12 October 2019 | New Scientist | 27Want to get in touch?
Send letters to New Scientist, 25 Bedford Street, London
WC2E 9ES or [email protected]; see terms at
newscientist.com/lettersthat are capable of signalling their
presence includes the period in
which each actually transmits
across the galaxy.
We have existed for several
hundred thousand years, but have
broadcast in this way for only about
100 years. We are now moving to
less noisy laser and cable signals,
so that period is unlikely to be
much greater than 1000 years.
A circle with a radius of
1000 light years covers less than
0.04 per cent of the area of the disc
of our galaxy; 1000 years is a tiny
fraction of its 13-billion-year age
and it is likely that it will exist for
as long again.
We have been looking for
these signals for less than 100
years. This is like shining a tiny
torch into the Grand Canyon on a
pitch-black night. The probability
of seeing anything is surely very
low, however much has been, is
and will be out there.
From Harold Worby,
Wheaton, Illinois, US
To answer the question “where
is everybody?” we must consider
the time period in which a
technologically advanced
civilisation maintains a broad
coalition with the desire to put
an immense amount of resources
into interstellar travel. I can’t see
anything in human history that
indicates we are capable of that
kind of long-term commitment. If
the course of human development
to date is a model of how other
civilisations develop, then we
will never meet any others.
Prospecting for metal with
plants goes way back
17 August, p 12
From Brian King,
Barton on Sea, Hampshire, UK
David Hambling reports that a
company is using trees to find gold
deep underground in Australia.
Plants have been used for such
purposes at least since modern
metal prospecting began. Possibly
the best known is Ocimum
centraliafricanum, the copper
flower, which has been used in the
Central African Copperbelt since
the 1920s to confirm the presence
of copper in soil in clearings where
the absence of trees is thought to
be due to the poisoning of their
seeds by copper.
More recently, there have been
attempts to recover nickel from
the ash of trees that concentrate
it (22 March 2014, p 46).Keep those fossil fuels
until we really need them
10 August, p 34
From Andrew Scott,
Perth, UK
Tom Chivers discusses solar
technologies that could be
used instead of fossil fuels,
which would help address the
increasingly urgent requirement
to control global warming. There
is a second reason to do this.
All understanding of Earth’s
long-term cycling tells us that, on
a much longer timescale than the
current warming phase, a new
colder spell within our present ice
age will eventually loom.
If humanity is still around then,
it may need fossil fuel reserves to
burn to counter that threat. Long-
term atmospheric management
in both directions of temperature
will be necessary for a truly long-
term future for our species.Engineering obstacles to
electrolysing seawater
Letters, 21 September
From Clive Semmens,
Ely, Cambridgeshire, UK
Why can’t we use seawater to make
hydrogen, asks Albert Lightfoot.
We can, but corrosion of the anode
by chloride ions in seawater is a
problem. It isn’t insurmountable:
you could use anode materials like
gold or platinum, but they are
expensive. Researchers at Stanford
University are working on exactly
this issue: see bit.ly/NS-brine.I wonder whether we could
use graphite for the electrodes. I
don’t think it would be corroded,
but its relatively low conductivity
would mean the cells would have
to be bigger for a given rate of
hydrogen generation.
Lightfoot suggests that there
might be useful by-products, but
sadly, rare earth metals and cobalt
aren’t present in significant
amounts in seawater. Lithium
only forms 160 parts per billion
by weight of seawater and the
hydrogen production process
wouldn’t help much in its
extraction from that water.Stroppy teenagers are just
how they should be
14 September, p 56
From Richard Hambly,
Sydney, Australia
It was good to read your interview
with neuroscientist Dean Burnett
and his conclusion that teenagers
are how they are because it was
evolutionarily useful.
I’ve been going on about
our adventurous species and
the drive of the young towards
risky behaviour and exciting
experiences – looking to see
what is over the next hill and so
on. Now, I can quote Burnett as
an authority on the subject when
my listeners’ eyes glaze over.How can my circadian
rhythm be so precise?
21 September, p 15
From Howard Owens,
Stoke Canon, Devon, UK
Jessica Hamzelou reports that
boosting circadian rhythms can
help relieve perinatal depression.
This prompts me to wonder how
such rhythms work. How is it that
I always wake at 7.20 am, plus or
minus 30 seconds? How can the
wetware of the mind be so precise?
I get no external cues, visual oraural, and this routine has
survived three house moves.
It even resets for daylight saving
time after about three weeks.Do take into account the
effects of the effects
24 August, p 17
From Mike and Linda Hutchinson,
Pamber Heath, Hampshire, UK
We read with interest your snippet
reporting that sleep loss is worse
for young people’s mental health
than social media. Taking into
account sleep, physical activity
and cyberbullying, the effect
of frequent social media use in
causing unhappiness and anxiety
was found to be insignificant.
We suggest a story along similar
lines. Cancer is worse for you than
tobacco: people who smoke
tobacco frequently tend to be
more prone to breathlessness and
lung cancer than those who smoke
less. But taking into account tar,
nicotine and carbon monoxide,
the effect of frequent smoking
was found to be insignificant.A proposition about the
use of the word ‘theorem’
21 September, p 6
From Doug Clark,
Edinburgh, UK
Leah Crane says that because an
estimate by physicist Maximiliano
Isi of the mass and spin of a black
hole is based on the no-hair
theorem, which holds that no
information about a black hole
beyond its mass, spin and
electrical charge is visible beyond
its event horizon, this suggests
that the theorem is correct.
A theorem is a mathematical
proposition not self-evident but
proved by a chain of reasoning,
a truth established by reason and
based on accepted axioms.
I suggest that this “theorem”
would more accurately be called
a conjecture.The editor writes:
We have to call things what they
are universally called and this is
the language cosmologists use. ❚