Phys.org recently reported that physicist Martin Savage thinks this might actually be the case, and that the idea is testable:
Savage and colleagues […] suggest that the [simulator] signature could show up as a limitation in the energy of cosmic rays. In a paper they have posted on arXiv, […] they say that the highest-energy cosmic rays would not travel along the edges of the lattice in the model but would travel diagonally, and they would not interact equally in all directions as they otherwise would be expected to do [under Einstein’s theory of relativity]. “This is the first testable signature of such an idea,” Savage said.
This is how US News describes the proposed test:
[A] few creative researchers from the University of Washington believe they’ve developed a way to test the [Matrix or Lattice] theory [of the universe]. […]
By studying the highest-energy cosmic rays known in the universe to see if they travel in straight lines along the edges of the space-time continuum (which would likely mean that we’re not in a simulation), or if they cheat a bit and cut across it diagonally (a “signature” limitation in the energy of these cosmic rays that would tell us we’re actually living in a highly complex, but still resource-constrained, simulation).
In other words, the Matrix may be moving from a speculative idea in philosophy to a testable idea in physics. Here’s how Ray Villard puts it at Discovery News: … More.
Sure it’s testable, if the sim lets us. A fundamental rule of reasoning seems to get lost here: We start by assuming that the world around us is reality. Otherwise, we can go anywhere, everywhere and nowhere. Oh wait, there’s a word for that nowadays – cosmology.