#streams2015, day 5

Today was the last (and half) day of the Ringberg meeting. At breakfast, we discussed an argument James Binney (Oxford) had made the previous day about n-body simulations not being the answer to physics questions: His view is that simulations should just inspire theories that are continuous, large-scale, and manipulable with other tools. He gave some examples. I, in the end, disagreed with Binney's argument and his examples: There are many fields of science where all of the predictions come from small-scale (n-body or molecular or finite-element) simulations and all the “understanding” is pure story-time about those simulations. For example, structural and aerospace engineering is all about finite-element analysis. And climate and weather are all about simulations. And many of the beautiful, effective theories for solid-state physics and so on are not working very well as we push to new regimes; we have to go back to molecular-level simulations. All that said, I am sympathetic to Binney's point, which is that we don't always get a lot of understanding out of the crank-turning on n-body simulations.

Today's talks were very lively, with Carlberg (Toronto) and Küpper talking about stream substructure created by dark-matter substructure, and Bonaca talking about our work on streams in realistic (rather than analytic) potentials. Bonaca shows that our conlusions from analytic potential models can be very wrong, even in gross properties, but that things improve as we include more and more streams into the analysis. She got some lively questioning from Evans, who was not buying it. I'm with Bonaca, of course!

The drive home was a long discussion between Rix and me about all that had happened and what to do next. We are fired up about new approaches to stream searching, to use now on SDSS and PanSTARRS data, but also to have very ready for (what we are calling) Gaia DR2.

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