Researchers have discovered that in the exotic conditions of the early universe, gravitational waves can shake space-time enough to spontaneously create radiation. The concept of physical resonance surrounds us in everyday life. When you sit on the swing and want to go higher, you naturally start swinging your legs back and forth. You find the right rhythm very quickly to swing higher. If you go out of rhythm, the swing stops rising. This particular phenomenon is known in physics as parametric resonance.

Your legs act as an external pumping mechanism. When they match the system’s resonance frequency, then your body sitting on the swing transfers energy to the system, causing the swing to go higher. This kind of resonance occurs everywhere, and a research team has found that an exotic form of parametric resonance may have occurred even in the very early stages of the universe.

Perhaps the most dramatic event in the history of the universe was inflation. This is a hypothetical event that occurred when our universe was less than a second. During inflation, our universe grew to impressive dimensions and became much larger than before. The end of inflation was a messy affair, with gravitational waves moving back and forth through space.

Gravitational waves are usually extremely weak. To find gravitational waves traveling through the Earth, we must make detectors that can measure distances smaller than the width of an atomic nucleus. However, the researchers noted that in the very early stages of the universe, these gravitational waves can be very strong.

And they may even have created standing wave models where gravitational waves don’t propagate and the waves freeze where they are, almost all of space. Since gravitational waves are literally gravitational waves, the places where the waves are strongest represent an extraordinary amount of gravitational energy.

The researchers discovered that this could have serious consequences for the electromagnetic field that existed in the early universe. Intense gravitational fields can excite the electromagnetic field enough to create light by releasing some of its energy as radiation. This result leads to an entirely new phenomenon: light production by gravity alone. There’s nothing in the modern universe that would allow this process to happen, but researchers have shown that the early universe is a much stranger place than we could have imagined.