The mind-bending physics of time | Sean Carroll

Oct 29, 2025

The guest, Sean Carroll, is a Homewood Professor of Natural Philosophy at Johns Hopkins and a theoretical physicist renowned for his insights into cosmology. In this discussion, he delves into the enigmatic nature of time, exploring how the Big Bang set the stage for our understanding of past, present, and future. Carroll explains entropy and the second law of thermodynamics, illustrating how the universe's low-entropy beginning influences the arrow of time. He also speculates on the tantalizing possibilities of time travel and the multiverse.

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INSIGHT

Time As An Event Label

Time is a label that orders events and distinguishes moments in the universe.
The real puzzles are time's properties like past, present, and future, not time's existence.

INSIGHT

Physics Lacks A Built-In Arrow

Fundamental physical laws don't distinguish past from future even though we experience a clear arrow of time.
The arrow of time is analogous to spatial directions: laws are symmetric but contexts create apparent directions.

INSIGHT

Arrow From A Historical Event

The perceived direction of time arises from an influential historical condition, not from fundamental laws.
We experience an arrow of time because we live in the aftermath of the Big Bang.

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How the Big Bang gave us time, explained by theoretical physicist Sean Carroll. In this Big Think interview, theoretical physicist Sean Carroll discusses the concept of time and the mysteries surrounding its properties. He notes that while we use the word "time" frequently in everyday language, the real puzzles arise when we consider the properties of time, such as the past, present, and future, and the fact that we can affect the future but not the past. Carroll also discusses the concept of entropy, which is a measure of how disorganized or random a system is, and the second law of thermodynamics, which states that there is a natural tendency for things in the universe to go from a state of low entropy to high entropy. He explains that the arrow of time, or the perceived difference between the past and the future, arises due to the influence of the Big Bang and the fact that the universe began in a state of low entropy. Carroll also touches on the possibility of time travel and the concept of the multiverse.

0:00 What is time? 1:32 How the Big Bang gave us time 3:31 How entropy creates the experience of time ---------------------------------------------------------------------------------- About Sean Carroll: Dr. Sean Carroll is Homewood Professor of Natural Philosophy — in effect, a joint appointment between physics and philosophy — at Johns Hopkins University in Baltimore, and fractal faculty at the Santa Fe Institute. Most of his career has been spent doing research on cosmology, field theory, and gravitation, looking at topics such as dark matter and dark energy, modified gravity, topological defects, extra dimensions, and violations of fundamental symmetries. These days, his focus has shifted to more foundational questions, both in quantum mechanics (origin of probability, emergence of space and time) and statistical mechanics (entropy and the arrow of time, emergence and causation, dynamics of complexity), bringing a more philosophical dimension to his work. ----------------------------------------------------------------------------------

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