The gemoroh definitely seems to say that meisim know what is happening in the world. But this makes the tosafos in sotoh 34b hard to understand. He says that the ovos needed to be told that Caleb was there. How did he read our daf?
shmuel siegel, yerusholayim
Your question was raised by two great marginal commentaries in the Vilna Shas (Rebbi Akiva Eiger in Gilyon ha'Shas, Berachos 18b, and Rav Yeshayah Pik, Sotah 34b).
In fact, we addressed this question in our Insights to Berachos 19:1:b, from which I copy the following.
Best wishes,
Mordecai Kornfeld
For what purpose did Hash-m command Moshe to tell the forefathers about the Jewish people's entry into Israel? It must have been so that the forefathers would continue to watch their children and pray for them when they would wage war to conquer the land. The Gemara asks, then, that if dead people do not know what is going on the world, what good would it do for Moshe to tell them? True, they may be aware of the events as they are informed of them, but Moshe could not tell them when the Jews would go to war and when to pray for them. (M. Kornfeld)
This explanation is consistent with the reading of the text that Tosfos (Sotah 34b, DH Avosai) had in our Gemara. In Tosfos' text, there appeared the word "Ela" ("rather") before the Gemara's answer, "So that they would express gratitude to Moshe." According to Tosfos, this answer is not answering the question that immediately precedes it ("If they know [what is happening in the world], what is the point in telling them [what is happening]?"), but rather, it is answering the first question, "If they do not know [what is happening in the world], what is the point in telling them [what is happening]?" The point in telling them is so that they will appreciate what Moshe did for their children up until the point when they entered Eretz Yisrael.