Universe is expending faster than scientists expected

Since 1990s, scientists have known that our universe is expending faster and faster, but whatever is causing it remains a mystery. According to the latest measurement, the universe is expending more quickly than it should be. That is to say, the expansion rate is greater than what is predicted. Hence, scientists start to create some hypothesis that can explain this phenomenon.

  Some physicists believe that the expansion of universe is caused by the "dark energy". Dark energy arise from empty space, which according to quantum mechanics, is not empty at all, but rather filled with virtual particles which keep pop in and out of existence. These particles would carry energy, and they might exert negative energy, pushing everything in universe outward. In the past, the influence of dark energy was thought to be a constant. However, the influence of dark energy might change over space and time. That might be the reason why universe is expanding faster than it was predicted.

  The other explanation is that universe contains an extra type of fundamental particle--- a nearly mass-less neutrino. If this type of particle exists, the more of universe's energy would take a form of radiation rather than mass. (this kind of particle have almost no mass, travel near light speed, so it should be count as radiation in calculation.)  Wherever matter clumps under gravity, a greater radiation would allowed universe to expand faster at that space.

In addition to find new hypothesis, scientists are also trying to find flaws in the data. They want to make sure whether the divergence of expansion rate is caused by the mistake of measurement.  “Basically is there something going on in cosmology that we don’t understand, or is there something going on with the data?” says Charles Bennett of Johns Hopkins University, who has worked on measurements of the Hubble constant from the early universe and was not involved in the latest study.  
   
   I believe, scientists will find out the answer sooner or later. Personally, I hope the the increasing expansion rate is not simply caused by the measurement error. If the increasing rate is caused by other reasons, the whole thing will be more interesting. Don't you think so?