Recently, I have heard of some heuristics that would suggest that the rank of elliptic curves are bounded (specifically in the congruent number family). I always though that the best way to prove something about the rank of an elliptic curve is to look at the rank of the 2-Selmer group. Indeed, I was able to find a reference that says that the rank in the congruent number family of elliptic curves is bounded by the 2-Selmer rank.
Clearly it is not known that the 2-Selmer rank is bounded, but is it known that it is unbounded in the congruent number family? What about in general? Is this equivalent to asking if the rank of elliptic curves is unbounded?
I would appreciate any answers or references.