Technically not impossible, just very very difficult. It isnt actually forbidden by any universal law. Ask Stephen Hawking, who recently pronounced on the subject. As for the golden egg thing....You can colour eggs yellow in goose using xanthine dyes. In fact modern eggs are the colour they are (yolks I mean) because of coloured foodstuffs, natural or unnatural. A chicken on a natural diet produces a yolk that is lemon yellow. To get a goose to lay a golden egg you need to make a golden egg, anaesthetise the goose, put the egg into the goose in a reverse laying sense (keeping a good eye out for RSPCA inspectors) and t5hen wait for the goose to wake up. Preferably from a distance as geese are very violent and are unlikely to derive much pleasure from an enormous gold pessary. It will then lay a golden egg, and you will probably get 5 years and a psychiatric assessment.