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[Urist Tilaturist]

Thats... pretty much exactly what most of the "harder" half of Science Fiction is designed to do, i.e. to take partial explanations of science, extrapolate things to fill in the gaps, and then give them as explanations. Mohs Scale of Science Fiction Hardness exists specifically to differentiate the "softer" works that basically boil down to "magic, but dressed up as technology", to more "medium" works that give some sort of explanation (be it logical or not), to "harder" ones that actual follow totally real science of the point when they were written.

Which brings up another point, in that there is tons of stories out there who's explanations were totally consistent when they were written, but have been shown to be impossible since that date. Are we proposing to suddenly ban all the books that fall into that category if science ever evolves to the point where it shows their explanations are impossible and they are now "misusing [...] real scientific terms"? You state that you want to "keep the divide between truth and fiction clear", but the a major "point" of science fiction, is to do exactly the opposite, and to ask "what if" questions that specifically blur the boundaries.

I would make an exception for works written at a time where the dubious science was thought to be a real possibility. That would excuse writers like HG Wells, Jules Verne and possibly even the writers of that tachyon engine, since that was a few decades ago. I did not know how old it was.

Were tachyons moving faster than light thought to be possible in the 1970s? Relativity was well established by then.

[Sergarr]

What if we raise the speed of light?

Not possible without another Big Bang, I'm afraid.

Nothing is impossible. Not if you can imagine it. That's what being is a scientist is all about.

Where did I said that it was impossible? It just requires Big Bang-levels of energy concentration.

Thats... pretty much exactly what most of the "harder" half of Science Fiction is designed to do, i.e. to take partial explanations of science, extrapolate things to fill in the gaps, and then give them as explanations. Mohs Scale of Science Fiction Hardness exists specifically to differentiate the "softer" works that basically boil down to "magic, but dressed up as technology", to more "medium" works that give some sort of explanation (be it logical or not), to "harder" ones that actual follow totally real science of the point when they were written.

Which brings up another point, in that there is tons of stories out there who's explanations were totally consistent when they were written, but have been shown to be impossible since that date. Are we proposing to suddenly ban all the books that fall into that category if science ever evolves to the point where it shows their explanations are impossible and they are now "misusing [...] real scientific terms"? You state that you want to "keep the divide between truth and fiction clear", but the a major "point" of science fiction, is to do exactly the opposite, and to ask "what if" questions that specifically blur the boundaries.

I would make an exception for works written at a time where the dubious science was thought to be a real possibility. That would excuse writers like HG Wells, Jules Verne and possibly even the writers of that tachyon engine, since that was a few decades ago. I did not know how old it was.

Were tachyons moving faster than light thought to be possible in the 1970s? Relativity was well established by then.

http://en.wikipedia.org/wiki/Tachyon

"A tachyon /ˈtæki.ɒn/ or tachyonic particle is a hypothetical particle that always moves faster than light."

Tachyons are by definition particles moving faster-than-light.

EDIT: http://en.wikipedia.org/wiki/Tachyonic_field
Ah, so that's what you're referring to.

[i2amroy]

The idea of tachyons, particles that always moved faster than light, was coined by Gerald Feinberg in his paper that he published in 1967, though the particle was first theorized in a 1962 paper. I don't claim to understand what his reasoning was behind it or what theories he used to back up his ideas, I'm not a physicist as Feinberg was.

[10ebbor10]

For relativistic particles, this law applies.

E = (mc^2)/sqrt(1 - (v^2)/(c^2))

Since energy must be a real number this means if the bottom part of the equitation is imaginary, then the rest mass be as well.

[i2amroy]

Yep, don't think anyone in the thread is debating that any actual tachyonic particle would need to have imaginary mass.

[Urist Tilaturist]

The article on the tachyonic field says that the idea that they could possibly go faster than light was proposed in 1967, but was "very soon" disproved. The question is, how soon is "very soon"? It is feasible that during the brief period when it was thought possible, the fictional space engine was designed, in which case it is spared by the grandfather clause I gave earlier (if the science was plausible at the time of writing, it is acceptable to use real scientific terms).

[i2amroy]

The show first aired in late 1974, though it obviously would have been in planning before it. Don't forget to account for the fact that it's a Japanese show, so you'd need to account for any translation time needed in the scientific concepts (assuming we are thinking that the group of manga artists that came up with the idea actually bothered to follow the recent cutting edge trends in physics, which personally I find a bit of a silly idea ).

[wierd]

Thats... pretty much exactly what most of the "harder" half of Science Fiction is designed to do, i.e. to take partial explanations of science, extrapolate things to fill in the gaps, and then give them as explanations. Mohs Scale of Science Fiction Hardness exists specifically to differentiate the "softer" works that basically boil down to "magic, but dressed up as technology", to more "medium" works that give some sort of explanation (be it logical or not), to "harder" ones that actual follow totally real science of the point when they were written.

Which brings up another point, in that there is tons of stories out there who's explanations were totally consistent when they were written, but have been shown to be impossible since that date. Are we proposing to suddenly ban all the books that fall into that category if science ever evolves to the point where it shows their explanations are impossible and they are now "misusing [...] real scientific terms"? You state that you want to "keep the divide between truth and fiction clear", but the a major "point" of science fiction, is to do exactly the opposite, and to ask "what if" questions that specifically blur the boundaries.

I would make an exception for works written at a time where the dubious science was thought to be a real possibility. That would excuse writers like HG Wells, Jules Verne and possibly even the writers of that tachyon engine, since that was a few decades ago. I did not know how old it was.

Were tachyons moving faster than light thought to be possible in the 1970s? Relativity was well established by then.

Tachyons came about BECAUSE of relativity.  Just an FYI, but no actual particle has ever been detected that satisfies their hypothetical basis---

That said, what a tachyon is, is a particle which, at the very moment of its creation, is traveling faster than light speed. It thus will experience a unique phenomena (mathematically) where it has "Inverse time". 

Normally, a massed particle approaching light speed will have time dilate, and time for that object slows down. When the object reaches light speed (Impossible mathematically, but let's nod our heads a moment), all time for that object stops.  But what happens if you were able to go faster? Time continues to dilate, and becomes negative! This is one of the reasons why tachyons could theoretically be used to create a device capable of sending a message into the past.

To overcome the "Requires infinnite energy" problem, some clever theorists have proposed "Imaginary mass" as a possible means of particles like this to "maybe" exist.

http://en.wikipedia.org/wiki/Tachyonic_field

What is 'Imaginary mass'?  In this case, it is a massed particle with a negative mass quanta. EG, instead of getting "Stuck" to the higgs field, it instead gets more slippery; instead of being attracted to gravity wells, it is repelled by them.  However, such particles will also exhibit negative inertia.  Negative mass quanta turn special relativity on its head, and results in some very novel math, but as the wikipedia article points out, these particles are not stable, and cannot achieve superluminal velocity, since they will instead spontaneously decay into more stable, properly massed or massless particles as their energy increases from interaction with gravity fields.

Related to this idea of "imaginary Mass" is the Alcubierre warp drive.
http://en.wikipedia.org/wiki/Alcubierre_drive

In this example, a pocket of spacetime is towed around by the action of a normal mass ineration (Gravity well) chasing after an imaginary mass interaction (inverted gravity well), with a neutral frame between.

However, the alcuibierre drive requires the exotic imaginary massed particles mentioned previously to create this forward facing inverse gravity well. It also becomes a subject of quantum tunnelling and a number of other curious things when examined riggorously. Should such a device be actually possible to construct, it would not be a pretty thing to see a ship powered by it drop out of warp. A tremendous energy build up would develop around the warp field, which would decay in a massive flash of highly energetic particles. Some estimates place the intensity of this discharge as being stronger than a supernova explosion.

The short in of the stick:

Tachyons have not been observed scientifically, and the mathematical basis they were postulated from says that if they exist, they are highly unstable.  They are typically regarded as being impossible, because they would induce causality violations simply from existing. (So, either they exist and the universe is not causally connected, or they dont exist because the universe is causally connected.)

I personally dont think that devices like Alcuibierre's warp drive can function, owing to the requirement of exotic matter that does not appear to be stable in our universe.

I am much more inclined to look at curious devices like the "em-drive", which while always being sublight, are reactionless. Unlike the alcuibierre drive, there are head-scratching, real-world examples of this phenomena.
http://en.wikipedia.org/wiki/EmDrive

This device makes use of the quantum vacuum's propensity to create charged antiparticle pairs, which can be accelerated using a strong magnetic field. This means that stable particles can have a change in momentum by conveying energy to the unstable virtual particle pairs via this electromagnetic interaction.   There have been a few rigorous tests of this technology, which caused a great deal of scoffing and not-nice things to be said, because it was popularly derided as snake-oil by the physics community- however, those tests have consistently revealed an impulse, which is of interest.  It may not operate under the proprosed method, but when all you want it for is generating an impulse, how it generates that impulse is a secondary concern. That it DOES generate one is what is of real interest.

The em-drive will *NEVER* achieve FTL-- but you dont NEED FTL, if you can get a significant fraction of C over the course of your voyage by having constant acelleration.  (Once you go a significant fraction of C, time for you slows down to non-trivial levels, and while your voyage still takes hundreds of thousands of years outside time, does not take nearly that much relativistic time for you inside the vehicle.) Slap enough of these bad boys on a huge fusion reactor, and off you go.

[Urist Tilaturist]

Why? Any interstellar journeys are fairly likely to be one way given the time and energy requirements, so it makes absolutely no difference if everybody is dead back home. The spacecraft crew will never go home to find out.

All this tachyon stuff seems rather unlikely - I doubt anything with imaginary mass can exist - but I thought that quantum theory had proven that the universe was not absolutely causally linked - or is this still largely contested?

[wierd]

That is not a rational statement.  According to that mode of thought, slime molds shouldn't exist:

A sime mold is propelled forward by its metabolic activity. It leaves a nutritionally denuded environment in its wake. Taken to the fullest, your argument could be applied here: There is no point for the slime mold to move forward, if the material it leaves behind dies.

Clearly, this argument is false, as slime molds exist, and it is a viable survival stratagem.


Your argument relies on a baseless conjecture that the ONLY reason to explore space is to bring things back to earth.  Abandoning the earth is a viable solution. There is no reason whatsoever to hold that all resources must be returned to the epicenter of human expansion. In fact, that mode of thought is not logical, even with FTL thrown in- Bringing energy and resources back to earth will upset the earth's equilibrium. If you think climate scientists are screaming NOW..... Just wait to see what they would be doing if you were bringing back huge chunks of exo-planet with you to satisfy greedy humans in the future.

Even if we limit what is brought back to being merely information, we still have a top limit threshold of what the earth could endure, and what all available communications mediums are able to handle before saturating. This would impose a top limit on the size of human civilization.  EG-- At some point, the simple energy of everyone calling home to grandma with their coms arrays pointed at the Sol system, would irradiate the sol system with enough energy to kill all life in the system.  Long before then, the ability to effectively seperate individual broadcasts into intelligable data streams and not just noise, would long be exceeded, posing another significant limit.

Even if we say that all messages are hand delivered using FTL ships, humanity's use of exo-planetary materials to produce FTL capable ships means that at some point, the mere traffic in and out of the sol system would present a significant issue on the orbits of the planets in the sol system.

No.  I would say that your pre-condition is the thing that has no point.

[Urist Tilaturist]

I agree with wierd mostly. Why does it matter if everyone on Earth is dead if the spacecraft crew are not on Earth?

[wierd]

Why does the colony ship need that many people on board?

5000 humans, with frozen sperm and egg (Or better yet, genetic data in digital form with equipment to synthesize whole genomes on the fly from that data) is more than adequate to supply sufficient genetic diversity to a human colony vessel.

We could send several of these every year, and not outpace human reproductive rates on the global scale. Earth's population could be held static at some 7bn people, and still be sending colony ships as a yearly event.

The issue is getting the resources to send the humans on their way. The earth is a finite ball of resources. Ships that go one way (away from earth) would result in the earth's resource pool shrinking over time.

If however, we expanded the scope to the whole of the sol system, then we have a considerable reserve of material in the kuiper belt and oort cloud that we can make use of.

[ShadowHammer]

In addition to this^, the Sun will die eventually anyway and kill the Earth with fire when it does, so getting any eggs into any basket by the time that happens is better than dying here along with the Solar System.

[Urist Tilaturist]

Ispil, you are assuming that mankind is working together for this, and that we are important to it. As if there is a "we" of 7 billion that means anything for practical purposes. Why could it not be a crazy billionaire and his army of clone/robot retainers, who really do not give a damn about the rest of us? No colony ships, just a new genetically engineered/bio-mechanical race somewhere very far away and having no effect on us.

[BurnedToast]

I am much more inclined to look at curious devices like the "em-drive", which while always being sublight, are reactionless. Unlike the alcuibierre drive, there are head-scratching, real-world examples of this phenomena.
http://en.wikipedia.org/wiki/EmDrive

This device makes use of the quantum vacuum's propensity to create charged antiparticle pairs, which can be accelerated using a strong magnetic field. This means that stable particles can have a change in momentum by conveying energy to the unstable virtual particle pairs via this electromagnetic interaction.   There have been a few rigorous tests of this technology, which caused a great deal of scoffing and not-nice things to be said, because it was popularly derided as snake-oil by the physics community- however, those tests have consistently revealed an impulse, which is of interest.  It may not operate under the proprosed method, but when all you want it for is generating an impulse, how it generates that impulse is a secondary concern. That it DOES generate one is what is of real interest.

The EM drive has not been conclusively proven to work, and (imo anyway) probably is snake oil. The "nasa test" was really flawed... and produced a comparable amount of thrust in the "null test article" which should not have produced any at all. It's actually pretty shameful how poor a job they did testing it.

The em-drive will *NEVER* achieve FTL-- but you dont NEED FTL, if you can get a significant fraction of C over the course of your voyage by having constant acelleration.  (Once you go a significant fraction of C, time for you slows down to non-trivial levels, and while your voyage still takes hundreds of thousands of years outside time, does not take nearly that much relativistic time for you inside the vehicle.) Slap enough of these bad boys on a huge fusion reactor, and off you go.

This is completely impractical. I started to do the math but it was just completely absurd.

The energy required to accelerate even a single human (ignoring the need for a spaceship and supplies) to the required speeds to compress 100,000 years, or even 10,000 years into a single human lifespan even with a 100% efficient reactionless drive is just utterly impractical... not even "impractical right now but maybe in the future..." but "impractical unless we manage to break physics somehow".