It is often said that something CANNOT come out of nothing? Is this true? Is there a way to test the properties of nothing to make this assertion?
closed as not a real question by Waffle's Crazy Peanut, John Rennie, Manishearth♦ Jan 19 '13 at 9:48
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Something and nothing are not physics terms.
In physics as we know it there are conservation laws for specific measurable quantities, as are momentum and energy for example, which have been tested extensively and hold absolutely.
Energy both within classical physics and special relativity and quantum mechanical formulations, cannot appear out of nothing and this holds in all our experiments up to now.
Cosmology though is the realm of General Relativity and there are phase space regions where energy is not a well defined concept , early early universe, very high energies,...
So energy could come out of nothing there, where nothing is defined as no apparent energy. There is no way to test this experimentally,as far as I know.