Albert Einstein's theory of special relativity explains how space and time are linked, but it doesn't include acceleration. By including acceleration, Einstein later developed the theory of general relativity, which explains how massive objects in the cosmos distort the fabric of space-time. The theory explains how this distortion is felt as the force of gravity, as it predicts how much the mass of an object curves space-time. Scientists test relativity by observing objects in space and seeing if their behaviors match up with Einstein's explanations of space-time and gravity, for instance by observing how light bends around massive objects as it travels towards Earth.
A look into the foundations of relativity, and how Einstein's subsequent fame affected his later science.
Scientists still aren't sure exactly why the universe began with a Big Bang 13.8 billion years ago. Will humanity ever really understand the Big Bang's true nature?
Inside black holes dwell quantum remains of the stars from which they were formed, say a group of scientists, who also predict that these stars can later emerge once the black hole evaporates.
A fast-spinning star packed tightly with two white dwarf companions may be the best test yet of Einstein's theory of general relativity.
Gravity waves, predicted by Einstein, have yet to be seen, but new advanced experiments are in the works.