“As we enter the second half of the 2020s, it is an incredibly exciting time for dark matter research…”
SAKKMESTERKE/SCIENCE PHOTO LIBRARY
Now is a surreal time to be a dark matter researcher. Even as research funding is being cut by governments around the world, dark matter remains one of the biggest and most exciting open problems in all of physics – in all of science, frankly. Most of the matter in the universe appears to be invisible: for every kilogram of visible matter, there are apparently 5 kilograms of dark matter. We know this only because we have seen the impact of dark matter on how the visible elements of the universe are structured.
Clusters of galaxies are best explained when dark matter is a presumed component. Observations of the distribution of the earliest free-flying light in the universe only match our theoretical predictions if dark matter is part of the model. A host of other observations confirm the same: there is a lot of dark matter, invisible to us unless we look for how it shapes visible matter.
As we enter the second half of the 2020s, it is an incredibly exciting time for dark matter research. The European Space Agency’s Euclid space telescope’s work will lead to a better understanding of galaxy structure. In tandem, the Vera C. Rubin Observatory is just beginning a 10-year survey of the sky, and it will almost certainly transform our knowledge of the satellite galaxies that live in the orbit of larger companions. These dynamics will help us map out how dark matter governs visible matter in more detail.
To study something that we know is out there but we can’t see directly is to push the boundaries of our creativity as scientists. Among the questions we have to ask and try to creatively answer are: How shall we look for it? Can we capture a dark matter particle in the lab? How do we study its properties if we can’t?
The only way out is through. We have to start with what we do know and try to grow our knowledge from there. We are fairly confident that dark matter is matter-like, suggesting we can use the same mathematical tools to study it that we use to study ordinary particles, such as quantum field theory (QFT).
“
Increasingly, we are now looking for evidence of dark matter scattering off electrons, not just hitting a target
“
QFT sounds complicated – and it is – but a non-expert can still get a feel for it. It is perhaps our most fundamental theory of physics, since it combines special relativity and quantum mechanics (but not general relativity). The idea behind it is that throughout the universe, the potential for a particle to be created exists at each point, due to the presence of a field associated with that particle type.
Think about strawberry fields. The strawberries only manifest in some places, not others. This is due to the specific properties of those points in space-time – they are the places where the right conditions exist for a strawberry flower to blossom. The potential for strawberries is everywhere in a strawberry field, but only in some places will they actually come to be. In a loosely similar fashion, this is how QFT tells us particles come into existence.
QFT is a tough subject that even experts spend many years really developing a feel for. And even if we think it is sensible to apply QFT to dark matter in order to make some smart guesses about it, there comes the question of how we could write down equations to describe something whose properties mostly elude us.
From a sociological standpoint, it is quite fun to see the myriad ways scientists have responded to this question. Over the past decade or so, one popular approach to characterising things we don’t know is to develop an “effective field theory” (EFT). EFTs are a neat way of writing down a generalised set of equations with characteristics that can be tuned depending on observations.
EFTs can also be developed with a particular experimental framework in mind. For example, one important way we attempt to understand dark matter is through direct detection experiments. With these, we hope that some kind of interaction between dark matter and visible matter will yield an effect that is observable in a terrestrial experiment. Over the years, direct detection approaches have matured and multiplied. Instead of just looking for evidence of dark matter hitting a target, increasingly we are now looking for signs of dark matter scattering off electrons. This experimental shift means EFTs must evolve alongside it.
In a preprint paper published this month, researchers Pierce Giffin, Benjamin Lillard, Pankaj Munbodh and Tien-Tien Yu propose an EFT that can better account for these scattering interactions. While the paper has yet to go through peer review, it caught my attention because it is a great example of work that might never be front-page news, but nonetheless is exactly the sort of thing that drives research forward. Science requires patience, and I hope our leaders remember that.
Chanda Prescod-Weinstein is an associate professor of physics and astronomy at the University of New Hampshire. She is the author of The Disordered Cosmos and the forthcoming book The Edge of Space-Time: Particles, poetry, and the cosmic dream boogie
What I’m reading
I have just finished Addie E. Citchens’s astonishing debut novel, Dominion.
What I’m watching
I recently caught up on the summer episodes of Emmerdale and HOLY SMOKES!
What I’m working on
My collaborators and I have some fun new research ideas about dark matter scenarios.
Topics:
- dark matter/
- space
