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Dark energy endures

There's fresh evidence that dark energy - the mysterious factor that appears to be driving the accelerating expansion of the universe and accounts for 70 percent of its matter-energy content - has been present for most of the history of the cosmos. A heads-up about the latest revelations appears in a NASA media advisory, touting a teleconference at 1 p.m. ET Thursday.

The fact that astrophysicist Adam Riess of the Space Telescope Science Institute is one of the speakers at the teleconference would imply that the evidence has to do with observations of supernovae by the Hubble Space Telescope. Particular types of supernovae can be analyzed to measure the universe's expansion rate over time - and in fact, Riess' team provided results a couple of years ago to support the view that dark energy has been a constant presence.

Scientists are just beginning their efforts to figure out what dark energy is, and one of the first questions is whether the effect has been constant over the life of the universe, or whether it can grow stronger or weaker.

If dark energy is found to be ever-present, it could be made to fit with Albert Einstein's theories as a "cosmological constant" - a concept that Einstein at first wrote into relativity, then retracted as "the worst mistake I ever made." If dark energy varies over time, a different class of theories (sometimes known as quintessence theories) would have to come into play. Then there are still other theories that say what we observe as dark energy is merely a misunderstood after effect of the Big Bang.

Each theory raises deeper questions about why the universe currently seems to be set up just right for our existence. 

Today's advisory hints that the fresh evidence strengthens the case for a cosmological constant - but you'll have to tune in NASA's briefing on Thursday for the details.