Archive for January 9, 2018

Crunch time for Dark Matter?

Posted in The Universe and Stuff with tags , , on January 9, 2018 by telescoper

Gratuitous picture of the cluster Abel 2218, showing numerous gravitational lensing arcs

I was reading through an article by Philip Ball in the Grauniad this morning about likely breakthroughs in science for the forthcoming year. One of the topics discussed therein was dark matter. Here’s an excerpt:

It’s been agreed for decades that the universe must contain large amounts of so-called dark matter – about five times as much as all the matter visible as stars, galaxies and dust. This dark matter appears to exert a gravitational tug while not interacting significantly with ordinary matter or light in other ways. But no one has any idea what it consists of. Experiments have been trying to detect it for years, but all have drawn a blank. The situation is becoming grave enough for some researchers to start taking more seriously suggestions that what looks like dark matter is in fact a consequence of something else – such as a new force that modifies the apparent effects of gravity. This year could prove to be crunch time for dark matter: how long do we persist in believing in something when there’s no direct evidence for it?

It’s a good question, though I have to say that there’s very little direct evidence for anything in cosmology: it’s mostly circumstantial, i.e. evidence that relies on an inference to connect it to a conclusion of fact…

Anyway, I thought it would be fun to do a totally unscientific poll of the sort that scientists find  fun to do, so here’s one. It’s actually quite hard to make this the topic of a simple question, because we know that there is ordinary (baryonic) matter that we can’t see, and there is known to be some non-baryonic dark matter in the form of a cosmic neutrino background. What the question below should be interpreted to mean, therefore, is  `is there a dominant component of non-baryonic dark matter in the Universe in the form of some as-yet undiscovered particle?’ or something like that.

For the record, I do think there is dark matter but less convinced that it is simple cold dark matter. On the other hand, I regard its existence as a working hypothesis rather than an article of faith and do not lose any sleep about the possibility of that hypothesis turning out to be wrong!