Dark energy is a theoretical form of energy that physicists use to explain how our universe appears to be expanding at an accelerated rate. It's a hypothesis that has gone from seeming like a suspicious physics "cheat," to now becoming widespread accepted cosmology.
But a theory-shattering new paper now threatens to throw dark energy right back into the realm of speculation. It turns out, the most direct and strongest evidence we have for dark energy to date looks to be based on a faulty assumption, reports Phys.org.
Dark energy catapulted into mainstream thought in 1998 after landmark distance measurements using type Ia supernovae for galaxies at high redshift showed that the more distant a galaxy is, the faster it appears to be moving away from us. This formed the core evidence for the idea that our universe must be expanding at an accelerated rate. It was such a landmark discovery that this research led to the 2011 Nobel Prize in Physics.
But it might be all wrong. A team of astronomers at Yonsei University in South Korea have shown that those distance measurements using type Ia supernovae are probably in error.
"Quoting Carl Sagan, 'extraordinary claims require extraordinary evidence,' but I am not sure we have such extraordinary evidence for dark energy. Our result illustrates that dark energy from SN cosmology, which led to the 2011 Nobel Prize in Physics, might be an artifact of a fragile and false assumption," said project leader Prof. Young-Wook Lee.
By "SN cosmology," Lee is referring directly to the types of conjecture that emerged from that Nobel-winning research. The key assumption made back then was that the corrected luminosity of type Ia supernovae would remain relatively constant even across the redshift (objects moving away from us appear to shift toward the red as the light gets stretched out with the increasing distance). That's what appears to be incorrect, however.
The Yonsei team performed high-quality spectroscopic observations of nearby host galaxies of type Ia supernovae. They found a significant correlation between the luminosity of these supernovae and stellar population age, at a 99.5 percent confidence level. What this means is that previous research did not account properly for the fact that the supernovae in host galaxies are getting younger with redshift (which is also a look back in time).
When properly taken into account, the luminosity evolution of these supernovae essentially cancels out the need to postulate dark energy. In other words, maybe our universe isn't expanding at an accelerated rate after all.
It's a humbling reminder of how our grand cosmological theories are often held together by a very delicate house of flimsy cards. There's only so much we can observe from our little blue home in a corner of the vast cosmos; we have to extrapolate a lot with only a thin slice of data to go on. While our theories are always advancing, it's foolhardy to believe that the information we have today is sufficient for achieving final answers to the big questions.
While that might mean we have to go back to the drawing board, it also means we've got much more left to discover. That's what makes doing science so enthralling: the further along we get, the longer we have yet to go.