For colliders, where accelerated particles collide with each other, a high-grade vacuum is even more important.

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Even they disagree about the actual risks, though, and most of us do not worry about runaway atomic colliders.

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While particle-physics colliders and space-based observatories could rule out some of the more exotic versions of each, no one has been able to suggest a way to decide between them in general.

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In reality, no one has ever been able to drop an anti-apple and watch it fall down (or up), and the antimatter produced in particle colliders is so energetic that it is hard to examine with the tools of precision physics.

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