Five things Einstein’s theories correctly predicted

Gravitational Waves

Einstein’s general theory of relativity predicted ripples in the fabric of space-time called gravitational waves. Set off by violent cosmic cataclysms, they were finally observed in 2016 – a little over 100 years after they were proposed – when the Laser Interferometer GravitationalWave Observatory picked up two neutron stars colliding. Gravitational waves have been notoriously difficult to prove because their distortion of space-time is miniscule by the time they reach us.

Light’s Speed Limit

Einstein predicted that light always travels at the same speed – 299,792 kilometres (186,000 miles) per second – and claimed it didn’t matter how much energy is contained in a particle of light because there will not be any difference in speed. Some scientists predicted this may not be the case, and that higher energy photons travelled slower than those of lower energy. But an observation by the Fermi Gamma-ray Space Telescope found Einstein was correct.

Black holes

The theory of relativity predicted that space-time could be deformed by a compact mass to form a black hole. It also said the gravitational pull of a black hole would bend light waves, as well as release them from the other side. This was proven in July 2021 when Stanford University astrophysicist Dan Wilkins detected light from behind a black hole for the first time. He and his colleagues observed X-rays coming from the far side.

Gravitational lensing

Einstein predicted that each ray of light that we detect on Earth has been deflected as it travels through space. Massive celestial objects are able to bend the passing light by a small degree, and that would need to be taken into account during observations. The first gravitational lens was discovered in 1979, when the Twin Quasar was observed. Its appearance was distorted by the gravity of a galaxy closer to Earth in the same line of sight.

The universality of free fall

The theory of general relativity says two objects dropped in a gravitational field will fall with the same acceleration regardless of mass or composition. This was confirmed by astronomers at the University of Manchester in 2020 by measuring the movement of a white dwarf and a pulsar orbiting a second white dwarf. Both the pulsar and the white dwarf orbited exactly the same, falling “with the same acceleration in the gravitational field of a third”.