Mr. Lisi, who has cultivated a surfer dude image that the media is eating up, has posted a "Theory of Everything", a model of physics that encompasses all known particle (described by "The Standard Model") and all four forces (described by "The Standard Model" plus "General Relativity"). Now, TSM has been very good to physicists and answers pretty much all questions except it has no room for gravity (or if you prefer, General Relativity, which describe how spacetime works). Both of these models are well-tested and considered pretty much "right". The problem is they don't work together. You can describe space and planetary orbits with one but not the other. You can describe how a proton + an electron = a neutron with one but not the other. So physicists have been trying to find a theory to smoosh them together. The best candidate so far has been string theory.

The main problem with String Theory? It sucks dog balls. Now, of course this is my opinion but I think a theory that is untestable is not an actual theory. Sure, they were working towards something testable but it's been years and still nothing has come of it. These aren't very good arguments against ST but intuitively I think it's plain wrong. Of course, intuition and science are polar opposites but my opinion is just that, an opinion. However, it's certainly not a unique one in physics.

So when Lisi's theory comes along, physicists like me (well, actual ones instead of armchair ones) are going to eat it up. It's a really nice piece of work that has some serious weaknesses but those weaknesses are not enough to overcome the truthiness of it.

The gist of it is that we only need 3 space dimensions and one time dimension (as opposed to ST's minimum of 6) to describe the physical universe and each particle is simply a different facet of a 248 parameter system called E8. Now having said that, imagine if I described people as "water with stuff in it" and you'd get a sense of how inadequate that is. I'd never be able to really explain it because, frankly, I understand it very, very superficially. But I did find a nice slashdot post by "iabervon" that someone might find useful:

Okay, the context is that you've got particles, and they're fundamentally all the same, but they're "turned" in different ways. Think of a ball with 3-color LEDs inside: you can rotate it around three axes, and move it in three directions, and you can also cycle its color and change its blinking pattern. Particles are like that, except that the topology is weird: it's not back to the same orientation until you turn it around 720 degrees, instead of 360 like normal objects. The "gauge group" is the rules for how you can change things. For example, the total color of the universe is white: if you turn something from red to blue, you have to turn something else from blue to red; but you can also create a pair of a green and a purple (anti-green). They write all these rules up in math, and it's tricky because a lot of the features vary continuously (that is, you can rotate something an arbitrarily small amount). And due to the interaction of the rules for one property with the rules for other properties, there are only certain combinations of properties that you can get. They work out all the combinations that you can have and those are what you see as "different" particles that your experiments show. Of course, we don't know what the rules are, and we're trying to figure that out from what combinations of properties we've seen and which ones we're speculating are impossible. And it's hard and takes a lot of calculation to figure out what a candidate set of rules would even mean as far as results. And people are looking at known results and trying to describe them better than "we've done a billion things, and a billion things happened".

Now, the math of rules for how things can interact turns out to be sort of limited; there are basically 4 normal cases, which are boring, and then there are a few exceptional cases, which are interesting. Of these, the hardest to prove stuff about is E8, and it's just now becoming clear what combinations it allows. It's like one of those puzzles where you press a corner and lights change, and you have to turn off all the lights, but it's got dozens of corners and dozens of lights and every time you press a corner a bunch of things change at once, and there are different kinds of corners and it also matters exactly what angle you're holding it at, so there are hundreds of things you can say about each move.

And the mathematicians working on E8 recently said, "well, you can get positions like this and not like that", where "this" and "that" are big complicated lists. And this physicist read that paper and said, "hey, those lists are familiar; I made similar lists of particle interactions". So the proposal is that particles work like E8 in what kind of rules they follow. And it's a really nice theory, because E8 is essentially the most flexible set of rules you can have without it falling apart into just anything being possible (and some rules or properties just not mattering).

Okay, the context is that you've got particles, and they're fundamentally all the same, but they're "turned" in different ways. Think of a ball with 3-color LEDs inside: you can rotate it around three axes, and move it in three directions, and you can also cycle its color and change its blinking pattern. Particles are like that, except that the topology is weird: it's not back to the same orientation until you turn it around 720 degrees, instead of 360 like normal objects. The "gauge group" is the rules for how you can change things. For example, the total color of the universe is white: if you turn something from red to blue, you have to turn something else from blue to red; but you can also create a pair of a green and a purple (anti-green). They write all these rules up in math, and it's tricky because a lot of the features vary continuously (that is, you can rotate something an arbitrarily small amount). And due to the interaction of the rules for one property with the rules for other properties, there are only certain combinations of properties that you can get. They work out all the combinations that you can have and those are what you see as "different" particles that your experiments show. Of course, we don't know what the rules are, and we're trying to figure that out from what combinations of properties we've seen and which ones we're speculating are impossible. And it's hard and takes a lot of calculation to figure out what a candidate set of rules would even mean as far as results. And people are looking at known results and trying to describe them better than "we've done a billion things, and a billion things happened".

Now, the math of rules for how things can interact turns out to be sort of limited; there are basically 4 normal cases, which are boring, and then there are a few exceptional cases, which are interesting. Of these, the hardest to prove stuff about is E8, and it's just now becoming clear what combinations it allows. It's like one of those puzzles where you press a corner and lights change, and you have to turn off all the lights, but it's got dozens of corners and dozens of lights and every time you press a corner a bunch of things change at once, and there are different kinds of corners and it also matters exactly what angle you're holding it at, so there are hundreds of things you can say about each move.

And the mathematicians working on E8 recently said, "well, you can get positions like this and not like that", where "this" and "that" are big complicated lists. And this physicist read that paper and said, "hey, those lists are familiar; I made similar lists of particle interactions". So the proposal is that particles work like E8 in what kind of rules they follow. And it's a really nice theory, because E8 is essentially the most flexible set of rules you can have without it falling apart into just anything being possible (and some rules or properties just not mattering).

Now I mentioned a few weaknesses and, to be brief, they appear at first glance to be two big ones:

1) The equations we already know that are supposed to describe some particles don't come out naturally from the system. At one point, there's a step where an equation needs to describe something. He chose the equation to make the system give all the equations we would be expecting. So that tweaking is troublesome but not a deal-killer, for all we know, this might arise form something else.

2) How gravity comes into it is not fully fleshed out. It needs to be developed in conjunction with Loop Quantum Gravity which I seriously know nothing about. However, the 'hooks' into the system are just sitting there waiting to be plugged in. It's apparently sitting there ready to have all the numbers filled in but Lisi doesn't know enough about it to make the right assumptions and patch that section up completely.

The reason this TOE is big news (and there have been plenty that were big news that fizzled out and this might weel be one of them) is that this one has 2 big things going for it:

1) it's a nice match of what we know in physics with what we know in math (and by we I mean about 100 people on this planet who know this). This structure has a very strong symmetry using well-developed tools in both fields. Lisi just happened to make the connection between the two (ah, synthesis!). Now the connections he's made and how he's made them may turn out to be spectacularly wrong but it seems to have passed an initial BS vetting and closer scrutiny will certainly poke more holes in it but it's at least right enough to be simply wrong instead of "pulled out of someone's butt".

2) Whether it's wrong or not can be shown as it makes some potentially testable predictions about some particles we have not yet seen which is why the physics community so long exhausted by string theory's eternal promises of "not tonight, honey" is jumping up and down at an "undo this bra clasp and I'm all yours".

The best description for all of this I've heard, and I saved it for the end because it's the most succint, is that it's the new periodic table, perhaps the physics equivalent to chemistry's famous grid. Of course, it's a grid that's 453,060 by 453,060 but to describe universe, it would be disappointing if it were any simpler.

BTW, the paper is called "An Exceptionally Simple Theory of Everything" which is intentionally tongue-in-cheek because E8 is a system of "Lie algebras". These can be classed as "exceptional" or as "simple". E8 is both of these so Lisi gets bonus points for the wah-wah factor.

If you are morbidly curious about the details, check this out for some discussion.