Addressing the horizon and causality problems in cosmology and astrophysics, No. 19 in series

FUNDAMENTAL UNSOLVED PROBLEMS IN PHYSICS AND ASTROPHYSICS 2.9 The Microwave Background Horizon Problem. This arises because the microwave background is believed to have been produced in the fireball that followed the big bang, but the field today is too 9 uniform in temperature to be compatible with standard cosmological models based on general relativity (Misner, Thorne and Wheeler, 1973; Kramer et al. 1980; Mann and Wesson 1991; Will 1993). Put another way, causal contact is defined in general relativity by the concept of the horizon (Rindler 1977); and photons we see now in the microwave background with the same temperature should have been outside each other’s horizons and so out of causal contact in the early universe. Of course, this problem can be avoided by altering the model for the early universe. The appropriate modification is to have a phase of rapid, perhaps exponential, expansion at early times. This idea - inflation - now has a big literature. But the energy source has not been identified. One possibility is that the cosmological “constant” actually decays with time, producing a vacuum that was unstable early on (see Sections 2.3 and 2.8). Another possibility is that inflation was powered by the collapse of other dimensions of space which are now microscopic (see Sections 2.1 and 2.14). However, while much has been written about the horizon problem for the photons of the microwave background, this problem is only part of a larger one to do with causality.

2.10 Particle Properties and Causality. Causality as defined in general relativity involves photons moving on null geodesics within a region of space defined in size by the (particle) horizon. Photons within our horizon can be expected to have the same energy or temperature, as discussed in the preceding Section. But how do particles in general “know” to have the same properties, such as mass, charge and spin? And if there was causal disconnection early on, why do we now observe that particles in (say) widely separate QSOs have the same properties? A conceptual way to answer these questions is to invoke the Strong Equivalence Principle in a form wherein it is taken to mean that the properties of particles are the same everywhere in an (unbounded) universe, even if there are portions of the latter which were out of causal contact with each other in the past. However, most workers would prefer a more concrete and testable mechanism to explain this form of communication, especially since astrophysical data show a remarkable degree of uniformity of properties in the universe (Tubbs and Wolfe 1980). One mechanism, often attributed to J.A. Wheeler, is that instead of there being of the order of 10^80 electrons (say) inside the visible universe, there is in fact only one. By dint of being able to move at apparently superluminal speeds by virtue of moving through a multiply-connected universe, this one particle could manifest itself as many. Another, and less speculative mechanism, involves modifications to the usual laws of causality in 4D by virtue of the influence of extra Kaluza-Klein type dimensions (Davidson and Owen 1986; Wesson 1999). This idea might work, since the size of the horizon depends on the dimensionality, but needs careful investigation. -- Paul S. Wesson Department of Physics University of Waterloo Waterloo, Ontario N2L 3G1 Canada prepared for California Institute for Physics and Astrophysics 366 Cambridge Avenue Palo Alto, California 94306 U.S.A. Email: [email protected] 

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Since particles are seen as sinks rather than sources (Nos. 12, 13, 15, 16 in series), they are seated in all of space, but appear on recording devices as discontinuous infinitesimal points where they are NOT. Also, all particles are seen to derive from an ambient pure repulsive (complex) gravitational field.* Under these circumstances the horizon and causality problems are moot.

* Another view of Newton's law of gravity, https://www.researchgate.net/profile/Warren-Frisina-3/publications

Image credit: https://www.newscientist.com/term/causality/