This article is a preview from the Summer 2015 edition of New Humanist. You can find out more and subscribe here.

It is exactly 50 years since Gordon Moore, co-founder of the silicon chip maker Intel, published a remarkable paper in the journal Electronics. In “Cramming more components onto integrated circuits”, he observed that the computational power available at a particular price – or, equivalently, the number of transistors on a chip – doubles every 18 to 24 months. “Moore’s law”, as it has become known, has continued to operate ever since. In fact, it is responsible for today’s world of ever-accelerating change, where we confidently expect that this year’s technological gizmos will always be out-performed by next year’s.

But think how unprecedented this is. Moore’s law has spawned computers that are around 100 million times more powerful than those of 1965. If cars had improved their performance by such an astonishing factor they would now be doing about 350 million miles to the gallon – travelling the equivalent of the distance from the Earth to Jupiter for little more than a fiver. Not only that but vehicles would be streaking down our motorways at close to the speed of light – more than a million times faster than a Boeing 747.

To be living in an epoch when computing power (or anything, for that matter) doubles roughly every two years is extraordinary. It is never going to happen again. Future generations will look back and marvel. Maybe they will even define our era as the time of “exponentially” increasing computer power. Because of the operation of Moore’s Law you can carry around in your pocket a smart phone – literally, a pocket computer – that is millions of times more powerful than the onboard computers that took the Apollo 11 astronauts to the Moon.

The limit on how small components can be made on a chip is determined by light which is shone through a “mask” to create the city map of a computer circuit. Chip makers have made ever smaller components – packing in more and more transistors – by using light with a shorter wavelength such as ultraviolet or X-rays, which can squeeze through smaller holes in a mask. They have even replaced light with beams of electrons since electrons have a shorter wavelength than light. Chips have as a result become remorselessly more powerful. Nevertheless, claims that “Moore’s law” is about to break down have been made every decade since it was formulated. So far they have always been wrong.

Currently, transistors are continuing to shrink according to Moore’s prescription. However, computer makers are having difficulty removing the waste heat which such electronic switches puff out: the more components that are squeezed into each square centimetre, the more heat that must be removed. But a range of different strategies are being used to tackle this problem, and there currently seems little reason to doubt that Moore’s Law will continue for the foreseeable future.

Undoubtedly, however, Moore’s law will break down one day. It is a sociological law; a law of human ingenuity. But even human ingenuity cannot do the impossible. There are physical limits set by the laws of nature that are impossible to circumvent and these will ultimately determine the limits of computers.

The speed of a computer, which is the number of logical operations it can perform in a second, turns out to be limited by the total energy available. Today’s computers use only the “electrical energy” in transistors. But this energy is totally dwarfed by the energy locked away in the mass of the computer, which provides nothing more than the scaffolding to keep a computer stable. The ultimate computer would have all of its available energy in processing and none of its energy in its mass. In other words, it would have its mass-energy converted into light-energy, as permitted by Einstein’s famous E = mc2 formula.

The computing power of such a device would be formidable. In a ten-millionth of a second it would be able to carry out a calculation that would take a state-of-the-art computer today the age of the Universe to complete. But it would carry out the calculation at a price. If all the available energy is converted into light-energy for computing, a computer would not be anything like a familiar computer. Far from it. It would be a billion-degree ball of light. It would be like a nuclear fireball, a blindingly bright piece of the big bang. Though it might be nice to have the most powerful computer imaginable on your desk, it might be just a little inconvenient. Perhaps we should hope that Moore’s law fails long before it reaches that stage.