{"product":{"product_id":"0393965015","title":"Gravitation and Spacetime","price":"100.0","image_url":"https://m.media-amazon.com/images/I/51A5W1Kz4UL._SL500_.jpg","url":"https://www.amazon.com/dp/0393965015"},"comments":[{"body":"We affectionately called them Christ Awful symbols in my SR/GR class for a reason. *Everybody* hates them.  A good book for it is https://www.amazon.com/Gravitation-Spacetime-Second-Hans-Ohanian/dp/0393965015 if you want to explore - it's what we used.","subreddit_name":"wallstreetbetsOGs","author":"splat-y-chila"},{"body":"Thank you for your opinion.\r  \r\n====\r\n\r\nThe Einstein field equation is exact,  \r\n====  \r\nI saw the following in Hans Ohanian's book, [\"Gravitation and Spacetime\"](https://www.amazon.com/Gravitation-Spacetime-Second-Hans-Ohanian/dp/0393965015).\r\n\r\nIn writing the field equation (48) we have assumed that the quantity T\\^{\\\\mu \\\\nu is the energy-momentum tensor of matter. In order to obtain a linear field equation we have left out the effect of the gravitational field upon itself. Because of this omission, our linear field equation has several (related) defects:   \r\n\r\n\r\n(1) According to (48) matter acts on the gravitational field (changes the fields), but there is no mutual action of gravitational fields on matter; that is, the gravitational field can acquire energy-momentum from matter, but nevertheless the energy-momentum of matter is conserved ({\\\\partial \\_\\\\nu }{T\\^{\\\\mu \\\\nu }} = 0). This is an inconsistency.   \r\n\r\n\r\n(2)Gravitational energy does not act as source of gravitation, in contradiction to the principle of equivalence. Thus, although Eq. (48) may be a fair approximation in the equivalence. Thus, although Eq. (48) may be a fair approximation in the case of weak gravitational fields, it cannot be an exact equation.\r  \r\n\r  \r\nThe obvious way to correct for our sin of omission is to include the energy-momentum tensor of the gravitational field in T\\^{\\\\mu \\\\nu }. This means that we take for the quantity  T\\^{\\\\mu \\\\nu } the total energy-momentum tensor of matter plus gravitation:","subreddit_name":"cosmology","author":"Signal-News9341"}]}