Anthropics Explained (by Rejecting the Copernican Principle)

Many paradoxes in philosophy, like the Simulation Argument, the Boltzmann brain argument, and the Doomsday argument, rest on what’s called the Copernican Principle. This is the idea that among all of the observers that exist in the universe you are equally likely to be any one of them. There is little reason to think this is true, and these paradoxes give us a strong reason to reject the Copernican principle. Instead, the question of what observer you are should be approached like any other scientific question: be open to many theories and judge them by their parsimony and their fit with your observational data.

This is easiest to understand in the “anthropic” puzzles in eternal inflation theories. In these theories the process of inflation creates an infinite number of “bubble universes” which may have different effective laws of physics (although the rules for how these different effective laws of physics come about, as well as what happens in high-energy experiments with these bubble universes, should be determined by shared universal laws of physics). Already the mere possibility of there being an infinite number of observers kills the Copernican principle as a necessary truth, as when this occurs it is impossible to weigh each observer with an equal probability. This is a practical as well as a theoretical problem. There are many proposals for how to sample bubble universes within the full universe/multiverse, and they give different predictions for what a “typical” bubble universe is like. I think such sampling procedures for where our observable universe fits in the full universe should be considered to be a component of any specific eternal inflation theory. This means that if a single inflation mechanism has multiple substantially different ways a universe like ours might be picked out these different ways should be considered different theories. It also means that a simple inflation mechanism which requires a complex sampling procedure to describe how our currently observed universe arises should be penalized as more complex.

Your knowledge of where you are in the universe is something philosophers of science call an auxillary hypothesis. No scientific theory makes predictions entirely on its own, but it must be augmented with auxillary hypotheses that relate the theory to things we can directly observe. For example, if you test Maxwell’s equation by measuring the force between a current through a wire and magnet, the test depends on the auxillary hypothesis that your battery generates a voltage, your wire conducts electricity, and your magnet generates a permanent magnetic field. An unexpected result can be explained by changing either the theory or the auxillary hypotheses. The famous example from astronomy: When Uranus’s orbit did not match predictions this lead to the discovery of Neptune whose gravity was affecting Uranus, so Newtonian gravity still worked but required a new auxillary hypothesis. When Mercury’s orbit diverged from predictions a planet Vulcan was theorized to affect it, but Mercury’s orbit was eventually explained by general relativity, a new theory. People usually don’t explictly include auxillary hypotheses when assessing the elegance or complexity of a theory, but it is necessary to do so when comparing explanations that involve changing the auxillary hypotheses. Perhaps some fine-tuned invisible Vulcan is what’s really affecting Mercury, but general relativity is the simpler theory.

Every theory about cosmology or the nature of reality implicitly includes our place in the universe as an auxillary assumption. After all, it is tested through observations we make. You expect to see a galaxy only when you’re actually looking through a telescope. In particular, if you are actually in a VR or simulated environment then what you see through a virtual telescope won’t be determined by cosmology but by the will of the creator of your environment. That means that when we consider the hypothesis that everything we’ve ever experienced is simulated, then we have absolutely no direct evidence on the cosmology and laws of physics of the underlying “real” universe. These theories must be re-examined from scratch, and for the underlying universe to have the same laws and cosmology is possible but highly speculative. That is not how the simulation argument is usually presented. Instead, it’s thought that simply by taking our current cosmological model seriously a false egalitarianism forces us to take far more seriously our cosmological model existing in a simulation which in turn exists in the exact same cosmological model, in spite of the latter model being obviously more contrived. That’s because the simulation argument treats the auxillary hypothesis of self-location through a dogma rather than as an aspect of a scientific model.

I only covered two examples in depth, but I hope you get the idea. Again, every paradox that works using the Copernican principle can inverted to produce an argument against the Copernican principle:

  • It looks like the future population will be a lot larger than the current population, so there will be far more observers in the distant future than all observers that ever lived up to the present day. Therefore living in the present, we are not typical observers.
  • It looks like our descendants will make many simulations of us that are indistinguishable to an observer from the real thing. These simulated observers will vastly outnumber us, but unlike us, they won’t be able to make simulations in turn. Therefore we are not typical observers.
  • If the universe ends in heat death, then afterwards thermal or quantum fluctuations can create conscious observers. This is incredibly rare, but if the heat death is eternal such observers will eventually outnumber those that live in a non-equilibrium universe. Most such observers only experience the bare minimum of conscious experience that counts as such, rather than the rich lives we live. Therefore we are not typical observers.
  • In an infinite inflationary universe the very notion of a “typical observer” doesn’t make sense. Therefore we aren’t typical observers.

Strictly speaking, nothing here produces an actual contradiction, but it’s all evidence. The Copernican principle forces us to take many contrived positions about the past and future of our universe, when we could just not do that. Reject the Copernican principle!