Depends somewhat on the particular negative. We can claim with certainty that dinosaurs are not alive today, even though there are theoretically places that are not sufficiently explored where, in principle, a dinosaur might live. We are well aware that the fossil record is globally consistent and demonstrates the timing of their extinction, as well as the lack of any fossils of dinosaurs since then.

Similarly, I can claim with confidence that a force does not exist in the universe that would allow me to teleport from place to place instantaneously, because such a force would violate many of the known laws of physics.

There are various types of god-beings that cannot exist because of a logical contradiction. An omnipresent entity, for instance, would be always detectable if it had any measurable effect on the world, but no such measurable effect can be observed. If it is not capable of a measurable effect, then it is indistinguishable from not existing.

Other types of negatives are not easily proven. That is why scientists will say things like, “Based on 3478 measurements, there is currently no evidence to support the existence of higher values than those reported here.”

What was going on five years ago?