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FIRST the bad news for geeks. Computing power is fundamentally limited by the rate of expansion of the universe. The good news, however, is that if Moore鈥檚 law continues to hold, chip makers have more than five centuries before they hit the limit.

Computer scientists have long wondered whether an infinitely powerful computer could be built, and some have suggested that such a machine might be possible, in principle, if calculations could be performed with infinitesimal amounts of energy. But others have pointed out that since any calculation can only occur as part of a physical process, factors such as the speed of light will limit how fast any computer can transmit information, and so an infinite calculation would require an infinite amount of time.

Another problem is that the universe is expanding. This means that a computer would only have access to the resources in a limited amount of space. This led the physicist Freeman Dyson to predict in 1979 that if the universe continued to expand forever, infinite time would be available, making an infinite calculation possible. The trick, he said, would be to constantly upgrade to increasingly efficient machines that run at lower and lower energies as the ever-expanding universe cooled down.

But we now know that the universe is not only expanding, it is also accelerating away from us. This might, at first sight, seem to mean that any calculation could continue forever, but Lawrence Krauss and Glenn Starkman, physicists at Case Western Reserve University in Ohio, say that an accelerating universe is actually bad news for the computing world.

The acceleration causes space to emit a form of energy known as de Sitter radiation, a phenomenon that would drain the region of energy and starve the computer of resources much sooner than previously thought. They calculate that the maximum number of bits that can be processed at a point in the entire future of the universe is 1.35 脳 10¹²⁰ ().

In 1965, Gordon Moore, one of the founders of the chip maker Intel, speculated that the number of transistors on a chip would double every 18 months or so. He was right, and computers have more or less followed this trend, now known as Moore鈥檚 law, ever since.

The physicists say their work means Moore鈥檚 law will eventually have to be modified. 鈥淚t cannot continue unabated for more than 600 years for any technological civilisation,鈥� they say.