I don't understand quantum physics (2018)
southampton.ac.uk
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As a non-physicist, QM only clicked for me when I learned the linear algebra of one- and two-qubit systems and observables on those systems [1]. The math is accessible at a pre-calculus level, and the most "counter-intuitive" aspects of QM (interference, the uncertainty principle, entanglement) make perfect sense in this framework. I think it's the best starting point for understanding what QM really says.
[0] That's not to say they aren't important historically or for a complete understanding of QM. I'm talking about conceptual understanding for someone, especially an amateur, encountering QM for the first time.
[1] Chapter 2 of Nielsen and Chuang is what did it for me. It's heavygoing if you've never seen linear algebra before, but I don't know of a clearer explanation of the postulates of quantum mechanics.
Axler's "Linear Algebra Done Right" https://linear.axler.net/LADR4e.pdf
Nielsen and Chuang's "Quantum Computation and Information" Chapter 2. (Available online, but legality depends on where you live)
If you're interested primarily in QM rather than linear algebra, I'd recommend not working through all of Axler, but instead using Nielsen and Chuang to learn about qubits and observables, and using Axler to fill in the gaps.
I loved it.
Your stupid brain thinks, oh I am just 10ish over the limit.
The exact numbers are more nuanced (both in simulation and in terms of available data on the topic), but to illustrate the effect, suppose typical reaction time allows you to slow to 0mph from 25mph just before striking a child with your car, assuming somebody with perfect training and a typical car applying proper emergency braking and decelerating at around 0.8 gs. I'll consider both the 0.5s reaction time estimate (median results in places where people are primed to have to react) or 1.5s (median for an alert driver expecting hazards occasionally). Let's assume we're going 10 over.
The fact that you were going faster means you cover more distance before you even hit the brakes. The 25mph traversed either 44.43ft in 1.92s (at 0.5s reaction time) or 81.1ft in 2.92s (at 1.5s reaction time). By the time the 35mph even applies the brakes, it only has either 18.77ft left or 4.1ft left (0.5s vs 1.5s reaction time).
Then how much can you slow down in that time? In the 0.5s reaction time case the impact speed is 27.85mph. In the 1.5s case it's 33.57mph.
In either case, you're actually striking the child above the posted speed limit in the same emergency-braking scenario, at a speed likely to cause significant injury.
Details obviously vary depending on how you set up the parameters, but 25mph is an approximate cutoff below which we empirically tend to have pretty safe traffic outcomes in residential areas and above which we tend to have pretty dangerous traffic outcomes. I don't know if people choose to speed in those situations because they don't know or because they don't care, but either way, it makes our roads much more dangerous than they need to be.
Instead of mph/kph the speed limit and speedometers could be on QuadraticSpeedUnits.
> Would you father get hit with:
> * a 1 kg object moving at 1 m/s or
> * a 1 g object moving at 1 km/s?
1 m/s is just 3.6 km/h, or slow walking speed. You'll be fine.
And to illustrate the point a bit further, that same argument doesn't work in other speed/mass regimes. Would you rather get hit with:
- A 1000 kg object moving at 1 mm/s or
- A 1 kg object moving at 1 m/s
It's suddenly no longer intuitively obvious because both are totally fine. Like...roll a die, and my squishy human body will be equally happy with either result. Or, shifting the argument the other direction, would you rather get hit with:
- A 1000 kg object moving at 1 km/s or
- A 1 kg object moving at 1000 km/s
Pretty obviously the 1 kg object, despite its much higher kinetic energy. If I'm lucky it just takes off an arm or something, whereas the 1000 kg object is definitely splattering me.
And that sort of thing is why kinetic energy can be hard to reason about. Our intuition is calibrated around our squishiness, which only loosely relates to energy. There are other factors at play.
Why?
- Why more dangerous: A 1g steel ball is around 1/4 inch in diameter. A 1/4 inch hole in any major artery is an immediate life-threatening event, same if it hits the lungs, heart, or brain (gut-reaction: I think it'd be quite hard to penetrate the skull with this projectile, so to hit the brain you'd have to go through the eyes or pterion or something, but ignoring that sort of potential quibbling). It'll have pretty significant negative effects on any other system if it can actually pierce that system. If we pick a denser material like lead, the hole is smaller but still life-threatening. If we pick a less-dense material like wood, the hole is larger, and you're still pretty majorly screwed. Contrast that with the 1kg object, which is roughly equivalent to dropping two cans of beans from a height of 2 inches; it just doesn't matter.
- Why pierce: That's a big can of worms with a lot of answers. A halfway okay way to think about it for common hard materials and common shapes in the speed regime being discussed is that you have a higher energy to surface-area ratio.
Critically (in case you're using some sort of Socratic method to guide me to the increased energy being the rationale), the important number for piercing injuries is closer to being that ratio than the total energy, hence my example of 1mg at 1km/s in some recent comment. That has the same energy as our 1kg at 1m/s object, but it's still extremely dangerous because it physically punches out a 1mm hole through your body. If that strikes a location like your eye or a superficially exposed major artery (like the one on the inside of your elbow), you're still going to have a very bad day.
One can build new intuitions.
Quantum Processes, Systems, & Information by Benjamin Schumacher and Michael Westmoreland is another good treatment along those lines.
The classic double-slit experiment is kinda bizarre when one considers the “single electron” case.
The modern record for a matter-wave superposition stands at a nanoparticle composed of roughly 7,000 sodium atoms (about 8 nanometers wide), achieving a massive "Schrödinger's cat" state at the scale of a small virus.
So then particles don't exist, and viruses also don't exist? Is "reality" just a dynamic pattern that doesn't exist in the naive sense? As astute stoics we should not worry ourselves with such matters, "shut up and calculate"?
There is something about quantum theory that is different in character from any physical theory posed before. To put a finger on it, the issue is this: The basic statement of the theory—the one we have all learned from our textbooks—seems to rely on terms our intuitions balk at as having any place in a fundamental description of reality. The notions of “observer” and “measurement” are taken as primitive, the very starting point of the theory. This is an unsettling situation! Shouldn’t physics be talking about what is before it starts talking about what will be seen and who will see it? Perhaps no one has put the point more forcefully than John Stewart Bell:
> What exactly qualifies some physical systems to play the role of ‘measurer’? Was the wavefunction of the world waiting to jump for thousands of millions of years until a single-celled living creature appeared? Or did it have to wait a little longer, for some better qualified system . . . with a PhD?
"reality" is just a picture painted on consciousness. A particle exists because consciousness, for some reason, perceive a particle. Physicists should stop looking for smaller particles, and look into space and time as something that emerge out of consciousness...
Without a common understanding of that word, any further discussion is useless..
You are enthralled! "There is something there still!" you say to yourself.
But there is nothing there! The game engine just figured that the particle would collide with the triangle, and altered its velocity accordingly. But you are too caught up in your assumption that you do more experiments (I think this is what our physicists are doing in our world). But what ever you do, you can only observe the behavior implemented by the game engine, and not the game engine itself, or the computer that is running it....
But you can imagine it. You can imagine an explicitly implemented program and a computer with limited memory that is running it. And if you are allowed to consider it, they can do other experiments. Instead of looking into smaller and smaller things, you can look for other observations that might confirm this. Maybe you can go really far and see if they are not allowed to go beyond some threshold (Ref: The movie "The thirteenth floor").
And would that be pursuing something metaphysical?
Yes, physics is about learning about the rules that the game engine implements. It’s not about learning about some reality outside our own, that’s the domain of metaphysics. Physics can’t answer questions about what is happening outside our own reality, and indeed neither can anything else inside reality because (as you pointed out) we can only test and observe what the game engine allows.
But the observation that I describe does happen in our reality. It is just that if you look for a reason for such observations here, you are not going to find it.
It is just like when say, biology have to reach out to chemistry and chemistry to physics and physics to math for deeper explanations for processes and observations that are native to their domain. So as unprecedented as it may be, physics should may be try to reach out to metaphysics as a way to explain observations that happen in its domain..
I don't know what observation you're talking about--you were giving an analogy, right? What am I misunderstanding about your claim?
> It is just like when say, biology have to reach out to chemistry and chemistry to physics and physics to math for deeper explanations for processes and observations that are native to their domain.
Yes, this is emergent complexity and physicists already look into this (e.g., holographic principle). In your game/engine analogy, we're still talking about examining the game, not the game engine.
In my example, the observation would be something alters the path of a particle that is shot at the center of the triangle (where it is empty space). This happens in the game reality, but cannot be explained by looking within the same (for example, if you expect to find a smaller triangle at the center of the bigger triangle)
The one-two punch of the photoelectric effect and the double slit experiment (the classic first two labs of QM) force you to accept that photons behave both like waves, and like particles.
This is the reason for statistical interpretation of QM that states that a wave function is just a way to calculate probability with no inherent meaning.
So wave-particle duality is just an artifact of Copenhagen interpretation of QM, not something that one can observe. What one clearly observes that photons travel through a region where they should not classically be and never appear in the region where they should be classically.
Note that even classically waves does not exist as they are just an artifact of motion of collection of molecules that on average can be described by wave-like equations.
The same could be said of the entirely unsurprising many-photon case. The individual photons aren't demonstrating the interference pattern, just the "big enough sequence of single photon measurements". Again, that's not the interesting part of the double slit experiment. We're perfectly used to the concept of a collection of many interacting particles having wave-like properties.
The double slit experiment has non-interacting photons demonstrating wave-like properties.
Scott Aaronson’s “Quantum Computing Since Democritus” makes a similar assertion about learning QM from a linear algebra perspective and completely sidestepping all the thorny interpretation questions. It’s mostly a book about complexity theory and what quantum computers actually buy you, but it gives a lot of insight into the mathematics of it.
That applied for almost every module, not just quantum.
My books went from 2 slit experiments, to particle in a box (1d and then 2d harmonic oscillators) with tunneling, and then the Hydrogen atom potential with electron orbitals as an extension, to perturbations for He, to Hartree-Fock and Born-Oppenheimer for large atoms and molecular models. Learning the <bra/ket> formalism can be useful for thinking about it, but it has to be motivated by the math.
I guess black body and scattering were pretty early too as motivation for the developments (as they historically were). Whereas EPR/Bell, Decoherence, and "Interpretations" were mostly discussed as interesting flavor and philosophical arguments.
Before quantum computers, the only reason to learn quantum mechanics was so that you could learn to explain the electron orbitals of the hydrogen atom. And after that proceed to understand how other atoms and other matter works.
And for this you need vector calculus, partial differential equations, Schrödinger equation, orthogonal functions (spherical harmonics, Laguerre polynomials) (with hint of the theory of Hilbert spaces).
The idea that someone would like to learn the basic principles of QM without applying it to solve the 3-dimensional probability distribution of electrons around the atomic nucleus, is rather new.
Basic Concepts Of Quantum Mechanics by L. V. Tarasov
https://archive.org/details/tarasov-basic-concepts-of-quantu...
The dialogues of the author engages with various personas and the reader that are interspersed as Prelude and Interludes are really enlightening.
For example:
Classical Physicist: Can one seriously speak about an object without having an idea of what it looks like? Isn’t it strange that we study, for example, the behaviour of an electron in a crystal while we don’ t even know what an electron actually is?
Author: I don’t agree that we don’t even know what an electron is. I have just indicated a number of precisely determined characteristics and properties of an electron. More detailed properties of microparticles in general and electrons in particular were considered in the preceding sections of the book (and will be considered in the following sections). In fact, we know quite a lot about the electron and know, in particular, about its behaviour in a crystal. This is evidenced by the large number of semiconducting devices fabricated and used by us in practice. As you will see, the absence of a “physically intuitive” model of the electron has in no way turned out to be a serious obstacle. We may even go a step further and state that an understanding of natural phenomena in which Planck’s constant plays an important role is possible only through a significant rejection of a graphic description. By the way, this idea was given by Heisenberg, in whose works much attention was given to questions of the use of physically intuitive methods.
Also checkout Tarasov's other books - https://mirtitles.org/?s=Tarasov Relevant here are his books on Probability and Lasers.
The Physics of the "very small" is essentially probabilities applied to Atomic, Molecular and Optical (AMO) domains where light and matter interact.
Not sure how it feels to a beginner, but to someone with a good deal of familiarity in the field it put everything in such a nice tight conceptual package.
I think these lectures are a good intro to QM. This statement feels very emotional though. Many-worlds just states there is no such thing as wave function collapse. The many worlds are a logical conclusion following. Copenhagen simply refuses to elaborate to when wave-function collapse happens, which to me is not a complete theory.
You could have some critique of many-worlds in relation to statistics, although I think many people have given quite satisfactory explanations.
Many worlds is just bare bones QM.. If any other theory is proposed, it should be falsifiable (like pilot wave theory for example). Doesn't mean it won't be difficult to measure.
Any good scientific theory must create falsifiable hypotheses.
Otherwise it’s just a nice story.
For any behavior inside the world, this is good.
But for the world itself and what harbor's it, asking for falsifiability is like measuring the expansion of space using a ruler that inhabits the same space.
Even science, that works in terms of cause and affect, which implies space and time, cannot be used to describe space and time itself.
Vanilla "scientists" have been trying to do that, but that is a dead end.
Which exactly is what general relativity is centrally about and the reason why general relativity is defined in terms of intrinsic properties of the Einstein manifold describing the space of the universe. Intrinsic properties are, colloquially, indeed properties that can be measured "using a ruler that inhabits the same space".
Gauß' Theorema Egregium [1] is an early predecessor of intrinsic properties of general manifolds, and says that the curvature of a surface can indeed be "be determined entirely by measuring angles, distances and their rates of change on a surface, without reference to the particular manner in which the surface is embedded in the ambient 3-dimensional Euclidean space" ([1]).
[1] https://en.wikipedia.org/w/index.php?title=Theorema_Egregium...
In LIGO, we detect the far away distortions propagating through our rulers and the differential effect of those waves.
But Michelson-Morley failed because the ruler distorted synchronously with the signal we tried to measure — since we mistakenly believed EM and matter were different fields.
General-relativistic effects are relevant for the outcome of the Michelson-Morley experiment in the sense that the general theory of relativity is a generalization of the special theory of relativity. :-)
Otherwise: the additional predictions that the general theory of relativity makes about gravity, curvature of space etc. are not relevant for the outcome of the Michelson-Morley experiment.
You seem to think I’ve said something very technical, while I’ve merely pointed out a well-known effect of Lorentz invariance and interferometry: you can’t detect an “aether” signal coincident with the detector, because the detector is distorted synchronously.
Michelson-Morley was never going to work because it relied on the assumption matter wasn’t subject to aether wind — which turned out to be wrong, as matter is subject to relativistic effects and fields unify. You needed that independence to generate the differential the interferometry amplified.
By contrast, LIGO measures an effect far removed and not co-moving with the detector. So it works.
We do that, routinely: that’s how we do cosmology.
Yea, that is why we are not getting any where...
Which alternative way of doing measurements do you propose? As far as I know, measuring intrinsic properties, i.e. "using a ruler that inhabits the same space" is with our current technology the only possible way of doing measurements.
A continuum of variants of myself is bought.
What is the value of assuming that literally every possible trajectory actually happens, but somehow I am only in one of them, while also being a continuum of other ones? If everything is true, than nothing is true.
As far as multiverse goes, there isn't any inherit value in assuming that the wavefunction as given actually happens, it's just a simpler explanation than trying to come up with (arguable unprovable) ways to cull the wavefunction.
It is not, it is the Schrödinger equation plus an extra rule that says that classical observers are only certain kinds of quantum states. There's no explanation in the MWI for why a device never reads out that a particle is 1/sqrt(2) |here> + 1/sqrt(2)|there>, even though that is exactly as probable a state as being |here>. And it turns out that this is exactly equivalent to positing wave function collapse / the Born rule.
And no, decoherence has nothing to do with this. Decoherence explains why there is no observable interference at the classical level between these states, not why you can only observe some states.
This is known as the preferred basis problem, for anyone who wants to read more about it.
For example, "Many Worlds, the Born Rule, and Self-Locating Uncertainty" notices that the rule doesn't mean anything, but it is rational to behave like it does. It's not a very satisfying position, I'd say.
The real issue here is the preferred basis problem, not an infinity of worlds: a single state vector can be decomposed many ways, and the bare math doesn't say which decomposition counts as "the branches." Decoherence picks it out: once the cat is entangled with its environment, the alive/dead decomposition becomes effectively unique and stable, through ordinary unitary dynamics. No collapse, no consciousness (that's von Neumann–Wigner, not Everett). MWI does have an open problem, but it's a different one: the Born rule, i.e. why |c|^2 should count as probability when every branch is real. Also, the normalization is |c1|^2 + |c2|^2 = 1.
They don't disappear. This is the entire point of MW.
That’s a more physically plausible interpretation than ever “tick” of the universe actually creates infinitely more universes because every fundamental particle is quantum and each one is constantly interacting under the wave function every plank second. And the infinite number of possible events that a single particle would experience is multiplied by the joint combination of all particles in the entire universe. It doesn’t seem plausible.
And on the ‘every tick creates more universes’: we are completely fine with superposition in nanoscopic systems. It’s just uneasy to follow that conclusion to the logical end. Just my two cents. I think just because the conclusion seems hard to grasp, the reasoning to get there is completely sound..
Just like Newton’s equations are accurate to describe gravity and motion but only because the full equations Einstein worked simplify to them at small speeds.
So similarly it would make more sense that quantum equations and relativity are two sides of the same coin and there’s some missing mathematical bridge where at small particle sizes it simplifies to quantum and at large particle scales gravity matters and we get Newton and then further relativity.
Using Occam’s razor that’s at least my prior vs some undefined mechanism of action where all possible interactions of every particle actually creates an infinite superposition of universes where that did happen and you get an infinite number of such superpositions ad infinitum. Much easier to believe the huge gaping hole between two very accurate theories explains how quantum mechanics turns into classical mechanics, especially since we know gravity exists, what it is, and quantum mechanics can’t explain gravity.
He argues that the wavefunction collapses on a timescale of h-bar / E_G, where E_G is the gravitational self-energy of the quantum system.
Quantum computing was explicitly proposed as a way to prove the truth of many worlds. As far as we can tell, quantum computing appears to work.
I don't think most people believe QC truly proves many-worlds, but I think it is considered some evidence in its favor, and historically it was I think one of the reasons for the development of QC originally.
OTOH, I don't think any of the other interpretations really struggle to explain quantum computing so I agree it's not much of a distinguishing factor.
If you only like predictions and disparage explanations, I might start calling you names, specifically instrumentalist.
Because I only believe one of these propositions, even though I can't imagine any test that would discriminate between the two.
Not to get all reddit atheist here, but as far as we can tell, the universe is predictable and explainable by fundamental mathematical laws. (We don't see, for example, unexplainable violations of conservation as Michael Landon pops in and out of existence.)
This could mean there is no god or they don't interfere or whatever, but in any case it's pretty good evidence that we can reason about how the universe works.
That's about as good as you can know anything. Beyond that is the "Are you a brain in a jar" kinds of philosophical arguments that are fun when you're 21 and get old after.
Plus astronomical observations used in cosmology to model the state of the universe milliseconds after the big bang which eventually evolved into our locally observable region of space around 13.8 billion (not 6000) years later?
That doesn't prove the dinosaurs were in fact living beings but this isn't necessary to disprove the other assumptions of the alternative hypothesis. By parsimony that leaves the hypothesis that dinosaur fossils emerged by natural processes like everything else we've observed on Earth to date.
Am I missing a joke? Because this is definitely not a good example of a hypothesis impossible to disprove with available evidence.
(If the response is "how do you test whether all that evidence was faked 6000 of years ago to deceive scientists" then we're not actually doing science anymore but games of make believe)
Instead, we can use other forms of reasoning, such as probability and Ockham's razor. These are perfectly valid approaches.
You seem to agree with me on this point, so I direct your attention to the grandparent comment:
> I'm interested in logical arguments for why I should be convinced that something completely impossible to ever test, not even in theory, is correct.
Since QM goes beyond our material world intuitions, I am personally loathe to clothe nrs in words, until we have more and better experiments. I think prematurely translating it into material-level intuitions just leads to a waste of time and much confusion.
Many worlds is falsifiable, if you can show wave function collapse actually happens (not just decoherence). I believe that in the not so distant future we will get more and more proof that wave function collapse never happens. Quantum computing at scale to me is an indication that Everett was just right..
With many words, every postulate has been tested and very verified. What more can you ask from a theory?
Now objective collapse is a testable postulate but none expects that to pan out.
This can be done in any other interpretation? Any unitary evolution on an isolated system can be reversed. This is a mathematical statement.
> Many worlds is falsifiable, if you can show wave function collapse actually happens
So, what experiments do you think would falsify it? How can you show that collapse actually happened?
Showing collapse happened is really tricky because of decoherence. Similar to unmixing coffee and milk. But all systems we have observed so far do not show wave function collapse (granted these systems are generally small, but otherwise decoherence starts messing about).
These are just fundamentally different theories. Not just an interpretation, physically different outcomes.
In the Copenhagen interpretation, there is a difference between measuring a system and entangling with it. There exists a unitary that entangles you with the cat, just like there exists a unitary that entangles the cat with the quantum device. By definition, unitary evolution is not a measurement in the Copenhagen interpretation.
> Showing collapse happened is really tricky because of decoherence. Similar to unmixing coffee and milk.
Unmixing would show the lack of collapse (in the specific case), though? To show collapse you'd need somehow experimentally prove that it is impossible to unmix. And to falsify collapse, you'd need to somehow experimentally prove that it is always possible to unmix. And if we go with your analogy, would you say the coffee with milk hasn't forgotten its initial state because it is technically possible to unmix them? Being able to manipulate the whole universe's wavefunction to unentangle particular subsystems is akin to having access to Maxwell's daemon, since decoherence increases entropy.
In normal physics people often use occamz razor and subscribe to what the interpretation with the simplest postulates says.
So the reality is the opposite. You don’t like what the physics is saying so for emotional reasons you’ve come up with a completely new and novel framework to discount what the simplest set of equations is saying.
Nah, physics is not saying anything. I do physics because I enjoy discovering and modeling new phenomena. If someone wants to do philosophy and ask questions like "but what is __really__ happening when we measure an atom", it's his business, but I don't believe we'd be doing the same thing, because these questions are impossible to answer with empirical evidence and don't help us model reality in any way. I don't see any difference between QM interpretations; one of them might be "true"
Just like the AI nerds and the AGI singularity or Musk saying we are in simulation...
ie so many crazy ideas.. for the rationalist, its like being in an insane asylum and trusting one mental patient or another..
I suppose at some level its just not rational why we exist. We must accept some wild, fundamental metaphysical assumption
Where in MWI do you believe the preferred unique macroscopic reality is defined?
My interpretation of the interpretation is that the universe is a giant constraint resolution system. Particles are free to be anywhere randomly as long as they do not randomly interact with other particles. As soon as they interact they have fewer "degrees of freedom", since now they interacted. When they interact with anything macroscopic they have no freedom left. Makes sense to me anyway.
- That humans can't be put into quantum superpositions, or
- That a human being in a quantum superposition of two states A and B would feel at all to that human like being in a quantum superposition of two states A and B, when neither of those states is "a human feeling like they're in a superposition of two states A and B".
Follow this to its conclusion, and you end up with a superposition of A and B meaning: "the universe is in a superposition, containing a component where a human believes that they're in state A, and a component where a human believes that they're in state B. Within both branches, the human thinks their wavefunction collapsed in that state". This is exactly the way that all interpretations of QM already understand things to work with particles in superpositions.
"Doc, I feel pain in my toe."
"No, sorry, the math says you don't."
"Okay, but like... I do."
"Sorry, you're just not good at accepting math!"
Not a perfect analogy, of course, but people have competing intuitions of what to do when the map fails to match the territory. MWI abandons the latter, most prefer the former.
The problem is that this is not what Schrodinger predicts, though. If |alive> and |dead> are valid solutions to the Schrodinger equation of some system, then so is any linear combination of them whose norm is one, such as 1/sqrt(2) |alive> + 1/sqrt(2) |dead>. So the math of QM predicts that there should be infinitely many cats that should feel partly alive and partly dead, many times more than the one live cat and the one dead cat. And yet you don't find this in any classical experiment.
1/sqrt(2) |alive> + 1/sqrt(2) |dead> is a valid solution to the Schrodinger equation. That cat is half alive and half dead.
That is different than |A cat that feels half alive and half dead>, which is its own completely different state. For a cat to feel like it is half alive and dead, or to notice that it is half alive and half dead, there are distinct things that happening in its brain that don't happen in either the |alive> or |dead> basis vectors, let alone any linear combination of the two.
We could even put all those states in a superposition!
1/sqrt(3) |alive> + 1/sqrt(3) |dead> + 1/sqrt(3) |half alive and half dead>.
So how did the classical world arise? Or how come we happen to be in the classical world, when there are infinitely many other non-classical observers? And note that the anthropic principle doesn't help here - all of the real laws of physics are the same for those other observers, you get the same chemistry etc, it's just the classical approximations that fail.
Many worlds isn't falsifiable, either. There's no reason to accept one over the other.
The Copenhagen wavefunction collapse is unfalsifiable.
If anyone is interested in self-studying quantum physics, QFT for the Gifted Amateur [1] is very well regarded.
It is much more shut up and calculate.
But I do believe that is atleast in part Feynmans point. The way we have explored QM for the past... 120 years (? Wow is it really that old!?) is you don't need to understand it, here are the rules and tools to carry out extraordinary calculation.
I believe the likes of Sean Caroll are trying to bring understanding back to physics and meet philosophy.
Superdeterminism and retrocausality both allow for local hidden variables - it’s just that they don’t satisfy Bell’s assumptions.
Similarly, superdeterminism is simply the application of the determinism that was believed to apply to physics before QM, to QM itself. In a way, one might have expected it to be the default interpretation.
Laplace expressed this in "A Philosophical Essay on Probabilities" in 1814: "We ought then to regard the present state of the universe as the effect of its anterior state and as the cause of that which is to follow. [...] For [an intelligence that has sufficient information] nothing would be uncertain, and the future, as the past, would be present to its eyes."
Superdeterminism essentially extends this idea of deterministic physical evolution to quantum mechanics. It could be considered an appropriate default simply because it was previously considered to be, not only the default, but the strongly believed truth.
> Superdeterminism says that there’s no way to pick your experimental choices in a way that reveals things because any possible random number sources you could use have contrived correlations that prevent that
You're arguing against a consequence of superdeterminism, not its motivation. Its motivation is as I've described.
The word "contrived" is doing some heavy lifting in your statement. Nothing needs to be contrived in superdeterminism, even if it seems that way to an observer within the universe.
The explanatory problem you've alluded to only arises because we're trying to understand the universe from within the universe. The universe is under no obligation to make itself sensible to us.
Essentially, you're saying little more than that you don't like the idea of superdeterminism.
(And yeah, preference for any of these interpretations will essentially boil down to what idea you like the most, or more likely what idea you dislike the least. With QM you pick your reasonable base assumptions and then take the uncomfortable conclusions that result)
Right, but we're talking about alternative interpretations here - something that is not MWI, Bohmian, or a collapse theory like Copenhagen, GRW, CSL. So without many worlds or pilot waves, we want to explain how measurement outcomes could be deterministic.
Conceptually, superdeterminism does that simply by positing that as part of a deterministic universe themselves, measurement settings are not independent of the systems being measured.
Actual models of superdeterminism (e.g. Donadi–Hossenfelder (2022)) seem inelegant and mathematically more complex than MWI. Which doesn't mean it's physically wrong or "weirder than MWI".
A theory that says that unicorns exist but only go places where no one will discover them (even though they aren’t invisible), is dumb.
A scientific theory should be compatible with experimentation.
It doesn't require a contrivance or a conspiracy. It simply requires determinism, which before QM, is something that was assumed to be true.
If superdeterminism is true, we'll have difficulty demonstrating that scientifically. Searching under a streetlight for the truth, because that's the only place you can see, isn't going to save you from that.
Superdeterminism implies that things are fixed in advance in such a way that the things we "choose" to measure always looks as if there are no local hidden variables (e.g. Bell's inequality) even though there are.
Meanwhile, superdeterminism is the idea that you can still have realism and locality by claiming that Bell's Inequality experiments are invalid because the universe could somehow "know" you are performing a Bell's Inequality experiment and rig it to get the "wrong" answer. Superdeterminism is equivalent to saying that we can't prove smoking causes lung cancer, because the universe might rig any science experiments to make it look like smoking causes cancer. Anytime you ask why the universe would do that or how you can prove anything in such a universe, they shrug their shoulders. It's a completely BS idea that got traction because specific people pushed it and others don't understand quantum physics enough to know how unserious of an idea it is.
This is a metaphor and not the state or experiment that superdeterminism seeks to answer. I am also speaking well outside the areas of physics I was trained in. So huge grain of salt.
In classical determinism, the trajectories of all billard balls can be derived precisely from their initial conditions. Due to sensitivity to initial conditions and our ability to know them precisely, we can see chaotic mixing behavior where the trajectory of even two billiard balls that start at nearly the same place become more and more uncorrelated as time goes on as they bounce around and into each other. One expects that many accessible observables and functions loose detectable correlations as this billiard ball universe goes on and the billiard balls go on to roughly fill the full 6D state space up to conservation of momentum.
Now imagine the weirder scenario, that there exists some function and statistical comparison you can make between state variables from sets of billiard balls. Although these state variables themselves seem uncorrelated after enough time has passed, there are these properties that always hold with perfect correlation even after infinite chaotic time bouncing around. The points in state space that the balls cover is restricted to some manifold where these statistical properties are true when checked. The system cannot evolve in a way where those correlations of bulk quantities would disappear.
In this toy metaphor it’s not so horrifically odd. Superdetermism gets more flak because: (i) the state space and property in question is so much weirder and more complicated than the kinematic example, the correlations are between objects that measure and the objects being measured! (ii) if these properties are always true under any check we can make there is no way to falsify. Then it doesn’t matter if the behavior is from some unimaginable underlying universal state space geometry or local quantum effects. This same argument could also be applied more generally and inappropriately to reduce any experiment to “that’s just the way the structure of the universe is”.
Perhaps we've got it backwards and quantum entanglement is what defines "locality" rather than mysteriously existing in the face of it.
"The number of different wavelengths of electromagnetic radiation, N(λ)dλ, with wavelengths in a small interval between λ and λ + dλ, (dλ means a small interval in wavelength) can be shown to be proportional to 1/λ⁴."
doesn't make sense. It should not talk about a number of wavelengths, but the number of allowed standing-wave modes (number of eigenmodes that a mathematical solution to the electric field in the relevant situation has) in the small wavelength interval.
I don't have much to add on the article itself except that it's almost certainly worth reading.
https://web.archive.org/web/*/https://scholarpedia.org/artic...
“Now, what happens if you try to come up with a theory that's like probability theory, but based on the 2-norm instead of the 1-norm? I'm going to try to convince you that quantum mechanics is what inevitably results.
Let's consider a single bit. In probability theory, we can describe a bit as having a probability p of being 0, and a probability 1-p of being 1. But if we switch from the 1-norm to the 2-norm, now we no longer want two numbers that sum to 1, we want two numbers whose squares sum to 1.”
This doc is the first one I've seen that explains upfront what a wave means here: "The quantity which travels in this way is known as a 'disturbance'. Precisely what this disturbance is depends on the wave," and for EMR, "it is an electric field and a magnetic field which are perpendicular to each other and also perpendicular to the direction of the wave." So now I'm going to read the rest.
A lot of weird predictions pop out if you do that. Those predictions (where we can test them) turn out to be true.
This kicked off an argument about what exactly this means in a physical sense and a hundred years later, it's still going.
It was also weird to know that then as it still is today, the only wave function that can be solved is single atom hydrogen.
Tl;dr spacetime does not exist as a global background where things are "placed", it is not ontic. "Things" are first, and spacetime is derived from interaction statistics of "things". This eliminates nearly all naive paradoxes like double slit etc. Now, these "things" are somewhat complicated and non-intuitive (e.g. there are no individual "particles", they are a limit of discrete distributions), but that's a good start.
When the "measurement"/"interaction" has a catastrophic :) impact on what you want to understand, won't be easy to "understand" anything.
On the bright side, the universe did throw at us some nibbles through that 'catastrophic' fog which can be "useful".
I think, it is important to teach the mathematical emergence of our classic physics from quantum physics (well... not gravity ofc).
Another important thing to teach kids: the difference between models and reality. We were lucky this emergent physics was not chaotic and have had strong predictability and has been very stable... well we would not exist otherwise.
My theory: The reason we perceive collapse as irreversible is because the computational complexity of reversing the equations is very high. Especially as the state converges towards an eigenvalue of the measurement operator, it becomes more difficult to reverse. This is similar to how a hash function is reversible in principle but not practice. My two cents.
Many worlds and such are just pseudo religious nonsense.
I don't know what that has to do with religion or nonsense. Everett and physicists, mathematicians and philosophers since then of a like mind thought the math applied to the entire universe, and the was no classical cutoff where the wave function "collapsed" upon a measurement. Everett was providing a deterministic interpretation competing with the Copenhagen one, which he thought was insufficient.
If by different branches you mean something like « now there is one, now there are two » it seems that branching is no less mysterious than collapse.
Blokhinstev's ensemble interpretation, which I like, is unattractive to many.
Quantum Bayesianism (QBism): We need to eliminate the interpretational conundrums that have beset quantum theory. A quantum state should not be thought to offer a description or representation of physical reality – instead it represents the degrees of belief an agent has about the possible outcomes of measurements.
Situation: There are 13 major interpretations of quantum mechanics.
[1] https://en.wikipedia.org/wiki/Action_at_a_distance [2] https://en.wikipedia.org/wiki/Mechanical_explanations_of_gra...
But isn’t that how EM actually works ?
The photon mediates the electromagnetic force
1) Disregard many worlds as a purely remaining mathematical outcome of bounded probability rather than discrete reality. (No 1 thing exists just 1ish things but ultimately that doesn’t mean there are many versions of any give 1)
2) just accept you can’t find the “stuff” of reality. You simply measure increasingly small probability domains which interact with other probability domains
3) time is the sequential working out of probability of anything existing and other things that might exist co defining themselves.
4) space is just the interaction of these probabilities working themselves out into a stable projection.
- Richard Feynman
Feynman's own QED is a part of QFT, but this is no longer quantum mechanics. Special relativity and quantum physics are reconciled since then. Now, we only need to reconcile GR and QFT, but this leap was so far beyond our attempts to scale it. Yet, QED/QFT/SM can be "understood" as there are fewer obvious paradoxes that plagued QM.
>The next reason that you might think you do not understand what I am telling you is, while I am describing to you how Nature works, you won't understand why Nature works that way. But you see, nobody understands that. I can't explain why Nature behaves in this peculiar way.
>>>Physics steeped enough in quantum theory do understand QM enough to have meaningful discussions free (at times) of rigorous math.
That sounds a lot like gate keeping and has no actual backing - to understand QM you still need to understand Physics, as mechanics of both of them are explaining each other - the scale is the only difference.
Most of the times the formal version with equations agree with the hand waving, but sometimes you have nasty surprises and must learn to hand wave better.
With quantum mechanics, there's a lot that you have to accept when you learn the subject without understanding why. Why complex numbers? Why infinite-dimensional Hilbert spaces? Why non-commutative algebra? You can kind-of, with great effort, make arguments that all of these are at least reasonable. But nobody really understands "why" at a level beyond "because the theory works".
The famous interview I know is when he said:
"I really can't do a good job, any job, of explaining magnetic force in terms of something else you're more familiar with, because I don't understand it in terms of anything else that you're more familiar with"
His point was that fundamental forces cannot be understood as "like" everyday objects, because we don't "understand" everyday objects except as applications of fundamental forces. Using those things to explain fundamental forces would just be circular. He can tell you that a stretching rubber band is due to the electric field, but he can't then turn around and "explain" that the electric field is like a stretching rubber band! Fundamental forces just are, and you understand them by studying them.
>Fundamental forces just are, and you understand them by studying them.
This is largely the point I was trying to make. One must understand QM using non-everyday ideas developed with math and measurement. But once those ideas are held, similes/metaphor (sometimes actual isomorphs) can be useful parts of that understanding and its communication between those that share the basis for that understanding.
He also wrote another similar popular article on Relativity, I DO Understand Relativity - https://news.ycombinator.com/item?id=50220891
With article titles like these, i just had to share it on HN!
Somebody should work on the above two webpages to make them more readable with html+pdf formats. That would make these more accessible to the "interested layman".
Yes but it's a very large institution. Thousands of staff, tens of thousands of students across a bunch of campuses.
The author also wrote a sequel; I DO Understand Relativity - https://news.ycombinator.com/item?id=50220891
Just because at a quantum scale everything becomes potential doesn’t mean all potential has been manifested.
It baffles me that so many serious scientists don’t understand this basic tenet.
That's a pretty bold assumption.
Sadly, being right about something like that does not, in fact, automatically entitle me to founders' shares in OpenAI or Anthropic. But I'll keep preaching it, nonetheless.
This is known as a "hidden variable theory". People will tell you that a local (things can only affect their immediate surroundings) version of the theory is impossible because it would be a violation of Bell's inequality, but there is a loophole that requires accepting the idea of "superdeterminism". This is the idea that where what measurement a scientist chooses to measure is predetermined and correlated with what the particle being measured is going to do.
So if a particle lands on a screen according to distribution p when going through a double slit, but with distribution p' when one of the slits is measured at, conventional QM says that the measurement "collapses the wave function". But a superdeterministic local hidden variable theory would imply that the choice of whether to measure at the slit or not was already set in stone at the same time that the particle "decided" which path to take to land on the screen, more or less.
The important distinction in this case is about FTL existing but not being able to exploit it for FTL communication.
In reality the entangled particle will interact with something almost instantly thus collapsing it. The cat is actually dead or alive from the perspective of the microscopic things in the box. A world never witnessed or measured by a being doesn't collapse it's entire history of interactions of every subatomic particle, atom, molecule and emergent property from the start of the universe to 'now' instantaneously upon being viewed. The photons from that world have been hitting earth continuously since earth existed after all.
The new thing you're mentioning is a common observation about observers: if there are two cats in the box, should they be |dead dead> + |alive alive> or is one measuring the other and they've collapsed to a classical state? This depends on a person being outside the box; the scenario is called Wigner's friend. It's been used to show many other unintuitive aspects of quantum physics.
Quantum physics makes predictions that suggest this isn't so. You can design experiments (e.g. A Bell inequality test) in which quantum physics predicts correlations that go beyond what would be possible with some hidden local information attached to the entangled particles that we just don't know about. Experiments don't prove theories to be correct. That's not how science works. However, experimental tests of Bell inequalities have pretty conclusively shown that local hidden variable theories are inadequate to explain what's going on.
Yes, it appears what Einstein called "spooky action at a distance" seems to propagate close to instantly. It's important to appreciate that you can't transmit information this way though. We can only make sense of the quantum correlations after communicating other information at classical speeds. Sometimes you see quantum entanglement devices allowing FTL communication in sci-fi, but that's pure horse hockey.
That all being said, I don't understand quantum physics either.
The math does indeed work, and many experiments and practical uses seem to show that there is something to quantum broadly. But to throw determinism out the window and believe that quantum is fundamentally probabilistic, and that one can never really run scientific experiments because observing state collapses superposition, has always seemed asinine to me.
I could be completely wrong, but it's always seemed obvious to me that the need for probabilities in quantum is a clear indicator that something is missing in the theory. I'm never surprised when a person can't understand quantum as its described today.
Unrelated, but I also wish scientists properly used the term "theory".
Measure the spin of electrons in direction X (that's done with a weirdly shaped magnet). You'll get either +1 or -1 in a conveniently chosen unit system. That's already weird, you'll never measure +0.5 for example. Keep only the +1 electrons. You can measure them again and again, you'll always get +1 in the X direction.
Now measure those electrons in the Y direction, you'll also get either +1 or -1.
But now, if you measure in the X direction again, you'll get +1 or -1 with 50% probability; although before measuring in the Y direction, these electrons always had spin +1 in the X direction.
The math works and the experiments work, but it feels like a broken clock situation. It happens to correlate well, but the understanding and models are missing something in the actual underlying physics that, if understood, would throw the whole randomness part out the window.
My mental model of it is kinda reversed. The maths assign a specific, deterministic state to each electron between each measurement. However, the "left" state is equal to "(up + down) / sqrt(2)". It then follows that when we measure an electron that is in the "left" state along the vertical direction, we get 50% up and 50% down: the probabilistic behavior happens when measuring, which "forces" an electron that was in the "left" state to become either "up" or "down".
I agree though that it would be less frustrating if there was some property of the electrons that would allow to predict in which state it'll collapse.
It does this because it necessarily interacts with the measurement apparatus, which in this case is an anisotropic magnetic field!
“Things rotate when they are rotated! News at eleven!”
The vast majority of quantum mechanics has easily explained with ordinary wave mechanics.
I think the equivalent one with photons is better. They say it's a quantum paradox that if you put a polarization filter between two others it can increase the total transmittance. But actually, classical electrodynamics explains that just fine.
With the measurement direction, yes, but the other axes are not constrained, and hence measurement along those directions returns unpredictable values.
It cannot be usefully analogized to things you can experience (or even to other things you might already understand).
It sounds all superior and mysterious to quote Feynman here, but the fact is many people absolutely do understand quantum mechanics.
Ancient humans could build boats 5000 years ago and expand throughout the planet, but they didn't know about water being made up of hydrogen+oxygen, or the tides being caused by the moon, etc.
Their calculations served them on the layer they operated on.
Mostly because people around the mediterranean sea didn't have to care, tides being so small there. Yet the Greek had fairly advanced models of tide schedules.
Pretty sure peoples that were experiencing bigger tides and depended on it e.g for fishing figured out the relationship with the moon pretty quickly, whatever esoteric reason they may have plastered upon it.
Nobody takes this to mean that classical physics is generally incomprehensible.
We can build black boxes and exploit the behavior of what we see.
But we can’t always go to deeper and deeper layers of understanding.
QM is not a black boxes we built but one could perhaps say it’s a black box that we see.
For QM the main issue is that we are barely able to see results of that black box and have to make guesses even about observable results, because what we see is result of particle long gone and the result has been a mess of paths that it took. And basically we are operating at identifying single particle, while clearly the path that particle took was defined by other particles and "gravity"? from interacting with other particles bumping it around. I'm even less knowledgeable when it comes to QM terminology, but I get impression that most of the commenters here simply are parroting things they have read or being taught without actually trying to understand and taking into account all the unresolved problems in QM, which is why so many of them sounds so confident is my guess. Because knowing limitations of my brain I would be not so confident of anything, only because of massive load of unresolved issues that QM has.
It isn't about being superior, mysterious, or clever. The following "nobody understands" type of quips and thought experiments are different ways of saying our intuitions don't help us understand it :
- "God does not play dice with the universe.", Albert Einstein
- "Shut up and calculate", N. David Mermin
- "Schrödinger's cat" being both alive and dead
- various interpretations/analogies explaining quantum physics leading to absurdities or contradictions
Yes, humanity has harnessed quantum mechanics with mathematic frameworks and repeatable experiments to make useful things... but that's a different layer of "understanding" than the deeper levels in the above quotes.
"Nobody understands what gravity is." ... Wait, if nobody "understands" gravity, how did we send people to the moon?!?
Because those are different usages of the word "understand".
Our monkey minds evolved to throw rocks at birds, and our metaphors are based on concepts like position, velocity, and temperature. We added first-level abstractions like energy and cause-and-effect, then built higher level abstractions on those basic concepts.
QM clearly doesn't work like that. It's probabilistic, possibly non-local, possibly subjective, possibly a holographic projection of some underlying reality that is nothing like this one, and its relationship with causality is slippery.
We have a mathematical UI for it, but that's not at all the same thing as understanding the machinery on the other side of the UI.
Anyway, I prefer LEDs as an example.
The example the author gives, transistors that somehow rely on quantum tunneling to produce gain, is not a good example at all. In fact it's downright wrong. The essay could have been titled "I don't understand transistors."
Also billions of people understand how to operate mobile phones, but "understanding how they operate" would be rather stretch and even the biggest specialists of QM have understanding only on how to interpret end results in QM - at best and that is basically it.
Quite frankly, I'm confused about these bold statements. I assume there seems to be some knowledge background of what you are saying - it very much reminds me what stupid strawman arguments I had in high school with my schoolmates then as a part of learning process, but rather far from actual wisdom.
Many people of course, Feynman obviously included, understand the theory in the sense of knowing how to correctly apply it to make predictions.
It doesn't. It's model. All models are wrong (including quantum mechanics and attention) but some are useful. You understand the domain of the model, the problems it can solve, the math behind the models and use the model to make predictions. If you are competent at linear algebra and functional analysis, you can do quantum mechanics.
If you make the error of believing that quantum mechanics is ontological god's honest truth of nature, you will end up with blunders like using it to explain consciousness like Prof Penrose. His math was impeccable, but he was making a category error.
Quantum mechanics is a framework for how theories are built, not a specific theory, and it's really all or nothing. There's not much between the quantum and classical ways of viewing the world.
But it just turns out that there's a limit in which the quantum world looks approximately classical.
But as a physicist I have no illusion that any of our theories are actually true. They are all models that help us making sense of an unimaginably complex universe.
0. Special Relativity is already baked into the Standard Model, which is a quantum theory. It's General Relativity that causes problems.
...unless I have understood it otherwise, but quantum mechanics is still an approximation of things we simply are unable to measure individually - mostly because of speed and have to resort to guessing that approximation of that limited time period, which is still too long. It would be the same as trying to guess position of a ship during voyage across the ocean and taking the smallest measurable time period as 100 years, in which the ship has been already sunk out of existence, while smaller time period would have given us better picture and quantum mechanics that we are able to use has exactly that issue - we are unable to measure and record particles at smaller time intervals. At best we can see trajectories of particles long gone.
Also, this book is not agreeing with your statement, to me which sounds like Religion(because you have no explanation at all!) and should not be part of Science.
what about gravity? If we don't know the correct account of that, how can we know those are exactly correct?
So we really are stuck with quantum mechanics, and there must be a quantum theory of gravity. In fact, there are actually quantum theories of gravity (including String Theory), but we don't know whether they're the correct theory that describes our universe.
Sure, but what if you don’t understand the model?
Models are simplifications/approximations made on purpose, as in "I know this is wrong on some level, but it's close enough for my use case", or "this makes the maths solvable".
Heck your descriptions of a model is also what we would call an effective theory (i.e. a description valid for a specific range of parameters/scale).
I don't think there's a commonly agreed difference between model and theory and I sure have heard many physicists use them interchangeably when it suits them (and I'm guilty of it myself). Perhaps theory feels 'wider', as in quantum theory encompasses models for many quantum systems, but that's as far as I'd go.
> [...] when people thought the Earth was flat, they were wrong. When people thought the Earth was spherical, they were wrong. But if you think that thinking the Earth is spherical is just as wrong as thinking the Earth is flat, then your view is wronger than both of them put together.
... which "we think" is functioning that way not to mention that theory itself might be wrong and be replaced as most of the supporters of quantum theory doesn't seem to look on it as something that explain mechanics of it, but rather how magic of "unexplainable" quantum mechanics works.
What a theory is, is more like a model (or maybe meta-model) with a particularly broad scope or high explanatory value, often a mathematical framework that gives a common foundation and theoretical justification for multiple experimentally-derived models.
Quantum electrodynamics is a quantum theory. Quantum chromodynamics is a quantum theory. String theory is a quantum theory. I'm sure there is a correct quantum theory of gravity - we just don't know what it is yet.
> Quantum physics is a theory, as in "as far as we can tell, this is an exact mathematical description of the world".
Is it?
If by "mathematical exactness" you merely mean we have somehow been able to produce some numbers that later on we measured in experiments, then yes. (Though we haven't been able to produce such numbers in all cases, see e.g. [0].)
I my book, though, mathematical exactness means your model is mathematically consistent and is applied with the necessary mathematical rigor.
Quantum mechanics and quantum field theory, as they are commonly taught in universities, are everything but. They are a bunch of concepts and recipes that, albeit successful, are held together loosely with duct tape and lots of hand waving to make you ignore the logical gaps & jumps and the fact that many of the "mathematical" objects physicists refer to don't even exist[1]!
[0]: https://www.scientificamerican.com/article/this-simple-exper...
[1]: Haag's Theorem, Aizenman–Fröhlich Triviality Theorem, etc.
Penrose has fallen into the same logical fallacy that many older, retired theoretical physicists have (notable einstein?).
> All models are wrong
That famous quote could use attribution: https://en.wikipedia.org/wiki/All_models_are_wrong
> If you make the error of believing that quantum mechanics is ontological god’s honest truth of nature
This is why science & experiment exists. The author holds no such belief, and the paper makes that very clear. That is what he actually meant by “I Don’t Understand Quantum Physics”. Jump to the very last section, “Is Quantum Theory Correct and Complete?” He’s pointing out the confusing and contradictory nature of the model so far, and saying that Quantum is incomplete and needs work. He is not making any category error.
It could, but doesn't need it.
That models are not direct truth is just logical. If there were such a thing that were indistinguishable from the direct truth, it would be the direct truth, not some other thing called a model.
This is why I've never understood the "revalatory" nature of Godel's incompleteness. Of course any axiomatic system must not contain all truths. Axiomatic systems are models and models can't contain all truth. If an axiomatic system contained all truth it would just be all truth rather than some other thing called an axiomatic system.
The only case in which Godel's argument surprises is the case in which one has a fundamental misunderstanding of what a model can and cannot be, which I suppose must have been more common in his time, but I was really confused when my highschool teacher went to great lengths to explain that a model cannot contain the whole truth because...of course it can't?
If obvious, can you prove it without reading Gödel’s proof or anyone else’s?
The important (2nd) part of Gödel’s proof is not that a model can’t contain all truth, it’s that a model cannot prove itself true, which is a far stronger statement than the intuition you describe. Of course, belief that your own intuition is independent of history is also highly questionable; you were raised and educated in an environment in which people were already aware of Gödel. It’s like saying the number zero is obvious (which it is now) despite the fact that it took thousands of years before it was used formally as a number. There was a time when it wasn’t obvious to the smartest people alive.
Note that formal axiomatic systems aren’t physical systems; what Gödel was talking about and what George Box was talking about are related but somewhat different concepts. It is obvious in physics that a parabolic ballistic trajectory model doesn’t account for air turbulence. It’s not at all obvious that all of math itself is guaranteed to produce contradictions and cannot prove itself, especially if you’re allowed to change math or use any system you want.
I also think you can be a realist without having to make the jump to ontological irreducibility. You can say that our latest theory is a better approximation than the previous one and the previous one was an approximation as well.
It's useful, not metaphysically real. (Hot take btw) This is called Instrumentalism. The belief that it's real is called Scientific Realism. However over and over again, science can't cover edge cases, and we find better fitting models. The Copernician revolution is a good example of this dichotomy.
2. Academia basically forces you to believe the doctrine or you fail the class. From philosophy to physics to sociology. If you read the philosopher survey, you will find trendy things being quite high. It's a religion in itself.
Bonus 3: Philosophical Pragmatism and Instrumentalism generally solves this, but is intellectually a dead end. There is a reason analytic philosophy continues despite gaping holes in linguistics (late Wittgenstein) that ruin it. But at the same time, best fits might be missing a new paradigm. I wish I could tell people to ask AI to explain Hegel to understand, but I think people need to read it themselves.
Tl;dr: quantum mechanics is the best we have. It's definitely wrong, but it's the most useful we have.
Yes, but if you can make a reliable experiment that disagree with the doctrine, it will change, even if everyone hates the idea. In particular https://en.wikipedia.org/wiki/Wu_experiment
If you read late Wittgenstein or Karl Popper, you will find that science is a useful simplification. Rorty is boring and not useful, but he kills any sort of Realism.
The 3 gigantic holes:
1. It's all language. (Wittgenstein)
2. The edges of systems do not connect with each other.
3. There are exceptions to everything.
I know that might seem a bit generic, but these are the major flaws in the philosophy of science.
I was a true believer too.
If you ever want to learn a ton about science, read Popper. He tortures himself, but he's also scientific meta.
I guess if/when we discover a theory of everything then we could claim "this is real/reality", but what would that even mean other than modelling reality/outcomes with 100% fidelity?
[0] I personally don't think Science concerns itself whether things are real, only whether the result of model and realness match, but that's what we are discussing here.
Uh oh, some people have no sense of humor =\
That depends on how you define nature, world and universe. For me nature is defined by things that can be perceived by human senses.