First it was dark matter,1 then came dark energy,2 followed by dark fluid,3 dark flow,4 and dark radiation5; and now a new entity is suggested for the dark sector of particle physics—dark photons. The dark sector is full of hypothetical entities designed to save the big bang story but it is really just a lot of cosmic storytelling.6

Previously I have argued that dark matter is a sort of ‘god of the gaps’, the ‘unknown god’,7 in astrophysics. It is an unknown invoked to explain the inexplicable,8 which, if you follow the chain of logic, is required to maintain a belief in the big bang paradigm. Its existence is only inferred from the application of known physics to certain observations in the universe.9 Without assuming the existence of some exotic unknown dark matter comprising about 25% of the matter/energy content of the universe10 the standard big bang model would have to be discarded as a total failure.

Dark matter has never been observed in space or in any laboratory experiment.

Colliding galaxies

Now a new observation of four colliding galaxies in the Abell 3827 cluster apparently may shed new light on the conundrum.11 See the four galaxies in the centre of the figure here.

With the aid of the theoretically modelled effects of what you expect to observe from the phenomenon known as gravitational lensing (i.e. the bending of light as it passes near massive objects, in this case galaxies) a new claim is made:

“Observations made with the Hubble Space Telescope and the Very Large Telescope in Chile revealed that the dark matter surrounding at least one of the galaxies significantly lagged behind the ordinary matter there, suggesting dark matter particles were interacting with one another and slowing themselves down—a phenomenon never seen before.”11

The idea is that the collision of the galaxies separates the normal matter from the dark matter due to the interaction of the galaxies. And because the dark matter, which is not observable, is separated from the normal matter, which is observable, the dark matter affects the bending of light from the cluster differently to the case if no dark matter was involved.

Of course several important assumptions are being made here. The most important two: 1) that gravitational lensing effects are what is being observed, without any independent method of verification, and, 2) the exotic dark matter exists, even though it cannot be seen. But this could all be completely wrong. However, astrophysicists believe that because their model for gravitational lensing is based on Einstein’s General Relativity, and that that theory has been well-tested elsewhere13 then it should be reliable here too.14

The new observations have led astronomers to propose that these unknown dark matter ‘particles’ have another property, in addition to being influenced by gravity and not electromagnetic radiation (light, etc.), and that is that they can interact with each other. One suggested that an exchange of ‘dark photons’ may create the force needed, in an analogous way to how photons are the force carriers of electromagnetic radiation. The latter might be manifested as two positively charged particles approach each other, each exchanging photons and momentum with the other causing them to repel each other. In a similar way, it is now suggested that dark matter particles might exchange ‘dark photons.’

But since the observations have only shown the possible effect in one galaxy (no others ever anywhere else) one researcher admitted that they may not have thought of everything. He said:11

“There are unknown unknowns that may be changing the result.”

Translation: “Our interpretation of the observational evidence might be totally wrong.”

A separate survey, the results from which were published in the journal Science in March 2015, analyzed 72 collisions of galaxy clusters rather than individual galaxies, in contrast to this new report. In that survey no evidence of self-interacting dark matter was observed. Remember the dark matter itself is never observed, only inferred from computer simulations which model where the unseen stuff should be. But, it is claimed that since galaxy clusters collide faster than individual galaxies, there is less time for dark matter to interact and drag behind, so the earlier survey results do not necessarily contradict the newer one.

Meanwhile, back on earth, searches for dark sector particles in underground detectors continue to come up empty, and dark matter has so far failed to appear in CERN’s Large Hadron Collider. In fact, proposed candidates are being rapidly excluded. Over 40 years now many major experiments have looked for evidence of the dark sector and none has been found.

Conclusion

Could it be that all we observe with light and other forms of radiation is all there is? The Universe did not evolve out of a big bang and as a result the model which attempts to describe the expansion needs fudge factors to get it to fit observations. Now, one more fudge factor is proposed—dark photons from interacting dark matter particles. A new unknown invoked to explain an unknown.15 But they are still all lost in Darkness.

References and Notes

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