Physics is all about constants, but what if they’re not as constant as we thought? This is not just a whimsical idea, but the base of serious scientific investigations. Hypothetical changes in the speed of light have recently been in the news, but astronomers have also been testing another value, known as the fine structure constant, for variation.

The Arecibo radio telescope has proved that the fine structure constant has not changed by more than 1.3 parts per million in the last 3 billion years, slightly improving upon the previous estimation (which was on a longer time period). These results were presented at the American Astronomical Society’s meeting in Grapevine, Texas, on January 4, 2017.

The fine structure constant characterizes the strength of the electromagnetic interaction between elementary charged particles, which has far-reaching consequences. A 4 percent variation would stop stars from making carbon (and then us), and if it were larger stars, they wouldn’t even shine. It is also responsible for how chemicals interact in our bodies, and indirectly explains why toast falls on the buttered side.

The precise measurements were possible thanks to an incredibly favorable cosmic arrangement. Astronomers discovered that the bright quasar PKS 1413+135 was surrounded by a cloud of hydroxyl molecules. They were able to measure the fine structure constant from how these molecules absorb radio waves around the quasar, which is 3 billion light-years away, and then compare it to the value obtained in the lab.

It might not seem like it, but improving on such measurements is very difficult. It took almost 150 hours of data integration to achieve this new accuracy. To improve the new estimate by a factor of 10, it would require 100 times more observing time. Unfortunately, this cannot be justified due to the amount of resources involved.

Astronomers might improve on this value by finding more objects like PKS 1413+135, hopefully even further away, and pushing our certainty that the value remained constant for a longer period.

“We are hopeful that current searches for more quasar candidates showing the necessary OH lines will be successful," lead researcher Dr. Tapasi Ghosh, from the University Space Research Association, said in a statement. "These could provide even tighter constraints on any possible variations of this atomic constant."