1 Ophelia: So, to destroy the Universe, we need to have several people destroy the Universe individually...
2 Mercutio: ... all at the same time - while living in different times?
3 Shakespeare: How??
4 Head Death: LOOK, IF IT WAS EASY, SOMEONE WOULD HAVE DONE IT BEFORE NOW.

Forsooth.

The very fact that we're here right now implies that it is incredibly difficult to destroy the Universe. Some people are worried that the Large Hadron Collider will cause some sort of disruption to the space-time continuum and destroy the Universe.* But if it were possible to build a machine with our technology to do that, it's pretty much inevitable that some other alien culture will already have done it. In fact, it'd be so common as to be a function on alien cell phones and portable videogame machines. Imagine a culture of alien 12-year-olds armed with PlayStation Portables with the ability to destroy the Universe, and ask yourself how long it would last.

* In fact most of the doomsayers are merely worried about it destroying the Earth. But that's fairly minor by comparision and not even worth bothering about.

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2021-06-12 Rerun commentary: If it were easy to destroy the Earth, someone would have done that by now too.

Some people might argue that we're in fact in the process of doing it right now. So maybe it's not that hard after all.