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Hello! - aliendude777 - 03-25-2015

I first found out about OA when I was poking around the internet for information about AIs.
I was wondering about why wormholes are unstable above .74c, as described in the linear instabilities section in the wormholes article, since from the wormhole's frame of reference it is staying still while the universe is moving around it. Thus, the rest of the universe would be undergoing Lorentz contraction while the wormhole is staying is still.


RE: Hello! - Drashner1 - 03-25-2015

Hi there, Welcome to OA!

To a certain degree this aspect of OA wormholes is one that decided to engineer by fiat, since we really hate time machines around here. We used to allow wormholes to experience significant time dilation and essentially become time machines in the setting and it ended up causing nothing but headaches.

That said, based on our desire to minimize this effect in OA wormholes, Adam Getchell, the 'inventor' of OA wormholes referred to real world science when designing them.

This paper HERE makes mention of the instability issue and in turn references a real research paper that apparently discusses this issue. Beyond that, although Adam is not very active with the project just now, he does check in occasionally (and was just here recently) and if he sees this thread, he can probably shed more light on the matter. Warning, it will probably involve a lot of math Smile

If Adam doesn't respond to this thread in the fairly near future, I can try to contact him offlist and ask if he has time to drop in for a quick explanation on this.

Hope this helps and once again, Welcome to OASmile

Todd


RE: Hello! - aliendude777 - 03-25-2015

(03-25-2015, 12:52 PM)Drashner1 Wrote: Hi there, Welcome to OA!

To a certain degree this aspect of OA wormholes is one that decided to engineer by fiat, since we really hate time machines around here. We used to allow wormholes to experience significant time dilation and essentially become time machines in the setting and it ended up causing nothing but headaches.

Thanks for the answer. Is time dilation also the reason wormholes can't exist except outside a gravitational field? Or is that just an example of a limitation that a sufficiently advanced Archailect might find a way around?

I ask because I had an idea that a sufficiently advanced sophont could use wormholes inside of a star to remove large amounts of material, or add in new hydrogen to lengthen the life of the star, but then I remembered that wormholes would collapse in the gravitational field of the star.


RE: Hello! - stevebowers - 03-25-2015

We do have wormholes that operate on the surface of a star, but they are described as being different to normal traversable wormholes, and asymmetric;.
http://www.orionsarm.com/eg-article/480d45f717577

I'm not sure what form this asymmetry takes, but I think they couldn't be used as normal traversable holes - maybe it is not so vital to send star-stuff through the 'hole in one piece.


RE: Hello! - Drashner1 - 03-26-2015

(03-25-2015, 03:42 PM)aliendude777 Wrote: Thanks for the answer. Is time dilation also the reason wormholes can't exist except outside a gravitational field? Or is that just an example of a limitation that a sufficiently advanced Archailect might find a way around?

Not exactly. The reason for this is known as 'asymptotic flatness' and essentially boils down to a matter of having to accept tradeoffs when engineering space-time to create wormholes. This is explained in more detail in the papers listed as references on the Wormholes: A Layman's Guide page.

Basically, when considering a wormhole, there are three main factors you need to look at: Stability, Mass, and Internal Tidal Forces.

There are apparently many many many possible types of wormholes, combining these elements in different ways. So there can be wormholes that are really really stable, but which require a galaxy's worth of mass-energy and exotic matter to create. Or you might have a wormhole that doesn't need a lot of mass and is very stable - but the internal tidal forces will shred anything made of matter that tries to go through. Or maybe it has reasonable mass and tidal forces - but is so unstable that even a single atom trying to pass through it will cause it to implode. And so on.

When trying to come up with a wormhole 'design' that would allow for a reasonable amount of mass, stability, and low tidal forces, Adam found that there were some other effects that came along for the ride, that you pretty much just have to live with. He also found (or invented if you prefer) several different types of wormholes, each having different values of the factors listed above. So far, in the current era in the OA universe you have:

Traversable Wormholes (aka Stargates):

These have relatively low mass for their size, low internal tidal forces, and are metastable, meaning they require active stabilization to prevent them from imploding. But they also have a large feature called the Transition that extends out from them for several hundred AU (essentially this can be thought of as the start of the mouth of the WH). Within the transition, 'asymptotic flatness' comes into play, which is a fancy way of saying that if anything sufficiently massive enters the transition, it will destabilize the WH and cause it to implode. In practice, if anything massing as much as even 1% of the WH enters the transition it can overwhelm the active stabilization systems and cause implosion. However, this is offset by the huge mass of the WH. A 'standard' 1000m radius gate (the radius being that of the WH Throat, not the Transition) generally masses as much as a planet and may outmass Jupiter by quite a bit. So getting 1% of it's mass inside the transition undetected (or at all) is no easy or common thing.

Hayward type Wormholes (aka Comm-gates):

Comm-gate type wormholes have a MUCH smaller Transition zone than a stargate. Only about 10,000x their own radius. However, they are also MUCH less mass efficient (a 1000m radius comm-gate masses more than 33x the mass of the sun) and have internal tidal forces that will shred anything made of conventional matter. But make them in sizes ranging from micrometers to nanometers and fire a modulated gamma ray laser through them and you can send messages over virtually any distance more or less instantly. Hence the name. And gates that small mass about as much as a large asteroid and can be scattered around a solar system or even placed inside the brains of the larger archailects to speed up internal signalling and their thoughts to 'ftl' levels.

Comm-gates are also harder to make than stargates btw.

Grazers:

These are the asymmetric wormholes that Steve mentioned. For all wormholes, passing matter or energy through them will calls the 'entrance' mouth to gain mass and grow larger, while the 'exit' mouth loses mass and shrinks (this due to conservation laws). With proper scheduling of two-way traffic you can balance this process so both WH mouths stay approximately the same size and mass (you can also add/remove mass-energy to/from a WH directly using specialized machinery).

With a Grazer, this process still happens (as do the asymptotic flatness requirements of a transport gate and the tidal forces of a comm-gate), but the grazer has the ability to 'shift' it's mass from one mouth to the other, causing one mouth to grow/become more massive, while the other mouth shrinks/becomes less massive. Done properly, and with enough mass-energy to feed into it, you can transport the small mouth across space to the vicinity of a star, set it on course to pass close to the star while still far enough away for it to remain stable, and then start shifting mass so that the mouth gets larger and more massive to the point that the solar system, up to and including the star, is sucked into it, shredded down to component atoms by the tidal forces, and spit out the 'exit' gate light-years away. Have machinery around the exit gate to grab, process, and transport the exiting matter flow and you can take whole star systems apart and convert them into whatever you want with a minimum of fuss.

There are also inter-universal wormholes, connecting this one to artificial space-times created by the archai (although these largely work like transport gates), wormhole bombs (metric bombs) and it's been suggested that we should add in a type of WH that converts anything that passes through it into anti-matter (or back again if going the other way). Although we haven't written up that last one yet, it has a theoretical basis in the real world and we probably will eventually.

Hope this helps,

ToddSmile


RE: Hello! - Rynn - 03-28-2015

(03-26-2015, 11:17 AM)Drashner1 Wrote: For all wormholes, passing matter or energy through them will calls the 'entrance' mouth to gain mass and grow larger, while the 'exit' mouth loses mass and shrinks (this due to conservation laws). With proper scheduling of two-way traffic you can balance this process so both WH mouths stay approximately the same size and mass (you can also add/remove mass-energy to/from a WH directly using specialized machinery)

I'm a bit confused by this, I didn't realise this was the case for all our wormholes. If the net transport of mass has to be zero then how can we have wormholes in systems designed to export huge amounts of resources, like Himmelsschmiede? And for megastructures requiring multiple solar masses does an Archai have to use grazer's exclusively?


RE: Hello! - stevebowers - 03-28-2015

One reference for this is the interesting discussion on the detection of wormholes between Geoff Landis, John Cramer, Greg Benford and Robert Forward.
http://www.geoffreylandis.com/ftl.htp

Quote:Because if you have a wormhole, and mass passes through it, it sort of trails its gravitational field lines, and so on the way in it increases the mass of the wormhole mouth, and on the way out it decreases the mass of the wormhole mouth. This will be sort of dynamically unstable, because the the object gets on the positive gravitational end, the more mass it will attract and suck through, and therefore the more negative the other end will get.
These august gentlemen seem to think that such an imbalance might not be a problem, so long as you are prepared to put up with an unbalanced wormhole.


RE: Hello! - Drashner1 - 03-28-2015

(03-28-2015, 12:05 AM)Rynn Wrote: I'm a bit confused by this, I didn't realise this was the case for all our wormholes. If the net transport of mass has to be zero then how can we have wormholes in systems designed to export huge amounts of resources, like Himmelsschmiede? And for megastructures requiring multiple solar masses does an Archai have to use grazer's exclusively?

It's something we've gone back and forth on over the years. I remember a discussion between Luke and Adam on this issue, and I'm pretty sure it was agreed that inter-universal WHs definitely have this property.

For intra-universal gates, I've seen an article talking about this in terms of conservation laws. IIRC Adam took the position (in at least one discussion) that this effect didn't happen with WHs, but Luke disagreed. But I don't remember what conclusion, if any, that they came to.

That all said, if this effect does happen with all WHs, it's not an insurmountable problem. Mainly it would require a bit of a change in how we describe/think about this sort of thing. Let's see...

a) For high value items (like manufactured devices, exotic matter components, or whatever you're going to make a star into, you might consider them sufficiently valuable to make onsite, ship through a WH and then feed in raw energy at the 'exit' end to make up the losses.

b) As an alternate to (a), you could have several grazers nearby, perhaps leading to major construction projects, or hubs on the Nexus where the end products could be easily shipped to wherever you want them and incoming traffic could make up part of the losses. You could ship material through the grazers as raw matter and then set up manufacturing systems at the far end, which would convert the raw material to finished products and then ship it out via the Nexus. Or get incorporated into that huge megastructure you mention (we already indicate something like this happens in the Valhalla Clusters article.

c) Instead of using WHs you could ship stuff via flatspace, maybe using space-time catapults. Sure it will take a while to get to the destination, but it's going to take you thousands of years to take the star apart anyway - and after the initial wait for the 'pipeline' to get going, the incoming material/products can arrive on quite a regular schedule (but cancellations with less than a centuries notice will incur a service feeWink)

Todd