Nothing can go faster than light. It's a rule of physics woven into the very fabric of Einstein's special theory of relativity. The faster something goes, the closer it gets to its perspective of time freezing to a standstill.
Go faster still, and you run into issues of time reversing, messing with notions of causality.
But in a study published late last year, scientists pushed the limits of relativity to come up with a system that doesn't run afoul of existing physics, and might even point the way to new theories.
The researchers – from the University of Warsaw in Poland and the National University of Singapore – developed an "extension of special relativity" that combines three time dimensions with a single space dimension ("1+3 space-time"), as opposed to the three spatial dimensions and one time dimension that we're all used to.
Rather than creating any major logical inconsistencies, the study adds more evidence to back up the idea that objects might well be able to go faster than light without completely breaking our current laws of physics.
"There is no fundamental reason why observers moving in relation to the described physical systems with speeds greater than the speed of light should not be subject to it," said physicist Andrzej Dragan from the University of Warsaw in Poland.
This study builds on previous work by some of the same researchers suggesting superluminal perspectives could help tie together quantum mechanics with Einstein's special theory of relativity – two branches of physics that currently can't be reconciled into a single overarching theory that describes gravity in the same way we explain other forces.
Particles can no longer be modelled as point-like objects under this framework, as we might in the more mundane 3D (plus time) perspective of the Universe.
Instead, to make sense of what observers might see and how a superluminal particle might behave, we'd need to turn to the kinds of field theories that underpin quantum physics.
Based on this model, superluminal objects would look like a particle expanding like a bubble through space – not unlike a wave through a field. The high-speed object, on the other hand, would 'experience' several different timelines.
Even so, the speed of light in a vacuum would remain constant even for those observers going faster than it, which preserves one of Einstein's fundamental principles – a principle that has previously only been thought about in relation to observers going slower than the speed of light (like all of us).
"This new definition preserves Einstein's postulate of constancy of the speed of light in vacuum even for superluminal observers," said Dragan.
"Therefore, our extended special relativity does not seem like a particularly extravagant idea."
However, the researchers acknowledge that switching to a 1+3 space-time model does raise some new questions, even while it answers others. They suggest that extending the theory of special relativity to incorporate faster-than-light frames of reference is needed.
That may well involve borrowing from quantum field theory: a combination of concepts from special relativity, quantum mechanics, and classical field theory (which aims to predict how physical fields are going to interact with each other).
If the physicists are right, the particles of the Universe would all have extraordinary properties in extended special relativity.
One of the questions raised by the research is whether or not we would ever be able to observe this extended behavior – but answering that is going to require a lot more time and a lot more scientists.
"The mere experimental discovery of a new fundamental particle is a feat worthy of the Nobel Prize and feasible in a large research team using the latest experimental techniques," said physicist Krzysztof Turzyński from the University of Warsaw.
"However, we hope to apply our results to a better understanding of the phenomenon of spontaneous symmetry breaking associated with the mass of the Higgs particle and other particles in the Standard Model, especially in the early Universe."
The research was published in Classical and Quantum Gravity.
An earlier version of this article was published in January 2023.