Forewords
My opinion about this issue shifts as more data are accumulated according to the Bayes theorem, so it may change in the near future after the LHC Run2 starts. Anyway, it seems to me that data are pointing towards J. A. Wheeler’s self-aware Universe. What if the truth was that we are afraid of asking the right questions? We might not like the answers.
The Chemistry amongst us
Now that we analyzed most of the LHC 7 and 8 TeV data, I think I can safely say that the Standard Model of particle physics is alive and kicking. No Supersymmetric particle showed up, no extra dimensions, no excited quarks, no leptoquarks.
From an experimentalist’s point of view, this was a great accomplishment after more than 40 years of research. Anyway, I feel quite uneasy with the theoretical interpretation of this discovery. I’m not going to give detailed explanations of all the points, but here you are:
* fact: life-as-we-know-it is a consequence of the chemistry of Carbon. Like it or not, I think that a Universe like ours is bound to give rise to life-as-we-know-it sooner or later. And in fact, after 13.4 billion years, here we are. It’s just a matter of probability. Perhaps other kinds of life are possible (some say Silicon-based) but this one is the only we know about.
* fact: chemistry-as-we-know-it depends on few fundamental parameters, for instance the mass of the electron and the elementary electric charge (if you prefer, the fine structure constant). Change them by much less than a few percent, and you’re dead.
Let me elaborate a bit more:
* fact: the radius of the atom (or Bohr radius) depends on the mass of the electron, the Planck constant, the speed of light in vacuum and the fine structure constant. The atomic radius defines the energy levels that in turn define chemical bonds and structures.
* fact: the mass of electron depends on the coupling with the Higgs boson. This, which is a free parameter in the Standard Model of particle physics, affects the radius of the atom, and thus chemistry. Draw your own conclusion.
All these facts are actually even more intertwined: for instance, Carbon exist thanks to a peculiar resonant effect called triple-alpha process. To some extent, the structure of the quantum chromodynamics (QCD) defines inter-nucleon interactions, hence these resonant processes. We don’t have a proof of how nuclear potential emerges from residual QCD interactions, but we believe that its behavior is similar to the Van der Waals force. I think it’s reasonable to suggest that these properties can be traced back to the high value of the Strong coupling constant and to the non-abelian nature of the strong interaction.
* fact: nuclei are produced inside stars in nuclear fusion processes. However, without weak nuclear force, stars would collapse or do not even form. Moreover, the beta decay generates neutrons via p p -> p n l v process. Without neutrons, heavy nuclei are unstable. Weak interaction is weak because its mediators, the W+/W- and Z bosons, are very massive.
The high mass of the W/Z bosons is explained by the Higgs mechanism: the Higgs boson interacts with a set of four fields (called B and W+, W- and W0) giving mass to them. It is some sort of freeze-out process called electroweak spontaneous symmetry breaking: it gives rise to the vector bosons Z0, W+/W- and the photon. So, the existence of a Higgs boson, together with its properties, is responsible for the weak interaction, hence beta decay, hence stars, hence carbon. Draw your own conclusion. To be honest, some propose a “weakless Universe“, but it’s not at all clear how heavy elements (including Carbon) get dispersed in space if no supernova mechanism can happen.
In the Standard Model there is no reason why the electroweak scale (200 GeV) is close to the QCD scale (0.3 GeV), it’s just so. Apparently, this closeness is necessary for the stability of matter.
An Anthropic Explanation?
At this point, one may invoke the the anthropic principle to explain this quite embarrassing fine tuning: the parameters that we measured are just so because otherwise we wouldn’t be here in the first place. There could be other Universes separated from ours, but at least in this Universe the fundamental parameters allow the existence of life-as-we-know-it. In others, it doesn’t. This is why we line in this tiny-tiny island amidst the vast landscape of the possible values that the parameters can take at the same time.
We’re not yet finished: according to Quantum Mechanics, the state of a system is not defined until an observer measures it. If you apply the mechanism to the Universe as a whole, you understand that everything is in a suspended state until some conscious being observes it for the first time! In the end, it looks like consciousness selects the set of parameters suitable for life to exist in a sort of back-reaction. The point is: is the observer part of the observed system (the Universe)? To my understanding, the observer is coupled to the system, but it’s not a part of it, strictly speaking. Some suggest that a phenomenon called decoherence could explain the collapse of the wave function (i.e. the process of measurement) without resorting to an external observer. If a quantum system interacts with its environment in a thermodynamically-irreversible way, there is a de-phasing effect that breaks the superposition of states and picks up only one possible outcome (the observation). It is said that the classical limit emerges from quantum mechanics.
Also, there is a proof by Von Neumann that states that the result of the measurement does not depend on where the wave function collapsed – in the system? in the apparatus? in the brain of the observer? Some other suggest that consciousness is an emergent property of complex systems, such as the brain. Even if there is no mathematical proof of that, this might be still a possible explanation, once coupled to decoherence. In any case, it still fits into the picture that the Universe needs an observer to get into a definite state of existence!
The hypothesis that consciousness is external, and that the brain is somehow an interface that may drive the decoherence seems to me quite tantalizing if not actually an explanation. For sure, it’s not in constrast with the Simulated reality hypothesis.
The catch is: we don’t have a theory elastic enough to fit all the observed data and consciousness. We don’t know for sure: at the moment, the only two candidates are i) String Theory (or Supergravity as an effective theory) and ii) Loop Quantum Gravity. Both look quite promising, but come with a lot of assumptions. Is there a place for the human mind in all these equations?
Beyond the Standard Model Pub 