Smashter wrote: ↑Tue Jul 01, 2025 8:59 am
- Several blog posts about whether the universe is "fine tuned" or not. Is it true that it's totally improbable that we live in a world with physics perfectly suited for our flourishing? I don't grok the math at all, but I like readying really smart people as they go back and forth on this. This summary post was entertaining:
https://maximumeffort.substack.com/p/hi ... ments-on-a
When it comes to philosophy, metaphysics, and physics, it's very useful to frame it in terms of the
https://en.wikipedia.org/wiki/Structural_differential
In terms of abstractions, most philosophy, for example, happens above the "descriptive level". Taken to the extreme, we get kooky notions like deconstructivism and its ilk that takes the position that "everything is made out of words"(*?) However, going with the "structural differential", I find that philosophical positions often depends on the nervous system of the person espousing their respective position: It makes sense to them.
(*?) To be fair, I'm not sure that this is what the original deconstructivists asserted even if that's what their students eventually went with. Originally, the posit was simply that "words are useless because they merely refer to other words, etc. and so on turtles all the way down." Yeah, well, if all one has in the department of philosophy are words, I can see how this would be limiting /snark/
But ... if we take it all the way down to the particle physics level, there are very good arguments that the universe simply can not be any other way. IOW, there's no "fine tuning" at this level. To give a brief overview...
(Caveat: I haven't really thought much about this for the past 25 years.)
If we assume that the universe has certain symmetries (a symmetry is an invariance under some transformation and obeys a principle of causality. (Examples of transformations include e.g. relocating the particles (their interaction doesn't change if they are moved in space), rotating the perspective (ditto whether we look from above or from the side, negative charges work opposite of positive charges, ...) ... then "particles" (<- not a word but a concept) can only have certain numbers of spin, e.g. 0, 1/2, 1, 3/2, 2, 5/2, ...
Spin relates to how much you have to rotate (transform under a symmetric principle) the particle (or your observation of it, see above) before you see the same thing. Think of a cube with 2 differently colored sides (red-green-red-green). This only has to be rotated 180 degrees before you see the same thing, so it has spin 2. Spin 1/2 is a bit weird since you have to rotate it 720 degrees to see the same thing.
It turns out that particles with half spins (1/2, 3/2, ...) obey something called the Pauli exclusion principle. This means that two particles with the same configuration can't occupy the same position in space. If you add more particles, they will spread out. We call such non-integer spin particles "matter". Basically, what we call "matter" has the property of space-filling particles.
Whereas integer spins (0, 1, 2, ...) can sit on top of each other without pushing each other away. We call these particles "forces". Recall that "particle" was not a word but a concept. So now it should be clear that "forces" and "matter" are just two aspects of the same general "thing" or aspect about the universe which ultimately comes down to spin... which again comes down to rotational symmetry constraints.... which is very simple.
There is no fine-tuning here. There are TWO and only TWO options and we observe them both.
Now the question is how do different categories of spin "particles" behave. This is determined by their quantum propagator which determines how their wave function evolves in time and space. IOW, how the particles move and interact. Turns out that spin also determines this. Each kind of spin has a different propagator.
Spin 1/2 particles are electrons, positron, neutrons, protons, ...
The key idea for the following is to look at ALL POSSIBLE INTERACTIONs and see which are physically allowed. If the theory is correct, we should observe ONLY physically allowed solutions and never see solutions that are not allowed under the theory. It turns out that if we look at all the allowed solutions (this was historically done by hand using Feynman diagrams, but now the diagrams are just made by computer, there's a mechanical process for making increasingly elaborate ones of all possible interactions) for spin 1/2, we can derive (from these principles) something that looks EXACTLY like the classical theory of electrodynamics.
IOW, electrodynamics can be explained as an inevitable consequence from simple assumptions about spin.
Spin 1 particles (remember they carry force) are the photon, the gluons, and the bosons. Remember, integer spins don't obey the exclusion principle. They can occupy the same space. Thus two photons can cross each other without being aware of each other. This is why the universe is TRANSPARENT to light. More generally, because of not obeying the exclusion principle, forces can not crowd each other out. You can not "block" a force with another force.
Still no fine tuning. This is the ONLY way.
The spin 1 particle propagators don't go far (compared to spin 1/2). If they did, the particles would be infinitely massive. This explains why the nuclear forces are strong AND short-ranged. This, in turn, is how we get atoms but only up to certain size. The spin 1 particles interact with the spin 1/2 particles and hold them together in nucleons, atoms, molecules, etc.
Spin 2 is really interesting because with this high a spin number, a spin 2 particle ought to be really short-ranged. It turns out, though, that ALL the higher order terms (very complicated Feynman diagrams) for all the possible solutions cancel out. In addition and more remarkable, the spin 2 particles couple EQUALLY to all other spin numbered particles. Is there anything or any force in the universe with those features? Yes, gravity! So the spin 2 particle is the graviton. IOW, the principle assumptions of General Relativity follows from the graviton being a spin 2 particle. This basically explains why gravitational mass and inertial mass are the same thing. This was something Einstein had to assume (with his accelerated elevator gedankenexperiment) but modern particle physics does not.
What about spin 0, 3/2, and more than 2? Well, the only spin 0 particle that has been observed is the Higgs Boson. Spin 3/2 has never been seen (in this universe, I don't know why) and neither has fundamental particle above spin 2 (likely because there are no solutions to their propagators that can be observed with our current energy level of particle accelerators---we can't access sub-subatomic physics).
General conclusion: The fundamental structure of particles and forces in the universe have only ONE solution. We see this solution because we can. There is no other way.
My conclusion: When people debate philosophically about these things, it's due to a limited range of their "structural differential". For example, trying to ascribe "cause and effect" or "prime mover" to events is trying to apply macroscopic thinking about inference and generalization to quantum level reality. It doesn't work.
But what about ...
One of the things I got paid to do was to calculate the ratios between various observed isotopes in the universe. Since [nuclear chemistry] is a bit closer to the "object level of human experience" it seems a bit more "real". Hence, of course, people have made more "fine tuning"-arguments here since it's closer to home. For example, why are we humans and all other life that we know of based on carbon? Or more fundamentally, why is there so much carbon in the universe? It turns out that the amount of carbon is HIGHLY sensitive to two nuclear resonances. If either is off by 0.1%, then either carbon would not be made (out of helium) in the first place or it would be quickly eliminated (turned into oxygen) in the second place.
Again, though, it's possible to calculate these resonances since the 1960s. Using the same calculation for the thousands of different isotopes that exist and their tens of thousands of resonances, you can calculate the isotopic distribution theoretically for a very close match to observed reality. There is NO OTHER WAY.
Basically, the only thing left to "fine tune" in terms of imagining or parametrizing different kinds of universes are the constant of nature. We do not have a theory that allows us to compute those. We do, however, as described above have a complete lock on the STRUCTURE of the natural laws and how they behave. It is rather amazing to me that one can mathematically derive all these conclusions from very very simple assumptions.
I'm rather meh about what this means for the "human condition" or place in the universe. If a giant meteorite hadn't wiped out the dinosaurs, humans would never have come into existence in the first place.