Comment by ants_everywhere | Hacker News Reader

Comment by ants_everywhere | Hacker News Reader

ants_everywhere

My understanding of the situation (which may be wrong, in which case please let me know) is that physics is stuck at a local optimum.

There are two obvious ways to get out

(1) Surprising physical observations, or

(2) Mathematical advances

Way (1) is what kicked off quantum mechanics. Way (2) is what kicked off Newtonian mechanics.

I see string theorists and loop quantum gravity people as working on (2). Their models are mathematically interesting and aren't totally understood from a mathematical perspective. But they're different enough that studying them may break the impasse.

I see (1) as largely limited by the budgets and technology needed to build things like particle accelerators and spacecraft.

For (2) you have to decide whether to only explore mathematics that defines physical reality, or whether to also allow exploration of non-physical systems. For example, you might explore a universe that is almost physical but has time machines. Restricting the search space to only physically realistic systems is a significant constraint, so there's a debate to be be had about how much weight to give it.

> physics is stuck at a local optimum.

I think I heard somewhere that the trouble with string theory is it can describe anything if you tune it just in a right way. It reminds me of epicycles, they also had this property, you can add more and more epicycles to describe literally any observation data.

> Way (1) is what kicked off quantum mechanics. Way (2) is what kicked off Newtonian mechanics.

Hmm... What was the way that kicked Copernicus to redraw epicycles with the Sun in the center? I mean, is there some notes on these? For example, Newton took as granted that celestial bodies move by elliptical orbits, and somehow he guessed that the gravitation law has r^2 in its denominator, and so he invented calculus to prove, that if you have r^2 in the denominator then you'll get elliptical orbits. The question where Newton got his guess it remains open for me, but back to Copernicus, what was his way?

Maybe he thought how movements of planets will look if seen from the Sun, and so he had redrawn epicycles to take a look, and he got circles? (I'm not sure that it could work this way, I propose this answer to my question just to give an example of the kind of an answer I'd like to have).

I ask this question for two reasons.

1. I believe that Copernicus advanced the science not with surpising physical observation and not with mathematical advances, to me it seems more like surprising mathematical observation. I'm not sure what was that observation exactly.

2. Can one apply techniques of Copernicus to the modern physics? I suspect that it will not. I'm sure physicist already tried everything and there were (is) a lot of them and they are pretty smart people, so it is highly unlikely that Copernicus can help them in any way. But I'm still curious, what Copernicus would do? Would he tried to imagine how electron flying through a double-slit might observe scientists-observers? Or maybe it would try to feel the pain of a black that may believe that the whole universe is falling on it? I bet that the true Copernicus idea would require to use some pretty hard mind-altering substances, and I like such ideas.

My understanding as a layman:

1. Copernicus figured out that if you put the sun at the center, then epicycles weren't necessary, and the math got easier --- because epicycles were based on a mis-understanding of the actual state of the universe --- I don't believe that anyone has identified such a non-alignment of fact and reasoning and observation for contemporary physics.

2. The problem is, modern physics is arguably getting boxed into a corner by approaching an end game state where the fundamental particles are getting identified, but are so small and difficult to separate out, that measurements are challenging to the point that while one can speculate and do math, actually proving out the speculations experimentally and taking actual measurements is expensive or so difficult to reason about that there doesn't seem an obvious path to an experiment, e.g., it looks as if the electron may be a fundamental particle, which is a sufficiently difficult concept to parse that it led to "The one-electron universe"/"The single electron hypothesis" and if that is the case, it walls off a not insignificant portion of particle physics at a size/state which can't be gotten smaller than.

> Copernicus figured out that if you put the sun at the center, then epicycles weren't necessary

Actually, his model assuming circular orbits still required epicycles to explain retrograde motion etc. A major reason it never caught on was that it was less accurate than the Ptolemaic model but was more of a mathematical curiosity rather than a serious contender.

Yep, it didn't really seem convincing until Kepler replaced the circles with ellipses, and even that step took a lot to move past established ideas about the perfection of nature.

1. is a common belief, but mistaken. Copernicus didn't get rid of epicycles: https://farside.ph.utexas.edu/books/Syntaxis/Almagest/node4....

Copernicus used the same circular-orbit-plus-epicycles system as Ptolemy, just the orbits were centered around the sun (kind of---each planet had its own circle, with the sun only approximately in the middle). The system actually had more epicycles than Ptolemy's and was less accurate. It wasn't an advance in any meaningful sense.

The real breakthrough was Kepler, who dropped the idea that planets moved in circles. It was indeed partly a mathematical breakthrough and the reason Kepler's work took a while to catch on is that people couldn't understand his math at first. But it was also empirical, as Kepler had access to new and much more precise observational data collected by his mentor Tycho Brahe.

I'd say that Galileo spotting the phases of Venus was also a big deal.

That only ruled out one particularly broken model (everything revolving directly around the earth). The dominant model at the time had the sun and moon revolving around the earth and everything else revolving around the sun, with epicycles. All the information Galileo was able to present to people was equally consistent with heliocentrism and geocentrism, and Galileo's favored heliocentric model was less elegant and explained no extra data.

(Not entirely for lack of trying, though Galileo's favored rhetorical approach was 'I'm obviously right and you're all idiots', he did work with some others to try to demonstrate the rotation of the earth via displacement of dropped objects, but didn't succeed because it's quite a tricky measurement)

IIRC what this comes down to is Copernicus had no desire to tangle with the church. I remember reading he has some footnotes that go “Hey, obviously it works in epicycles but the maths works really well with ellipses and heliocentrism.”

Before Newton, Kepler already figured out that orbits were ellipses. Newton figured out why orbits are ellipses.

I can probably answer the r^2 question: it’s the scaling associated with the surface area of a sphere. So if you have light source, or a sound source, that’s how it scales with distance. It would have been relatively simple for someone as smart as Newton to guess that gravity worked the same way.

It’s only really our current understanding of gravity that makes it unobvious.

Everett proposed that observation happens relative to observer, it's exactly Copernicus's observation. Some people buy it, many don't, so I guess heliocentric style thinking is still counterintuitive. Ironically, an argument against Everett's interpretation is the same Aristotle used against heliocentrism: "it's not supported by observation" (meaning relativity is unobservable).

Those mathematical advances weren't developed in a vacuum, but made to solve some very specific problems which came from better measurements. So even Newtonian mechanics originated in solving problems trying to explain measurements, not that someone sat in their chamber and dreamed up cool math that happened to be very useful.

I agree.

Generally, the scientific method has mutually recursive turns of theory and observation. And I don't mean to imply that exist independently.

I'm just saying that if you get stuck, the two clearest ways out are to provide more observations or perturb the theory.

Number theory and algebraic geometry were developed for their own sake (i.e. "it is cool"), but later people found practical applications in cryptography.

So "useful math must be motivated by practice" is empirically false

> So "useful math must be motivated by practice" is empirically false

That was not the claim. The claim is that useful physics originates in measurements.

Name a single physics phenomenon that was discovered purely with way 2. I can only think of one, the positron.

Newtonian physics was not kicked off by math "advances". Approximately speaking it was the other way, Newton created the math to explain p^2 ~ r^3, which was a surprising observation.

Even theory of relativity wasn't really a math advance, the math was already mostly worked out by mach, lorenz, and minkowski. Einstein put it together into a coherent story (v. Important)

The Higgs.

Also, the W's and the Z.. neutrino oscillations. There is actually a long list. Physics is the poster child science of theory-experiment interplay and this shows up constantly in the philosophy of science and other things resulting in expressions like "physics envy" ( https://en.wikipedia.org/wiki/Physics_envy ).

No the higgs mechanism was directly proposed from how particles masses were not explainable from the existing model -- so it's clearly in the "surprising observation" category.

The positron was, "oh what if we had this thing that is mathematically possible". Very different. IIRC the discovery was kind of independent. It was in the data the whole time so if the physicists didn't just ignore those "impossible" bubble tracks they might have found it before the math.

If we discovered superluminal tachyons that would definitely count. But we haven't found those.

Bose-Einstein statistics, which originated purely from finding a derivation of an equation, without immediately understanding of the true physical meaning of the derivation.

And then Bose-Einstein condensates; a thought-experiment consequence of Bose-Einstein statistics.

Radio waves etc., from formulating Maxwell's equations.

(1) is also limited by imagination

Isn't it (2) that's limited by imagination? Nobody imagined quantum theory, they observed it first.

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