New atomic clocks are more accurate than those used to define the second, suggesting the definition might need to change ...

从古埃及的日晷到现代的原子钟，人类对时间测量的精度不断提升。而如今，光学钟的精确度已超越了当前以铯-133原子跃迁定义的“秒”。这引发了一个关键问题：我们是否应该重新定义时间的基本单位？本文将系统解析当前时间计量的框架、光学钟的革命性突破，以及重新定 ...

All the snow last week and the cold air this week is making for some dangerous temperatures.But how can snow, make the cold ...

In discussions of the pros and cons of this procedure, potential risks from radiation exposure frequently are ignored. In this analysis, Columbia University researchers estimated risks for cancer ...

Galaxies, planets, black holes: to most people, everything about our Universe sounds and feels enormous. But while it's true that much of what happens millions of light years away is large, there ...

Radiotherapy, or radiation therapy, is the clinical use of high energy rays (ionizing radiation) to induce DNA damage in all exposed cells to ultimately kill cancer cells or prevent cancer growth.