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October 28, 2004

Roundup

Around the blogs:

  • Matt continues his excellent review of Lattice Gauge Theory, with a post on the classic paper of Lepage and MacKenzie.
  • Luboš blogs about the paper of Itzhaki and McGreevy that I discussed a while ago.
  • Urs is musing abut the n 3n^3 degrees of freedom in the low-energy theory on nn coincident M5-branes.

  • Sean writes about his new paper with Jennie Chen, on an attempt to explain why the initial state of the universe was one of low-entropy.

    I haven’t read their paper yet, but the idea is that our universe originated as a thermal fluctuation in an ambient de Sitter space, which then inflated. Personally, I’m sceptical that quantum gravity in (eternal) de Sitter space makes sense. Tout court, while there are certainly metastable de-Sitter-like solutions, I don’t think eternal de Sitter space exists as a solution to String Theory. But an approach like that of Carroll and Chen certainly has the advantage that one is not immediately plunged into the tangled thicket of quantum cosmology. Those discussions never go anywhere because, sooner or later, someone mentions “the wave function of the universe,” the physics-equivalent of Godwin’s Law, and all rational discussion comes to an end.

Posted by distler at October 28, 2004 12:31 AM

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16 Comments & 0 Trackbacks

Re: Roundup

Maybe this is the right place to annouce that the other day, reading in Lubos’ blog I made the mistake of clicking the “creat your own blog” button. So, here it is: atdotde.blogspot.com. There is not much there as, yet, but I promise I will do my best to make it interesting. I just don’t know how you people (esp. Lubos) manage to fit in blogging into a day of only 24 hours.

Posted by: Robert on October 28, 2004 5:33 AM | Permalink | Reply to this

Re: Roundup

This is evolving from a coffee table to an entire coffee house. ;-)

What can I do to let my RSS reader list new entries on the BLOGGER blogs, like Robert is using now? I can’t find a ‘syndicate’ link.

Posted by: Urs Schreiber on October 28, 2004 8:08 AM | Permalink | PGP Sig | Reply to this

Syndication

Blogger doesn’t do RSS, they do Atom Syndication. If your News Aggregator is recent enough, it should support Atom as well.

The Atom feed is a file, atom.xml, at the root level of the blog, e.g. http://atdotde.blogspot.com/atom.xml .

This is evolving from a coffee table to an entire coffee house.

I guess I should also remind both Robert and Luboš that they are still registered as authors at the Coffee Table too. So if they have a something in which they want the equations to be rendered, they can post (or cross-post) it to the Coffee Table.

Posted by: Jacques Distler on October 28, 2004 8:35 AM | Permalink | PGP Sig | Reply to this

Re: Syndication

Ok, thanks. Now I am using ‘sage’. atom.xml gives me the entries, how do I get the comments?

Posted by: Urs Schreiber on October 28, 2004 9:52 AM | Permalink | PGP Sig | Reply to this

Custom feeds

Now I am using ‘sage’. atom.xml gives me the entries, how do I get the comments?

You don’t. Blogger doesn’t provide them, and Blogger users can’t add their own Comment Feed.

Yet another reason (as if being able to use inline TeX weren’t sufficient) to prefer MovableType.

Posted by: Jacques Distler on October 28, 2004 12:20 PM | Permalink | PGP Sig | Reply to this

Re: Custom feeds

I see. Is it also the case that Blogger does not support trackbacks, or is there a way to make my SCT entry commenting on some Blogger entry appear as a link in the latter?

Posted by: Urs Schreiber on October 28, 2004 12:39 PM | Permalink | PGP Sig | Reply to this

Trackbacks

I don’t believe they do.

It’s only with their recent redesign that they started offering (Atom) syndication feeds and a Comment System (previously, some Blogger users used 3rd party comment services, like HaloScan).

Trackbacks are not implemented (sending or receiving).

Posted by: Jacques Distler on October 28, 2004 12:58 PM | Permalink | PGP Sig | Reply to this

Re: Syndication

“I guess I should also remind both Robert and Lubos that they are still registered as authors at the Coffee Table too. So if they have a something in which they want the equations to be rendered, they can post (or cross-post) it to the Coffee Table.” [how do I get blockquote to work?]
No need to be reminded. Its just that on my own blog I can write about things that would be off topic at the coffee table (like computer stuff, radio hosts, politics, other nonsense). String theory discussions still have their appropriate place at the coffee table.

Posted by: Robert on October 28, 2004 10:47 AM | Permalink | Reply to this

Re: Syndication

String theory discussions still have their appropriate place at the coffee table.

Nice to hear! I find myself posting almost exclusively to the SCT, while I would much rather be listening to what others have to say.

Speaking of which: Did you get any comments on your recent paper on quantization of the string?

Posted by: Urs Schreiber on October 28, 2004 11:58 AM | Permalink | PGP Sig | Reply to this

Re: This and that

Speaking of which: Did you get any comments on your recent paper on quantization of the string?

Quite a few. I had some positive feedback from people I talked to, José Velhinho pointed out his paper gr-qc/0406008 which talkes about related issues in the cosmology version of LQG (the approach formerly known as mini-superspace) and Max Niedermaier (the guy who started the Bogdanov affaire by sending around an email about their papers to some friends, he was a postdoc at AEI when I was a grad student there) telling me that he thought about the harmonic oscillator in Bohr representation as well and how our results fit together with theirs.

We had put out the paper just before Giuseppe and I were leaving Cambrige (he to LMU Munic and me to IU Bremen) and thus we haven’t got around puting out a revised version but that will happen soon. Hopefully.

I have already talked about this stuff in Golm and here and I will do as well at DESY on 10/11 and in Jena on 18/11. If you are interested, here are the slides.

And then there was the discussion on s.p.s. That was essentially killed by Lubos way of not even responding but inserting distorting moderator comments into my postings. I also found his attidue of knowing all and not listening not worth spending more time on further discussion.

Posted by: Robert on October 29, 2004 4:43 AM | Permalink | Reply to this

Re: This and that

Quite a few.

Anyone who is concerned with the implications for proposals to quantize gravity?

In your paper you make the point that non-continuous reps are quite different in a more formal way than has been done before. On the other hand, this difference has been known and addressed before, for instance by Ashtekar,Fairhurst & Willis. But at the end you also discuss that their proposal for obtaining one from the other (by means of ‘shadow’ states) does not work. That should interest them.

Posted by: Urs Schreiber on October 29, 2004 8:42 AM | Permalink | PGP Sig | Reply to this

Re: This and that

And then there was the discussion on s.p.s. That was essentially killed

Whenever you don’t want to discuss on s.p.s. you could still move the discussion to some blog, like - let’s see - the SCT maybe? :-)

I bet that as soon as some critical number of regular posters at the SCT establishes the attention and comments it will get will be comparable to that of a newsgroup.

Posted by: Urs Schreiber on October 29, 2004 9:14 AM | Permalink | PGP Sig | Reply to this

Blockquotes

[how do I get blockquote to work?]

Several ways:

  1. Choose Textile formatting and write

    some stuff

    bq. quoted material

    some more stuff

  2. Choose Markdown formatting and write

    some stuff

    > quoted material

    some more stuff

  3. Use the default Convert Linebreaks formatting and write

    some stuff

    <blockquote><p>quoted material</p></blockquote>

    some more stuff

The same thing works if you are using one of the “itex to MathML with …” filters.

Posted by: Jacques Distler on October 28, 2004 12:15 PM | Permalink | PGP Sig | Reply to this

Re: Roundup

[…] thicket of quantum cosmology. Those discussions never go anywhere because, sooner or later, someone mentions ‘the wave function of the universe,’ the physics-equivalent of Godwin’s Law, and all rational discussion comes to an end.

Not that I would want to discuss the ‘wave function of the universe’ but this concept, popular in the old days of quantum cosmology, while pretty intractable, has resurfaced in a slightly different guise in terms of the ‘landscape’, I’d think. Your comments on that are one example that rational discussion need not come to an end at this point.

Posted by: Urs Schreiber on October 28, 2004 8:17 AM | Permalink | PGP Sig | Reply to this

Re: Roundup

Jacques, thanks for the link. I’m not sure about eternal de Sitter either, but in fact it’s not required by our scenario. So long as the decay rate to a lower vacuum energy is less than the Hubble time (which it must be, phenomenologically), the phase transition never percolates, just as in old inflation. More and more space has decayed, but the physical volume in the de Sitter phase grows without bound, which is all we need.

Not that I would also place great odds that our scenario is “correct” in some strict sense. I’d be happy if something like it were on the right track.

Posted by: Sean on October 28, 2004 10:19 AM | Permalink | Reply to this

Lifetime

They won’t percolate, but the de Sitter space needs to persist long enough for them to have an appreciable probability to form in the first place.

In a specific context (say, the Landscape), the bubble formation time and the lifetime of the de Sitter (which, itself may be a bubble inside an ambient (flat?) space) are not, a priori, independently adjustable.

But I should probably shut up and read your paper before I comment further.

Posted by: Jacques Distler on October 28, 2004 12:30 PM | Permalink | PGP Sig | Reply to this

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