Hardware random number generation may be harder than you think
It's very difficult to find a source of entropy that's truly random, but sources that are based on some sort of physical process are usually good places to start. You might think that radioactive decay would be a good process to use to create random bits, but new research has actually shown a correlation between decay rates and the Earth's orbit around the Sun.
The researchers who found this unexpected correlation were puzzled by the conflicting measurements of radioactive decay rates that other researchers had measured and tried to find which estimates were the right ones. It turns out that all of the measurements may have been right, and the variation between experiments may be due to unexpected effects instead of errors on the part of the researchers.
By the Hoary Hosts of Hoggoth! This certainly is strange. What's going on here?
When I first heard of this research, I wasn't too surprised. After all, General Relativity tells us that time is distorted when you go fast or are near a very massive object. These effects are significant enough that the GPS system won't work without accounting for them, so they're very real. Knowing this, my first thought was that the change in decay rates were probably due to similar effects from the elliptical orbit of the Earth around the Sun. Maybe when the Earth is closer to the Sun, time is just slowed a bit more that when the Earth is further away from the Sun. Maybe the difference in speed between when the Earth is the closest to the Sun and when it's farthest away is also part of this.
The researchers who found the correlation between decay rates and the Earth's orbit don't mention this as a possible cause of the variations in decay rates, however. Instead they suggest that the changing rate of solar neutrino flux may be responsible for it. This something that I know absolutely nothing about, and it looks like my first guess wasn't even close.
So it looks like a source of entropy that based on radioactive decay may have non-random components that are actually measurable. In light of this research, one thing is still certain: it's hard to find a source of entropy that's truly random.