New Zealand Scientists Find Cheaper Faster Way to Measure Gravity

The method to determine an official kilogram is getting an update. Researchers in New Zealand come up with a new way of measuring gravity which could be used in determining the new standard for the kilogram.
Jessica Miley

How do we know exactly how heavy a kilogram is? Weight is measured using official kilograms and calibrated scales, all of which are measured against the single official kilogram which lives in France.

But a scientist in New Zealand is questioning this method of accuracy. 

What if the official weight deteriorates? Or accumulates deposits on its surface? Slight differences in kilogram weight across the world could have serious impacts in pharmaceutical or engineering applications. 

Method of defining kilogram to change

If Dr. Mikkel F. Andersen, of the University of Otago’s Department of Physics, has his way the world will soon away from the artifact definition of a kilogram. “The kilogram is going to change, come May next year it won’t be that one in France,” he says. 

The new way to define a kilogram will be by choosing an exact value of Planck’s constant, a quantity that relates weight to electrical current. To do this there needs to be an ‘accurate measure of the gravitational pull at the precise spot future calibration weights are being measured.’ 

A cheaper and faster way to measure gravity

Portable devices capable of accurately measuring gravity are called gravimeters, but they are large and expensive. New Zealand doesn't have one, the closest is in Australia. 

“However, if there is only one type of device in the world that can measure gravity, what happens if that device is off for some reason?

Then all the scales in the world will be off. It is important to have a variety of devices capable of measuring gravity. My goal was to make a smaller, more compact device, which was also easier and cheaper to build,” Dr. Andersen says.

Dr. Anderson is in collaboration with Ph.D. candidate Shijie Chai and Postdoctoral Fellow Dr. Julia Fekete have created such a device using simple laser technology, and ideas from the arcane theories of quantum chaos. The research has been described in the journal Physical Review A.

A new device has commercial application

“We have shown the principle works and believe it could be as precise as others currently available,” Dr. Andersen says.

“The device drops a cloud of atoms, then makes interference patterns in those atoms to allow an accurate measurement to be taken with a laser. The speed of light and measure of time are clearly defined so there is no guesswork in those elements of the device.” 

Gravimeters are currently used extensively in geological surveys to find out what rocks are below the ground’s surface, a method cheaper than digging.

Archaeologists also use them to identify buried bones. Commercially they are used to locate possible sites for mineral exploration as oil is lighter than rock. 

Dr. Andersen says there has already been interest in the project from possible commercial partners.

The team will now work to secure funding for the next stage of research, they hope to decrease the model's size and increase the length of the atmos drop which will increase with devices overall accuracy. 

You can read the full journal article in Physical review here.

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