# bigjeff5 comments on How to Convince Me That 2 + 2 = 3 - Less Wrong

53 27 September 2007 11:00PM

You are viewing a comment permalink. View the original post to see all comments and the full post content.

Sort By: Old

Comment author: 04 March 2011 04:12:24AM 9 points [-]

When it was noticed in the 1800's that the perihelion of Mercury did not match what Newton's inverse-square law of gravity predicted, did we change the way math works? Or did we change our understanding of gravity?

Math is the most fundamental understanding of reality that we have. It is the most thoroughly supported and proven aspect of science that I know of. That doesn't mean that our understanding of math can't be fundamentally flawed, but it does mean that math is the last place we expect to find a problem when our observations don't match our expectations.

In other words, when assigning probabilities to whether math is wrong or Newton's Theory of Gravity is wrong, the probability we assign to math itself being wrong is something like 0.000001% (sorry, I don't know nearly enough math to make it less than that) and Newton's Gravity being wrong something like 99.999999%.

See what I'm saying?

Comment author: 04 March 2011 04:23:02AM 4 points [-]

Yup. I think we agree. My disagreeing post was a mere misunderstanding of what you were saying.

Comment author: 04 March 2011 04:53:16PM 4 points [-]

After a few recent posts of mine it looks like I need to work on my phrasing in order to make my points clear.

No harm no foul.

Comment author: 21 March 2011 03:58:34AM 12 points [-]

Woah, I think that's a little overconfident...

You're saying that in the mid nineteenth century (half a century before relativity), the anomalous precession of Mercury made it seem 99.999999% likely that Newtonian mechanics was wrong?

After all, there are other possibilities.

cf. "When it was noticed in the 1800's that the perihelion of Neptune did not match what Newton's inverse-square law of gravity predicted, did we change the way math works? Or did we change our understanding of gravity?" In this case we actually postulated the existence of Pluto.

Similar solutions were suggested for the Mercury case, e.g. an extremely dense, small object orbiting close to Mercury.

And that's leaving aside the fact that 99.999999% is an absurdly high level of confidence for pretty much any statement at all (see http://lesswrong.com/lw/mo/infinite_certainty/ ).

If I were a nineteenth century physicist faced with the deviations in the perihelion of Mercury, I'd give maybe a 0.1% probability to Newton being incorrect, a 0.001% probability to maths being incorrect, and the remaining ~99.9% would be shared between incorrect data /incomplete data/ other things I haven't thought of.

However, I agree that we can probably be more confident of results in maths than results in experimental science. (I was going to distinguish between mathematical/empirical results, but given that the OP was to do with the empirical confirmation of maths, I thought "mathematical/experimental" would be a safer distinction)

Comment author: 23 March 2013 12:07:15PM *  2 points [-]

For well-established math, sure. We certainly will look for experimental mistakes, unnoticed observables (e.g. the hypothesized planet Vulcan to explain Mercury's deviation from Newtonian gravity), and better theories in about that order. However for less well established mathematics at the frontiers we do consider the possibility that we've made a mistake somewhere.

Off the top of my head the biggest example I can think of was von Neumann's proof that hidden variables were inconsistent with quantum mechanics, which was widely believed and cited at least into the 1980s, despite the fact that David Bohm published a consistent hidden variables theory of quantum mechanics in 1952. I'm curious if anyone can recall a case in which an experimental result led us to realize that a previously accepted mathematical "fact" was incorrect.