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What is antigravity, and is it scientifically possible?

I encounter this term often in popular science and fringe theories. As a physicist, I want to give a precise answer to students who ask about it. Does general relativity or quantum field theory contain any legitimate, non-speculative mechanisms for generating a repulsive gravitational interaction between masses, or is the term fundamentally misleading?

 

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By Rajeev Answered 1 year ago

We must separate two ideas. Within general relativity, repulsive gravitational effects absolutely exist. The cosmological constant dark energy causes a repulsive acceleration on cosmic scales. However, this is a property of spacetime itself, not a force between local objects you can switch on. True "antigravity," meaning a device that makes an object repel or levitate against Earth's gravity, violates the Equivalence Principle, a cornerstone of GR. I have seen no proposal for such a device that doesn't require exotic, unproven matter with negative energy density. So, while the universe exhibits repulsive gravity, a local anti-gravity machine remains in the realm of fiction with no credible theoretical pathway.

 

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