How Cosmological Supercomputers Evolve the Universe All Over Again

This is clearly good work, but I believe that the article glosses over real problems with these kinds of simulations. The short version of the problem is that the agreement between the model and the observations doesn't provide a huge degree of confidence in the model being tested. It appears that both the model and the starting setup are per-disposed to produce results that match observations.

There has been no perturbation testing of the model. It does not seem that they did any runs that were intended to produce a result that did not match observations. They have no idea what range of input or modeling change produce a result that matches observations.

The greatest utility of these simulations is when they don't match observations. This opens the possibility that the current ideas are incorrect, and that new ideas are needed.

I also wonder about scaling issues. The three simulations at different scales are unconnected. There is no way to see how events at one scale effect events at other scales.

The author also said one specific thing that bothered me:

Astrophysicists can model the growth of density fluctuations at these early times easily enough using simple linear equations to approximate the relevant gravitational effects.

I am not a physicist or cosmologist, but that seems to be a huge assumption. We have no idea what dark energy or dark matter are, but they can be modeled by "simple linear equations."

I know that the shear cost and complexity of these computational experiments means that they are hard to accomplish. Even so, I will be less skeptical about their value when they are done in ways that test how the simulations fail, as well as how they verify current ideas.

Source: http://rss.slashdot.org/~r/Slashdot/slashdotScience/~3/4OUPjz7WeX0/how-cosmological-supercomputers-evolve-the-universe-all-over-again

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