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Although the origin of zero is controversial, some historians believe that it was invented by the Babylonians in about 500 BCE. In the sixth century, it was discovered by the Hindus and Chinese, and 700 years later, it reached the Western world via the Arabs. Zero is the only integer (whole number) that is neither positive nor negative. In a sense, zero makes negative numbers possible, as a negative number added to its positive counterpart always equals zero. When zero is added to or subtracted from a number, it leaves the number at its original value. Zero is essential as a position holder in the system known as positional notation. In the number 203, for example, there are two hundreds, zero tens, and three ones. Zero indicates that the value of the tens place is zero. In the number 1024, zero indicates that the value of the hundreds place is zero. Scientists use the term absolute zero (0° Kelvin) to refer to the (unattainable) theoretically lowest possible temperature, at which the kinetic energy of molecules is zero.