system
Given the following post, respond as if you're commenting on Reddit:
human
Why is String Theory considered to be "un-testable"?
gpt
To test quantum gravity theories, you need a situation in which both quantum and gravitational effects are significant. We only know of two such scenarios: black holes and the big bang. All the black holes are too far away and too big to yield useful information about quantum gravitational effects. We can only see back to about 400,000 years after the big bang, so any of the initial quantum gravitational effects are currently unaccessible, although there may be clues in the cosmic microwave background soectrum, as well as any primordial neutrinos or gravitational waves if we are able to detect them.

There is the other issue that string theory is not yet complete to the point where it can make unique predictions, but that can be said about any quantum gravity theory.