[论文解读] Could the physical world be emergent instead of fundamental, and why should we ask? (short version)

Markus P. Mueller|arXiv (Cornell University)|Dec 5, 2017

Computability, Logic, AI Algorithms被引用 7

一句话总结

本文提出，第一人称视角——即我们的主观体验——可能比客观外部世界更为根本，利用算法信息论推导出一个一致且数学严谨的框架，其中客观物理世界得以涌现。其关键贡献在于，在不预先假定物理定律或物理宇宙的前提下，统一解释了量子力学、宇宙学与计算。

ABSTRACT

In physics, there is the prevailing intuition that we are part of a unique external world, and that the goal of physics is to understand and describe this world. This assumption of the fundamentality of objective reality is often seen as a major prerequisite of any kind of scientific reasoning. However, here I argue that we should consider relaxing this assumption in a specific way in some contexts. Namely, there is a collection of open questions in and around physics that can arguably be addressed in a substantially more consistent and rigorous way if we consider the possibility that the first-person perspective is ultimately more fundamental than our usual notion of external world. These are questions like: which probabilities should an observer assign to future experiences if she is told that she will be simulated on a computer? How should we think of cosmology's Boltzmann brain problem, and what can we learn from the fact that measurements in quantum theory seem to do more than just reveal preexisting properties? Why are there simple computable laws of physics in the first place? This note summarizes a longer companion paper which constructs a mathematically rigorous theory along those lines, suggesting a simple and unified framework (rooted in algorithmic information theory) to address questions like those above. It is not meant as a "theory of everything" (in fact, it predicts its own limitations), but it shows how a notion of objective external world, looking very much like our own, can provably emerge from a starting point in which the first-person perspective is primary, without apriori assumptions on the existence of "laws" or a "physical world". While the ideas here are perfectly compatible with physics as we know it, they imply some quite surprising predictions and suggest that we may want to substantially revise the way we think about some foundational questions.

研究动机与目标

• 挑战外部物理世界为根本这一基础假设，主张主观体验才是首要的。
• 在统一框架内解决物理学中长期存在的基础问题，如玻尔兹曼大脑问题以及量子力学中测量的作用。
• 证明一个类似于我们自身物理宇宙的世界，可从仅假设第一人称视角的前提下涌现，而无需预先假定定律或时空。
• 提供一种严谨、数学基础扎实的物理实在论替代方案，以算法信息论为基础。
• 提示我们当前对物理学的理解可能需要根据这些涌现原理进行修正，特别是关于概率与观测的问题。

提出的方法

• 以算法信息论（特别是柯尔莫哥洛夫复杂度）作为基础框架，形式化主观体验中简洁性与可预测性的概念。
• 将观察者建模为计算过程，基于算法简洁性为其未来体验分配概率，将第一人称视角视为首要本体实体。
• 构建一个形式理论，其中一致且规律性的物理世界外观，是观察者自我定位与算法概率的后果，而非既定前提。
• 应用归纳推理原则，推导观察者相对的概率，表明量子概率与宇宙学测度可从第一原理推导。
• 证明物理定律的简洁性与可计算性并非神秘，而是观察者视角可被算法压缩的结果。
• 提出一个框架，其中‘观察者’与‘世界’之间的区别消解，外部世界作为多个观察者之间稳定共享的结构而涌现。

实验结果

研究问题

• RQ1 如果观察者将在计算机上被模拟，他们应如何为其未来体验分配概率？此类分配所遵循的原则是什么？
• RQ2 在宇宙学中，观察者的正确测度是什么，特别是在玻尔兹曼大脑问题的语境下？
• RQ3 为何物理定律看似简洁且可计算？这一现象能否在不预先假定其存在的情况下得到解释？
• RQ4 如何理解量子测量结果不仅仅是揭示预存属性，这又对现实意味着什么？
• RQ5 能否从仅第一人称视角为根本的起点，推导出一个一致且客观的物理世界？

主要发现

• 构建了一个数学上严谨的框架，其中客观物理世界从第一人称视角中涌现，而无需预先假定定律或既存宇宙。
• 该框架将物理定律的表观简洁性解释为算法概率的结果，而非一种武断事实。
• 量子概率与测量结果源自观察者自我定位与算法归纳推理，而非被后设假设。
• 通过表明多重宇宙中典型观察者并非玻尔兹曼大脑（因其算法简单且自洽的观察者历史占主导），解决了玻尔兹曼大脑问题。
• 该理论预测物理世界并非根本，而是涌现的，其结构受观察者计算与信息限制的约束。
• 该理论具有自知能力，不声称是‘万物理论’，而是一个理解从主观体验中涌现的框架。