Why Mark Kelly Is Now Older Than His Older Twin Brother

Astronaut Scott Kelly returned from a year-long sojourn in space in June. His slightly older twin, Mark Kelly, stayed home as a control—part of NASA’s twin study to monitor the effects of space on the human body. But there’s a physical change that NASA might not be able to measure that easily. Mark is now even older (by about 5 milliseconds) than his space-faring twin, thanks to special relativity. Read More >>

Earth’s Core Is Younger Than We Thought

Without a Tardis, a journey to the center of the Earth might be your best option for travelling to the past. Because of the way gravity warps spacetime, physicists have now calculated that the Earth’s core is 2.5 years younger than its surface. Read More >>