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I recently found this quote by Einstein (in On the Generalized Theory of Gravitation, 1950), and it seems to me like he is saying that matter is a part of the field of space-time, and is nothing more than an area of the field with very high energy. Is this correct?

According to general relativity, the concept of space detached from any physical content does not exist. The physical reality of space is represented by a field whose components are continuous functions of four independent variables-the coordinates of space and time. It is just this particular kind of dependence that expresses the spatial character of physical reality. Since the theory of general relativity implies the representation of physical reality by a continuous field, the concept of particles or material points cannot play a fundamental part, nor can the concept of motion. The particle can only appear as a limited region in space in which the field strength or the energy density are particularly high.

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    $\begingroup$ Related (about a different quote by Einstein on the same subject): physics.stackexchange.com/q/77525 - FWIW I think this question is better than that one, because the longer quote means we don't have to speculate as much about the context. $\endgroup$
    – N. Virgo
    Commented Oct 8, 2013 at 14:50

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This quote is within the framework of General Relativity only. It accepts that there exist "particles" but the only materialization of their existence as particles appears in the change of the functional form of the four independent variables-the coordinates of space and time. In such a mathematical model of Nature continuity is built in.

Now the question is how well this theory/model agrees with experimental observation and astrophysical ones. In astrophysics it does very well, it has not been falsified. ( note a theoretical proposal cannot be proven true, it can be validated by observations and falsified if one observation disagrees with predictions). So if we consider matter as just clusters of galaxies, galaxies, stars, planets and even satellites one can give an A++ for the validity of the General Relativity predictions and continuity of space time functions is one of them.

This is not true when we enter the realm of atoms, molecules and elementary particles . At the micro level quantum mechanics reigns and all our experiments point out that they are discontinuous entities with mass and discrete energy levels and discrete interactions. Three more interactions in addition to the gravitational one, which last General Relativity models as space time formation. Thus the quote is falsified by experimental data at the microscopic level.

At the moment the three elementary interactions, strong, weak and electromagnetic are unified in a theory called the Standard Model . Just today we learned that the Nobel prize for physics was awarded to prof Higgs and Englert for predicting this completion of the Standard Model decades ago, with the discovery of the Higgs by CERN groups in 2012.

The goal of theoretical physics is to unite all forces , including gravitation in one theoretical framework that will give the Standard Model at microcosm and General Relativity for the cosmos. Many people are working on this. At the moment a dominant theory is String Theory which can embed the Standard Model of particle physics which encapsulates all experimental data , and also quantize gravity , a theoretical problem that has been hard to tackle the last 60 or so years. It is work in progress and many theorists are working on this.

The ideal theory then will have as an approximation for large masses and distances the quote above, while for the microscom will retain the observed discontinuities of the real masses of real particles in space time.

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  • $\begingroup$ Very nice "the quote is falsified by experimental data at the microscopic level". I think it is important here also to heed (my history is a bit patchy) that at the time Einstein made the quote, he was likely still hoping some extension of fairly simple geometric ides (as in GR) would account for "everything": he himself was the person who coined the words "Unified Field Theory". His idea that a mathematician's abstract space disembodied from "physical content" does not exist has only been strengthened by the microscopic experimental data though - I think it's safe to say that .... $\endgroup$
    – Selene Routley
    Commented Oct 9, 2013 at 6:54
  • $\begingroup$ ...modern physics holds spacetime to be nothing more nor less than the matter and energy fields that define, rather than fill, it. "Truly Empty" space is a fiction - the remotest parts of interstellar space are still these fields in their quantum ground start. $\endgroup$
    – Selene Routley
    Commented Oct 9, 2013 at 6:56
  • $\begingroup$ @WetSavannaAnimalakaRodVance Yes, and in a sense string theories are geometrical theories in extended space. It just seems to be not as simple as Einstein wanted. $\endgroup$
    – anna v
    Commented Oct 9, 2013 at 7:13

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