On Time

The Physics That Makes the Universe Tick

Jim Al-Khalili

• Publisher: Princeton University Press
• Year: 2026
• Print ISBN:
  9780691267043
  9780691267036
• eBook ISBN:
  9780691291024
• Topic: Physical Sciences
• Subtopic: Philosophy & Ethics in Science

From quantum physicist, New York Times bestselling author, and BBC host Jim Al-Khalili, essential insights into the meaning and fundamental nature of time

While we have come a long way toward deciphering the laws of the universe, many physicists still regard time to be one of the greatest unsolved mysteries. On Time provides answers to the questions about time that philosophers and scientists have been asking for millennia, such as whether it has a beginning and an end, why it only points toward the future and not the past, whether it can be stretched and squeezed or even reversed, and whether it is even real.

In this mind-altering book, Jim Al-Khalili tackles the enduring problems of time head-on, carefully examining them across the three central pillars of physics—quantum mechanics, general relativity, and thermodynamics. He shows how, in each domain, time can be understood differently: as a coordinate or label, as an inseparable dimension of space-time, or as a direction or “arrow.” He explains why it can be difficult to reconcile these different perspectives and describes how theorists at the frontiers of physics are attempting to do just that. Al-Khalili makes the persuasive case that time is real, not illusory, and that a master arrow of time is not merely a trick of our senses but is rather a fundamental feature of reality that was baked into the structure of our universe from the very beginning.

Sharing fresh insights into some of the most complex and profound questions in science, On Time will forever change the way you think about the passage of time and your place within it.

Table of contents

• Cover
• Title Page
• Copyright
• Dedication
• Contents
• Preface
• Introduction—Time According to Physics
• Part I: Time Is a Label
• Part II: Time Is a Dimension
• Part III: Time Is an Arrow
• Part IV: The Reality of Time Revisited
• Afterword
• Bonus Chapter: Is Time Travel Possible?
• Acknowledgments
• Notes
• Further Reading
• Index