My father told me that he was taught a Rashi in school that suggests that Rashi knew about radio waves.
What Rashi might hint to this conclusion?
My guess is that your father is referring to Bemidbar 7:89. There, the passuk tells us that whenever Moses entered the Tent of Meeting he would hear the voice of God speaking with him, only the word for "speaking" (מדבר) is spelled abnormally. Instead of a shewa under the mem, there's a chireq under the mem and a dagesh in the daled.
Some grammarians, like Ibn Ezra, see it as a contraction of מן דבר: that Moses heard God as a result of his speaking to him, but Rashi disagrees. Rashi reads the dagesh as indicative of an assimilated tav: מתדבר. In Rashi's words, this indicates that God was conversing with himself (kind of like a background chatter to the universe), and Moses' skill was an ability to tune in (if you will) and listen in.
Here is the passuk, followed by Rashi's comment:
וּבְבֹ֨א מֹשֶׁ֜ה אֶל־אֹ֣הֶל מֹועֵד֮ לְדַבֵּ֣ר אִתֹּו֒ וַיִּשְׁמַ֨ע אֶת־הַקֹּ֜ול מִדַּבֵּ֣ר אֵלָ֗יו מֵעַ֤ל הַכַּפֹּ֨רֶת֙ אֲשֶׁר֙ עַל־אֲרֹ֣ן הָעֵדֻ֔ת מִבֵּ֖ין שְׁנֵ֣י הַכְּרֻבִ֑ים וַיְדַבֵּ֖ר אֵלָֽיו׃
מדבר: כמו מתדבר. כבודו של מעלה לומר כן מדבר בינו לבין עצמו ומשה שומע מאליו
Like mitdabber. It is out of respect for God that the passuk is worded thus: [the voice of God] was speaking to itself and Moses was listening in.
I have seen references to a spiritual explanation of this concept.That is, rather than explicitly stating that Rashi knew about radio and television, it is a spiritual meaning of unseen forces. Similarly, the statement that Adam Harishon could see from one end of the world to the other. The medrashim about k'fitzas haderech (teleportation) as experienced by Eliezer on his way to meet Rivkah., etc.
On his last day of life, Moshe Rabbeinu addresses the Klal Yisrael. After a thorough explanation of the vast rewards and ghastly punishments that hinge on the choices made, he offers a final note: Let the heavens and the earth bear witness.
Rashi explains that Moshe was giving them a tool to help them stay on the proper path. “Look at the heavens and the earth did they change their ways? Did the sun ever say, ‘I won’t rise this morning?’ Did the ground ever say, ‘I won’t produce?’ Or did it say, ‘I will grow wheat instead,” when you planted barley? As they dutifully follow Hashem’s commands, so too should you.”
In our modern world we regularly harness forces that our eyes don’t see. No human has ever seen electricity. We can see the burning of impurities in the air as lightening streaks across the sky. But the flow of electric current is not visible
We don’t see radio waves. We don’t see Wi- fi. We don’t see electron. But they exist. And we know it.
This seems to be the answer to this Rashi. The Jewish People then were on the highest spiritual level of any generation. They experienced all of the miracles in mitzraim . They lived
through the splitting of the sea. They were there at the foot of Har Sinai, when Hashem spoke. The heavens were opened up and they witnessed things that no other people saw. And so they had an understanding of the ways of the world that we don’t. As we know electricity exists, they knew the spiritual counterpart exists. To them it was real.