Our scientists are often giving us visual displays designed to impress us with their grasp of nature. Such visuals should sometimes be taken with a large grain of salt, as they are often examples of dubious dogma. An example is the type of “composition of the universe” pie graph that shows the universe as about 71% dark energy, 24% dark matter and 5% regular matter. But as I discussed in my previous post “A Second Bullet in the Chest of Dark Matter?” the case for dark matter is wobbly, and two recent findings are hard to reconcile with standard accounts of dark matter. Commenting on one of these findings, an astrophysicist has said, “Nothing in the standard cosmological model predicts this and it is almost impossible to imagine how that model could be modified to explain it, without discarding the dark matter hypothesis completely.”
In my previous post I suggested that we should replace the dogmatic “composition of the universe” pie chart with a table listing the universe's contents as ? % dark matter, ? % dark energy, ? % atoms, and ? % unknown. Coincidentally, a few days after making this post, there appeared a news science story that seems to further shatter all confidence that we understand the composition of the universe.
The new science story dealt not with dark matter but dark energy. No one has any idea what dark energy is, but there is a vague idea that the vacuum of space may be filled with dark energy. The case for dark energy seemed to solidify when scientists announced that the expansion of the universe is accelerating. Scientists said that only dark energy in the vacuum of space could account for this acceleration. We were told that dark energy has a kind of expansive pressure, rather like the gas pressure that keeps a helium balloon from collapsing, and that this is causing the universe's expansion to accelerate.
But now dark energy may have taken its own bullet in the chest. It comes from this paper dealing with supernova explosions. The conclusion that the universe's expansion is accelerating was based largely on an analysis of the star explosions called supernova explosions. The new paper also analyzes supernova explosions, but uses a more sophisticated technique and a larger database. The new paper says, “We find, rather surprisingly, that the data are still quite consistent with a constant rate of expansion.”
As discussed here, the new paper casts doubt on the claim that the expansion of the universe is accelerating. In doing so, it seems to undermine the main evidence for dark energy.
Ouch! It looks like our swaggering, strutting cosmologists may have little idea about what they are talking about when they pontificate about the composition of the universe. But we shouldn't be surprised by such dogmatic overconfidence, seeing how extremely common it is in the fields of physics, biology and neuroscience. Should we tear out those pages of the astronomy textbooks that have dogmatic “composition of the universe” pie charts? Perhaps instead we can print up some candid stickers resembling the visual below, and paste them over such “composition of the universe” pie charts. The figure in the white coat represents a scientist with the proper degree of intellectual humility.
Postscript: Some news reports said that the authors of the new paper on supernova explosions had said that the expansion of the universe is not accelerating. But their paper was actually entitled "Marginal evidence for cosmic acceleration from Type Ia supernovae." They merely claimed that the evidence for an accelerating universe was marginal. Their paper is rebutted by this paper from today, entitled "Is the expansion of the universe accelerating? All signs point to yes."