Wednesday, April 27, 2016

divergence-free tensors

can you find apart from the Einstein-tensor and the metric tensor new tensors whose covariant divergence vanishes? would they be viable terms for the field equation?

Wednesday, April 20, 2016

eternal sunshine

can you estimate the life-time of the Sun with the result from previous week, assuming that the source of energy is fusion? What about Jules Verne's idea that the Sun was powered by meteors hitting the surface or by burning coal (to be found in "Round the Moon")?

Wednesday, April 13, 2016

more power, R2!

can you estimate the power density of the Sun, i.e. the amount of power produced by fusion in each cubic meter? what measurements would you need to carry out, and what assumptions do you make?

Wednesday, April 6, 2016


can you use mechanical similarity to explain why astronauts on the moon appear to move in slow motion or as if they were under water?