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July 5, 1687: When Newton explained why you don't float away
- roenxi 1y ago> Halley’s intervention saved science from being reduced to “things fall down because they do” for another century. Well, that might be stretching it. Speaking as someone who has done a little university level physics the understanding still seems to be basically that things fall because they do - we haven't made much progress beyond a firm strike-through of the word "down". Newton's contribution was a very precise description of how rapidly they fall, and how we can calculate and understand the direction that things fall in complex multidimensional settings.
- 725686 1y agoIsn't it because of the curvature of spacetime? Not that that means much to a layman, but I think that progress has definitely been made.
- bravesoul2 1y agoIt's funny. We don't float away. We can never say why. Just produce better and better models. The whys never end!
- DanielVZ 1y agoIt’s interesting how it’s not turtles all the way down (as I understand it at least). The things you learn of one scale do not completely translate to the next but serve as the “shadow” projected by the next level down the line. And this probably brings up the complexity that lets us exist and perceive. I say probably because who knows what else is going on in the universe. All this to say who knows if we are ever going to learn the fundamental why if there is one.
- adastra22 1y agoYes, general relativity explains gravity pretty darn well, tying it to the fundamental fabric of causality that makes up the universe. It goes from “it just happens” to “it must happen and there is no other way it could be.”
- layer8 1y agoThere is no notion of causality in our laws of physics, and from all we know gravity could certainly be different, or absent. You could have a universe with just the other three forces.
- adastra22 1y agoThere absolutely is. The speed of light is the speed of causality. It is very tightly integrated into the framework of modern physics. Maybe you are confusing causality for the arrow of time?
- layer8 1y agoModern physics says little about causality. The fundamental laws are all field equations. Those set constraints about how the physical state of a system can evolve between two points in time, but there is no notion of causation, only of consistency or (im)possibility. Causation in physics is a complex and problematic notion: https://plato.stanford.edu/entries/causation-physics/ https://plato.stanford.edu/entries/causation-physics/
- adastra22 1y agoI think we are talking past each other. Defining how the system evolves is defining how initial conditions must lead to (cause) intermediate and final states. That’s causality in the logical sense. What I’m talking about is most similar to the “Causal Explanation” section at the end of the article you link.
- noman-land 1y agoDoesn't mass bend spacetime (do we know why? No idea) and cause matter to "fall" into the gravity well?
- kimixa 1y agoMaybe? That's one theory - but what is "spacetime", and what does it mean to "bend", or "fall into" something like that? In many ways we've just given things names as if that suddenly means they're understood. And even then how can that be measured and proven vs other theories? Is it some other mechanism that simplifies to "close enough" that it measures similarly? We didn't really see the effects of relativity until we got to a sufficient accuracy of measurement, Newtonian mechanics was sufficient to explain things to the accuracy they could reproduce for a very long time. Einstein couldn't have done anything like what he published if he didn't have evidence from new (at the time) equipment suggesting there was something wrong with the current model. And then testing proposed new models against those same measurements.
- silisili 1y agoI've always been a bit flummoxed we haven't expanded a ton on this given how long it's been. I'm not sure if it's wrong or right, and not smart enough to posit much, other than it -feels- wrong. But it wouldn't take a ton to convince me otherwise. You'd think by now we'd have more supporting evidence of such a concept.
- griffzhowl 1y agoDo you mean evidence for general relativity? Because there's a lot: gravitational waves, black holes, gravitational redshift, the bending of light by gravity, the expansion (or contraction, depending on density) of the universe, are all new phenomena predicted by GR and experimentally verified
- silisili 1y agoOh I meant expanded it down, if that makes any sense, applying it to more things that we'd normally learn in high school. At least in my case, you're taught gravity as this standalone force, and even the Newtonian idea in high school. Not until later college do they then throw that away and go into gr and the ideas you mention. Though I guess this is more a failing of public education than science at large.
- eternauta3k 1y agoIs "why" really a meaningful question? These are all models. The best we can do is to show how to derive the phenomenon from the (hopefully simple) rules of our model.
- SilasX 1y agoIt's relative. I operationalize "why is X true?" as "update my worldmodel to the point that X is not surprising". The typical way to do that is to show a more general rule that applies, and which implies X. But yes, you can keep asking the question about the more general rule. Why do things fall? -> A special case of the general law of gravitation. Why does reality adhere to the general law of gravitation? A implication of matter distorting the shape of spacetime. Why is reality such that matter distorts space-time?
- thaumasiotes 1y ago> Is "why" really a meaningful question? ...of course? If you want something that won't fall down, your only options are (1) luck into noticing something that already does that, or (2) understand why things fall down, so you can prevent your thing from falling.
- tralarpa 1y ago> ...of course? No, it isn't. That sounds strange, right? But here is an explanation what eternauta3k probably meant: In modern physics, there is a kind of consensus that asking “why” has often been inappropriate or even misleading and should be therefore left to philosophers. The real questions are: Does our current model describe all observations? If not, can we find a model that does? And, even better, can that new model make predictions that we can verify?
- mensetmanusman 1y agoNewton’s title has philosophy in it. It’s probably a modern error to separate all the fields and ignore philosophy when doing science etc and vice versa.
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- Micoloth 1y agoThat’s what i though as well > Why apples fall, why planets don’t wander off, and why we aren’t all quietly drifting into space every time we sneeze. Newton didnt really explain the why.. Einstein added something much later, but it might be that really we still don’t have a clue. All we can do is measure how fast it happens, very precisely
- TMEHpodcast 1y agoYou’re correct. Newton wasn’t proposing a mechanism or deeper cause for gravity; he just described its effects. Einstein did add a “why” of sorts, with general relativity, he reframed gravity not as a force but as the curvature of spacetime caused by mass and energy. That’s closer to a mechanism, but even there we might ask: why does mass curve spacetime? And we don’t have a deeper answer to that.
- dataflow 1y agoOh come on. Things fall down because matter has a property called gravity that attracts other matter, and below us is a giant earth with a lot of matter. And it has more of a net effect on us than any other matter in the universe because gravity scales with distance and mass in that particular way. That's as darn good of an explanation of why we fall down as one could possibly give. "But why does mass have gravity?" Why does Newton have to have all the answers to every other question too? Maybe ask that and someone will answer that question in a few hundred years? He answered your original question, he didn't claim he can answer every subsequent question you think of. It's quite ridiculous to suggest Newton just tautologically concluded "things fall down because they do" just because he doesn't go on and explain the "why" of every sub-question ad infinitum.
- 2b3a51 1y agoI'd just throw in that this idea of universal gravitation coupled with the laws of motion and dodgy ideas like force and momentum enabled a wide range of phenomena to be described and some predictions to be made that could be compared with observations. Yes, ideas like 'force' and 'momentum' were a bit dubious but the resulting theory was effective[1] within its domain of applicability. [1] https://en.wikipedia.org/wiki/Effective_theory https://en.wikipedia.org/wiki/Effective_theory
- tralarpa 1y ago> That's as darn good of an explanation of why we fall down as one could possibly give Well, around two hundred years later they found out that it is not a good explanation (which of course in no way diminishes Newton's achievements).
- TMEHpodcast 1y agoNewton’s physics is still taught and used everywhere because it’s simple and accurate enough for 99% of practical situations. Einstein’s relativity isn’t a better explanation, it just extends it to extreme conditions. NASA still uses Newtonian law to launch rockets.
- sanderjd 1y ago
- jrowen 1y agoIt's actually 338 years. I turn 38 today and was born in 1987. TIL Newton published the Principia exactly 300 years before I was born.
- AStonesThrow 1y ago[dead]
- Simon_O_Rourke 1y agoIn fairness, he only explained why a vast vast majority of people don't float away. He didn't adequately explain edge cases like Joseph of Cupertino - https://en.m.wikipedia.org/wiki/Joseph_of_Cupertino https://en.m.wikipedia.org/wiki/Joseph_of_Cupertino
- hermitcrab 1y ago"Alleged eyewitness reports of Joseph's levitations are noted to be subject to gross exaggeration, and often written years after his death." That sounds super reliable. ;0) "Poisoning due to the consumption of rye bread made from ergot-infected grain was common in Europe in the Middle Ages. It was known to cause convulsion symptoms and hallucinations. British academic John Cornwell has suggested that Joseph had consumed rye bread (see ergot poisoning). According to Cornwell "Here, perhaps, lay the key to his levitations. After sampling his own loaves he evidently believed he was taking off–as did those who partook of his high-octane bake-offs."" Eilmer of Malmesbury showed a bit more commitment to his flying: https://en.m.wikipedia.org/wiki/Eilmer_of_Malmesbury https://en.m.wikipedia.org/wiki/Eilmer_of_Malmesbury
- zabzonk 1y agoI like Eilmer: > Eilmer said he had "forgotten to provide himself with a tail."
- progre 1y agoTo me, the funniest part of why Principica was bankrolled by Edmund Halley is that is was supposed to be funded by the Royal Academy. Only, their previous publishing project "The history of fishes" had faceplanted and they had no money. Also, when Principica was funded and Halley was himself short on cash, RA decided that they could not afford to actually pay him money (he was the RA secretary). Instead he would get copies of The History of fishes
- ykonstant 1y agoHe ended up swimming with the history of fishes.
- zabzonk 1y agosleeping, surely?
- perihelions 1y agoI enjoyed this anecdote. As gratitude, please accept this copy of History of Fishes https://archive.org/details/francisciwillugh00will/page/n321/mode/2up https://archive.org/details/francisciwillugh00will/page/n321...
- moffkalast 1y agoEight hundred pages? Well at least he got his money's worth.
- metalman 1y agowait! wait! so you are saying that there is an official exchange rate for fish books to pounds strerling, guinies? all I can say is that hopefully someone keeps a copy of the fish book next to a copy of the Principica as a demonstration/proof of the vast leap and gap that suddenly occured
- dotancohen 1y agoOr as an example of he who gets the funds, not necessarily being the worthy of the two. Many in academia might like to remember this example.
- dr_dshiv 1y agoAnd, in the last paragraph of the general scholium, the appendix of the Principia, Newton describes electromagnetism and the role of electrical oscillation in the nervous system. It’s actually the root of the the history of “vibes” “And now we might add something concerning a certain most subtle Spirit, which pervades and lies hid in all gross bodies; by the force and action of which Spirit, the particles of bodies mutually attract one another at near distances, and cohere, if contiguous; and electric bodies operate to greater distances, as well repelling as attracting the neighbouring corpuscles; and light is emitted, reflected, refracted, inflected, and heats bodies; and all sensation is excited, and the members of animal bodies move at the command of the will, namely, by the vibrations of this Spirit, mutually propagated along the solid filaments of the nerves, from the outward organs of sense to the brain, and from the brain into the muscles. But these are things that cannot be explain'd in few words, nor are we furnish'd with that sufficiency of experiments which is required to an accurate determination and demonstration of the laws by which this electric and elastic spirit operates.” https://web.archive.org/web/20100524103006/http://www.isaacnewton.ca/gen_scholium/scholium.htm https://web.archive.org/web/20100524103006/http://www.isaacn...
- mensetmanusman 1y agoPeople today are confused by the word spirit because the word fields quietly replaced it, and they are just as mysterious because we don’t know if they are real.
- gavmor 1y ago"Field" is a less mysterious term because it's not polysemous with a supernatural being (ghost) or a distilled alcoholic beverage (soluble liquid). Sure, it's polysemous with "a cultivated expanse of land", but AFAIK there is no popular, problematic pseudoscientific quackery about suggesting our bodies possess rows of oats.
- mensetmanusman 1y agoFields give breath to the math that perfectly describes reality but which isn’t found anywhere in reality. Kind of mysterious:)
- tristramb 1y agoBack in 1987 I was standing outside Thorns Bookshop in Newcastle upon Tyne. In its window was a display of books by Professor Paul C. W. Davies. I was saying to someone beside me that Davies wrote too many books for them to be any good. Then I turned round and almost bumped into the man himself. Fortunately he hadn't heard what I'd said and just carried on his way. He was hurrying to give a lecture at the university commemorating the 300th anniversary of Newton's Principia. Several years later I was to revise my view of his writings after reading his 'Fifth Miracle' which I enjoyed very much.
- d4rkn0d3z 1y agoFor the record, Newton was vastly conceptually wrong which is not the same as saying his work is useless because being wrong in a precise way is science. Time does not "flow immutably from one moment to the next" and there are no gravitational "forces" acting magically at a distance. Even if the linear approximatiins he made hold on a narrow domain they offer little in the way of conceptual framework. In fact, mostly Newton played mathematical parlour tricks. If you are waiting for science to tell you "why" things happen you will wait forever because science answers "how" things happen. There is no way for a successor scientific theory to completely subsume all of the predictions of its predecessor because they are often incommensurable. Which is to say that there is simply no way to define one in the terms and concepts of the other. If you think of GR as some extension or modification of Newton's work you're doomed to misunderstanding the mathematical facts.
- sixo 1y agooh, what the hell, I'll argue with you. > vastly conceptually wrong Only for a useless definition of "wrong". Modeling reality well is an end in itself, and to the extent that model predicts well and "factors" reality cleanly into distinct mechanisms, it is conceptually right. This is all "conceptually right" needs to mean. You can not, as I'm sure you'll agree, even hope to explain the "root cause" of motion and time-evolution. at some point you have to base any theory on some postulate or assumption about why things happen at all. But the point of work like Newton's is to get things right above that level, and he was enormously successful at this. > mostly Newton played mathematical parlour tricks. Only for a useless definition of "parlour tricks". The hard part of new ideas (1) is getting to the point where you're posing the right problem and thinking about it the right way. Once you get that right, the predictions (2) hopefully fall out as simple tricks! Then they have to be validated (3) against data—also hard. Newton pulled off all three, the hard parts and the tricks. Not single-handedly, mind you, but almost. To bring such a big picture into view and fill out its details with credibility was a monumental task. I think of it as akin to evolution developing a new organ system—the genome usually has to find its way down on a very long limb to get there and to be stable enough to stay there. For a species this can happen over many generations, but for a human thinker it is has to happen by imagining and testing many subsequent ideas. Newton did an enormous amount of this on his own, over decades. > are often incommensurable Newton being absorbed into relativity is like the one case where they are commensurable. Newton is a clear limiting case! The "ways of thinking" about reality are perhaps not, but nobody (except cranks) is still stuck on Newtonianism at this point. > as some extension or modification Obviously it contains new math and new abstractions, as needed to match empirical reality on new data. Its content doesn't extent logically out of Newton, because how could it? The data wasn't there. But the conceptual gesture of devising a mathematical framework which can handle the data is the same one Newton used. Postscript: philosophy of science folks always like to show up in physics discourse ready to fight various tired, old battles which mostly mattered in the context of the particular ideological dispute of some decade or another. The matter in question is always how to generalize the success of physics by fitting various philsci "models" to the "data" of physics' history. This can be interesting, but they never contribute much to the physics itself, which has always proceeded by its own internally-coherent and immensely-successful logic.
- mattmaroon 1y ago“In the 337 years since, Newton’s ideas have been used for all sorts of fussy yet vital activities: building bridges that don’t collapse, plotting planetary orbits, and explaining why toast inevitably lands butter-side down. NASA still uses Newton’s framework today. They strap adventurous humans into enormous cylinders, set off controlled explosions underneath, and fling them into space—because three centuries later, it’s still the best idea we’ve got.” Someone should tell them about relativity!
- TMEHpodcast 1y agoRelativity isn’t needed because rockets never get anywhere near the speeds or gravitational extremes where Einstein’s equations matter. At rocket speeds, Newtonian mechanics is so accurate the difference is negligible, so why make things harder? NASA sticks with Newton because it’s simpler, faster to calculate, and gets the job done perfectly for launching rockets into orbit.
- mattmaroon 1y agoIt was just ELI5-style writing and I was being tongue in cheek about it. Newtonian physics are fine for determining how much propellant will launch a rocket into orbit, but you couldn’t build a GPS satellite without accounting for space time distortion. NASA does a lot of things.
- xandrius 1y agoCouldn't you engineer that away with a bunch of magical numbers? I'm curious.
- mattmaroon 1y agoWell, you can’t get to a GPS using Newtonian physics alone because of gravitational time dilation. The clock in space runs at a different speed than the clock on earth. If they tried, scientists could perhaps have come up with some sort of fudge factor (like what I think they do with dark matter) and made it work, sure. But it would have been really confusing to them when they figured out that all the clocks in space run at a different speed than the same clocks on earth. Relativity plays a big role in astronomy too. One of the big questions in physics in Einstein’s day was why the planets didn’t appear exactly where you expected given Newtonian laws. Becoming spacefaring without general relativity would have been difficult.
- tiahura 1y agoHe avoided the why. “Hypotheses non fingo”, I frame no hypotheses.
- Liftyee 1y agoSidenote: Is anyone else distracted/unsettled by that faint animated circle of dots that snaps to your mouse whenever it's moving?