Flippiefanus

Previously, I pointed out that string theory is dead. However, we’ll be confronted with it’s festering corps for decades to come. One of the symptoms of this confrontation is the hype about string theory that still pollutes the media.

So, to fend ourselves against this hype, we can remind ourselves of a few pertinent aspects about string theory. By now it is generally known that string theory is just a name for an idea that produced a lot of papers, gobbled up a lot of research funding, and trapped whole generations of physicists in dead-end careers. It is actually not a theory that one can write down and use to compute numerical predictions that can then be compared to experimental observations. It can only make vague predictions, most of which have been shown to be wrong anyway.

Why the hype? It has to do with funding. The proponents of string theory tend to have large groups of students that they need to keep funded. To get the funding they need to maintain a public impression that what they do is the right thing.

Now what about the idea? It turns out that string theory is actually based on a flawed idea. To understand this flaw, we need to appreciate the evolution of understanding in particle physics based on quantum field theory. It is unfortunate that the terminology in physics doesn’t always keep up with the change in understanding. Although it was original thought that nature at the fundamental level consists of physical particles, we gradually understood that the quanta in terms of which nature operates are not actually particles. Instead, the quantized property of nature at the fundamental level is represented in terms of discrete point-like interactions. So, when we think we see a particle due to a physical point-like detection of a quantum, it is in fact the detection process itself that produces this point-like property. As a result, quantum field theory is not a theory of particle trajectories, but a theory of fields. Even Feynman’s path integral does not integrate over particle trajectories. It integrates over fields.

So, the originators of string theory took the idea that fundamental physics is based on particles, and replaced the particles by strings. So instead of particle trajectories, we now get branching tubes. That puts it back in the misconception the prevailed at the time when the original theories of particle physics were being developed. No wonder that string theory does not even succeed at being a proper theory.

Sadly, the biggest competitor of string theory, loop quantum gravity, is more or less still based on this flawed idea. In this case, the particles are replaced by quantized Wilson loops. The idea of a Wilson loop originated in non-abelian gauge theories. When gravity is regarded as a kind of gauge theory, one also gets Wilson loops there, representing the properties of the theory. In its pure mathematical form, it provides a powerful concepts. But now they quantize it, raising it to the level of a physical thing that replaces particles. This step does not bode well for the future success of this approach.

Well, if it is a bad idea to try and replace the “particles” in quantum physics by some other object, what would be a better approach? Physics at the fundamental level needs to progress in the same way it has always progressed. In the first place, we need to remember that physics, fundamental or not, is a science. That means it must follow the scientific method: compare theory with physical experimental results or physical observations.

But how do we find the theory to compare with experiments in the case of quantum gravity? What does not work is to storm blindly into theory space with some random idea and derive complicated theories based on this idea. The chances that such a random idea will turn out to be correct is negligible. Even if the theory seems to provide the required complexity, it does not guarantee that it is successful.

If random ideas don’t work, how does one find ideas that can work? Take a leave from Einstein’s book. Before he developed general relativity, he spend a long time thinking about the problem until he found some simple physics principle from which he then derived general relativity.

Often, some arguments about what happens at the (hypothetical) Planck scale is used is a kind of physics principle to justify certain approaches. Well, these arguments are themselves based on non-scientific notions. Moreover, what happens at the Planck scale cannot lead to a scientific theory, because we cannot perform experiments at that scale.

A better approach to derive physics principles to guide our investigation of quantum gravity comes from the simple question: what happens when gravity is confronted with an entangled mass distribution? Does it mean that spacetime also becomes entangled? This question has intrigued a number of physicists and they have proposed tentative solutions. The resulting theories are much simpler than those associated with string theory and loop quantum gravity. Moreover, they are closer to the scientific process of physics, because they are testable in terms of physical experiments. However, they don’t in general focus on the formulation of a physics principle. Perhaps that may still emerge somehow. In my view, this approach has the highest probability of success in formulating a theory that unifies gravity with quantum physics.