Gravity: The Cosmic Mirage

Gravity: The Cosmic Mirage

In 1687, Isaac Newton mathematically demonstrated that the physics that govern the apple falling from the tree also govern the stars and the planets. The law of universal gravity explained how things moved around in space, but they didn’t answer an important question – why? Why is there gravity, and why do things move the way they do? Newton was famous for never trying to answer this question. The status quo remained so until the universe conspired to make the synonym of genius – Albert Einstein.

At 36, Einstein published the General Theory of Relativity, putting forth that spacetime is a fabric stretched from all sides. When objects like our Sun reside on it, they add their indentation on it. Gravity moved things along the curving pathways due to these indentations in spacetime. This revolutionary idea became the basis of our modern understanding of how things work in the universe.

The simplest and most captivating explanation of the fabric of spacetime you could find.

This theory didn’t mean Newton was wrong. Newton’s laws still work on everyday objects, even being used to approximate gravity to considerable accuracy in many applications today. Relativity chips in when greater accuracy is needed.

A cosmic lens

Einstein’s theory also predicted an amusing possibility – light can bend when under the influence of strong gravity. It made sense because light has a mass and any object with mass is subject to gravity. The proof for this radical thought came from a famous experiment during the 1919 total solar eclipse, when Sir Arthur Eddington, an English astronomer, observed how the Sun bent the lights of distant stars. This bending shifted the stars from their expected position in the sky. This validation made Einstein an overnight hero worldwide for eternity.

This video by Vox explains with great ease and detail the 1919 Eddington Experiment

The validation of relativity opened up a new way to observe distant objects in space. Similar to how the lenses in a binoculars bend and magnify the light coming from objects at a distance, objects with large mass can bend light due to gravity, acting as a magnifying glass in space. This phenomenon is called gravitational lensing.

Gravitational Lensing
An example of gravitational lensing by a quasar. The distant galaxy’s light bends and appears as two different objects when seen by a telescope.

New Horizons

While the observations in 1919 were indeed gravitational lensing, the first discovery is attributed to the 1979 observation of “Twin Quasars” from the Kitt Peak National Observatory in Arizona, United States. Scientists observed two quasars (a massive black hole releasing extreme amounts of energy) close to each other with eerily similar characteristics. It was later determined that they are the same object, mirrored due to a gravitational lens.

With the launch of the Hubble Space Telescope, we have observed quite many gravitational lenses. In some instances, the light from the source object, the gravitational lens, and the Earth can perfectly match up, resulting in a ring-like appearance of the object being lensed. Today, these rings are called Einstein Rings, commonly found when a galaxy occludes another distant galaxy, causing the latter to appear as a ring around the former.

The gravity of the luminous red galaxy at the center creates a gravitational lens and distorts the image of a distant galaxy behind it to appear as a ring around it. Image by NASA.

Closing Thoughts

To conclude – Gravity rules the universe. Nothing, not even light, can escape its influence. In doing so, it manifests itself in many forms – often in a dazzling, artistic way like these gravitational lenses. All we have to do is keep looking up and notice, and appreciate its grandiosity in the process!

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