Gravitational backreaction during inflation adjusts constants but preserves exponential expansion.

During the rapid expansion of the early universe, called inflation, quantum ripples might affect the overall geometry of space. This effect is called backreactionbackreactionHow quantum fluctuations affect the background geometry they live in.. Physicists want to know if these ripples destabilize the expanding universe. The authors built a mathematical framework based on gravity equations called the canonical ADM approach. It tracks the expanding background by treating it as an average quantum field. They tested this method on two ingredients in an expanding space called de Sitter spacetime: a massless spectator scalar field and physical graviton ripples. They calculated the effects at the one loop level. They found that these ripples adjust the link between the cosmological constant and the expansion rate. Crucially, the ripples do not trigger a runaway shift away from the steady expansion over time.

Why it matters

Cosmologists studying the early universe need to know if quantum effects disrupt inflation. This work shows that gravitational backreaction does not destabilize the exponential expansion, reinforcing the reliability of inflationary models.

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