MadSci Network: Astronomy |
Leaving aside the vitriol in the question, Why is there continuing talk about "dark energy"? (I've addressed elsewhere on MadSci why astronomers think that the Big Bang model is the best explanation for the evolution of the Universe.)
The reason that there is continuing talk is because we have a problem. The
problem is summarized in this diagram, stolen from Tony Smith's Cosmology
document:
On the horizontal axis the matter density of the Universe, relative to what it
would take to cause the Universe to recollapse. So if Omegam is
larger than 1, the Universe recollapses; if it is smaller than 1 the Universe
expands forever. On the vertical axis is OmegaLambda or the
equivalent energy density contributed by a cosmological constant,
"anti-gravity," or dark energy. If this value is greater than 0, dark energy
exists.
The shaded regions show what values of Omegam and OmegaLambda are allowed by a subset of the currently available data. There are actually two shaded regions shown. One shows the allowed values as indicated by measurements of the cosmic microwave background. The other shows the allowed values as indicated by measurements of the distances to Type Ia supernovae. The essential region of the plot is where the two shaded regions overlap. It is quite obvious that the overlap region is around Omegam ~ 0.3 and OmegaLambda ~ 0.7.
That's the problem. If we look at only one or the other of the measurements, then the shaded region for that particular measurement encompasses OmegaLambda = 0, and we have no need of dark energy. We're not allowed to pick and choose the data in science, though. We have to consider all of the measurements.
Moreover, as I indicated above, this graph doesn't show all of the data. If one includes measurements from things like the masses of clusters of galaxies, the constraints on Omegam and OmegaLambda become even tighter, and it is even more difficult to avoid dark energy.
(Heuristically, why is dark energy needed? One simple explanation is that distant Type Ia supernovae appear too dim. One way to explain why these supernovae appear too dim is to say that they are more distant than we thought, which means there must be some kind of repulsive force or dark energy in the Universe, accelerating its expansion.)
So what are the possible solutions? There are three:
Dump general theory of relativity and/or the Big Bang model. The problem with this "solution" is that general relativity is a fairly well tested theory as is the Big Bang model. If we dump them, with what do we replace them? Nobody's come up with a better explanation.
There's something wrong with the measurements. This is certainly possible and was considered quite seriously about 5 years ago when the news of the Type Ia supernovae distant measurements were first reported. However, repeated attempts to find flaws in the measurements have found none. Moreover, the data continue to pour in, witness the recent results from the Wilkinson Microwave Anisotropy Probe (WMAP). Of course, there still could be a problem with the measurements, but until somebody can figure out what it might be, we have to accept that the measurements are accurate.
Dark energy exists.
In the absence of any other, better explanations, astronomers generally have settled on the third option. The result has been a combination of elation and unease. On the one hand, we're learning things about the Universe! That's one of the neatest feelings one can experience, and it's why many astronomers do astronomy. On the other hand, we don't understand dark energy and there's always the nagging worry at the back of one's mind that maybe we've missed something.
In conclusion, I think that dark energy is far from being accepted as "fact," though there are a number of strong indicators that the Universe might really work this way. Until somebody comes up with a better explanation, most astronomers will continue to think that the Universe contains dark energy.
Try the links in the MadSci Library for more information on Astronomy.