[论文解读] Bad Babies; or, Vacuum Selection and The Arrow of Time

Brett McInnes|arXiv (Cornell University)|Jun 13, 2007

Cosmology and Gravitation Theories参考文献 23被引用 1

一句话总结

本文认为，通过弦理论中的真空衰变产生的婴儿宇宙极不可能发展出与我们宇宙匹配的热力学时间箭头，原因在于实现所需低熵初始条件的可能性极低。文章最终得出结论：唯有通过熵原理‘从无中创造’的宇宙——如我们自身——才能自然解释观测到的时间箭头，因此这在弦理论景观中构成了一个强有力的筛选机制。

ABSTRACT

Even if string theory has a landscape of internally consistent universes, and even if one has a mechanism for actually creating these universes [as “baby universes”], it may well prove to be the case that the babies will not resemble the Universe we observe. For they may not have an Arrow of time: even if some of them have basic physical laws essentially identical to those we have discovered, they may have the wrong initial conditions. We argue that it is extremely difficult, indeed probably impossible, for a baby universe to have an Arrow of time [of the kind we observe]. Therefore it cannot resemble our Universe. The only Universe[s] with an Arrow like ours may be the one[s] that was [were] “created from nothing”, in accordance with the Ooguri-Vafa-Verlinde “entropic principle”.1. The Arrow of Time and its Uses One of the most basic observations about our Universe is also one of the most difficult to explain: the existence of an Arrow of time [1][2][3][4]. Whether one examines the entropy that the early Universe might have had due to black holes [1] or uses “holographic” estimates of that entropy [4], the conclusion is that the initial conditions must have been “non-generic ” to an almost unimaginable degree. The difficulties involved in explaining this extraordinary feature of the Universe have recently attracted some attention, leading to a variety of proposed solutions [5][6][7][8]. In this challenge, however, there lies a great opportunity. For if an Arrow of time is something that is very difficult to establish, if in fact extremely few universes have an Arrow, then the Arrow becomes a powerful tool for selecting universes in any theory that presents us with a multitude of them. That is, demanding the existence of an Arrow may allow us to rule out large classes of universes which might have exactly the right gauge group, spectrum of particles, and so on — which might, in short, have everything except the right initial conditions. The importance of settling this question can hardly be overstated: in particular, it is clear that nothing meaningful can be said about populating the string landscape [9] until one has a good understanding of the Arrow. For whatever an “observer ” may be, one can feel confident that such devices do not exist if there is no

研究动机与目标

• 研究通过弦理论中真空衰变产生的婴儿宇宙是否能自然发展出与我们宇宙匹配的热力学时间箭头。
• 评估此类宇宙是否能实现产生与我们宇宙相同热力学箭头所必需的极低熵初始条件。
• 评估时间箭头能否作为筛选标准，以排除弦理论景观中绝大多数宇宙。
• 论证唯有通过熵原理‘从无中创造’的宇宙才能合理重现观测到的时间箭头。

提出的方法

• 分析通过虚假真空衰变中的量子隧穿产生的婴儿宇宙的初始条件。
• 应用全息原理和熵估计，评估婴儿宇宙中极低熵初始态的可能性。
• 将早期婴儿宇宙的熵与我们自身早期宇宙的熵进行比较，特别关注黑洞的贡献。
• 以Ooguri-Vafa-Verlinde熵原理作为基准，评估能够自然发展出热力学时间箭头的宇宙。
• 评估婴儿宇宙中非典型初始条件的概率，表明其被指数级抑制。
• 得出结论：唯有具备‘从无中创造’机制的宇宙才能实现产生热力学箭头所必需的初始条件。

实验结果

研究问题

• RQ1 通过弦理论中真空衰变产生的婴儿宇宙是否能自然发展出与我们宇宙匹配的热力学时间箭头？
• RQ2 婴儿宇宙拥有实现热力学箭头所必需的极低熵初始条件的概率是多少？
• RQ3 熵原理与真空衰变机制相比，在解释时间箭头方面有何差异？
• RQ4 时间箭头能否作为筛选标准，以排除弦理论景观中绝大多数宇宙？
• RQ5 为何我们宇宙的初始状态如此非典型？这一现象能否由基本机制解释？

主要发现

• 通过真空衰变产生的婴儿宇宙极不可能具备产生热力学时间箭头所必需的低熵初始条件。
• 此类初始条件在婴儿宇宙中自然出现的概率被指数级抑制，因此实际上不可能。
• 唯有通过熵原理‘从无中创造’的宇宙，才能合理解释与我们宇宙匹配的热力学时间箭头。
• 时间箭头在弦理论景观中构成一个强有力的筛选机制，可排除大量原本物理上自洽的宇宙。
• 热力学时间箭头并非婴儿宇宙的普遍特征，而是一种高度非典型的结果，需依赖特定的创造机制。
• 唯有通过熵原理‘从无中创造’的宇宙，才能自然解释观测到的时间箭头。