The best theoretical physics from the last 30 years?

Image by Thomas T from Unsplash

I recently reviewed a book called Fantastic Numbers and Where to Find Them by Antonio Padilla. In my review, I was dubious about the way that Dr Padillia referred to the highly speculative holographic principle as 'the holographic truth'.

Something many publishers drum into their authors is that it is not a good idea to respond to reviews. If anything, it can reinforce any negative comments in the review. But Dr Padilla replied on Twitter 'thanks for your thoughts. You may be interested to see this perspective on importance of the holographic principle, which obviously I share.’ He then quotes Caltech physicist John Preskill, who had tweeted: ‘Someone asked: What are the most important ideas in physics over the past 30 years? Three immediately came to mind: The holographic principle, topological order, quantum error correction.’

Now, this seemed to me to be a depressing statement if true. What we've got with those three is firstly a principle that is largely self-referential maths that has no current way of being tested. Then there's something quite interesting if not giving huge insights or new experimental directions, but that actually predates the last thirty years. And finally there's a very important and useful mechanism that is an important contribution to physics-based engineering - but can it really be so significant in the annals of theoretical physics?

Bear in mind the last thirty years has seen a whole host of experimental breakthroughs, from the detection of the Higgs boson to gravitational waves. Could it be that major developments in theoretical physics have been so sparse? I asked theoretical physicist and science communicator Sabine Hossenfelder whether she agreed with those three ideas. She pointed out that one problem is that many scientists measure the importance of an idea by the number of people who work on it or the number of papers that have been written about it.

This clearly isn't a useful measure of the significance of a piece of theory. After all, vast numbers of people have worked on theories such as string/M theory which seem to have run out of steam. Similarly, many papers have been written on the existence of dark matter, which has as a theory been tested by large numbers of experiments that have failed to detect it - increasingly it seems likely that alternative theories, such as variants of modified gravity, have more potential. 

Dr Hossenfelder highlights two potential big developments in relatively recent theory - topological phases of matter and phase transitions (see the Nobel Prize in Physics for 2016 for more detail) and chaos control, which she noted was highly valuable both in robotics and nuclear fusion. 

Of course any attempt to do a 'best of' list is subjective - and that wasn't my aim here. Relying on either number of papers produced or an individual's hits list is not a good way to give support to a theory. I may be biassed, but for me theories can only be considered to have proved their worth once they can be directly supported by experiment or observation. For the moment, I'd suggest, the holographic principle remains a mathematical curiosity rather than truly valuable physics.

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