Comments on: Meetings Small and Large http://blogs.discovermagazine.com/cosmicvariance/2006/05/11/meetings-small-and-large/ Random samplings from a universe of ideas. Mon, 09 Nov 2009 00:09:16 -0600 http://wordpress.org/?v=2.8.4 hourly 1 By: Mark http://blogs.discovermagazine.com/cosmicvariance/2006/05/11/meetings-small-and-large/comment-page-1/#comment-15944 Mark Thu, 11 May 2006 23:44:04 +0000 http://blogs.discovermagazine.com/cosmicvariance/2006/05/11/meetings-small-and-large/#comment-15944 Hi Shantanu. Indeed, any modification of gravity has the potential to affect the physics of compact objects, and one needs to check this carefully in each case. How this is evaded (if it is) can be different in each case, but one way is that the modifications are constructed to be significant only when densities or curvatures are cosmologically low. As for Mannheim's talk - it was a very good presentation. There are lots of well-known arguments against his ideas, but he does have answers in his seminars(and I haven't checked technically whether they are correct or not) for most of them. The one question I have raised that he claims his theory doesn't give the correct answer for is that of nucleosynthesis, but he does claim there might be some loopholes to this. There are other questions, such as structure formation, that he hasn't calculated yet. Hi Shantanu. Indeed, any modification of gravity has the potential to affect the physics of compact objects, and one needs to check this carefully in each case. How this is evaded (if it is) can be different in each case, but one way is that the modifications are constructed to be significant only when densities or curvatures are cosmologically low.

As for Mannheim’s talk – it was a very good presentation. There are lots of well-known arguments against his ideas, but he does have answers in his seminars(and I haven’t checked technically whether they are correct or not) for most of them. The one question I have raised that he claims his theory doesn’t give the correct answer for is that of nucleosynthesis, but he does claim there might be some loopholes to this. There are other questions, such as structure formation, that he hasn’t calculated yet.

]]> By: Shantanu http://blogs.discovermagazine.com/cosmicvariance/2006/05/11/meetings-small-and-large/comment-page-1/#comment-15945 Shantanu Thu, 11 May 2006 22:26:51 +0000 http://blogs.discovermagazine.com/cosmicvariance/2006/05/11/meetings-small-and-large/#comment-15945 Mark, one question I have is wouldn't all these alternate theories of gravities used to explain dark energy/matter, also affect the physics of compact objects and maybe have some observable consequences? Or is the physcis of compact objects in all these theories virtually same as GR? I have hardly seen any papers on this issue. so maybe you can clarify. also how was Mannheim's talk (as I think we discussed his theory here.) Mark, one question I have is wouldn’t all these alternate theories of gravities
used to explain dark energy/matter, also affect the
physics of compact objects and maybe have some observable consequences?
Or is the physcis of compact objects in all these theories virtually same
as GR? I have hardly seen any papers on this issue. so maybe you can clarify.
also how was Mannheim’s talk (as I think we discussed his theory here.)

]]> By: adam http://blogs.discovermagazine.com/cosmicvariance/2006/05/11/meetings-small-and-large/comment-page-1/#comment-15950 adam Thu, 11 May 2006 17:19:48 +0000 http://blogs.discovermagazine.com/cosmicvariance/2006/05/11/meetings-small-and-large/#comment-15950 Good luck to Levon, who will doubtless be searching for new victims to slaughter on the squash court. Good luck to Levon, who will doubtless be searching for new victims to slaughter on the squash court.

]]> By: Plato http://blogs.discovermagazine.com/cosmicvariance/2006/05/11/meetings-small-and-large/comment-page-1/#comment-15949 Plato Thu, 11 May 2006 15:13:22 +0000 http://blogs.discovermagazine.com/cosmicvariance/2006/05/11/meetings-small-and-large/#comment-15949 Just curious as to the basis of that thought process in regards to <a href="http://pancake.uchicago.edu/~carroll/talks/mond05/img4.html" rel="nofollow">Modified gravity</a> for layman views? Is Sean's basis the place from which you are dealing? And also, is the Coleman-De Luccia instanton, part of that assessment? <a href="http://www.damtp.cam.ac.uk/user/gr/public/qg_qc.html" rel="nofollow"><blockquote>The quantum tunnelling of the matter in the early universe was described by Coleman and De Luccia. They showed that false vacuum decay proceeds via the nucleation of bubbles in the false vacuum. Inside each bubble the matter has tunnelled. Surprisingly, the interior of such a bubble is an infinite open universe in which inflation may occur. The cosmological instanton describing the creation of an open universe via this bubble nucleation is known as a Coleman-De Luccia instanton.</blockquote></a> Oh, nice to see who Moshe finally is. Just curious as to the basis of that thought process in regards to Modified gravity for layman views? Is Sean’s basis the place from which you are dealing? And also, is the Coleman-De Luccia instanton, part of that assessment?


The quantum tunnelling of the matter in the early universe was described by Coleman and De Luccia. They showed that false vacuum decay proceeds via the nucleation of bubbles in the false vacuum. Inside each bubble the matter has tunnelled. Surprisingly, the interior of such a bubble is an infinite open universe in which inflation may occur. The cosmological instanton describing the creation of an open universe via this bubble nucleation is known as a Coleman-De Luccia instanton.

Oh, nice to see who Moshe finally is.

]]> By: Moshe http://blogs.discovermagazine.com/cosmicvariance/2006/05/11/meetings-small-and-large/comment-page-1/#comment-15948 Moshe Thu, 11 May 2006 14:07:26 +0000 http://blogs.discovermagazine.com/cosmicvariance/2006/05/11/meetings-small-and-large/#comment-15948 Hey Mark, meeting was a lot of fun, I learned a lot. I like the format, we should definitely try something similar in Vancouver. About Levon- your loss is our gain, hopefully also his, I am looking forward to all these cross-town trips (you see, all the really good chinese restaurants are out east...). Hey Mark, meeting was a lot of fun, I learned a lot. I like the format, we should definitely try something similar in Vancouver. About Levon- your loss is our gain, hopefully also his, I am looking forward to all these cross-town trips (you see, all the really good chinese restaurants are out east…).

]]> By: Mark http://blogs.discovermagazine.com/cosmicvariance/2006/05/11/meetings-small-and-large/comment-page-1/#comment-15947 Mark Thu, 11 May 2006 13:18:56 +0000 http://blogs.discovermagazine.com/cosmicvariance/2006/05/11/meetings-small-and-large/#comment-15947 It really was a workshop RedPete, and so, apart from one person who brought a few photocopied overheads, we were describing and hashing out ideas on the board. There really weren't formal presentations, rather just a framing of the questions and then lots of discussion. So no links. Sorry. It really was a workshop RedPete, and so, apart from one person who brought a few photocopied overheads, we were describing and hashing out ideas on the board. There really weren’t formal presentations, rather just a framing of the questions and then lots of discussion.

So no links. Sorry.

]]> By: RedPete http://blogs.discovermagazine.com/cosmicvariance/2006/05/11/meetings-small-and-large/comment-page-1/#comment-15946 RedPete Thu, 11 May 2006 13:11:36 +0000 http://blogs.discovermagazine.com/cosmicvariance/2006/05/11/meetings-small-and-large/#comment-15946 What, no links to slides from the workshop presentations??!! What, no links to slides from the workshop presentations??!!

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