物理与天文2021arxiv.org
外星文明不可探测的量子计算与通信
Undetectable quantum computation and communication for alien civilizations
入门 · 约 45 分钟读完前置知识：量子纠缠基础、量子通信基础
导读
这篇论文探讨外星文明是否可能利用量子计算与量子通信，且其通信信号在观测上与噪声无法区分。作者指出分布式量子计算所需的经典通信只传输纯随机结果，因此即使存在也难以被识别为智慧信号。
HN 关注点：对费米悖论/SETI 的另类解释：外星文明可能存在但使用我们无法探测的通信方式。
HN 评论精选
这几条评论里：质疑 2 补充 2
补充外星文明可能早已弃用电磁通信，我们探测不到是因为我们只盯着过时的技术窗口
我一直认为，考虑到宇宙中天体数量之巨，存在先进文明几乎是必然的，而探测不到光通信意味着：外星文明已经找到了远胜于电磁波的通信方式，因此放弃了电磁手段。思想实验是：如果我们发现了某种远超现有方式的通信手段，我们大概也会弃用光通信。如果我们把新的'天线'对准太空，发现成千上万个文明在用新方式交流，我们还会再用电磁波吗？这意味着每个文明使用电磁通信的时间只是从发现电磁通信到发现'新机制'之间的窗口期。目前还在用电磁通信的外星文明，只是恰好处于这个窗口期内的少数，其比例约等于（该窗口期的平均时长）除以（文明的平均年龄）。这就像地球上还在用烟雾信号的文明，试图通过在地平线上寻找烟雾来判断是否存在其他文明。
jboy55查看英文原文
I've always thought that given the sheer numbers involved its a given there are advanced civilizations and that the lack of detectable light communications means the following. Alien civilizations have found such a vastly superior method of communications that they have given up on electromagnetism as a method. The thought experiment is this, if we discovered a vastly superior method of communication, we would probably switch over and abandon light. And if we turned this new 'dish' towards space and found thousands of civilizations communicating... why would we ever try to communicate with EM in space ever again? This means that the time each civilization spends trying to communicate with EM is the time between discovering EM comms and the 'new' mechanism. The number of current alien civilizations communicating in EM are just those currently in that band, and the ratio of alien civilizations doing EM is the (average duration of this band) to the (average age of a civilization). It would be like a civilization currently on earth, only at the level of smoke signals, trying to determine if there are other civilizations by looking for smoke on the horizon.
质疑质疑'不可探测'：经典信道虽内容随机，但通信行为本身仍可被观测到
论文说'分布式计算需要接收方之间的经典通信，但类似标准测量型计算，这种通信传输的是纯随机结果，因此与噪声无法区分'。这个想法的主要问题在于：你仍然需要一个经典信道来传输信息。即使可以按提议使用天然纠缠光子源，你也需要一个可被探测到的经典信道。在这个经典信道上你会看到一串随机数据流，虽然无法解码，但仍然能看出那里存在某种通信。
gus_massa查看英文原文
> The distributed computation requires classical communication between receivers, however, similar to standard measurement-based computation, that communication is of purely random outcomes and so can be indistinguishable from noise. The main problem of this idea is that you also need a classical channel to transmit the information. You can use natural sources of entangled photons as proposed[1], but you will need a classic channel that can be detected. In the classic channel you will see a random stream of data, so it will be impossible to decode, but you can still see that there is some communication. [1] I think it's not so easy, but let's ignore this second objection.
质疑长距离量子通信受纠缠坍缩和熵增的根本限制，难以持续维持
量子通信需要持续更新的共享纠缠对来源。纠缠态一旦坍缩——而发送信息时必然坍缩——粒子对就不再纠缠，也就无法继续传递信息。这些文明必须找到一种能在不使量子态坍缩的情况下进行观测的稳定量子配对方式，这相当于找到阻止黑洞发出霍金辐射的办法；本质上他们需要找到阻止熵增的方法，才能让长距离量子通信可持续。
suifbwish查看英文原文
Quantum communication requires a continually renewed source of mutually shared entangled pairs to send communication. When entangled states collapse, which they must do in order to send information, the particle pairs are no longer entangled and can thus no longer send information. These civilizations would have to find a way to keep a stable quantum pairing which can be observed without collapsing the quantum state, which is the equivalent of finding a way to stop black holes from emitting Hawking radiation; essentially they would need to find a way to stop entropy as we know it in order to make long distance quantum communication sustainable.
补充玩笑：建议把作者的猫列为共同作者（F. D. C. Willard 典故）
作者使用了第一人称复数，我建议他把自己的猫加为共同作者。
godelski查看英文原文
The author uses the first person plural, I suggest he adds his cat as a co-author[0] [0] https://en.wikipedia.org/wiki/F._D._C._Willard
历次讨论
- 2021Hacker News 讨论帖156 分 · 83 评
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