I've always been interested and intrigued by the idea of light cones and how they fit in with other theories in physics. I have a couple of questions about them that I hope make sense are easily clarified: (1) I understand why the shape of the Past Light Cone is a Cone. I don't understand how the Future Light Cone takes on a definite Cone Shape. Wikipedia on Events outside of Light Cone: "All other events are in the (absolute) elsewhere of E" (E being an Event occuring at the origin) "and are those that can not affect and can not be affected by E." Example: A Light source emits a flash here on earth (Call this Event E). Looking at the Future Light Cone, a second later, Mars lies in the "absolute". The planet cannot affect or be affected by Event E. But what about an electron. We can't say that a second later it lies in the absolute because QM tells us we can only know its future location to a certain probability. So technically it could affect E, but it lies outside the future light cone. Any ideas?