What is the Planck constant?

What is Planck length?

I am NOT an expert in this field. But I thought Planck length is the length at which there is no difference between space and time, i.e. at which quantum effects screw everything up.

I am really interested to know how far off I am with this.

This should be in the Physics & Math forum.

Max Planck found that everything is quantized, that is it comes in "lumps," or minimum quantities. A photon is quantized light, protons, electrons, etc. are quantized matter, and space and time have minimum units too. These are measured using Planck's constant, which is 6.62606891 x 10-34 Joule-seconds, with an uncertainty of 89 parts per billion. 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 ‘quantum of length’, the smallest measurement of length with any meaning. It is equal to 1.610*10^-35 m. 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 ‘quantum of time’, the smallest measurement of time that has any meaning, and is equal to 10^-43 seconds. No smaller division of time has any meaning.

My understanding so far is that these aren't necessarily minimums, just the minimums that we can measure. In order to measure a particle we have to bombard it with a photon. The act of bombarding the particle however changes it. Hence Heisenberg's uncertainty principle. Planck's constant measures the minimums one can bombard something and still be accurate in your measurings. Not to sure on this, have to do a bit more reading.

Not just the minimum we can measure, but the minimum that can be measured. As for accuracy, there is a maximum amount of accuracy we can have. There will always be a certain amount of uncertainty. See here.
Since anything below a certain range can't be measured or in any other way observed, it effectively doesn't exist.