Continued slow liveblog of the New Frontiers in Astronomy and Cosmology Conference at the Franklin Institute.

We have had coffee and we are rested and ready after yesterdays 14 hour marathon session (graduate students please note – though it did include breakfast, lunch, dinner and two coffee breaks (“working breaks” natch, apart from the hour+ break before dinenr) – and I don’t think any of the faculty could actually keep it up for more than 2-3 days, except in our imagination (‘course we then went back to the hotel and had to catch up on class and administrative issues left unattended, but lets not go there).

Morning sessions starts with

Big Question IIIs our universe unique or is it part of a much larger multiverse

and we are off…

1) up first is Anthony Aguirre from UCSC – “Testing the Multiverse”

Premise – eternal inflation, continuing nucleation of new vacuums from a background of ongoing high energy inflating vacuum.
Ensemble of bubbles of expanding (or collapsing) inifinite space-time bubbles, possibly with different ground states and physics as well as initial conditions.

Very good graphics and visualizations of the concepts – I want them!

Science if signature of bubble collisions.
Big IF is why bubble collisions don’t trigger a phase transition within the bubbles to a new vacuum state – which would be BAD, for us.
Modeling CMB signature, including polarization, assuming gentle perturbative collisions

Like this: Hierarchical Bayesian Detection Algorithm for Early-Universe Relics in the Cosmic Microwave Background – Feeney et al (2012).
No, they didn’t find anything.

2) Matthew Kleban from NYU on “Testing the Multiverse with Cosmic Bubble Collisions”

Believe in the Multiverse (eternal inflation edition)!
Ok, testing the multi-bubble large inflationary universe is clearly the trendy thing to do – looks timely in that some quantitative observables can indeed test some of the models.

Circles on the CMB sky…

Basic problem: we don’t know the a priori statistics of the number of (observable) bubble collisions per bubble

Ah, but he is really looking at global imprints of extra dimensional collisions, not bubble collisions – sounds like an interesting direction to explore

3) Chao-Lin Kuo from Stanford on “CMB polarization, 21-cm cosmology and testing the multiverse”

Chao-Lin could not make it, Matt gave a quick precis of his presentation on high precison CMB polarization measurements and possible constraints on the multiverse.

4) Wim Ubachs from Vrije Universiteit on “Search for Drifting Constants via Extra-Galactic Alcohol”

Testing fine structure constant etc at high redshift
CH3OH sadly
getting interesting constraints at 10 parts per billion in radio observations

5) Alexander Vilenkin from Tufts on “Global structure of the multiverse and the measure problem”

Hard to define metrics on infinite sets of events, even if they are only countably infinite
Therefore hard to define metric to calculate stuff like expected number of bubble-bubble collisions in eternal inflation.
Even harder to define “when” collisions happen.

Choice is hard when there are infinite choices…

uses eternal observer to resolve paradox
problems with collapsing bubbles terminating observer worldlines

might be a way around that