Halloween is approaching, and the Scots have a rhyme:

From ghoulies and ghosties

And long-leggedy beasties

And things that go bump in the night,

Good Lord, deliver us!

There are many things that go bump in the night.

This time of year, it could be those ghoulies and ghosties, goblins, wandering witches, vampires or demons. Mythic creatures are expected to be moving about during this holiday season and hopefully leaving your door with treats instead of tricks.

However, there are other dark forces that fill the night (and the day) out in the wildness of space; ones that are perhaps more of a mystery than those seasonal beings and which will persist after all your holiday candy is gone.

Dark matter and its sister, dark energy, go bump in the universe. These forces are difficult to describe. French physicist Christophe Galfard explains, “Even today...we still don’t have a clue what this dark matter is made of. We know it exists. We know where it is. We have maps of its presence within and around galaxies throughout the universe. We even have stringent constraints on what it is not, but we have no clue what it is. And yes, its presence is overwhelming: for every one kilogram of ordinary matter made out of neutrons and protons and electrons, there are five kilograms of dark matter, made out of who-knows-what.”

To bring light to the darkness of the galaxy and illuminate the confusion over dark matter comes Dark Matter Day, described as a “globally-recognized celebration of a cosmic riddle” and a “historic hunt for the unseen.” Interactions Collaboration, an international community of particle physics laboratories that seeks to shed light on these dark mysteries of the universe and engage people in their understanding, sponsors this Oct. 31 event, which coincides with Halloween.

It is easier to describe what dark matter isn’t. It isn’t black holes and it isn’t even regular baryonic matter (mat

ter composed of the familiar protons, neutrons, and electrons). It isn’t anti-matter, nor is it ordinary matter (like that which makes the stars or planets) and it doesn’t emit light or energy. What can be said about dark matter is that it mathematically must exist, or else much of space would fall apart, so to speak. We know dark matter is present because, without it, galaxies would unravel and fling matter into space. It manifests itself through its gravitational effects and has been described as the glue that keeps the universe together.

The ordinary matter that we can observe and test makes up only five per cent of the total mass and energy of the universe. The rest is hypothesized to be dark matter (26.8 per cent) and dark energy (68.3 per cent). If this sounds confusing to you, you are not alone. American science journalist William J. Broad agrees: “A cosmic mystery of immense proportions, once seemingly on the verge of solution, has deepened and left astronomers and astrophysicists more baffled than ever. The crux...is that the vast majority of the mass of the universe seems to be missing.”

Missing? Some research suggests that the missing (dark) matter might result from weakly interacting massive particles (WIMPs) or from Massive Compact Hollow Objects (MACHOs) — one may be forgiven for suspecting that physicists are having a little fun with their nomenclature. Perhaps, also, axions, hypothetical elementary particles, might begin to explain this phenomenon.

Scientists accept that — in regard to dark matter — there is more unknown than known but Dark Matter Day is an attempt to put research front and center and highlight the work that might provide answers. Across the country and the world, there are podcasts, events and activities to bring dark matter to the attention of more people.

If all of these dim discussions have you curious, then Dark Matter Day will have done its job. We should be thankful for those curious particles bumping around the cosmos and, even if we don’t understand their origins or characteristics, we know it would be wrong to say their presence doesn’t matter.

Suzan Bellincampi is director of the Felix Neck Wildlife Sanctuary in Edgartown, and author of Martha’s Vineyard: A Field Guide to Island Nature.