Top best answers to the question «What travels the speed of light underwater»
Originally Answered: How fast does light travel in water? Light travels at 299,792.458 kilometers per second in a vacuum, which has a refractive index of 1.0, but it slows down to 225,000 kilometers per second in water (refractive index of 1.33).
As a vacuum is devoid of such particles, light can attain its maximum velocity, which, as far as we know, cannot be surpassed. However, light travels at about 0.75c (75% light speed) through water.