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	<title>Comments on: Susskind Lectures on General Relativity</title>
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	<link>http://blogs.discovermagazine.com/cosmicvariance/2009/06/02/susskind-lectures-on-general-relativity/</link>
	<description>Random samplings from a universe of ideas.</description>
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		<title>By: Daily Quippages - June 9, 2009 &#124; The Starnes</title>
		<link>http://blogs.discovermagazine.com/cosmicvariance/2009/06/02/susskind-lectures-on-general-relativity/comment-page-1/#comment-78496</link>
		<dc:creator>Daily Quippages - June 9, 2009 &#124; The Starnes</dc:creator>
		<pubDate>Tue, 09 Jun 2009 20:26:18 +0000</pubDate>
		<guid isPermaLink="false">http://blogs.discovermagazine.com/cosmicvariance/2009/06/02/susskind-lectures-on-general-relativity/#comment-78496</guid>
		<description>[...] Susskind Lectures on General Relativity [...]</description>
		<content:encoded><![CDATA[<p>[...] Susskind Lectures on General Relativity [...]</p>
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		<title>By: Count Iblis</title>
		<link>http://blogs.discovermagazine.com/cosmicvariance/2009/06/02/susskind-lectures-on-general-relativity/comment-page-1/#comment-78145</link>
		<dc:creator>Count Iblis</dc:creator>
		<pubDate>Sat, 06 Jun 2009 23:38:48 +0000</pubDate>
		<guid isPermaLink="false">http://blogs.discovermagazine.com/cosmicvariance/2009/06/02/susskind-lectures-on-general-relativity/#comment-78145</guid>
		<description>Uncle sam, in your problem General Relativity is not important, the Newtonian treatment of gravity yields almost the exact answer. The reason why a naive appication of the equivalence principle gives you the wrong answer, is because if the equivalence principle were to apply, the boundary conditions for the fields at infinity would necessarily have to be different.

So, if you consider an electron at rest in some inertial frame and then you switch to an accelerating frame, then in that accelerating frame, the electron is accelerating in the opposite direction, but it is not emitting any radiation. Now, compare the electromagnetic fields of this accelerating electron in the non-inertial accelerating frame to the electromagnetic fields of an electron that is accelerated in an inertial frame which we know will radiate electromagnetic waves.

In the latter case, you know that the fields are given as an integral over the charge and current densities at the retarded time, which then gives you radiation fields that fall of as 1/r at large distances. But in the former case, you simply have the Coulomb field that falls off as 1/r^2 at large distances which remains the case if you switch to the accelerating frame.</description>
		<content:encoded><![CDATA[<p>Uncle sam, in your problem General Relativity is not important, the Newtonian treatment of gravity yields almost the exact answer. The reason why a naive appication of the equivalence principle gives you the wrong answer, is because if the equivalence principle were to apply, the boundary conditions for the fields at infinity would necessarily have to be different.</p>
<p>So, if you consider an electron at rest in some inertial frame and then you switch to an accelerating frame, then in that accelerating frame, the electron is accelerating in the opposite direction, but it is not emitting any radiation. Now, compare the electromagnetic fields of this accelerating electron in the non-inertial accelerating frame to the electromagnetic fields of an electron that is accelerated in an inertial frame which we know will radiate electromagnetic waves.</p>
<p>In the latter case, you know that the fields are given as an integral over the charge and current densities at the retarded time, which then gives you radiation fields that fall of as 1/r at large distances. But in the former case, you simply have the Coulomb field that falls off as 1/r^2 at large distances which remains the case if you switch to the accelerating frame.</p>
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		<title>By: Brian Mingus</title>
		<link>http://blogs.discovermagazine.com/cosmicvariance/2009/06/02/susskind-lectures-on-general-relativity/comment-page-1/#comment-78130</link>
		<dc:creator>Brian Mingus</dc:creator>
		<pubDate>Sat, 06 Jun 2009 18:09:07 +0000</pubDate>
		<guid isPermaLink="false">http://blogs.discovermagazine.com/cosmicvariance/2009/06/02/susskind-lectures-on-general-relativity/#comment-78130</guid>
		<description>This is a really boring lecture. 

You might try these lectures on quantum computation by David Deutsch: http://www.quiprocone.org/Protected/DD_lectures.htm

They are very well produced but also very technical. I wasn&#039;t able to truly follow them, but I probably could have had I come armed with pen and paper.</description>
		<content:encoded><![CDATA[<p>This is a really boring lecture. </p>
<p>You might try these lectures on quantum computation by David Deutsch: <a href="http://www.quiprocone.org/Protected/DD_lectures.htm" rel="nofollow">http://www.quiprocone.org/Protected/DD_lectures.htm</a></p>
<p>They are very well produced but also very technical. I wasn&#8217;t able to truly follow them, but I probably could have had I come armed with pen and paper.</p>
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		<title>By: Jdhuey</title>
		<link>http://blogs.discovermagazine.com/cosmicvariance/2009/06/02/susskind-lectures-on-general-relativity/comment-page-1/#comment-77871</link>
		<dc:creator>Jdhuey</dc:creator>
		<pubDate>Thu, 04 Jun 2009 21:32:27 +0000</pubDate>
		<guid isPermaLink="false">http://blogs.discovermagazine.com/cosmicvariance/2009/06/02/susskind-lectures-on-general-relativity/#comment-77871</guid>
		<description>I was about mid-way through Susskind&#039;s _The Cosmic Landscape_ when I listened to this lecture (this is the  first time I&#039;ve heard his voice).  Now, when I&#039;m reading, I&#039;m hearing his &#039;voice&#039; in my head.  Tres cool.</description>
		<content:encoded><![CDATA[<p>I was about mid-way through Susskind&#8217;s _The Cosmic Landscape_ when I listened to this lecture (this is the  first time I&#8217;ve heard his voice).  Now, when I&#8217;m reading, I&#8217;m hearing his &#8216;voice&#8217; in my head.  Tres cool.</p>
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		<title>By: Sam Gralla</title>
		<link>http://blogs.discovermagazine.com/cosmicvariance/2009/06/02/susskind-lectures-on-general-relativity/comment-page-1/#comment-77747</link>
		<dc:creator>Sam Gralla</dc:creator>
		<pubDate>Thu, 04 Jun 2009 05:52:18 +0000</pubDate>
		<guid isPermaLink="false">http://blogs.discovermagazine.com/cosmicvariance/2009/06/02/susskind-lectures-on-general-relativity/#comment-77747</guid>
		<description>There are no &quot;problems with self-force in general&quot;.  In classical physics bodies move according to coupled Maxwell and matter equations, and you can derive lorentz force and self-force as approximations to that motion.  There are no runaway solutions in a &lt;a href=&quot;http://arxiv.org/abs/0905.2391&quot; rel=&quot;nofollow&quot;&gt;proper derivation&lt;/a&gt;.</description>
		<content:encoded><![CDATA[<p>There are no &#8220;problems with self-force in general&#8221;.  In classical physics bodies move according to coupled Maxwell and matter equations, and you can derive lorentz force and self-force as approximations to that motion.  There are no runaway solutions in a <a href="http://arxiv.org/abs/0905.2391" rel="nofollow">proper derivation</a>.</p>
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		<title>By: uncle sam</title>
		<link>http://blogs.discovermagazine.com/cosmicvariance/2009/06/02/susskind-lectures-on-general-relativity/comment-page-1/#comment-77739</link>
		<dc:creator>uncle sam</dc:creator>
		<pubDate>Thu, 04 Jun 2009 02:05:27 +0000</pubDate>
		<guid isPermaLink="false">http://blogs.discovermagazine.com/cosmicvariance/2009/06/02/susskind-lectures-on-general-relativity/#comment-77739</guid>
		<description>Allright Sean, point taken re glib use of EP.

GR: I&#039;ve noticed this &quot;reaching different conclusions&quot; about too many offbeat topics of physical speculation. Why should competent authors reach different conclusions, if we have the wherewithal to know how to find the right answer? It happens with radiations issues (gravity as noted; problems with self-force in general such as Schott energy, averaging, runaway, etc.), the stressed extended body in SRT (right-angle lever paradox, with wrangling for decades in Nuovo Cimento and AJP about whether the &quot;von Laue Energy current&quot; is appropriate versus internal torques, how best to find conservation of angular momentum in the case of Thomas Precession, etc.) and of course the old &quot;4/3 paradox&quot; about EM mass.

Clearly, IMHO that means some things haven&#039;t been fully hashed out properly and that physics isn&#039;t &quot;finished&quot; even not counting traditional frontier areas like ultimate particle theory and ur-cosmology. Take another look at my &quot;complaints&quot; and see if anything impresses you.</description>
		<content:encoded><![CDATA[<p>Allright Sean, point taken re glib use of EP.</p>
<p>GR: I&#8217;ve noticed this &#8220;reaching different conclusions&#8221; about too many offbeat topics of physical speculation. Why should competent authors reach different conclusions, if we have the wherewithal to know how to find the right answer? It happens with radiations issues (gravity as noted; problems with self-force in general such as Schott energy, averaging, runaway, etc.), the stressed extended body in SRT (right-angle lever paradox, with wrangling for decades in Nuovo Cimento and AJP about whether the &#8220;von Laue Energy current&#8221; is appropriate versus internal torques, how best to find conservation of angular momentum in the case of Thomas Precession, etc.) and of course the old &#8220;4/3 paradox&#8221; about EM mass.</p>
<p>Clearly, IMHO that means some things haven&#8217;t been fully hashed out properly and that physics isn&#8217;t &#8220;finished&#8221; even not counting traditional frontier areas like ultimate particle theory and ur-cosmology. Take another look at my &#8220;complaints&#8221; and see if anything impresses you.</p>
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	<item>
		<title>By: Krebscafe Blog &#187; Fundstücke (3.6.09): Wieder gesund werden...</title>
		<link>http://blogs.discovermagazine.com/cosmicvariance/2009/06/02/susskind-lectures-on-general-relativity/comment-page-1/#comment-77720</link>
		<dc:creator>Krebscafe Blog &#187; Fundstücke (3.6.09): Wieder gesund werden...</dc:creator>
		<pubDate>Wed, 03 Jun 2009 21:15:11 +0000</pubDate>
		<guid isPermaLink="false">http://blogs.discovermagazine.com/cosmicvariance/2009/06/02/susskind-lectures-on-general-relativity/#comment-77720</guid>
		<description>[...] Susskind Lectures on General Relativity - Wer sich f&#252;r die Relativit&#228;tstheorie interessiert und tiefer in die Materie einsteigen m&#246;chte, sollte sich dieses Video anschauen: Eine Standford-Vorlesung des Professors f&#252;r theoretische Physik Leonard Susskind. Es handelt sich um den ersten Teil einer Reihe. [...]</description>
		<content:encoded><![CDATA[<p>[...] Susskind Lectures on General Relativity &#8211; Wer sich f&uuml;r die Relativit&auml;tstheorie interessiert und tiefer in die Materie einsteigen m&ouml;chte, sollte sich dieses Video anschauen: Eine Standford-Vorlesung des Professors f&uuml;r theoretische Physik Leonard Susskind. Es handelt sich um den ersten Teil einer Reihe. [...]</p>
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		<title>By: GR</title>
		<link>http://blogs.discovermagazine.com/cosmicvariance/2009/06/02/susskind-lectures-on-general-relativity/comment-page-1/#comment-77717</link>
		<dc:creator>GR</dc:creator>
		<pubDate>Wed, 03 Jun 2009 21:08:11 +0000</pubDate>
		<guid isPermaLink="false">http://blogs.discovermagazine.com/cosmicvariance/2009/06/02/susskind-lectures-on-general-relativity/#comment-77717</guid>
		<description>uncle sam,

If you have access to it, 

A. Kovetz, G.E. Tauber, American J. Physics, 37(4) 382-385 (1969) has a pretty good treatment of the problem. It is complicated, though, and it seems a paper or two about it (reaching different conclusions...) appear every few years.</description>
		<content:encoded><![CDATA[<p>uncle sam,</p>
<p>If you have access to it, </p>
<p>A. Kovetz, G.E. Tauber, American J. Physics, 37(4) 382-385 (1969) has a pretty good treatment of the problem. It is complicated, though, and it seems a paper or two about it (reaching different conclusions&#8230;) appear every few years.</p>
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		<title>By: Sean</title>
		<link>http://blogs.discovermagazine.com/cosmicvariance/2009/06/02/susskind-lectures-on-general-relativity/comment-page-1/#comment-77708</link>
		<dc:creator>Sean</dc:creator>
		<pubDate>Wed, 03 Jun 2009 20:10:59 +0000</pubDate>
		<guid isPermaLink="false">http://blogs.discovermagazine.com/cosmicvariance/2009/06/02/susskind-lectures-on-general-relativity/#comment-77708</guid>
		<description>David, nope, sorry.

uncle sam, I have no idea how to do the calculation (not that I&#039;ve tried) nor who has done it.  All I know is that arguments from the Principle of Equivalence that lead to purported puzzles are misguided.</description>
		<content:encoded><![CDATA[<p>David, nope, sorry.</p>
<p>uncle sam, I have no idea how to do the calculation (not that I&#8217;ve tried) nor who has done it.  All I know is that arguments from the Principle of Equivalence that lead to purported puzzles are misguided.</p>
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		<title>By: David Nataf</title>
		<link>http://blogs.discovermagazine.com/cosmicvariance/2009/06/02/susskind-lectures-on-general-relativity/comment-page-1/#comment-77707</link>
		<dc:creator>David Nataf</dc:creator>
		<pubDate>Wed, 03 Jun 2009 19:52:24 +0000</pubDate>
		<guid isPermaLink="false">http://blogs.discovermagazine.com/cosmicvariance/2009/06/02/susskind-lectures-on-general-relativity/#comment-77707</guid>
		<description>Sean,

Any plan on a 2nd edition of your spacetime book?</description>
		<content:encoded><![CDATA[<p>Sean,</p>
<p>Any plan on a 2nd edition of your spacetime book?</p>
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