Is dark matter real? Is there an unknown particle that could reshape our thinking of the fabric of the Universe? What is time? What's the extent of the observer’s role in the world we investigate in science?
By rethinking fundamental beliefs in the field of physics, the University of Sydney’s Faculty of Science is shaking up established world views.
At the University of Sydney, astroparticle physicist Professor Celine Boehm is hunting for a particle – or something else – that could change our beliefs in the structure of the Universe.
An expert in dark matter, Professor Boehm says: “The physics we know on Earth is insufficient to explain the observable Universe. The missing piece is likely to spark a conceptual revolution—perhaps as profound as the one initiated by Copernicus,” she says, referring to the shattering revelation in the 16th century that the Earth revolves around the sun, not the other way round.
She describes dark matter as this missing piece.
“Instead of modifying these laws, we assume that the observed anomalies are caused by the presence of an invisible form of matter permeating the Universe. For now, all evidence suggests that every galaxy is embedded in a halo of dark matter, and that this invisible component – which is likely made of particles – fills the Universe and create an invisible structure known as the cosmic web or cosmic skeleton.“
There is a key problem, however – none of the known particles can explain dark matter: they are either visible (having an electrical charge), too light or too short lived.
“Under the ‘particle’ hypothesis, if dark matter exists, it must consist of a new type of particle that has never been detected on Earth. This strongly suggests that the Universe is governed by fundamental laws we have not yet discovered — and that there are physical phenomena yet to be uncovered, potentially even on Earth.”
After witnessing immense progress in instrumental and experimental technologies — yet still seeing no confirmed signs of dark matter particles — I began to explore the possibility that a radical shift in thinking about the Universe might be needed.
“I have been questioning whether dark matter particles were indeed the solution to all the puzzling observations. This has led me to explore new mathematical frameworks and to investigate how methods from theoretical physics might contribute to global progress in artificial intelligence.”
She’s also exploring how emerging technologies like nanotechnology could help detect the extremely faint signals associated with dark matter.
Professor Boehm predicts that a convergence of astronomical observations and particle physics experiments in the next decade will likely reshape the field of dark matter research.
“With the emergence of powerful simulation capabilities and unprecedented observational accuracy, we are, for the first time, within reach of probing realistic dark matter interactions through cosmic observations – a prospect I find extremely exciting.
“These efforts may confirm that dark matter is made of particles or, if they fail to do so, force us to fundamentally rethink the problem and its solution.”
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With the foundations of the Universe being re-examined, it's an exciting time for scientists.
Professor Dean Rickles, Professor of History and Philosophy of Modern Physics, says: “Physics is completely up in the air at the moment. The foundations are really unstable, which is a big opportunity to do very interesting, radical new work.”
Professor Rickles is co-director of the University’s Centre for Time research hub, which brings together physics, psychology and philosophy to answer fundamental questions about time and our relationship with it.
While scientific investigation traditionally removes the observer, Professor Rickles’ recent work indicates that the observer’s influence may be at the centre of everything. This idea was sparked by his previous studies of the history of quantum gravity.
He says physicists have a massive problem that needs to be resolved: there is a clash between our two supposedly fundamental theories, general relativity and quantum mechanics.
While quantum theory views space and time as unmovable, absolute structures, general relativity describes gravity as a dynamical spacetime, which can be curved by mass and energy.
“You can treat time and space as fixed parameters against which particles and fields move around. They just sit in the background and act as a sort of stage for matter. Or, in general relativity, the stage is replaced by an actor and spacetime becomes an active part of the problem you’re examining.
“General relativity works when we're dealing with large objects like black holes; quantum theory works when we're dealing with very small objects like protons and electrons, but we can't bring the two together because they have a clashing view of what reality is.”
Quantum gravity – the attempt to bring together quantum mechanics and Einstein’s view of gravity as spacetime – has so far eluded physicists.
“A quantum theory of gravity would involve a theory of space, time, and matter. But whenever we try to make a consistent theory, we find that space and time disappear in it. However, we know full well that there is such a thing as time because it's the basis of our lives. Our two theories don't work together, so our world view doesn't make any sense whatsoever,” he says.
Settling on a world view isn't a matter of just choosing the most scientific set of facts. There are approaches to science and physics that enhance, rather than diminish, the role of humanity in the world.
Professor Rickles’ work addresses a fundamental question: do we ignore our human experience and focus only on the things that can be measured – the traditional scientific approach – or do we respect the fact that the worldview represents our view of the world, as observers?
He says: “We've been living with a world view that all that scientifically matters is ‘matter’. If you've got that view, you can treat the Earth – and people – as nothing but ‘matter’.
“It's a mistake to think that the science itself pushes us towards a specific world view. There is no objective state of affairs until you've linked it to some question we put to the world that was made subjectively,” he says.
He cites John Wheeler’s Delayed Choice Experiment, which shows that a photon does not exhibit a definite history as a particle or a wave, until a free decision is made about which quantity is measured, position or momentum.
“It shows that the quantum world doesn't know what properties it's going to take until you've decided what experiment you're going to perform. So my recent work has been trying to find scientifically respectable world views that put back the first-person component – which is controversial.”
His latest work at the Centre for Time is exploring the very nature of existence.
He says: “We can never step outside of ourselves to see whether our version of reality is correct. We have no way of knowing absolute reality. The idea is to become okay with that.”
Professor Dean Rickles with model of a Calabi-Yau manifold, used to represent the tiny curled up dimensions in superstring theory.
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LinkFaculty of Science Associate Dean (Research), Professor Kate Jolliffe, says: “Expanding the frontiers of science is one of the key missions for our faculty, and these projects are among the purest type of foundational research we do. Simply uncovering new scientific knowledge is thrilling on its own, and the interconnectedness of scientific disciplines with these projects is also really exciting. The discoveries they make could apply across a really broad section of what we do in our lives.”
Professor Boehm points out that without general relativity, there would be no GPS or electronics, and without the work of particle physicists at CERN, there would be no Internet.
She says: “Historically, every time we have uncovered a new fundamental law, it has led to transformative technologies. It is not just about discoveries themselves, but also about the ways we get there. It is hard to predict how the discovery of dark matter might shape future technology, but its impact is likely to be profound.”
For now, it’s a case of watch this space.
Without the work of particle physicists, the internet and our highly connected lives wouldn’t exist.
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