Part of the show BSE, Cervical Cancer and Toxoplasmosis
Alan in Kent asked:
Do TV and radio signals travel vertically, and if they do, do they disappear or travel off into space forever? If so, does that mean that a signal from the 1950s is still in space somewhere?
Yes the signals we create are creating a sort of bubble around the earth which is expanding at the speed of light. That means that the bubble is roughly 100 light years across now and spreading away from the earth. But when you think that the Milky Way is easily about 100 000 light years across, it's going to take a long while for many of the stars just in our own galaxy to hear us. When you consider that there are 10 000 000 000 000 000 000 000 stars out there, it is going to take a long while before the messages get to anyone else. So it is not surprising we haven't heard anyone replying yet.