NOTE:
What follows is more of a ramble, exploring the question without actually answering it. No one else can answer it either, so I am in good company. And bad.
END OF NOTE.
Well, the Universe certainly can be explained.
For example:
“God done it.”
That is a theory of everything.
The question is whether such an “explanation” is a “theory” at all, let alone “complete” or even “useful” in any “real” way. Not to mention withstanding “scrutiny” or “peer review”.
As you can see from all the quotation marks, you can very quickly sink into the semantic bog that is the paddling pool of philosophers.
So let’s just take words at face value and, also, avoid the pitfalls of including subjective reality as part of “the Universe”. Slash and burn, all the way down to the nub:
By the Universe, I mean all that physically is, which helps to cut through a lot of garbage, especially about consciousness. And by “Theory”, I will mean a theory of physics, which puts paid to theists of a fundamental leaning, snake oil sales men and flat earthers, all in one swoop.
Nobel laureate Steve Weinberg, was a strong advocate of ToEs other than the Goddunnit one.
When he went to Washington, cap in hand, to argue the case for VBS (Very Big Science) and the huge funding it requires, he pointed out that there is a pattern to the history of physics:
An arrow of explanation, as he eloquently called it.
The idea is seductive.
Since Galileo’s stubborn genius, we have been unifying our scientific explanations, narrowing down the variety whilst expanding the scope.
And as these explanations (scientific explanations, as opposed to narrative ones) accumulated at an ever increasing pace over the last 5 or 6 centuries, a pattern does indeed emerge:
A pattern of convergence of ideas and theories towards some as yet inaccessible core
Weinberg’s thesis was that this core is the so called Theory of Everything. The ultimate ToE.
So, is he right?
Well, the answer to that is a question is, actually, erhmmm…, quite subjective.
The “evidence” is Weinberg’s arrow of explanation, but the evaluation of that “evidence”, if you really look hard at it, is subjective. And the thesis, based on past experience, is optimistic at best, with highly selective evidence.
Weinberg was one of the “fathers” of the Standard Model, the most successful and beautiful of them all. The only force it did not encompass was Gravity.
Surely it was just a matter of time before Gravity could be brought into the fold?
Well, time has passed. A lot of it. Weinberg is now an old man of 86.
And yet, still Gravity holds out, aloof from the Standard Model, let alone from any attempt to give it its own Quantum version. Quantum Theories of Gravity are not theories at all, they are instead beautiful speculations stuffed with brand new maths.
String theory, M Theory, Quantum Loop Gravity…
But still, nothing, no break through.
Worse still, these theories are not converging or unifying. They are proliferating.
And then there is Dark Energy and Dark Matter.
So it seems something is rotten in the state of Denmark. Suddenly, the arrow of explanation does not seem quite so convergent.
This isn’t the first time this has happened.
Newton unified the laws of Kepler into one theory. The heavens and the Earth obey one law:
Gravity.
But then electromagnetism was discovered.
With a pesky little constant, imaginatively called “c” for “constant”, that predicted that the speed of light in a vacuum was independent of the motion of the observer.
Which to a 19th Century physicist was a whole shitload hitting a long line of fans:
Cos that fact stuck two defiant fingers up Galileo’s nose, in the shape and form of his principle of Relativity.
No bother. Along comes Einstein and gives people something to ask about on Quora.com
But just then, just as everyone was saying that’s it, physics is dead, job done, along comes new experimental technology. People start looking closer at stuff, probing to see what it really is made of:
Double slits, crystal refraction, atomic structure, nuclear physics…
And people start asking new questions about stuff. And scientists come up with new definitions of what counts as “stuff”.
People like Planck, Einstein (yes, that’s Albert in the thick of it again), Schrodinger, Heisenberg, Marie Curie, Rutherford (OK, timeline issues here), Pauli, Dirac, Fermi... All the nerd’s pinups, they seemingly turned the arrow of explanation on its head.
And hey, presto! suddenly we have two totally new forces of nature (the weak and strong nuclear forces), we start find a proliferation of sub atomic particles begging new questions and new theories.
Suddenly, the arrow of explanation seems anything BUT convergent:
And then, 50 years on, with Einstein dead, Feynman and Weinberg et al, start wrestling with the problem and the Standard Model emerges into the light in all its glorious shining beauty, but just as everyone starts to cheer and celebrate that arrows are now convergent again, Gravity goes and digs its heels in, Vera Rubin finds stars in distant galaxies that prove dark matter must exist, regardless of what it is, or else General Relativity is wrong. Leonard Susskind becomes the Nick Kyrgios of Physics and everything goes pear shaped again.
So, it has all happened before and who’s to say it won’t happen again?
So all the talk of ToEs is a bit premature, to put it mildly.
Lets blame it on Einstein. After all, unification was his idea in the first place!
Having figured out General Relativity, Einstein decided to UNIFY electromagnetism with gravity. Piece of cake, for Albert.
Well, not quite.
Kaluza and Klein got there first. They added another dimension and hey, presto! Maxwell’s equation pop out at in the form of extra equations in addition to Einstein’s 4D equations.
Surely, physics is dead now?
Well, no. Because by now everyone knew about electrons and positrons, that annihilate with each other, and you have the nuclear weak and strong nuclear forces and all the weird and ugly but beautiful quantum world.
So what looked like a beautiful convergence of ideas, a grand unification, was just a dead end:
Arrows get stuck in tree trunks, and stop converging.
And yet, when you zoom out from all the chaos of everyday physics, that convergence of ideas is plainly evident.
And it is this convergence that crushes the life out of narratives of Flat Earthers and Einstein deniers and Creationists and Young Earthers, and every other crank with a “theory” and no equations, and you get Freshly Squeezed Stupid Juice with Bits.
Or the fundamentalist Christians stuck, in their quiet little mid-west churches.
And all the while, a global society rages past the door, with all its outrageous highs and dehumanising anonymity and potentially lethal consequences.
Who am I, or you, to say if a ToE is an achievable goal for humanity?
I personally think we will never catch up with the the horizon or even the rainbow. They will always be out of reach. Paraphrasing Shakespeare, there are more things in Heaven and Earth than can ever be dreamt of in your ToE.
We will never fully grasp reality not just because we aren’t equipped to, but because it simply can’t be grasped*.
But that, to be quite honest, is just my subjective take on the question.
I would never dare to say I had an answer to your question.
Unlike Steve Weinberg.
(*): There is a philosophical reason, or illustration, of the fact that a ToE is not feasible:
A ToE, if it really, really is to explain everything, cannot be falsified.
Therefore, it is not scientific, at least in the sense of “scientific” defined by the philosopher Sir Karl Popper. Instead, it would be an absolute truth.
Which a scientific theory, by definition cannot be.
So there is always a gap between “real” and “true”, and in that gap you can fit an entire Universe.