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Friday, November 29, 2019

When Quantum Mechanics and Relativity Collide | Frontiers - Now. Powered by Northrop Grumman.

The two greatest achievements of modern physics — quantum mechanics and Einstein’s theory of general relativity — share one serious problem: They don’t agree, argues Rick Robinson, writer and blogger.

Photo: Getty Images
As a result, physicists find themselves in the awkward position of seeking to explain the universe using two theories that are not quite able to explain or account for each other.

In fact, these two theoretical frameworks differ not just in their abstruse mathematics, but in the basic ways in which they view the world. As puts it, general relativity treats the universe as fundamentally smooth and curved. What looks like sharp edges are simply zones of more rapid change, like musical notes recorded on tape or old-fashioned vinyl.

In contrast, quantum mechanics treats the universe as essentially lumpy and sharp-edged, like a digital music recording. Even transitions that appear smooth, if closely examined, resolve into a series of tiny but abrupt changes.

The Large and Small of It
Most of the time, these very different approaches to nature do not get in each other’s way. Einstein’s relativity theory, in spite of its popular association with nuclear energy, is mainly used to explain how the universe works at large scale: the physics of baseballs, planets, galaxies. Quantum mechanics, in contrast, deals with the very small scale: atomic nuclei and smaller, down to the most fundamental building blocks of matter, quarks...

Misadventures in Renormalization
When the mathematical technique called renormalization is used to demonstrate how this unity is applied to gravity, it doesn’t work. In the quantum mechanics framework, gravity should be associated with theoretical particles called gravitons. But gravitons, by reshaping space, render renormalization calculations endlessly complicated, says 


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