Light speed constant?

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Light can change speed depending on the material it passes through. In a vacuum, light travels at a constant speed known as the speed of light. The slowest speed recorded was 38 mph, caused by directing a laser beam at cold sodium atoms. Light slows down in materials like glass, water, alcohol, whale oil, and fused quartz due to scattering. The speed of light in a vacuum is 186,282 miles per second.

Light doesn’t always travel at the speed of light. The speed of light can change, based on the type of materials it is passing through. Light will travel at a constant speed known as the speed of light if it travels in a vacuum or in a situation where there is no impediment to slowing the progress of that light. The slowest traveling light obtained in a controlled laboratory environment was 38 miles per hour (61 km/h), or 17,647,768 times slower than the speed of light. This phenomenon was created by directing a laser beam at cold sodium atoms, triggering a significant reduction in the speed of light.

Learn more about light travel:

Light traveling through glass or water loses speed when the light photons come into contact with the other molecules that make up those substances. This activity causes the photons to scatter, slowing forward motion.
The speed of light in a vacuum is 186.282 miles per second (299.792.5 km/s). The speed of light in a vacuum is usually described as the speed c.
Materials that have a high level of refraction tend to slow down light considerably. In addition to water and glass, materials such as alcohol, whale oil, and fused quartz are considered optically dense media that have the ability to scatter photons of light and slow down the speed of light.




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