What is the approximate speed of light in space?

• A. 3.0 x 10^8 m/s
• B. 3.0 x 10^6 m/s
• C. 3.0 x 10^10 m/s
• D. 1.0 x 10^8 m/s

Answer: (A)

Light travels in space at a universal constant: the speed of light in a vacuum, about 3.0 × 10^8 meters per second. In space there’s almost nothing to slow it down, so this is the speed you use for light traveling through empty space. In any material, light slows down depending on the material’s refractive index, which is why it isn’t this fast in air, water, or glass. The numbers that are much smaller aren’t representative of light in a vacuum, and a value larger than this would contradict relativity, which sets this speed as the ultimate limit. So the approximate speed of light in space is 3.0 × 10^8 m/s.