As far as I know inflationary theory is suppor…

As far as I know inflationary theory is supported by observational physics, but then I read (in the wikipedia article) that Paul Steinhardt, one of the early proponents of inflation, is now one of the main opponents, and he and others physics said the most recent Plank satellite data rule out the simplest inflationary models and the remaining ones requiere more fine tuned starting conditions and less inflation. So is inflation theory becoming more or less reliable? I´m confused…

I have written about this profusely, and should actually have a book about inflation coming out sometime next year.

In the meantime, you may enjoy this article that goes into some depth on the issue, and here is the money quote:

“On all three counts — of reproducing the successes of the non-inflationary Big Bang, of explaining observations that the Big Bang cannot, and of making new predictions that can be (and, in large number, have been) verified — inflation undoubtedly succeeds as science. It does so in a way that other theories which only give rise to non-observable predictions, such as string theory, does not. Yes, when critics talk about inflation and mention a huge amount of model-building, that is a problem; inflation is a theory in search of a single, unique, definitive model. It’s true that you can contrive as complex a model as you want, and it’s virtually impossible to rule them out.

But that is not a flaw inherent to the theory of inflation; it is an indicator that we don’t yet know enough about the mechanics of inflation to discern which models have the features our Universe requires. It is an indicator that the inflationary paradigm itself has limits to its predictive power, and that a further advance will be necessary to move the needle forward. But simply because inflation isn’t the ultimate answer to everything doesn’t mean it isn’t science. Rather, it’s exactly in line with what science has always shown itself to be: humanity’s best toolkit for understanding the Universe, one incremental improvement at a time.”