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The Science of Radiance 
14th-Feb-2009 05:55 pm
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   Radiance is a far-future science fiction setting that I used for a linked tabletop scenario and freeform at Sydcon last year, and will revisit in RADIANCE: RELICS at Eye-Con over Easter.

   For the most part, Radiance is Plausibly Hard SF, with futuristic science and technology that includes "things that may or may not be possible, but can still be considered plausible or reasonable, at least until proved wrong by future discoveries". Some of the technology in Radiance is considered improbable or even impossible by conservative physicists, but certainly not all physicists. Some is well within the range of possibility.

   I am not a scientist. Some of the people reading this may have a better scientific understanding of these issues than I do, and disagree with me about the plausibility of some of this science. The important thing is that "plausibly hard" science fiction is an aesthetic choice – I enjoy science fiction in which the technology presented is interesting and yet plausible. It's not intended to be a valid prediction of future history (as if that could be possible), but a fictional universe which feels like it could exist.

   The scientific and technological assumptions of Radiance include:

  • Navigable Wormholes are still controversial among physicists, with about as much evidence in favour as there is against. Warpgates are basically navigable wormholes. These are an engineering challenge for very advanced civilisations (requiring exotic matter to work), and were constructed in the deep past of the Radiance universe.
     
  • Faster-than-light travel with time-travel effects because any method of travelling FTL creates time-travel paradoxes (according to General Relativity and the propagation of information through the universe). Wormholes are no different – they avoid the problem that acceleration to the speed of light requires an infinite amount of energy, but closed timelike curves (i.e., time travel) and causality violations. If it is possible to travel faster than light, then it is possible to time travel. Either the universe is acausal, or causality doesn't work the way we think it does, or faster-than-light travel is only possible in a way that does not allow causality violations.
       The option that I've chosen means that travelling through a wormhole is a form of time travel, but wormholes cannot be created in a way that allows causality violations or paradoxes. One theory states that stable wormholes are possible, but that any attempt to use a network of wormholes to violate causality would result in their decay; this is how warpgates work in Radiance. This is a bit complicated – I'll describe it in detail later.
     
  • Reactionless Drives are controversial but considering that Radiance already has exotic matter (involved in warpgates), they could be possible. This is definitely an aesthetic issue, allowing spacecraft to accelerate to high speeds without subjecting characters to enormous g-forces or flooding living compartments with cushioning foam.
     
  • Primitive non-terran life has evolved in extreme environments (non-carbon-based life, cold-chemistry, and so on). There's not a lot of "xenogen" life in the setting, but the organisms that are known have some very exotic biologies.
     
  • The galaxy has few or no current alien civilizations as an explanation for the Fermi paradox – the apparent contradiction between high estimates of the probability of the existence of extraterrestrial civilisations and the lack of evidence for, or contact with, such civilisations. In the history of life on the Earth only one species has developed space flight capability and radio technology; this lends credence to the idea that technologically advanced civilisations are a rare commodity in the universe.
     
  • Advanced mechanical nanotechnology exists in some form, although not every possible use for nanotech proved to be possible or has been pursued.
     
  • Very rapid terraforming of uninhabitable planets into habitable worlds is possible given very advanced nanotech. Some of the worlds of the Radiance universe were terraformed over centuries (rather than millennia or tens of millenna) by previous civilisations. The current civilisation of the Radiance setting do not have this capability.
     
  • Digital uploads of human minds is not impossible, given a greatly advanced understanding of human neuroscience. The primary cultures of Radiance are now hostile to the idea of uploading human minds, but it happened in the distant past, and if advanced nanotech was developed that can record human minds and brains, these methods could be replicated.
     
  • Ubiquitous information technology is a basic assumption. Computers are practically ubiquitous right now. In my pocket I have a multifunction device that can connect me to a global information network, record pictures and audio, not to mention make telephone calls, multimedia messages, and email. And I hardly have the most advanced mobile phone on the market.
       Most people in Radiance have immediate personal access to local versions of the internet, communications, and information databases. These computers are integrated almost invisibly into clothing or personal accessories. Interfaces are sophisticated and intuitive. Only in unusual circumstances does anybody have to rely on just their personal knowledge or abilities – most of the time, you have computer assistance at your fingertips.

   So what doesn't exist in Radiance? Alien civilisations that are very humanlike in appearance and culture. A galactic monoculture or uniform future society, whether human or alien. Faster-than-light travel allowed due to handwavium physics. Psionics and fantastic abilities such as telepathy or "the Force". Force fields, disintegrator weapons, and energy beam weapons that violate basic physics and engineering. Spacecraft that act like WWII fighter planes. There's nothing inherently bad about stories that include this kind of thing (many people have gained a lot of enjoyment from Star Wars), but I'm aiming for a plausible and consistent universe, so I have tried to avoid fantastical elements like these.

   Radiance on Facebook: http://www.facebook.com/home.php?#/group.php?gid=26163137003

Comments 
14th-Feb-2009 02:53 pm (UTC) - Warpgates and Wormholes

   For a brief explanation of how wormholes allow for time travel, look over this section from the Wikipedia article Wormholes: Time Travel:

   A wormhole could allow time travel. This could be accomplished by accelerating one end of the wormhole to a high velocity relative to the other, and then sometime later bringing it back; relativistic time dilation would result in the accelerated wormhole mouth aging less than the stationary one as seen by an external observer, similar to what is seen in the twin paradox. However, time connects differently through the wormhole than outside it, so that synchronized clocks at each mouth will remain synchronized to someone traveling through the wormhole itself, no matter how the mouths move around. This means that anything which entered the accelerated wormhole mouth would exit the stationary one at a point in time prior to its entry. For example, if clocks at both mouths both showed the date as 2000 before one mouth was accelerated, and after being taken on a trip at relativistic velocities the accelerated mouth was brought back to the same region as the stationary mouth with the accelerated mouth's clock reading 2005 while the stationary mouth's clock read 2010, then a traveler who entered the accelerated mouth at this moment would exit the stationary mouth when its clock also read 2005, in the same region but now five years in the past. Such a configuration of wormholes would allow for a particle's world line to form a closed loop in spacetime, known as a closed timelike curve.

   This would certainly violate causality, which is unacceptable. Either we live in an acausal universe, or any phenomena that might allow a violation of causality does not actually exist. Fortunately there is another possibility – that while traversable wormholes are possible, attempting to create a traversable wormhole system that would allow a closed timelike curve is not:

   ... some analyses using the semiclassical approach to incorporating quantum effects into general relativity indicate that a feedback loop of virtual particles would circulate through the wormhole with ever-increasing intensity, destroying it before any information could be passed through it...

   In other words, if you attempt to create a wormhole system that allows the creation of a closed timelike curve, the whole thing implodes.

14th-Feb-2009 02:54 pm (UTC) - Warpgates and Wormholes

Wormholes and Warpgates in Radiance

   Every inhabited star system in Radiance has a warpgate. Warpgates temporarily open and stabilise a wormhole between two that star system and another, up to ten parsecs away. Evidence suggests that the warpgates were created by one of the ancient human civilisations, first in one of the central systems (Ancius, Austron, Ixion, Oreus, or Savitar), and then moving ever outwards through the galaxy at relativistic speeds. Travelling from a central star system such as Ancius to a more distant system like Njetker is not only a journey of nearly six parsecs in distance, but hundreds of years into the "future" – however long it took the ancients to transport the original apparatus form the central systems to Khnum in the first place. Travelling from Njetker to Ancius is likewise a journey backwards in time. This does not create a closed timelike curve; a traveller from Njetker to Ancius could send a message back to Njetker, but travelling at the speed of light it would still arrive years after he left. Causality is preserved.

   If it became possible to create a new warpgate in the Njetker system and carry it at relativistic speeds to Ancius, this would allow a violation of causality. A traveller could leave Ancius via gate one, arrive in Njetker system in the "future", and then trabel through gate two to reach Ancius in that "future". Upon observing "future Ancius" the traveller could then retrace his journey to "present-day Ancius" and make changes that violate "future Ancius". Fortunately, as gate two is carried towards "future Ancius" the feedback loop of virtual particles between these warpgates causes one or both warpgates to implode. It simply is not possible to create a closed timelike curve-enabling system.

   

   This is some of the theory and thought behind how interstellar travel works in Radiance. It is a lot more involved than you'll need to think about during a typical game!

14th-Feb-2009 09:26 pm (UTC) - reactionless drives
James,

the only other comment would be that reaction-less drives don't require fuel. You need energy to turn them on, but they for instance don't use up petrol and need to be refilled after a period of time.

Essentially, they allow for unlimited acceleration unlike modern spaceships which fire engines for a little bit, and then rely on Newton's lst law to keep travelling in the same direction at the same speed until they need to stop/change.

In short it means faster travel times as you can keep accelerating/deccelerating throughout the journey with no thought about burning up delta-V.
15th-Feb-2009 08:39 am (UTC) - Re: reactionless drives
That's right! And it's the primary reason for including them.

For reasons of the plausibility of Radiance's cultures, I've placed most warpgates in fairly remote orbits of their star systems. The fictional history requires a lengthy time in which interstellar travel did not occur, which seems unlikely if warpgates are located within 5 AU or so of their primary.

But this means that travelling from haitable planets to a warpgate ten or twenty astronomical units away will take enormous amounts of time, or enormous amounts of fuel, or technologies that are way too easily used as weapons for my liking.

Using antimatter as a power source to allow decent delta-v is just asking for story problems. If the antimatter engines are very large, then you've got the potential for kamikazi spacecraft that can release their antimatter fuel and destroy small continents. If they can be miniaturised to a size that doesn't create weapons of mass (heh) destruction, you can create relativistic missiles or even bullets.

A reactionless drive can be plausibly large enough that it's restricted to spacecraft, and doesn't require dangerously large energy output. Murderously suicidal players could still accelerate a vessel to relativistic speeds and smash it into something, but I feel that's a lot more obvious and easier to prevent than sneaking a vessel up to the enemy, and remotely dropping the magnetic bottle that contains all of the vessel's antimatter.

So: reactionless drives. They provide an adequately fast way of getting about for a roleplaying game, and if it's something like a bias drive then I can postulate some kind of artificial gravity inside the spacecraft as well. Enormous amounts of fuel are unnecessary, although energy is still required for other vessel functions so operating the spacecraft isn't "free". The only qualm that I have is that the technology required seems a little more advanced than that which is readily available in the current setting – exotic matter is required for warpgates, but those artefacts are beyond humanity's current ability to recreate. It means that humanity has some small-scale technology involving this level of technology, which should be extrapolated to other plausible practical uses.

At the moment I think that humanity uses very small amounts of exotic matter to create a version of the ansible, which they use to basically piggyback communication through the warpgate network. It allows a limited "instantaneous" communication across the interstellar civilisation, while remaining within the same reference frame.

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