The problem is, 'beginningless time' (if such a concept makes any sense), or infinite series, or whatever, is not something that Abhidhamma or Theravada has the authority to define. It is a matter for physicists. Attacking Theravada or Abhidhamma on the basis that it makes some mistakes in its cosmology is a child's game, fitting for people who want to win at child's games - Abhidhammikas lived thousands of years ago, before the advent of the scientific method. Of course they made some mistakes.
In point of fact, whether or not Germann's hypothesis is correct is irrelevant, despite what he or anyone else might say, for the simple reason that correctness on convoluted expositions and scholastic evolutions of doctrine is not the point. We are (supposed to be) here to practice for the end of suffering, not play tiddlywinks with children. What bearing does this byzantine mathematical argument have on those aspects of the doctrines which are actually relevant to guiding practice? I'm talking about salayatanas, khandas, paticca-samuppada, sati, samadhi, and so on - the practically relevant core. As far as I can see, none at all. Which makes this a fun pastime for Germann (the mathematician, who, by refusing to answer whether he as ever meditated, forces the conclusion that he has not), and a waste of time for everyone else (or an amusing arena for jokes, depending on your predisposition).
"Does Master Gotama have any position at all?"
"A 'position,' Vaccha, is something that a Tathagata has done away with. What a Tathagata sees is this: 'Such is form, such its origination, such its disappearance; such is feeling, such its origination, such its disappearance; such is perception...such are fabrications...such is consciousness, such its origination, such its disappearance.'" - Aggi-Vacchagotta Sutta
'Dust thou art, and unto dust thou shalt return.
' - Genesis 3:19
'Some fart freely, some try to hide and silence it. Which one is correct?' - Saegnapha