The Planck length is the scale at which classical ideas about gravity and space-time cease
to be valid, and quantum effects dominate. This is the ï¿½quantum of lengthï¿½, the smallest
measurement of length with any meaning.
And roughly equal to 1.6 x 10-35 m or about 10-20 times the size of a proton.
The Planck time is the time it would take a photon travelling at the speed of light to
across a distance equal to the Planck length. This is the ï¿½quantum of timeï¿½, the smallest
measurement of time that has any meaning, and is equal to 10-43 seconds. No smaller
division of time has any meaning. With in the framework of the laws of physics as we
understand them today, we can say only that the universe came into existence when it
already had an age of 10-43 seconds.
Answered by: Dan Summons, Physics Undergrad Student, UOS, Souhampton
'The strength and weakness of physicists is that we believe in what we can measure. And if we can't measure it, then we say it probably doesn't exist. And that closes us off to an enormous amount of phenomena that we may not be able to measure because they only happened once. For example, the Big Bang. ... That's one reason why they scoffed at higher dimensions for so many years. Now we realize that there's no alternative... '