tag:blogger.com,1999:blog-7315236707728759521.post1252294270239531036..comments2024-03-27T22:28:06.861-06:00Comments on Dispatches From Turtle Island: Musings On General Relativity Degrees of FreedomAndrew Oh-Willekehttp://www.blogger.com/profile/02537151821869153861noreply@blogger.comBlogger5125tag:blogger.com,1999:blog-7315236707728759521.post-12993440187675819452018-08-09T20:17:17.680-06:002018-08-09T20:17:17.680-06:00I will review the hefty GR textbook I have ("...I will review the hefty GR textbook I have ("Gravity").<br /><br />I don't disagree that the equation "Einstein tensor proportional to stress-energy tensor" is still the basic equation of GR, or that "in each case the stress-energy tensor involves gradients of energy-momentum density."<br /><br />But, it is not obvious to me that the number of components in the stress-energy tensor does not influence the number of degrees of freedom in the field which is relevant to how you extrapolate from classical GR to potential QG theories. <br /><br />Also, while I agree that assumptions about the non-metric fields are not axioms that were important to the development of GR, I have never seen the non-metric fields formulated in any other manner in GR. It is not obvious to me that the way that they are formulated is an irrelevant detail in the way that, for example, a choice of units for the physical constants involved, or a coordinate system, would be. It may be that they really aren't, but I can't easily see that this is true.andrewhttps://www.blogger.com/profile/08172964121659914379noreply@blogger.comtag:blogger.com,1999:blog-7315236707728759521.post-3661175006193699442018-08-09T06:52:25.833-06:002018-08-09T06:52:25.833-06:00@andrew Please check out a textbook or serious int...@andrew Please check out a textbook or serious introduction to general relativity. GR is not based on any specific assumption as to what the non-metric fields are. The equation "Einstein tensor proportional to stress-energy tensor" is still the basic equation of GR, whether or not the non-metric fields are absent, are just a Maxwell field, or are all the fields of the standard model. And in each case the stress-energy tensor involves gradients of energy-momentum density. Mitchellhttps://www.blogger.com/profile/10768655514143252049noreply@blogger.comtag:blogger.com,1999:blog-7315236707728759521.post-64597353301516407402018-08-08T11:43:58.810-06:002018-08-08T11:43:58.810-06:00@neo I'm not proposing an alternative other th...@neo I'm not proposing an alternative other than to note a potential issue which may make GR as currently formulated less sacred.<br /><br />@Mitchell While the stress energy tensor can be defined for any combination of fields, it isn't, and if it is defined for a different combination of fields, it isn't obvious to me that it would have the same number of degrees of freedom.andrewhttps://www.blogger.com/profile/08172964121659914379noreply@blogger.comtag:blogger.com,1999:blog-7315236707728759521.post-37689321098090338192018-08-08T05:23:42.725-06:002018-08-08T05:23:42.725-06:00The electromagnetic field plays no essential role ...The electromagnetic field plays no essential role in the formulation of general relativity. The stress-energy tensor can be defined for any combination of fields.Mitchellhttps://www.blogger.com/profile/10768655514143252049noreply@blogger.comtag:blogger.com,1999:blog-7315236707728759521.post-8874714050549557712018-08-07T20:47:46.793-06:002018-08-07T20:47:46.793-06:00interesting read
what are you proposing insteadinteresting read<br /><br />what are you proposing insteadneohttps://www.blogger.com/profile/17318664916557810347noreply@blogger.com