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Death Star Science: The Physics Of Destroying An Earth-Sized Planet
StartsWithABang writes: The ability to destroy an Alderaan-like (or, ahem, Earth-like) planet has long been the dream of slashdotters everywhere. But generating the power necessary to unbind a planet — some 2.24 x 10^32 Joules — is simply impossible on board an object only the size of a small moon. But if, instead, you could house a 1-2 trillion ton asteroid (about 5-7 km across) made of antimatter and deliver it to the planet's core, Einstein's E=mc^2 ensures that the planet will be destroyed in seconds.
I don't think it would work as well as TFA suggests. Even if you could instantly insert a 5-7 tera-ton anti-matter asteroid into earth's core, it would not just instantly detonate. Only the surface, that was in contact with matter, would explode, sending a compression wave both inward and outward, pushing the matter and anti-matter apart. Plasma would occupy the space in between, but it would be too tenuous to provide enough energy to instantly blow the planet apart in just a few seconds. Sure, all life would be wiped out, and the planet would be blown apart, but I am not sure it would happen in just a "few seconds" like in the movie.
It isn't a normal laser, it is a gravity laser. The gravity laser compresses all of the matter in the way to the point where fusion occurs between all elements. This lets you poke a whole through the planet since the beam can get past the matter it has already compressed. While the beam is still on it will be pulling more and more of the planet into it. When you get enough captured in the beam, turn it off and left the compressed matter explodes via nuclear fusion.