The Octonion Math That Could Underpin Physics

https://www.quantamagazine.org/the-octonion-math-that-could-underpin-physics-20180720

by jonbaer • 8 years ago

412 188 8 years ago

ianai4• 8 years ago

I think the following quote is the QED for academia ruining any chance at actual research:

“What I had was an out-of-control intuition that these algebras were key to understanding particle physics, and I was willing to follow this intuition off a cliff if need be. Some might say I did.”

btrettel2• 8 years ago

As a current PhD student, I'd say the vast majority of researchers aren't anywhere near that enthusiastic about their research.

ianai4• 8 years ago

Many marriages fail in the time it takes to complete a phd. If academia can’t find a way to fund people with actual interest then somethings wrong.

_bxg1• 8 years ago

It's my understanding that most of Einstein's theory was the product of intuition, backed up after-the-fact with mathematics and experimentation. Intuition isn't a bad compass, as long as you can set it aside if reality measurably contradicts it. In fairness, Einstein never accepted quantum mechanics because they flew in the face of his intuition, but it still got him pretty far.

madhadron2• 8 years ago

This is very false. Einstein's reputation was built on explaining known phenomena such as the photoelectric effect and Brownian motion. Special relativity was heavily motivated by a pile of puzzling evidence and a bunch of existing mathematics.

arketyp3• 8 years ago

Gödel was motivated by convictions about meta-mathematics, motivated by his Catholic fatih. Perhaps a purely mechanistic world view would have eventually generated the same result, e.g. Turing's halting problem, but who knows.

gowld2• 8 years ago

Thought experiments, not intuition. Thought experiments are kind of theoretical physics: Making an assumption ("c is the universal speed limit"), and thinking about the implications ("addition of velocity cannot be linear"), even though available experimental tools are not powerful enough to demonstrate the implications in a way observable to the though-experimenter.

nessus425• 8 years ago

Einstein never accepted quantum mechanics

Wait? Since when did Einstein not accept Quantum Mechanics? He won the Nobel Prize for his work in discovering an important part of Quantum Mechanics.

Einstein rejected the Copenhagen Interpretation of Quantum Mechanics. That's not the same thing as rejecting Quantum Mechanics.

I've seen no claims that he would object to either the Everett or Bohm Interpretations of QM. (But then again, he died before they were invented.)

Einstein, by the way, is far from the only critic of the Copenhagen Interpretation. Quite a few physicists are drawn to the Everett Interpretation instead, for instance.

Obi_Juan_Kenobi• 8 years ago

Eh, there's a balance to be struck, and that's obvious to anyone that's seriously thought about this issue.

There's no shortage of specious ideas. From outright quackery, the naive, or the simply misguided, there are countless ways to waste a lot of time and money on ideas that will lead nowhere. Especially when all you're guided by is intuition.

That's not to say that intuition isn't valuable; rather, intuition shouldn't be the only guiding principle. If an idea is 'real' in the sense that it will produce substantive research findings, it's reasonable to expect some kind of evidence for this. Maybe you're trying to show that A -> D. Well, showing a bit about B or C can go a long way to convincing people it's worth looking at the link between A and D.

The counter-argument is that it's possible there is not B or C, that a large and courageous leap is required to get to D. That's indeed possible, and arguably has been demonstrated with some famous results. But it doesn't follow that you simply must take everyone's giant leaps seriously and give them funding.

Ultimately, we go by proxies. If A -> D is required, well, at least show us that you got from A to B in some other issue. Give us evidence, however imprecise, that you might be that 1 in a 1,000 (or 1,000,000?) leaper that lands somewhere successfully.

So yes, there's an art to knowing when an idea is 'ripe' for a wider audience, and when it's time to stake your career on it. There's no reason you can't work on something in the background or during a sabbatical. The notion that 'academic incrementalism' is so destructive is a tenuous one, and certainly isn't being demonstrated here. To argue this is to say that Dixon would have been successful, if only he had gotten this or that position. Yet is appears that his approach was the issue, not financial or departmental support. I'd argue that the academic system correctly identified that his idea wasn't ready yet. Now that some demonstrable progress is being made, even if it falls far short of 'D', it's attracting attention and enthusiasm.

Finally, the notion that academia produces no actual research is farcical.

anaphylactic3• 8 years ago

There the game stops. Proof surfaced in 1898 that the reals, complex numbers, quaternions and octonions are the only kinds of numbers that can be added, subtracted, multiplied and divided.

1. I think they meant "the only kinds of numbers constructed in this way". 2. Sedenions can still be added, multiplied, subtracted and divided. it's just that multiplication and division lose most of their useful properties. With octonions you've already lost associativity and commutativity, though.

Maybestring• 8 years ago

it's just that multiplication and division lose most of their useful properties.

Specifically they lose the property of not having zero divisors.

There exists sedonions a,b != 0 such that ab = 0

OscarCunningham5• 8 years ago

Another (related) property that fails is that inverses stop being useful for cancellation. Inverses still exist, for every p there's a q with pq = qp = 1, but if you've got an equation ap = b you can't cancel to get a = bq, because we don't have associativity. The left hand side (ap)q doesn't equal a(pq), so you can't reduce it to a.

Of course associativity doesn't hold in the octonions either, but it holds just enough for cancellation to work.

qubex• 8 years ago

That happens in general for matrices too.

gowld2• 8 years ago

Are there 32-onions that lack power associativity?

https://en.wikipedia.org/wiki/Power_associativity

https://en.wikipedia.org/wiki/Cayley%E2%80%93Dickson_constru...

nabla9• 8 years ago

Being composition algebras makes R,C,Q and O more interesting than others:

N(xy) = N(x)N(y) - N is called norm.

Without this property, you have zero divisors.

edit: throwawaymath uses better notation: |xy| = |x| • |y|

jstanley• 8 years ago

What type of thing is N? What you wrote doesn't seem to make sense if N is just a constant, but I don't see how it makes sense if N is a function? Or maybe you didn't mean multiplication?

E.g. N = 3, x = 2, y = 3

N(xy) = 3(2 . 3) = 18

N(x)N(y) - N = 3(2) . 3(3) - 3 = 51, which is not 18

donbright2• 8 years ago

is there a proof that real numbers can be added?

kgilpin2• 8 years ago

As far as I know, addition is something you define (an axiom) in order to construct the real (or other) numbers.

https://sites.math.washington.edu/~hart/m524/realprop.pdf

whatshisface3• 8 years ago

I think that maybe if you lock a mathematical physicist in a box forever with an x-TeV collider without letting them upgrade it, they will eventually find a theory that hits all of the datapoints and depending on their philosophical weakness then declare it "final."

OscarCunningham5• 8 years ago

Surely what we're looking for is the simplest theory among the theories that hit all the datapoints. That's the theory that's most likely to be the "Theory of Everything" and therefore to continue working when we upgrade our collider.

whatshisface3• 8 years ago

Why would the simplest theory be the most likely to be true?

arketyp3• 8 years ago

Isn't it strange how the probabilistic motivation of Occam's razor loses its foundation when applied to a Theory of Everything? Simple is beautiful, that's all I've got.

firethief• 8 years ago

Well they will and they won't, until you open the box

ChrisLomont• 8 years ago

"Proof surfaced in 1898 that the reals, complex numbers, quaternions and octonions are the only kinds of numbers that can be added, subtracted, multiplied and divided. "

Not true. Any field (in the algebra sense) has these properties. [1]

Quaternions and octnonions also have weirder properties: quaternions are non-commutatve (jk=-kj) and octnonions are non-associative: a(bc) != (ab)c.

I think the article meant these are the only Euclidean Hurwitz algebras [2], which is a far cry from the claim.

[1] https://en.wikipedia.org/wiki/Field_(mathematics) [2] https://en.wikipedia.org/wiki/Hurwitz%27s_theorem_(compositi...

paulddraper• 8 years ago

Example: rational numbers

throwawaymath5• 8 years ago

The rationals are a subfield of the reals.

pishpash4• 8 years ago

It's in the article towards the end, but these are the only kinds of ... "over real numbers," which constraint Furey believes may be only an approximation.

HerrMonnezza• 8 years ago

Even when adding "over the real number", the claim in the article is wrong: R(x), the algebra of rational functions of one variable with real coefficients is a field, and a module over R containing a isomorphic image of R as a subfield.

You really do need the additional constraint of the Hurwitz form to restrict the possibilities to R, C, H, O ...

(Of course this has nothing to do with the work of Furey - I'm just seconding that the claim in the article is incomplete and inexact as worded.)

adamnemecek4• 8 years ago

I’ve been exploring this idea as well however I have a hunch it’s not actually octonions but dual quaternions as they are the perfect formalism for representing 3d movement over time.

And to add to that, the are a Lie group I.e. they are anticommutative I.e. AB=-BA.

I’ve also been exploring this relationship between dual quaternions and linear logic. It’s pretty wild. I’m curious if anyone has any opinions on this.

stochastic_monk• 8 years ago

Do you have an understanding of Clifford algebras? I’ve read a little about them here on hn, and they seem quite powerful. I don’t understand them enough to know if they could also be an appropriate abstraction.

adamnemecek4• 8 years ago

Yes! Dual quaternions are a Cl(2,0,1) Clifford algebra. Good ol Cliffy invented them too.

http://www.chinedufn.com/dual-quaternion-shader-explained/

Check the guy on the right getting deformed like an idiot. Compare it with the smooth criminal on the right.

joppy• 8 years ago

There is a process where you put in a space (number of dimensions) and a metric (Euclidean, for example) and produce a Clifford algebra. This is also sometimes called “geometric algebra”, although there are a lot of sensationalist posts using this name on the internet.

This Clifford algebra has an odd and even part, and the even part is an algebra in its own right, and is very useful for representing “rotations” in the space.

With the Euclidean metric, with one input dimension, the even Clifford algebra is just the reals. With two dimensions, you get the complex numbers. With three, the quaternions. However, since a Clifford algebra is always associative, you don’t get the octonions in this way.

Finally, if you put in four dimensions and the minkowski metric, the even Clifford algebra construction gives you a lovely algebra representing spatial rotations in three of the dimensions, and “boosts” along the time direction - exactly what you need to do calculations in special relativity.

ssivark2• 8 years ago

Incidentally, I've also been thinking about dual quaternions for modeling rigid objects in 3d. For anyone who's curious about the topic, these seem to be a decent set of notes: http://web.cs.iastate.edu/~cs577/handouts/dual-quaternion.pd...

Linear logic always reminded me of the no-cloning property in quantum physics, where a resource can only be used once -- no copying for multiple use.

Can you elaborate on the sense in which you think of linear logic as "squaring to zero"? UPDATE: A little googling throws up this: http://www.seas.upenn.edu/~sweirich/types/archive/1999-2003/...

adamnemecek4• 8 years ago

Good point about no copy.

So this is kinda roundabout however there’s homotopy type theory which states that topology=logic=type theory. For a second let's say that theres a fourth "element" in this equation and that's quaternions (this isn't a stretch I can provide some papers that hint at this).

Linear logic is classical logic with the added reference to time without explicitly referencing time.

Dual quaternions all about modeling deformation over time.

Therefore, I would conclude that linear logic and dual quaternions are related.

chombier• 8 years ago

one of the most intriguing/funny things about dual numbers (and dual quaternions in particular) is how they encode the derivative of the real part into the dual part, and how everything plays out nicely algebraically.

this could be a nice implementation trick for an automatic differentiation framework.

c54• 8 years ago

Her name is Cohl Furey, that is SO COOL!

sdenton4• 8 years ago

I think this is the first article I've ever read about the octonions that didn't include the following John Baez quip:

"There are exactly four normed division algebras: the real numbers ($\R$), complex numbers ($\C$), quaternions ($\H$), and octonions ($\O$). The real numbers are the dependable breadwinner of the family, the complete ordered field we all rely on. The complex numbers are a slightly flashier but still respectable younger brother: not ordered, but algebraically complete. The quaternions, being noncommutative, are the eccentric cousin who is shunned at important family gatherings. But the octonions are the crazy old uncle nobody lets out of the attic: they are /nonassociative/."

throwawaymath5• 8 years ago

For the curious, John Baez has written about octonions pretty extensively: http://math.ucr.edu/home/baez/octonions/

leecarraher• 8 years ago

happy to see John Baez fans on here, i like his series on his favorite numbers https://www.youtube.com/watch?v=vzjbRhYjELo

byproxy• 8 years ago

Also, Joan Baez's cousin. And her father, Albert Baez, explaining elliptictal orbits: http://www.youtube.com/watch?v=_qpKhCa64Eo

PurpleBoxDragon• 8 years ago

Is there an easy explanation of what problems quaternion or octonions solve?

Imaginary numbers are needed to take the square root of a negative number, and complex numbers result from combining the new numbers with the real numbers. Complex numbers also allow solving roots that aren't found in just real numbers.

But I have no similar comparison of what I can do with a quaternion or octonion that I can't do with a complex number. I remember seeing some w based number system derived from the cube root of either 1 or -1 (forget which, but w and -w were the solutions that weren't 1 or -1), but it did all the same things that complex numbers do and was considered mostly uninteresting.

It also seems like there is a pattern to go infinitely beyond octonions, but they all behave identical to octonions, but are the octonions even needed in the same way complex numbers are needed, or do they just make some math problems easier to work with?

uryga2• 8 years ago

Quaternions, in three words: "Rotations in 3D". I like this explanation: https://probablydance.com/2017/08/05/intuitive-quaternions/

NotPhysicsPhd• 8 years ago

Not sure about octonions. But quaternions are somewhat used in mechanics, specifically for dealing with rotations. The usage of quaternions is computationally simpler for describing arbitrary rotations in 3d dimensions.

yaks_hairbrush• 8 years ago

Historically, quaternions came about as a way to try to reason about three dimensional physics. I mean, complex numbers were obviously really nice -- two dimensional numbers you could meaningfully add, subtract, multiply and divide. But they were only 2-D and we live in a 3-D world and we want to do 3-D physics.

So Hamilton was trying really hard to find a way to have 3-dimensional numbers that behaved nicely, and he couldn't do it. But he did find 4-dimensional numbers -- the quaternions. And they were really neat. You can use them quite well for classical mechanics, and electromagnetism, and even special relativity. So, why don't we?

We look at Maxwell's equations of electromagnetism today, and they're really nice, single-line vector formulas. You can also write them as nice, single-line quaternion formulas. Our notion of vector didn't exist at the time the quaternions were first used, and it was a boon to have quaternion notation to simplify some of these physical laws. Vectors and quaternions competed for a bit, and vectors won since they generalize to arbitrary dimensions.

Hidden inside of quaternion multiplication, you can find the three-dimensional versions of the dot product and cross product. And they do have some theoretically interesting properties for number theory and abstract algebra. In the end, however, sometimes items are discarded in favor of better items. I'd rate quaternions as one of the coolest items that ultimately wound up in the discard pile.

daze42• 8 years ago

I've known about quaternions for many years and even used them to program rotation matrices for a few 3d projects but I've never really given them much thought beyond that. For some reason, your comment just completely changed the way I thought about them. To think that the i part of ijk is the same i = sqrt(-1) is mindblowing to me. I had never considered that there may be other "more imaginary" dimensions that were required to solve yet more complicated problems.

logfromblammo2• 8 years ago

If you code a system with 3D rotations coded as Euler angles, you can align two axises and lose a degree of freedom. This is gimbal lock.

Using unit quaternions (aka versors) to code the rotation instead, you cannot lose a degree of freedom. 4x4 matrices also solve this problem, but quaternions are more mathematically efficient. They also give very smooth interpolation for computer-assisted animations.

Also related to spinors in quantum physics and exists as a subalgebra of some conformal geometric algebras.

sleepyams2• 8 years ago

https://en.wikipedia.org/wiki/Quaternions_and_spatial_rotati...

IDK much about octonions, but quaternions have similar algebraic properties to rotation groups and can be used to encode rotations in 3D graphics.

sleepyams2• 8 years ago

In addition to the other replies, check out Clifford algebras which generalize these types of numbers:

https://en.wikipedia.org/wiki/Clifford_algebra

scotty793• 8 years ago

Complex numbers tell you what happens if there is an i that i^2=-1. What happens is that you get cool way to express 2d rotations.

Quaternions tell you what happens if there are three different i's that have this property. And it tells that it leads to nice algebra that expresses 3d rotations very well (and even 4d if you believe the article).

Octonions tell what happens if there are seven such i's. And it leads to cool algebra that helps expressing.... we don't quite know yet.

Also considering other numbers of i's doesn't lead to anything coherent. Also considering different possibilities of what should be the result of multiplying one i by another different i doesn't lead to anything cohesive.

So... i^2=-1 apparently can have either zero, one, three or seven solutions and they have to have very specific relationships between themselves for calculations to make sense

Curious...

romwell3• 8 years ago

Is there an easy explanation of what problems quaternions solve?

Sure. Unit quaternions form a double-cover of SO(3).

In other words, you can encode a rotation of a 3-dimensional object with a single unit quaternion.

But wait, there's more! You could do the same with a matrix, or a triple of angles. Why not do that?

Answer: interpolation. The "natural" way you want to go from one rotation to another corresponds to exponentiation of quaternions. If you linearly interpolate matrices, the intermediate steps will do something nasty: they won't even be rotations!

The natural way to implement the Arcball interface for rotations is using quaternions. Here[1], I have implemented it in ProcessingJS and wrote up the math behind it.

Quaternions (like complex numbers) can do other things too, but this alone is a good start. Also gives you intuition why they aren't commutative: because rotations in 3-space aren't.

TL;DR: Unit complex numbers = rotations of plane. Unit quaternions = rotations of 3-space.

PS: you shouldn't think of complex numbers as the solution to the problem of "taking the square root of -1". Think of them as "how can I multiply/divide a 2D vector by another 2D vector?" - there's only one way to do it sanely (multiply/divide lengths, add/subtract angles). This is what the complex numbers are.

Hamilton was trying to solve the same problem in 3D, and couldn't (turns out, it is not possible[2]), but solved it in 4 dimensions, and later found many applications for them.

[1] http://www.math.tamu.edu/~romwell/arcball_js/index.html

[2] https://en.wikipedia.org/wiki/Frobenius_theorem_(real_divisi...

donbright2• 8 years ago

i did not understand quaternions until I read Hamilton's original works. Maybe i just have a 19th century brain or something. but i found them delightfully free of modern gobbldeygook.

https://www.maths.tcd.ie/pub/HistMath/People/Hamilton/

posterboy• 8 years ago

Imaginary numbers are needed to take the square root of a negative

No, they are not. That problem is not well defined. A symbol is not a solution.

Complex numbers are needed to solve the polynoms of a higher degree. Eg. x^4+x^2=-1 can be simplified to y^2+y=-1 with y=x^2 which wouldn't have a solu

Retra• 8 years ago

One way to think of it is that numbers are mainly used to solve problems by studying the behavior of subsets of them that have specific properties. Like "prime numbers", "square-free numbers", and "solutions to this given equation", etc., and the interesting feature of numbers in general is that they can embed multiple such concepts at the same time. This is helpful because you can find numbers that share multiple properties in order to bridge between otherwise unrelated problems -- it makes it easier to compose solutions of simpler problems into solutions for larger, more complex problems.

From that point of view, quaternions and octonions solve problems in the same way more common numbers do, they just have different sets of properties and so help solving a different set of problems. Of course, they can only do this if we study them well enough to have a sufficiently large suite of concepts and relations in our toolbox.

fifnir2• 8 years ago

A layman's quest to understand wtf this is...

In mathematics, the octonions are a normed division algebra over the real numbers .

wtf is a normed division algebra??

In mathematics, Hurwitz's theorem is a theorem [...] solving the Hurwitz problem for finite-dimensional unital real non-associative algebras endowed with a positive-definite quadratic form.

... right.

I have the same problem when I try to understand anything statistics related, I get hit by a barrage of unknown words and my brain just melts.

Is there any place that explains mathematical concepts in ... different ways?

davebryand• 8 years ago

Here are a few that I love:

3 Blue 1 Brown: https://www.youtube.com/channel/UCYO_jab_esuFRV4b17AJtAw

VSauce: https://www.youtube.com/user/Vsauce

Numberphile: https://www.youtube.com/user/numberphile

throwawaymath5• 8 years ago

Those are good for supplementary exposition (especially 3Blue1Brown), but they're not suitable for learning on their own. They're also a bit of a hodge podge beyond calculus and linear algebra.

To understand what's going on here in any meaningful sense, the parent commenter should pick up an accessible undergrad textbook on abstract algebra. It doesn't have to be particularly advanced. Then they'll have a better foundation for understanding the algebraic features of various number systems.

empath75• 8 years ago

Unfortunately there’s a lot of domain knowledge wrapped up in very short phrases. What you want to learn is abstract algebra, if you want to google for YouTube videos that break it down for you.

Micoloth• 8 years ago

Well yeah, math books...

Jokes aside, i too think we need a new framework for divulgating math that actually tells what you need to know, without just handwaving at it, BUT without the amount of technical details of a mathematics class.

What do you know, i think this is Possible, too.. You can communicate a surprising amount of information if you use words properly.

Of course, since this has never been done except from basic maths, it would be quite a task to embark in, and one would only do it if it made economic sense..

fifnir2• 8 years ago

only do it if it made economic sense

What if writing wikipedia articles was treated like publishing on prestigious journals? (somehow)

sigstoat2• 8 years ago

Jokes aside, i too think we need a new framework for divulgating math that actually tells what you need to know, without just handwaving at it, BUT without the amount of technical details of a mathematics class.

oh man, have i got bad news for you about the amount of technical detail present in math classes.

amelius• 8 years ago

I'm still hoping for an ELI5 version of Wikipedia (e.g. as a language option).

DougBTX• 8 years ago

For more brain melting, here's a roadmap for learning React in 2018, React and associated tech is what, 20 years old?

Here's what that looks like: https://github.com/adam-golab/react-developer-roadmap

Then consider maths, how long and how many people have been contributing to that field?

booleandilemma• 8 years ago

What’s funny is most of those projects in the leaves probably won’t even be around in another 10 years.

throwaway375853• 8 years ago

Some useful advice: https://math.stackexchange.com/questions/617625/on-familiari...

77pt77• 8 years ago

unital -> there is a multiplicative identity 1 such that 1.a = a for all a.

normed -> there is a norm. A way of saying how big an element is. In the reals |x| - x if x is positive and -x if x is negative. In the complex numbers |a+bi| = (a^2 + b^2)^(1/2)

Division -> Division (except possibly by zero) is always possible. That means for a and b not zero there exists c such that a=cb (c is a divided by b)

I could be wrong about these things since I'm quite rusty

ducttapecrown• 8 years ago

I think division is normally framed rather as the existence of multiplicative inverses for all non-zero elements of the ring. That is, R is a division ring if

a) there exists a 1 in R

b) for all x in R, there exists y in R such that x * y = 1.

I'm pretty sure these are equivalent.

Proof:

(==>) Let a = 1, and b in R be arbitrary. Then there exists a c such that b * c = 1. So inverses exist!

(<==) Let a and b in R be arbitrary. Then a = a * b^-1 * b, so c = a * b^-1. QED.

pdonis• 8 years ago

wtf is a normed division algebra??

An "algebra" is a set of thingies that have binary operations defined on them (i.e., operations that take two thingies as input and output another thingie). The thingies are usually referred to as "elements" of the algebra. Any algebra will at least have the "add" and "multiply" operations, but might also have others.

A "division algebra" is an algebra where the operations are add, subtract, multiply, and divide, and all of them work basically the same as they do with ordinary numbers (but they won't have all of the same properties--see below).

A "normed division algebra" is a division algebra with one additional operation called "norm", that takes as input any element of the algebra and outputs a real number, the "norm" of that element. On the ordinary real numbers, the norm is just the absolute value.

The "over the real numbers" part means that you can construct the normed division algebra by starting with real numbers; or, to put it another way, all of the elements of the algebra are "made of" real numbers. The simplest way of viewing this is as a repeated operation of pairing: complex numbers are made of pairs of real numbers, quaternions are made of pairs of complex numbers (hence sets of four real numbers, hence "quater"), and octonions are made of pairs of quaternions (hence sets of eight real numbers, hence "octo"). But each step in this series loses a key property. The reals are totally ordered; the complexes are not. The complexes are commutative under multiplication; the quaternions are not. The quaternions are associative under multiplication; the octonions are not.

Is there any place that explains mathematical concepts in ... different ways?

Not really, because the only way people have found to really understand mathematical concepts is to build them up out of simpler mathematical concepts. That means you can't just encounter a complicated mathematical concept and expect to understand it if you don't understand all the simpler concepts it is built from. There are no shortcuts.

Ono-Sendai• 8 years ago

I have to disagree that quaternions underlie Special Relativity. Although special relativity does use 4-vectors, those aren't quaternions.

madhadron2• 8 years ago

I remember going down that path when I was an undergraduate. Fortunately I had a very experienced theorist to hand who explained that, yes, people did try that, but stopped bothering because it doesn't generalize to general relativity, and there was no point keeping two mathematical toolboxes around when you could have one.

eigenspace• 8 years ago

Clifford algebras are great for both SR and GR and have all the properties that one likes in quaternions (and more)

blutfink• 8 years ago

There are equivalent formulations of SR using quaternions.

throwaway375853• 8 years ago

But do they generalize to GR?

imglorp• 8 years ago

How does this tie into E8? Does this work validate Garret Lissi or is it parallel?

https://en.wikipedia.org/wiki/An_Exceptionally_Simple_Theory...

atonalfreerider• 8 years ago

I remember hearing Garret Lisi's TED talk on the E8 ToE (link below) years ago and hoping that components of the theory would eventually come to light through advances in particle physics research. Has anyone heard anything supportive or to the contrary since?

TED Talk: https://www.ted.com/talks/garrett_lisi_on_his_theory_of_ever...

Paper: https://arxiv.org/abs/0711.0770

Edit I remember seeing an update from him two years ago where he addresses some of the criticism: https://www.quora.com/What-is-the-status-of-Garrett-Lisis-E8...

ansible• 8 years ago

There's been some criticism of his work, back when it first came out.

I'm fuzzy on the details now, but the criticism was along the lines of "mixing things together that don't make sense".

stcredzero• 8 years ago

I wonder how many hardcore Harry Potter fans are smiling at the 1st photograph?

scotty793• 8 years ago

“Because while it’s very easy to imagine noncommutative situations — putting on shoes then socks is different from socks then shoes — it’s very difficult to think of a nonassociative situation.” If, instead of putting on socks then shoes, you first put your socks into your shoes, technically you should still then be able to put your feet into both and get the same result. “The parentheses feel artificial.”
The octonions’ seemingly unphysical nonassociativity has crippled many physicists’ efforts to exploit them.

I'd say nonassociativity is extremely physical property. And example with shoes and socks, if anything, shows just that. In idealised mathematical model, if you put socks inside shoes and then insert feet into socks you could end up with same thing as if you put feet in socks an then both in shoes. But in real world or just accurate model of physical world you'll end up with very different result.

I feel that nonassociativity is what's missing to take into account time which unidirrctuonality is suspiciously missing from almost all of the physics.

politician• 8 years ago

If you're looking for a deep look at time -- a Total Perspective Vortex, I'd recommend "Spontaneous Inflation and the Origin of the Arrow of Time".

https://arxiv.org/abs/hep-th/0410270

scotty793• 8 years ago

I don't know. Unidirectionality of time just feels like something that should be everywhere. Nonassociativity of basic math that governs all of matter seems for me to be a better source for it than inflation or entropy or gravity or any one specific thing.

danbruc5• 8 years ago

In the approach from the article it seems as you are picking a mathematical structure in the middle of nowhere with the universe faintly visible at the horizon and then you start wandering around hoping that you will stumble across a path leading to the horizon.

But there don't seem to be many reason to believe that such a path exists, there are countless mathematical objects you could pick as a starting point and almost none of them have a path leading to the universe at the horizon. And even even of those with path going roughly into the right direction many will take a turn before you arrive at your destination.

So it seems much more promising to me to start at the universe and the mathematical structures describing our observations in a straight forward way and then explore from there the surrounding mathematical structures to see if they are a better fit, suggest new ideas, or whatever.

sannee2• 8 years ago

In the approach from the article it seems as you are picking a mathematical structure in the middle of nowhere

Quaternions were very popular way of expressing the "classical" physics around the 19th century (and the vector algebra we know today is in some ways just a derivative of quaternion algebra). Complex numbers are extremely useful in many fields even today. It's hardly in the middle of nowhere.

danbruc5• 8 years ago

But the article is not really talking about quaternions - which are surly a useful tool, probably best known for the nice way in which they can describe rotations - but about R⊗C⊗H⊗O. And it's at the very least not obvious that this thing is anywhere close to where they journey is hopped to lead to.

simcop2387• 8 years ago

Yep complex numbers get used extensively for doing calculations with electronics when doing analysis.

https://www.khanacademy.org/science/electrical-engineering/e...

pishpash4• 8 years ago

The article briefly alluded to this, that C, R, H are both already seen in features of the universe, so it's not "middle of nowhere."

chunky1994• 8 years ago

It's rather amusing that the author assumes that non-associtiave objects are "weird" for physicists (or at least that was my reading), since the velocity addition formula is in general non-associative and that has been extensively studied.

(I remember three separate occasions in my undergrad particle physics class where we actually went through all the calculations involved with the velocity addition formula and finally saw that SOL was wacky).

https://en.wikipedia.org/wiki/Velocity-addition_formula

I wonder if that is uncommon or if the article is just a bit ungenerous towards our understanding of non-associative objects.

ssivark2• 8 years ago

To be fair, one never talks of relativistic "velocities" beyond undergrad physics. It is much easier to talk about Lorentz "boosts", and as members of a Lie Group, they are associative, though not commutative.

throwaway375853• 8 years ago

This. It's better to just make the full leap into spacetime geometry (4-vectors and 4-tensors) than keep trying to slice it into annoying 3-vectors.

smaddox2• 8 years ago

Not to mention operator calculus. Operators do not, in general, associate. Feynman developed his own notation for operator calculus.

gjm113• 8 years ago

How do operators in general fail to associate? Usually the "multiplication" operation for operators is function application, which is a paradigmatic example of a thing that is associative.

pnutz• 8 years ago

Under what conditions is velocity addition not associative? In 1d they are associative right, but cant think in 3d

theoh• 8 years ago

The other thing that contains non-associative elements is logic. Due to the Curry-Howard correspondence, that means functional programming too.

So this quote about mathematicians seems a bit off. Baez is talking about mathematical physicists, I guess, not logicians and computer scientists. I know he is not a functional programmer from various online remarks he has made. So maybe it's more of a personal perspective that we shouldn't take too seriously.

'“Nonassociative things are strongly disliked by mathematicians,” said John Baez, a mathematical physicist at the University of California, Riverside, and a leading expert on the octonions. “Because while it’s very easy to imagine noncommutative situations — putting on shoes then socks is different from socks then shoes — it’s very difficult to think of a nonassociative situation.” If, instead of putting on socks then shoes, you first put your socks into your shoes, technically you should still then be able to put your feet into both and get the same result. “The parentheses feel artificial.”'

amai• 8 years ago

Why are complex numbers not called duonions then?

OscarCunningham5• 8 years ago

And why are the real numbers not called "onions"?

amw• 8 years ago

I went upstairs to find the machine where I was already logged in so I could hunt down and upvote this comment.

kibwen• 8 years ago

Obviously due to potential confusion with the zero-dimensional numbering system, "0nions".

wolfgke• 8 years ago

Why are complex numbers not called duonions then?

Why are pairs not commonly called duples?

pishpash4• 8 years ago

So, did Furey get a faculty job or can she be viewed with her accordion somewhere?

selimthegrim2• 8 years ago

FWIW, I'll certainly tell my department chair in New Orleans about her if they're doing another faculty search soon. Maybe she can have her cake and eat it too that way.

didibus• 8 years ago

Are we getting to the point where physics actually isn't showing any more useful properties for us to leverage?

Isn't that kind of what it would mean if it turned out octonions were at its core?

mikorym• 8 years ago

As a math graduate, octonions (and quaternions) at least to our group, was something that got discussed once or twice and not much after that. However, I would not call them weird or unusual, at least not more weird than something like a near-ring which similarly simply drops one of the common assumptions for rings (I'm not sure which, actually). As mentioned in some of the comments, nonassociative fields do get studied. Studying not necessarily commutative structures such as (all) groups is in fact an even much more common thing to do.

I would say that studying octonions exclusively would be something I personally would avoid, as I would rather try to study the four structures (reals to octnonions) together, either more generally (e.g., group theory and ring theory) or more abstractly (e.g., as members of categories) and form an opinion on whether I think octonions in particular are useful for the questions that I want to ask.

That is not to say that the research here is not interesting, but it is difficult to judge that from "popular" mathematics articles. I got the impression that the author of the article places a much higher priority on the pictures accompanying the post.

I remember that I found it interesting that studying the four dimensional spacetime bears more fruit than stopping at three space dimensions, and that at the same time from complex numbers the next structure ends up also having four dimensions (i.e., being modelled by 4-tuples). However, apart from being interesting in this narrow sense, I do not know whether this suggests any creative yet precise mathematical questions.

forkandwait• 8 years ago

If anyone can make octonions cool it would that physicist

bvinc• 8 years ago

Can anyone expand on the current successful similarities between octions and the standard model in plain English?

marlag• 8 years ago

They “imagined that the next bit of progress will come from some new pieces being dropped onto the table, [rather than] from thinking harder about the pieces we already have,”

When the best minds we have divide into two camps, one saying that (a) "with X and Y we don't have enough information to solve Z" and the other saying (b) we do but we need to think harder, the first camp builds a particle collider, the other creates what, string theory? Aren't we doing "fuzzy science" here?

It seems that the experts in one of the camps should go back and retrace their steps because somewhere along the line they made an assumption based on some data that they (I assume) forgot to encode into their equations and now they have trouble taking it to the next level. Why is it not clear to us that eiher a or b is true?

dbdoug• 8 years ago

'Looking like an interplanetary traveler, with choppy silver bangs that taper to a point between piercing blue eyes' WTF? for a few minutes, I thought this was a serious article by a serious journalist. Apparently not.

lifeformed• 8 years ago

If it goes: 1D, 2D, 4D, 8D, why does it stop at 8? Is there a hexadeconion?

danbruc5• 8 years ago

They are called sedenions [1] and you can repeat the construction taking you one level up [2] infinitely.

[1] https://en.wikipedia.org/wiki/Sedenion

[2] https://en.wikipedia.org/wiki/Cayley–Dickson_construction

pooya13• 8 years ago

I never liked the name complex numbers. Something like dual numbers would have been much nicer and more descriptive.

By the way any idea why they don't mention the sedenion numbers? https://en.m.wikipedia.org/wiki/Sedenion

steamer25• 8 years ago

This reminds me a bit of atomic orbitals and how they're based on spherical harmonics. I was curious why there were e.g., eight electron 'sockets' in the second shell. Eight seemed like a very arbitrary number to me and my high school chemistry teacher's inability to explain at the time did it's share to put me off chemistry.

Many years later I remembered my old question and started looking it up. It turns out that eight is the sum of 1+3+3+1 perhaps similarly to what's in the article.

Spherical harmonics ends up giving rise to a three dimensional 'overtone' series (borrowing from my understanding of music theory). In the first order there's only one mode of vibration. In the second order there are three additional modes. The summands above are something like positive and negative degrees of freedom for each mode in the second shell.

Here's a diagram of what the modes look like in each order:

https://i.ytimg.com/vi/OkDYbIhisZE/maxresdefault.jpg

...and here's an animation of a sphere undergoing the differing modes of vibration:

https://youtu.be/EcKgJhFdtEY

If I understand correctly, the math related to atomic orbitals can be described with 3 dimensions of space: x, y and z plus one more orthogonal dimension of frequency/time which would mean quaternions would be most directly applicable?

stultifying• 8 years ago

The really interesting part in all this, is that we're still reduced to bouncing values off of imaginary numbers to obtain accurate readings.

We toss our known quantities into a void, anticipating that if some impossible, imaginary thing really can fill the gap, and if or when it does, we'll catch the rebound off of it, and the rest of the universe proceeds predictably.

Somehow, we're always put into a position where we have to close our eyes, fly blind for some undisclosed intervening moment of unspecified length, and when we open our eyes again, we're grounded by familiar territory again.

It really is kind of stultifying.

starchild_3001• 8 years ago

This article reminded me of wave function being a complex-valued function! Does this have anything to do with octonion, nature's symmetries/invariants or the standard model?

kentbrew• 8 years ago

Pachimari, of course, is the official mascot of octonions everywhere: https://kotaku.com/overwatchs-little-onion-octopus-has-becom...

fouc• 8 years ago

Why do I feel like the octonions are likely related to the spin networks of LQG (loop quantum gravity). The non-associative property is probably key to explaining how change in space is propagated through the spin networks. And thus why time is directional..

csoroz• 8 years ago

https://motls.blogspot.com/2018/07/cohl-furey-understands-ne...

The Octonion Math That Could Underpin Physics

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