A question from the audience: are we only asking about the connection between an “eigenstate” of a causal set and a classical spacetime.  Fletcher agrees that for present purposes, this is the question he’s interested in.  The concern is that perhaps the only workable way to approximate a spacetime is with a superposition of causal sets.  Fletcher agrees that this is an important problem but would like to focus on a more tractable one.

The theorem that inspires CST is due to Malament, and shows that causally isomorphic spacetimes must be entirely isomorphic up to some conformal factor.  The causal relations uniquely determine a spacetime up to a volume.  The idea of CST is that, if spacetime were composed of discrete parts, we could get the volume as well by “counting” the parts composing any region.

The Hauptvermutung: If we have two faithful or “uniform” embeddings of the same causal set into relativistic spacetimes, with a given density, then the two spacetimes are approximately isometric above the volume scale of 1/(the density).  But what is it for an embedding to be “uniform”?

Normally this is defined in terms of the spacetime, but of course the causal sets are fundamental (not the spacetime), so uniformity must fundamentally mean something like “with high probability.”
 
But what does “high probability” mean?  This is where observables can help.  Uniformity will be an instrumentally useful standard relative to the observables we’re hoping to predict.

Fletcher notes that previously work on quantum gravity has focused on reduction and emergence of properties as opposed to intertheoretic reduction.  He’d like to help correct this omission.  His topic here is causal set theory.  He’d like to show that the “Hauptvermutung” or primary conjecture of causal set theory has, as yet, no rigorous formulation, but that paying attention to observables may help show the way to such a formulation.

Some of you may be interested to know there’s a couple of good shows on Saturday: Stereophonics are playing The Vic (a small venue) and Phoenix and The Vaccines are playing the Aragon Ballroom (big, but not huge). Of course there is also the Space, Time and Spacetime party!

Coming from the O’Hare? To go straight to the conference take the blue line subway to Halsted/UIC stop. To go to the hotel, take the blue line to Washington and walk or taxi it – less than a mile (and our taxis are cheap). See the map on the accommodations page.

Also for drivers – the Morgan Street exits from, and bridge over, I290 is closed. As far as can tell that is the only problem caused by the roadworks.

The meeting will take place in the Institute for the Humanities, in Stevenson Hall, University of Illinois at Chicago – roughly 701 S.Morgan St. See more directions above.

Some of the papers to be presented are now available through the website – see “Paper Discussion”. We have also set up a comment thread for each so that they can be discussed both before and after the meeting. The intension is that participants will have read the papers before the meeting to facilitate discussion.

Others will be posted as they become available!

Graduate students – if you would like a couch to sleep on and save hotel costs, please contact Josh Norton (<joshua.d.norton@gmail.com>) who has a list of local graduate students happy to put you up.

People attending the meeting can obtain a reduced rate (of $159/night ~ $180 with taxes) at the Crowne Plaza Chicago Metro: http://www.thechicagometro.com. The hotel is a 15 minute walk to the conference, and about the same to downtown – but there are plenty of places to eat and drink in the vicinity. 

To book, call 312-829-5000 and request the UIC rate – mention the conference if asked. The rate will be available until the hotel is 80% full – so please don’t wait!

If you would like us to try to help find you a roommate to split the cost, please contact us at beyondspacetimeseminar@gmail.com.