Can I please first note that Lisi’s infamous title is a PUN!
It is a joke, folks, and it is funny.
See, E8… it is an exceptional Lie group, and it is simple… argh. Never mind.
Now I might have let this slide, but even Chad is getting perturbed by all the negative vibes, so may I please remind people of some history.
Once upon a time: there were some bold imaginative young theorists, somewhat fresh out of grad school.
There was a newish theory around, that boldly proposed to solve a major problem in classical physics, using a new, large symmetry with mysterious and undefined properties, many of which had not been well resolved. The young ‘uns decided to play around with bigger symmetries to see if they could do stuff, so they tried crazy stuff like SU(6) symmetry groups.
That was 40 years ago, and the problem was the strong interaction, and the solution was SU(3) colour symmetry, but it took some time to solve minor details, like the issue of asymptotic freedom.
Some of teh Young ‘Uns, went off on a tangent, they considered “dual” theories – these had some nice properties, but honestly, any rigorous theorist could see they were pathological.
Then some clever clog pointed out that these theories were equivalent to quantizing an elastic string, which had terrible problems if you tried to pull on the ends – the fundamental particles couldn’t propagate freely, and most sensible folks dropped this like a hot potato and went off to do sensible stuff like trying to calculate strong interactions using integers on a discrete lattice.
But some persisted, and played with this new concept: it had a nice property, it seemed to automatically include something that looked like gravity with something that looked like the strong force: there was a massless spin-2 state in the theory.
Ok, there were some problems, people realised:
the ground state was tachyonic – which people seemed to think was a possible model for the pion, for a while;
and, the symmetry groups were actually wrong to explain the actual real world, but they looked like they might be interesting in parts, if you kinda squinted at them;
and, it might have a graviton, but it came with a spin-3/2 “gravitino” (hah! what jokers) which didn’t seem to actually exist;
and, there was this “anomaly” – the model was pathological in the self-interaction with gravity, bummer;
oh, and the fermions had “ghost” states – negative probability propagating particles (where have I heard that one before);
but, despite all that, it was kinda an interesting theory.
Or so some people thought.
so… a decade, or so, passed…
graduate students came,
graduate students graduated,
ex-graduate students went to work for graphics companies and software companies
(before hedge funds this was…)
some few, extraordinarily smart, kind, hospitable, wonderful people worked very hard on this problem, because deep down inside they had the insight to realise that this really was important – they ignored the
tauntsignoring of all the other physicists who wouldn’t let them join their reindeer games – and they came up with somethings clever.
See… if you just swap the bosons and the fermions, it kinda works.
In two dimensions, anyway.
Oh, wait, these other people decided to try it in 4-D and it works there too. Nifty.
Well, it doubles the number of particles, and we don’t actually see any of those, but we can just arbitarily break the symmetry and pretend they have masses so high we don’t see them, yet, and we need an extra particle or two anyway.
Oh, and this circumvents the Coleman-Mandula theorem also. Phew. That was fortunate, ’cause you know we didn’t actually think about that till afterwards. Worked out ok.
But it was still not a theory.
But… IF we change the number of space-time dimensions (and why not) then it all works.
At least in
26, er, 10 dimensions (actually 11 works well also, maybe).
We won’t worry about the extra dimensions, ’cause we can hide them, and it gets rid of the tachyons, and the anomalies. The ones we introduced at the beginning, remember. And we did some funky stuff to suppress the ghosts.
So we have a Theory, which has some extra hidden dimension, and it has all these super particles,
but it has some really, really nice mathematical properties.
It seems like Teh Theory includes gravity, which is good; and it has gauge symmetries, which are not actually the Standard Model but are plenty big enough to probably contain the Standard Model in a consistent way, we think, if we can ever actually calculate it.
We can do calculations in two dimensions, for some problems, and we think we can state plausible conjectures for some 10 or 11 dimensional problems, and it is terribly interesting.
Seriously, it is really a very interesting theory.
But, it took 5-10 years to realise it was really interesting, IF you were smart enough and you were there.
It took just over a decade for some extraordinarily smart people to show it was actually interesting, and then many hours for most of the rest of the theoretical physics community to jump on the bandwagon.
And in the 20+ years since, much has been conjectured, a few things have been proved and almost nothing actually calculated.
And it is still the best theory around.
So, lets not get too snide when someone points out that there may be something interesting possible in a mathematical structure that may eventually with some very hard work lead to something interesting and physically relevant.
He may be wrong, but so may all of you.
In fact most of us are wrong most of the time, comes with the turf.
PS: Lee is not paying me for this, in fact he hasn’t even bought me a cup of coffee for, like, years. John bought me a drink more recently (very nice Italian red, may I say), but even that wasn’t very recently at all. So there.