Sunday, April 17, 2016

Hubble Hubbub

New measurements of the local rate of expansion of the universe are creating a stir. The measurements found that the current value does not seem to agree with data from the Cosmic Microwave Background and the so-called Lambda CDM model. The second link, to a Scientific American news story, discusses potential implications in a bit more speculative manner than the paper.

From SA:

The Hubble constant discrepancy, though, suggests that dark energy might actually change over space and time, potentially causing an increasing acceleration of the cosmos instead of a constant outward force. One theory proposing this type of dark energy is called quintessence, which posits that dark energy results not from the vacuum of space but from a field that pervades spacetime and can take on different values at different points.

An alternative explanation for the discrepancy, however, is that the universe contains an additional fundamental particle beyond the ones we know about. In particular, a new species of neutrino—a nearly massless particle that comes in three known varieties so far—could account for the divergence in Hubble constant measurements. If an extra type of neutrino exists, then more of the universe’s total energy would take the form of radiation rather than matter. (Neutrinos, because they have almost no mass, travel near light speed and therefore count as radiation in this calculation). Whereas matter clumps together under gravity, a greater radiation budget would have allowed the universe to expand faster than it would have otherwise.

or maybe there is a flaw in the measurements. TBD