Newton vs. Mach vs. Einstein
I was always confused with the "Machianity" of general relativity. After partially reading Brans and Dicke's famous paper on their alternative gravity theory, I settled on the following view:
*Newton claims that space-time exists and it is absolute. Matter moves with respect to that.
*Mach claims that space-time does not exist as a physical entity. Matter moves with respect to other matter. Space-time somehow is an emergent entity used to describe the perceived change. Though I don't think that Mach himself would propose it this strong, because emergent concepts were not in the mental language and braveness to deny the existence of space and time was not common among physicist. He was just operational and believed only in observable things. I wonder how he would react to gravitational waves, Aharonov-Bohm effect or modern gauge theories. I certainly believe that Hulse-Taylor pulsar would puzzle him.
*Einstein claims that space-time exist as a physical entity. But both matter and space-time move (or change) with respect to the others. So it is a mixture of Newtonian and Machian views. When I go back I see that this is the explanation of the Einstein theory as told in Rovelli's book. (See here for the free draft.) His book also gives different realizations of Mach's principle and stating if they are true in general relativity or not.
It may not be quite right to summarize these giants' ideas with today's words, but this is pretty much the picture that is referred as Newtonian, Machian and Einsteinian point of view. I still don't feel that Einstein gravity is the last word on gravity, even in the classical level. But total Machianity is certainly losing some points.
Tegmark says that I am finally finding peace with Einstein and not worry anymore that his theory is not totally Machian. I should say that Gödel universe which has nonvanishing angular momentum (with respect to what) still worries me along with some other issues but I will wait for further settlement of dust in my mind.
For a beautiful discussion on Mach see also Wilczek's article in Physics Today, April 2004.
*Newton claims that space-time exists and it is absolute. Matter moves with respect to that.
*Mach claims that space-time does not exist as a physical entity. Matter moves with respect to other matter. Space-time somehow is an emergent entity used to describe the perceived change. Though I don't think that Mach himself would propose it this strong, because emergent concepts were not in the mental language and braveness to deny the existence of space and time was not common among physicist. He was just operational and believed only in observable things. I wonder how he would react to gravitational waves, Aharonov-Bohm effect or modern gauge theories. I certainly believe that Hulse-Taylor pulsar would puzzle him.
*Einstein claims that space-time exist as a physical entity. But both matter and space-time move (or change) with respect to the others. So it is a mixture of Newtonian and Machian views. When I go back I see that this is the explanation of the Einstein theory as told in Rovelli's book. (See here for the free draft.) His book also gives different realizations of Mach's principle and stating if they are true in general relativity or not.
It may not be quite right to summarize these giants' ideas with today's words, but this is pretty much the picture that is referred as Newtonian, Machian and Einsteinian point of view. I still don't feel that Einstein gravity is the last word on gravity, even in the classical level. But total Machianity is certainly losing some points.
Tegmark says that I am finally finding peace with Einstein and not worry anymore that his theory is not totally Machian. I should say that Gödel universe which has nonvanishing angular momentum (with respect to what) still worries me along with some other issues but I will wait for further settlement of dust in my mind.
For a beautiful discussion on Mach see also Wilczek's article in Physics Today, April 2004.
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