[astro-ph/0410281] What does inflation really predict?
Posted: October 14 2004
This seems like an interesting paper just asking for discussion! I have two comments
* Presumably there could easily be a physical prior (e.g. from string theory) that changes the conclusion about it boding "well for detecting an inflationary gravitational wave signature". For example if the underlying theory gives a prior distribution for the energy scale of inflation sharply peaked at TeV scales, then the quest may be hopeless. The actual physical prior over functions (as opposed to the Gaussian process assumed) could presumably change the conclusions about [tex]n_s[/tex] and Q.
* I'm a bit worried about using observations to determine the correct measure and ordering - e.g. using the "coolness problem" to rule out t-ordering. Surely the correct statement is if t-ordering is correct, inflation is highly disfavoured compared to almost any other model. Otherwise however wrong inflation is you can probably always keep changing your ordering/measure until you find one which gives acceptable predictions - inflation becomes even more untestable! I would think that only if you assume inflation is right can you use observation to determine the ordering: using observations to argue about the correct logic for calculation seems odd to me. (However I completely agree that t-ordering is almost certainly wrong.)
I would be interested to know how well people think the Gaussian process prior over functions encapsulates the predictions of the string landscape.
* Presumably there could easily be a physical prior (e.g. from string theory) that changes the conclusion about it boding "well for detecting an inflationary gravitational wave signature". For example if the underlying theory gives a prior distribution for the energy scale of inflation sharply peaked at TeV scales, then the quest may be hopeless. The actual physical prior over functions (as opposed to the Gaussian process assumed) could presumably change the conclusions about [tex]n_s[/tex] and Q.
* I'm a bit worried about using observations to determine the correct measure and ordering - e.g. using the "coolness problem" to rule out t-ordering. Surely the correct statement is if t-ordering is correct, inflation is highly disfavoured compared to almost any other model. Otherwise however wrong inflation is you can probably always keep changing your ordering/measure until you find one which gives acceptable predictions - inflation becomes even more untestable! I would think that only if you assume inflation is right can you use observation to determine the ordering: using observations to argue about the correct logic for calculation seems odd to me. (However I completely agree that t-ordering is almost certainly wrong.)
I would be interested to know how well people think the Gaussian process prior over functions encapsulates the predictions of the string landscape.