Wednesday, January 4, 2012

Thoughts from last night

I wanted to get these thoughts down quickly, as I tend to forget.

These relate to the Collatz conjecture.

1. There might be some surprising results when looking at large numbers of elements simultaneously, studying the graph the same way one might study a gas. There could be some analogue to pressure and temperature which stays constant as a set of elements evolves through time.

There might also be an analogue to entropy. If one could demonstrate that entropy must increase over time as a well-ordered set evolves (say for instance all integers from 1 to 2^n), then the existence of a loop might disturb this entropy.

2. There is an almost-but-not-quite predictive relationship between the binary expansion of a number and its parity sequence. By parity sequence, I mean the sequence of ups and downs that happen to an element x under the accelerated Collatz function. For instance, the number 3 has an up (to (3(3) + 1)/2 = 5) then another up (to (3(5) + 1)/2 = 8) then a down (to 8/2 = 4). If we label ups with 1s and downs with 0s, then the parity sequence of 3 starts with 110. 3s binary expansion is 011. In fact, for all numbers from 1 to 4, the binary representation is a mirror image of the first two terms of the parity sequence. However, as you start examining more terms, random errors start cropping up. For instance, the parity sequence of 5 is 100, but the binary expansion is 101. At any given step, only a fraction of elements exhibit a new parity error. For the life of me I can't find a pattern. If I could demonstrate that the sequence of elements that develop a new parity error is random (i.e. irreducibly complex), then I could demonstrate that a proof of the conjecture would be impossible.

There are two sequences that never develop errors. Anything with ...000000 as a binary expansion always has parity sequence 000000..., and anything with ...1111111 as a binary expansion always has parity sequence 1111111... It appears that parity errors happen more regularly on elements with binary expansions with roughly equal numbers of 0s and 1s.

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