Scientific American is doing a good job this month of putting out stories related to quantum gravity that actually make sense, steering clear of the multiverse and other pseudo-science. This month’s magazine has a very nice article by Steven Carlip about quantum gravity in 2+1 dimensions. For a more technical introduction to the subject, Carlip’s book and review article are good places to start.
I haven’t seen the new May issue yet, but from their web-site, it seems that their cover story on new ideas about “A Unified Physics” is what looks to be an interesting article from Zvi Bern, Lance Dixon and David Kosower: Quantum “Graviton” Particles May Resemble Ordinary Particles of Force, summarized as
Maybe unifying the forces of nature isn’t quite as hard as physicists thought it would be.
I’m curious to see the full article, but I assume it’s about the intriguing work on amplitudes of recent years that has shown that supergravity theories have fewer divergences than people thought, for reasons that are still unclear. There’s presumably some new symmetry structure here, and understanding it may offer a way around the old argument that “you can’t put quantum mechanics and general relativity together, the quantum fluctuations at short distances are just too violent.” Maybe you don’t need strings, M-theory, the multiverse, and all the other baggage theorists have been weighed down by for the last quarter-century. There has been quite a bit of discussion about this topic here, the earliest posting is this one from 2005. For another take on how these ideas might lead to a new way to handle quantum gravity, the latest visionary talk by Nima Arkani-Hamed from last week at the Simons Center is available here.
Also at Scientific American, George Musser has been producing some interesting blog entries on these topics. There’s a video here about the Carlip piece, a story about Darth Vader and the Emperor Palpatine that was discussed here, and a recent nice explanation of work on higher spin theories here.
Update: Also in the May issue, from Davide Castelvecchi, there is a shorter article, Is Supersymmetry Dead? with summary
The grand scheme, a stepping-stone to string theory, is still high on physicists’ wish lists. But if no solid evidence surfaces soon, it could begin to have a serious PR problem.
Peskin is still a believer though:
“It is the next step up toward the ultimate view of the world, where we make everything symmetric and beautiful,” says Michael Peskin, a theorist at SLAC National Accelerator Laboratory…
Many are still hopeful. “There are still very viable ways of building supersymmetry models,” Peskin says. Expecting to see new physics after just a year of data taking was unrealistic, says Joseph Lykken, a theorist on the CMS team.
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