(……) String theorists and other would-be unifiers of physics face a basic problem. The theories they seek to unify, quantum field theory and Einstein’s general theory of relativity, are well-grounded and well-tested, yet mutually incompatible. Reconciling them will demand that some deeply held intuition must give way. One such intuition is that the world exists within space and time. Participants at the Kavli workshop were inclined to think that space and time are not fundamental, but emergent. The universe we seeing playing out in space and time may be just the surface level, where we float like little boats while leviathans stir in the deep.
Black holes provide the strongest argument for this point of view. The laws of gravity predict that these cosmic vacuum cleaners obey versions of the laws of thermodynamics, which is strange, because thermodynamics is the branch of physics that describes composite systems, such as gases made up of molecules. A black hole sure doesn’t look like a composite system. It just looks like a warped region of space that you would do well to stay away from. For it to be composite, space itself must be.
In that case, black holes represent a new phase of matter. Outside the hole, the universe’s “degrees of freedom”—all that its most fundamental building blocks are capable of—are in a low-energy state, forming what you might think of as a crystal, with a fixed, regular arrangement we perceive as the spacetime continuum. But inside the hole, conditions become so extreme that the continuum breaks apart. “You can make spacetime melt,” Verlinde told me. “This is really where spacetime ends. To understand what goes on, you need to use these underlying degrees of freedom.” Those degrees of freedom cannot be thought of as existing in one place or another. They transcend space. Their true venue is a ginormous abstract realm of possibilities—in the jargon, a “phase space” commensurate with their almost unimaginably rich repertoire of behaviors.(……)
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