The oldest known nuclear fission reactor on Earth is about 1.5 billion years old and located in Gabon, Africa. Near a villiage called Oklo, a natural nuclear fission reactor was discovered in 1972 while mining uranium in the area. Wait a minute – who was building nuclear reactors that long ago? How is it possible to have such a technological marvel occur naturally? After all, doesn’t a nuclear reactor take a high degree of technology and manpower to operate?

Apparently nature beat us to it. The French scientists that discovered the reactor found that some of the uranium had either been undergoing spontaneous, intense nuclear reactions – or apparently was much older than the rest of the planet (Terry Pratchett mentions this in his excellent book “The Science Of Discworld”, a great read). Of course, the more plausible explanation is that the uranium underwent nuclear reactions naturally – not that it was dumped there by some ancient civilization that had atomic technology and then disappeared.

The Oklo reactor provided an important insight regarding one of the fundamental physical constants called the “fine structure constant“. The Oklo reactor gave evidence that the fine structure constant has indeed been just that – a constant – at least for the last 2 billion years or so. Interesting, but why is this important?

Calculations on what occurred in the early universe assume that so-called fundamental constants haven’t changed since then: the speed of light, the gravitational constant, the charge of an electron, etc. When what we believe now to be a constant can be shown to have changed over billions of years, then physics as we know it today must have been very, very different in the past.

In 1999 and 2001, two published papers (found here and here) indicated that in fact this particular constant has indeed changed : the behavior of atoms a long time ago was very different than what we observe today. The fine structure constant is, in fact, not constant – the universe that we live in now probably doesn’t work the same as it used to.  Just one more piece of the puzzle in our quest of understanding how the universe works.