The UniverseAnswer
Can a Planet Orbit Two Stars?
Two stars can circle each other while a planet travels around them both. Astronomers confirmed it by watching the moving stars dim.
THE QUESTION LIBRARY THE UNIVERSE
Could our universe be a thin sheet floating inside a bigger space?
The sheet picture starts a question; a model must explain what moves where and reproduce measured gravity.
THE SHORT ANSWER
Some models place our three spatial dimensions and time on a brane in larger spacetime, the bulk. Ordinary fields, including light, are confined in particular setups; gravity can access extra directions. Recovery of familiar gravity is model-specific. Mathematical success is not discovery.
- 3-brane means three spatial dimensions, with time adding another spacetime dimension.
- Confinement of ordinary fields is a model condition, not light being held down by gravity.
- Compact dimensions and warped gravitational localization are different mechanisms.
- A model must confront measurements, not only produce an appealing diagram.
WHERE THE EVIDENCE STANDS
How sure are we?
- An event has a position and a time.Three familiar spatial coordinates plus time describe four-dimensional spacetime.
- Extra dimensions necessarily prevent familiar gravity.The Randall–Sundrum warped one-brane setup gives Newtonian and linearized relativistic behavior with corrections suppressed in the specified regime.
- Our universe is a brane in a larger bulk.The theoretical examples and dated gravity test cited here do not establish that geometry.
- Gravity accessing the bulk means light is trapped by gravitational attraction.Ordinary-field confinement is a separate condition in the reviewed models.
- One successful gravitational calculation proves every braneworld agrees with Einstein.Agreement must be checked for the particular model, assumptions and observable.
WHAT WE DON’T KNOW YET
Whether a braneworld describes nature, which fields would access a bulk, and what geometry and dynamics would apply remain open. The models discussed here supply examples to examine, not a measured map of a surrounding space.
WHAT WOULD CHANGE THIS ANSWER
A repeatable observation favoring a specified braneworld prediction over ordinary physics and competing explanations would strengthen its case. The model would also need to remain consistent with other measurements. A striking picture or a result under assumptions alone would not settle the question.
Could our universe be a thin sheet floating inside a bigger space? That is a useful starting picture for a braneworld, provided we unpack each word before taking it literally.
Braneworld models distinguish a brane, where ordinary fields are confined, from a bulk spacetime accessible to gravity. These are proposals, not an observed sheet.
Three questions matter: what does the picture represent, why could light and gravity behave differently, and how would the proposal preserve the gravitational predictions already tested? Those questions need a named model, not a general promise that another dimension explains everything.
THE LONG ANSWER
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Keep asking
What is an extra dimension, and why can't we see one?
An extra spatial dimension would add an independent coordinate to locate a position.
New here?
God Plays Dice answers big questions in plain words, with sources and one of six honest labels.
Words worth knowing (8)
- Brane
- A lower-dimensional surface within a larger spacetime; a 3-brane has three spatial dimensions.
- Bulk
- The higher-dimensional spacetime containing the brane in a braneworld model.
- Spacetime
- The collection of events specified by position and time.
- Field confinement
- Restriction of particular fields to the brane under a model’s stated conditions.
- Compact dimension
- A spatial direction that closes back on itself rather than extending without limit.
- Warped geometry
- How distances and times are measured along a brane depends on the extra coordinate.
- Inverse-square force
- A force whose strength scales as one divided by the square of separation.
- Model result
- A conclusion derived under stated assumptions; it does not by itself establish those assumptions in nature.
Sources & further reading
(6) · Checked Oct 2, 2026
- Spacetime, dimensions and coordinates ↗Einstein Online, Max Planck Institute for Gravitational Physics (undated)Coordinate counting, events and surface dimension; drawing space is distinct from an object’s dimension.
- The Hierarchy Problem and New Dimensions at a Millimeter ↗Nima Arkani-Hamed, Savas Dimopoulos and Gia Dvali (1998)Compact geometry, ordinary-field localization and long-distance gravity under the proposal’s assumptions.
- An Alternative to Compactification ↗Lisa Randall and Raman Sundrum, Physical Review Letters (1999)Warped single-brane gravity calculation under specified assumptions.
- Brane-World Gravity ↗Roy Maartens and Kazuya Koyama, Living Reviews in Relativity (2010)Brane/bulk definitions, confinement and differences among recovery conditions for different setups.
- New Test of the Gravitational 1/r² Law at Separations down to 52 µm ↗J. G. Lee and colleagues, Physical Review Letters (2020)Dated Newtonian agreement and conditional interpretation; no latest global bound is asserted.
- Extra dimensions, gravitons, and tiny black holes ↗CERN (undated)Conditional missing-momentum interpretation; used without adopting a collider-access guarantee.
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CONTINUE THE THREAD
Where this question leads.
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