Physics

Proposed dark matter detector watches a billion tiny pendulums swing

Proposed dark matter detector ...
An illustration of how the new dark matter detector would work. Left: a pendulum is dragged towards a passing dark matter particle. Right: An array of these pendulums would highlight when a particle passes through
An illustration of how the new dark matter detector would work. Left: a pendulum is dragged towards a passing dark matter particle. Right: An array of these pendulums would highlight when a particle passes through
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An illustration of how the new dark matter detector would work. Left: a pendulum is dragged towards a passing dark matter particle. Right: An array of these pendulums would highlight when a particle passes through
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An illustration of how the new dark matter detector would work. Left: a pendulum is dragged towards a passing dark matter particle. Right: An array of these pendulums would highlight when a particle passes through

Despite hunting for it for decades, scientists have so far been unable to detect any definitive signs of dark matter. But a new detector design, using an array of billions of tiny pendulums, could finally break the silence by searching for the effects of dark matter’s incredibly strong gravitational pull.

Mass and gravity are inextricably linked. The more mass an object has, the stronger its gravitational pull. That’s how we know that dark matter exists in the first place – decades of astronomical observations indicate that there isn’t enough visible mass to account for the gravitational effects we can see. Some other invisible substance must be outnumbering ordinary matter by a ratio of five to one.

Since it doesn’t emit, reflect or interact with light in any way, dark matter has unsurprisingly eluded direct detection so far, but it’s not from a lack of trying. One of the main methods of searching involves a huge tank full of a detector fluid, such as xenon, superfluid helium or supercooled water, and waiting for a reaction that could only mean a dark matter particle has bumped into an atom in the tank.

Other experiments focus on detecting disturbances to electricity and magnetism, which are predicted to be side effects of hypothetical particles called axions. The problem is, these systems rely on presumptions about other properties of dark matter particles. Instead, the new detector design focuses on the one thing we do know about dark matter – its strong gravitational influence.

In the new proposed experiment, a billion tiny pendulums would be suspended in a cubic space some 10 m (32.8 ft) long, with their movement tracked by lasers. The principle sounds simple – if a dark matter particle happens to whiz through the instrument, its mass should briefly pull the nearest pendulums towards it.

Environmental “noise” would make the pendulums wobble around constantly, but a dark matter signal would stand out. Since one of these particles would pass right through unimpeded, you’d see a row of pendulums suddenly disturbed one after the other. Studying how much force a passing particle imparts on each pendulum could also reveal details about dark matter, including the particle’s speed and direction.

The team says this method is promising because it doesn’t rely on dark matter having other properties – only the gravitational influence that’s already known about it. The only unknown factor would be its mass, and this instrument would be sensitive to particles with a wide range of masses, from around one 5,000th of a milligram to a few miligrams. That’s much heavier than the usual range hunted for in experiments.

“Our proposal relies purely on the gravitational coupling, the only coupling we know for sure that exists between dark matter and ordinary luminous matter,” says Daniel Carney, co-author of the study. “if someone builds the experiment we suggest, they either find dark matter or rule out all dark matter candidates over a wide range of possible masses.”

Until somebody does implement the design, the idea remains purely conceptual – but intriguing, nonetheless.

The research was published in the journal Physical Review D. The team describes the concept in the video below.

Measuring the mass of dark matter

Source: NIST

10 comments
Mevlja Pascal
It can’t work, black matter isn’t just on one side of the pendulum to be able to attract it, but all around
WONKY KLERKY
From yours:
(The proposed apparatus will be)
'sensitive to particles with a wide range of masses, from around one 5,000th of a milligram to a few miligrams.
That’s much heavier than the usual range hunted for in experiments'

A Q from the floor:
Just wot sub-atomic / even atomic range particles have a mass of
'a few miligrams'
or indeed
'around one 5,000th of a milligram'

Confused of Manc-shire, UK.
PS.
Please don't tell me Father Christmas doesn't exist.
paul314
Back of the envelope say 1/5000 of a milligam is about 10^26 electronvolts (the usual measure of energy in subatomic stuff). The heaviest particles people usually talk about are around 100 gigaelectronvolts (aka 10^11), so the difference is a mere factor of a quadrillion.
piperTom
Asserted that dark matter "doesn’t emit, reflect or interact with light in any way". That's too absolute. The one OTHER thing we know about dark matter is that it clusters. It's not uniformly distributed in the universe, but rather in clusters corresponding to visible galaxies. The only way for it to cluster is through collisions that lose energy. It may emit SELDOM, but not never.
Username
One other thing we don't know about dark matter: That it actually exists. There are several models that explain what is observed without the need to invent a substance. Modified Newtonian dynamics (MOND) being one of them. The real problem is , because of our very limited point of view, that most of what we think we see is not what is actually going on. If the pendulums swing it won't confirm the existence of dark matter it will only indicate that something made them swing.
bwana4swahili
Another waste of research $$$'s! Just go with the KISS principle, i.e.: gravity isn't a constant!
WONKY KLERKY
An Addendum to my first on this:
Should really have included my back of fag-packet calc' as / paul314 did
(Count done proper - I took me socks off as well as using me fingers and did a back check on me best slide rule).
The conclusion was the question reached noted in my first -
ie. Just wot is going on here?
and does now remind me of the tale of
(for those of you without a classical education):

'There was young fellow named Bright,
Who traveled much faster than light,
He set off one day, in a relative way,
And came back the previous night.'

Put other:
As Paddy said when he ordered a Pint of Plain and was given Guiness:
'Oi tink we're into something else here'
ie. The 'other dimensional' conceptual arguments and 'inter-dimensional' conceptual arguments need to be brought in.

And/so, me doth predict, at the very least, this thread is going run for a bit!
Here we go, here we go, here we go - etc!
ColinChambers
Gravitation is property with atoms... A structure exists that interacts with galaxies external periphery, this power is from sunlight -neutrinos.... this has one-seventh pi order @negative mass . That’s ‘two’ considerations that should have not been missed. Jacktar.
Heckler
The graphic does not do the 10 m pendulums justice. Am I looking at masses belonging to simple pendulums, or is this more like a lattice cube of masses belonging to complex pendulums?
neutrino23
It seems unlikely that individual particles of dark matter, if they exist, are this heavy. However, since we know nothing about this stuff, it may be that they clump together as normal matter does so there may be heavier lumps of this stuff. Regardless, it sounds like an interesting experiment. It seems like every time we look at the universe with a new kind of instrument we find something new.