Light floating joyfully in the absolute void of space travels a constant distance of 299,792,458 meters every second. Neither more nor less. All this changes when this wave of electromagnetism is forced to overcome the electromagnetic fields surrounding matter particles. The overall speed of light passing through this swamp can slow down to a relative slowdown.

We see this phenomenon in the bending of light as it passes through a glass of water, or even in the dazzling splitting of waves in a rainbow. Although physicists have been able to describe this delay using 19th century equations for light and electromagnetism, they have not yet been able to adequately capture the dramatic change in the speed of light between different media in terms of physical waves.

Three physicists from the University of Tampere have found a potential solution to this problem, but not before revisiting some pretty basic principles of how a light wave travels through time and in a discrete dimension of space.

“Basically, I found a very nice way to obtain the standard wave equation in 1+1 dimensions,” says first author Matias Koivurova, now at the University of Eastern Finland.

“The only assumption I needed was that the speed of the wave was constant. Then I thought to myself: What if it’s not always constant? That turned out to be a really good question.”

The speed of light – or c for short – is the universal limit of information traveling in space. Although matter can effectively slow down the overall motion of a particle, special relativity says that this fundamental property cannot really change.

But sometimes physics requires an occasional dash of imagination to explore new territory. So Koivurova, together with her colleagues Charles Robson and Marco Ornigotti, put aside this inconvenient fact to consider the consequences of the standard wave equation, according to which an arbitrary light wave could be accelerated.

At first their decisions didn’t make sense. It wasn’t until constant velocity was added as a frame of reference that the pieces came together. When you send a spacecraft into deep space at high speed, its passengers will experience time and distance differently than observers watching their journey from afar. This contrast arises thanks to the theory of relativity, which has been successfully tested many times at all scales.

When we compared the accelerating wave to the constant speed of light, the strange effects of the team’s new solution to the standard wave equation were similar to the effects imposed by the theory of relativity. This realization had profound implications for the debate over whether the momentum of a light wave increases or decreases as it passes through a new medium.

“We showed that from the wave’s point of view, nothing happens to its momentum. In other words, the momentum of the wave is preserved,” says Koivurova.

Regardless of what the wave is, whether it is in an electromagnetic field, a wave in a pool, or the vibration of a string, as speed increases, measurements of relativity and conservation of momentum need to be taken into account in the equation. This generalization would have another rather noteworthy, if somewhat disappointing, consequence.

Whether it’s our brave space travelers flying to Alpha Centauri at well below the speed of light, or their slowly aging families on Earth, each of their clocks is ticking at the right time. These two times may not coincide in terms of a one-second period, but each is a reliable measure of the passage of years in its own way.

Physicists argue that any wave-driven physics must have a precise time direction if all waves also experience the proper temporal maintenance of relativity. Something that cannot be easily undone for any part.

So far the equations have been solved for only one dimension of space (and time). Experiments are also needed to see whether this wave perspective is correct. If so, our journey together through the universe is truly a one-way street.