In 1915 Einstein published his ground breaking theory of General relativity.
According to his theory Space and Time are so interconnected. It called four dimensional fabric of space time. Massive object can warp the space-time and everything in the universe move through this uneven fabric. If the mass of and object wrap the space time, the light travels in that region of space also bend along with it.
The problem was there’s no way to test this idea in the lab. Only a massive object can bend the space time that can case light to bend noticeable to any equipment. Luckily soon after Einstein published his theory Sir Arthur Eddigton tested this with a total solar eclipse.
Scientist knew where the stars normal appear in the sky, but when the sun crossed those star cluster, due to the bending of space time it shifted the start further away from the sun. This experiment demonstrated that the space time bending, just as Einstein predicted.