Comments on: The universe is the poor man’s particle accelerator http://blogs.discovermagazine.com/cosmicvariance/2005/12/19/the-universe-is-the-poor-mans-particle-accelerator/ Random samplings from a universe of ideas. Tue, 24 Nov 2009 19:54:46 -0600 http://wordpress.org/?v=2.8.4 hourly 1 By: Plato http://blogs.discovermagazine.com/cosmicvariance/2005/12/19/the-universe-is-the-poor-mans-particle-accelerator/comment-page-1/#comment-8688 Plato Fri, 23 Dec 2005 16:04:35 +0000 http://blogs.discovermagazine.com/cosmicvariance/2005/12/19/the-universe-is-the-poor-mans-particle-accelerator/#comment-8688 Hope you all have a <a href="http://eskesthai.blogspot.com/2005/12/collapse-of-blackhole.html" rel="nofollow">Merry Christmas</a> Hope you all have a Merry Christmas

]]> By: Science http://blogs.discovermagazine.com/cosmicvariance/2005/12/19/the-universe-is-the-poor-mans-particle-accelerator/comment-page-1/#comment-8687 Science Wed, 21 Dec 2005 11:13:10 +0000 http://blogs.discovermagazine.com/cosmicvariance/2005/12/19/the-universe-is-the-poor-mans-particle-accelerator/#comment-8687 On quantum gravity: the error is not necessarily in quantum mechanics, but in the incompleteness of GR. My point is that if the difference between electromagnetic force and gravity is the square root of the number of charges in the universe (and there is only one proof of this available), this ratio is nearly fixed to the present-day figure within 1 second of the big bang by the creation of quarks. If gravity was x times weaker during the fusion of nucleons into light elements in the first few seconds to minutes, then Coulomb's law would also be x times weaker. So the gravitational compression would be less, but so would the Coulomb barrier which hinders fusion. The two effects cancel each other out. Therefore you have no basis whatsoever to claim G only varies by 20%. What you should say is that fusion calculations validate that the ratio of gravity to electromagnetism was the same to within 20% of today's ratio. On quantum gravity: the error is not necessarily in quantum mechanics, but in the incompleteness of GR.

My point is that if the difference between electromagnetic force and gravity is the square root of the number of charges in the universe (and there is only one proof of this available), this ratio is nearly fixed to the present-day figure within 1 second of the big bang by the creation of quarks.

If gravity was x times weaker during the fusion of nucleons into light elements in the first few seconds to minutes, then Coulomb’s law would also be x times weaker. So the gravitational compression would be less, but so would the Coulomb barrier which hinders fusion. The two effects cancel each other out. Therefore you have no basis whatsoever to claim G only varies by 20%.

What you should say is that fusion calculations validate that the ratio of gravity to electromagnetism was the same to within 20% of today’s ratio.

]]> By: Plato http://blogs.discovermagazine.com/cosmicvariance/2005/12/19/the-universe-is-the-poor-mans-particle-accelerator/comment-page-1/#comment-8686 Plato Wed, 21 Dec 2005 06:43:10 +0000 http://blogs.discovermagazine.com/cosmicvariance/2005/12/19/the-universe-is-the-poor-mans-particle-accelerator/#comment-8686 <a href="http://eskesthai.blogspot.com/2005/12/has-speed-of-light-changed-recently.html" rel="nofollow"><blockquote>JUst as one might have asked Max Tegmark what the shape of the universe was, he might of quickly discounted John Baez's soccer ball? Yet little did we know, that such a push by Magueijo might have had some influences? How would you measure such inflationary models?</blockquote></a> Always a work in progress, but never fully understood?
JUst as one might have asked Max Tegmark what the shape of the universe was, he might of quickly discounted John Baez’s soccer ball? Yet little did we know, that such a push by Magueijo might have had some influences? How would you measure such inflationary models?

Always a work in progress, but never fully understood?

]]> By: Sean http://blogs.discovermagazine.com/cosmicvariance/2005/12/19/the-universe-is-the-poor-mans-particle-accelerator/comment-page-1/#comment-8685 Sean Tue, 20 Dec 2005 22:15:58 +0000 http://blogs.discovermagazine.com/cosmicvariance/2005/12/19/the-universe-is-the-poor-mans-particle-accelerator/#comment-8685 We use the term "Big Bang" loosely, to refer either to the singularity predicted by classical GR or to whatever will replace it in the eventual theory. Most of us believe that the singularity will be replaced by something, but we'll still call it the Big Bang. We use the term “Big Bang” loosely, to refer either to the singularity predicted by classical GR or to whatever will replace it in the eventual theory. Most of us believe that the singularity will be replaced by something, but we’ll still call it the Big Bang.

]]> By: Elliot http://blogs.discovermagazine.com/cosmicvariance/2005/12/19/the-universe-is-the-poor-mans-particle-accelerator/comment-page-1/#comment-8684 Elliot Tue, 20 Dec 2005 21:24:54 +0000 http://blogs.discovermagazine.com/cosmicvariance/2005/12/19/the-universe-is-the-poor-mans-particle-accelerator/#comment-8684 Sean, Is the Big Bang "really" a singularity? Or is that what the best available (GR based) theories tell us. Don't people generally believe that singularities are eventually going to be extinguished by a quantum theory of gravity. (both in black holes and the big bang) or is there something special about the Big Bang which truly make it singular. Thanks, Elliot Sean,

Is the Big Bang “really” a singularity? Or is that what the best available (GR based) theories tell us. Don’t people generally believe that singularities are eventually going to be extinguished by a quantum theory of gravity. (both in black holes and the big bang) or is there something special about the Big Bang which truly make it singular.

Thanks,

Elliot

]]> By: Sean http://blogs.discovermagazine.com/cosmicvariance/2005/12/19/the-universe-is-the-poor-mans-particle-accelerator/comment-page-1/#comment-8676 Sean Tue, 20 Dec 2005 17:06:27 +0000 http://blogs.discovermagazine.com/cosmicvariance/2005/12/19/the-universe-is-the-poor-mans-particle-accelerator/#comment-8676 Hi Helge-- A perfectly good question. When we speak informally of something happening a certain time after the Big Bang, we're being sloppy in three different ways: first because the Bang itself is a singularity that isn't really part of spacetime, second because all sorts of unexpected things might be happening in the early universe that make things different from our current expectations, and third because time is not universally defined in relativity. But all that is okay. What we really mean is "the time that would be experienced by an observer co-moving with the cosmological fluid between this moment and a moment arbitrarily close to the singularity, in a standard radiation-dominated Friedmann-Robertson-Walker cosmology." But that's not nearly as snappy as "the time since the Big Bang," so we're going to keep on saying that in the hope that all the caveats are understood. As far as the book is concerned, I'm the wrong guy to bitch to, you should talk to the publisher. But I estimate the amount of intellectual fulfillment contained in my book to be worth at least $200, so it's still a bargain! Hi Helge– A perfectly good question. When we speak informally of something happening a certain time after the Big Bang, we’re being sloppy in three different ways: first because the Bang itself is a singularity that isn’t really part of spacetime, second because all sorts of unexpected things might be happening in the early universe that make things different from our current expectations, and third because time is not universally defined in relativity. But all that is okay. What we really mean is “the time that would be experienced by an observer co-moving with the cosmological fluid between this moment and a moment arbitrarily close to the singularity, in a standard radiation-dominated Friedmann-Robertson-Walker cosmology.” But that’s not nearly as snappy as “the time since the Big Bang,” so we’re going to keep on saying that in the hope that all the caveats are understood.

As far as the book is concerned, I’m the wrong guy to bitch to, you should talk to the publisher. But I estimate the amount of intellectual fulfillment contained in my book to be worth at least $200, so it’s still a bargain!

]]> By: Helge http://blogs.discovermagazine.com/cosmicvariance/2005/12/19/the-universe-is-the-poor-mans-particle-accelerator/comment-page-1/#comment-8677 Helge Tue, 20 Dec 2005 15:07:02 +0000 http://blogs.discovermagazine.com/cosmicvariance/2005/12/19/the-universe-is-the-poor-mans-particle-accelerator/#comment-8677 Hey Sean :-) Something I have always wondered about is: You write: "Between a few seconds and minutes after Big Bang." How do I have to understand this? Thinking about everything I know about general relativity it makes no sense to speak about "that event took place at that time." But all physicists and cosmologists do it when speaking about the Big Bang. And now some random bitching: Why is your book so expensive? Can't you bring it out in paperback, so it would be a little less? Helge Hey Sean :-)
Something I have always wondered about is: You write: “Between a few seconds and minutes after Big Bang.” How do I have to understand this? Thinking about everything I know about general relativity it makes no sense to speak about “that event took place at that time.” But all physicists and cosmologists do it when speaking about the Big Bang.
And now some random bitching: Why is your book so expensive? Can’t you bring it out in paperback, so it would be a little less?
Helge

]]> By: Plato http://blogs.discovermagazine.com/cosmicvariance/2005/12/19/the-universe-is-the-poor-mans-particle-accelerator/comment-page-1/#comment-8683 Plato Tue, 20 Dec 2005 05:09:36 +0000 http://blogs.discovermagazine.com/cosmicvariance/2005/12/19/the-universe-is-the-poor-mans-particle-accelerator/#comment-8683 <a href="http://eskesthai.blogspot.com/2005/12/big-bang-nucleosynthesis.html" rel="nofollow"><blockquote>Having seen the nature of Kravtsovs computer simulations, as cosmic strings, then you would have understood that each of the events in the galaxies would have been connected to each other? Never older, then the age of the universe itself?</blockquote></a>
Having seen the nature of Kravtsovs computer simulations, as cosmic strings, then you would have understood that each of the events in the galaxies would have been connected to each other?

Never older, then the age of the universe itself?

]]> By: Aaron http://blogs.discovermagazine.com/cosmicvariance/2005/12/19/the-universe-is-the-poor-mans-particle-accelerator/comment-page-1/#comment-8682 Aaron Tue, 20 Dec 2005 04:31:43 +0000 http://blogs.discovermagazine.com/cosmicvariance/2005/12/19/the-universe-is-the-poor-mans-particle-accelerator/#comment-8682 Whoa! I'd never heard of BBN before... it sounds really cool! Whoa! I’d never heard of BBN before… it sounds really cool!

]]> By: Eugene http://blogs.discovermagazine.com/cosmicvariance/2005/12/19/the-universe-is-the-poor-mans-particle-accelerator/comment-page-1/#comment-8675 Eugene Tue, 20 Dec 2005 00:19:16 +0000 http://blogs.discovermagazine.com/cosmicvariance/2005/12/19/the-universe-is-the-poor-mans-particle-accelerator/#comment-8675 Just a note on those constraints by Copi et.al. They didn't use He or Li abundances constraints; they just use deuterium abundances and WMAP baryon-photon ratio. I also don't like their direct use of the latter : since if G is changing, then one should not trust the WMAP results as the CMB peaks will change too. Anyway, their constraints are pretty weak, the 20% values quoted is 68% confidence. At 95%, it's about 40%. Standard dG/G values with the full load of abundances, are around 10% give or take a few. I think He gives the best constraint, but somebody please correct me if I am wrong since I'll like to know the real answer... http://lanl.arxiv.org/abs/astro-ph/0011179 gives the most recent He abundances constraint. Just a note on those constraints by Copi et.al. They didn’t use He or Li abundances constraints; they just use deuterium abundances and WMAP baryon-photon ratio. I also don’t like their direct use of the latter : since if G is changing, then one should not trust the WMAP results as the CMB peaks will change too. Anyway, their constraints are pretty weak, the 20% values quoted is 68% confidence. At 95%, it’s about 40%.

Standard dG/G values with the full load of abundances, are around 10% give or take a few. I think He gives the best constraint, but somebody please correct me if I am wrong since I’ll like to know the real answer…

http://lanl.arxiv.org/abs/astro-ph/0011179 gives the most recent He abundances constraint.

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