It’s not a theory that makes quantitative predictions, it’s more a blueprint for a future theory, and the critics would say that the blueprint is hopelessly flawed—that no such theory is mathematically possible.
The larger theoretical context of Lisi’s work is the attempt to describe 4D gravity as a gauge theory, the viability of which is the central dispute between string and loop theories of quantum gravity. Lisi’s theory is a “GraviGUT” theory which then adds to this problematic foundation, even wilder hopes about getting fermions from “BRST ghosts”, and about finding loopholes in theorems which say that even then, you couldn’t get the necessary three generations of them, out of a single E8 gauge field.
Incidentally, there are various ways to get three generations of particles “from E8” in string theory, so perhaps those should be regarded as the real “E8 theories”.
I’ve looked at the theory myself, if that’s what you mean (I have a background in mathematical physics). If you like, I can give more explanation about the severe drawbacks of the theory and why it’s considered to be pseudoscience and probably not worthy of further investigation.
Those last six words are what I’d like to find out, as soon as possible, if it’s possible to do so; and I would appreciate any assistance on that score. (I regularly read ‘Not Even Wrong’, whose author puts forward a strong case that string theory is also worth skipping; which doesn’t leave too many possibilities on the ground to pick from, these days.)
As Mitchell pointed out below, there are severe theoretical issues. The theory predicts 22 new particles (and doesn’t even specify their masses thus making detection difficult) and fails to account for the properties of many existing ones. Most importantly, the theory has no chirality, and chirality is extremely important for fundamental particles. This error is severe and no way to avoid it has been found. E8 does crop up in string theory in other settings but it’s unrelated to Lisi’s work.
A deeper problem is that the theory doesn’t actually solve a lot of problems, even if it were true. You mentioned Not Even Wrong; here is an excerpt from Peter Woit on the E8 theory:
One idea Garrett is fond of that has generally left me cold is the idea of unification via a large simple Lie algebra like E8. While there may be some sort of ultimate truth to this, the problem is that, just as for GUTs and for superstring models, all you’re doing when you do this is changing the unification problem into the problem of what breaks the large symmetry. This change in the problem adds some new structure to it, but just doesn’t seem to help very much, with the bottom line being that you get few if any testable predictions out of it (one exception is with the simplest GUTs, where you do get a prediction, proton decay, which turns out to be wrong, falsifying the models).
I personally consider the publicity over the theory as simply a failure mode of science journalism. The theory got some tentative endorsement from some physicists (before they could look at it more deeply) and thus it was prematurely promoted by journalists despite not being distinguishable from the thousands of other theories-of-everything that crop up and never get any attention.
As others have said, it really depends what level you’re on and what you’re interested in. At the very least I recommend familiarity with quantum field theories before even attempting to touch more speculative physics. This includes general Yang-Mills theories and their algebraic underpinnings.
The E8 theory of particle physics is also largely considered to be pseudoscience.
How do you tell whether those who claim it’s pseudoscience are more reliable than those who claim it’s not?
It’s not a theory that makes quantitative predictions, it’s more a blueprint for a future theory, and the critics would say that the blueprint is hopelessly flawed—that no such theory is mathematically possible.
The larger theoretical context of Lisi’s work is the attempt to describe 4D gravity as a gauge theory, the viability of which is the central dispute between string and loop theories of quantum gravity. Lisi’s theory is a “GraviGUT” theory which then adds to this problematic foundation, even wilder hopes about getting fermions from “BRST ghosts”, and about finding loopholes in theorems which say that even then, you couldn’t get the necessary three generations of them, out of a single E8 gauge field.
Incidentally, there are various ways to get three generations of particles “from E8” in string theory, so perhaps those should be regarded as the real “E8 theories”.
I never understood how Lisi’s E8 got around the Weinberg-Witten no-go. Was there some reason it didn’t apply?
I’ve looked at the theory myself, if that’s what you mean (I have a background in mathematical physics). If you like, I can give more explanation about the severe drawbacks of the theory and why it’s considered to be pseudoscience and probably not worthy of further investigation.
Those last six words are what I’d like to find out, as soon as possible, if it’s possible to do so; and I would appreciate any assistance on that score. (I regularly read ‘Not Even Wrong’, whose author puts forward a strong case that string theory is also worth skipping; which doesn’t leave too many possibilities on the ground to pick from, these days.)
As Mitchell pointed out below, there are severe theoretical issues. The theory predicts 22 new particles (and doesn’t even specify their masses thus making detection difficult) and fails to account for the properties of many existing ones. Most importantly, the theory has no chirality, and chirality is extremely important for fundamental particles. This error is severe and no way to avoid it has been found. E8 does crop up in string theory in other settings but it’s unrelated to Lisi’s work.
A deeper problem is that the theory doesn’t actually solve a lot of problems, even if it were true. You mentioned Not Even Wrong; here is an excerpt from Peter Woit on the E8 theory:
I personally consider the publicity over the theory as simply a failure mode of science journalism. The theory got some tentative endorsement from some physicists (before they could look at it more deeply) and thus it was prematurely promoted by journalists despite not being distinguishable from the thousands of other theories-of-everything that crop up and never get any attention.
Fair enough.
Do you have any suggestions of other theories that would be better worth the time to read up on?
As others have said, it really depends what level you’re on and what you’re interested in. At the very least I recommend familiarity with quantum field theories before even attempting to touch more speculative physics. This includes general Yang-Mills theories and their algebraic underpinnings.