an advanced earth-space
infrastructure for the new millennium, on
http://flightprojects.msfc.nasa.gov/fd02_elev.html鈥抬诲
Clarke's coups
Science fiction fans may be familiar with “Clarke’s three laws”. I suggest a
fourth: “You have to get up early to get ahead of Arthur C. Clarke.”
Regarding the “figure of eight” solution to the three-body problem
(14 April, p 16),
the mathematician Douglas Heggie suggests that the presence in space of
objects arranged in this pattern would signal the intervention of intelligent
beings.
When the “figure of eight” was mentioned in Science last year, I wrote to
Clarke and made the same suggestion. He politely replied he had used a similar
idea in “City and the Stars” (The Seven Suns) as early as 1956.
The secret's out
Further to the announcement in Feedback
(5 May)
of a prominent sign directing
visitors to a “secret nuclear bunker” in Brentwood, Essex, I must report that
the situation is far more serious.
In a recent A-level French oral exam, candidates had to accurately divulge
the location of the same bunker to the representative of a group of tourists and
persuade them to visit it. Do we have foreign agents hidden inside our country’s
exam boards?
Letter
My own town has its own signs to a “secret nuclear bunker”. So far I have
resisted the urge to add the word “formerly” in spray paint to these signs, on
the grounds that I might be arrested for acts of gross pedantry as well as
vandalism.
I went to see this bunker, advertised as “an all weather visitor attraction”.
Inside I found the most remarkable advertising poster. It showed the brutal,
modernist outlines of what is visible of the bunker from above ground, with
several people in the foreground waving while dressed in radiological protection
suits.
Behind bunker and people was the mushroom-cloud outline of a nuclear
explosion destroying the nearby town. Underneath it said, “Welcome to Hack Green
nuclear bunker.”
Letter
We can be sure that any species living today has a strong and stable sex
drive in times of both plenty or adversity, or it would not be here
(12 May, p 26).
In his study of the 10-spined stickleback, Desmond Morris showed that if
their territory was restricted, males without territory of their own would begin
to respond in a female way to males who had territory, thus neatly reducing the
breeding male population. In our overcrowded world, humans are showing a similar
response. Because it is a deeply instinctive response, it “feels” right to the
people involved.
Homosexuality does not lead to reproduction, therefore there cannot be a gene
for homosexuality. If there is one, its function must be to allow this diversion
of sexuality during times of plenty. This possibility is present to some extent
in all of us.
There are four possible choices open to us鈥攁ccepting or rejecting our
masculinity, and accepting or rejecting our femininity. This allows for every
variety of relationship.
There’s a seaside postcard that shows a hen-pecked man doing the washing up.
The wife is standing over him with a rolling pin. Society accepts this role
reversal because they can reproduce, but rejects the relationship if the woman
is a man with exaggerated masculinity or the man is replaced by a masochistic
woman.
As Charlotte Bach was fond of saying, “If you want to know what is ‘normal’
then study the abnormal. ‘Normal’ will be somewhere between those limits.”
Letter
Your feature notes that the first question we ask about a new baby is “boy or
girl?” But we humans may not be alone in that.
I once observed a troop of monkeys in Kenya as a new mother returned to the
compound with her baby, having just given birth. The others crowded around,
cooing over the baby and grooming the exhausted mother. And, sure enough, the
first thing every one of them did when they inspected the infant was check its
genitals to see whether it was a boy or girl.
Colour-coded plants
Having read your article about a smart sensor which can give crops just the
amount of water they need
(12 May, p 23),
I wondered whether this same approach could be applied to plant feeding.
Each of the three main nutrients required for plant growth鈥攏itrogen,
phosphorus and potassium鈥攃an induce a specific change in leaf colour when
it is in short supply. Nitrogen deficiency tends to result in a yellowing of
leaves, low phosphorus turns them a purple/blue colour, and a shortage of
potassium makes their edges brown.
If a sensor could detect the nutrient needs of the plant by checking the
colour of its leaves, then it might be possible to avoid the overapplication of
fertiliser common to modern agriculture.
In the case of nitrogen-based fertilisers, such reductions are crucial, not
only in increasing the efficiency of crop production, but also in reducing the
amounts of nitrous oxide, a powerful greenhouse gas, produced by
agriculture.
Drummed out
In their entertaining article on Houshang Ardavan’s superluminal pulsar model
and the Oxford project
(28 April, p 28),
Nick Appleyard and Bridget Appleby mention my scepticism, but they could have
said a little more about why I think the experiment is doomed to failure.
Their line of drummers illustrates the physics rather well. Suppose there are
many drummers in a large circle and each gives a single beat. Then, starting
from the back of the circle and moving to the front, it is possible, in
principle, to arrange the timing so that the sonic pulses reach a distant
observer simultaneously, who will then hear a single very loud beat. This will,
of course, have the same audio-frequency spectrum as a single drumbeat.
Alternatively, the beat pattern could be made to travel around the ring at a
constant supersonic speed. This is an acoustic analogue of the Oxford
experiment, using drums instead of electrodes. In this case there are just two
locations on one side of the ring where the time interval between adjacent
drummers equals the difference in travel time to the observer, so he will hear a
rapid succession of beats including two louder ones. As before, the audio
frequencies are unchanged.
By contrast, Ardavan’s “formidable” maths predicts that vastly higher
frequencies are produced. Static drummers cannot generate Doppler-shifted sound
waves, however their beats are superposed. That requires drummers on a
supersonic turntable, a genuine synchrotron. There has to be a flaw in the
analysis.
Letter
With respect, Feedback’s
5 May
report on the article in the British Medical
Journal about the incidence of a fungal infection called tinea imbricata amongst
the Gungan inhabitants of Naboo (Star Wars Episode 1: The Phantom Menace) was at
least quoting a “possible” occurrence from the past鈥攁lthough, having
happened a long, long time ago and far, far away, it hardly has first-hand
corroboration.
In contrast, your article on Ardavan’s idea for travelling faster than light
quoted the Picard manoeuvre to back up the theory. All standard chronologies
place this latter event as not having even happened yet.
Beyond he, she and it
Thank you for highlighting the issues facing intersex people in “Beyond two
sexes”
(12 May, p 26).
People with intersex conditions continue to be abused by
the majority of the medical community all over the world, and these practices
will not change unless we educate the broader community.
We also need to consider changes to the law, and continue to strive for legal
recognition of intersex as a bona fide gender for people with intersex
conditions who identify themselves as such. I am not suggesting that we raise
children with intersex conditions as “its”. However, adults who do not identify
themselves as exclusively male or female should have their gender recognised
legally, complete with all the benefits associated with that legal
recognition.
Above all, I would just like to reiterate what I say to people when
discussing intersex conditions: “Intersex is a variation, not a defect.”