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Indistinguishable macroscopic behaviour of Palatini gravities and general relativity.

Li, B. and Mota, D. F. and Shaw, D. J. (2009) 'Indistinguishable macroscopic behaviour of Palatini gravities and general relativity.', Classical and quantum gravity., 26 (5). 055018.


We show that, within some modified gravity theories, such as the Palatini models, the nonlinear nature of the field equations implies that the usual naïve averaging procedure (replacing the microscopic energy–momentum by its cosmological average) could be invalid. As a consequence, the relative motion of particles in Palatini theories is actually indistinguishable from that predicted by general relativity. Moreover, there is no WEP violation. Our new and most important result is that the cosmology and astrophysics, or put more generally, the behaviours on macroscopic scales, predicted by these two theories are the same, and as a result the naturalness problems associated with the cosmological constant are not alleviated. Palatini gravity does however predict alterations to the internal structure of particles and the particle physics laws, e.g., corrections to the hydrogen energy levels. Measurements of which place strong constraints on the properties of viable Palatini gravities.

Item Type:Article
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Publisher statement:This is an author-created, un-copyedited version of an article accepted for publication in Classical and Quantum Gravity. IOP Publishing Ltd is not responsible for any errors or omissions in this version of the manuscript or any version derived from it. The Version of Record is available online at
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Date of first online publication:March 2009
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