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I wonder if you could model this in Universe Sandbox [0]? (I live in Seattle so I've met the author Dan Dixon a few times at meetups but have no other relations

by yodon 10y ago

I wonder if you could model this in Universe Sandbox [0]? (I live in Seattle so I've met the author Dan Dixon a few times at meetups but have no other relationship to it) [0] http://universesandbox.com/ http://universesandbox.com/

ISL 10y ago
I expect so -- at least one of the people on the team is a relativist. Sending her an email now...
- BrendanD 10y ago
  Nope: http://universesandbox.com/faq/ http://universesandbox.com/faq/ Does it account for relativity? No, the physics in Universe Sandbox ² is currently only Newtonian. Why? The short answer is that you need a supercomputer to accurately simulate general relativity. Jenn, astrophysicist and Universe Sandbox ² developer, explains more in a blog post: "General relativity requires simulating the spacetime itself. That is, taking your simulation space, discretizing it to a hi-res 3-D grid and checking the effect that each and every point in that grid has on all neighboring points at every timestep. Instead of simulating N number of bodies, you are simulating a huge number of points. You start with some initial data of the shape of your spacetime and then see how it evolves according to the Einstein equations, which are 10 highly non-linear partial differential equations." We are, however, interested in adding in a few features which would address some effects of relativity. One example is setting gravity to travel at the speed of light, instead of instantaneously taking effect as it currently does. You can read more about these in Jenn's blog post: Gravitational Waves & Universe Sandbox ².
  - marxidad 10y ago
    Sounds like it would need Minecraft.
  - athom 10y ago
    Finite element analysis on the spacetime continuum? Yikes!
  - btilly 10y ago
    First and second order corrections are a lot more reasonable to calculate than the whole theory! Furthermore calculating the whole theory runs into interesting challenges where the coordinate system is twisted and and distorted but underlying space-time is not. For a well-known example, a black hole can be described with both Schwarzschild coordinates and Kruskal–Szekeres coordinates. The first coordinate system blows up at the event horizon, the second doesn't. The fact that it blows up is due to a bad choice of coordinate system there, and not due to local space time being particularly bizarre at that spot.
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  - yodon 10y ago
    How cool - asking the question "does gravity propagate at the speed of light and if so what impact does that have on orbital dynamics" was the event that led me down the path to my PhD, so it's awesome the answer to the question is now (or soon to be?) baked into a science toy.
jerf 10y ago
Despite the other replies, at only 1% of the speed of light you could set up a reasonably similar situation. The deviations between Newton and Einstein here would be significant if you were trying to literally plot an orbit for your visiting spaceship (and why the bloody hell would you want to do that?!), but not if you just want to watch two high mass objects dance around each other really quickly for a bit. My question would be more about whether the simulation has sufficient granularity to avoid the star flying away due to the time step being too large, rather than concerns about relativity. And of course Universe Sandbox won't be simulating the black hole tearing away bits of the star, or at least, so I'd presume.
- Symmetry 10y ago
  If I recall my physics correctly the most important thing it would miss is the orbital energy of the start slowly being radiated away as gravity waves and the star eventually being swallowed by the black hole.
- hatsunearu 10y ago
  Universe Sandbox's n body algorithm has dubious stability at large time steps. I've seen the whole thing explode when I crank up the time steps.
strainer 10y ago
Here is a basic model in my physics project: http://strainer.github.io/fancy#10 http://strainer.github.io/fancy#10 The two objects are the size of our sun, the green one represents the black hole. I put in the orbital distance as 2.5 times the Earth to Moon distance as stated in the article, and just tweaked the mass of the black hole (green orb) until the star orbits once every 30 minutes. The mass of the star will hardly matter. The mass of the black hole in this model is 60 solar masses. The model timestep is here is 1 minute, five or ten minutes should still work for this engines integration scheme. Its a Newtonian model, at 0.01 lightspeed there will be innaccuracy but I guess just a few percent in measurements.

by yodon 10y ago

ISL 10y ago

I expect so -- at least one of the people on the team is a relativist. Sending her an email now...

BrendanD 10y ago
Nope: http://universesandbox.com/faq/ http://universesandbox.com/faq/ Does it account for relativity? No, the physics in Universe Sandbox ² is currently only Newtonian. Why? The short answer is that you need a supercomputer to accurately simulate general relativity. Jenn, astrophysicist and Universe Sandbox ² developer, explains more in a blog post: "General relativity requires simulating the spacetime itself. That is, taking your simulation space, discretizing it to a hi-res 3-D grid and checking the effect that each and every point in that grid has on all neighboring points at every timestep. Instead of simulating N number of bodies, you are simulating a huge number of points. You start with some initial data of the shape of your spacetime and then see how it evolves according to the Einstein equations, which are 10 highly non-linear partial differential equations." We are, however, interested in adding in a few features which would address some effects of relativity. One example is setting gravity to travel at the speed of light, instead of instantaneously taking effect as it currently does. You can read more about these in Jenn's blog post: Gravitational Waves & Universe Sandbox ².
- marxidad 10y ago
  Sounds like it would need Minecraft.
- athom 10y ago
  Finite element analysis on the spacetime continuum? Yikes!
- btilly 10y ago
  First and second order corrections are a lot more reasonable to calculate than the whole theory! Furthermore calculating the whole theory runs into interesting challenges where the coordinate system is twisted and and distorted but underlying space-time is not. For a well-known example, a black hole can be described with both Schwarzschild coordinates and Kruskal–Szekeres coordinates. The first coordinate system blows up at the event horizon, the second doesn't. The fact that it blows up is due to a bad choice of coordinate system there, and not due to local space time being particularly bizarre at that spot.
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- yodon 10y ago
  How cool - asking the question "does gravity propagate at the speed of light and if so what impact does that have on orbital dynamics" was the event that led me down the path to my PhD, so it's awesome the answer to the question is now (or soon to be?) baked into a science toy.

jerf 10y ago

Despite the other replies, at only 1% of the speed of light you could set up a reasonably similar situation. The deviations between Newton and Einstein here would be significant if you were trying to literally plot an orbit for your visiting spaceship (and why the bloody hell would you want to do that?!), but not if you just want to watch two high mass objects dance around each other really quickly for a bit. My question would be more about whether the simulation has sufficient granularity to avoid the star flying away due to the time step being too large, rather than concerns about relativity. And of course Universe Sandbox won't be simulating the black hole tearing away bits of the star, or at least, so I'd presume.

Symmetry 10y ago
If I recall my physics correctly the most important thing it would miss is the orbital energy of the start slowly being radiated away as gravity waves and the star eventually being swallowed by the black hole.
hatsunearu 10y ago
Universe Sandbox's n body algorithm has dubious stability at large time steps. I've seen the whole thing explode when I crank up the time steps.

strainer 10y ago

Here is a basic model in my physics project: http://strainer.github.io/fancy#10 http://strainer.github.io/fancy#10 The two objects are the size of our sun, the green one represents the black hole. I put in the orbital distance as 2.5 times the Earth to Moon distance as stated in the article, and just tweaked the mass of the black hole (green orb) until the star orbits once every 30 minutes. The mass of the star will hardly matter. The mass of the black hole in this model is 60 solar masses. The model timestep is here is 1 minute, five or ten minutes should still work for this engines integration scheme. Its a Newtonian model, at 0.01 lightspeed there will be innaccuracy but I guess just a few percent in measurements.