One of those big open questions that we have in physics goes like this.
Einstein’s theory of General Relativity is elegant and accurate. It makes many correct predictions, including the prediction of gravitational waves, the observation of which won the Nobel Prize in physics today. Yet if we use General Relativity to predict the motion of galaxies, we get the wrong answer.
The favoured response to this is to invent a new form of so-called ‘dark’ matter. Adding the right amount of this to the visible matter in the galaxies brings theory and observation into agreement. But this is not just a minor correction – there needs to be much more of the dark matter around than normal matter.
What is more, dark matter doesn’t seem to be made up of quarks and electrons like all other matter. In fact it doesn’t seem to be made up of any of the particles in the Standard Model of particle physics.
So that’s the big question.
To answer it, theorists postulate new extensions to the Standard Model, containing new particles, from which dark matter might be made. We are actively searching for such things, at the Large Hadron Collider at CERN and using sensitive underground detectors.
But there may be another way.
Perhaps General Relativity can be modified instead, to give a new theory, in which the motions of galaxies, and the structure of the universe, are correctly predicted, without the need for dark matter. Maybe even the accelerating expansion of the universe, another current conundrum of physics, can be explained in such a theory.
A candidate for such a theory will be the topic of the first Perimeter Lecture of this season, on 4 October, from Erik Verlinde; the live link is above.
Perhaps dark matter is a mythical beast, a figment of our ignorance which will evaporate as we explore nature more thoroughly. We shall see.
A recording will replace the live link soon after broadcast.
Jon Butterworth’s book A Map of the Invisible: Journeys into Particle Physics is released on 5 Oct 2017.
