<s>[INST] What is the speed of light in a vacuum? [/INST] The speed of light in a vacuum is 299,792,458 meters per second.</s>\ <s>[INST] Perfect, thanks! Does light always travel at that speed in space? [/INST] In general, the speed of light in a vacuum has been considered to be constant. However, a team of Scottish scientists proved this is not the case. The scientists used a mask to change the shape of a proton, and showed that afterwards it traveled slower, even in a vacuum.</s>