A long-standing theory that appears to contradict a key effect of general relativity has been validated by a research team that, instead of accelerating an object to a significant portion of the speed of light, employed strategic camera and lighting effects to simulate these nigh-impossible speeds, showing that objects moving at near-light speed appear to be rotated or skewed, rather than simply compressed along their length.

While the idea that an object moving at relativistic speed might appeared skewed or rotated was first proposed by Anton Lampa in 1924, the idea went unexplored until 1959 when the idea was revisited independently by physicists James Terrell and Roger Penrose, the latter of whom, along with anesthesiologist Stuart Hameroff, has been working on a theory that consciousness is a non-local quantum process independent of our physical brains.

The Penrose–Terrell effect (typically referred to simply as Terrell rotation) seems to run contrary to the perceived idea that an object moving at speeds approaching the speed of light (c) will appear to be contracted along its length, instead positing that the object will instead appear to have been either rotated or skewed with the side closer to the observer appearing to lead the object.

When we perceive an object, the light coming from a point at the rear of the object, being further away, takes more time to reach us than the light coming from the front, meaning that in the image we’re seeing at any given moment, the light from the far side of the object had to have left before the light from the side nearest to us (but don’t worry, the light that left at the same time is still on its way, it just hasn’t reached us yet).

Under ordinary circumstances this slight discrepancy in the timing of when the light is emitted or reflected from different parts of an object is miniscule enough to not distort our perception of the object; however, if that object is moving at an extremely high speed then in the time that it took for the rearward light to cover the distance of the length of the object, the front itself has already traveled a noticeable distance, or as Penrose put it, using a sphere as an example, “the light from the trailing part reaches the observer from behind the sphere, which it can do since the sphere is continuously moving out of its way”.

In addition to the predicted lengthwise contraction of the object, the effect results in a perceived rotation or skewing of the object, with the leading portion of the object appearing to rotate away from the observer and the trailing portion toward.

It’s important to note that this effect isn’t actually being experienced by the object itself, but is a relativistic illusion that balances the effects of the speed of light being a constant: as far as the object is concerned, it’s sitting still, while the rest of the universe—including our external observer—appears to be moving at tremendous speed, so everything else appears to have been contracted, gained mass and, as Penrose and Terrell have pointed out, rotated or skewed.

Enter the research team led by Vienna University of Technology quantum physicist Dominik Hornof, who devised a method of testing the Penrose–Terrell effect by not accelerating something to near-light speeds, but simulating light at a speed of only a fraction of its usual 299,792,458 meter-per-second clip, using ultra-fast laser pulses and gated cameras to achieve the desired effect.

“What I like most is the simplicity,” Hornof remarked, playing down the precision timing required to coordinate laser pulses only a tenth of a billionth of a second long with a camera shutter open for an equally infinitesimally short amount of time. “With the right idea, you can recreate relativistic effects in a small lab. It shows that even century-old predictions can be brought to life in a really intuitive way.”

Using these 300-picosecond pulses the team was able to generate an image of an object that appeared to be moving at a significant portion of the speed of light, but was actually only moving no faster than a few meters per second. The images generated by the experiment produced the effect predicted by Penrose and Terrell: a set of contracted-yet-skewed images of the test objects that appear to allow the viewer to see around their sides.

“The rotation is not physical,” Hornof pointed out. “It’s an optical illusion. The geometry of how light arrives at the same time tricks our eyes.”

The team ran the experiment on two different objects at different speeds: the first was a one-meter (3.3-foot) cube that was moved forward 4.8 centimeters (1.9 inches) between exposures, simulating a speed of 80 percent of the speed of light; the second was a sphere shifted 6 centimeters (2.4 inches) for each exposure, simulating a velocity of 99.9 c.

While the expected length contraction was observed in the resulting images, with the 80 percent and 99.9 percent c squashing to 60 percent and 4.5 percent of their actual lengths, respectively, the effect was offset by their visual rotation, so that the contraction appeared across the depth of the object from the camera’s perspective, rather than along the objects’ simulated paths.

“When we did the calculations, we were surprised how beautifully the geometry worked out,” Hornof remarked in regards to the results that validated the 66-year-old theory. “Seeing it appear in the images was really exciting.”