Are Diamonds A Cosmologist’s New Best Friend?

Back in the 1930s, cosmologists thought they were beginning to get the universe all figured out. Thanks to Einstein and others, they understood how space and time were related. Einstein had also worked out how gravity works in his General Relativity. Astronomers had telescopes that let them see faraway galaxies. Scientists knew that the universe was expanding in all directions thank to Edwin Hubble.

Then, a problem arose in 1933. Astronomer Fritz Zwicky was studying the Coma Galaxy Cluster. He was able to calculate the gravitational force necessary to hold that cluster together. He was also able to measure the mass of everything that he could see in that cluster. The trouble was, they didn’t come close to adding up. The mass that Zwicky could account for in the cluster was less than 1% of the mass needed to cause the gravity that he observed. He called this problem the “missing mass”.

Nobody managed to explain this discrepancy between mass and gravity in the universe for another forty years. Astronomers Vera Rubin and W. Kent Ford confirmed Zwicky’s conclusion. They calculated that the visible mass of a typical galaxy is less than 10% of the mass needed to hold the stars orbiting around its centre in place. They reasoned that there had to be some unseen inner mass in each galaxy that caused the orbital behaviour of the stars. If some sort of mass wasn’t there, the galaxies would fly apart, and yet they don’t. Since this hidden mass gives off no light, it can’t be observed with a telescope. That’s why they coined the term “dark matter” to describe it.

Most Dare to Know readers will know something about how gravity bends and distorts light. Astronomers have used this phenomenon to confirm that galaxies are much more massive than their visible stars can account for. Scientists have also detected this wide discrepancy between a galaxy’s mass and its visible matter using X-ray telescopes. In all these cases, far more mass is out there than anyone can account for.

The remarkable thing is that, based on these findings, everything we can see makes up a mere 4% of the universe. Forms of matter and energy that scientists don’t yet understand make up the other 96% of what’s out there. Even so, they can surmise certain characteristics of dark matter.

Dark matter must consist of heavy, slow moving particles to add so much mass. Since they don’t give off light, these particles mustn’t have an electromagnetic charge. Physicists have called them “Weakly Interacting Massive Particles” or WIMPs for short.

Why did I mention diamonds in the title of this post? It’s because a group of scientists are proposing a new way to look for dark matter. In this week’s issue of Physical Review D, Noah Kurinsky, To Chin Yu, Yonit Hochberg, and Blas Cabrera propose using high-purity lab-grown diamond crystals to detect particles of dark matter. They argue that, since nobody has succeeded in tracking down these theoretical WIMPs, it’s time to try another approach.

They believe that dark matter can be detected by looking for particles that are lighter than WIMPs. In spite of making better and better detectors, scientists have not found anything in the heavier range that resembles a WIMP. They propose that we redirect the search to lighter particles and use diamonds to detect them.

Diamonds are better for this work because they have a light, carbon nucleus. If a particle of dark matter collides with this nucleus, the resulting vibrations are easy to detect. Diamonds are also unusually pure. They form from a single carbon isotope. Diamonds can hold large electric fields and have low electrical impurity. Along with all these advantages, it isn’t hard to replace the types of crystals used in existing detectors with diamonds.

Can we afford to use diamonds for this application? The proponents say “yes”. The electronics and quantum computing industries need diamonds too. We have better and cheaper ways to make synthetic diamonds.

The diamond business is a virtual monopoly. Diamond producers don’t like the idea of producing cheap, high quality synthetic diamonds. They are afraid that this will make natural diamonds obsolete. Even so, we haven’t seen other precious gems lose their value. Consumers are still willing to pay a premium for genuine, natural gems in their jewelry.

If we could find a way to detect particles of dark matter, it would be a profound discovery. Those of us who love learning about the cosmos would be thrilled to see this mystery solved. Humanity can’t claim to understand gravity, or the true nature of our universe, without explaining what’s going on with Zwicky’s “missing matter”.

In his novel The Age of Reason, Sartre wrote “”This moment. It is round, it hangs in empty space like a little diamond; I am eternal.” Discovering dark matter will be that kind of moment. It may be that diamonds will lead us there.

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