Fine-tuning

[Pulsar]

Hi Nelson. Sorry, I somehow completely overlooked this thread. So let me answer one of your questions:

My argument may break down as I am not sure that the inflationary cosmological model and the standard big bang model DO make identical predictions about the CMB. If it is the case that they do not, then the argument can easily converted into a hypothetical situation in which two models make the same predictions but one covers a larger area of parameter space.

No, they make different predictions about the CMB, and inflation matches the observations better than alternative models. It's rather technical, so I'm going to be lazy and copy directly from wiki:

Inflation predicts that the structures visible in the universe today formed through the gravitational collapse of perturbations which were formed as quantum mechanical fluctuations in the inflationary epoch. The detailed form of the spectrum of perturbations called a nearly-scale-invariant Gaussian random field (or Harrison-Zel'dovich spectrum) is very specific and has only two free parameters, the amplitude of the spectrum and the spectral index which measures the slight deviation from scale invariance predicted by inflation (perfect scale invariance corresponds to the idealized de Sitter universe).
Inflation predicts that the observed perturbations should be in thermal equilibrium with each other (these are called adiabatic or isentropic perturbations). This structure for the perturbations has been confirmed by the WMAP spacecraft and other cosmic microwave background experiments, and galaxy surveys, especially the ongoing Sloan Digital Sky Survey. These experiments have shown that the one part in 10,000 inhomogeneities observed have exactly the form predicted by theory. Moreover, there is evidence for a slight deviation from scale invariance. The spectral index, ns is equal to one for a scale-invariant spectrum. The simplest models of inflation predict that this quantity is between 0.92 and 0.98. From the data taken by the WMAP spacecraft it can be inferred that ns = 0.963 ,± 0.012, implying that it differs from one at the level of two standard deviations (2σ). This is considered an important confirmation of the theory of inflation.

I can add that inflation was initially proposed to solve the horizon problem. The fact that it automatically solved the flatness problem and the magnetic monopole problem was an important bonus, and the CMB fluctuations seem to validate inflation further, although more theoretical and observational evidence is needed to settle the matter.
Oh, and I agree with AW, of course.

 

[Nelson]

No, they make different predictions about the CMB, and inflation matches the observations better than alternative models.

Thank you, I was far too lazy to look this up on my own when I first posted it. These are the sorts of differences I expected though. Inflation simply explains more things. The standard big bang model COULD be correct without a period of inflation, we would just have to assume some very specific conditions, which is highly undesirable.

I also didn't know that the flatness problem was not originally a motivation of the theory, which is quite interesting. However, reading through observational time-lines on few wiki pages suggests that we didn't even have a solid measure of the curvature until WMAP, so I suppose the horizon problem was more immediately apparent.

 

[Deleted member 619]

I'm willing to concede the point, but I still think it's a bit of a stretch to use 'fine-tuning' in that context. The parameters aren't really being fine-tuned, they just have to match certain specific values for the models to work which, AFAIC, is pushing the applicability of the term. That's why it isn't rigorous. Not only that, it leaves it open to equivocation of exactly the sort we see with the word 'entropy', which is why I raised that.

Oh, and it isn't because of supernaturalists' use of the term that I object to, it's the context in which it's being applied here. That said, I'm happy to concede, not least because it's a trivial point in many respects.

 

[AndromedasWake]

Sorry about the thread necromancy, but I just wanted to let anyone interested in this topic know that I'll be giving a talk about Fine Tuning at an all-day skeptics event this coming Sunday. Apparently it'll be recorded in some way and I can put it on YouTube, which would be good because it was spun out of a video I had planned to make for some time. I just thought a talk might make the format a little more interesting. I'm looking forward to presenting my ultimate skeptical approach to fine tuning arguments.

 

[Deleted member 619]

I'll look forward to it.

Meanwhile, any sign of any more WTTU?