What word in ancient Greek would be used to describe scientific discoveries like when the laws of physics were first worked out?

Ancient Greek for scientific discovery, eh?

Well, don’t go to Google Translate, man. That’s Modern Greek.

Start here instead: English-Greek Dictionary

“Discovery” gives us heuresis, aneuresis; mēnysis (disclosure), heurēma and exeurēma (invention, thing discovered).

Mēnysis is “messaging”, so it’s not what you’re after. The others are all derived from the verb heuriskō “I find” (as in Eureka). Of the two suffixes, –ma is a thing discovered, while –sis also allows the meaning of the action of discovery.

The prepositional prefixes in Greek are often not very important; aneuresis is “up-finding”, which can have a more intense connotation of bringing something to light, not just finding it. Similarly exeurēma “out-find” is about bringing something out as a discovery.

I think heuresis is your safest bet, but aneuresis is pretty close.