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 ...

The universe is expanding, and while that fact is fascinating, it also creates a question that trips people up: if it’s growing, what exactly is it expanding into? Our brains are used to picturing ...