Has ‘dark matter’ really been proven?
Clarifying the clamour of claims from colliding clusters
Published: 8 September 2006 (GMT+10)
Recently, a paper claimed that direct empirical proof of the existence of ‘dark matter’ has been finally found.1 This has been dutifully repeated in the more popular media. 2 It is claimed that this demolishes the criticisms of ‘dark matter sceptics’ (myself among them) who claim that the whole dark matter scenario is the result of incorrect physics being applied to the dynamics of astronomical bodies.
What was found?
Clowe, Bradac and co-authors claimed that the Bullet cluster (1E0657-558) at a redshift of 0.296 is a unique merger of two clusters, and that new analysis just accepted for publication in Astrophysical Journal Letters has ‘…enable[d] a direct detection of dark matter,…’
This topic has been in the news and on several websites over the past few days. The arguments all hinge on Clowe, Bradac et al.’s interpretation of the gravitational lensing evidence. That is, whether the correct physics has been applied to these visible arcs seen in and around galaxies in the two Bullet sub-clusters. The usual interpretation is that it is gravitational lensing,3 and a reconstruction allows one to correctly locate the dark matter.4
Is it really dark matter?
They claim ‘direct proof’. That seems to be stretching things a bit, to put it mildly, given the many assumptions and interpretations necessarily involved (see this explanation of some of the logic of proof in general). In this case they were out to disprove some alternate gravity theories that purport to explain the anomalies which cause others to postulate ‘dark matter’. Those theories made predictions, and according to the analysis being discussed here, the researchers have found data that contradicts those theories. However, a recent paper claims that this is mistaken, namely that at least one of those same theories can explain the ‘lensing’ that is observed in this cluster.5
Even if we were to grant them the disproof, though, it is not a proof nevertheless. Let’s be clear here: “dark matter” is not an explanation for what we see; it’s an admission that no one has an explanation. Perhaps a more accurate headline would have been, ‘Scientists have proved that they haven’t got a clue what the universe is made of’, rather than, ‘Dark matter revealed’.6 Because it isn’t revealed. But if you give a name to an admission of gross ignorance—‘dark matter’, ‘dark energy’—then you may eventually believe you have explained something!
The main problem I see hinges on where the x-ray-emitting gas is. The shock heating from the collision of the clusters might well bias the mass calculations for the normal matter. The determination of the mass from x-ray emission is linked to the assumption of hydrostatic equilibrium,7 and the equation used to calculate the location of the mass is the collisionless Boltzmann equation. But by the authors’ own admission, the system is not in equilibrium. Also, they claim one cluster passed through another,8 so the x-ray gases are heated to hundreds of millions of degrees, hardly collisionless. That is why it was named the Bullet cluster. There is a clear picture9 of the x-ray emission shaped like a bow shock wave. The article says:
‘The cluster is also known as the bullet cluster, because it contains a spectacular bullet-shaped cloud of hundred-million-degree gas. The X-ray image shows the bullet shape is due to a wind produced by the high-speed collision of a smaller cluster with a larger one.’
They argue that the separate methods (gravitational lensing, and x-ray emissions) allow the authors to separate where the normal matter is from where the dark matter is. But still, many assumptions have been applied which may be wrong. So I suggest that the location of the mass is still in question.
Claims of ‘direct proof’ of dark matter have been made before, and have fizzled.10 Considering that we live in a part of the galaxy that is meant to be dominated with the stuff and is allegedly six or seven times more concentrated than normal matter, i.e. all around us, what is it? Some claim it comprises heavy neutrinos. If standard neutrinos, there would need to be about 10 billion times the amount of the normal matter made from protons and neutrons. Hence the need to look for a massive neutrino. But there are supposed to only be about 20 particles per cubic centimetre! It seems more than prudent to adopt a ‘wait and see’ approach on this alleged ‘proof’.
Another question that might be asked is: if gravitational lensing is correct in the Bullet cluster, why don’t we see it in the CMB?11 After all, cosmic microwave radiation is supposed to come from the background of all the galaxies (supposedly containing putative dark matter) in the visible universe and therefore should be lensed by foreground galaxies—but it isn’t.
I believe we need to apply Occam’s razor.12 We should be wary of claiming the existence of anything where ad hoc assumptions are introduced to the norm, resulting in a complex system of more components than are really necessary. I suggest that dark matter, dark energy, inflation, etc are such items, ones on which history will ultimately pass unfavourable judgement.
Dark matter—vital for big bang believers
But why all the fuss? A lot has to do with ‘big bang belief’. It seems that dark matter is necessary to prop-up the failing paradigm of the Friedmann cosmologies commonly believed by many to describe not only the structure but also the true (‘big bang’) beginning of the universe. The many well-qualified critics of the big bang have rightly lambasted dark matter and dark energy as ‘hypothetical entities’ or ‘fudge factors’ (see Secular scientists blast the big bang, which cites An Open Letter to the Scientific Community (PDF version) published in New Scientist). However, to get the theory to work, a universe comprising 22% dark matter is an absolute must. Therefore it has become now an all-out battle to prove that the dark matter sceptics (like me), who dispute the existence of the stuff, are wrong.
As well as propping up the big bang, dark matter is needed to explain certain motions in galaxies that appear not to follow the laws of physics. It is reminiscent of the proposal around the turn of last century about the existence of another planet, Vulcan. No, not the home of Mr Spock, but a hidden planet that allegedly perturbed Mercury’s orbit and thus explained why it did not follow Newtonian physics. But the proposed planet could not be observed, and had a strange quality to it—how could it remain hidden from Earth by the sun, when a planet near Mercury must orbit the sun much faster than Earth does?
Nowadays, this proposal is regarded as quaint, because Einstein’ theory of general relativity (GR) explains the orbit of Mercury. That is, rather than introducing a fudge factor that really explained and predicted nothing, what was needed was new physics that both explained current observations and predicted new ones.
Dark matter is the Vulcan of today. It is a ‘fudge’, with unknown properties, and strange behaviour, such as being in a non-collapsing halo around galaxies. The equivalent of GR in the Vulcan saga, i.e. the new physics required to do away with this whole ‘dark matter fudging’, could well be a new theory proposed by Israeli cosmologist/physicist Moshe Carmeli. His 5D space-time-velocity metric explains both galactic rotation curves13 and the flatness of the universe14—without dark matter or other fudge factors. Like Einsteinian relativity did to Newtonian physics, it encompasses today’s physics but explains more of the data.
Why this matters
If you believe we live in a universe that is the chance product of evolution (in all senses of the word), then since we are here to observe the universe, you may also believe this universe just happens to be the type that permits life to exist … but ultimately there is no plan. If so, then how can you understand anything outside your own experience, or even trust that your thoughts are reliable?
If, on the other hand, we believe we live in a universe designed by a Creator, then we should expect the universe to make sense, and to have defining properties that we can analyze locally and apply globally. These sorts of biblically-based assumptions are what made science possible in the first place, historically. Whether or not dark matter in some form turns out to be real stuff, its ‘existence’ at present appears to be largely based on an underlying motive to keep a belief system that is fundamentally flawed.
References and notes
- Clowe, D., M. Bradac, et al, A direct empirical proof of the existence of dark matter, http://arXiv.org, 2006. Return to text.
- www.universetoday.com/2006/08/21/galaxy-collision-separates-out-the-dark-matter/ (30th August 2006). Return to text.
- An effect predicted by general relativity that foreground matter should act like a giant lens on background light sources. Return to text.
- Halton Arp suggested that these arcs, which are very prominent in the Abell 2218 cluster, are not the result of gravitational lensing but ejections of galaxies and matter from other clusters. Of course that flies in the face of standard big bang cosmology, which assumes all matter originated in the initial big bang. See H. Arp, Seeing red, redshifts, cosmology and academic science. Montreal: Apeiron, 1998; and review, The heavens declare a different story! Note also that the redshift of the Bullet cluster is near 0.3 which is one of the discrete values that Arp claims is associated with ejection events of one galaxy giving birth to another. Return to text.
- Moffat, J, Gravitational Lensing in Modified Gravity and the Lensing of Merging Clusters without Dark Matter, arxiv.org, 30 August 2006. Return to text.
- www.sciencebuzz.org/blog/dark_matter_revealed (15th December 2016). Return to text.
- Hydrostatic equilibrium means that gravitational force is balanced by outward pressure. Return to text.
- It is interesting too that this is called a merger when they say one cluster passed through another. It seems more like an ejection event. Return to text.
- www.universetoday.com/wp-content/uploads/2006/08/2006-0821chandra.jpg (30th August 2006). Return to text.
- Prof. G. Gilmore claims ‘It’s the first clue of what the stuff might be.’ and “For the first time ever, we’re dealing with its physics”, news.bbc.co.uk/1/hi/sci/tech/4679220.stm (30th August 2006), and www.space.com/scienceastronomy/060221_stues_dark_matter.html (30th August 2006). Return to text.
- Lieu, R, Mittaz, J.P.D., On the absence of gravitational lensing of the Cosmic Microwave Background, ApJ 628(2):583–593, 2005. Return to text.
- William of Occam (or Ockham) (1284–1347) was an English philosopher and theologian. Occam’s (or Ockham’s) Razor, or the law of parsimony: a problem should be stated in its basic and simplest terms. In science, the simplest theory that fits the facts of a problem is the one that should be selected. Return to text.
- Hartnett, J.G., Spiral galaxy rotation curves determined from Carmelian general relativity, Int. J. Theor. Phys., (in press) 2006, arxiv: astro-ph/0511756 Return to text.
- Hartnett, J.G., The distance modulus determined from Carmeli’s cosmology fits the accelerating universe data of the high-redshift type Ia supernovae without dark matter, Found. Phys. 19(2), 2006; Springer Online First DOI: 10.1007/s10701-006-9047-y, arxiv: astro-ph/0501526; Oliveira, F.J., Hartnett, J.G., Carmeli’s cosmology fits data for an accelerating and decelerating universe without dark matter nor dark energy,, Found. Phys. Lett. (in press) 2006, arxiv: astro-ph/0603500. Return to text.