Huge masses and astronomical length scales are typically needed to study how gravity influences light propagation but researchers from Friedrich-Alexander-Universität Erlangen-Nürnberg and Friedrich Schiller University Jena in Germany showed that there is another method that doesn't involve those data.

Examining the effect of gravity on the propagation of light can also be done by looking at surface curvature, allowing astronomical questions to be answered in the lab.

In a study published in the journal Nature Photonics, Ulf Peschel and colleagues detailed how they used a special trick to assess light propagation in curved spaces, reducing the four dimensions of spacetime to two (there are four, according to the general theory of relativity by Albert Einstein) to focus on curved surfaces.

However, not all surface curvatures are the same. Vincent Schultheiss, the study's lead author, explained that while it is easy to unfold cylinders or cones into flat sheets of paper, it would be impossible to do so with a sphere without having to distort some parts of it. World maps are great examples of this problem as they always show distorted surfaces.

To examine the effects of intrinsic space curvature on light propagation, the researchers captured light in a small area near the surface of a specially-made object and then forced it to follow the curve of the surface. They found that changing the surface curvature made it possible to control light propagation.

When applied to astronomical observations, this shows that light reaching the Earth from stars far away carries valuable information regarding the space it traveled through.

As part of their study, the researchers also tackled intensity interferometry. Developed by Richard Twiss and Robert Hanbury Brown, intensity interferometry is used for determining the sizes of stars close to the sun with the help of two telescopes. Light fluctuations captured by the two telescopes are compared and the result gives researchers clues with which they can make conclusions about the size of the star being observed.

Light emissions from stars appear as patterns of light dots when intensity interferometry is used. The size of the dots change depending on the surface curvature the light emissions pass. According to the researchers, knowing the curvature helps in better interpreting results, and interferometry experiments are ideal for measuring the universe's general curvature.

"The main goal of our research is to transfer findings based on the general theory of relativity to materials science by carefully modeling the surfaces of objects," said Peschel.

Sascha Batz also contributed to the study.

Photo: Amy Nelson | Flickr

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