Quantized Gravity...

The effect of a gravitational wave on a ring of particles, as space-time is compressed and stretched. Source

Observations of the Cosmic Microwave Background (CMB) have already revolutionized modern cosmology, providing evidence that the nature of our Universe can be beautifully described by six fundamental parameters. And yet, the authors of this work say that the CMB has even more insight to offer, this time into how gravity behaves on microscopic scales. It is believed that the gravitational force is transmitted by a hypothetical, fundamental particle called the graviton, similar to how the photon carries the electromagnetic force. Unfortunately, the gravitational force is much weaker than the electromagnetic force1, and while scientists can easily measure a single photon, the prospects of detecting a single quantum of gravity are much graver. However, the authors argue that precise measurements of the CMB can do just that, proving the existence of the graviton and the quantized nature of gravity. Such a detection would provide evidence for the unification of general relativity and quantum mechanics, one of the most profound problems in current theoretical physics.

The prevailing description of the early universe involves a period of exponential expansion, known as inflation, beginning about 10-36 seconds after the Big Bang. During this expansion, which lasted just a tiny fraction of a second, the volume of the Universe increased by at least a factor of 1078, making microscopic density fluctuations astronomically large. This rapid expansion solves several problems with the standard cosmological picture, including the near-perfect uniformity of the CMB temperature and the Universe’s nearly flat spatial geometry. Astronomers have strong evidence for the occurrence of inflation; all relevant observations are consistent with the predictions of inflation, but they do not yet provide direct, conclusive evidence for inflation.

Astrobites: Detecting the Quantization of Gravity