Diagoras wrote: ↑Tue Sep 20, 2022 5:54 pm
Others would say, “refine the original model based on the results of experiment.” It’s pretty much standard for many physical sciences.
Not so for cosmology.
The scientific approach to the situation would be to choose a model, determine the parameters that best fit observations, and then revise the model as necessary – i.e., as new data comes in. But that’s not what cosmologists presently do. Instead, they have produced so many variants of models that they can now “predict” pretty much anything that might be measured in the foreseeable future.
As for refining inflationary theory, even one of the originators of cosmic inflation theory, Paul Steinhardt, has abandoned inflation theory.
Horgan: You were one of the originators of inflation theory. When and why did you start having doubts about it?
Steinhardt: From the very beginning, even as I was writing my first paper on inflation in 1982, I was concerned that the inflationary picture only works if you finely tune the constants that control the inflationary period. Andy Albrecht and I (and, independently, Andrei Linde) had just discovered the way of having an extended period of inflation end in a graceful exit to a universe filled with hot matter and radiation, the paradigm for all inflationary models since. But the exit came at a cost — fine-tuning. The whole point of inflation was to get rid of fine-tuning – to explain features of the original big bang model that must be fine-tuned to match observations. The fact that we had to introduce one fine-tuning to remove another was worrisome. This problem has never been resolved.
But my concerns really grew when I discovered that, due to quantum fluctuation effects, inflation is generically eternal and (as others soon emphasized) this would lead to a multiverse. Inflation was introduced to produce a universe that looks smooth and flat everywhere and that has features everywhere that agree with what we observe. Instead, it turns out that, due to quantum effects, inflation produces a multitude of patches (universes) that span every physically conceivable outcome (flat and curved, smooth and not smooth, isotropic and not isotropic, scale-invariant spectra and not, etc.). Our observable universe would be just one possibility out of a continuous spectrum of outcomes. So, we have not explained any feature of the universe by introducing inflation after all. We have just shifted the problem of the original big bang model (how can we explain our simple universe when there is a nearly infinite variety of possibilities that could emerge from the big bang?) to the inflationary model (how can we explain our simple universe when there is a nearly infinite variety of possibilities could emerge in a multiverse?).
I have to admit that I did not take the multiverse problem seriously at first even though I had been involved in uncovering it. I thought someone would figure out a resolution once the problem was revealed. That was 1983. I was wrong. Unfortunately, what has happened since is that all attempts to resolve the multiverse problem have failed and, in the process, it has become clear that the problem is much stickier than originally imagined. In fact, at this point, some proponents of inflation have suggested that there can be no solution. We should cease bothering to look for one. Instead, we should simply take inflation and the multiverse as fact and accept the notion that the features of the observable universe are accidental: consequences of living in this particular region of the multiverse rather than another.
To me, the accidental universe idea is scientifically meaningless because it explains nothing and predicts nothing. Also, it misses the most salient fact we have learned about large-scale structure of the universe: its extraordinary simplicity when averaged over large scales. In order to explain the one simple universe we can see, the inflationary multiverse and accidental universe hypotheses posit an infinite variety of universes with arbitrary amounts of complexity that we cannot see. Variations on the accidental universe, such as those employing the anthropic principle, do nothing to help the situation.
Scientific ideas should be simple, explanatory, predictive. The inflationary multiverse as currently understood appears to have none of those properties.
These concerns and more, and the fact that we have made no progress in 30 years in addressing them, are what have made me skeptical about the inflationary picture.
The irony is that our understanding of inflation has changed dramatically. We no longer believe that inflation makes any of those predictions so that none of the magnificent observations made over the last 30 years can be viewed as supporting inflation.
Since 1983, it has become clear that inflation is very flexible (parameters can be adjusted to give any result) and generically leads to a multiverse consisting of patches in which any outcome is possible. Imagine a scientific theory that was designed to explain and predict but ends up allowing literally any conceivable possibility without any rule about what is more likely. What good is it? It rules out nothing and can never be put to a real test.
Horgan: Do you think the BICEP2 observations may still turn out to support inflation?
Steinhardt: As just explained, it is not possible to find evidence to support or refute inflation because an inflationary multiverse includes patches with cosmic gravitational waves and without them.
Inflation was proposed more than 35 years ago, among others, by Paul Steinhardt. But Steinhardt has become one of the theory’s most fervent critics. In a recent article in Scientific American, Steinhardt together with Anna Ijjas and Avi Loeb, don’t hold back. Most cosmologists, they claim, are uncritical believers:
“[T]he cosmology community has not taken a cold, honest look at the big bang inflationary theory or paid significant attention to critics who question whether inflation happened. Rather cosmologists appear to accept at face value the proponents’ assertion that we must believe the inflationary theory because it offers the only simple explanation of the observed features of the universe.”
And it’s even worse, they argue, inflation is not even a scientific theory:
“inflationary cosmology, as we currently understand it, cannot be evaluated using the scientific method.”
The problem with inflation isn’t the idea per se, but the overproduction of useless inflationary models. There are literally hundreds of these models, and they are – as the philosophers say – severely underdetermined. This means if one extrapolates the models that fit current data to regimes which are still untested, the result is ambiguous. Different models lead to very different predictions for not-yet made observations. Presently, it is therefore utterly pointless to twiddle with the details of inflation because there are literally infinitely many models that one can think up, giving rise to infinitely many different “predictions.”
And, to actually get closer to the OP, can you honestly say that the description in Genesis of how the world was formed is a robust and accurate one?
I would say the idea that the universe had a beginning and was designed will continue to outlast any other competing explanation. So, yes, I would say it is a robust and accurate one.