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Scientists Can Now Measure Gravity More Accurately Than Ever Before

We want to know.

DAVID NIELD
28 DEC 2016
 

A new way of measuring gravity is giving scientists more precision than ever before, and could help answer some of the fundamental questions of physics at the same time.

Gravity is one of the four fundamental forces of nature, and quite literally holds the Universe together. But despite how crucial it is, there's still a lot we don't understand about how gravity works.

 

There's so much more gravity than we can account for that researchers have had to come up with dark matter to explain it all.

And there are still inconsistencies when it comes to the Standard Model - the best set of equations we currently have to explain how the Universe works. In fact, despite how ubiquitous gravity is, a recent hypothesis suggests that it might be nothing more than an illusion.

One of the main problem is that it's incredibly hard to measure gravity in accurate detail, so it's hard to tell if the anomalies researchers see in the data are just measurement errors, or real inconsistencies in space.

Which is why this new study is so important, because if we can finally measure gravity in more detail, we might be a lot closer to answering some of the biggest mysteries in physics.

The new technique uses a process called atom interferometry, where differences in the wave phases of atoms are measured in order to work out the strength of the forces pulling on them – forces such as gravity, acceleration, and rotation.

Atom interferometry itself isn't new, but a team from the Massachusetts Institute of Technology (MIT) has come up with a new variation on the idea, one which cuts out some of the errors in existing designs.

 

"[The solution] is very elegant and very clever," says physicist Dominik Schneble, from Stony Brook University, who wasn't directly involved in the research. "It fits the situation like a natural glove."

The most sensitive, modern atom interferometers use states of matter called Bose-Einstein condensates (BECs), which are clusters of atoms cooled to absolute zero.

When laser light is shined through these BECs, the atoms are trapped in place. By measuring the trapped positions against the untrapped positions, scientists can figure out the strength of the external forces working on them.

There's one problem with this, though: the laser light splits the atoms up into groups that aren't precisely equal, which can introduce errors.

To fix this, the researchers from MIT used two condensates with different magnetic alignments, subjecting them to both a laser light and a magnetic field.

The magnetic charges mean some of the atoms naturally shuffle themselves out evenly across the wave of laser light, giving scientists groups of atoms that are exactly equal, and gravity readings that are more accurate as a result.

What's more, the technique of containing one BEC inside another – which the researchers are calling superfluid shielding – means the atoms can be measured for longer, which also makes the technique more accurate.

Then there's the quantum physics aspect. When you cool BECs to absolute zero, the groups of atoms all occupy the same quantum state, which means they can be described in terms of waves as well as particles.

Effectively, they become a group of atoms that acts like a bigger, single atom.

That's important, because BECs are larger than most forms of matter where quantum effects can be observed, and they could help bridge the gap between quantum physics (which works at very small scales) and Newtonian physics (which works at larger ones).

"The idea here is that Bose-Einstein condensates are actually pretty big," says one of the research team, William Burton.

"We know that very small things act quantum, but then big things like you and me don't act very quantum. So we can see how far apart we can stretch a quantum system and still have it act coherently when we bring it back together. It's an interesting question."

While it's too early to say how superfluid shielding could teach us more about the laws of quantum physics, in the meantime we have access to atom interferometers that are more accurate than ever.

And we're definitely big fans of anything that helps us understand more about our Universe.

The research has been published in Physical Review Letters.

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