whenWhen we want to find a high rank curve over $\mathbb{Q}$ among an elliptic curve over $\mathbb{Q}(t)$ ,we we give some scores for the curves (the curves with bigger points on them over various primes in reduction module p: #$E(F_p)$,i mean $S(E,N)=\sum_{p<N}\frac{2-a_{p}}{|E(F_p)|}*log(p)$,it it is briefly called Mestre's sum) and the curves with bigger scores usually have bigger rank than the original curve over $\mathbb{Q}(t)$.the The specialization theorem helphelps us to be sure that the group does't becomesdoesn't become smaller.
itIt is interesting that when we do the same thing from $\mathbb{Q}(t,t')$ to $\mathbb{Q}(t)$ and try to compute the rank of surfaces with conjectural limit ( proposedproposed by Nagao,the the special case of Tate's conjecture,proved proved by Rosen and silvermanSilverman for rational surfaces) it always gives the same rank always, not bigger rank in any cases ( iI tried an example and computecomputed about 100000 surfaces and computecomputed the limit,limit; all of them waswere equal).
what'sWhat's happening?