Quantum Gravity And The Search For A Unified Physics – Science 2.0

Quantum gravity has fascinated scientists for over a century. The term refers to any theory that seeks to describe gravity in the regimes in which quantum effects cannot be disregarded. Scientists have proposed string theory, loop quantum gravity, and many other theories, but none has achieved universal recognition or been confirmed by the evidence. In that sense, when we speak about quantum gravity, we are speaking not about any single theory, but about one of the great unsolved scientific problems. According to ScitechDaily, a new theory has emerged to compete with these research programs, and it is one that many people will instinctively understand: the universe is pixelated.

ScitechDaily suggests that as digital images become more pixelated the closer you zoom into them, the universe may have a similar structure. Rana Adhikari is one of many scientists who believe that the universe is not perfectly smooth, but is made up of infinitesimally small, discrete units. These spacetime pixels are so small that if they were enlarged to the size of grains of sand, then atoms would become as large as galaxies.

If scientists can find evidence of pixelation, it will be a predictor of quantum gravity. Quantum gravity is important because it unifies two types of physics: the physics of Newton and Einstein, with the physics of Niels Bohr, Erwin Schrdinger, Werner Heisenberg, Max Born and others. It is about bringing together the physics of mass structures, such as the solar system, which are governed by general relativity, with the physics of the very small, which is governed by quantum physics.For many scientists, there has always been a feeling of unease at the fact that there is no unifying principle that brings these two together. If gravity can be quantized, then that great problem is solved and this uneasy state of affairs comes to an end.

Although many people get the impression that these two parts of physics cannot be reconciled, this is in fact not true. There is ample evidence that quantum mechanics exists on this planet, and that alone is evidence of consistency. The problem for many scientists comes when questions around black holes arise, and when they are asked to explain the two in terms o a unified framework in very short distance scales.

This problem has proved so challenging that many scientists do not believe that it can be solved in the next generation. This has not prevented scientists from looking for ways to find evidence of quantum gravity, around black holes, or the early universe, or by using the famed LIGO gravitational wave interferometer.

Yet, there still has not been any evidence of quantum gravity, The absence of evidence is not the evidence of absence. We know from first principles that quantum gravity exists. Indeed, this is also a philosophical problem about the nature of science. Although the Science for Dummies version of what science is about, highlights the importance of evidence, often, there are technological or financial, or other barriers to finding evidence. For example, until LIGO detected gravitational waves in 2016, there was no evidence of them, even though Einsteins work told us that there should be such evidence. A century passed without anything to prove Einstein right.

A new project funded by the Heising-Simon Foundation, and headed by Kathryn Zurek, is attempting to find the evidence that science has been sorely awaiting. Tasked with finding evidence of quantum gravity, the Quantum gRavity and Its Observational Signatures (QuRIOS) is composed of a medley of complimentary talents. There are string theorists, who understand the formal tools of the subject, but typically have no experimental expertise, and particle theorists and model builders, who have a great understanding of experimental design, but little understanding of quantum gravitys formal tools.

Zurek is aware that mainstream science does not believe that you can look for observable features of quantum gravity. This has not dissuaded her or her team. She believes that unless we can link quantum gravity with the world we live in, we will not be able to make any meaningful advances. Observational signatures bring theorists together and allow for more concrete progress to be made.

Zurek and Adhikari will work together in order to design an experiment, the Gravity from Quantum, Entanglement of Space-Time (GQuEST), using tabletop instruments, which, it is hoped, will detect, not so much discrete spacetime pixels, but the connections between them that lead to observable signatures.

The process, akin to tuning an old television set, could bring us closer to observable signatures. The team understands that there are no guarantees. At this stage, what they have is an idea, and it could turn out to be a very bad idea, but the point of science is to experiment, even at the risk of falsifying theories, in the quest for robust theories of how our world works. Truth itself is provisional, in the scientific world. Scientists exist in a perpetual state of experimentation.

Excerpt from:

Quantum Gravity And The Search For A Unified Physics - Science 2.0