Gravity has always been an essential tenet of astrophysics. The formation of our planet, much less the universe, is inconceivable without gravity. When most of us think of gravity, our minds go to how we stay on the ground, the book that dropped on our foot this morning, or even the apple that supposedly fell next to Isaac Newton and sent his brain turning about why it fell. Contradictory to popular belief, the Earth does not pull us down, and when the apple was falling, it wasn't really. Rather, the Earth's gravity is so great that it causes a curve in space that the apple rolled down. This concept was one of Einstein's greatest discoveries, and gravity continues to surprise us to this day.
Above is a video showing an amazing discovery. Although the video is just an artist's depiction, the event actually occurred. This proves that gravity's force can actually bend light and distort our perception by altering what we see. While it has been thought for a while that black holes can bend light in, this was a fantastic illustration of the power of gravity. Below is an illustration of how black holes could bend light.
This concept of gravity distorting light is key in helping determine the shape of the universe.