## Symmetry and General Relativity

One may think, “Woaah! Is there a connection between symmetry and general relativity?” The answer is yes, but the relationship is not that obvious.

Albert Einstein, the main proponent of the Theory of General Relativity, was a visual person. Whenever he encountered a concept in his studies, he tries to imagine the image of that particular concept.

For example, imagine someone moving towards you holding a light source, say a flashlight, with a speed of 1000 meters/sec. You would think that the photons would be travelling at (300 million + 1000) meters/sec. However, this is wrong. Einstein said that the photons would still be travelling at 300 million meters/sec, in relation to you and the person holding the flashlight.

Where does symmetry enter? Symmetry is represented in the concept of the “conserved quantity” – something that retains itself no matter the perspective in which you look at it. This is basically symmetry. In the example above, no matter where you are located or where the flashlight holder is running from, the photons will still travel at the same speed, as if some underlying symmetry is present.

Source: https://www.thenakedscientists.com/articles/features/importance-symmetry