物理与天文2021arxiv.org
来自隐藏几何结构的正能量曲速引擎
Positive Energy Warp Drive from Hidden Geometric Structures
专业 · 约 90 分钟读完前置知识：广义相对论、微分几何、负能量条件
导读
这篇论文研究曲速驱动（warp drive）所需的负能量问题，提出利用隐藏的几何结构来构造满足正能量条件的曲速泡解，试图绕过传统曲速驱动需要奇异物质（负能量）的障碍。这是曲速驱动理论研究中关于能否用普通物质实现超光速旅行的一个进展。
HN 关注点：HN 读者长期关注曲速驱动和超光速旅行话题，讨论焦点集中在因果律问题、Fermi 悖论以及这类研究的现实与伦理影响。
HN 评论精选
这几条评论里：质疑 1 补充 3
补充超光速技术不仅是旅行问题，还带来动能武器和通信等深刻的伦理与安全考量
大家总在谈飞船的超光速旅行，但从武器角度看也很有意思（这也是需要谨慎思考伦理的原因）。超光速动能武器将是毁灭性的：如果伴随曲速泡坍缩，那基本上就是一束以极高速度飞行、在质量前方伴随伽马射线的“枪”。看看国际空间站上的撞击痕迹就知道一个小物体能造成多大破坏。在研发旅行装置时，你很可能会先发射小物体或“子弹”，而那个物体到达的地方可能面临严重危险。另外还有通信：如果能超光速移动物体或信息，一大堆技术都可能被改进或发明。
godelski查看英文原文
Everyone always talks about FTL travel for spacecraft, but there's also an interesting perspective from weapons side (and this a reason to be a bit careful and think about some ethics as we move along). A FTL kinetic weapon would be devastating. If it comes with a collapsing warp bubble then there's basically a gamma ray "gun" that travels right in front of your mass that is traveling at tremendous speeds. You look at impacts on the ISS and you can see how much damage a small object does[0]. This is also especially important when trying to develop such a device for travel as you'll probably be sending small objects before a spaceship, or rather a "bullet". Where that object ends up may be in serious danger. Edit: And as others are pointing out, communication. There's a whole slew of technologies that could be improved/invented if you can move things/information FTL. [0] https://www.esa.int/Safety_Security/Space_Debris/Hypervelocity_impacts_and_protecting_spacecraft
质疑质疑：超光速必然破坏因果律，广义相对论没有允许这种行为的漏洞
这些曲速驱动论文的作者认为，当飞行器实际上超过光速 c 时，因果律上会发生什么？不破坏你的光锥、实际上回到自己的过去，你做不到这一点。难道接受曲速驱动的前提是无视因果律？据我所知，广义相对论中没有任何合理的漏洞能让你在时空中任意出现在任何地点、任何时间。
gary_0查看英文原文
What do the authors of these warp drive papers think will happen causality-wise when the proposed vehicle effectively moves faster than c? You can't do that without doing nasty things to your light cone[0] and effectively traveling into your own past. Is a prerequisite of entertaining the idea of a warp drive that we disregard causality? As far as I know, there aren't any plausible loopholes in General Relativity that allow you to pop up anywhere and anywhen you want in spacetime. [0] https://en.wikipedia.org/wiki/Light_cone
补充希望这类理论研究能为分析 UAP 现象提供可证伪的科学假设工具
这些理论有一个门槛是让人类可行的曲速驱动成立，还有一个更弱的门槛是让它们足以作为 UAP 所展示的“先进技术”的严肃解释。我想知道如果这里的几何表述是正确的，作为观察者我们应该期待从这样的装置看到什么，即使我们无法解释能量管理问题。如果这项研究能给科学界提供工具，在假设某次事件是技术演示的前提下形成可证伪的假设，那就太好了。
api查看英文原文
If FTL is possible (and engineerable) then the Fermi paradox becomes a serious problem. There "should" be aliens all over the place unless... (1) We are wrong about the nature of the universe and strong theism / creationism or the simulation hypothesis (which is the same thing more or less) are right. (2) Life or complex life are so phenomenally unlikely that we are literally the only example in the local galactic supercluster at least, if not the whole universe. Speaking of creationists they often argue that the probability of life forming from non-life is insanely low. Maybe they're right about those probabilities and it only happened once. (3) We live in a cosmic cemetery. There is a big nasty great filter ahead of us, and nobody has passed so far. Maybe the great filter is when you try to actually build FTL and cause a space-time catastrophe. (4) We live in a "dark forest" and should be very, very quiet. Shhhhh.... (5) We live in a nature preserve. See #6. (6) Last but not least, at least some UFOs really are ETs in which case there is no Fermi paradox. They're here and we have seen them. They're just laying low and not making overt contact. My money would be on 6. If we demonstrated some kind of engineerable FTL I'd take the possibility that at least a few UFOs are ETs very seriously.
补充可工程化的超光速旅行将使 Fermi 悖论更加尖锐，作者押注 UFO 即外星人的解释
如果超光速可行且可工程化，Fermi 悖论就成了严重问题。除非：(1) 我们对宇宙本质的认识错了，强神创论或模拟假说是对的；(2) 生命或复杂生命极其罕见，我们可能是本星系团甚至全宇宙唯一的例子；(3) 我们身处宇宙墓地，前方有巨大的大过滤器，也许过滤器就是试图建造超光速装置并引发时空灾难；(4) 我们身处“黑暗森林”，应该保持安静；(5) 我们生活在自然保护区；(6) 至少某些 UFO 真的是外星人，那 Fermi 悖论就不存在了。我押第 6 种。
gfodor查看英文原文
There is the threshold where these theories rule in human plausible warp drives, and then there is the weaker threshold where these theories rule in that they should be taken as serious explanations for the alleged “advanced technology” demonstrated by UAPs. I wonder what we ought to expect to see from such a device as an observer if the geometric formulation here is correct, even if we can’t explain the energy management problems. It sure would be nice if this research adds tools to the scientific community to start forming decent falsifiable hypotheses within the scope of an assumption of a given incident being such a tech demo.
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