物理与天文2017arxiv.org
如果时间真的存在呢？(2008)
What If Time Really Exists? (2008)
进阶 · 约 35 分钟读完前置知识：相对论基础、量子力学基础、时间哲学/形而上学
导读
这篇 2008 年的论文追问：在物理学中，时间究竟是真实存在的基本要素，还是只是幻觉或涌现现象。它不侧重实验方案，而是从概念和理论层面分析“时间存在”到底意味着什么，并探讨若时间确实存在应如何理解。
HN 关注点：HN 读者被“时间/现实是否是幻觉”的哲学冲击吸引，讨论焦点很快转到这类问题是否可检验、以及“时间”是不是语义之争。
HN 评论精选
这几条评论里：质疑 1 补充 2
质疑科学理论必须可检验；无法检验的“时间/现实是否幻觉”讨论没有实际推进意义。
科学按定义就是不完整的。它只提供提出理论、检验观测现象、再外推预测的机制，这些预测可能推翻或加强理论。比如我们甚至不知道现有物理是普适的还是只适用于可观测角落；唯一证据是尚未看到反证，但这不是证明。弦理论可被视为教条，但至少提供可检验预测的途径，只是我们离能力还很远。若我们生活在幻觉中，很可能根本无法探测——这或许正是此类“程序”的首要要求。你尽可喊“计算机，结束程序！”，全息甲板只会无视你 :) 如果对时间实在性的思考不能带来可检验、可影响或推进理解的东西，那想它没意义。你也可以说宇宙只是无限多元宇宙之一，不断在宇宙海中产生，但这不改变什么。
dirkg查看英文原文
Science is by definition incomplete. It only provides a means for proposing theories to test observed phenomenon, test them, and use them to extrapolate and make future predictions, which can invalidate or strengthen the theory. e.g. we don't even know if the physics we have is universal or local to our observable corner, the only evidence we have is we haven't seen any evidence to disprove it, but that's not proof. String theory could be considered dogma. But it at least provides means to test its predictions, its just that we are very very far off from ever getting close to that capability. If we live in an illusion, its entirely possible and in fact likely that it is beyond our ability to even detect that. In fact that would be one of the first requirements of such a 'program'. You can should 'computer, end program!' all you like but the holodeck will just ignore you :) There really is no point to wondering about the reality of time if it doesn't lead to anything we can test/influence or use to advance our understanding and so far there is none. You could just say the entire universe is but one of infinite multiverses which are being continuously spawned in the cosmic sea, but that doesn't change anything.
补充时间可能只是变化/反应的别名，而非可穿越的第四维；传统时间旅行在物理上要求复原全部粒子状态。
关于“时间”的很多问题似乎是语义问题。事物会变化吗？会；若以此定义，时间当然存在。但人们通常不这么看，他们把时间想成一种介质或第四维，可能可以穿越。这种时间并不存在（就像任何东西可以说不存在）。只有粒子及其位置。回到过去需要把宇宙每个粒子移回你想体验的状态；这不是传统时间旅行，只是对粒子的神级操控。人们幻想的回到过去，需要每个普朗克时间复制一个宇宙供你访问；即使那样也只是另一个 3D 空间，恰好看起来像你见过的。时间是化学和物理反应；反应发生所需最短时间可能是普朗克时间，没有东西能比普朗克时间更快“发生”，所以时间可能是颗粒性的。如果反应停止，时间也停止。这是一套观点。
thinkloop查看英文原文
Seems like a lot of the problem with "time" is semantic. Do things change? Yes, and if that's the definition then it certainly exists. But people don't generally see time like that, they think of it as some medium, or 4th dimension, that can possibly be traveled through. This kind of time does not exist (as much as anything can't exist). There are only particles and their positions. Traveling back in time would require moving every particle in the universe back to the state you want to experience. But this is not "traditional" time travel, just god-like influence over particles. Traveling back in time, in how people fantasize about it, would require copies of the universe being made every plank-time, that you can visit. And even that is just another 3d space that happens to look like one you saw before. Time is chemical and physical reactions. The minimum amount of time (sorry) a reaction can take to happen is possibly plank-time. Nothing can "happen" faster than plank time. So time is possibly granular. If reactions stopped happening, time would stop. That's one set of views.
补充不同来源都指向“现实是幻觉”，值得认真对待。
现代物理暗示时间和空间可能是幻觉，顶尖技术专家也同意我们几乎肯定生活在模拟现实中，而许多古老传统确信这一切都是幻象——看来我得认真对待这件事了……
monktastic1查看英文原文
Between modern physics suggesting time and space may be illusions, leading technologists agreeing that we're almost certainly in a simulated reality, and many ancient traditions being certain that this is all an illusion, I may have to have to go ahead and take this seriously....
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