Controlling the universe through the "Many-worlds" interpretation I was reading upon a comic when I found some interesting content concerning the "Many-worlds" interpretation and how it could be used in quite an extreme manner.
Imagine we had a "END" machine.  When activated, it does what its name suggests, it brings the said universe to the end.  However, it only has the ability to bring its own universe to an END.
From here, I will be using the Schrodinger's cat to explain how this will work.
We start by putting a cat, in a box.  Within the box is also a radioactive source and a mechanism designed to kill the cat should it detect any radioactivity.
The moment the source becomes radioactive is considered random.  Eventually, though, it will become radioactive and the cat will die.
However, instead of killing a cat, it will activate the "END" machine, spelling the end of the universe as we know it.
However, from the view of an outsider, the universe never dies.  Every instance, there is a continuum of universes created, some which will activate the "END", some which won't.  To the view of an outsider, who couldn't possibly know what were occurring inside the box, all of the said universes will remain to appear the same.  The only difference between each universe is what happens inside of the box, which is unknown.
Every universe in which the "END" is activated is essentially terminated from existence.  However, there is still a lot of universes in which the "END" is not activated.  In these universes, everything proceeds as it would have.
Being an outsider, you can't actually see any difference between one universe to the next, and since the only observable outcome is a future in which the radioactive source is never sensed, then the only possible outcome is, theoretically, that non-radioactive future.
The comic book takes this and asserts that this is how the ice cream man sells his ice cream for free, he simply connects an ice cream sensor to an "END" machine and activates the "END".  If there is ice cream, everyone lives.  If there isn't ice cream, that universe "ENDs".
And against all odds, apparently the air inside of the container is converted to ice cream, since it is a possible outcome.
Is this a possible result of the "Many-worlds" interpretation?  Isn't it a little bit extreme, forcing results that defy probability?
 A: It is indeed a somewhat extreme result of the many-worlds interpretation. The formal idea is that you can factor a semiprime N by choosing a prime p, say 15,485,867, then rolling three appropriately sized quantum prime-rolling dice that can roll the factors of N but also p: call them A, B, C. The idea is that you kill yourself if simultaneously: (A does not divide N), (C is not equal to p), (D is not equal to p). If you somehow screwed up the range for N, then C and D save you; otherwise A is a factor of N.
This is called "postselection" in the quantum computing literature. The quantum computing illuminary Scott Aaronson proved that if you add it to the bounded-error polynomial-time quantum computing class BQP (producing PostBQP) then you actually get back a computer which is from a "classical" quantum computing class called PP. See the Wikipedia article on PostBQP for further details.
Of course, the cost that you pay for it is that in most universes, people see you kill yourself. It's worth understanding that we are all subject to it eventually: if this notion of the many worlds interpretation is correct, you probably do not need to develop an explicit quantum algorithm to kill yourself; the forces of nature will have enough quantum uncertainties in them that you will simply live forever in some parallel worlds.
