E8

You may have heard some of the news stories about E8, such as:

  • E8 provides the densest sphere packing in 8 dimensions (media, arxiv).
  • Experimental physicists reported detecting “emergent E8 symmetry” in the laboratory, corroborating predictions made 20 years earlier by Zamolodchikov and others. The experiment is fascinating on its own, even ignoring the connection with E8. For an exposition of this aimed at mathematicians, see my paper with David Borthwick.
  • The “calculation the size of Manhattan” was widely reported in the news media in 2007.  This was the result of some serious mathematical effort by the Atlas of Lie groups project.  They calculated the Kazhdan-Lusztig-Vogan polynomials for the split real E8.  David Vogan described it for mathematicians in this paper.
  • The “Exceptionally Simple Theory of Everything” claimed to unify the four fundamental forces of physics using a real form of E8.  This turned out to be no more scientific than cold fusion; see my paper with Jacques Distler for a disproof.  It was described in an article in Ars Technica.

E8 is also mentioned as playing a role in the fictional Beard-Einstein Conflation in the novel Solar by Ian McEwan.

But what does “E8” mean?

Picture of the E8 root system

Picture of the E8 root system

It can be:

  • a root system.  This is a collection of 240 points in 8-dimensional space.  The graphic you see here shows a projection of it into a well-chosen plane.
  • a lattice in 8-dimensional space.
  • a complex Lie group.  The Wikipedia entry on E8 gives an introduction to this and the two items below.
  • one of three different real Lie groups whose complexification is the complex Lie group E8.
  • an algebraic group over a field related to the complex Lie group

New developments

There have been exciting recent developments about E8 also in pure mathematics, especially related to cohomological invariants.

For a more detailed and technical discussion of these subjects, see the survey in Bulletin of the AMS.