Actual infinities.

[Jehanne]

No... that is what is referred to as a potential infinity.

Mathematicians (and, by extension, physicists) do not make that distinction:

Actual infinity is the idea that numbers, or some other type of mathematical object, can form an actual, completed totality; namely, a set. Hence, in the philosophy of mathematics, the abstraction of actual infinity involves the acceptance of infinite entities, such as the set of all natural numbers or an infinite sequence of rational numbers, as given objects. This is contrasted with potential infinity, in which a non-terminating process (such as "add 1 to the previous number") produces an unending "infinite" sequence of results, but each individual result is finite and is achieved in a finite number of steps.

There is no distinction between actual and potential infinity found in modern mathematics. Instead, infinite sets are assumed to exist in the axiomatic approach of the Zermelo–Fraenkel set theory.

https://en.wikipedia.org/wiki/Actual_infinity