Hacker News Board Hacker News, browsed like a classic message board
Live data from Hacker News

Something peculiar in my 2yo's bedroom led me to a revelation about our universe

twitter.com

Post reply on HN
Print view View original

41–50 of 53 posts

Re: Something peculiar in my 2yo's bedroom led me to a revelation about our universe

#41

Post by grey_earthling »

SushiHippie wrote: post #18
thunderbong wrote: post #16

Earlier quoted context omitted.

Thank you. That was wonderful! I couldn't figure out from the linked X (formerly Twitter) post what it was all about. I think it's time for the good samaritans of HN to post nitter links for every X (formerly Twitter) post. Also, is there some extension which I could add in the browser which would show the corresponding Nitter link?

Most of the time you can just replace twitter.com with nitter.net or nitter.it but when these instances are down or blocked you can use other instances listed here: https://github.com/zedeus/nitter/wiki/Instances But as the other commenter said Libredirect is the way to go: https://libredirect.github.io/

Or you can prepend "farside.link/" — https://news.ycombinator.com/item?id=39154536

Re: Something peculiar in my 2yo's bedroom led me to a revelation about our universe

#42

Post by npteljes »

potamic wrote: post #37
k310 wrote: post #8

It's a thread, and mere mortals without accounts see only the OP (OT?) I'm starting to get the hang of nitter.net and here's the thread. https://nitter.lanterne-rouge.info/latifnasser/status/175095... Other nitter instances were rate-limited or down. This one worked for me. It's actually interesting.

I find it amusing that in this age of information technology, we still struggle to share a small page of text.

I think it's how one can imagine technology won't solve "humanity's problems". It's not that we are incapable - it's that we have different goals.

Re: Something peculiar in my 2yo's bedroom led me to a revelation about our universe

#44

Post by dreamcompiler »

chmod600 wrote: post #38
dreamcompiler wrote: post #23

> Anyway, I think this is so cool because everything else on the solar system map is so regular and orderly, but not quasi-moons! Nothing in the solar system is regular and orderly. It's chaotic because 3-body problems are almost always chaotic, and >3-body problems are always chaotic. Our solar system is a hundred-body problem (or more depending how small a "body" you want to include). So why then does our solar sys…

We must have some idea where the planets were back in the time of dinosaurs. I mean, Earth was still approximately the same distance from the Sun, and presumably still #3 right?

Probably the order of the planets was the same but we can't be sure of the eccentricity of their orbits back then. We do know Saturn probably didn't have rings back then.

Re: Something peculiar in my 2yo's bedroom led me to a revelation about our universe

#45

Post by chmod600 »

dreamcompiler wrote: post #44
chmod600 wrote: post #38

Earlier quoted context omitted.

We must have some idea where the planets were back in the time of dinosaurs. I mean, Earth was still approximately the same distance from the Sun, and presumably still #3 right?

Probably the order of the planets was the same but we can't be sure of the eccentricity of their orbits back then. We do know Saturn probably didn't have rings back then.

"We have no idea where Venus will be exactly [ten] million years from today."

I'm trying to figure out what this is supposed to mean. Of course we don't know exactly, but also of course we have some idea.

Like, could Venus have had an eccentric orbit that extended further from the Sun than Earth or closer than Mercury? Could it have had a moon?

Re: Something peculiar in my 2yo's bedroom led me to a revelation about our universe

#46

Post by dreamcompiler »

chmod600 wrote: post #45
dreamcompiler wrote: post #44

Earlier quoted context omitted.

Probably the order of the planets was the same but we can't be sure of the eccentricity of their orbits back then. We do know Saturn probably didn't have rings back then.

"We have no idea where Venus will be exactly [ten] million years from today." I'm trying to figure out what this is supposed to mean. Of course we don't know exactly, but also of course we have some idea. Like, could Venus have had an eccentric orbit that extended further from the Sun than Earth or closer than Mercury? Could it have had a moon?

Sorry I should have been more specific. We can't predict the accurate position of Venus in its orbit ten million years from now, and it's possible its orbit will have a different shape then too. However it's unlikely that the orbit would be so eccentric that it would intersect with Earth's orbit. That kind of deviation becomes more likely when we talk about a billion years.

Re: Something peculiar in my 2yo's bedroom led me to a revelation about our universe

#47

Post by joaogui1 »

dreamcompiler wrote: post #23

> Anyway, I think this is so cool because everything else on the solar system map is so regular and orderly, but not quasi-moons! Nothing in the solar system is regular and orderly. It's chaotic because 3-body problems are almost always chaotic, and >3-body problems are always chaotic. Our solar system is a hundred-body problem (or more depending how small a "body" you want to include). So why then does our solar sys…

What's the definition of chaos here? I thought chaos implied the measurement error growing quickly during propagation, but here it looks like it's growing pretty slowly. In what way is this more chaotic than the movement of a single accelerating body (where the error grows linearly with time)?

Re: Something peculiar in my 2yo's bedroom led me to a revelation about our universe

#49

Post by SushiHippie »

SushiHippie wrote: post #18
thunderbong wrote: post #16

Earlier quoted context omitted.

Thank you. That was wonderful! I couldn't figure out from the linked X (formerly Twitter) post what it was all about. I think it's time for the good samaritans of HN to post nitter links for every X (formerly Twitter) post. Also, is there some extension which I could add in the browser which would show the corresponding Nitter link?

Most of the time you can just replace twitter.com with nitter.net or nitter.it but when these instances are down or blocked you can use other instances listed here: https://github.com/zedeus/nitter/wiki/Instances But as the other commenter said Libredirect is the way to go: https://libredirect.github.io/

:( oh well, not anymore: https://news.ycombinator.com/item?id=39161194

Re: Something peculiar in my 2yo's bedroom led me to a revelation about our universe

#50

Post by dreamcompiler »

joaogui1 wrote: post #47
dreamcompiler wrote: post #23

> Anyway, I think this is so cool because everything else on the solar system map is so regular and orderly, but not quasi-moons! Nothing in the solar system is regular and orderly. It's chaotic because 3-body problems are almost always chaotic, and >3-body problems are always chaotic. Our solar system is a hundred-body problem (or more depending how small a "body" you want to include). So why then does our solar sys…

What's the definition of chaos here? I thought chaos implied the measurement error growing quickly during propagation, but here it looks like it's growing pretty slowly. In what way is this more chaotic than the movement of a single accelerating body (where the error grows linearly with time)?

Chaos requires nonlinearity. A gravitational body's motion affects every other body, which in turn affects the original body, etc. So you can't analyze the parts of the system independently and then just add up the results. A body's motion indirectly affects its own future motion. Spacetime tells matter how to move and matter tells spacetime how to bend, as Wheeler said.

In two-body problems, this infinite recursion converges to a closed-form solution, which means we can just write down the solution to the differential equations that describe the system's state and predict it at any time in the future.

Unfortunately there are no true two-body orbits in the universe. And with 3 and greater numbers of bodies that pleasant closed-form convergence doesn't happen. You get sensitive dependence to initial conditions (SDIC), with faster-than-linear divergence, and you can't solve the differential equations: You have to integrate them numerically.

The time horizon over which this divergence happens for planets is long relative to the time horizons we care about, but it's still SDIC and it's faster than linear. The same thing happens with the weather (the "butterfly effect") but there the time horizon for divergence (the Lyapunov time) is short enough that we humans can easily notice it.

https://en.m.wikipedia.org/wiki/Lyapunov_time

Post reply on HN