如果光速是一个万能常数,为什么最精确的时钟使用放射性衰变作为基准,而不是光通过真空? Steve Baker 这样说...

2020-10-14 12:18

If the speed of light is a universal constant, why is it that the most accurate clocks use radioactive decay as a reference, and not light passing through a vacuum? PeO世界播

如果光速是一个万能常数,为什么最精确的时钟使用放射性衰变作为基准,而不是光通过真空?PeO世界播


Answered by: Steve Baker,Blogger at LetsRunWithIt.com (2013-present) PeO世界播

回答者:史蒂夫·贝克(Steve Baker),LetsRunWithIt.com的博客作者(2013年至今)PeO世界播


The specific reason why not is that the international standard for a “second” is : “9,192,631,770 cycles of the radiation produced by the transition between two levels of the cesium 133 atom.” PeO世界播

具体原因是“秒”的国际标准是:“铯133原子的两个能级跃迁产生的辐射循环数为9,192,631,770周。”PeO世界播


So a device that correctly counts that number of cycles of that transition is BY DEFINITION, a perfectly, 100% accurate clock. PeO世界播

因此,根据定义,正确计算转换周期数的设备是一个完美的、100%准确的时钟。PeO世界播


If instead, you were to build a box of some known length with (say) a laser beam at one end, a mirror at the far end and measure the time it takes the beam to travel the length of the box and return - then you could make a clock by dividing the distance traveled by the speed speed of light. PeO世界播

相反,如果你建造一个已知长度的盒子,一端是激光束,远端是镜子,然后测量光束穿过盒子长度并返回所需的时间-那么你就可以用旅行距离除以光速来制造时钟。PeO世界播


But to do that, you’d need to know the length of the box to 100% precision - and the speed of light to 100% precision. That’s going to be impossible because any real box will change dimensions depending on temperature, external air pressure - maybe also curve due to gravity, bend due to tidal forces from the moon, change length fractionally due to magnetic fields, etc, etc. You’d also need to know that the mirror was at some precise angle to the light beam. PeO世界播

但要做到这一点,你需要知道盒子的长度达到100%的精度,以及光速达到100%的精度。这是不可能的,因为任何真正的盒子都会根据温度、外部气压来改变尺寸-可能也会因为重力而弯曲,由于月球潮汐力量而弯曲,由于磁场而微小地改变长度,等等。你还需要知道镜子与光束的某个精确角度。PeO世界播


There would be all sorts of possible sources of error in your clock… where the “atomic clock” is correct by definition. PeO世界播

您的时钟…中会有各种可能的误差源。“原子钟”的定义是正确的。PeO世界播


It is tempting to change the definition of “one second” to be the time it takes for a photon to travel 299,792,458 meters… which would make it be possible for your clock to be accurate “by definition”. But this would introduce another problem. It would tie the definition of a “second” to the definition of a “meter”. PeO世界播

将“一秒”的定义更改为光子旅行299,792,458米…所需的时间很有诱惑力。这将使你的时钟有可能“按照定义”是准确的。但这会带来另一个问题。它将把“秒”的定义与“米”的定义联系起来。PeO世界播


But a “meter” is currently defined as the distance traveled by light in 1/299,792,458 seconds. PeO世界播

但“米”目前的定义是光在1/299,792,458秒内行进的距离。PeO世界播


So what you’d have would be a “circular definition” - the length of a meter depends on the duration of a second - which would depend on the length of a meter! PeO世界播

所以你会有一个“循环定义”-一米的长度取决于一秒的持续时间-这将取决于一米的长度!PeO世界播


Hence we define a second in terms of something that can just be counted… it depends on no other definitions. The definition of a meter depends only on the definition of a second. Life is good! PeO世界播

因此,我们用可以仅算作…的东西来定义秒。它不依赖于其他定义。米的定义只取决于秒的定义。生活是美好的!PeO世界播


The standardization folks are currently in the process of changing the definition of a “kilogram” to be the mass of some specific number of atoms, which would reduce that definition to another thing that can just be counted. PeO世界播

标准化人员目前正在将“千克”的定义更改为特定数量的原子的质量,这将使该定义简化为另一种只能计数的定义。PeO世界播


So what we’d end up with would be standards that can (at least in theory) be 100% perfectly accurate. PeO世界播

因此,我们最终得到的标准将是(至少在理论上)百分之百完全准确的标准。PeO世界播

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