Random number generators are used for a variety of purposes, from complex mathematics to security and encryption, or for selecting the winner of the church raffle. But did you know that your computer's random number generator is only--gasp!--pseudo-random? These generators are based on algorithms, and therefore, with enough information about the algorithm, it is possible to predict the next number in a sequence. That defies the one true rule of randomness: that the results be totally unpredictable. Using the standard model of randomness--beta decay--a Web service called Hotbits will generate, upon individual request, genuinely random sequences of numbers, when the pseudo just won’t do.
Random is, by definition, a totally uninspired event. There is no apparent cause or series of events leading up to it. Even the roll of a die could be called non-random, since the numbers that come up are actually the result of a number of forces acting together on the die, including the force of the rollers hand, gravity, air gusts, the surface they fall on, etc.
Hotbits uses the decay of the isotope cesium-137 to generate random numbers. An atom undergoes beta decay when a neutron in its nucleus turns into a proton. It's not magic: it's the weak force that makes this possible. The weak force is the only force that will allow for the switch (despite being weaker than the electromagnetic and strong forces). To conserve charge, beta decay also releases an electron (sometimes called the beta particle).
Atoms want to move to the lowest energy state possible, and beta decay is one way to get there. However, an energy barrier sits in the way and the amount of time it takes on average for the atom to surmount the barrier this depends on its height, which differs for different isotopes.
The time it takes a half of a given sample of any particular element to decay is known as that material's half-life. If you have a cluster of cesium-137 atoms, half of them will decay in about 30.17 years. The more energy it takes to initiate the decay, the longer the half-life.
So how does this lead to random numbers? Statistically, a cesium-137 atom has a fifty-fifty chance of decaying in 30.17 years. BUT, there is absolutely, positively no way to predict exactly when any individual atom will decay. Odd, right? While the whole batch obeys a statistic, each atom’s decay time is totally unpredictable.
The Hotbits program is based on the premise that since the decaying of each atom is random, the time between decay events is also random. Hotbits measures the time between two atoms decaying, then the time between the next two atoms decaying (a total of four events, not three, to avoid a bias the author explains). If time one is less than time two, that gets a zero. If time two is shorter, that gets a one. The result is a sequence of genuinely random numbers.
The very best algorithm-based pseudo-random number generators can produce sequences that are nearly indistinguishable from genuinely random ones. So, there’s no immense demand for a service such as Hotbits, but it might meet someone’s very specific needs. Various online websites will generate random numbers for you one at a time, but it would be too time consuming to use one of those for any long sequence. These sites use different methods to generate random numbers, including atmospheric noise. Hotbits takes individual requests to produce random number sequences of any size.
Over some period of time, many elements will naturally decay. One way or another, they’ll find the energy to slip into their more stable, low energy state. We just don't know exactly when. It's an incredible phenomenon that, upon deeper reflection, makes some physicists and philosophers a little nervous. Is the whole universe inherently unpredictable? Is there no method to the madness? Along with explaining the theory behind their product (while admittedly glossing over some of the details), the Hotbits website serves a piece of physics humility by reflecting on the implications of this awe-inspiring phenomenon:
"[Sodium-35’s] half-life is only 1.5 milliseconds—one and a half thousandths of a second. On the other hand, Indium-115 has an energy barrier so high that you have to wait 4.4×1014: 440 million million years for half the nuclei in a sample to decay. It kind of takes your breath away to discover a mundane physical process which occurs at rates varying over 24 orders of magnitude—from about a thousand times a second to a thousand times the age of the universe."
"Ever since physicists realized how weird some of the implications of quantum mechanics were, appeals have been made to "hidden variables" to restore some of the sense of order on which classical physics was based. For example, suppose there's a little alarm clock inside the Cæsium-137 nucleus which, when it rings, causes the electron to shoot out. Even if we had no way to look at the dial of the clock, it's reassuring to believe it's there—it would mean that even though our measurements show the universe to be, at the most fundamental level, random, that's merely because we can't probe the ultimate innards of the clockwork to expose its hidden deterministic destiny.
But hidden variables aren't the way our universe works—it really is random, right down to its gnarly, subatomic roots."
