[dwh452]

I'm curious how the Turing machines can resemble problems which take input? BB(n) is defined as a n-state Turing machine that starts off with an empty tape. Collatz(n) is how many steps are taken before it terminates when starting with input 'n'.

Does this mean a BB(6) machine which resembles Collatz is testing all possible values as part of it program and not part of anything on the tape (since the tape start out empty)?

[LegionMammal978]

It's not testing all values, but one particular starting point. In all likelyhood, it will never reach its stopping condition from this starting point, but proving this even for a single value is currently intractable. Compare with the "5x + 1" variant of the Collatz cojecture, where many values are believed (but not proven) to run off to infinity, never to return.

[srcreigh]

Edit:nvm see thread

For collatz, the empty input machine loops over all natural numbers and halts if it finds one which doesn’t eventually reach 1.

To prove that it never halts, you’d have to prove the collatz conjecture. Otherwise you’d have to find the smallest counter example of the collatz conjecture.

[LegionMammal978]

Suppose that there exists a natural number that diverges to infinity under the Collatz map. Then the Collatz conjecture would be false, but your machine would still run forever on that diverging number. As far as I am aware, there is no known machine that halts iff the Collatz conjecture is false.