It is remarkable that the primordial fluctuations as revealed by the CMB coincide with what quantum fluctuations would look like if they were stretched across the sky by accelerated cosmic expansion. It has been observed that this same stretching also brings very small — even trans-Planckian — length scales up to observable sizes if extrapolated far enough into the past. This potentially jeopardizes later descriptions of late-time cosmology by introducing uncontrolled trans-Planckian theoretical errors into all calculations. Recent speculations, such as the Trans-Planckian Censorship Conjecture (TCC), have been developed to avoid this problem. We revisit old arguments why the consistency of (and control over) the Effective Field Theory (EFT) governing late-time cosmology is not necessarily threatened by the descent of modes due to universal expansion, even if EFT methods may break down at much earlier times. Failure of EFT methods only poses a problem if late-time predictions rely on non-adiabatic behaviour at these early times (such as is often true for bouncing cosmologies, for example). We illustrate our arguments using simple non-gravitational examples such as slowly rolling scalar fields and the spacing between Landau levels for charged particles in slowly varying magnetic fields, for which similar issues arise and are easier to understand. We comment on issues associated with UV completions. Our arguments need not invalidate speculative ideas like the TCC but suggest they are not required by the present evidence.

值得注意的是，CMB 揭示的原始涨落与量子涨落通过加速宇宙膨胀在天空中伸展时的样子相吻合。已经观察到，如果外推到过去足够远，同样的拉伸也会带来非常小的——甚至是跨普朗克长度——的长度放大到可观察到的大小。通过将不受控制的跨普朗克理论错误引入所有计算，这可能会危及后来对晚期宇宙学的描述。最近的推测，例如跨普朗克审查猜想 (TCC)，已经被开发出来以避免这个问题。我们重新审视旧的论点，为什么支配晚期宇宙学的有效场论 (EFT) 的一致性（和控制）不一定受到由于普遍扩张而导致的模式下降的威胁，即使 EFT 方法可能在更早的时候失效. 只有当后期预测依赖于这些早期的非绝热行为时，EFT 方法的失败才会造成问题（例如，弹跳宇宙学通常是这样）。我们用简单的方法来说明我们的论点非引力的例子，例如缓慢滚动的标量场和缓慢变化磁场中带电粒子的朗道能级间距，类似的问题也会出现并且更容易理解。我们评论与 UV 完成相关的问题。我们的论点不必使诸如 TCC 之类的推测性想法无效，但表明目前的证据不需要它们。