Cosmology Notes

Modified Gravity Theory (MOG)

John Moffat (of University of Toronto) proposes the Gravitational constant G is actually a new tensor varying with spacetime such that G/c is constant (Modified Gravity Theory). No dark matter or dark energy.

Galactic rotation

Computer and laboratory simulations show that at least the ISM (if not the stars themselves) could be rotating as a plasma filament pair constrained by MHD, producing the observed flat rotation profile. These simulations also produce a time progression through the observed galactic spiral and barred spiral morphologies, and may also explain the observed independence of the motions of the stars from that of the spiral arms, if only someone would run the simulations again. However this substitutes "we need dark matter to make it work" with "where does the colossal current driving the filaments come from?"

Expansion as illusion

There are many interesting alternative explanations of the observed Hubble relation of H₀ ≈ 70 km s⁻¹ Mpc⁻¹. The question is whether they raise more problems than they solve.

Tired light hypothesis

The hypothesis that light is red-shifted as it loses energy to the cosmos travelling across vast distances, through some unknown mechanism that does not result in photon scatter. One potential mechanism is the Wolf Effect, where diffuse plasmas can produce a redshift in transmitted light.

Time dilation

Using the antisymmetric temporal part of the Ricci tensor to replace the symmetric g tensor in General Relativity, it is possible to derive H₀ = c/R as a general time dilation of approximately 70 km s⁻¹ Mpc⁻¹, where R is the Einstein radius of the Universe (approx. 13 Gly). This would mean that the observed Hubble redshift relation results from time dilation across cosmological distances, rather than the relativistic motion of galaxies in an expanding spacetime.