[icapybara]

That's not true. It's a basic tenet of science. Even astronomical theories (for which no experiments are possible) are backed up by observation.

Scientific theories must be testable. It must be possible to prove them wrong with experiments or observation.

[VortexDream]

Except in many cases, we didn't have the tools or technology to be able to test theories that eventually turned out to match real-world measurements. But the theories existed beforehand anyway and weren't any less science.