The standard theory of cosmology is called the Lambda cold dark matter (ΛCDM) model. As that name suggests, the theory postulates the existence of dark matter – a mysterious substance that (according to the theorists) comprises the bulk of the matter in the Universe. It is widely embraced. Every cosmologist working today was educated in the Standard Model tradition, and virtually all of them take the existence of dark matter for granted. In the words of the Nobel Prize winner P J E Peebles: ‘The evidence for the dark matter of the hot Big Bang cosmology is about as good as it gets in natural science.’
There is one problem, however. For four decades and counting, scientists have failed to detect the dark matter particles in terrestrial laboratories. You might think this would have generated some doubts about the standard cosmological model, but all indications are to the contrary. According to the 2014 edition of the prestigious Review of Particle Physics: ‘The concordance model [of cosmology] is now well established, and there seems little room left for any dramatic revision of this paradigm.’ Still, shouldn’t the lack of experimental confirmation at least give us pause?
In fact, there are competing cosmological theories, and not all of them contain dark matter. The most successful competitor is called modified Newtonian dynamics (MOND). Observations that are explained under the Standard Model by invoking dark matter are explained under MOND by postulating a modification to the theory of gravity. If scientists had confirmed the existence of the dark particles, there would be little motivation to explore such theories as MOND. But given the absence of any detections, the existence of a viable alternative theory that lacks dark matter invites us to ask: does dark matter really exist?David Merritt, “A non-Standard model” at Aeon
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