In a vacuum all colors of light travel with same speed and this is the reason a white ray travels through the vacuum without going through any dispersion..
Speed of light is the distance per time light waves propagate through different materials. The value for the speed of light in a vacuum is now defined as exactly 299,792,458 metres per second.
Therefore, In a vacuum all colors of light travel with same speed and this is the reason a white ray travels through the vacuum without going through any dispersion
Learn more about speed of light here.
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