The Universe's Secret Text Messages: Gravitational Waves

Gravitational waves are produced in space, moving at the speed of light, which is 300,000 kilometers per second; they are invisible and extremely fast, explained Miguel Alcubierre Moya, researcher at the Institute of Nuclear Sciences (ICN) of the UNAM.

In addition, they occur very far from us, so they weaken and are difficult to detect from Earth. They spread in a similar way to the waves generated in a body of water when a stone is thrown, and they are capable of contracting and stretching anything they find in their path. “If they passed through us, we would become tall and thin, and then fat and short, again and again,” he said.

During a conference offered at the invitation of the Institute of Physical Sciences, Morelos campus of the UNAM, the former director of the ICN explained that gravitational waves are created when objects move at very high speeds.

They can be generated by the asymmetric explosion of a supernova (a star in its terminal phase), two large stars orbiting each other, collisions of neutron stars, and two black holes orbiting each other and merging.

But these objects in the universe are very far away, and sometimes only cause small waves. When they reach Earth, the gravitational waves are very weak.

“Accelerated objects such as two orbiting stars emit gravitational waves, which take energy from the system, so the orbit slowly decays. But since gravity is very weak, enormous masses are required in very close orbits and moving at very high speeds for the effect to be noticed,” explained the university researcher.

Described theoretically by Albert Einstein more than a century ago, it is only in our time that they can be detected with an international network of observatories formed by LIGO, in the United States; VIRGO, in Italy; GEO 600, in Germany; and KAGRA, in Japan.

Before students and academics, the doctor in physics offered some background information that first allowed to infer and then detect gravitational waves.

Two Fundamental Theories

Alcubierre Moya described that the classic theory of gravity is Isaac Newton's Law of Universal Gravitation, which explains the fall of objects and the orbits of the planets.

"This theory has a serious drawback, because it assumes that gravity acts instantaneously: if someone moved the Sun, the Earth would notice it immediately. Newton did not like this 'action at a distance', but he considered that it should be left like this until the nature of gravity was better understood," he mentioned.

He emphasized that the problem worsened when Albert Einstein developed the Theory of Relativity, which showed that nothing could travel faster than light and that nothing can act instantaneously.

Einstein spent 10 years looking for a new theory of gravity. “This effort culminated in 1915 with the Theory of General Relativity, which predicts that gravity is not instantaneous, but rather propagates precisely at the speed of light,” he said.

The university researcher said that the Theory of General Relativity is not a small modification of Newton's theory, but a revolution in the concepts of space and time.

“According to general relativity, space and time are not rigid. The geometry of space and the flow of time are modified by the presence of concentrations of mass and energy: space-time is curved.”

The doctor in physics added that, just as electromagnetism predicts “electromagnetic waves” (such as light and radio waves), general relativity does so with “gravitational waves,” which are disturbances in space-time that propagate at the speed of light.

The first direct observation of a gravitational wave was made on September 14, 2015 with LIGO. Its acronym stands for Laser Interferometer Gravitational-Wave Observatory.

This detection confirms the theory that predicts its existence in massive cosmic phenomena such as galaxy collisions, supernova explosions, and the formation of black holes or neutron stars.