Portal: door or gateway.
You’ve probably read more than one fantasy or science fiction story about going through a door into another world or dimension; think of The Lion, the Witch and the Wardrobe or Dr. Who. If you eavesdrop on particle physicists’ chatter these days, you may hear them seriously discussing the possibility that “portals” to a world of dark (or invisible) matter may exist! Not only that they may exist, but they may be discoverable in ongoing or future experiments – otherwise it would not be so exciting. Theoretical physicists think up many new scenarios about the subatomic world, but their ideas must not conflict with existing knowledge and should make testable predictions allowing them to be disproven. They should also explain something mysterious.
Prominent among the many mysteries in physics is dark matter – strictly speaking invisible matter – but the name stuck. The evidence is overwhelming that there is about five times more mass in the universe than we can see in the stars, planets, gas and dust. We know it is there, because it exerts a gravitational force keeping galaxies from flying apart and bending light from more distant galaxies, among other phenomena.
Physicists believe that all matter (and antimatter) is in the form of subatomic particles and know of a dozen that fit in a neat 3 x 4 pattern, called the Standard Model. Particles of dark matter do not fit in that pattern and have not yet shown up in any laboratory experiments. Are they thousands of times more massive than protons, so that even the most powerful Large Hadron Collider cannot make them? Or are they much lighter but interact so weakly with the particles we know that they have escaped detection so far?
The recent “portal” idea is that there are other undiscovered particles that connect known matter and dark matter particles. One possibility is called, weirdly, a “dark photon” connecting our matter world with a sort-of parallel world of dark matter, and those we might discover in the coming years.
Dark matter particles might even interact strongly among themselves, forming invisible lumps or even worlds. Astronomers could discover such invisible worlds through their gravitational effects.
I would not bet on dark – or invisible – planets and living creatures, but it will be difficult to disprove their existence. Science progresses by disproving false notions, but science fiction thrives on them!
