Imagine an advanced civilization somewhere in the universe, which developed a particle accelerator that collides electrons at the Planck energy, the scale where gravity must be described quantum mechanically. This energy scale is no small feat for a collider, as it corresponds to ten quintillion (1019) times the rest mass of the proton. To reach this energy with our existing acceleration technology would require a linear collider 10,000 light-years in length.
But various concepts of laser plasma accelerators, on which I worked during my Ph.D., can possibly shorten the required acceleration distance by a factor of 10,000, shrinking the size of such a collider to the size of the Oort cloud that surrounds the solar system. And so, one could optimistically imagine that a highly advanced civilization could generate electron collisions at Planck energies within its home planetary system.
As it turns out, the hypothetical feasibility of such an experiment is a reason for concern to all civilizations in the universe. Let me explain.
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