快猫短视频

IT MAKES a Pentium chip look like an abacus. But it鈥檚 not a military supercomputer or colossal number cruncher. This computer was booted up at the big bang and has been running for 13 billion years. Yes, it鈥檚 the Universe.

快猫短视频s know that a single fundamental particle such as an electron or a photon will carry a single bit of information, and that they can perform calculations with the information by manipulating the particle. Researchers are trying to build quantum computers to do just that (see 鈥淪aline solution鈥�). Such devices would be far more powerful than conventional computers. But how powerful could they be?

鈥淐learly the ultimate is a computer that uses all of the particles in the Universe,鈥� says Seth Lloyd, a quantum computing expert at MIT. 鈥淚 thought it would be interesting to work out its limits.鈥�

He began by working out the number of particles in the Universe and the total amount of information they could hold, in the region of 10⁹⁰ bits. The number of logical operations that could have been performed on those bits is limited by: the energy available to carry out the operations, the speed of light, which determines how fast information can move, and the running time鈥攖he age of the Universe. Do the maths and you get the maximum number of logic operations that the Universe could have carried out since the big bang: around 10¹²⁰.

By contrast, the number of bits that can be stored in all the computers ever manufactured on Earth is about 10²¹ and the number of logical operations carried out is roughly 10³⁰, tiny fractions of the theoretical maximum.

The idea has curious philosophical implications. If the Universe is a giant quantum computer, then everything in it is just part of its calculations. But there鈥檚 no need to invoke a supernatural programmer. Lloyd believes random quantum fluctuations provide the information input, 鈥減rogramming鈥� the Universe to create complex structures such as living things.

He likens this to a million monkeys typing random numbers into a computer. The chances of these monkeys typing the first billion digits of 蟺 is vanishingly small, he says. But the chances of them typing out a program that calculates these digits is much higher, because such a program need only be relatively simple.

But Charles Bennett, pioneer in the theory of quantum computation at the IBM T. J. Watson Laboratory in Yorktown Heights, New York, cautions against taking the idea of the Universe as a computer too literally. 鈥淭he real question is whether we will ever come up with a good fundamental theory that describes the Universe, and if so whether a quantum computer will be able to simulate it efficiently,鈥� he says.