Reality Is Not What It Seems: The Journey to Quantum Gravity

by Carlo Rovelli

There is an intuitive way of understanding what happens. Suppose we want to observe a very, very, very small region of space. To do this, we need to place something in this area, to mark the point that we wish to consider. Say we place a particle there. Heisenberg had understood that you can’t locate a particle at a point in space for long: it soon escapes. The smaller the region where we try to locate a particle, the greater the velocity at which it escapes. (This is Heisenberg’s uncertainty principle.) If the particle escapes at great speed, it has a great deal of energy. Now let us take Einstein’s theory into account. Energy makes space curve. A lot of energy means that space will curve a great deal. A lot of energy in a small region results in curving space so much that it collapses into a black hole, like a collapsing star. But if a particle plummets into a black hole, I can no longer see it. I can no longer use it as a reference point for a region of space. I can’t manage to measure arbitrarily small regions of space, because if I try to do this, these regions disappear inside a black hole.