chaos and the LGP-30

Jecel Assumpcao Jr jecel at
Sun Jul 26 19:44:10 CDT 2020

Jay Jaeger wrote on Sun, 26 Jul 2020 19:24:24 -0500
> So, either he mis-entered something, or possibly the result of a
> different state of a random number generator somewhere?

He dumped the full state of the simulation to paper with six digits
after the decimal point even though the internal calculations used eight
digits (I don't remember the actual precisions involved). So when he
restarted the simulation from the middle he introduced errors of less
than 1 per million and fully expected the results to be the same for the
days he had already simulated so he could continue a little further. But
he was shocked that the simulation went in a different direction and the
results were totally different after only a few days.

This is an absurd sensitivity to initial conditions that had never been
noticed in any system before. He compared it to whether a butterfly
flapped its wings or not in the middle of the Amazon making a difference
on there being a nice day or a huge storm on the other side of the world
a week later. This is the infamous "butterfly effect".

All this came after eliminating all kinds of possible errors, of course.
The first thing we thought back then when something like this happened
was not "I found a new theory" but "the hardware is probably flaky or
there is a compiler bug".

- Jecel

More information about the cctalk mailing list