20090501
Roy Sorensen, Spinning shadows
If a spinning sphere casts a shadow, does the shadow also spin? This riddle is the point of departure for an investigation into the nature of shadow movement. A general theory of motion will encompass all moving things, not just physical objects. Ultimately, I argue that round shadows do indeed spin. Shadows are followers of the objects that cast them. Parts of the shadow correspond to parts of the leader, so motion of the caster's parts accounts for motions of the shadow's parts. I conclude with a discussion of how the dynamic aspects of shadows impose subtle constraints on other puzzles about shadows.
20090430
20090428
From New Scientist
Astronomers have spotted the most distant object yet confirmed in the universe – a self-destructing star that exploded 13.1 billion light years from Earth. It detonated just 640 million years after the big bang, around the end of the cosmic "dark ages", when the first stars and galaxies were lighting up space.
20090426
20090423
20090422
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