※ 引述《WaitElevator (等不到电梯)》之铭言： : In its own frame of reference, a proton take 5 min to cross the Milky Way : galaxy which is about 10^5 light-year in diameter. : a.What is the approximate energy of the proton in electronvolts? : b.About how long would the proton take to cross the galaxy as measured by an : observer in the galaxy's reference frame? : 请问要如何计算能量? : 质子速度要怎麽算? 假设 protone和银河的相对速度为v (记住，银河看protone和protone看银河的速度大小是一样的) 银河原长 L0=10^5 light-year 在protone的坐标中变成 L(v) [用lenth contraction算] 在protone的坐标中花的时间就是 L(v)/v = 5 min 即可解得v 之後要算什麽都简单 另外要注意单位的换算 --

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