54 | New Scientist | 7 March 2020
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Full terms and conditions at newscientist.com/lw-termsThe back pages Almost the last word
CAVAN^ IMAGES/GETTYIMAGESAtomic space
A hydrogen atom consists of a
proton with an electron whizzing
around it. What is in the space
between them, and what happens
to the space when the atom loses
its electron?Richard Swifte
Darmstadt, Germany
Thinking of an atom as a
nucleus with electrons circling it
and empty space in between, like
a mini solar system, is a useful
analogy, but it isn’t a true picture.
Humans sense material objects
in terms of solid particles or waves,
so we apply this same imagery to
the microworld of atoms. This
solar system viewpoint has been
replaced by quantum descriptions
that produce predictions verified
by experiments. These depict
a hydrogen atom’s electron as
occupying one of several discrete
energy levels, but with a position
that is never well defined.
Quantum physics sees the space
within the atom not as empty, but
as a vacuum fluctuating in energy,
represented by the continuous
creation and destruction of virtual
particle-antiparticle pairs. In a
hydrogen atom, the binding of
the proton and electron by an
electromagnetic field can be
viewed as consisting of additional
quantum particles – photons –
occupying the space in between.
In truth, the reality of the
atomic world is something we will
probably never comprehend fully.
Richard Feynman supposedly
said: “If you think you understand
quantum mechanics, you don’t.”
To adapt another quote, ascribed
to both Arthur Eddington and
J. B. S. Haldane, the atomic world
isn’t only stranger than we
imagine, it is stranger than
we can imagine.David Muir
Edinburgh, UK
It is more accurate to imagine
the electron as a fog where an
electron is more likely to be
found, rather than a particle.
The fog is less dense in someplaces, like next to the nucleus,
and more dense in areas with
higher probability of finding
an electron.
When an atom loses an electron,
the quantum “wave function”
describing the electron changes
so that it has a lower probability
of being where it was, but there is
a chance that it still could be there.Blowing hot and cold
In summer, I feel comfortably warm
when the thermometer in my living
room reads 20°C. Yet in winter, I feel
cold at the same temperature. What
causes this?Richard Horton
Whixley, North Yorkshire, UK
One explanation may be
convection currents, or the lack
of them. The room’s thermostat
is likely to be positioned roughly
midway between floor and ceiling.
On a 20°C day in the summer, the
temperature in the room will
be within a few degrees of the
temperature outside, so you
will feel comfortable.In winter with the heating on,
the radiators produce convection
currents. Colder, denser air falls,
displacing warmer air.
If the thermostat records 20°C,
the temperature at floor level will
be significantly lower. The air in
the layer just below the ceiling
will be above 20°C, but you won’t
feel this warmth unless you climb
a stepladder.Jan Meulendijk
Haverfordwest, Pembrokeshire, UK
Air temperature is only one of
three parameters that influence
thermal comfort. The others are
air movement and the radiant
temperature of the surroundings.
In winter, you may experience
more discomfort from draughts,
as air entering the room is likely
to be colder. This gives you an
increased feeling of cold at the
same air temperature, just asyou feel less comfortable in strong
winds than on a calm day.
The radiant temperature of your
surroundings is a function of the
temperatures of all the surfaces
around you. These are likely to be
lower in winter than in summer.
We feel pleasantly warm in bright
sunshine and out of draughts,
even when the air temperature is
low. Conversely, you have probably
experienced “cold” radiating from
cool surfaces, even in a warm
environment. This is akin to the
process that may be going on in
your living room in winter.
This also shows why it pays
to draughtproof and insulate.
Combined, they give more
comfort at the same air
temperature and, when done
properly, allow for cosy living
at lower air temperatures.Christine Warman
Hinderwell, North Yorkshire, UK
There is a psychological element
to this feeling. It has been
suggested that the most energy
efficient way to keep people
comfortable indoors is not to turn
up the heating, but to provide
stronger lighting. Lack of sunlight
is a strong predictor for seasonal
affective disorder. Its symptoms
are similar to those of clinical
depression, and feeling cold
can be part of this condition.
Winter often offers less
sensory stimulation and social
contact. Conversely, stimulating
activity, even if only mental, goes
some way to distracting from the
cold. The most striking example
of mood affecting perception can
be seen on the streets of any city
at night, when hordes of young
people intent on having a good
time appear to be completely
impervious to cold. ❚This week’s new questions
Running while cycling Why is it that whenever I go out on
my bike in cold weather, my nose starts to run? Is there an
evolutionary advantage? James Fradgley, Wimborne Minster,
Dorset, UKBroadly speaking How do we know the universe is
expanding? Why can’t there be an alternative explanation,
say that all atoms are shrinking? Alexander Cowie, Oxford, UKWhy does cold air make
your nose run, and is
this advantageous?