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- From high school to string theory -

Lina, Kai, and Mei

  • Professor Lina... Leopard
  • Student 1: Kai... Shark
  • Student 2: Mei... Rabbit

New here? Start with Introduction — Before the Four Journeys.

You can switch the language and theme (light / dark mode) at any time using the buttons in the top-right corner.

This site explains advanced physics through dialogue and rich illustrations, making it accessible to anyone with a high school math background. Content is continuously improved.

If you find something unclear or incorrect, please use the feedback form at the bottom of each page. Your input helps us improve the content.

About This Site

This site is a study guide that assumes high school math and physics knowledge and aims for understanding quantum gravity — one of the greatest unsolved problems in modern physics. The site name "PhysTrail" is a portmanteau of "Physics" and "Trail," and we systematically trace the path to that goal through four courses:

  • General Relativity — the geometry of gravity and spacetime (30 chapters)
  • Quantum Mechanics — the laws of the microscopic world (33 chapters)
  • Quantum Field Theory — the unified description of particles and forces (29 chapters)
  • The Quest for Quantum Gravity — the frontier where the above three converge (26 chapters)

Chapters 1–7 are free for each course; Chapter 8 onward requires a one-time purchase.

The content draws on multiple well-known textbooks in each field. Specific references are listed at the end of each chapter.

Who Is This For?

  • High school and early university students interested in physics but finding textbooks too difficult
  • Readers of popular science books who want to see the math behind the metaphors
  • Working adults looking to relearn physics

About the Creator

In high school, I was captivated by Einstein's world through a TV program and decided to study physics at university. But back then, both lectures and textbooks were too difficult for me, and I graduated without truly understanding the material.

Ever since, "someday I'll really understand this" has been an unfinished homework assignment in the back of my mind. I've even organized casual physics study groups as a hobby. When AI arrived, I saw an opportunity to combine my own relearning with building "the site I wish I'd had back then" — and that's how this service was born.

Introduction →