Guide to Radiation Doses

fascinating chart of the “ionizing radiation dose a person can absorb from various sources;” from using a cell phone to CT Scans to being at Chernobyl and Fukushima when disaster struck.

Solution to the Grandfather Paradox

If you could travel back in time, and you killed your grandfather, would you be killing your future self? What do physics, complexity theory, and computer science have to say about this famous murderous time-travel paradox?