For the first time, physicists have demonstrated a phenomenon known as the Terrell-Penrose effect, which causes an object moving close to the speed of light to warp before our eyes.
The new findings, a collaboration between TU Wien and the University of Vienna, once again confirm a key prediction of Einstein’s theory of relativity by making an optical illusion of relativistic motion observable for the first time.
Terrell-Penrose Effect
According to Einstein’s special theory of relativity, objects moving close to the speed of light experience unusual effects, including changes in length and time compared to objects at rest. Many relativistic effects have been confirmed experimentally, but not the one proposed by James Terrell and Roger Penrose in 1959: that objects moving at extremely high speeds should appear rotated.
“Suppose a rocket whizzes past us at ninety per cent of the speed of light. For us, it no longer has the same length as before it took off, but is 2.3 times shorter,” explained Prof. Peter Schattschneider from TU Wien. This phenomenon, known as Lorentz contraction, can’t be directly photographed due to the complex way light interacts in such conditions.
“If you wanted to take a picture of the rocket as it flew past, you would have to take into account that the light from different points took different lengths of time to reach the camera,” Schattschneider said.
Light Speed Illusions
When viewing an object, the image humans perceive doesn’t truly capture it at a single moment. Because light travels at a constant speed, light from more distant parts of an object— even slightly in the background—must be emitted slightly earlier than light from the foreground to reach our eyes at the same time. Normally, objects don’t move fast enough for these tiny differences in light arrival time to affect perception. But when an object moves close to the speed of light, this time difference becomes significant, making the object appear rotated.
“This makes it look to us as if the cube had been rotated,” says Peter Schattschneider.
This apparent rotation results from a combination of relativistic length contraction and the varying light travel times from different points on the object, just as Terrell and Penrose predicted.
Slowing Down Light
Even the most advanced rocket technology can’t achieve speeds high enough to observe the Terrell-Penrose effect directly. However, a team led by Peter Schattschneider from USTEM at TU Wien replicated it using a high-speed precision camera and brief laser pulses.
“We moved a cube and a sphere around the lab and used the high-speed camera to record the laser flashes reflected from different points on these objects at different times,” explained Victoria Helm and Dominik Hornof, the two students who carried out the experiment. “If you get the timing right, you can create a situation that produces the same results as if the speed of light were no more than 2 metres per second.”
The team’s combined image was created by photographing an object multiple times, across space and time. By perfectly synchronizing the laser flashes and the camera’s speed, the researchers simulated a situation where light moved at only two meters per second, making the Terrell-Penrose effect visible for the first time.
“We combined the still images into short video clips of the ultra-fast objects. The result was exactly what we expected,” says Peter Schattschneider. “A cube appears twisted, a sphere remains a sphere, but the North Pole is in a different place.”
The paper “A Snapshot of Relativistic Motion: Visualizing the Terrell-Penrose Effect” appeared on May 1, 2025 in Communications Physics.
Ryan Whalen covers science and technology for The Debrief. He holds an MA in History and a Master of Library and Information Science with a certificate in Data Science. He can be contacted at ryan@thedebrief.org, and follow him on Twitter @mdntwvlf.