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New proof finds the ‘ultimate instability’ in a solar system model
- cvoss 3y agoEarly in the article, we get a discussion of the precession of Mercury, known for centuries. Then: > (In this context, Newtonian mechanics gives such a good approximation of reality that these models don’t need to consider the effects of general relativity.) But wasn't the precession of Mercury already known to be inadequately explained by Newtonian gravity, even before Einstein?
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- eimrine 3y agoKnown by whom?
- opless 3y agoAstronomers...
- eimrine 3y agoThose guys used to believe in geocentric. Their claims were too easy to disbelief.
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- eimrine 3y agoAm I deserve those downvotes? I consider that my answer is too cocky but the question is definitely about the scientific consensus and I did my best to imagine what the consensus could be like at that time, considering the so hard to believe conception about non-linearism in speed. For me, the conception of relativism was the hardest to believe among all science fields I stepped in.
- djkorchi 3y agoThe precession of mercury has a few contributions. The largest is the tug of planets (500 arc seconds/century), the next largest is from general relativity (50 arc seconds /century). There are other, smaller contributions stemming from the sun being oblate. Knowledge about the anomaly in the precession was partly what motivated Einstein, and was one of the early predictions of the theory.
- hindenburg 3y agoThe article is a little bit breathless about this work as though evidence of solar system instability is completely novel and unexpected, but investigation in the area using simulation isn't exactly unprecedented. Gerry Sussman and Jack Wisdom were working on the question of solar system instability in the late 1980s and Sussman and his students built a specialized computer called the Digital Orrery at MIT. They ran some very long simulations and found strong numerical evidence that the orbit of Pluto is chaotic. https://en.wikipedia.org/wiki/Stability_of_the_Solar_System#Digital_Orrery https://en.wikipedia.org/wiki/Stability_of_the_Solar_System#... These weren't obscure results; further work was published in Science. See "Chaotic Evolution of the Solar System," in https://www.science.org/doi/10.1126/science.257.5066.56 https://www.science.org/doi/10.1126/science.257.5066.56
- cwmoore 3y agoI have also built a digital orrery, that generates interestingly complex images: https://news.ycombinator.com/item?id=34861546#34861552 https://news.ycombinator.com/item?id=34861546#34861552
- samus 3y agoThese are numerical simulations though. The novelty is the proof that these instabilities don't come from numerical artifacts, but are an inherent part of the system.
- salty_biscuits 3y agoI had it in my head that the lyapunov exponent for the solar system is approx 15 million years.
- PaulHoule 3y agoThere’s no doubt at all that there is some chaos in the solar system (e.g. you can’t quite predict which side of the sun the Earth will be on in 100 million years) but the question is does something big happen, like a planet getting ejected. In a low number of configuration space dimensions (N=2) you get “KAM tori” in phase which are an absolute barrier to the evolution of the system so chaotic motion is hemmed in. In N>2, however, KAM tori are still there but it is possible for chaotic trajectories to go around them. It’s clear that the trajectories of the planets behave like KAM tori on short timescales (1000s of years, that is how each one seems to be on an independent stable orbit) but what happens in the long term is not clear at all.
- deepsun 3y ago> billions of years into the future They didn't seem to account Sun's global warming. In 500 million years it will boil out all the Earth oceans, and in 1 billion years it will swallow Mercury, Venus, Earth.
- samus 3y agoTA found instabilities that can occur on a scale of a few hundreds of millions of years. But yes, nothing to worry about on the timescale human civilization is likely to last
- thriftwy 3y agoPerhaps we should consider why exactly are we living in something likely described as the most beautiful star system in our galaxy. The overall beauty of layout, the variety and the perfectly spaced orbits is something we may no longer take for granted. The fact that Moon has the same apparent size as the Sun, too. It is also a cold, calm beauty for technically developed species instead of immediate joy of having multiple visible hot Jupiters in the system.
- steve_adams_86 3y agoCouldn’t what we find beautiful be emergent from where we find ourselves to begin with? It seems extremely arbitrary to try to define what’s beautiful about any star system.
- thriftwy 3y agoI would argue that any kind of aliens will see our Solar system as beautiful because everything is regularly spaced, a great variety of all kinds of planets and moons, planetary rings, etc. We take all that for granted, but it really isn't. Many of other solar systems we know contain an irregular set of planets.
- trilbyglens 3y agoThe spacing of the planets isn't due to random chance. They are all in orbits defined by resonances with the other planets, as they effect gravitational drag on each other. They have pushed and pulled on each other for billions of years, until they have settled into the ordered structure we see today. https://en.wikipedia.org/wiki/Orbital_resonance https://en.wikipedia.org/wiki/Orbital_resonance It could also be well possible that this sort of stability is required for multi-billion year evolutionary processes to take place. Systems with more chaos would likely also have chaotic seasons even if their planets were to have the other needed conditions for live. If the summer-winter cycle were more unpredictable that it is on earth, maybe that acts as a limit on the complexity that live can achieve as it would constantly be getting pruned back. Systems with "unstable" or "irregular" planetary arrangements are probably just in an earlier stage of development, and might likely lose planets or push them into more stable orbits eventually. Similarly "stable" or "ordered" systems are likely just older systems which have been able to develop without being disrupted by outside phenomena. In that sense looking for well structured systems might be a good place to start looking for life, as they are likely old and stable enough to have had evolution take place.
- enriquto 3y agoNotice that this is about new, particularly wild, solutions of the multi-body problem. By Kolmogorov-Arnold-Moser theorem, such unstable solutions form a negligible set among all possible initial conditions. The solar system is, still, stable with probability one.
- londons_explore 3y agoThe article suggests around 1% of simulations show unstable behaviour...
- TheOtherHobbes 3y agoPerhaps you can explain why you think KAM somehow proves this while there are simulations - and this new work - which prove the opposite. Those models are all perfectly Newtonian. The solar system isn't. It's usefully Newtonian on the timescales we use to push things around it. But over much longer timescales planetary orbits are influenced by variations in the solar wind, visits from external objects, redistributions of mass in the Kuiper Belt and Oort cloud, and so on. These are mostly tiny influences, but enough to make claims of unconditional stability rather questionable.
- selimthegrim 3y agoIf you read the paper that the article cites on Arnold diffusion KAM is certainly considered and discarded
- enriquto 3y ago[Disclaimer: not an expert on ODE, so I don't really know what I'm talking about] I was just astonished by the title of the article, because it seemed to contradict KAM. Yet, upon careful reading, you can interpret the title in that "a solar system model" is unstable, but not all of them. Which does not contradict KAM. If I understand it well, KAM is compatible with the following two sentences: (1) the set of stable initial conditions is of volume 1 in phase space (2) the set of unstable initial conditions is dense in phase space. Like the rationals are dense inside the reals, but still most reals are irrational. What is the case here? I'm not knowledgeable enough to read past the abstract of these publications.
- londons_explore 3y ago> shifting the assumed position of one planet by a mere meter [...] the system can look very different. Humans have probably already done this by slingshotting spacecraft around planets. I wonder if future people will say 'if only we hadn't shifted the planet by a meter back in 1969, the solar system wouldn't have fallen apart!'
- wirrbel 3y agoPretty sure shifts by similar magnitudes happen all the time in the solar system with meteors hitting planets and moons and gas evaporating.
- BiteCode_dev 3y agoYes, and it's probably self-re balancing constantly through emerging phenomenons like all the complex systems humanity has studied so far.
- scotty79 3y agoI think the proof shows that these kinds of systems can be stable without any rebalancing for very long periods of time but then suddenly they are not.
- jvanderbot 3y agono way. Earth orbital speed is 20,000 m/s. Meteroites are about the same speed. Earth mass is 10^25, total meteorite mass / day is 44t, or about 4x10^4. Generously assuming all meteorites hit from the same direction, given the mass of the meteorite swarm is 1e-21 smaller, the total delta v is 10 to the minus 16. Double integrate that, and you get x^2/20000000000000000 Set equal to your desired difference, say one meter. You get over 100,000,000 days. That's 273,973 years to affect a 1 meter difference in position in the worst case. Caveat: I am probably wrong.
- brookst 3y agoOr the opposite: wow were we lucky Voyager launched when it did; the solar system would have collapsed had it not slingshotted past Jupiter.
- TheOtherHobbes 3y agoInteresting because there are 100,000,000,000 stars in the galaxy. If even a small percentage have unstable systems there are going to be quite a few stray planets floating around.
- throwaway290 3y agoWe just don't find a stray planet without a sun because the entire way we find exoplanets is through their suns. Doesn't mean they don't exist. There are probably many more strays than non strays.
- scotty79 3y agoThis might be another piece of the puzzle of Fermi paradox. Life is not much younger than universe. Maybe we owe development of life to the unusually lucky period of stability in our solar system right when the life began to be feasible here. I think there's a very good chance that we are one of the first intelligent species in our galaxy.
- aleph_minus_one 3y ago> Maybe we owe development of life to the unusually lucky period of stability in our solar system right when the life began to be feasible here. Obvious literature reference: > https://en.wikipedia.org/wiki/The_Three-Body_Problem_(novel) https://en.wikipedia.org/wiki/The_Three-Body_Problem_(novel) and its two sequels > https://en.wikipedia.org/wiki/The_Dark_Forest https://en.wikipedia.org/wiki/The_Dark_Forest > https://en.wikipedia.org/wiki/Death%27s_End https://en.wikipedia.org/wiki/Death%27s_End
- mensetmanusman 3y agoWill be funny if they find out this instability will likely happen long before the sun dies.
- hughw 3y agoAre there planets hurtling through interstellar or even intergalactic space?
- aaomidi 3y agoIt’s nearly impossible to see them. There’s no light.
- hughw 3y agoRight. They might occlude a star though.
- PaulHoule 3y agoOr gravitationally lens a star, see https://en.wikipedia.org/wiki/MACHO_Project https://en.wikipedia.org/wiki/MACHO_Project
- jjk166 3y agoOnly for the brief period of time they happen to be in line with it. For orbiting planets, we can see these occlusions happening multiple times and thus filter them out from the noise, but there are countless reasons the light from a star could briefly dim once. We can find bodies within the solar system as they'll occlude multiple stars in a row as they move along, but for rogue planets to move far enough across the sky to occlude another star would take millennia.
- krapp 3y agoYes, they're called rogue planets[0]. There are also rogue stars[1]. [0]https://en.wikipedia.org/wiki/Rogue_planet https://en.wikipedia.org/wiki/Rogue_planet [1]https://en.wikipedia.org/wiki/Intergalactic_star https://en.wikipedia.org/wiki/Intergalactic_star
- hughw 3y agoHoly smoke, there's a lot of them.
- 1970-01-01 3y agoHow does one use a blackboard outside? What happens when your work day is going well but you have light rain in the afternoon?
- kkylin 3y agoTake a picture and move to a blackboard inside.
- chickenimprint 3y agoI guess we are Trisolaris.