The universe may be dominated by particles that break causality and move faster than light, new paper suggests

A delicate sphere of gas created by a supernova blast wave 160,000 light-years from Earth.
A delicate sphere of gas created by a supernova blast wave 160,000 light-years from Earth. (Image credit: NASA Goddard)

Could the cosmos be dominated by particles that move faster than the speed of light? This model of the universe agrees surprisingly well with observations, a pair of physicists has discovered.

In a new paper that has yet to be peer-reviewed, the physicists propose that our universe is dominated by tachyons — a hypothetical kind of particle that always moves faster than light. Tachyons almost certainly don't exist; going faster than light violates everything we know about the causal flow of time from past to future. But the hypothetical particles are still interesting to physicists because of the small chance that even our most closely held notions, like causality, might be wrong.

The researchers suggest that tachyons might be the true identity of dark matter, the mysterious form of matter that makes up most of the mass of almost every single galaxy in the universe, outweighing normal matter 5 to 1. Astronomers and physicists alike currently do not know what dark matter is made of, so they are free to cook up all manner of ideas —– because, after all, sometimes a far-out idea is right, and even if it's wrong, it can help us on the path to a better understanding.

The researchers calculate that an expanding universe filled with tachyons can initially slow down in its expansion before reaccelerating. Our universe is currently in an accelerating phase, driven by a phenomenon known as dark energy, so this tachyon cosmological model can potentially explain both dark energy and dark matter at the same time.

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To test this idea, the physicists applied their model to observations of Type Ia supernovae, a kind of stellar explosion that allows cosmologists to build a relationship between distance and the expansion rate of the universe. It was through Type Ia supernovae that astronomers in the late 1990s first discovered that the universe's expansion rate is accelerating.

A Type Ia supernova seen in the galaxy M82 by the Hubble Space Telescope. These explosions allow astronomers to estimate the expansion rate of the universe. (Image credit: NASA Goddard)

The physicists found that a tachyon cosmological model was just as good at explaining the supernova data as the standard cosmological model involving dark matter and dark energy. That itself is a surprise, given how unorthodox this idea is.

However, that's only the beginning. We now have access to a wealth of data about the large-scale universe, like the cosmic microwave background (remnant radiation released just after the Big Bang) and the arrangement of galaxies at the very largest scales. The next step is to continue testing this idea against those additional observations.

The tachyon cosmological model is unlikely to pass those rigorous experimental tests, given the unlikely nature of tachyons. But continuing to push in new, even unorthodox, directions is important in cosmology; we never know when we might get a breakthrough. Scientists have been attempting to understand dark matter for 50 years and dark energy for a quarter century, without any conclusive results. The solutions to these conundrums are likely to come from unexpected directions.

The team's research was published to the preprint database arXiv in March.

Paul Sutter

Paul M. Sutter is a research professor in astrophysics at  SUNY Stony Brook University and the Flatiron Institute in New York City. He regularly appears on TV and podcasts, including  "Ask a Spaceman." He is the author of two books, "Your Place in the Universe" and "How to Die in Space," and is a regular contributor to, Live Science, and more. Paul received his PhD in Physics from the University of Illinois at Urbana-Champaign in 2011, and spent three years at the Paris Institute of Astrophysics, followed by a research fellowship in Trieste, Italy.