物理与天文2014arxiv.org
在互联网上寻找时间旅行者的证据
Searching the Internet for evidence of time travelers
入门 · 约 20 分钟读完前置知识：基础概率与假设检验概念、时间旅行悖论常识
导读
这篇论文（arXiv:1312.7128）尝试用实证方法在互联网上搜寻时间旅行者存在的证据：作者在 Twitter 上定向邀请未来时间旅行者提前留言，并搜索互联网上是否出现过对重大事件（如教皇方济各当选、彗星 ISON）的提前提及。结果未发现任何时间旅行者的迹象。
HN 关注点：HN 读者觉得用严肃的实证方法检验一个荒诞假设很有趣，讨论焦点集中在：这种检测方法在逻辑上是否自洽、时间旅行者是否真的会留下可检测的痕迹。
HN 评论精选
这几条评论里：质疑 1 补充 3
质疑方法假设不成立：纪律严明的时间旅行者不会留下预言性痕迹，但大规模数据挖掘仍有副产品价值
这很有趣，但这些方法在我看来并不可行。Twitter 那部分专门针对愿意配合的时间旅行者，而彗星 ISON 肯定不值得提前提及。这个假设（也许是不得不做的假设）是时间旅行者会脱口说出重要的预言信息——但如果他们纪律严明或从事历史研究，这就不成立了，那样他们对近期未来的了解不会比我们多。我不是在主张时间旅行者存在，但推测起来确实有趣。现实中还得考虑：时间旅行者仅仅存在本身，长期就会改变历史进程。更彻底的做法可以是对互联网上的预言性词汇做大规模自动化数据挖掘——即使找不到时间旅行者，也能顺便研究思想的传播规律。
Udo查看英文原文
This is interesting, but these methods don't strike me as really viable. The Twitter outreach was specifically targeted at the cooperation of Twitter-using time travelers, and while Pope Francis might or might not be historically significant enough to warrant prescient mentioning, I'm sure comet ISON is not. The assumption is also (and maybe it has to be) that time travelers would blurp out important prescient information - however, I don't think that holds true if they were either well disciplined or engaged in historical research - which would mean they know little more (if anything) about our immediate future than we do. I'm obviously not advocating time travelers are present (I would think with the certain prospect of leaving your time line in order to create another one, the proposition of time travel seems akin to a one-way change in universes that doesn't sound very inviting), but it's definitely fun to speculate about. Realistically, one would also have to take into account the fact that, by mere virtue of being present, a time traveler will change the course of history in the long run. A more thorough effort could center on large-scale automated data mining for prescient terms on the internet. Of course, there would be many false positives, but as a side effect we could learn more about the epidemiology of ideas even if we don't discover time travelers. It seems to me that a disciplined time traveler would not purposefully drop historically significant hints - however, if they are from a future and culture close enough to our own, they might still reveal themselves inadvertently through idiosyncratic phrases and reference to concepts that are from the future. Hand-picked phrases are not enough to discover this, it would have to be large-scale AI-supported text mining.
补充检测方法会自我失效，且时间旅行的影响可能伪装成不起眼的历史事件
问题难道不在于：他们描述了自己检测时间旅行的方法，等于告诉未来的人该避免什么？再假设有人回到过去杀了希特勒，我们的时间线只会记录一个奥地利画家在 1920 年代被谋杀，我们不会觉得这有历史意义。我认为时间旅行本质上极难检测——即使时间旅行者'丢下'了科技，也可以回到过去把东西收回去。
awjr查看英文原文
Isn't the issue here that they are describing the methods through which they are trying to determine time travel. In effect, telling anyone in the future exactly what not to do. Let's also assume that somebody had a reason to travel into the past, say to kill Hitler. Our timeline would record that an Austrian artist was murdered in the 1920s. We would not consider this historically significant. I think time travel is inherently very difficult to detect. Even if a time traveller 'dropped' tech. This tech would be recoverable by popping back in time and recovering it.
补充发表研究结果本身就会促使时间旅行者回去消除痕迹
这完全说不通……'嘿 Bob，你这个蠢货！有人通过你发的一条推文找到了你，然后他们把研究论文发到网上，现在所有人都知道时间旅行者了。回去修一下。''搞定了。'发表这项研究结果这个行为本身，就可能已经导致结果被改变，从而表现为无阳性匹配……
jsonmez查看英文原文
This makes no sense... here is why: "Hey Bob, you idiot! Someone found you by a stupid tweet you made. Then they posted a research paper online and now everyone knows about time travelers. Go back and fix it." "Done" The very act of publishing the results of this study could have caused the results to be changed, thus showing a non-positive match...
补充更合理的假设是时间旅行者会利用未来知识在金融市场获利，应从市场异常数据入手
我不明白未来时间旅行者为什么要在网上留预言信息，动机是什么？我能想到他们会做的是利用对未来事件的了解操纵当今金融市场（比如大宗商品短缺或意外矿产发现），复利之下小操作也能带来巨大收益。所以也许该去市场数据里找异常——特别是现有的内幕交易检测系统，或长期无人动过的投资账户。当然这类数据通常受保护、难以获取。
andyjohnson0查看英文原文
I'm not sure why time travellers from the future would bother to leave prescient messages on the net. What's the motivation? Something like graffiti artists tagging difficult locations? What I can see them (hypothetically) doing is manipulating present-day financial markets by exploiting their knowledge of future events (e.g. sudden commodity shortages or unexpected mineral discoveries) to increase their wealth. Even small manipulations would produce large downstream gains due to compound interest. So perhaps market data is a place to look for abnormalities - particularly in existing systems that look for signs of insider trading, or investment accounts/trusts that are untouched over very long periods of time. Of course, such data is usually protected and inaccessible anyway.
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