### [0704.2630] Are We Typical?

Posted:

**April 23 2007**This paper argues that the correct datum for comparing cosmological theories is

The main problem is that it seems to be unclear how to apply this kind of reasoning in infinite theories where all observations exist at least once. e.g. regarding Boltzmann brains: it's true that brains with different observations are irrelevant; however any infinite theory with Boltzmann brains will have my observations an infinite number of times, and so using this reasoning alone a theory with only brains cannot be distinguished from a more 'physical' theory where my brain evolved. [note that in a Boltzmann brain theory the Earth and other cosmologists are just fake memories in by brain, so the entire information, gathering and utilizing system is just my brain]

*There exists at least one observing system with our observations*. This seems to be essentially the same as 'full non-indexical conditioning' advocated in considerably more detail in arXiv:math/0608592. It is certainly reasonably compelling, at least for finite theories. One feature is that it favours models with larger volume (because usually the probability for an observer to exist with all our observations is proportional to volume), which is the 'presumptuous philosopher' objection (which is an objection based purely on intuition and does not mean it is necessarily wrong; e.g. see gr-qc/0009081).The main problem is that it seems to be unclear how to apply this kind of reasoning in infinite theories where all observations exist at least once. e.g. regarding Boltzmann brains: it's true that brains with different observations are irrelevant; however any infinite theory with Boltzmann brains will have my observations an infinite number of times, and so using this reasoning alone a theory with only brains cannot be distinguished from a more 'physical' theory where my brain evolved. [note that in a Boltzmann brain theory the Earth and other cosmologists are just fake memories in by brain, so the entire information, gathering and utilizing system is just my brain]