Why do we need semiclassical quantum physics

Semiclassical gravity

Gravity stays as it is!
  1. Most physicists assume that one can only unite gravity and quantum physics through a theory of quantum gravity.

  2. The most promising experiments, such as loop quantum gravity and string theory, have so far not led to satisfactory results.

  3. Another way is semiclassical gravity, in which gravity retains its well-known character. A first model now shows how such an approach works.

At the beginning of the 20th century, two theories emerged that turned our worldview completely upside down: quantum physics, which describes the strange behavior of microscopic particles, and general relativity, which deals with spacetime and the force of gravity it creates. From the smallest to the largest scale, these two ideas revolutionized our idea of ​​the universe: that objects sometimes behave like a particle, sometimes like a wave and that space and time are by no means rigid, but can change.

However, the two concepts are not compatible with each other. Since their discovery, physicists have been looking for a fundamental theory that brings the two together. A solution is not yet in sight. But is a merger even necessary? And if so, is a theory of quantum gravity the only way to do that? Some scientists - including myself - are now taking a different path. We try to reconcile both worlds without developing a quantum theory of gravity.

This article is featured in Spectrum of Science August 2019

To do this, we need to rethink the fundamentals of quantum physics ...