In Star Trek why is warp speed the ultimate litmus test on "galactic acceptance" of a civilisation?

Star Trek really was not utopia; it may have had the appearance on the surface but we saw beneath that surface to the ugly truth of human nature many times on all the series.

The Prime Directive is not entirely sacrosanct; it gets violated on many occasions but that's neither here nor now. The simplest explanation is the fact that once a civilization achieves warp flight you are going to encounter them or they are going to encounter you it is not really about "enlightenment" it is about the maximum amount of time you can reasonably put off meeting the new neighbors.

On a broader scope, it's about not influencing development, would humans have achieved their "utopia" if the Vulcans had contacted Earth in the 1970s or did the human civilization require forging in the fires of WW3 to be ready to unify?

To be a tad cynical, it's also about covering the Federations a** if something goes wrong, there was an episode of Voyager where a pre Federation probe led to a population annihilating itself with anti-matter warheads.

Strangely, it appears that if a civilisation was part of the Federation, and/or had enough ties with the Federation (which ostensibly MUST have involved warp speed and first contact initiated by the "new" civilisation) ...then that civilisation is deemed to be "acceptable for co-operation", if you get my drift.

I'm not certain what you meant by that part of your question.

I think you’re misinterpreting the Prime Directive. (It’s not actually written down in any official Star Trek work, so any discussion of it is necessarily going to be a bit vague.)

The Prime Directive is, in part, intended to prevent Starfleet from visiting less-advanced civilisations and dicking around with their development, whether for fun, profit, or just simply by accident. Before a civilisation has warp speed, they’re not likely to encounter Starfleet on their own in practice. Once they do have warp speed, they’ll likely meet their galactic neighbours soon anyway, so it’s a good time for Starfleet to go say hi, and attempt to make friends on behalf of the Federation (which is, basically, Starfleet’s mission).

But the Prime Directive is not designed to assess whether civilisations are “acceptable for co-operation” by the Federation. The Federation basically wants to have co-operative diplomatic relations with pretty much anyone — it’s what they do, and it’s part of the utopian vision of Star Trek.

It’s impractical to do that when you can travel faster than light and they can’t, but that doesn’t mean that every civilisation with warp drive is going to be nice, or unified, or friendly to the Federation.

And bear in mind that the Prime Directive forbids interference in the internal affairs of any other civilisation, warp-capable or not — for example, Picard cites it when briefing Sisko on his mission to help bring Bajor into the Federation.

Kirk: Er, well, sir, volatile is all relative. Maybe our data was off..
Pike: Or maybe it didn't erupt because Mister Spock detonated a cold fusion device inside it right after a civilisation that's barely invented the wheel happened to see a starship rising out of their ocean. That is pretty much how you describe it, is it not?
_{(Star Trek Into Darkness)}

The Prime Directive has been established to give natural evolution of a species freedom and space. Growing up too fast can be disastrous for natural evolutionary processes as Picard pointed out:

The Prime Directive is not just a set of rules; it is a philosophy... and a very correct one. History has proven again and again that whenever mankind interferes with a less developed civilization, no matter how well intentioned that interference may be, the results are invariably disastrous.
- Picard

Why Warp Drive as a litmus test?
Because invention of warp drive by an species denotes that the time has come for natural evolutionary processes to reap the fruit of millions of years of hard work. It means, they are ready to exchange technologies with other advanced species based on their own evolutionary track. Look at it carefully: They have got warp drive and even if you don't meet them first, they are going to meet someone out there (so why not you make the First Contact first and maybe give them some guidance for their upcoming adventure). Also, when you see some species with warp drive, it is assumed that they have already made contact with other species, so making First Contact with them should be easy.

Warp Drive shouldn't be assumed as indication of some moral quality or wisdom
Klingons love to war and Romulans were a**holes to cripple regional peace and all of the wars between warp drive species indicates that warp drive can't be indication of spiritual wisdom when you won't misuse advanced technologies.
When mankind invented the warp drive, Earth's atmosphere had high amounts of radiations (thanks to 3rd World War) which Vulcans could easily detect. But, Vulcans helped Earth get to its feet and have a stable government because with warp drive a violent neighbor can create problems. Better if you make them friends.

In the episode First Contact, Riker is on a planet that is finishing its warp drive. Eventually, Picard meets with the president, and explains that in spite of their other advances, the ability to visit new life is both a wonderful and scary decision. The president ultimately decides to scrap the project, because people are so scared of the extra-terrestrials and unknowns and still so religion-dependent that to attempt to contact other species now would be disastrous. It could be argued that warp speed was achieved in that episode, so first contact was made. But first contact was made before it was finished, to view and possibly deter the current status quo.

While other answers are right to point out the fact that once a species has warp capability, they're going to be meeting other species no matter what, there's also the idea that warp capability is supposed to be a big achievement, one that is only likely to happen once a civilization has united as a single planet, so it's somewhat used as a bar to gauge the level of social advancement too.

I wish I had a reference, but I'm sure I remember that argument being made by Picard or someone during some episode (there are so many).

A work of science fiction like Star Trek that supposes the galaxy to be densely populated with intelligent beings capable of interstellar travel needs to offer an answer to the question, "why didn't they visit Earth earlier?" (The "Fermi paradox".)

The SF Encyclopedia discusses a number of common ways in which science fiction writers answer this question, including:

4. Aliens are indeed frequent visitors to our solar system but choose to conceal themselves, as in [...] the many stories in which humanity is not yet deemed fit to be told of and initiated into galactic society. Examples of the latter trope include Robert A Heinlein's Have Space Suit – Will Travel (August-October 1958 F&SF; 1958), Lloyd Biggle Jr's All the Colors of Darkness (1963), Clifford D Simak's Way Station (June-August 1963 Galaxy as "Here Gather the Stars"; 1963) and Frederik Pohl's Narabedla Ltd (1988).

This is much the most optimistic of the scenarios: other applicable answers include:

3. The universe is a highly dangerous place in which any civilization drawing attention to itself is liable to be snuffed out [...]

5. Humanity is abhorred and shunned [...]

8. The aliens are so very different that they do not recognize us, nor we them, as sentient beings. [...]

It's easy to see why in the mostly optimistic Star Trek setting the writers chose to use this trope rather than one of the others.

Let's say that a species believes in the concept of FTL, however, like our own do not know how to achieve it. Meeting an advanced civilization may give them the clues on how to do it. That would be one of the first reasons that interactions with a less advanced planet could be problematic.

Alternatively, let's say that a more aggressive species achieves warp capability by themselves. This means that there is the possibility of creating war on other neighboring planets. Having Warp 1 does not give you much capability but a more advanced species can 'spot' the warp signature and then decide whether that species is a threat to others. And if so take appropriate action re limiting their capabilities. One way would be to disrupt the subspace around their star system so that warp drive is not possible - thus quarantining them.

The premise of your question isn't really true. If you watch the various series and movies, you'll see that the Federation has dealings with many, many, many starfaring races that are manipulative, greedy, or warlike. Contact isn't a function of moral purity, good behavior, good government, or anything like that. Due to the Federation's peaceful philosophy, they will offer diplomatic and trade relationships to pretty much anyone, only going to war in the face of a very serious threat. Species wanting Federation membership are held to a higher standard, but that has nothing to do with the Prime Directive or the achievement of warp technology.

So given this general willingness to deal peacefully with pretty much anyone, what is the purpose of the Prime Directive? It's to prevent relationships that could become exploitative and dangerous due to the huge disparity in power between the Federation and a planetbound society. In particular, the scenario in A Private Little War, where the people of a primitive society become pawns in a proxy war between the Federation and the Klingons, is what they hope to avoid with the Prime Directive.

So why use the achievement of warp flight as the yardstick of who to contact? It seems a bit arbitrary, and from the point of view of the Federation, it probably also seems a bit insufficient. An early warp civilization isn't really going to be able to negotiate on equal terms with the rest of the Federation. But others here have already hit on the answer — as long as a species keeps to their own star system, they aren't going to encounter any aliens as long as everyone else keeps to the Prime Directive. But as soon as they discover warp and go exploring, the cat is out of the bag. They're going to run into their neighbors, so it's best to contact them in an organized manner and let them handle the surprise as gracefully as possible.

Finally, from an out-of-universe perspective, the Prime Directive gives a good explanation of how present-day humanity could be living in a galaxy as full of alien life as the Star Trek one is, and yet not have encountered any of them. It's not that they aren't out there, it's that they're deliberately keeping away.

I think one point has been missed in this thread, but I'm no Trekkie. I do know for sure that Earth's first contact was made due to the Vulkan's detection of a warp signature (what movie was that in?). I also know for a fact that in the TV show Enterprise that T'Pol tells Archer that that is Vulkan policy, but I don't know when the idea first appeared. I know Kirk & company expressed a similar Prime Directive, but I don't recall if it was specific about Warp 1 (1?) being the criteria for contact. Anyway, my point is that the decision to continue the Vulkan tradition may have been a pure political decision in the politics of founding the Federation. The only (apparent) logical reason for it is that warp signatures are easily detected light years away. The Star Trek Universe isn't particularly a consistent Universe.

I'll look at this from two angles.

The first is setting the bar. Obviously, you need some form of measurement for the prime Directive to work. Achieveing FTL travel is something that is not debatable. its a clear-cut, simple rule to follow. There are no interpretations posssible. Its quite clear wether you violate the prime Directive or not.

That makes it usable in the field. Captains can easily see wether the Prime Directive applies or not. If you take anything less clear, it opens room for interpretation. Are they advanced enough? have they demonstrated their worthß What if the Capatain determines they have, but later Starfleet decides that was wrong? Its a hassle. So they stick to simple, easy to check and easy to enforce rule.

The other thing is that moving the bar just means moving the bar. Lets say you take something else, like developing writing. Then the same question on SE would be "Why is writing considered the bar for the Prime Directive"? It doesn't fundamentally change anything, other then moving the bar.

Lets view my second angle. The Prime Directive is about the impact the Federation has on the development of a species and society. Once they achieve FTL travel, it is only a matter of time before they meet other species. There is no longer any harm to their development by introducing yourself to them.

The other alternative would be to let them chase you for a tiny while. But at the point at which they achieve FTL travel, they will most likely try to seek out new life and new civilizations themselves (thats the point of FTL travel, isn't it?). You only help them do that. You no longer influence their natural development. You might speed it up a bit since they find you a bit earlier.

So, why not introduce yourself when they are clearly on the track to develop FTL travel? Well, that goes back to my first point. You need to draw the line somewhere. And what "close to achieve FTL travel" actually is is open for debate in each case and difficult to decide. Seeing them do an FTL flight is absolutely and unmistakenly clear.

So, its not about being "enlightened" at all. Its purely practical. A civilization that has FTL travel will encounter other species anyways (rather sooner then later), and its an easy measure for captains out in the field to follow. Its about technological advancement of the species, not moral/ethical/cultural (but it sometimes is implied that FTL travel somewhat also means cultural advancement for most species).

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Another thing to consider is that the Fedaration is peacefully and not dead set on expansion. They will include new members if those memebers ask for it and achieve high enough standards for doing so - but the Federation does not actively conquer systems. The Prime Directive prevents them from just overtaking lesser developed planets. It show non-agression, especially towards the more agressive species like Klingons and Romulans. It can be used very effectively as a political/diplomatic tool.

A couple of things here:

• Some civilizations and species are capable to travel between star systems without warp drive, per se. For instance, Q.
• Some civilizations may develop communications systems - subspace radio - before they develop warp drive itself.

However, warp drive definitely precipitates the need for contact. "You're now in Federation space. Stay in your lane." I am sure that any other FTL, or slower-than-light-speed, but interstellar spacefaring would also qualify for consideration.

I am not sure warp drive needs to be developed prior to first contact or Federation membership. I am certain that if a species developed subspace radio, and was listening in to the chatter going on around them, the Federation wouldn't freeze in place and go radio silence on them. "Shh! Just ignore that developing race! Uhm... so, Uhura, you were telling me about the space probe..."

There's also the issue of having multiple races within the same solar system. What if one can do FTL, but not the other?

A good hypothetical thread on this was posted on Reddit back in 2010.

The point of once you achieve warp speed you're going to meet people anyway is perfectly valid, but I wish to add to that.

It is a statement about your culture as a whole, to be ready for first contact.

Just think of the beliefs we had to discard to get us this far, Galileo had to disprove that we are at the center of the universe. Dozens of other things, horses had to be eliminated as a means of travel, so our cities could grow to their current sizes.

Achieving light speed is no trivial task, a task we have yet to achieve. We are not even close to achieving that goal. Our best effort, VASMIR, is like 10% of the speed of light best case and even that has issues.

https://en.wikipedia.org/wiki/Variable_Specific_Impulse_Magnetoplasma_Rocket

https://arstechnica.com/science/2017/02/nasas-longshot-bet-on-a-revolutionary-rocket-may-be-about-to-pay-off/

A civilization that makes it that far probably has a single global government, or a couple at most. Also most superstitions have probably been cast aside by the time your reach that goal. Reaching light speed requires global cooperation for many years to achieve. Many scientists from all over our world have been working to exceed the speed of light, and we still can't do it.

Einstein's formula suggests that energy is converted to mass, thus light speed is the fastest you can go. Except for the wormhole thing. Our understanding of nature is still very limited, and much needs to be learned. The fact we just discovered dark matter/energy proves how little we know. Either dark things exist or our understanding of the universe is so fundamentally flawed we had to invent it to cover our ignorance. We still can't reconcile the world of the atomic with the sub atomic quantum world. Black holes also cause our science issues as they meld both in the same place.

From an education stand point, the dumbest person is still going to be relatively smart given how the top end of society understands how to exceed warp speed.

At the point you can achieve warp speed your culture has probably had all the world wars your going to have, and probably aren't going to blow yourself up and end up going extinct. If your working on warp speed, your people probably already have some kind of first contact plan in place. You have probably also solved poverty, and other issues that plague lower civilizations.

Think about earth; if I were an alien who was listening in on our planet I would not want to have to deal with the 130+ different governments found throughout our planet just to get something done. Imagine aliens make first contact with the US, and give us technology; now the rest of the world become paranoid, we are going to attack them. Imagine tomorrow we could build the Enterprise, we could do attack any country from space. Countries like North Korea and others might even attack the aliens to chase them away. Mentality like "if we can't have it, neither can you have it" needs to be eliminated.

It is also a statement on the viability of your economy, just look at http://www.buildtheenterprise.org ; we at no other point in history could even think of affording such a project. Billions of dollars for 20+ years to build the Enterprise. Also the secondary technological inventions needed for such a project would affect everyone. Just look at the technologies the US invented just to land a person on the moon, and how that affected our society as a whole.

The Prime Directive, as it concerns first contact (there are other situations where a Prime Directive applies, such as time travel), is designed to prevent outside influence on a civilisation which could damage it. Usually this is done by limiting access to their star system(s).

Faster-than-light travel is the usual criterion because at that point a civilisation cannot be prevented anymore to meet other species, and it's not possible to pretend anymore that they are alone. The same probably applies

• they develop a transwarp drive, construct wormholes, intercept subspace communications, or other stuff like that. It's likely though that they develop the warp drive first because those technologies seem far more challenging and therefore rare. *
  • if it is known that they already made contact. As far as I know, the Federation is pretty unique in having this directive. The Borg seem to be the only ones ignoring (most) pre-warp civilisations because most of the time their knowledge and technology are not very interesting to them.

As some other answerers have indicated, in principle it applies to all civilisations. This puts firm limits upon any imperialistic policy of the Federation by making it unconstitutional.

There are some corner case where the rule is applied differently:

• When the Voyager encountered the world ship of a civilisation fleeing from their doomed star system, the Prime Directive was ignored since that civilisation would have been wiped out otherwise.
• If a ship without FTL drive reached a planet outside their home system(s), that planet would be declared off-limits. Contact would be established only if the planet is inhabited, because at that point it's not possible to pretend anymore that there are no other civilisations.

It would be interesting to discuss what the Federation would do if they asked for any aliens to come by and establish contact :-D

* Anyways, they tend to completely unbalance a setting if not nerfed properly because the galaxy would turn into a village where everyone could just show up and drop quantum singularities into sun cores.

Apparently the Federation didn't have any first contact protocols in place originally. As I understand it in a TNG episode, Picard explains the reasons for the protocols for establishing first contact with an alien civilization. As Picard ended up explaining that first contact with the Klingons didn't go all that well and lead to war. It isn't mentioned concerning the Romulans who are also hostile, but I'm sure it didn't help either. And the fact that the Federation had a war with them quite early in the Federation's history. So the Federation decided to use the methods that the Vulcan's had great success with. Which was to gage an alien civilization's maturity by whether or not they had developed a means of FTL. The Vulcan's were quite influential to the Earth's continued development of the warp drive after first contact was made. So it stands to reason that they would have been just as influential in the Federation after it developed. Whether or not the Prime directive was in place when the Federation was formed is unknown. I can see the Prime directive being formed around the same time as the first contact protocols. Once again the Vulcan's were most likely the source for the Prime Directive which was how they dealt with primitive alien civilizations.

Well, development of Warp Drive implies that a civilization reached a technological and social level where it seems that it could be capable of 'coping' with the realities of other alien civilizations existing... but as it was seen in TNG episode 'First Contact' (yes, TNG episode, not the movie with the same title), an alien society sometimes reaches the ability for Warp travel sooner than social development has reached a point that a civilization might cope with other space faring races.

This is also somewhat seen in the movie First Contact. Humanity barely emerged from a global war, but Vulcans detected the Phoenix and decided to pay us a visit. And while they did visit Earth in the past (ENT Carbon Creek), there was no indication they visited Earth since then... so they may have thought Humanity finally evolved sufficiently with development of Warp drive... but once landing on Earth they discovered that Humanity barely emerged from a Third World War... and was apparently starting (barely) to make changes to recover - it was also one of the reasons why they hadn't exactly shared technology with Humanity nor deemed them ready to join the wider interstellar community (albeit Humanity DID eradicate war, poverty and disease in 50 years following First Contact with the Vulcans - so Humanity was 'technically' a lot more prepared to join the interstellar community 50 years after First Contact compared to right when they made First Contact with the Vulcans - but Vulcans were still skeptical and they kept Humanity under a 'tight leash' at least for the next 40 years - until the launch of NX-01).

I suspect that this also led Starfleet to adopt more precautions to examine a society on a social level (just prior to that society launching their first Warp ship) to see if they would be able to cope with realities of space travel and other alien species. The Malkorians (sadly) did not exhibit that they were ready.

However, generally speaking, once a society develops Warp technology and is capable of Warp flight, they seem to be able to cope with the concept of other alien cultures and basic interaction/dialogue.

On the other hand, a society can be pre-Warp but socially developed to the point where they wouldn't have issues in accepting other alien life at all. We've seen this happen in Enterprise episode Dear Doctor.

In TNG however, there may be 1 example in the episode Who Watches the Watchers with the Mintakans. Granted, Starfleet's accidental exposure and displays of technology shocked a Mintakan and being severely pre-industrial even, they had no immediate frame of reference so he resorted to religious explanation (as did others once he spread that concept).

However, because the Mintakans also adopted a more rational/logical approach to life (unlike most other species) and abandoned superstition and religion early in their development, Picard was (eventually) able to explain who and what they were, and in the end, the Mintakans were able to understand (and accept Picard for who and what he was).