外星人Alien在哪？

外星人存在吗？ 目前这个问题人类还没有能力去回答，因为没有任何证据证明外星人存在！

但是根据费米脖论有10种猜想：

可能 1：超级智能可能已经造访过地球，但是那时候我们还不在。智能人（sentient humans）只存在了 5 万年左右，算不上什么。如果和外星智能的接触发生在人类之前，那发生了什么我们无从得知——有记录的人类历史只有 5500 年，在那之前就算发生了什么牛逼的接触也没有办法流传下来。

可能 2：银河系已经被殖民了，我们只是生活在一个荒芜的角落里而已。就好像欧洲国家殖民了美洲很久之后，加拿大北边的因纽特部落才知道这个事情。高等物种的城市化可能已经在周围几个恒星系发生了，这些相邻的恒星系已经被殖民并且有交流，那专程跑到悬臂的一个莫名的角落（太阳系所在）实在没什么意义。

可能 3：对于高等物种来说，物理殖民是个很落后的概念。还记不记得前面提到的 II 型文明能建造的戴森球？有了那么多的能源，他们完全可以给自己建造一个完美的生存环境。或者他们有很先进的办法来减少对资源的需求，从而没有理由离开自己生活的乌托邦去探索冰冷、空白、未开化的宇宙。

一个更高等的文明可能把物质世界看做很原始的存在。当他们战胜了自身的生理，然后把大脑上传到虚拟现实的永恒天堂之后，生活在物质世界就好像我们看待原始物种生活在暗无天日的深海中一样无趣。

可能 4：存在着很有攻击性的文明，绝大部分智能生命都好自为之，不向外广播自己的位置。也就是大家熟悉的黑暗森林理论，这也可以拿来解释为什么 SETI 生命信号都收不到。这同样表明向外发送信号的人类图森破，拿衣服。现在有关于 METI（Messaging to Extraterrestrial Intelligence，主动搜寻地外文明计划）的讨论，大部分人认为不应该做这个事情。霍金认为如果外星人造访我们，结果就会像哥伦布登陆美洲一样，对于美洲土著来说结果很糟糕。甚至是相信高等文明里面好人多的卡尔萨根也认为 METI 是很不明智很不成熟的，“初到新地方的小孩应该安静的倾听很久，耐心学习，然后再对着那未知的森林发声。”

可能 5：只存在一个高等智能生命——一个超级捕食者，一个比其他文明都要发达很多的文明，他们会消灭所有发展到了一定程度的文明。这是个很糟糕的可能性。消灭所有新生文明是很没有效率浪费资源的，很多新生文明自己就把自己玩死了，但是当一个文明越过了一定阶段后，超级文明就开始行动了。对于超级文明来说，一个新生的智能物种会像病毒一样成长和传播。这个理论表明第一个达成超级文明的种族会长赢下去，这也解释了为什么我们收不到任何信号。

可能 6：其实有很多活动和信号存在，只是我们的技术太原始，听到的都是错的东西。就好像我们走进一个现代化办公楼，然后打开一个对讲机，然后因为大家都是用手机和电脑的，所以你的对讲机什么都听不到，然后得出办公楼是空的这个结论。也可能如卡尔萨根所说，我们的大脑运作速度远远快过或者远远慢过别的文明，例如对方说一句你好要花 12 年，那我们接收到那个通讯的时候听上去就是白噪音罢了。

可能 7：我们已经和其它只能生命接触了，但是政府不让我们知道。这是个傻逼理论，列在这里纯粹是因为有很多人谈。

可能 8：高等文明知道我们的存在，并且在观测我们，就像观测动物园的动物一样。也就是说高等文明们存在于一个管制严格的星系，而地球是一个受保护的“国家公园”的一部分，对于这个“动物园”里面的我们，其他文明都要遵守一个“只能看不能摸”的规定。我们没有办法注意到观测者，因为如果一个远比我们聪明的物种想要观测我们，他们应该能很轻易的不让我们察觉到。就好像星际迷航里面的最高指导原则（Prime Directive）一样，超级智能生物不可以和人类这样的低等物种进行直接接触，直到人类发展到了一定程度为止。

可能 9：高等文明已经在我们身边了，但是我们太原始，以至于无法接触他们。物理学家加来道雄有这么个比喻：“比如说在森林中间有一座蚂蚁山，蚂蚁山旁边正在建造一条十车道的高速公路，蚂蚁会明白十车道高速公路是什么吗？蚂蚁会明白建造高速公路的技术，和建造公路的物种的意图吗？”

所以也许不是我们接收不到行星 X 发来的信号，而是我们根本不能理解行星 X 的生物是啥、想做什么。我们和对方的差距太远，就算对方想要给我们点指导，也会像教蚂蚁造高速公路一样没有意义。

这可能是对于“既然有那么多 III 型文明，为什么他们还没跟我们联系”这个问题的回答，当西班牙殖民者皮萨罗来到秘鲁的时候，他有没有停下来试图和蚂蚁山上的蚂蚁交流？他有没有帮助蚂蚁？他有没有对蚂蚁动武而延误他原本的使命？还是说，蚂蚁山上的蚂蚁，和皮萨罗完全、彻底、永远没有关系？

可能 10：我们对于现实的理解是完全错误的。有很多种可能性导致我们对于所有一切的想法都是错的。宇宙可能只是个投影，或者我们就是外星人，而只是被投放在地球做实验小白鼠的。甚至我们和黑客帝国里面一样，只是活在电脑的模拟现实中，而程序员忘了写其它物种的代码。

Here are 10:

Possibility 1) Super-intelligent life could very well have already visited Earth, but before we were here. In the scheme of things, sentient humans have only been around for about 50,000 years, a little blip of time. If contact happened before then, it might have made some ducks flip out and run into the water and that’s it. Further, recorded history only goes back 5,500 years—a group of ancient hunter-gatherer tribes may have experienced some crazy alien shit, but they had no good way to tell anyone in the future about it.

Possibility 2) The galaxy has been colonized, but we just live in some desolate rural area of the galaxy. The Americas may have been colonized by Europeans long before anyone in a small Inuit tribe in far northern Canada realized it had happened. There could be an urbanization component to the interstellar dwellings of higher species, in which all the neighboring solar systems in a certain area are colonized and in communication, and it would be impractical and purposeless for anyone to deal with coming all the way out to the random part of the spiral where we live.

Possibility 3) The entire concept of physical colonization is a hilariously backward concept to a more advanced species. Remember the picture of the Type II Civilization above with the sphere around their star? With all that energy, they might have created a perfect environment for themselves that satisfies their every need. They might have crazy-advanced ways of reducing their need for resources and zero interest in leaving their happy utopia to explore the cold, empty, undeveloped universe.

An even more advanced civilization might view the entire physical world as a horribly primitive place, having long ago conquered their own biology and uploaded their brains to a virtual reality, eternal-life paradise. Living in the physical world of biology, mortality, wants, and needs might seem to them the way we view primitive ocean species living in the frigid, dark sea. FYI, thinking about another life form having bested mortality makes me incredibly jealous and upset.

Possibility 4) There are scary predator civilizations out there, and most intelligent life knows better than to broadcast any outgoing signals and advertise their location. This is an unpleasant concept and would help explain the lack of any signals being received by the SETI satellites. It also means that we might be the super naive newbies who are being unbelievably stupid and risky by ever broadcasting outward signals. There’s a debate going on currently about whether we should engage in METI (Messaging to Extraterrestrial Intelligence—the reverse of SETI) or not, and most people say we should not. Stephen Hawking warns, “If aliens visit us, the outcome would be much as when Columbus landed in America, which didn’t turn out well for the Native Americans.” Even Carl Sagan (a general believer that any civilization advanced enough for interstellar travel would be altruistic, not hostile) called the practice of METI “deeply unwise and immature,” and recommended that “the newest children in a strange and uncertain cosmos should listen quietly for a long time, patiently learning about the universe and comparing notes, before shouting into an unknown jungle that we do not understand.” Scary.1

Possibility 5) There’s only one instance of higher-intelligent life—a “superpredator” civilization (like humans are here on Earth)—that is far more advanced than everyone else and keeps it that way by exterminating any intelligent civilization once they get past a certain level. This would suck. The way it might work is that it’s an inefficient use of resources to exterminate all emerging intelligences, maybe because most die out on their own. But past a certain point, the super beings make their move—because to them, an emerging intelligent species becomes like a virus as it starts to grow and spread. This theory suggests that whoever was the first in the galaxy to reach intelligence won, and now no one else has a chance. This would explain the lack of activity out there because it would keep the number of super-intelligent civilizations to just one.

Possibility 6) There’s plenty of activity and noise out there, but our technology is too primitive and we’re listening for the wrong things. Like walking into a modern-day office building, turning on a walkie-talkie, and when you hear no activity (which of course you wouldn’t hear because everyone’s texting, not using walkie-talkies), determining that the building must be empty. Or maybe, as Carl Sagan has pointed out, it could be that our minds work exponentially faster or slower than another form of intelligence out there—e.g. it takes them 12 years to say “Hello,” and when we hear that communication, it just sounds like white noise to us.

Possibility 7) We are receiving contact from other intelligent life, but the government is hiding it. The more I learn about the topic, the more this seems like an idiotic theory, but I had to mention it because it’s talked about so much.

Possibility 8) Higher civilizations are aware of us and observing us (AKA the “Zoo Hypothesis”). As far as we know, super-intelligent civilizations exist in a tightly-regulated galaxy, and our Earth is treated like part of a vast and protected national park, with a strict “Look but don’t touch” rule for planets like ours. We wouldn’t notice them, because if a far smarter species wanted to observe us, it would know how to easily do so without us realizing it. Maybe there’s a rule similar to the Star Trek’s “Prime Directive” which prohibits super-intelligent beings from making any open contact with lesser species like us or revealing themselves in any way, until the lesser species has reached a certain level of intelligence.

Possibility 9) Higher civilizations are here, all around us. But we’re too primitive to perceive them. Michio Kaku sums it up like this:

Let’s say we have an anthill in the middle of the forest. And right next to the anthill, they’re building a ten-lane super-highway. And the question is “Would the ants be able to understand what a ten-lane super-highway is? Would the ants be able to understand the technology and the intentions of the beings building the highway next to them?”

So it’s not that we can’t pick up the signals from Planet X using our technology, it’s that we can’t even comprehend what the beings from Planet X are or what they’re trying to do. It’s so beyond us that even if they really wanted to enlighten us, it would be like trying to teach ants about the internet.

Along those lines, this may also be an answer to “Well if there are so many fancy Type III Civilizations, why haven’t they contacted us yet?” To answer that, let’s ask ourselves—when Pizarro made his way into Peru, did he stop for a while at an anthill to try to communicate? Was he magnanimous, trying to help the ants in the anthill? Did he become hostile and slow his original mission down in order to smash the anthill apart? Or was the anthill of complete and utter and eternal irrelevance to Pizarro? That might be our situation here.

Possibility 10) We’re completely wrong about our reality. There are a lot of ways we could just be totally off with everything we think. The universe might appear one way and be something else entirely, like a hologram. Or maybe we’re the aliens and we were planted here as an experiment or as a form of fertilizer. There’s even a chance that we’re all part of a computer simulation by some researcher from another world, and other forms of life simply weren’t programmed into the simulation.