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Author Topic: Dark matter included in simulations?  (Read 9382 times)

Baleur

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Dark matter included in simulations?
« on: June 13, 2009, 07:55:16 PM »
I know this is probably a wierd question, considering that we dont even fully understand dark matter yet  ;D
But when creating galaxies and stuff, it seems as they just spin themselves apart, eventually. Even at very low timesteps (but still reasonably fast so you'll see a result within your lifetime lol).
This is, as you know, spot on to what our current model of gravity tells us that galaxies "should" do, and the reason why the dark matter theory has gained so much credibility. There simply has to be more mass to keep the galaxies intact..

Now, i'm just wondering if you have any plans to include some kind of dark matter equation? Obviously something very simple, like a very simplified more global gravity-calculation acting only on a bunch of stars/particles rather than on every tiny body.

I've found however that a semi-fix is to just increase the overall gravity modifier to 1.25 or something, though of course that applies to everything, even small moons orbiting planets, so it sort of only works well in galaxy sims :=)

I dunno why i made this thread lol, just wondering if you had any thoughts on including something like that, for the galaxy simulations that is. Thanks!

Naru523

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Re: Dark matter included in simulations?
« Reply #1 on: June 13, 2009, 10:31:15 PM »
I was wondering the same thing. Dark Matter is not an understandable thing. Soon, we'll understand when we get to study it more.  :D

Bla

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Re: Dark matter included in simulations?
« Reply #2 on: June 14, 2009, 10:25:06 PM »
I don't think it's needed. The galaxy has a fixed gravity already, and only the black hole in the center makes the gravity of it (in Universe Sandbox). The small particles (stars) don't have any mass in the simulations.
I think you can just increase the mass of the galaxy, then it has a larger gravity. But I think it's already fixed. The particles/stars will get off their path or even fly out of orbit if you run the simulation too fast, and that's the problem I think. Like the Milkyway and Andromeda collision, it starts with a high time step, and already there many stars fly out of the galaxies before I can slow the simulation.
But if the galaxies had more mass, the stars would have to orbit faster at the same distances, and then more stars would get out of orbit instead of the opposite. Running the simulation slow is the only thing we can do I think.

Dan Dixon

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Re: Dark matter included in simulations?
« Reply #3 on: June 15, 2009, 02:52:09 PM »
Now, i'm just wondering if you have any plans to include some kind of dark matter equation?

Galaxy simulations in Universe Sandbox are very simplistic. Currently they are represented by single point masses and thousands of mass-less points. I look forward to introducing distributed masses for galaxies in which case it would be fairly easy to add support for a 'hidden' distributed mass called dark matter.

Either way Universe Sandbox only uses Newton's law of gravitation and doesn't consider Einstein's theory of relativity.

But when creating galaxies and stuff, it seems as they just spin themselves apart, eventually. Even at very low timesteps (but still reasonably fast so you'll see a result within your lifetime lol).
...
I've found however that a semi-fix is to just increase the overall gravity modifier to 1.25 or something

I don't understand what you mean by spinning themselves apart. If you start with a blank simulation, drop in a galaxy, and set the time step to 50000 years it will spin for a long, long time.

I suggest adding some anti-gravity matter.
I want some matters repelling while some of 'em attracting at a same time ;)
changing the gravity constant to a negative # doesn't help cuz all of them repels :'(

In the next release I'll allow for negative masses. That will do it.

hbmp88

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Re: Dark matter included in simulations?
« Reply #4 on: June 15, 2009, 07:28:55 PM »
Quote
Galaxy simulations in Universe Sandbox are very simplistic. Currently they are represented by single point masses and thousands of mass-less points. I look forward to introducing distributed masses for galaxies in which case it would be fairly easy to add support for a 'hidden' distributed mass called dark matter.

Yeah I have noticed that the simulation cannot be used to test the theories that the universe will rip or crunch. When exploding any object to dust proportions space just expands between. Even when including dark matter I still don't believe that the simulation will be close to accurate unless mass can be distributed throughout the dust to allow them to interact with each other, and not just leave the center point in a straight line. But what i don't get is how can the dust particles be pulled back in to the center of mass when the explosion was weak (which your simulation will do) if they don't even have mass. This is where I think your simulation of dust has its biggest flaw. :-\

MonkeyDLuffy

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Re: Dark matter included in simulations?
« Reply #5 on: June 23, 2009, 03:59:25 PM »
Here's an video about it [Dark Matter]:
« Last Edit: June 23, 2009, 04:11:25 PM by Dan Dixon »

GreenJelly

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Re: Dark matter included in simulations?
« Reply #6 on: June 25, 2011, 09:12:53 PM »
This is a big thing for Me too... As I wish to create custom Galaxy's with real objects, but things do just spin out of control or they spin off the sim.  Simply put, there is not enough mater in the universe to keep it held together.

Dark Matter is "Dark" in that they don't know why it exists.  It explains a problem with Newtons law and its effect on Galaxies.  In particular Galaxies do not Shrink or Expand, they simply rotate.  Since their is not enough mater to account for the gravity needed to accomplish this, the term "Dark Matter" came about.

Here are some pictures of the Dark Mater in our solar system
http://www.solstation.com/x-objects/darkhalo.htm

Its been mapped using the lens effect, or watching light bend around gravity.  In this case, light is bending around things that do not exist.  Thus they mapped the gravitational pull using light.