“Can you think of a single advancement in theoretical physics, other than speculation like Strings and Loops and Safe Gravity and Twistors, and confirming things like the Higgs Boson and pentaquarks at the LHC, since Politizer and Wilczek and Gross (and Coleman) did their thing re QCD in the early 1980's?”Dear Steve:
What counts as “advancement” is somewhat subjective – one could argue that every published paper is an advancement of sorts. But I guess you are asking for breakthroughs that have generated new research areas. I also interpreted your question to have an emphasis on “theoretical,” so I will leave aside mostly experimental advances, like electron lasers, attosecond spectroscopy, quantum dots, and so on.Admittedly your question pains me considerably. Not only does it demonstrate you have swallowed the stories about a crisis in physics that the media warm up and serve every couple of months. It also shows that I haven’t gotten across the message I tried to convey in this earlier post: the topics which dominate the media aren’t the topics that dominate actual research.
The impression you get about physics from reading science news outlets is extremely distorted. The vast majority of physicists have nothing to do with quantum gravity, twistors, or the multiverse. Instead they work in fields that are barely if ever mentioned in the news, like atomic and nuclear physics, quantum optics, material physics, plasma physics, photonics, or chemical physics. In all these areas theory and experiment are very closely tied together, and the path to patents and applications is short.
Unfortunately, advances in theoretical physics get pretty much no media coverage whatsoever. They only make it into the news if they were experimentally confirmed – and then everybody cheers the experimentalists, not the theorists. The exceptions are the higher speculations that you mention, which are deemed news-worthy because they supposedly show that “everything we thought about something is wrong.” These headlines are themselves almost always wrong.
Having said that, your question is difficult for me to answer. I’m not a walking and talking encyclopedia of contemporary physics, and in the early 1980s I was in Kindergarten. The origin of many research areas that are hot today isn’t well documented because their history hasn’t yet been written. This is to warn you that I might be off a little with the timing on the items below.
I list for you the first topics that come to my mind, and I invite readers to submit additions in the comments:
- Topological insulators. That’s one of the currently hottest topics in physics, and many people expect a Nobelprize to go into this area in the near future. A topological insulators is a material that conducts only on its surface. They were first predicted theoretically in the mid 80s.
- Quantum error correction, quantum logical gates, quantum computing. The idea of quantum computing came up in the 1980s, and most of the understanding of quantum computation and quantum information is only two decades old. [Corrected date: See comment by Matt.]
- Quantum cryptography. While the first discussion of quantum cryptography predates the 1980s, the field really only took off in the last two decades. Also one of the hottest topics today because first applications are now coming up. [Corrected date: See comment by Matt.]
- Quantum phase transitions, quantum critical points. I haven’t been able to find out exactly when this was first discussed, but it’s an area that has flourished in the last 20 years or so. This is work mainly lead by theory, not experiment.
- Metamaterials. While materials with a negative refraction index were first discussed in the mid 60s, this wasn’t paid much attention to until the late 1990, when further theoretical work demonstrated that materials with negative permittivity and permeability should exist. The first experimental confirmation came in in 2000, and since then the field has exploded. This is another area which will probably see a Nobelprize in the soon future. You have read in the news about this under the headline “invisibility cloak.”
Dirac (Weyl) materials. These are materials in which excitations behave like Dirac (Weyl) fermions. Graphene is an example. Again I don’t really know when this was first predicted, but I think it was past 1980.
Fractional Quantum Hall Effect The theoretical explanation was provided by Laughlin in 1983, and he was awarded a Nobelprize in 1998, together with two experimentalists. [Added, see comment by Flavio.]
Inflation. Inflation is the rapid expansion in the early universe, a theoretical prediction that served to solve a lot of problems. It was developed in the early 1980s.
Effective field theory/Renormalization group running. While the origin of this framework go back to Wilson in 1975, this field has only taken off in the mid 90s. This topic too is about to become hot because the breakdown of effective field theory is one of the possible explanations for the unnatural parameters of the Standard Model indicated by recent LHC data.
Quantum Integrable Systems. This is a largely theoretical field that is still waiting to see its experimental prime-time. One might argue that the first papers on the topic were written already by Bethe in the 1930s, but most of the work has been in the last 20 years or so.
- Conformal field theory. Like the previous topic, this area is still heavily dominated by theory and is waiting for its time to come. It started taking off in the mid 1990s. It was topic of one of the first-ever arxiv papers.
- Geometrical frustration, spin glasses. Geometrically frustrated materials have a large entropy even at zero temperature. You have read about these in the context of monopoles in spin-ice. Much of the theoretical work on this started only in the mid 1980s and it’s still a very active research area.
- Cosmological Perturbation Theory. This is the mathematical framework necessary to describe the formation of structures in the universe. It was developed starting in the 1980s.
- Gauge-gravity duality (AdS/CFT). This is a relation between different types of field theories which was discovered in the late 1990s. Its applications are still being explored, but it’s one of the most promising research directions in quantum field theory at the moment.
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