The Landscape, the Swampland, and Information

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Albert Einstein's “biggest blunder” still haunts theoretical physics. Einstein originally introduced a “cosmological constant” term into his equations for gravity in order to model a static universe, but he dropped it when Hubble discovered that the universe is in fact expanding. Giving up on the cosmological constant turns out to be the mistake, though: careful measurements in 1998 (leading to the 2011 Nobel Prize in Physics) showed that the universe's expansion is in fact accelerating, and the simplest explanation is a very small cosmological constant. The problem lies in trying to calculate the cosmological constant from theoretical physics. The naive estimate gives an answer that is 100 billion billion googol larger than the value associated with measurements. One possible solution is suggested by string theory, a theory of subatomic physics that also describes gravity: there seems to be a gigantic “landscape” of states of string theory, each with a different cosmological constant. Our section of the universe may just lie in a state with a very small cosmological constant. The problem is that the landscape models are based on assumptions about four-dimensional physics, while string theory is itself ten-dimensional. Some physicists have conjectured that the 4D theories of the landscape actually belong to the “swampland,” 4D theories that look reasonable but are actually incompatible with string theory. As a world-recognized expert on the connection between 10D and 4D physics, I am working to settle this debate. The answer will have profound implications for our understanding of the origins and fate of the universe. Meanwhile, recent insights into quantum gravity and black holes suggest another approach; there is increasing evidence that gravity can be understood as a theory of information, the bits familiar from computing. I am building theories of the cosmological constant in terms of information, connecting this possibly fundamental principle of quantum gravity to aspects of the “landscape vs swampland” debate. My work is solving the biggest problem in theoretical physics, both in terms of the size of the error and in the conceptual implications, and it is positioning Canada at the forefront of the field.