Gravity May Shape the Flow of Time, Challenging Physics

A new theory called Shape Dynamics suggests gravity itself could be the source of time's arrow.

Mar. 12, 2026 at 2:48pm

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A growing group of physicists believe the arrow of time, the one-way flow of time we experience, may originate from the force of gravity itself. This radical idea, called Shape Dynamics, challenges the long-held view that entropy is the key to time's arrow. Shape Dynamics proposes that gravity, not entropy, naturally generates an arrow of time as particles interact. While the theory is still being tested, it offers a fascinating new perspective on one of the most fundamental mysteries in physics.

Why it matters

Our current understanding of the flow of time and its connection to entropy is likely incomplete. Shape Dynamics provides an alternative hypothesis that could reshape our theories of gravity and the origins of the universe if proven valid. Exploring this idea could lead to major breakthroughs in physics.

The details

Shape Dynamics recasts Einstein's equations of general relativity, focusing on the relationships between objects rather than the spacetime they occupy. In this framework, physicist Julian Barbour found that a random collection of particles interacting through gravity naturally develops an arrow of time, with the particles organizing into low-entropy, highly ordered states before increasing in entropy. However, this simple model needs to be expanded to account for the full complexity of the universe and its many particle interactions.

  • In 2014, physicist Julian Barbour and colleagues proposed the Shape Dynamics theory.
  • Over a decade has passed since Barbour's initial publication, and the theory has received both criticism and support from the physics community.

The players

Julian Barbour

A physicist who, along with colleagues, proposed the Shape Dynamics theory in 2014 as an alternative to the traditional view that entropy is the source of time's arrow.

Paul M. Sutter

A science educator, theoretical cosmologist, and contributor to this article exploring the implications of the Shape Dynamics theory.

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What they’re saying

“For over a century most physicists have believed that the key to time's arrow lies in the concept of entropy, which very roughly is a measure of a system's disorder. The second law of thermodynamics states that in closed systems entropy always goes up, meaning that systems always go from ordered to disordered.”

— Paul M. Sutter, Contributor, science educator and theoretical cosmologist

“But this connection raises an annoying problem. For entropy to generate an arrow of time, our universe had to start in an exceptionally low-entropy, highly ordered state. This strikes most physicists as a contrived, tacked-on assumption that doesn't mesh with our understanding of a messy, chaotic Big Bang, our best theory for how our universe began.”

— Paul M. Sutter, Contributor, science educator and theoretical cosmologist

What’s next

Researchers will need to continue testing the validity of the Shape Dynamics theory, ensuring it aligns with observations of the real universe and can accurately model the full complexity of cosmic evolution. Expanding the theory to encompass the four fundamental forces of nature, not just gravity, will be a key challenge.

The takeaway

The Shape Dynamics theory offers a fascinating alternative to the traditional view of time's arrow, suggesting gravity itself may be the source. While still unproven, this idea could lead to major breakthroughs in our understanding of the universe if it withstands further scientific scrutiny.