THE cosmic rays that crash into telescopes are normally just a nuisance for astronomers, but they may bring an unexpected benefit: they could be used to generate truly random numbers.
Exploding stars send subatomic particles speeding through space, and we see these on Earth as random cosmic rays. When these particles impinge on the electronic light detector of a camera they create a bright blip. Astronomers looking for distant bodies in their images have to identify these 鈥渉ot pixels鈥� and throw them away.
But Michael Bulmer and Kevin Pimbblet of the University of Queensland in Brisbane realised that these pixels have real value. They labelled the hot pixels as 鈥�1鈥� and all other pixels 鈥�0鈥�, and then applied a few rules to reduce the number of zeros 鈥� for instance, by discarding pairs of zeroes and ones in the sequence, while replacing 鈥�01鈥� and 鈥�10鈥� with the single digits 0 and 1, respectively. The result, they found, is a string of bits that passes the most stringent tests for randomness.
Advertisement
Unlike the pseudo-random numbers generated by computers, which can be cracked by anyone who figures out the rules used to create them, the bits generated by the cosmic rays are truly random, the Australians say. 鈥淚t is a novel and creative idea,鈥� says Robert Nemiroff of Michigan Technological University in Houghton, who runs a network of telescopes that photograph the night sky once every 4 minutes. He is discussing with the Australians the possibility of generating random numbers from these images.
Not everyone is convinced. 鈥淧eople have used thermal noise in electronic devices, radioactive decay and even lava lamps to generate random numbers,鈥� says Stephan Mertens, an expert in random number generating software at the University of Magdeburg in Germany. He says that using astronomical imaging will turn out to be just another chapter in a long but unsuccessful history.
Mertens points out that the main use of random numbers is in simulations such as modelling the evolution of the universe or traffic flow, which consume up to trillions of bits per second. Bulmer and Pimbblet can only generate a few thousand bits per second. 鈥淣atural processes are way too slow,鈥� Mertens says.
But Bulmer and Pimbblet have a different application in mind. They say their cosmic-ray bits could be used to encrypt data that needs to be transmitted securely. And their idea has the added attraction that individuals can create their own private random numbers from personal photos. Hot pixels are also generated in digital cameras and as long as the cameras don鈥檛 use a compressed format like JPEG, which smoothes out the hot pixels, the photos can be analysed in the same way as astronomical images. The work will appear in a future issue of Publications of the Astronomical Society of Australia.