A Speculation on Simulated Beings
If intelligent creatures in a simulated universe tried creating their version of physics, they might be able to get as far as identifying the characteristics of the machine language used. On the other hand, the source code is clearly more fundamental (from the point of view of the programmer) but they could find out that only by looking at large-scale patterns.
We can imagine philosophical debates between the reductionists and believers in the Source Code in which the reductionists correctly point out that nothing that violated the rules of the machine language had ever happened and think that meant they won the debate.
I was inspired by this post at Overcoming Bias.