What is Gravitational Lensing

A intriguing component of Einstein’s theory of general relativity is the phenomena of light being impacted by gravity, often known as gravitational lensing. The basic ideas of the theory can be used to explain how light interacts with gravity even if light itself has no mass. We must examine the fundamental concepts of General Relativity and the characteristics of gravitational fields in order to better comprehend this theory. Let’s explore in detail about What is Gravitational Lensing.

What is Gravitational Lensing

What is Gravitational Lensing

Sir Isaac Newton’s Universal Law of Gravitation was the first theory to explain gravity before Einstein’s General Theory of Relativity. Newton defined gravity as an instantaneous action at a distance and as the force of attraction between two large objects. However, when it came to describing specific findings, this traditional conception of gravity presented significant difficulties.

Our knowledge of gravity has been completely transformed by Einstein’s theory. General Relativity depicts gravity as the curvature of spacetime brought on by the presence of mass and energy, rather than as a force acting between masses. According to this theory, huge celestial bodies like planets or stars cause the spacetime fabric to distort everything around them. We experience the force of gravity as a result of the curvature of spacetime. Through this curved spacetime, objects move in curved pathways, which we understand as gravitational attraction.

The Equivalence Principle

One of the guiding principles of general relativity is the Equivalence Principle. It asserts that there is no distinction between being in a gravitational field and being in an accelerated reference frame locally, in a sufficiently tiny area of spacetime. This means that despite travelling along curved pathways in spacetime, things in a gravitational field seem to fall as though they are being pulled downward by a force. This idea contributes to the understanding of why gravity affects light.

Gravitational Lensing

A process known as gravitational lensing happens when huge objects, such as galaxies or stars, distort the course of light that passes by them. The huge object’s gravitational field warps spacetime, which results in this bending of light. When light from a far-off object comes into close proximity to a large object, it moves through the curved spacetime in a trajectory resembling that of a ball rolling on a curved surface.

The two basic types of gravitational lensing are as follows:

1. Weak Lensing : The gravitational field’s impact on light in weak lensing is minimal. It stretches or slightly distorts distant things without generating duplicate pictures. Astronomers frequently employ this kind of lensing to map the distribution of dark matter throughout the cosmos.

2. Strong Lensing : When the gravitational field is potent enough, several pictures of the same far-off object are produced. When light from a distant object is twisted in a circular pattern around a large foreground object, it can result in phenomena like Einstein rings.

Light’s Reaction with Gravitational Fields

What does this have to do with the fact that light has no mass, then? According to General Relativity, an object’s speed is governed by how closely it adheres to the curved trajectories in spacetime made by large objects. Both huge things like planets and massless particles like photons (light particles) are involved in this motion.

Despite having no mass, photons travel along the curved routes in spacetime that gravitational forces produce. This is related to the fact that photons travel at the speed of light and that even in the fabric of curved spacetime. When spacetime is bent due to gravity, the “straightest” path a photon can take is still curved.

In other words, according to the Equivalence Principle, light behaves as though it is subject to gravity even though it has no mass. According to General Relativity, gravitational lensing is the result of the curvature of spacetime brought on by enormous objects. This is what we see when we detect gravitational lensing.


In conclusion, Einstein’s General Theory of Relativity is what causes the phenomenon of light being impacted by gravity. This framework views gravity as the curvature of spacetime brought on by the presence of mass and energy, rather than a force operating between masses. Despite having no mass, photons travel along these curved routes in spacetime. And their actions in gravitational fields bear witness to the fundamental ideas behind this ground-breaking theory. Strong evidence for the validity of general relativity has been provided by the observation and confirmation of the gravitational lensing phenomenon through a variety of astronomical observations and experiments.

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