Three-in-one ΛCDM model and origin of ultra-high energy cosmic rays

General relativity is rewritten in flat spacetime in a theory called periodic relativity (PR) suggesting that gravity is not caused by the curvature of spacetime. This study investigates the cause of gravity by unifying dark energy, dark matter and the negative gravitational potential energy into the strain energy of the indivisible fundamental substance of the universe which replaces the spacetime fabric of general relativity. This is accomplished without changing Einstein’s field equations, Einstein’s law of gravitation, the derivation of Friedmann equations and [Formula: see text]CDM model. The theory proposes that the gravitational force is an elastic force and presents a perfect dark matter halo density profile consistent with the GAIA DR3 data set release for the Milky Way rotation curve. Dynamical equations leading to the conversion of all fermions into bosons and then gravity-assisted wave stacking of bosons in the extreme density environment of a black hole leading to boson condensate are discussed. The same formalism is applicable to the early universe where the boson condensate can acquire infinite frequency which is a characteristic of the motionless Fundamental Substance. The reversal of this process creates strain energy followed by inflation. Analysis of the binary pulsar B1913+16 suggests a dark matter halo with positive pressure.