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The Universe - I don't get it


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#1 DareDeveloper   GDNet+   -  Reputation: 953

Posted 11 March 2014 - 12:36 PM

Hi,

 

I have been trying to gather some universe related info ... kinda for procedural content generation experiments.

 

My problem is ... I don't get it. When reading about galaxies and how they use distance to measure the age ...

there must be something that I am missing or thinking about the wrong way.

 

The universe is expanding ... all galaxies are moving away from each other.

They are not moving away from a certain point, though ... or some galaxies would move away from us faster than others.

 

Is that something that people should simply not try to wrap their head around, or is there a better way to think about it than comparing it to an explosion (... which has things moving away from a center)?

I guess I need to move from thinking in 3 Dimensions to 4 Dimensions ... but I tried that and it still seems to me as if the way we look at galaxies in the distance implies that earth is at the center.

Is thinking in 3D wrong in general, for some reason?

 

Any thoughts or ideas? I hate feeling stupid ;-)


Given enough eyeballs, all mysteries are shallow.

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#2 Tom Sloper   Moderators   -  Reputation: 9883

Posted 11 March 2014 - 12:44 PM

1. When reading about galaxies and how they use distance to measure the age ...

2. The universe is expanding ... all galaxies are moving away from each other.
They are not moving away from a certain point, though ... or some galaxies would move away from us faster than others.
 
Is that something that people should simply not try to wrap their head around, or is there a better way to think about it than comparing it to an explosion (... which has things moving away from a center)?


1. Light travels at a constant speed, but when an object is moving away from you, light's wavelength is lengthened (it's called the Doppler effect). So you can tell by the light spectrum's "red shift" how fast it's moving away from you. The spectrum also reveals information about the star's actual brightness - comparing that with its apparent brightness tells you information about its distance from you. But why do you need to know this to develop a game?

2. What difference does it make that there isn't an actual physical center of the universe? All expansion is relative to everything else in the universe. Why do you need to understand this to develop a game?
-- Tom Sloper
Sloperama Productions
Making games fun and getting them done.
www.sloperama.com

Please do not PM me. My email address is easy to find, but note that I do not give private advice.

#3 DareDeveloper   GDNet+   -  Reputation: 953

Posted 11 March 2014 - 01:00 PM

Thanks for the reply.

 

I don't need to know this. I just feels wrong having read and heard about those things without "getting it" ... while it seemingly makes sense to everybody else.

I guess I would love to be able to visualize it roughly and simulate the creation of a universe (add time as a procedually controlled factor and render a time lapse ... something like that).

 

Yeah I know about the effect and red shift, still is seems to me like there is an assumption at work when they explain what the implications of the wavelengths are.

Don't many things affect the perceived wavelength? I think they say "how fast it is moving away from you" is the same as "how much distance the light had to travel"!?

To me is seems as if another assumption or fact is needed to come to that conclusion.


Given enough eyeballs, all mysteries are shallow.

ProcGames.com


#4 jHaskell   Members   -  Reputation: 1027

Posted 11 March 2014 - 01:02 PM

Let's try applying an analogy that should be familiar to all game developers.

 

The metric expansion of the Universe can be thought of as having a Scale transform applied to the Universe, and that Scale increases over time.

 

While that Scale is being applied and increased over time though, the speed of light continues to remain constant.  Thus any two points in the Universe can be observed to be moving away from each other at a constant rate.

 

That Scale is only being applied at the macro level though, which is why we don't see red-shift from local light sources, such as our own sun or stars visible with the naked eye (and even stars visible with most amateur level telescopes, I believe).  So the Scale gets applied to each Galactic component of the Universe, but those Galactic components don't apply the Scale to all their child components.

 

Now, if you're really trying to understand the WHY behind this apparent Scale transform being applied to the Universe, I think most (or perhaps all) theoretical physicists are still grappling with that one



#5 szecs   Members   -  Reputation: 2143

Posted 11 March 2014 - 01:02 PM

Think about a ball and that you slowly blow air into it. From any point on the surface, it seems that everything is going away from that point. And there is no specific center on the surface of a ball.

It shouldn't be hard to visualize that in 3D even without the warping.

 

As for the red shift: the reason is simple, yet I wasn't able to get a good explanation of it apart from the usual sound analogy bullshit.


Edited by szecs, 11 March 2014 - 01:07 PM.


#6 DareDeveloper   GDNet+   -  Reputation: 953

Posted 11 March 2014 - 01:15 PM

The ball and scale analogies are great. I can see how scale is different from an explosion.

Guess factoring in the red shift and the age of galaxies ... I'll need some time to think through those things.

 

Thanks!


Edited by DareDeveloper, 11 March 2014 - 01:16 PM.

Given enough eyeballs, all mysteries are shallow.

ProcGames.com


#7 jms bc   Members   -  Reputation: 428

Posted 11 March 2014 - 01:47 PM

'To me is seems as if another assumption or fact is needed to come to that conclusion'

 

you need to know the wavelength of the light in the reference frame of the source. We think we have this color spectrum data based on our studies of (relatively) nearby stars.

 

'I think they say "how fast it is moving away from you" is the same as "how much distance the light had to travel"!?'

 

Information about relative velocity comes from the shift in wavelength. How far away the objects are is calculated with triangulation and brightness (with brightness, like wavelength at source mentioned above, coming from studies of thousands of nearby stars). Knowing the distance the light traveled, one can say when the light was emitted.

 

You should read about dark energy. There is much related to space that scientists don't know.

 

Strange that selective quote button is not presented on some of these comments?


The Four Horsemen of Happiness have left.


#8 samoth   Crossbones+   -  Reputation: 4783

Posted 11 March 2014 - 01:58 PM

You just shouldn't worry. We don't know nearly as much about the universe as one would believe. Unless you want to become astronomer, it probably won't make any difference to your life either.

 

All you really know is that some guy looked through his goggles and noticed a red shift. Although numerous credible scientists have since then confirmed that it's there, you likely haven't even seen it yourself. For all you know, it might not be true at all. But assume it's true that there is a red shift.

 

One possible explanation is that the universe is expanding. Probably that's the reason, too -- but you don't know. Another explanation would be that the universe has been expanding a million years ago, which is what we see, but it isn't expanding any more (maybe it's shrinking right now!). We only know what we see (and not what is true), and light travels at a quite finite speed whereas the universe is huge. So anything we see has already passed from history to legend to myth a long, long, long time ago.

Another explanation would be that the "vacuum" is not a vacuum but a very light red mist, so you only see its tint at astronomic depths (or incidentially there is no such mist in the solar system). Or maybe there exists mass that you can't see (something like a black hole, but weak enough so light can still escape) which the light has already travelled past, and that mass is now acting in the opposite direction. Maybe there is ... whatever. Maybe it's the Devil playing tricks on your eyes to test your faith. We cannot know, we can only tell what's plausible.

 

If you want to procedurally create a galaxy, create something that "looks like a galaxy" to you. Plausible, good enough. Who cares about the truth.


Edited by samoth, 11 March 2014 - 02:01 PM.


#9 Bregma   Crossbones+   -  Reputation: 5133

Posted 11 March 2014 - 03:47 PM

Hubble's expanding universe is predicated on the observation that the farther an object is away from us, the more rapidly it's receding from us. If the universe is expanding at a constant rate everywhere, that is exactly what we'd expect to see from every point. Just like a balloon.

The radial velocity is observed by the way certain characteristic spectral lines (the Balmer series of the hydrogen emission spectrum) are shifted into longer wavelengths. You can imagine a spring being stretched to better understand how the lightwaves from a receding emission source get lengthened. Because red light has a longer wavelength than other colours, it's called a "red shift."

So, we can identify some object are receding from us faster than others. How do we know they're farther away? (1) relative magnitide: farther objects are smaller and dimmer. (2) observational parellax: farther objects appear stationary relative to closer objects over time. (3) spectral characteristics: certain emission lines indicate temperature and compostion, if the emission is weaker than a similar object, it's assumed to be farther away (for example, carbon fuses into heavier elements at a specific temperature, if the characteristic emission spectrum of carbon fusion is weaker in one object than another, we can assume the weaker spectrum has travelled farther). (4) occlusion: thing closer block the view of things behind them.

An so on.
Stephen M. Webb
Professional Free Software Developer

#10 Stainless   Members   -  Reputation: 941

Posted 11 March 2014 - 03:55 PM

A simple (ish) technique

 

http://beltoforion.de/galaxy/galaxy_en.html

 

If you try to understand the universe, you will fail. For the simple reason that no one does (yet).

 

We have a very nice set of theories and equations that work MOST of the time, but we have problems. Data loss at black holes is probably the most famous I guess.

 

My favourite theory is that the universe is a simulation created by a computer programmer from a more advanced civilization.

 

The theory goes like this.....

 

We can create a simulation of the universe with modern super computers, but since we don't fully understand it and don't have enough computing power to make it real time, it's not real.

 

However we have seen a vast increase in computing power in the last few decades, so it is very highly probable that one day we will have the programming power to create a 100% accurate simulation.

 

We have also seen a vast increase in our understanding of the universe, so it is very highly probable that with enough time we will fully understand the universe.

 

Since it is highly probable we will be able to simulate the universe, and highly probable we will be able to understand the universe, it is highly probable that someone will create an artificial universe.

 

Since more than one programmer can create a simulation, if the above premise is true, then it is likely that multiple universes will be created.

 

Since there is only one real universe, and there are probably many more simulated universes, then it is more likely that we live in a simulation than in the real world.

 

Wrap your head around that one blink.png



#11 phantom   Moderators   -  Reputation: 7279

Posted 11 March 2014 - 04:35 PM

Is that something that people should simply not try to wrap their head around, or is there a better way to think about it than comparing it to an explosion (... which has things moving away from a center)?


One thing to keep in mind, while it is an explosion the explosion started from the same place for everywhere in the universe at the same point as at that moment there where no 'other points'.

So, the universe started where I am, where you are, where the sun is and where the furthest galaxies are at the same time.

Which is kinda cool (and the reason why looking at the cosmic microwave background radiation (a) works and (b) is important) biggrin.png

#12 samoth   Crossbones+   -  Reputation: 4783

Posted 12 March 2014 - 08:16 AM

relative magnitide: farther objects are smaller and dimmer.
That made me think of: http://xkcd.com/1276/.

 

What's funny is that these figures are so totally unintuitive when you look at the sky. For example, from looking at the night sky, you'd say the moon's projected size is about the size of a hazelnut, not the size of London (except when close to the horizon where it seems to be rather the size of an orange). Obviously neither case is true, but it's what you see when you look up.

Venus appears just about big enough so you can tell it's probably something in the solar system and not something else. Pretty much everything else you can see with the naked eye is just a "tiny dot". You would never associate any of them with something like "ping pong table" or even "soccer field", would you?



#13 DareDeveloper   GDNet+   -  Reputation: 953

Posted 12 March 2014 - 11:52 AM

Yeah, I have read about the ... http://www.simulation-argument.com/ before.

Guess where I have a problem with that is the amount of data that is needed to simulate a whole universe and how much data the simulation would have to store somehow. Will it actually ever be possible to simulate several universes like the one we can observe (and, more importantly, interact with)?

Might be interesting to approach that as a Fermi Estimation problem and guesstimate how many planets we need to turn into computers and storage in order to simulate what we see.

 

Stainless, that link is seriously cool. Guess I need to start creating some gameplans with sketches now.

 

Nice one samoth, yes that is ... unintuitive huh.png.

 

Guess I am not pragmatical enough, emotionally speaking, to give up on raising my level of understanding to a point where I feel a little more comfortable (in an unexplainable way, I guess).

Found new input ... guess I'm still in the processing the new information stage, though.

http://arstechnica.com/science/2014/03/getting-the-math-of-the-universe-to-cancel-out/

I also have not read and thought through all posts, yet.


Edited by DareDeveloper, 12 March 2014 - 11:54 AM.

Given enough eyeballs, all mysteries are shallow.

ProcGames.com


#14 Stainless   Members   -  Reputation: 941

Posted 13 March 2014 - 03:06 AM


Guess where I have a problem with that is the amount of data that is needed to simulate a whole universe and how much data the simulation would have to store somehow. Will it actually ever be possible to simulate several universes like the one we can observe (and, more importantly, interact with)?

 

You don't store all of it.

 

Procedural generation.

 

Have a look at some of the modern terrain engines, hell yes it's possible. Actually I think it's inevitable. Some hacker in 3 or 4 hundred years will do it for fun.



#15 DareDeveloper   GDNet+   -  Reputation: 953

Posted 13 March 2014 - 04:31 AM

Yeah but only the part that we have not interacted with can be procedurally generated. It takes some serious optimization.

 

Interaction points have to be stored ... unless our interactions are procedurally generated as well, which is a thought that I personally don't like smile.png. Fake consciousness? Nooooo!


Given enough eyeballs, all mysteries are shallow.

ProcGames.com


#16 Bacterius   Crossbones+   -  Reputation: 8885

Posted 13 March 2014 - 04:41 AM


Interaction points have to be stored ... unless our interactions are procedurally generated as well, which is a thought that I personally don't like . Fake consciousness? Nooooo!

 

I suppose it depends whether you subscribe to determinism or not wink.png but I think a game that plays itself without user input is called a "simulation".


The slowsort algorithm is a perfect illustration of the multiply and surrender paradigm, which is perhaps the single most important paradigm in the development of reluctant algorithms. The basic multiply and surrender strategy consists in replacing the problem at hand by two or more subproblems, each slightly simpler than the original, and continue multiplying subproblems and subsubproblems recursively in this fashion as long as possible. At some point the subproblems will all become so simple that their solution can no longer be postponed, and we will have to surrender. Experience shows that, in most cases, by the time this point is reached the total work will be substantially higher than what could have been wasted by a more direct approach.

 

- Pessimal Algorithms and Simplexity Analysis


#17 samoth   Crossbones+   -  Reputation: 4783

Posted 13 March 2014 - 05:07 AM

It depends on what scale you simulate, and since you use words like "galaxy" and "universe", it likely matters very little.

 

We must not take ourselves too important. Most of your interactions don't matter an awful lot to the galaxy or to the universe. Not even to our planet.

 

Even though mankind has been working very hard to destroy the planet during our entire existence, we still haven't been successful. The entire existence of mankind is just a fly speck on earth's windscreen. It only hasn't switched on the wipers so far, because we're not annoying enough just yet. Nature on this planet will prosper perfectly fine ten million years after we have died out. Without us, and without all our great achievements. A couple of million years isn't a lot to a galaxy.

 

But even if we manage to completely destroy this planet (as in, doomsday bomb), the universe will hardly notice. Earth is a sandcorn in an unimportant solar system inside a not-very-special galaxy.

 

So if you simulate "galaxy scale" feel free to go procedurally and screw interactions, because your interactions don't matter anyway. Simulate interactions only on a scale where they are noticeable, e.g. on a space station or in a city on an inhabitable planet.



#18 ambershee   Members   -  Reputation: 528

Posted 13 March 2014 - 08:38 AM


Have a look at some of the modern terrain engines, hell yes it's possible. Actually I think it's inevitable. Some hacker in 3 or 4 hundred years will do it for fun.

 

It'll start to become possible as soon as we're capable of easily working with 128-bit coordinate systems (I'm not kidding by the way).



#19 samoth   Crossbones+   -  Reputation: 4783

Posted 13 March 2014 - 09:01 AM

It'll start to become possible as soon as we're capable of easily working with 128-bit coordinate systems (I'm not kidding by the way).
It's kind of possible already. 120,000 light years / 264 is 61.5 meters. That isn't a terrible resolution for something the size of the milky way.
 
Just make your galaxy a bit smaller (trust me, nobody will notice the difference!), say 12,000 light years and you're good. Or consider the fact that most of the galaxy is empty space, so you don't really need that resolution anyway.
 
For "empty space", 61 meters are just fine, even 6,100 meters are perfectly good. When two objects are a few dozen light years apart from each other, a few meters don't really make any difference.
You can handle what happens inside each solar system in its own local coordinate system, e.g.  50 AU / 264 = 4*10-7 m.
 
400 nanometers resolution is probably good enough for everybody biggrin.png


#20 ambershee   Members   -  Reputation: 528

Posted 14 March 2014 - 04:59 AM

Sure, but the maximum range of a quad-precision float is around 1.1897 × 104932 whereas the size of the universe is estimated to be 4.35184307 × 1026 metres across.

 

You wouldn't even need a local set of coordinate systems within that :)






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