I really have trouble buying into all these "Dark Matter" theories.<br><br>At least from my point of view, there may be a simple explanation. Neutrinos and Photons.<br><br>Neutrinos, theoretically are massless but have been shown to have some non-zero mass. They are produced in nearly infinite numbers by stars and other energetic processes (supernova and probably black holes). <br><br>After the Big Bang, the number of stars has increased dramatically and the number of neutrinos streaming off into the far reaches of space has increased. The number of Photons has also increased. With every star, the numbers of these these extremely tiny bits of light and mass streaming off into the ever expanding universe has to add up to a fantastic amount of mass and energy. <br><br>Neutrinos travel at the speed of light as do Photons. There should be a lot of neutrino mass in and around where the stars are - the galactic center out to the halo. Since these particles radiate in all directions, they are carrying non-zero mass and the distance between them must increase with distance from the source as they travel away and so the density per cubic parsec would decrease at the square of the distance. Essentially this is the loss of mass at the center of the stars (and most stars are in galaxies and most stars in galaxies are nearest to the primary structures of the galaxies, this mass is densest near the centers of galaxies and in the structures (spiral arms) as well. <br><br>We know that gravity affects photons which suggests that photons, like neutrinos, have a non-zero mass albeit however small.<br><br>Neutrinos and Photons, ostensibly, result from the conversion of mass to energy that occurs in the hearts of stars, black holes, supernova ... Neutrinos and Photons are the "Dark Matter" in and around galaxies. This Dark Matter is produced by stars and as the amount of dark matter increases near galaxies, it precipitates the formation of more stars and so on.<br><br>This leads to a gradual redistribution of mass from the sources to the furthest reaches of the Universe. An ever expanding sphere growing at the speed of light. We know that photons can impart energy to matter (hence light sails and YORP effect, etc.). The continuous bombardment of photons must be pushing everything they interesect, no matter how slightly or gradually away from the sources of the photons. In a similar way, the same effect must be true for neutrinos. This then is "Dark Energy". <br><br>All these theories about Dark Matter and Dark Energy all require significant "constants" to be added to the theories of how the universe works. Perhaps it is all much simpler.<br><br>If Neutrinos or Photons are affected by the great gravitational wells of Galaxies would they not slow down and, perhaps, eventually be trapped by the universe (like the velocity of the voyager spacecraft - they keep slowing down due to the gravity of the Sun.)<br><br>Just seems that "Dark Matter" and "Dark Energy" may be artificial constructs that we may eventually find to be already accounted for.