Gravity can transform into light, mind-bending physics paper suggests

Abstract artist's impression of an energy vortex.
Can gravity create light? (Image credit: dani3315 via Getty Images)

Gravity can turn itself into light, but only if space-time behaves in just the right way, a research team has found.

Under normal circumstances, you cannot get something from nothing. Specifically, the Standard Model of particle physics, the reigning theory that explains the subatomic zoo of particles, usually forbids the transformation of massless particles into massive ones. While particles in the Standard Model constantly change into each other through various reactions and processes, the photon — the massless carrier of light — cannot normally change into other particles. But if the conditions are just right, it is possible — for example, when a photon interacts with a heavy atom, it can spontaneously split off to become an electron and a positron, both of which are massive particles.

With this well-known example in hand, a team of theoretical physicists, writing in a paper posted March 28 to the preprint database arXiv (opens in new tab), asked if gravity itself could transform into other particles. We normally think of gravity through the lens of general relativity, where bends and warps in space-time influence the motion of particles. In that picture, it would be very difficult to imagine how gravity could create particles. But we can also view gravity through a quantum lens, picturing the gravitational force as carried by countless invisible particles called gravitons. While our picture of quantum gravity is far from complete, we do know that these gravitons would behave like any other fundamental particle, including potentially transforming.

To test this idea, the researchers studied the conditions of the extremely early universe. When our cosmos was very young, it was also small, hot and dense. In that youthful cosmos, all forms of matter and energy were ramped up to unimaginable scales, far greater than even our most powerful particle colliders are capable of achieving. 

The researchers found that in this setup, gravitational waves — ripples in the fabric of space-time generated by collisions between the most massive cosmic objects — play an important role. Normally, gravitational waves are exceedingly weak, capable of nudging an atom through a distance less than the width of its own nucleus. But in the early universe, the waves could have been much stronger, and that  could have seriously influenced everything else.

Artist impression of gravitational waves. (Image credit: R. Hurt/Caltech-JPL)

Those early waves would have sloshed back and forth, amplifying themselves. Anything else in the universe would have gotten caught up in the push and pull of the waves, leading to a resonance effect. Like a kid pumping their legs at just the right time to send a swing higher and higher, the gravitational waves would have acted as a pump, driving matter into tight clumps over and over again.

The gravitational waves could also affect the electromagnetic field. Because the waves are ripples in space-time itself, they don't limit themselves to interactions with massive objects. As the waves continue to pump, they can drive radiation in the universe to extremely high energies, causing the spontaneous appearance of photons: gravity generating light itself.

The researchers found that in general, this process is rather inefficient. The early universe was also expanding, so the standard patterns of gravitational waves would not have lasted long. However, the team found that if the early universe contained enough matter that the speed of light was reduced (the same way light travels more slowly through a medium such as air or water), the waves could have stuck around long enough to really get things going, generating floods of extra photons.

Physicists do not yet fully understand the complicated, tangled physics of the early universe, which was capable of achieving feats never observed since. This new research adds one more strand to the rich tapestry: the capability for gravity to create light. That radiation would presumably then go on to influence the formation of matter and the evolution of the universe, so working out the full implications of this surprising process could lead to new revolutions in our understanding of the earliest moments of the cosmos.

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. 

  • Russ51
    This idea meshes well with one of the (half dozen) theories about multiverse generation. Imagine, using the proverbial metaphor of an elastic sheet to visualize gravity, a black hole weighting down the middle, eventually becoming so massive it drops off like a blob of honey, metaphorically speaking, creating a new universe. I forget the physicist or mathematician who proposed that. Perhaps Penrose.
  • Theo Prins
    Beyond the smallest particles, Electrons, Quarks, tau-Neutrinos, etc there are sub-sub atomic particles in the Sea of Dirac.
    These sub-sub atomic particles make up all the above particles including mass and charged Protons, Neutrons, neutrinos, etc, and extremely massless and chargeless Photons.
    Protons, Neutrons, and Electrons have a permanent either positive, neutral, or negative spin.
    The Electron spin is stronger than the Proton/Neutron spin.
    When an Electron falls back from a higher excited orbit to the normal lower orbit it remains in the same spin, decreases its mass, increases its charge, and releases a Photon.
    Spin is a motion whereas charge is an effect.
    Photons are more or less spherical particle-like waves of masses of these sub-sub atomic particles that are in a frequently varying negative/positive, repelling/attracting motion creating the Photon's electromagnetic wave.
    Photons do have spin but the effect is extremely weak due to very small momentum.
    The sub-sub atomic particles constituting the Photon remain in their locality like the water in the wave from a ship or a tsunami in the Sea/Ocean.
    Quantum Entanglement is a string made of these sub-sub atomic particles between two Photons and then two Electrons.
    Gravity is also a quantum entangled string between all particles with mass.
    Gravity and quantum entanglement of photons and electrons work dominantly on the macrocosmic scale whereas the strong and weak forces only work and are dominant on the microcosmic or atom scale.
    How quantum entangled strings composing gravity, are produced is unclear.
    All these particles and strings phenomena made of sub-sub atomic particles interact in a repelling or attracting manner caused by the same spin or opposite spin of these particles.
    Electromagnetism is caused by the spin of Electrons and Protons.
    Electromagnetism expresses in the interacting electromagnetic fields composed of sub-sub atomic particles in the Sea of Dirac around Electrons and Protons which are also composed of sub-sub atomic particles.
    Whether the strong force between Quarks within the Proton and even the weak force creating radiation is either a string-like entanglement or a sub-sub atomic field like in electromagnetism is unclear.
    The force of the Gravity strings is weak within the dimension of the atom because the gravitational force is predominated by the Electro-Magnetic, weak and strong forces.
    Like the Quantum Entangled strings the sub-sub atomic particles creating the Gravity string also remain in their locality. Strings might be very thin cosmic long helixes with some unmeasurable electromagnetic field.
    Gravity, Electromagnetic, strong, and weak forces are all the same phenomenon and made of the same sub-sub atomic particle but with different strengths.
  • Sovordi
    I think at some point the universe will know that we know too much and collapse in on itself.
  • dmdoren
    The idea that gravity (spacetime) can create light is not new. It was explicitly hypothesized in a 2021 article as part of a much larger cosmological theory called Probabilistic Spacetime (Doren, D.M. and Harasymiw, J. (2021) Everything is Probabilistic Spacetime: An Integrative Theory. Int J Cosmol Astron Astrophys, 3, 1: 130-144. https://doi:10.18689/ijcaa-1000127).