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The Planck length () is the smallest unit of length. It is calculated from three physical constants: the speed of light, the Planck constant, and the gravitational constant. The length was established as a way to simplify many of the more fundamental equations — if equations are written in Planck units, you can do away with many physical constants and not have to worry about dimensions. The Planck length does not have any precise physical significance, and it is a common misconception that it is the inherent “pixel size” or smallest possible length of the universe.[1] If a length smaller than this is used in any measurement, then it has a chance of being wrong due to quantum uncertainty.[2]
It is about 1.616255×10−35 m or about 10−20 times the size of a proton. It is one of the Planck units, defined by Max Planck. It is an important length for quantum gravity because it may be approximately the size of the smallest black holes.[3]
The speed of light is also one Planck length per Planck time.
If the universe were scaled down such that a quarter were the size of a Planck length, then the entire observable universe would be about one-hundredth the width of a human hair.
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