Atomic clocks on Earth could reveal secrets about dark matter across the universe

(Left) Atomic clocks in use at the NPL (Right) the bullet cluster a collision between two galaxies with a morphology that indicates the presence of dark matter
(Left) Atomic clocks in use at the NPL (Right) the bullet cluster a collision between two galaxies with a morphology that indicates the presence of dark matter (Image credit: X-ray: NASA/CXC/M.Markevitch et al.; Optical: NASA/STScI; Magellan/U.Arizona/D.Clowe et al.; Lensing Map: NASA/STScI; ESO WFI; Magellan/U.Arizona/D.Clowe et al/NPL/University of Sussex)

Scientists are using atomic clocks to investigate some of the universe's greatest mysteries, including the nature of dark matter, in a laboratory. In the process, they say they're bringing cosmology and astrophysics "down to Earth."

The project, which is a collaboration between the University of Sussex and the National Physical Laboratory (NPL) in the U.K., uses the ticks of these incredibly precise clocks to hunt for hitherto unknown ultra-light particles. 

These particles could be connected to dark matter, the mysterious substance that makes up an estimated 85% of all matter in the universe but remains effectively invisible to us because it does not interact with light or, more precisely, electromagnetic radiation. Scientists believe most galaxies are enveloped by a cloud of dark matter, but its presence can only be inferred by the effect it has on gravity.

"Our universe, as we know it, is governed by laws of physics, so gravity is governed by general relativity and particle physics by the Standard Model of particle physics," Xavier Calmet, project leader and a professor of physics at the University of Sussex, told "We call deviations from these laws  'breakdown in physics' — basically, that is a synonym for new physics beyond our current understanding of the universe."

Related: We still don't know what dark matter is, but here's what it's not

This new physics could be used to explain the nature of dark matter, something that doesn't fit within the Standard Model.

"One of the biggest mysteries is the nature of dark matter. We know that it is out there, we see its impact in our universe, but we don't have a valid explanation within the Standard Model of particle physics," Calmet continued. "There must be new physics, but we do not know how to describe these new particles and how they couple to regular matter."

How can "new physics" be spotted with atomic clocks?

According to established laws of physics, clocks should tick at a constant rate, but physics beyond the Standard Model's scope would result in tiny charges in atomic energy levels. This should affect the rate at which clocks tick, but the variation would be so small it could only be spotted with an incredibly precise clock — and that's where atomic clocks come in. 

"Atomic clocks bring cosmology and astrophysics down to Earth, enabling searches for ultra-light particles that could explain dark matter in a laboratory," Calmet said.

Atomic clocks measure time using atoms with two potential energy states. When atoms absorb energy, they go to a higher energy state. Then, they eventually release this energy and drop back down to their lower ground state. 

In atomic clocks, groups of atoms are prepared by placing them in a higher energy state using microwave energy, and the characteristic and consistent rates at which they vibrate between states — their resonance frequencies — are used to precisely measure time.

So, for example, all atoms of cesium resonate at the same frequency, meaning the standard measure of a second can be defined as 9,192,631,770 cycles of cesium. Because this cycling per second occurs with far less variation than, say, the swinging of a pendulum, this makes atomic clocks incredibly precise.

"It has been recently realized that dark matter could be made of ultra-light particles that interact extremely weakly with regular matter," Calmet explained. "If that is the case, dark matter would essentially behave as a classical wave that interacts with electrons and protons. This dark matter wave would give some small kicks to these particles."

Calmet added that these ultra-light dark matter particle kicks to the building blocks of the atom would lead to a time variation in fundamental constants of the universe, such as the fine-structure constant or "alpha" — a measure of how strong particles couple via the electromagnetic force — and the mass of the proton. 

"Because atomic clocks are amazingly precise devices, they would be able to detect these kicks and thus discover ultra-light dark matter," he continued. "By comparing two clocks, one sensitive to changes in alpha and the other one less sensitive to changes in alpha, we can obtain a limit on the time variation of this fundamental constant and thus set constraints on ultra-light particles."

Calmet thinks the technique could potentially also be used to investigate another problematic aspect of the universe for physicists: Dark energy, the unknown force that is driving the accelerating expansion of space.

While Calmet acknowledges that dark energy is more likely explained by the cosmological constant, a form of energy that acts almost in opposition to gravity to stretch the fabric of space and push apart galaxies, there is a small chance it could be connected to an ultra-light particle. In this vein, future clocks could also be sensitive to that particle and its associated wave.

"While the clocks have not discovered new physics at this stage, we were able to develop a new theoretical framework to probe generic new physics with clocks and were able to derive the first model-independent limits on physics beyond the standard model within this approach," Calmet concluded. "We are creating a new field at the interface of atomic, molecular, and optical physics and traditional particle physics. 

"These are exciting results!"

These results are set to be published in a future edition of the New Journal of Physics.

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Robert Lea
Senior Writer

Robert Lea is a science journalist in the U.K. whose articles have been published in Physics World, New Scientist, Astronomy Magazine, All About Space, Newsweek and ZME Science. He also writes about science communication for Elsevier and the European Journal of Physics. Rob holds a bachelor of science degree in physics and astronomy from the U.K.’s Open University. Follow him on Twitter @sciencef1rst.

  • Questioner
    Admin said:
    Using atomic clocks could help bring cosmology and astrophysics "down to Earth" by allowing scientists to investigate the mystery of dark matter in the lab.

    Atomic clocks on Earth could reveal secrets about dark matter across the universe : Read more

    What one 'sees' is almost certainly gravity, space-time curvature.
    What one doesn't see is some ridiculous form of matter that would defy the known laws of physics as well as logical sense.
    How many hundreds of billions of dollars have been squandered on something that a bit of sound reasoning exposes as fallacy?
    Humanity is comprised largely of dimwits,
    Including academics who imagine they own intelligence.
    Intelligence is a never ending working process that has no location in space-time including the skulls of presumptive sociopath academics.

    'Dark matter' is probably Wrong.
  • Classical Motion
    I discern it a little differently. I don't believe man can make a stable clock. I don't think a stable clock can be made from an oscillatory dynamic. The only stable ticker available is a rotation, not an oscillation. Our most sensitive sensors are oscillatory sensors because they are the most sensitive to external stimuli. We measure gravity, acceleration and orientation with oscillatory sensors. And unfortunately, we also measure time with atomic oscillations. Bad juju. Just asking for trouble.

    A stable clock will not change with a change in elevation. Or gravity....or acceleration. The simplest clock is a rotating shaft. A rotating shaft has the same time all along the shaft. No matter the angle, gravity or acceleration.

    Dark's not necessary yet. We can not measure the velocity of stars. Stars do not orbit in ellipses. As stars orbit, they spin. Stars are in helical orbits. And without knowing the radius of that spin, the length of the orbit remains un-known. Thus the velocity remains un-known. We can not measure this Z motion.

    These helical orbits give the galaxy a wavy structure when viewed from the edge. This can give you an idea of that extra un-considered motion. They also spin as they orbit. That's more un-accounted length.

    It would be very mis-leading to compare our solar system with a galaxy. The distribution of mass and gravity is much different. Solar systems have point gravity ratios, galaxies have shell gravity ratios. Star spins can vary greatly with radial position.

    But even if one could measure this and get the correct would still have great problems. Because gravity is not caused by "spacetime". Space and time are not physical. They do not have properties that can be varied. Only the properties of a physical entity can be varied.

    Like light. All star light has a different velocity. We just don't know how to measure it. All we can measure is a self made reflection. A false measurement. And then base a whole science on it. Silly science.

    But my discernments have always been contrary.