Science 4 min read

Negative Mass Particles Created for the First Time by Researchers

Andrea Danti /

Andrea Danti /

A new research study explained how negative mass particles could be created.

According to science, all things in this world have mass. Thus, everything that exists is governed by Isaac Newton’s laws of motion. For instance, if you push a chair, it will move in the direction of where you pushed it. However, that is not the case with objects consisting negative mass particles as they tend to do the opposite.

For years, physicists have spent time and effort to find real-world examples of negative mass. But now, for the first time in the fields of quantum physics, a team of researchers from the University of Rochester not only found examples but actually succeeded in creating particles with negative mass.

In a study published in the journal Nature Physics, Nick Vamivakas, an associate professor of quantum optics and quantum physics at Rochester’s Institute of Optics, together with his colleagues explained in details how they created the particles in an atomically thin semiconductor.

“Here we study the interaction between out-of-equilibrium cavity photons and both neutral and negatively charged excitons, by embedding a single layer of the atomically thin semiconductor molybdenum diselenide in a monolithic optical cavity based on distributed Bragg reflectors,” the researchers wrote in their paper.

Negative Mass Particles

According to the researchers, their experiment is the first example of how particles exhibiting negative mass could be made. During the experiment, the team used a device consists of two mirrors that create optical microcavity. Apparently, this kind of structure can confine the light at different colors of the spectrum based on how the researchers spaced the mirrors.

Schematic of the device used to create the negative mass particles
a. Schematic of the optical cavity b. A coupled spring and mass system representing photon (Ph), exciton, and trion c. Dispersion relation for both the uncoupled cavity photon, exciton and trion d. A single-shot angle-resolved photoluminescence (PL) measurement of the device exhibiting negative dispersion for the LPB | Vamivakas et al. |

The negative mass particles were then created when the photons on the laser and the excitons in the ultra-thin semiconductor made of molybdenum diselenide interacted with each other.

“The interactions lead to multiple cavity polariton resonances and anomalous band inversion for the lower, trion-derived, polariton branch—the central result of the present work,” the researchers explained.

“Our theoretical analysis reveals that many-body effects in an out-of-equilibrium setting result in an effective level attraction between the exciton-polariton and trion-polariton accounting for the experimentally observed inverted trion-polariton dispersion.”

According to ExtremeTech, an exciton is a bound quantum state of an electron, a so-called “electron hole” where an electron could exist in the semiconductor. Interaction with the electron in its quantum state eventually resulted in the creation of a new quasiparticle, dubbed as polariton, that has negative mass.

“By causing an exciton to give up some of its identity to a photon to create a polariton, we end up with an object that has a negative mass associated with it,” Vamivakas said. “That’s kind of a mind-bending thing to think about, because if you try to push or pull it, it will go in the opposite direction from what your intuition would tell you.”

While the researchers were able to verify the existence of the negative mass qualities during the experiment, they admit that they are still far from harnessing its power or creating something out of it. According to Vamivakas, he and his team will continue to explore the potentials of their device to produce laser substrates and learn the physical implications of creating the negative mass particles using the said device.

“We’re dreaming up ways to apply pushes and pulls—maybe by applying an electrical field across the device—and then studying how these polaritons move around in the device under application of external force.”

Now that negative mass particles have been created, in what ways do you think these quasiparticles could be used? Got any idea? Share it with us in the comment section below!

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Comments (5)
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  1. Kimberly Tregoning January 12 at 12:50 pm GMT

    Actually, negative mass is required to force open an Einstein-Rosenberg bridge (a wormhole). This could have huge implications. I also wonder if artificial gravity/anti-gravity effects could be utilized in the future from this line of research.

    • Sky Darmos January 13 at 9:36 am GMT

      There is no natural way how wormholes can emerge naturally. Also the full theory of quantum gravity will show that wormholes are not a possible structure of space, because a space made of space atoms is very different from the naive smooth space-time picture of general relativity. General relativity is only an approximation for a fundamental theory in which quantum mechanics and gravity are simply different aspects of one thing, without any reasonable distinction that could be made.

    • Igor Popov January 15 at 8:13 pm GMT

      This idea came in my mind as soon as I read “negative mass”. I am not an expert in the field but I think that negative mass they wrote about in the paper is not the negative gravitational or inertial mass in terms of the general relativity. Polariton is a kind of a quasiparticle, which is not a real particle, but just formally theoretically polariton can be treated as a particle. Taking this into account, I think some analogues to real space-time wormholes may be eventually build with help of polaritons. E.g. a laser field may eventually “tunnel” through the “wormhole” and emerge on other side of the material (molybdenum disulfide).

  2. disqus_jRNp9VTfTw January 15 at 4:19 pm GMT

    This effect seems to be very similar to effective mass in a semiconductor. While holes exist in semiconductors producing the negative electric field equivalent, it would be interesting to see if we could use a negative mass approach to create the same effect with higher mobility.

  3. Alan Glynne-Jones February 05 at 11:03 pm GMT

    Here is an article from someone who actually read the paper … and didn’t just fall for the cunningly worded press release by the university about it:

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