Physicist Explains Dimensions in 5 Levels of Difficulty | WIRED

The conversation begins with Sean Carroll, a theoretical physicist, explaining the concept of dimensions to Hank. He clarifies that dimensions are simply directions one can move in, such as up-down, left-right, forward-backward. Typically, we perceive three spatial dimensions, but the idea of additional dimensions is introduced, prompting a discussion on how these extra dimensions might be hidden or exist at a scale beyond our perception. The dialogue includes a discussion on 3D printing as an example of three-dimensionality and a thought experiment involving line segments to illustrate the concept of one-dimensional space. The conversation then transitions into exploring the idea of two and three-dimensional spaces, leading to the question of the possibility of more than three spatial dimensions.

The discussion continues with an exploration of higher dimensions. Sean challenges Hank to hold multiple objects at right angles to each other, demonstrating the limitations of our three-dimensional space. The concept of coordinates and the use of X, Y, and Z axes in defining positions in three-dimensional space are introduced. The conversation then delves into the idea of other coordinate systems, such as polar coordinates, and the theoretical existence of extra dimensions that could be too small to observe. The topic of time as a fourth dimension is broached, along with the concept of spacetime and its relation to Einstein's theory of relativity.

Sean explains the concept of relativity and its impact on the understanding of spacetime. He uses a blackboard to illustrate the idea of spacetime, where all of space is condensed into one direction and time is another. The concept of distance in spacetime and how it relates to an individual's movement through time is discussed. Sean describes how different paths in spacetime can represent different amounts of 'time traveled' due to the curvature of spacetime caused by massive objects like the Earth and the Sun. The conversation touches on Einstein's idea that gravity is a manifestation of the curvature of spacetime, rather than a separate force.

The conversation shifts to observational cosmology and the concept of extra dimensions. A cosmologist discusses their work on mapping the universe to understand dark energy and introduces the idea of bubble universes, which could potentially have different numbers of dimensions. The dialogue explores the possibility of a multiverse with different underlying laws of physics and the speculative nature of string theory, which posits that quantum gravity can only work in a ten-dimensional spacetime. The concept of 'branes' is introduced, suggesting that our observable universe might be a three-dimensional 'brane' embedded in a higher-dimensional space.

A string theorist shares their perspective on the implications of string theory and the concept of a multiverse. The conversation delves into the idea of compactifying extra dimensions and the possibility of large extra dimensions that could be part of a de Sitter space. The concept of 'black branes' is introduced, which are higher-dimensional objects similar to black holes but with different internal structures. The dialogue explores the potential for a multiverse to arise from an empty de Sitter space with positive cosmological constants, leading to various cosmological solutions and the potential need for the anthropic principle to explain our existence in a particular universe.

The conversation concludes with a look at the future of cosmology and string theory. The string theorist expresses optimism that our understanding of dimensions and spacetime will continue to evolve, suggesting that a more molecular-like description of the early universe could lead to the emergence of flat spacetimes. The discussion touches on the potential for new insights from quantum mechanics and the ongoing debate within the scientific community about the validity of certain cosmological models. The conversation highlights the excitement of exploring these complex theories and the potential for new discoveries in our understanding of the universe.