40 | New Scientist | 14 March 2020DOUG JOHN MILLER
Features
Number
crunch
Our appetite for data is becoming
unsustainable. We urgently need to
rethink computing, reports Edd Gent
T
HE modern world is drowning in data.
In 1984, the global traffic of the fledgling
internet amounted to 15 gigabytes per
month. By 2014, that had become the average
traffic per user. In 2019, each of us burned
through that much data in just over a week.
The floodgates show no signs of closing, either.
As billions of new users come online, and
ever more devices become web-connected,
the amount of data in the world is forecast to
rise to 175 zettabytes (10^21 bytes) by 2025 – more
than three times humanity’s output to date.
Processing these oceans of data requires
enormous infrastructure, extending beyond
smartphones and personal computers to
millions of energy-hungry data centres
around the globe. That combined hum
already uses 6 per cent of the world’s electricity,
an energy bill predicted to double by 2030,
raising concerns about the sustainability of
our digital habits.
For decades, technological improvements
kept the rising waters at bay, allowing hardware
to get smaller, faster and more energy efficient.
But the silicon chips we rely on are starting
to hit physical limits, threatening to leave us
with an energy bill we can ill afford to pay.
A plethora of alternative technologies
are vying to continue the upward march
in processing power, but most are still
languishing on the lab bench. That is why a
growing number of researchers are calling for
something more transformative: a complete
rethink of the thermodynamics underpinning
computing. If the idea gains traction, it could
revolutionise how computers are designed,
allow processors to grow more powerful
without huge extra energy demands, and
sate our growing appetite for data.Anyone who has ever sat with a laptop on
their knees knows computers give off heat. A lot
of heat. That is an unavoidable consequence
of how they work, and to understand why,
we have to think about what computers do.
Broadly speaking, they are machines capable
of storing and manipulating information.
Computers do that in the form of bits:
fundamental units of digital information that
can adopt one of two states, either a 0 or a 1.
These are represented in computers by tiny
electronic switches called transistors that
flick on and off when a voltage is applied.
This process generates electrical resistance
in computer chips, which manifests as heat.
Given that modern computer chips feature
billions of transistors working together, this
can raise the temperature considerably.
In 1961, IBM physicist Rolf Landauer set
out to calculate the theoretical efficiency of
a perfect computer – one that wasted none of
its energy in combating resistance. He knew
that such a device would still consume some
energy. That is because, like all machines,
computers are constantly fighting one of
the most powerful forces in the universe:
the second law of thermodynamics. This
states that the disorder of any closed system –
a measure known as entropy – will always
increase. It is why eggs don’t unscramble
and marbles are easier to spill than clean up.
As anyone who has tried to tidy up after their
children knows, restoring order costs energy.
Landauer reasoned that corralling
information is a rebellion against disorder
and so represents a decrease in entropy that
can only be bought with energy. He worked
out that even the simplest computation
possible – erasing a single bit – must incura tiny thermodynamic debt, no smaller
than 2.8 × 10-21 joules. Operating at this
efficiency, Summit, the world’s most
mighty supercomputer, could be powered by a
few milliwatts. In reality, it uses 13 megawatts,
the approximate peak output of two offshore
wind turbines.
Even this is astonishingly efficient
compared with early computers. The Cray 1
supercomputer, unveiled in 1975, used roughly
1 per cent of that power, but had less than a
billionth of the computational muscle. The
shift to where we are today was enabled by