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Sunday, July 1, 2012

A true random number generator

Generating random numbers is harder than it sounds. You can create a list of truly random numbers mechanically by flipping an actual coin. However, that can get tiring after the first hundred tosses. If you switch to a virtual coin, you can generate large numbers instantly, but they’re not quite random. These ‘pseudorandom number generators’ are useful for most purposes, but obviously have their limitations. In contrast, Thomas Symul, Syed Assad and Ping Koy Lam from Australian National University were able to generate true random numbers from vacuum fluctuations.

Vacuum fluctuations, also called quantum fluctuations, are the transitory appearance and disappearance of subatomic particles in a vacuum. We used to think a vacuum was absolutely empty, but we know now that these particles can spontaneously pop in and out of existence. These events are completely unpredictable, the most random occurrences possible. The physicists took advantage of that property in designing their true random number generator. Briefly, they split a beam of light into two pathways. Although the two beams were seemingly identical, those tiny vacuum fluctuations ensured that there was always a tiny but unpredictable difference between them. The researchers exploited this difference to generate true, real time random numbers.

By the way, sometimes pseudorandomness is not an unwanted artifact of the system, but rather is a designed property. For example, how often does the shuffle program on your MP3 play the same song twice in a row? If the playlist were truly random, that would happen fairly often.