Physics

Are there extra dimensions lurking at the quantum scale?

Are there extra dimensions lur...
Japanese researchers have probed gravity on the subnanometer level, in the search for extra dimensions
Japanese researchers have probed gravity on the subnanometer level, in the search for extra dimensions
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A diagram explaining how the neutron beam experiment works
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A diagram explaining how the neutron beam experiment works
Japanese researchers have probed gravity on the subnanometer level, in the search for extra dimensions
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Japanese researchers have probed gravity on the subnanometer level, in the search for extra dimensions

Our universe has three spatial dimensions – or rather, three that our human senses can actively perceive. Some theories suggest there could be many more dimensions that we're unaware of, mostly because they're imperceptibly tiny. Now, Japanese researchers have taken the search for extra dimensions down to the nanoscale, using a neutron beam to study the gravitational force more precisely than ever before.

According to the Standard Model of particle physics, the world is governed by four fundamental forces: gravity, electromagnetism, and the weak and strong nuclear forces. Although things act a bit "spooky" down on the quantum level, science has managed to generally describe all of these forces at both the macro and quantum scales – except gravity.

Newton's law of universal gravitation says that the gravitational force between two objects gets stronger as objects get more massive, and weaker the further apart those objects get. But it's only really been shown experimentally down to the submillimeter scale, which is still "macro". According to some theories of quantum gravity, on smaller levels that law might break down.

Gravity is the weakest of the fundamental forces, and it's been suggested that this is because some gravitons – the hypothetical particles that carry the gravitational force – tend to escape into extra dimensions. While we're not sure there are any more than the three spatial dimensions we're used to, M-theory (one of the current leading candidates for a theory of everything) takes place across 11 dimensions.

If it's hard to picture where these other dimensions are hiding, Professor Matt Strassler uses the excellent analogy of vessels on a canal. A submarine could move through the canal in three dimensions, but a small boat on the surface is restricted to two – it can't move up and down. Meanwhile a large ship would experience the canal as one-dimensional, since it can only move forwards or backwards. In this analogy, we humans are that ship – we're simply too big to travel through or even notice these other dimensions.

So, to study whether these extra dimensions are lurking in extremely tiny spaces, the researchers from Osaka, Kyushu and Nagoya Universities set out to test gravity on the subnanometer scale. To do so, they used the world's highest intensity neutron beam, which is housed at the Japan Proton Accelerator Research Complex (J-PARC).

A diagram explaining how the neutron beam experiment works
A diagram explaining how the neutron beam experiment works

The experiments involved firing pulses of neutrons into a chamber filled with either xenon or helium gas, and monitoring how long the neutrons took to move through the chamber, as well as their scattering angles. Because the neutrons have no charge, they're not affected by the electromagnetic background that may interfere with similar experiments.

The team found that the results matched predictions based on the known laws of physics, which indicates that Newton's law still applies as expected down to a scale of less than 0.1 nanometers. No unexplained force – ie, another dimension – is acting on these particles at this scale.

That doesn't mean those extra dimensions aren't there, just that they may be hiding at even smaller scales still. The researchers are currently working to further improve the sensitivity of the equipment, which might help them probe those tiny spaces.

"As the performance of the world's most powerful beamlines improves, we are able to significantly enhance our knowledge and understanding in step," says Tamaki Yoshioka, corresponding author of the study. "Such iterative improvements can be very revealing. In the case of gravitational interactions we have made substantial steps towards understanding the dimensions of the space around us."

The research was published in the journal Physical Review D.

Source: Osaka University, APS Physics

9 comments
Gene Preston
Sometimes extra dimensions are an indication we may not know the relationship between lower dimension quantities. Its a sort of workaround like renormalization, a math trick. At least that's my opinion. There might be a relationship between charge and gravity potential for example which is unknown at this time.
EZ
I prefer the "theory" that there is no gravity force at all. That it's all electromagnetism. Ever since I saw a craft the shape of a small river barge (30'X10" approx.) floating by my house one night. 10mph, roughly, no wings, no sound but lots of color in the windows. Believe it or not. Makes no difference to me.
b@man
This is backward. Gravity is BY FAAAAAAR the most powerful force in the universe and nothing else even comes close... AT ITs WAVELENGTH... which is 50 billion to 50 trillion light years in wavelength. The particle is not small, it is so big you can't imagine it. Big bang stands in the way of progress. The was no beginning and the universe is an infinitely large, isolated system, in regards to conservation of energy. You scientists need to get your noses off the billboard if you want to read it:) Infinite Wave Theory... simple, perfect
BrianK56
It may be that other dimensions are not at the atomic level. They may be right in front of us but we are unable to see or connect with them. AI might be able to figure this out over time.
Brian H
A neutron has 2 charges: it consists of an electron imbedded in a proton.
MarcUrruela
I like hugs...
BanisterJH
The creation of micro scale black holes will greatly advance investigations into the nature of gravitation at the quantum level. I only hope the work on creating them is done in a different orbit around the sun.
mike085
BrianH A neutron is NOT an electron combined with a proton. A neutron is composed of 1 up quark (+2/3 charge) and 2 down quarks (-1/3 charge), for a net neutral charge. A proton is 2 up quarks and 1 down quark (net +1 charge). An electron is not involved at all.
ricdesouza
i have an interesting thought experiment.... Three people at a table with a delicious 100 gm cake in the middle. Each person gets an equal share of this cake. No matter how hard they try to divide this equally- there is always a small residue of that delicious cake left behind in the plate. This residue is miniscule- possibly quantum and yet unattainable if dividing equally amongst 3 people- So, where is that core of this cake residing??