Light propagates in a vacuum at a constant, finite speed, the *speed of light*. The speed of light is defined to be $299,792,458\, \text{m}/\text{s} = 1,080,000,000\, \text{km}/ \text{h}$. The interesting word here is "defined". Since we assume that the speed of light is constant, we can use it to define units. In this case, the speed of light is used to define distance. Thus, the speed of light is just a conversion factor between space and time. Time (in seconds) is defined via [[Atomic Clocks|atomic clocks]], where one second is defined as a certain number of oscillations of a certain atomic transition. The finite speed of light has important consequences for many physical theories. According to the special [[Special Relativity|theory of relativity]], no information can propagate faster than the speed of light. Thus, there will be measurable delays between an action and its consequences at another point in space. >[!read]- Further Reading >- [[Light]] >- [[SI Units]] >- [[Special Relativity]] >[!ref]- References