Most people think the scientific endeavour is truly objective; scientists draw their conclusions from all the facts and are never swayed by fashion. Sorry, but that is not true, as I found out from my PhD work. I must post about that sometime, but the shortened version is that I entered a controversy, my results unambiguously supported one side, but the other side prevailed for two reasons. Some “big names” chose that side, and the review that settled the issue conveniently left out all reference to about sixty different sorts of observations (including mine) that falsified their position. Even worse, some of the younger scientists who were on the wrong side simply abandoned the field and tried to conveniently forget their work. But before I bore people with my own history, I thought it would be worth noting another issue, dark energy. Dark energy is supposed to make up about 70% of the Universe so it must be important, right?
Nobody knows, or can even speculate with some valid reason, what dark energy is, and there is one reason only for believing it even exists, and that is it is believed that the expansion of the Universe is accelerating. We are reasonably certain the Universe is expanding. Originally this was discovered by Hubble, who noticed that the spectra of distant galaxies have a red shift in their frequencies and the further away they are, the bigger the red shift. This means that the whole universe must be expanding.
Let me digress and try to explain the Doppler shift. If you think of someone beating a drum regularly, then the number of beats per unit time is the frequency. Now, suppose the drum is on the back of a truck. If you hear a beat, and expect the next one at, say, 1 second later, if the truck starts to move away, the beat will come slightly later because the sound has had further to go. If the truck goes away at a regular speed, the beats will be delayed from each other by the same interval, the frequency is less, and that is called a red shift in the frequency. Now, the sound intensity will also become quieter with distance as the sound spreads out. Thus you can determine how far away the drum is and how fast it is moving away. The same applies to light, and if the universe is expanding regularly, then the red shift should also give you the distance. Similarly, provided you know the source intensity, the measured light intensity should give you the distance.
That requires us to measure light from stars that produce a known light output, which are called standard candles. Fortunately, there is a type of very bright standard candle, or so they say, and that is the type 1A supernova. It was observed in the 1990s that the very distant supernovae were dimmer than they should be according to the red shift, which means they are further away than they should be, which means the expansion must be accelerating. To accelerate there must be some net force pushing everything apart. That something is called dark energy, and it is supposed to make up about two thirds of the Universe. The discoverers of this phenomenon won a Nobel prize, and that, of course, in many people’s eyes means it must be true.
The type 1A supernova is considered to arise when a white dwarf star starts to strip gas from a neighbouring star. The dwarf gradually increases in mass, and because its nuclear cycle has already burnt helium into carbon and oxygen, where because the mass of the dwarf is too low, the reactions stop. As the dwarf consumes its neighbour, eventually the mass becomes great enough to start the burning of carbon and oxygen; this is uncontrollable and the whole thing explodes. The important point here is that because the explosion point is reached because of the gradual addition of fresh mass, it will occur at the same point for all such situations, so you get a standard output, or so it is assumed.
My interest in this came when I went to hear a talk on the topic, and I asked the speaker a question relating to the metallicity of the companion star. (Metallicity is the fraction of elements heavier than helium, which in turn means the amount of the star made up of material that has already gone through supernovae.) What I considered was that if you think of the supernova as a bubble of extremely energetic material, what we actually see is the light from the outer surface nearest to us, and most of that surface will be the material of the companion. Since the light we see is the result of the heat and inner light promoting electrons to higher energy levels, the light should be dependent on the composition of the outer surface. To support that proposition, Lyman et al. (arXiv: 1602.08098v1 [astro-ph.HE] 2016) have shown that calcium-rich supernovae are dimmer than iron-rich ones. Thus the 1A supernova may not be such a standard candle, and the earlier it was, the lower the metallicity will be, and that metallicity will favour lighter atoms, which do not have as many energy levels from which to radiate so they will be less efficient at converting energy to light.
Accordingly, my question was, “Given that low metallicity leads to dimmer 1a supernovae, and given that the most distant stars are the youngest and hence will have the lowest metallicity, could not that be the reason the distant ones are dimmer?” The response was a crusty, “That was taken into account.” Implied: go away and learn the standard stuff. My problem with that was, how could they take into account something that was not discovered for another twenty years or so? Herein lies one of my gripes about modern science: the big names who are pledged to a position will strongly discourage anyone questioning that position if the question is a good one. Weak questions are highly desired, as the name can satisfactorily deal with it and make himself feel better.
So, besides this issue of metallicity, how strong is the evidence for this dark energy. Maybe not as strong as everyone seems to say. In a recent paper (Nielsen et al. arXiv:1506.01354v2) analysed data for a much larger number of supernovae and came to a somewhat surprising conclusion: so far, you cannot actually tell whether expansion is accelerating or not. One interesting point in this analysis is that we do not simply relate the measured magnitude to distance. In addition there are corrections for light curve shape and for colour, and each has an empirical constant attached to it, and the “constant” is assumed to be constant. There must also be corrections for intervening dust, and again it is a sheer assumption that the dust will be the same in the early universe as now, despite space being far more compact.
If we now analyse all the observed data carefully (the initial claims actually chose a rather select few) we find that any acceptable acceleration consistent with the data does not deviate significantly from no acceleration out to red shift 1, and that the experimental errors are such that to this point we cannot distinguish between the options.
Try this. Cabbolet (Astrophys. Space Sci. DOI 10.1007/s10509-014-1791-4) argues that from the Eöt-Wash experiment that if there is repulsive gravity (needed to accelerate the expansion), then quantum electrodynamics is falsified in its current formulation! Quantum electrodynamics is regarded as one of the most accurate theory ever produced. We can, of course, reject repulsive gravity, but that also rejects dark energy. So, if that argument is correct, then at least one of the two has to go, and maybe dark energy is the one more prone to go.
Another problem is that it is assumed that type 1a supernovae are standard because they all form by the gradual accretion of extra matter from a companion. But Olling et al. (Nature, 521: 332 – 335, 2015) argue that they have found three supernovae where the evidence is that the explosion occurred by one dwarf simply swallowing another, and now there is no standard mass, so the energy could be almost anyhting, depending on the mass of the companion.
Milne (ApJ 803 20. doi:10.1088/0004-637X/803/1/20) has shown there are two classes of 1a supernovae, and for one of those there is a significant underestimation of the optical luminosity of the NUV-blue SNe Ia, in particular, for the high-redshift cosmological sample. Not accounting for this effect should thus produce a distance bias that increases with redshift and could significantly bias measurements of cosmological parameters.
So why am I going on like this? I apologize to some for the details, but I think this shows a problem in that the scientific community is not always as objective as they should be. It appears to be, they do not wish to rock the boat holding the big names. All evidence should be subject to examination, and instead what we find is that only too much is “referred to the experts”. Experts are as capable of being wrong as anyone else, when there is something they did not know when they made their decision.