Monday, June 2, 2014

cosmology - Cosmological Inflation: If Photon expands, why not other matter?


I keep repeatedly reading in many Stack Exchange and Quora questions that space of universe expands but particles (matter) don't, see e.g. this Phys.SE post. The reason given is that particles are governed by much stronger Electromagnetic and Nuclear forces, where space expansion is relevant to only on much larger inter galactic scale where all natural forces including gravity is weaker.


How come photons in CMB (Cosmic Wave Background) which is also a kind of matter has expanded to radio wave range from gamma range? Is photon not affected by nuclear, Electromagnetic forces?


If the answer is Photons are weightless while subatomic particle like electron has mass, then does it mean space expansion affects other massless particles as well? Have the other massless particles proven to show expansion since big bang?


I am confused why space expansion affects Photons but not other forms of matter.




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