The Lisi story below is a good hook for a post on the theory of everything…so here goes.
One of the big discoveries of 20th century physics is that there exist only four independent forces or interactions. These are gravity (known since Newton), electromagnetism (the unification of electricity and magnetism achieved by Maxwell in the 19th century), the strong nuclear force (that holds the protons together in the nucleus), and the weak nuclear force (responsible for nuclear decay and radioactivity).
Einstein always suspected that these interactions were not truly independent and spent most of the latter part of his life trying to achieve a unified theory that could describe both gravity and electromagnetism (a program that became known as unified field theory, initiated by Kaluza and Klein). Einstein failed in this program, not least because we now know that gravity is the hardest nut to crack (we have no satisfactory quantum theory of gravity, while all the others interactions can be described in terms of quantum theory).
Nowadays, unified field theory works from the oposite direction. Using the methods of gauge symmetry, theoreticians in the 1970s established a strong connection between the electromagnetic and the weak nuclear interactions. The theory predicted the existence of unkown particles (W and Z bosons), which were subsequently discovered in high-energy experiments at CERN in the 1980s…ever since we talk about the electro-weak interaction as a single entity.
One of the giant particle detectors at CERN
This success of electro-weak unification resulted in furious attempts to extend the unification program to include the strong interaction (a program known as Grand Unified Theory) . However, the GUT program soon ran into serious trouble, with a clutch of ‘no-go’ theorems showing that such unification was mathematically unsound (see the O’ Raifeartaigh theorem and the Coleman-Mandula theorem). Various novel ideas to circumvent this problem gradually emerged in the 1970s, the most promising of which is probably the theory of supersymmetry. Anyway, there now are strong hints of connections between the electro-weak and the strong interactions at high energies. Most ambitious of all is the prospect of a unified theory that also includes gravity i.e. that describes all four interactions in a single framework – the so-called theory of everything.
All the above is really boils down to the simple idea of a single super-force existing at the tremendous energies of the Big Bang, which gradually split off into the four seperate entities we see today as the universe cooled…pretty neat eh? The problem is that the mathematics of such a theory of everything (TOE) remains elusive – the leading candidate is string theory – yep, the famous string theory that is controversial because it is so mathematically abstract that it makes almost no predicitions that can ever be verified/falsified by experiment…..but that’s a separate story!
Suffice it to say that Einstein’s famous quest for a theory that incorporates a description of the elementary particles and all their interactions, now continues under the title Theories of Everything, and is still the Holy Grail of theoretical physics. As regards Garrett Lisi’s paper, part of the unification program inviolves the description of all the elementary particles using the mathematical theory of groups. (For example, Gellman’s classification of the known particles in the 1960s using group theory led to the prediction of a deeper layer of matter making up most particles – the quarks, later detected experimentally). Lisi’s paper purports to show that a particular mathematical group, the E8 group, may offer a very useful way of decribing all of today’s known particles, in a very simple framework…hence the interest. Plus, he’s an excellent surfer!
Antimatter 
I’ve read some pretty strong critism of TOE.
From Wikki:
Given today’s status, Garrett’s model does not naturally lead to a unification of the Standard Model interactions with gravity (he has to choose the action by hand that contains both), it does not allow us to understand quantum gravity (since there’s nothing said about quantization), it does not explain the parameters in the standard model (since there isn’t yet a mechanism for symmetry breaking), it does not explain the cosmological constant or its value (as said above, to claim there has to be one, it would be necessary to show there’s no way to do it without one), it does not explain the hierarchy problem (and I see no way to do so), it does not explain why we live in a spacetime with 3 spatial and 1 timelike dimensions, it does not in my very humble opinion yet qualify for being called a Theory of Everything.
Some prof from Harvard called it childish theory.
Boy you guys are tough on each other! :)
Hoosier, all of the above is about right, but I think the important aspect of the Lisi paper is the drawing of attention once more to the E8 group as a promising classification group. Classification schemes for the elementary particles is an important, but not suffucient, part of any TOE.
Garrett himself later commented that he could have used a more modest title for the paper, it was probably a bit misleading!
Cormac
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Well that’s a great reply..
I have another question for you..
I come here because you are very smart and seem to have a spiritual side to you..like me, there is probably something that is a higher power than us..
I live in a family, sports family..We don’t talk alot about math or the big bang..
So let me ask you..
After watching all these shows about elements being born in the sun..or fused from lightess to the heaviest elements are created in the sun..yes we are children of the stars..ect. ect.
if we create elements without the power of the sun we would fuse the element of lead into gold..but your numbers and math says it can never happen…stay with me here..
Two biological cells meet at creation and make a baby..
( i’m not really religious so fetus or baby and when..who knows but a baby is born and they have every element in our bodies you can list..water..calcium, copper..whatever…in trace element in the human body..poof i have a frame of calcium yet none of it came from the sun..i grew and created it..without the power of the sun. in a human frame..
Are we really children of the stars?
This just doesn’t add up..biolgical cells create all the elements in the body..and grows them..even if you believe you got trace elements from mom ( or mum in your case)and dad can grow into a large frame with heavy elements..
you just can’t create .000001% of some element or dna and make into a bigger number or wieght without the power of fusion in a sun…
do you have insight to this?
Hey Hoosier, I think there are two different areas here.
The origin of the physical elements that make up everything in the universe (both inanimate and animate matter), and the origin of biological life (which is do to with cell biochemistry).
The former is fairly straightforward. We’re pretty sure the Big Bang left a huge amount of Hydrogen and Helium, the lightest elements, in the universe. As a star dies, these elements get fused into the heavier elements (the heaviest of all are formed when a star goes supernova). So that’s where the atoms of the different elements of the Periodic Table come from.
How the basic elements lead to the first biological cell is a far harder question – thankfully not in the area of physics.There is one similarity though – I gather from colleagues that question of the very first cell is a bit like the singularity of the Bang – no-one’s quite sure how the exact beginning occured…interesting.