Born in the year 1879 in Ulm, Germany, Albert Einstein was a curious firstborn. He was said to have first encountered a compass at age five, causing his lifelong fascination with invisible forces. In 1896, Albert enrolled in the mathematics and physics program at the Polytechnic college in Zurich and graduated in 1900.

Newton believed that space and time are absolute; while, James Maxwell said that light moves at one speed. Einstein saw a contradiction here and set on his own path. He did a lot of experiments, which helped lead to one of his greatest papers. One that would revolutionise physics and has stood the test of time. Up until today, special relativity stated that light is constant for all observers; eventually, this led him to his theory of general relativity, when trying to incorporate gravity, for a more complete idea of this universe.

Some simple quotes to understand relativity are, “space-time tells mass how to move, mass tells space-time how to curve,” and “the faster you move through space, the slower you move through time,” which brings up time dilation. Time dilation is a result of time slowing down either because of high speeds or due to a high gravitational field.

Einstein’s paper on general relativity, released in the year 1915, states that gravity is not a force. Rather, it is the curvature of space-time, meaning that gravity is the consequence of the fabric of space-time itself.

Some physical effects and experiments that have been fully consistent with this theory are planet Mercury’s irregular orbit around the sun. Mercury’s orbit is highly elliptical and it deviates from Newton’s predictions of orbital mechanics. Einstein managed to prove through his general relativity equations that the sun’s large mass was affecting its orbit. The full solar eclipse in Brazil on the 29th of May, 1919 showed that the sun deflected starlight. Gravitational redshift is another proof. In simple terms, when photons leave a gravitational pull, they change the energy state, which manifests as a change in the wavelength of the photon, since its speed must remain constant. While escaping the gravitational field, its frequency decreases and wavelength increases. Gravitational lensing is another loop phenomenon of general relativity, which is the fact that the entire sky is slightly distorted due to the gravitational deflection of light from the sun. The Hafele–Keating experiment is my personal favourite.

In October of 1971, two scientists took atomic clocks aboard commercial airlines. An atomic clock uses the interaction of electromagnetic radiation with specific atoms to measure time with extremely high precision, so they wanted to take advantage of this to prove gravitational time dilation (as well as kinematic time dilation) and, of course, they were successful. Gravitational waves, which is exactly as the name suggests, is a more recent proof, detected by the Laser Interferometer Gravitational-Wave Observatory back in 2015. They propagate through space and distort space-time as a result of high mass objects moving rapidly through space.

The problem with relativity is when we try to bring in quantum mechanics. We see that it only works on the classical scale, which is why we are trying to find a ‘theory of everything’ to connect it all. My hope is that this will be resolved in my lifetime and lead to new technology to allow interstellar travel.

## Sources

1- “General Relativity.” *Wikipedia*, Wikimedia Foundation, 30 May 2021, en.m.wikipedia.org/wiki/General_relativity.

Writer: Golda Abs

Editors: Lamar Albukhari/Rana Alqahtani