Resolves once 90% of cosmologists and theoretical physicists agree one way or the other, according to multiple reputable surveys taken at least 70 years after market creation.

So the market must remain open for at least 70 years (until May 28, 2093) to allow time for the idea to be considered thoroughly. After this, the market resolves as soon as at least 90% expert consensus is reached on the matter according to two or more independent surveys.

The market does not resolve if some reputable surveys say 90% of experts think YES and some say that 90% think NO simultaneously (i.e., the survey findings have to come to the same conclusions on what the consensus is). It will only resolve once all up-to-date surveys agree on the consensus.

Some info on the mathematical universe hypothesis can be found 