G. 't Hooft proposes that at the Planck scale, our world is not 3+1 dimensional but rather described by Boolean variables on a 2-dimensional lattice. This conclusion is based on unitarity, entropy, and counting arguments, implying severe constraints on quantum gravity models. He argues that dimensional reduction implies more constraints than freedom in model construction, explaining why consistent quantum gravity models are hard to find. He discusses the dimensionality of space and time, noting that while our world appears 3+1 dimensional, this may not hold at the Planck scale. He suggests that black holes provide a natural cut-off due to their formation when too much energy is concentrated in a small region. He argues that quantum mechanics remains valid at the Planck scale, though it becomes trivial, with quantum superpositions being irrelevant. He explores the black hole entropy, attributing it to quantized fields rather than the space-time metric. He shows that the number of Boolean degrees of freedom surrounding a black hole is proportional to the area of the horizon. This suggests that all information about a region of space can be encoded on its boundary, implying that physical degrees of freedom in three-space are not independent but must be infinitely correlated. He discusses the implications for quantum gravity, suggesting that it should be described by a topological quantum field theory where all physical degrees of freedom are projected onto the boundary. He also considers the possibility of wormholes, but argues that they are not allowed in a consistent quantum gravity theory. He explores cellular automaton models for quantum mechanics, noting that while the Copenhagen interpretation is natural, the stability of the vacuum state is a challenge. He also discusses the difficulty of reproducing Lorentz invariance in discrete models and the need for further research to understand the evolution laws of physical degrees of freedom on a 2-surface. He concludes that the dimensional reduction of space-time to a 2-surface is a fundamental feature of quantum gravity, with implications for the information paradox and the nature of physical degrees of freedom. He advocates for further research into this approach, noting that it may provide a path to a consistent quantum gravity theory.G. 't Hooft proposes that at the Planck scale, our world is not 3+1 dimensional but rather described by Boolean variables on a 2-dimensional lattice. This conclusion is based on unitarity, entropy, and counting arguments, implying severe constraints on quantum gravity models. He argues that dimensional reduction implies more constraints than freedom in model construction, explaining why consistent quantum gravity models are hard to find. He discusses the dimensionality of space and time, noting that while our world appears 3+1 dimensional, this may not hold at the Planck scale. He suggests that black holes provide a natural cut-off due to their formation when too much energy is concentrated in a small region. He argues that quantum mechanics remains valid at the Planck scale, though it becomes trivial, with quantum superpositions being irrelevant. He explores the black hole entropy, attributing it to quantized fields rather than the space-time metric. He shows that the number of Boolean degrees of freedom surrounding a black hole is proportional to the area of the horizon. This suggests that all information about a region of space can be encoded on its boundary, implying that physical degrees of freedom in three-space are not independent but must be infinitely correlated. He discusses the implications for quantum gravity, suggesting that it should be described by a topological quantum field theory where all physical degrees of freedom are projected onto the boundary. He also considers the possibility of wormholes, but argues that they are not allowed in a consistent quantum gravity theory. He explores cellular automaton models for quantum mechanics, noting that while the Copenhagen interpretation is natural, the stability of the vacuum state is a challenge. He also discusses the difficulty of reproducing Lorentz invariance in discrete models and the need for further research to understand the evolution laws of physical degrees of freedom on a 2-surface. He concludes that the dimensional reduction of space-time to a 2-surface is a fundamental feature of quantum gravity, with implications for the information paradox and the nature of physical degrees of freedom. He advocates for further research into this approach, noting that it may provide a path to a consistent quantum gravity theory.