TL;DR
Scientists have for the first time verified Einstein's equivalence principle at the quantum scale, showing that general relativity and quantum mechanics may not be irreconcilable at the microscopic level.
Modern physics has a century-old puzzle: Einstein's general relativity describes planets and galaxies, while quantum mechanics describes atoms and particles. Each set of rules works on its own, yet the two refuse to be reconciled.
Researchers used a new instrument, the Quantum Galileo Interferometer (QGI), to split one atom's wave into two paths, letting one fall freely and comparing the outcomes. They found that the equivalence principle holds in the quantum world too.
What is the equivalence principle?
Simply put, it says gravity and acceleration produce indistinguishable effects: the weightlessness of free fall feels the same as floating in space, and the weight felt by standing on Earth is the same as standing in an accelerating rocket.
The principle had been tested on macroscopic objects long ago, but this is the first confirmation at the quantum scale. The researchers admit that uniting the two pillars of physics is still far off, yet the result is an important step toward understanding how the two realms can coexist.
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