Paul Crowley

From London, now living in Mountain View.

The Goldbach conjecture is probably correct; so was Fermat's last theorem

Reminiscent of Freeman Dyson's 2005 answer to the question: "what do you believe is true even though you cannot prove it?":

Since I am a mathematician, I give a precise answer to this question. Thanks to Kurt Gödel, we know that there are true mathematical statements that cannot be proved. But I want a little more than this. I want a statement that is true, unprovable, and simple enough to be understood by people who are not mathematicians. Here it is.

Numbers that are exact powers of two are 2, 4, 8, 16, 32, 64, 128 and so on. Numbers that are exact powers of five are 5, 25, 125, 625 and so on. Given any number such as 131072 (which happens to be a power of two), the reverse of it is 270131, with the same digits taken in the opposite order. Now my statement is: it never happens that the reverse of a power of two is a power of five.

The digits in a big power of two seem to occur in a random way without any regular pattern. If it ever happened that the reverse of a power of two was a power of five, this would be an unlikely accident, and the chance of it happening grows rapidly smaller as the numbers grow bigger. If we assume that the digits occur at random, then the chance of the accident happening for any power of two greater than a billion is less than one in a billion. It is easy to check that it does not happen for powers of two smaller than a billion. So the chance that it ever happens at all is less than one in a billion. That is why I believe the statement is true.

But the assumption that digits in a big power of two occur at random also implies that the statement is unprovable. Any proof of the statement would have to be based on some non-random property of the digits. The assumption of randomness means that the statement is true just because the odds are in its favor. It cannot be proved because there is no deep mathematical reason why it has to be true. (Note for experts: this argument does not work if we use powers of three instead of powers of five. In that case the statement is easy to prove because the reverse of a number divisible by three is also divisible by three. Divisibility by three happens to be a non-random property of the digits).

It is easy to find other examples of statements that are likely to be true but unprovable. The essential trick is to find an infinite sequence of events, each of which might happen by accident, but with a small total probability for even one of them happening. Then the statement that none of the events ever happens is probably true but cannot be proved.

Paul Crowley's Shortform

No sarcasm.

Covid-19: My Current Model

You're not able to directly edit it yourself?

Paul Crowley's Shortform

On Twitter I linked to this saying

Basic skills of decision making under uncertainty have been sorely lacking in this crisis. Oxford University's Future of Humanity Institute is building up its Epidemic Forecasting project, and needs a project manager.

Response:

I'm honestly struggling with a polite response to this. Here in the UK, Dominic Cummings has tried a Less Wrong approach to policy making, and our death rate is terrible. This idea that a solution will somehow spring from left-field maverick thinking is actually lethal.

Paul Crowley's Shortform

For the foreseeable future, it seems that anything I might try to say to my UK friends about anything to do with LW-style thinking is going to be met with "but Dominic Cummings". Three separate instances of this in just the last few days.

New Year's Predictions Thread

I look back and say "I wish he had been right!"

New Year's Predictions Thread

Britain was in the EU, but it kept Pounds Sterling, it never adopted the Euro.

New Year's Predictions Thread

How many opportunities do you think we get to hear someone make clearly falsifiable ten-year predictions, and have them turn out to be false, and then have that person have the honour necessary to say "I was very, very wrong?" Not a lot! So any reflections you have to add on this would I think be super valuable. Thanks!

New Year's Predictions Thread

Hey, looks like you're still active on the site, would be interested to hear your reflections on these predictions ten years on - thanks!

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Thank you!