A Quantum Diaries Survivor

Just a few pages into chaper 2 of Lee Smolin’s quite nice new book “The Trouble with Physics”, I could not help laughing. He spends time in the introduction to explain that he does not mean to harm string theory with his book, and that he himself has worked on the field. And he explains that Giordano Bruno was burned on the stake by the roman inquisition for proposing that the stars are nothing but far-away copies of our sun.

In chapter 2 he deals with the subject of unification. And indeed, Bruno’s hypothesis is a nice unifying idea: sun and stars are one and the same, they just appear different but they aren’t: stars are just much more distant. And then Smolin writes:

“… Of course, this was an opportunity to make a novel prediction: if you could measure the distances to the stars, you would find they were in fact much farther away than the planets. Had it been possible to do this in Bruno’s day, he might have escaped the fire. But it was centuries before the distance to a star could be measured. What Bruno had done, in practical tests, was to make an assertion that was untestable, given the technology of the time. Bruno’s proposal conveniently put the stars at such a distance that no one could check his idea.”

Quite nicely put. Continuing the quote:

“So, sometimes the need to explain how things are unified forces you to posit new hypotheses you simply cannot test. This, as we have seen, does not mean you are wrong, but it does mean that originators of new unifications can easily find themselves on dangerous ground.”

Very witty understatement… I think it is about time we start setting up the stakes. Those who burned Bruno were wrong, but they died happily ignoring the fact. Would I prefer to be Bruno or the Archbishop who had him light up, and then went to sleep merrily in the knowledge he’d done his duty ? Hmmmmmm….

More seriously, indeed Bruno’s idea was not only untestable, but it plainly violated Occam’s razor. Stars had to be quite farther away than any other thing in the then known universe, to save a line in the list of heavenly bodies. Times were not right for his idea to be brought forward. So let it be with string theory.