Add Yahoo as a preferred source to see more of our stories on Google. About a century ago, scientists were struggling to reconcile what seemed a contradiction in Albert Einstein’s theory of general ...

Add Yahoo as a preferred source to see more of our stories on Google. In space, there are four dimensions: length, width, height and time. scaliger/iStock/NASA via Getty Images Plus About a century ...

For centuries, humans have looked to the stars and wondered about the universe’s vastness, shape, and structure. One question that has long persisted is the concept of the center of the universe. Is ...