[YeGoblynQueenne]

>> What irritated me about it was the assumption that, if most of your predictions are correct, your model is almost entirely correct, and just needs to be tweaked a bit.

Haha, no. We wish.

Epicycles worked very well and were highly accurate, because, as Fourier analysis later showed, any smooth curve can be approximated to arbitrary accuracy with a sufficient number of epicycles. However, they fell out of favour with the discovery that planetary motions were largely elliptical from a heliocentric frame of reference, which led to the discovery that gravity obeying a simple inverse square law could better explain all planetary motions.

https://en.wikipedia.org/wiki/Deferent_and_epicycle

A theory can explain observations even perfectly well and still be wrong- because the frame of reference is wrong. The worse thing is that you can't figure that out until you've figured out what the correct frame of reference is, and looked at your obsrevations in a new light.

[andrepd]

>A theory can explain observations even perfectly well and still be wrong- because the frame of reference is wrong. The worse thing is that you can't figure that out until you've figured out what the correct frame of reference is, and looked at your obsrevations in a new light.

Well strictly speaking, it wasn't wrong. It explained the observations perfectly well. What a heliocentric description brought was a simpler description that illuminated the principles behind it, in a way that enabled us to discover the inverse-square law of gravity, link that to Gauss's theorem for gravitation, explain it even from a more fundamental geometric perspective with general relativity, etc.

[TheOtherHobbes]

It was wrong in the sense that epicycles are an entirely imaginary math artefact, and reality works on different principles.

Revolutions happen when a new mental model - or frame of reference, or whatever you want to call it - can generate new kinds of math.

The old model is certainly wrong in the sense that it's not a good picture of how reality actually works.

If you really want to, you can still use epicycles for certain kinds of problem, just as you can use Newtonian physics for basic mechanics.

But this is engineering, not physics. These theories are useless for frontier research. They're absolutely wrong in the sense that their lack of completeness means they cannot be used to generate theory[n+1].

[pdonis]

> It was wrong in the sense that epicycles are an entirely imaginary math artefact, and reality works on different principles.

How do you distinguish "an entirely imaginary math artifact" from the "principles" that "reality works on"?

(Hint: planetary orbits are not ellipses once you take GR effects into account.)

[EForEndeavour]

The same way we distinguish the shadows cast in Plato's cave from the objects occluding the light. The more situations in which a theory or model makes accurate predictions, the more correct it is. Epicycles are much, much more wrong than mathematically perfect elliptical orbits.

[pdonis]

> Epicycles are much, much more wrong than mathematically perfect elliptical orbits.

Not if you define "wrong" as "inaccurate predictions". You can approximate ellipses with circles and epicycles to any desired degree of accuracy by putting in more epicycles. So you can match the predictions of ellipses to any desired accuracy with epicycles.

Also, as I noted, the actual orbits of the planets are not perfect ellipses once GR effects are taken into account. Have you proven mathematically that it is impossible to construct an epicycle model that makes more accurate predictions than perfect ellipses, based on the actual data (which confirms the GR predictions to within current observational accuracy)?

[EForEndeavour]

You're being intentionally obtuse. "Just add more epicycles!" isn't building a better model (for a sensible definition of "better"). It's just overfitting. You are the reason why regularization exists. https://en.wikipedia.org/wiki/Regularization_(mathematics)

[basurihn]

After reading this thread, I think I've discovered the real reason new physics isn't being done.

[newen]

> planetary orbits are not ellipses once you take GR effects into account

Super interesting. I'm a physics major (graduated) who didn't take GR, so I didn't know this. Want to learn GR now but very likely won't haha.

[sanxiyn]

As your article explains (but too briefly), epicycles do predict wrong. It predicts correct locations but incorrect phases.

"It was not until Galileo Galilei observed ... the phases of Venus in September 1610 that the heliocentric model began to receive broad support among astronomers."

[YeGoblynQueenne]

My understanding is that these had not been observed before Galileo, or at least not observed by many and not long before Galileo's time. In that case, they weren't so much incorrectly predicted, as not observed.

[Koshkin]

> the frame of reference is wrong

According to General Relativity, there's no such thing as a "wrong" frame.

[bluGill]

True, but there are frames of reference that make understanding (and the math) vastly simpler. I can calculate the orbits of the Saturn's moons using my location on earth as the origin. It will take me a lot of work, but I can do it.

[jerf]

It's a fun exercise to reframe the laws of physics in terms of your "stationary" frame on Earth and I recommend it to everybody. Consider the speed of light in the Andromeda galaxy... except under these physics we can't speak of the "speed" of light, but the permissible velocities as a function of the location in question.

Running through this exercise with some honesty can give one a greater understanding of why our physics is framed the way it is, and why it is that while all sorts of reference frames are valid, "inertial" reference frames are still important on their own merits.

[EForEndeavour]

The Earth is demonstrably not a "stationary" (inertial) frame, in the sense that it's constantly accelerating.

Is there a deeper meaning to "Consider the speed of light in the Andromeda galaxy" that I missed? The speed of light is known to be constant in every reference frame.

[jerf]

Your two paragraphs are connected to each other. The speed of light is known to be constant in every inertial reference frame. But reference frames are not required to be inertial, which is precisely why we call them inertial reference frames; the word "inertial" is not redundant.

You can reformulate all of physics into your Earthly non-inertial reference frame. You can formulate all of physics into a reference frame in which you personally are always stationary! Nothing stops you from doing it, and the physics will work, as much as they ever do (i.e., we know something's wrong with our theories). To the extent that the result is a hideous monstrosity, well, such is my point. Pondering the nature of that hideous monstrosity is something I think worth doing, at least for a bit. Not to the extent of actually writing the equations, though. It brings clarity to why inertial reference frames are so important that we almost consider "inertial reference frame" to be a single atomic word, because non-inertial reference frames are in general not very useful. (In specific they can be.)

[bluGill]

The earth is still stationary with respect to itself. The Universe is accelerating around it. In the case of Saturn's moons the Sun and Earth are not significant factors, if I use the Earth as my origin I have to account for those anyway, but if I were to use Saturn as my origin I could safely ignore them (probably - I could come up with sci-fi reasons that they matter).

[poelzi]

Sorry, but I have to correct you there. There is a infinite number of Relativistic Models possible. In the one that is currently used, you are indeed right.

But now I understand why Einstein wrote in his last book, after much thinking, that this perspective is wrong. He called it "unthinkable" for a good reason. The model I'm using also has relativity, but with an absolute frame. It also behaves differently in extreme situations like the surface of super massive black holes and and near field of a proton. In fact, I have much more relativity but not everywhere and it's paradox free :)

[YeGoblynQueenne]

I'm sorry, I don't know what General Relativity says, really. I'm not that kind of geek :0

What if I say there are frames of reference that are irrelevant to discovering the process that generates the observations?

Edit: Um, guys? I genuinely don't know what general relativity says and I didn't get the comment above. It'd be nice if someone explained.

[ZenPsycho]

General relativity holds that the universe has no “center”, either earth or sun. even more surprising, is that unlike newtonian physics, general relativity says the universe doesn’t even have a single “clock”, and what you observe in astrophysics depends on where you observe it from and how fast you are travelling when you observe it. the speed of light is constant, and space and time will bend in order to maintain the observation that light is always a constant speed.

The location, and speed with which you are travelling is what general relativity calls a "frame of reference", and none of them are "correct" or "incorrect", they're just predictors for what observations will be possible from that frame.

then the weirdest part is that one of the consequences is that planetery bodies are large enough for that “speed of light must remain constant” rule to matter in a particular way as to generate a warping of spacetime around them, the geometry of this warp perfectly explaining gravity. or put another way, we stick to the earth because time runs slightly faster at our heads than at our feet.

This youtube video explains it really well:

https://www.youtube.com/watch?v=Xc4xYacTu-E

[YeGoblynQueenne]

Thank you, that's a good explanation- in the sense that I understand now what the previous comment, by Koshkin meant in responding to mine that there is no "wrong" frame of reference.

>> The location, and speed with which you are travelling is what general relativity calls a "frame of reference", and none of them are "correct" or "incorrect", they're just predictors for what observations will be possible from that frame.

OK, I see- "frame of reference" is a technical term, in General Relativity, that refers to your position in space, and determines what you can observe. Instead, I meant "frame of reference" as a more general "point of view" or "frame of mind" - a set of assumptions that give context to any observations and that inform interpretations of them.

Even going by the technical sense of a frame of reference, though, there are frames of reference that will not permit the cocrrect identification of a process that generates a set of observations- or at the very least, they will tend to favour incorrect interpretations of the observations.

I think that is in keeping with what your comment says about a frame of reference in General Relativity allowing a range of physical observations.

[ZenPsycho]

Right, so what was ground breaking about General Relativity, is that it challenged the newtonian axioms (assumptions) that there's a single universal clock, and that all objects within the universe are effectively rigid and exist in something resembling euclidian geometric space, and all move forward through time at the same speed. Newtonian physics explains many things very well, but couldn't explain other phenomenon.

Going from observation, that the speed of light is constant, regardless of how fast the light emitter is travelling relative to you, he made that the unbreakable assumption, and made the shape of spacetime flexible to always satisfy a constant speed of light. This theory was then confirmed when the light of a distant star was observed to bend when travelling through the strong gravitational field of our sun during a total solar eclipse.

Therefore the physics described by General Relativity have greater predictive power.

Quantum physics, can also predict everything in general relativity, but doing so is a lot more complicated than using general relativity. However, Quantum Physics can explain things that happen on small scales that General Relativity cannot. Quantum Physics has greater predictive power, but it's more convoluted. Like Epicycles. Einstein didn't like quantum physics and spent a great deal of time trying to debunk it, but, well, he couldn't.

This is all to point out that one should not confuse predictive power with complexity. Ockham's Razor is a rule of thumb that prefers "simpler" explanations for things. But the predictive power of the two competing theories must be equal for that to apply.

[YeGoblynQueenne]

Thanks, I didn't kow about Einstein and quantum physics. I'll have to read a bit about that, it sounds interesing.

My original comment is grounded in an assumption that predictive power is not enough to identify a theory as correct, and neither is simplicity. There's nothing to stop any number of theories to have the same predictive power and the same kind of complexity. Sometimes, it's just very difficult to choose one, above the others.

Did I come across as confusing predictive power with complexity?

EDIT: it's interesting you bring Occam's razor up. It's part of what I'm studying, in the context of identifying relevant information in (machine) learning. There are mathematical results (in the framework of PAC-learning) that say that, basically, the more complex your training data, the more likely you are to overfit to irrelevant details. At that point, you have a model that explains observations perfectly well, but is useless to explain unseen observations (the really unseen ones- not those pretending to be unseen for the puprose of cross-validation).

...iiish. The result is that large hypothesis spaces tend to produce higher error. But, the size of the hypothesis space in statistical machine learning depends on the complexity of the data, as in the number of features. Anyway, I'm fudging it some. I'm still reading up on that stuff.

[Koshkin]

> Quantum physics, can also predict everything in general relativity

Unfortunately, the two theories, while both being extremely successful and accurate in their predictions, are incompatible with one another. Quantum Field Theory has successfully combined Quantum Mechanics with Special Relativity, but that is all.

[konschubert]

I think your "I'm not that kind of geek" comment came off as condescending. It also makes you sound like you're not really interested in understanding the other side's argument.

[taneq]

Sounded more to me like just a "that's outside my area of expertise so I can't really contribute".

Also, "frame of reference" has a specific meaning in relativity but it also has a more general meaning regarding the framework within someone understands something. It's pretty clear from the context (imo) that this latter is what was meant in this comment.

[YeGoblynQueenne]

Thank you, yes, that's what I meant- I dont' know physics (well, very little) so the OP's comment left me confused and I didn't realise there's a technical meaning of "frame of reference". It doesn't help that, in the case of the theory of epicycles and the location of the Earth in space, the technical and colloquial term can mean the same thing.

"I'm not that kind of geek" is a bit of an in-joke so my bad for using it where the context is missing, but I thought it would work even so. The missing context is that a colleague used to tease me for my deplorable lack of a science background, although we did hit it off in terms of our fantasy and science fiction tastes. So, I was not the science kind of geek, although I was the science fiction and fantasy kind of geek.

[sgt101]

I don't see that there is an argument - rather that a separate chain of discussion has started. It's fair to then say "well that's all fine but what I was thinking of was X" which is what I am reading. I think that there is a big difference between frames of Einstein (I don't understand these) and frames of reason and perception (I don't understand these either) but I do see that there are two different things!

Like I don't understand either Australia or Argentina.. but I know that they are not the same!

[jon_richards]

See also: relativity, quantum physics, etc.