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On FTL 
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Post On FTL
The speed of light is not a 'sort of speed limit'; it is absolute. Nothing can move faster in the ordinary sense of moving.
Why is that?
As an object is accelerated, kinetic energy is imparted to it. Energy and mass are two ways of looking at the same concept.
Thus, as the object nears the speed of light, its kinetic energy (and thereby mass) nears infinity. Near-infinite mass means near-infinite inertia, so accelerating becomes progressively harder. Also, local time for the object slows down.
Should the object somehow manage to overcome the inertia and reach the exact speed of light, local time for the object would come to a complete stop as its mass goes to infinity. There would be no way for the object to even attempt further acceleration, as doing anything requires time to be passing. That's quite aside from the fact that energy can't be greater than infinite, so adding more energy is out of the question.

So, to effectively travel faster than light requires another mechanism than simply acceleration.
The warp drive of Star Trek fame is actually one of the theoretical ways to accomplish it. Originally called the 'Alcubierre Drive', it operates by distorting spacetime locally around an object so that the portion within the area of effect ahead of the object is compressed while the area behind the object is expanded. This allows the object to move slower than the speed of light locally, but through compressed spacetime, giving it a higher apparent velocity when observed from the outside. This amounts to surfing a 4-dimensional wave. Of course, prodigious amounts of energy would be required to distort spacetime like this.
Another method could be the use of wormholes. The trouble with those is that they're tiny and collapse as soon as the humblest particle attempts to pass through them. To hold a wormhole open requires negative energy. Nobody knows how to produce negative energy, but the mathematics of it works; E is energy and -E is negative energy. The question is if it can really exist. If the obstacles are overcome, a wormhole would allow near-instantaneous travel from anywhere to anywhere, regardless of physical distance.


Tue Jul 06, 2010 9:00 am
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Post Re: On FTL
I've been out of the loop for a bit. I am assuming this is an addition to the FTL write up to make it more easily understood?

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Tue Jul 06, 2010 3:33 pm
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Post Re: On FTL
ilKhan Ozy wrote:
I've been out of the loop for a bit. I am assuming this is an addition to the FTL write up to make it more easily understood?

Not quite. It's an attempt at elaborating on the FTL entry in the tech manual, which is only a couple of lines :)


Tue Jul 06, 2010 4:02 pm
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Post Re: On FTL
Ok. So pretty much an expansion project then. I can dig it.

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Tue Jul 06, 2010 7:20 pm
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Post Re: On FTL
I think the idea was to keep it simple (i.e. a couple lines). However there should be a separate tech-manual write up that is much larger.

EDIT:

That is if you mean the 'sci-fi terms' section. That's the one that's supposed to be small. An actual tech manual write up is much larger.

It's kinda confusing, because there's nothing in the tech manual except the terms and one other write-up right now.

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Tue Jul 06, 2010 10:02 pm
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Post Re: On FTL
Here is the scifi terms page in the Techmanual....
http://rabiki.com/archives/index.php?ti ... cifi_Terms


But yeah, we could also do a full page article in the tech manual to make it complete.


What I meant by "sort of" was there are ideas that suggest that information can go faster than light....however, not proven.
http://www.phys.ncku.edu.tw/mirrors/phy ... t/FTL.html

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Tue Jul 06, 2010 11:27 pm
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Post Re: On FTL
TA Lucas wrote:
What I meant by "sort of" was there are ideas that suggest that information can go faster than light....however, not proven.


True enough. Apart from the two ways I mentioned, there may be the tachyon particle and quantum entanglement.
One has not been proven to exist yet and doesn't actually seem necessary to explain anything, and the other bars useful communication because of the inevitable observer effect triggering a spin change when all you're trying to do is check for incoming signals.

And other not-really-FTL phenomena as mentioned in your linked article, such as the movement of shadows and abstract points or sound waves in materials of absolute rigidity.

Other methods can't be ruled out, of course, but the least out-there methods would be warp drive and wormholes, and perhaps quantum entanglement as a means of communication (if the inherent difficulties of making the travel systems work can be overcome, it's no more unreasonable to imagine the observer effect being circumvented).
Tachyons for communication is not a good idea, as tachyons arrive before they're transmitted. The longer the distance, the longer before they'll arrive.

I know we're in the business of sci-fi, and that means sometimes we just have to wave our hands vaguely around and step firmly into the realm of pseudoscience - it would be too restrictive otherwise. I just personally prefer to keep the use of 'handwavium' to the minimum amount necessary. :)
My intention with these elaborations are to tell the story, to the best of my ability, of what current physics predicts and what it does not predict.

And that's why true FTL and even near-light-velocity travel must be considered deeply impractical. Certainly, velocities of a significant fraction of C could be used; contrary to intuition, a trip made from Sol to Alpha Centauri at 75% of C wouldn't take just over 6 years for the travelers, as their local time slows down. It would seem significantly faster. From the viewpoint of Earth, though, it would seem like just over 6 years. This leads to time travel into the future, and is usually not what you want from an interstellar travel method. It's not terribly bad when dealing with a nearby star and a relatively low fraction of C, but increase either the distance or the velocity, and the time discrepancy will make the running of a functioning interstellar 'empire' impossible with any degree of cohesion. Breaking through the 'light barrier' (although manifestly not an option, unless everything we think we know is wrong) would complicate matters even more by mimicking the tachyon and arriving before you depart; time travel into the past. A travel method that keeps everyone in roughly the same time frame is necessary for creating a story which doesn't feel to alien to us humans, even if that's not how the universe really behaves.
We need something which can make the round-trip to Alpha Centauri in, say, 8 hours and arrive back at Earth 8 hours after departing, Earth-time as well as ship-time and Centauri-time.
It's always fun to throw some relativistic causality-violating stuff into a plot, but it's better if the general means of conveyance used doesn't produce paradoxes :)


Wed Jul 07, 2010 4:07 am
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