Ripples in space-time known as gravitational waves could help reveal the secrets at the dawn of time, just moments after the Big Bang, new research suggests. And physicists say they can learn more about these primeval gravitational waves using nuclear fusion reactors here on Earth.
In a new study, physicists used equations that govern how electromagnetic waves move through plasma inside fusion reactors to create a theoretical model for how gravitational waves and matter interact.
That, in turn, could reveal a better picture of the earliest moments in time.
Moments after the Big Bang, the universe was permeated by a soup of hot, ultradense primordial plasma that sent powerful gravitational waves rippling out into the cosmos.
These ancient gravitational waves would have propagated throughout the universe and should still be present today, so the mutual influence that matter and gravitational waves had on each other in the universe's infancy would leave observable traces in both. Working backward from those observable traces could reveal a better picture of that early period.
"We can't see the early universe directly, but maybe we can see it indirectly if we look at how gravitational waves from that time have affected matter and radiation that we can observe today," said Deepen Garg (opens in new tab), a graduate student in the Princeton Program in Plasma Physics and lead author of the study, in a statement (opens in new tab).
A matter of great gravity
According to Einstein's theory of general relativity, massive bodies interact gravitationally by deforming space around them, generating ripples in space-time called gravitational waves that travel at the speed of light.
Until now, physicists have used detectors such as the Laser Interferometer Gravitational Wave Observatory (LIGO) to hunt gravitational waves born in the collisions of black holes. These cosmic cataclysms generate the most powerful gravitational waves, and they travel from the collision region to Earth in a vacuum, meaning that to describe them, physicists need only model the physics of these ripples in empty space.
However, when the universe was in its infancy, huge amounts of matter moved around, generating gravitational waves that had to propagate through a primordial plasma, which would have interacted with the waves, altering their shape and trajectory.
To calculate how this primordial plasma would have affected these ancient gravitational waves, Garg and his supervisor Ilya Dodin (opens in new tab) carefully analyzed the equations of Einstein's theory of relativity, which describes how the geometry of space changes as matter moves through it. Under certain simplifying assumptions about the physical properties of matter, they could calculate how gravitational waves and matter affect each other.
The team based part of their equations on the propagation of electromagnetic waves in plasma. This process not only occurs under the surface of stars, but also in fusion reactors on Earth.
"We basically put plasma wave machinery to work on a gravitational wave problem," Garg said.
Although scientists have taken an important step toward computing the measurable effects that gravitational waves and primordial plasma may have had on each other, they still have a lot of work to do. The scientists still need to make more accurate and detailed calculations in order to get a better picture of what these ancient gravitational waves would look like today.
"We have some formulas now, but getting meaningful results will take more work," concluded Garg.
The findings were published in The Journal of Cosmology and Astroparticle Physics (opens in new tab).
Wikipedia: "Emission theory, also called emitter theory or ballistic theory of light, was a competing theory for the special theory of relativity, explaining the results of the Michelson–Morley experiment of 1887...The name most often associated with emission theory is Isaac Newton. In his corpuscular theory Newton visualized light "corpuscles" being thrown off from hot bodies at a nominal speed of c with respect to the emitting object, and obeying the usual laws of Newtonian mechanics, and we then expect light to be moving towards us with a speed that is offset by the speed of the distant emitter (c ± v)."
Banesh Hoffmann, Einstein's co-author, admits that, originally ("without recourse to contracting lengths, local time, or Lorentz transformations"), the Michelson-Morley experiment was compatible with Newton's variable speed of light, c'=c±v, and incompatible with the constant speed of light, c'=c:
"Moreover, if light consists of particles, as Einstein had suggested in his paper submitted just thirteen weeks before this one, the second principle seems absurd: A stone thrown from a speeding train can do far more damage than one thrown from a train at rest; the speed of the particle is not independent of the motion of the object emitting it. And if we take light to consist of particles and assume that these particles obey Newton's laws, they will conform to Newtonian relativity and thus automatically account for the null result of the Michelson-Morley experiment without recourse to contracting lengths, local time, or Lorentz transformations. Yet, as we have seen, Einstein resisted the temptation to account for the null result in terms of particles of light and simple, familiar Newtonian ideas, and introduced as his second postulate something that was more or less obvious when thought of in terms of waves in an ether." Banesh Hoffmann, Relativity and Its Roots, p.92