What Is Time? | Professor Sean Carroll Explains Presentism and Eternalism

This paragraph delves into the exploration of time from both philosophical and scientific viewpoints. It highlights the historical relationship between physics and philosophy, emphasizing their distinct aims but overlapping subject matters. The discussion focuses on the importance of understanding the logical underpinnings of time from a philosophical standpoint, contrasting it with the physicists' approach to developing functional theories, such as quantum mechanics, which may not fully make sense but are effective. The lecture aims to address the philosophical questions surrounding time, its difference from space, and the continuous nature of the universe from moment to moment.

The second paragraph contrasts the rules governing time and space. It explains that while space has no inherent rules about what happens next to everything else, time is governed by the laws of physics that dictate a sequence of events. The paragraph discusses the concept that knowing the state of the universe at one moment allows us to predict what will happen next, unlike in space. It also touches on historical perspectives, such as Aristotle's, and introduces the idea of different physical laws that could involve the past more significantly. The discussion continues with the concept of reality as it pertains to different times and spaces, questioning the common perception of the past and future versus the present.

This paragraph introduces the concept of space-time as a four-dimensional framework that combines the three dimensions of space with the one dimension of time. It discusses the historical understanding of space-time by both Newton and Einstein, noting that while Newton saw space and time as distinct, Einstein's theories revealed that they are interconnected. The paragraph explores the philosophical viewpoints of presentism and eternalism, which offer different perspectives on the reality of the past, present, and future. It also introduces the idea of the 'block universe,' a concept that treats all moments in time equally as real, and discusses the implications of these philosophical stances on our understanding of reality.

The fourth paragraph expands on the idea of the block universe by proposing the growing block universe model. This model suggests that the present and the past are real, but the future is not yet real, aligning with our perception that we can influence the future but not the past. The paragraph discusses the implications of this model on our understanding of time and reality, and how it reflects our human experience of time as something that progresses and changes. It also touches on the concept of the arrow of time, which gives us the sense of time passing and the asymmetry between the past and the future, ultimately suggesting that our different access to past and future moments is due to entropy and the macroscopic configuration of matter in the universe.

The fifth paragraph discusses the importance of clocks in measuring and understanding time. It explains that clocks provide a consistent and repeatable action that allows us to quantify the passage of time. The paragraph explores the various natural and man-made clocks in our universe, from celestial bodies like the Earth and its rotation and revolution around the Sun, to pendulums and quartz crystals. It highlights the historical development of timekeeping, from Galileo's observation of a chandelier's pendulum motion to the precision of modern quartz clocks. The discussion emphasizes the reliability and predictability of clocks, which are crucial for our operational understanding of time and its passage.

The final paragraph explores the hypothetical scenarios of time stopping or slowing down and their implications. It argues that if time stopped or slowed down everywhere in the universe, there would be no way to know or experience it, as all processes, including those in our brains and clocks, would also stop. The paragraph uses thought experiments and a fictional story to illustrate the complexities and challenges of understanding such concepts. It concludes by reflecting on the social aspects of time and the pressures we feel due to coordinating with the outside world, emphasizing that time is not fundamentally a negative force but rather a tool that enables us to be social creatures.