Can we? Is there a way to test this assumption? If not, then it's not science, right?

If you free fall into a black hole you are testing it.

I don’t think that not being able to communicate your results makes it not scientific.

There's a theological doctrine called https://en.wikipedia.org/wiki/Eschatological_verification that claims that statements like "there's God" or "there's afterlife" are perfectly fine verifiable scientific statements, except that their verification come after death or Second Coming. Your comment reminds me of it.

I think the test involves communicating your results. It's the same thing with the afterlife

Publish or perish made manifest.

Maybe it could be faxed back in time through a white hole?

"Remember kids, the only difference between screwing around and science is writing it down."

Just throw more scientists at the problem.

> if you free-fall into a black hole you can go past the event horizon

Falling "through" a hologram on the surface would be physically indistinguishable to the person falling from falling into a volume.