Imagine an object so small that it is almost invisible, but that moves so fast that could circle the Earth more than seven times in a single second, while its mass multiplies exponentially. This is not science fiction; is the achievement that a team of physicists from the Vienna Institute of Quantum Science and Technology has achieved in a laboratory, accelerating nanoparticles to speeds that touch the absolute limit of the universe: the speed of light.
This experiment not only sets a new record, but opens the doors to testing the foundations of physics itself, where the impossible becomes real: an object that, in full motion, becomes seven times “heavier.”
The team, led by Dominik Hornof, has published their findings in Nature and, contrary to what one might imagine, it is not a miniature spacecraft or a powerful beam of subatomic particles. The protagonist of this story is a silicon microbubble, a hollow sphere thousands of times thinner than a human hair.
Hornof’s team’s experiment involved placing these microbubbles in a vacuum chamber and suspending them in air using “optical tweezers”: beams of laser light that can immobilize tiny particles. Once trapped, an incredibly short and intense pulse of laser light hits them, transferring a monumental amount of energy in a fraction of a second. The result: an acceleration so brutal that these microbubbles reach 99% of the speed of light (0.99c).
And this is where the experiment becomes interesting. According to Einstein’s Theory of Special Relativity, When an object approaches the speed of light, its kinetic energy manifests as an increase in mass. It is not that it gains more atoms, but that the energy set in motion is “materialized”, making the object behave as if it were much more massive.
How much does it increase? The calculations are conclusive. At 99% of the speed of light, the Lorentz Factor, the magnitude that quantifies this effect, is approximately 7. This means that the microbubble, during its ultrafast journey, has a relativistic mass about seven times greater than when it is at rest. If its rest mass were 1 microgram, at that instant it would behave as if it weighed 7 micrograms. This is not an abstract concept, but a physical reality that makes the object incredibly harder to continue accelerating, acting as a “relativistic brake” that prevents any object with mass from reaching the speed of light.
Why is it so important to achieve these speeds? Accelerating macroscopic objects (even if they are extremely small) to these speeds without destroying them and being able to measure these relativistic effects is a titanic challenge. This experiment is a qualitative leap for several reasons. First, it puts Einstein to the test by being a practical and direct demonstration of relativity in action on a workable object in a laboratory. It allows scientists to test the laws of physics in energy and velocity regimes that were previously inaccessible.
At the same time, These microbubbles, with their multiplied mass, become perfect high-energy projectiles. By studying their collisions, physicists can simulate and better understand the violent processes that occur around black holes or in cosmic rays.
And finally there is the future. The ability to control and measure matter in This extreme regime could have long-term applications in spacecraft propulsionthe creation of new materials or the development of compact radiation sources.
The interesting thing is that this achievement is not the end, but the beginning of a new era. Hornoff’s team plans to take the experiment even further, trying to reach 99.9% of the speed of light, where the increase in mass would be more than 22 times, measuring with unprecedented precision how relativity shapes the behavior of matter.