Not only is that not standard nomenclature (who knows what he thinks it means!), Lisi's $E_8$ theory is widely known among practicing physicists as, uh, not having any chance of actually describing our universe.

In fact, you should be very very suspicious of any physicist who takes a lot of time to promote their personal theories to the public. (This includes all public lectures -- the more prestigious, the worse.) They do this because they have failed to convince other physicists, and they want to talk to people who can't criticize them.

Added minutes and related info above. I am generally suspicious of this theory, but I'd like to at least understand how he arrives at the E8 structure before I make a judgement. I'm also intrigued by how mass could fit so nicely on there, when the standard model has a wide range of masses in a number of different orders of magnitude...

So maybe mass isn't one of them...? He mentions spin up and down when he adds them... Does this actually refer to spin and chirality or something?

6:55 -- this is well-established Standard Model physics. 7:57 -- this is completely standard for grand unified theories. (It's just that Lisi's particular grand unified theory doesn't stand a chance of working.) The two strong charges are the two Cartan generators of $SU(3)$ and, if you wish, correspond to like "red minus blue" and "red plus blue minus green". 9:31 -- no clue. This is Lisi's personal thing. Typically gravity is not included in grand unified theories at all.

Also, I'm sorry to say this, but the things you're saying just sound super naive and make little sense. It's like... "I heard they came out with C++17? That must mean there are 17 things in the programming language. So the first is clearly the CPU, the second is for loops, the third is a transistor, the fourth is quicksort, and..." It just doesn't make sense, it's a mishmash of vaguely related words. To say anything about physics that actually makes sense you have to study it for years, and no amount of video watching is going to cut it.

I believe I made it clear I was attempting to understand it. If I already understood it I wouldn't be here asking questions. Thank you for your answers thus far. The reason I mention spin and left/right handedness is that he mentions both of these at some point relating to the 8 charge directs, spin he mentions specifically when adding the 2 gravitational charge directions.

I know, but this is a deeply technical subject and no popular-level talks are going to remotely do justice to it. This is like trying to write a compiler from scratch, using a smartwatch only, if your only knowledge of programming is from watching The Social Network. If you want to make any progress, you're going to have to hit the books.

I have watched and read all the information I can find on this theory so far, and tried to find answers to these questions elsewhere on the internet by searching and cross referencing some of the things mentioned in both this video and others on the same subject. Everything I find either doesn't go into any where near the detail I would like, this video heavily included, or they are heavily equation based and are at a level I couldn't hope to understand without potentially days (or weeks?) of further reading.

Is it unreasonable to ask simply what the names of the forces are that he uses to plot his 8 dimensional geometry?

Honestly, if anyone can suggest links with more technical depth I would be excited to hear about it

@knzhow "they have failed to convince other physicists" - Not to defend this guy, but just in general, today's physicists are rather hardminded. They reject anything that contradicts the official dogma, even if it is completely nonsensical like that 95% of what the universe is made of is non observable. Try convincing them that perhaps instead the theory that claims this is 95% wrong.

Indeed. Many scientists of the past have been hard to convince of things that we now believe to be true. And I haven't yet seen evidence against this theory (willing to see that too if anyone has links). Considering it has made testable predictions it's probably at least worth seeing how they pan out.

@knzhou There is a gauge theory of gravity in which the Lorentz group is the gauge group. The two gravitational charges are apparently angular momentum and center of mass.

@safesphere This is simply incorrect. There are hundreds of papers out there on modified gravity, which reject dark matter, and hundreds more on modified cosmology, which reject inflation, and so on. It's not even hard to find them, just scroll through ArXiv.

@IronAttorney The main problem with the theory is that $E_8$ is too symmetric -- for every SM particle it predicts another with opposite charges, which we do not observe. (Technically, this is because it has no complex representations; see my answer here.) This has been known for over 30 years, which is why nobody else has even bothered publishing anything on $E_8$. (There is, however, plenty of work on $E_6$ GUTs because $E_6$ does have complex representations.)

@IronAttorney So Lisi's $E_8$ theory will only work if you allow these hundreds of extra particles to all coincidentally be very heavy, heavy enough to ensure we haven't seen any yet. Again, this is textbook stuff which was known in the 80's. See Georgi's classic Lie Algebras in Particle Physics for a discussion.

@MitchellPorter Ah, right, Lisi is also fitting the Lorentz group in there, plus I assume a family group. There's totally room within $E_8$ for that.

@IronAttorney If you want a deeper knowledge, Georgi's text is probably the best place to start. It will take months of reading, and I'm not gatekeeping here, that's simply how it is. Georgi was one of the inventors of $SU(5)$ and $SO(10)$ GUTs. (These groups are also known as $E_4$ and $E_5$.) From then on you can learn about $E_6$ GUTs. Again, physicists stopped there because the whole idea stops working; Lisi is basically choosing $E_8$ just because it's the most complicated, coolest looking option, not because it works.

@IronAttorney As for predictions, all GUTs make the same generic predictions, e.g. proton decay and heavy particles at the GUT scale. (It's just that Lisi's theory makes some additional predictions that are known to be wrong.) Since we haven't seen proton decay and can't probe those heavy particles, we've been at an impasse testing GUTs for 30 years. There's no panacea here.

@knzhou Have these papers convinced the physicists?

@knzhou makes Lisi's theory sound like it is a mathematically coherent theory (like GUTs) and the only problem is that certain physically unlikely things would have to happen for it to be true. In fact it is not even mathematically well-defined. Lisi's dream is that gravity and the standard model will fit inside the E8 Lie algebra. He wants to interpret certain objects from E8 as fermions, but then it's no longer an E8 algebra, and even then the standard model doesn't fit. By the usual standards of particle physics, it's not a theory, just an idea for a theory, that doesn't work even as math.

@knzhou, you may think that Lisi's theory is e.g. E8 gauge field coupled to an adjoint of fermions. But he actually wants to take a single 248-dimensional object, and have some of those degrees of freedom be bosonic, and others fermionic. See e.g. the very labored discussion at golem.ph.utexas.edu/category/2008/05/…

@IronAttorney So apart from the technicalities of particle physics, the discussion of Lisi's theory has always been confounded by the fact that he doesn't quite have a well-defined theory. See the places in the preceding link, where he says he wants to realize his idea in a "weird" way. In other words, if he plays by the usual rules, he does not have a theory that is both E8-symmetric, and that contains fermions and bosons. New rules are OK if they are specified, but all he has is hope that some other mathematical framework can give him what he wants. Thus no theory, only idea for a theory.

@MitchellPorter Thanks for the additional info! I don't have the mathematical firepower to critically evaluate the superconnection stuff -- it seems to require a lot under the hood, and runs afoul of the Coleman-Mandula theorem. I just know that the bog standard "no complex representations" problem is already enough to disqualify the theory from a model building point of view.

Thanks for all the info and reading reading material. I'll give some of the a go and see how I get on. @MitchellPorter well his hope for realising it in a "weird" way does sound like a fingers crossed kind of long shot... but fair play to him for trying even if it proves to be nonsense. Nothing wrong with trying to find a new approach.

@knzhou What are the additional predictions that are known to be wrong? Proton decay and the heavy particles are surely not ruled out yet if we don't have evidence to disprove the ideas?

@MitchellPorter - "The two gravitational charges are apparently angular momentum and center of mass." - I know spin is only meant to be thought of as angular momentum to help understand it's effects rather than it actually being angular momentum, but is that what you mean by angular momentum here? Because suggests in the video one of them is spin. And I have to say I've never heard of center of mass being used as a quantum property. Do you have any reading material links on this?

@IronAttorney There's nothing wrong with trying a new approach. But there is something wrong with spending all your time promoting your theory to journalists and the public as if it's the greatest breakthrough ever, without mentioning any of the theory's many problems (not mathematically well-defined, predicts hundreds of unseen new particles that all must be hidden somehow, doesn't fix any of the usual problems with GUTs), and ignoring tons of similar theories that do a better job, just to cultivate a "hippie guru" kind of air. It's not honest.

The long list of comments convinces me that the question is not within mainstream physics, and as such is not encouraged here. You could try asking your questions at the video site. There is also a later theory of everything arxiv.org/pdf/1506.08073.pdf , which has not taken the physics Arxiv community by storm as far as citations go. So I will also vote to close.

@annav If you check the ~150 citations of the original $E_8$ paper, over half of them are from rather strange papers, published in places like the "Journal of Consciousness Studies" with titles like "Vision of Oneness". A good fraction of the legitimate papers citing it just cite it to say why it doesn't work.

I would personally have thought that a thread about a questionable theory in which lots of knowledgeable people give good info and resources explaining reasons why it's probably bogus is a good thing to have to stop the spread of misinformation, right? There's plenty of misinformation about as it is...

you are asking detailed questions, needing somebody to look carefully into what must have been looked at by a lot of arxiv readers with a lot more background then the average users of this site. Also the fact that it has not passed peer review speaks of errors in the mathematics or the way it is used.