Lastly, I had to figure out exactly how quickly heat spreads through a steak. I started by looking at some papers from industrial food production that simulated heat flow through various pieces of meat. It took me a while to realize there was a much easier way to learn what combinations of time and temperature will effectively heat the various layers of a steak: Check a cookbook. Jeff Potter 8217;s excellent book Cooking for Geeks provides a great introduction to the science of cooking meat, and explains what ranges of heat produce what effects in steak and why. Cook 8217;s The Science of Good Cooking was also helpful. Putting it all together, I found that the steak will accelerate quickly until it reaches an altitude of about 30–50 kilometers, at which point the air gets thick enough to start slowing it back down. The falling steak 8217;s speed would steadily drop as the air gets thicker. No matter how fast it was going when it reached the lower layers of the atmosphere, it would quickly slow down to terminal velocity. No matter the starting height, it always takes six or seven minutes to drop from 25 kilometers to the ground. For much of those 25 kilometers, the air temperature is below freezing-which means the steak will spend six or seven minutes subjected to a relentless blast of subzero, hurricane-force winds. Even if it 8217;s cooked by the fall, you 8217;ll probably have to defrost it when it lands.
最后我还需要找出热量在牛排中的传导速度。我一开始查阅的是在工业食物生产中模拟不同种类肉的热传递的论文。后来我才意识到，要知道不同温度和时间搭配下，牛排会被加热到哪种程度的最简单的方法是：去找一本烹饪书来看。在《极客厨房》这本很棒的书中，作者杰夫•波特很好地介绍了肉类烹制的科学道理，并解释了不同温度范围下热量对牛排的影响及其原因。库克的《做好菜的科学》一书也很有帮助。把上面所有信息综合到一起，我发现牛排会迅速加速坠落直到到达30～50千米的高度，在这个高度，空气足够稠密到能让牛排开始减速下坠。随着空气密度越来越大，牛排下落的速度也会逐渐下降。不管牛排在下落到大气层下部时速度有多快，它最终都将减速到终端速度。无论一开始起落点多高，牛排从25千米的高度坠落至地面总是需要6～7分钟时间。在这段距离中，空气温度大部分时间都低于冰点，这意味着牛排会在温度低于0℃、风力媲美飓风的狂风中待上6～7分钟。就算在下落过程中牛排已经熟了，掉到地面后你还是需要解冻才能食用。
When the steak does finally hit the ground, it will be traveling at terminal velocity-about 30 meters per second. To get an idea of what this means, imagine a steak flung at the ground by a major-league pitcher. If the steak is even partially frozen, it could easily shatter. However, if it lands in the water, mud, or leaves, it will probably be fine. A steak dropped from 39 kilometers will, unlike Felix, probably stay below the sound barrier. It also won 8217;t be appreciably heated. This makes sense-after all, Felix 8217;s suit wasn 8217;t scorched when he landed. Steaks can probably survive breaking the sound barrier. In addition to Felix, pilots have ejected at supersonic speeds and lived to tell about it .To break the sound barrier, you 8217;ll need to drop the steak from about 50 kilometers. But this still isn 8217;t enough to cook it. We need to go higher. If dropped from 70 kilometers, the steak will go fast enough to be briefly blasted by 350°F air. Unfortunately, this blast of thin, wispy air barely lasts a minute-and anyone with some basic kitchen experience can tell you that a steak placed in the oven at 350 for 60 seconds isn 8217;t going to be cooked. From 100 kilometers-the formally defined edge of space-the picture 8217;s not much better. The steak spends a minute and a half over Mach 2, and the outer surface will likely be singed, but the heat is too quickly replaced by the icy stratospheric blast for it to actually be cooked. At supersonic and hypersonic speeds, a shockwave forms around the steak that helps protect it from the faster and faster winds. The exact characteristics of this shock front-and thus the mechanical stress on the steak-depend on how an uncooked 8-ounce filet tumbles at hypersonic speeds. I searched the literature, but was unable to find any research on this.
当牛排最终掉落到地面时，它的速度将会是约每秒30米的终端速度。如果想要对此有一个直观的认识，想象一下一块牛排被棒球大联盟的投手砸在地上的样子。就算牛排只有一部分被冻住了，这样也很容易被摔碎。不过如果牛排最后掉到了水里、泥里或者树叶堆里，那应该没事儿。从39千米高度掉下来的牛排应该不会像菲利克斯那样突破音障，它甚至不会被显著加热。这也说得通，毕竟在落地时菲利克斯的保护服也没被烤焦嘛。即使突破音障，牛排应该也不会支离破碎。因为除了菲利克斯，许多曾在超音速状态下弹射的飞行员都活了下来，并讲述了他们自己的故事。要想突破音障，你需要让牛排从50千米的高度落下来，但这仍然不足以把它烤熟。我们需要到更高的高度。如果从70千米高度落下，牛排的速度会快到把空气加热到177℃左右。不过这股纤弱稀薄的高温空气只会持续不到1分钟，任何具有基本厨房经验的人都会告诉你把牛排放到350°F的烤箱里烤60秒并不能把它烤熟。从100千米——太空边缘的正式定义——高度落下来并不会有太大区别。牛排超过2马赫速度的时间会有1分半钟，牛排的外表面很有可能会烧焦，但热量很快就会被冰冷的平流层狂风消散掉，因而内部并不会被烤熟。在超音速和高超音速条件下，牛排周围会形成激波，而激波会把牛排和越来越快的狂风隔离开来。激波前沿的准确性质，以及由此产生的对牛排的机械应力，取决于这块8盎司的生牛排如何在高超音速狂风中翻滚。我尝试着去找这方面的文献，但没有找到任何与此有关的研究。