# Why Astronaut Mark Kelly Is Now Even Older Than His Twin Brother

Astronaut Scott Kelly returned from a year-long sojourn in space in June. His slightly older astronaut 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…

# 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 traveling 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.

# Get Pelted Every Day With Particles That Confirm Special Relativity

Go outside and you will be showered, every day, with proof of the theory of special relativity. This proof comes in the form of muons, so you won't actually see it, but we'll tell you why the presence of these particles proves Einstein right.

# Time travel is possible – but where will it take us?

We know that time travel is possible, at least in the forward direction. In this recently released TEDEd video, educator Colin Stuart imagines where and when it might take us, while exploring the science behind time travel and time dilation.

# How Einstein's theory of relativity makes you smaller

Relativity is best known for giving us a new view of time. The faster you go, the slower time moves. There are other effects as well. For example, the faster you go, the more squished you get.

# Einstein's Pedometer App Measures Your Aging (or Lack Thereof)

In case you need a science class reminder, Albert Einstein's Theory of Relativity partly concerned the process of ageing—specifically that a stationary person actually ages faster than someone in motion. Using the iPhone's GPS, along with the Lorentz Transformations, this app will details exactly how much "life"…

# Ultra-accurate clocks prove time moves faster at your face than your feet

Einstein's theory of relativity says that time passes more slowly the closer you get to the ground, because you're closer to Earth's gravitational field. It's a tiny difference, but big enough for a pair of laser-powered clocks to actually measure.