A few hours ago the European Space Agency (ESA) launched a satellite which will hopefully lead to our being able to detect ripples in space. The LISA Pathfinder satellite took off from French Guiana just after 4am GMT, and its purpose is to test the feasibility of a far more ambitious experiment called LISA which will be launched in the 2030s.There are ground-based experiments to detect gravitational waves (the ripples in space that I referred to above), but doing such experiments from space should provide more sensitivity. These waves are a prediction of Einstein’s theory of gravity, the general theory of relativity. We are yet to detect any gravitational waves, but as I explain in my book on the cosmic microwave background, detecting them will provide us with another way of measuring properties of the Universe. In some ways, rather than seeing the Universe, we would be able to feel it.