I refer to it as the Planck line
The definition of Plank length below is a very elementary one, which can be found in Wikipedia. However, it can be broadly described as follows:
“Physicists primarily use the Planck length to talk about things that are ridiculously tiny. Specifically; too tiny to matter. By the time you get to (anywhere near) the Planck length it stops making much sense to talk about the difference between two points in any reasonable situation. Basically, because of the uncertainty principle, there’s no (physically relevant) difference between the positions of things separated by small enough distances, and the Planck length certainly qualifies. Nothing fundamentally changes at the Planck scale, and there’s nothing special about the physics there, it’s just that there’s no point trying to deal with things that small. Part of why nobody bothers is that the smallest particle, the electron, is about 1020 times larger (that’s the difference between a single hair and a large galaxy). Rather than being a specific scale, The Planck scale is just an easy to remember line-in-the-sand (the words “Planck length” are easier to remember than a number).”
The Planck length has a more formal meaning as well:
Importance of Planck
“… The idea of a fifth dimension is not new (our fourth dimension including time, plus one other)” “… extra dimensions needn’t be curled up as small as the Planck scale, their effects could be felt by particles at lower energy” “… unification happened when the forces were still weak enough to be handled by conventional mathematical techniques” “… researchers were amazed because unification at a such low energy was supposed to be impossible” “… Fortunately, a fifth dimension comes to the rescue” “… The implications of being able to observe events on the GUT (grand united theory), string and Planck scales are truly mind boggling. We would for the first time be able to see strings, the ultimate foundation stones of reality. And with the Planck scale lowered, experimental tests of quantum gravity-the long sought unification of Einstein’s theory of gravity with quantum theory-might just be around the corner” “… For physics however, the consequences are huge” “… Suddenly, people are seeing extra dimensions as not just a theoretical theory but as every day things whose consequences we could actually measure” “… If (unification) occurs at lower energy, it would change everything, including our picture of evolution of the Universe from the big bang” “… Even simpler laws of physics would change …” “… the discovery (of a timeless fourth dimension) is simply another vital piece of the cosmic jigsaw”
New Scientist, Volume 2157, page 28
You will notice that this latter Planck article also talks about the possible discovery of other dimensions, including where I noted the possible discovery of a timeless fourth dimension within this process. I argue that the fourth dimension can be located at the Planck length. This blog is also very relevant to my blog: The awareness model of physics. A new understanding about reality science. You will see where I mention other universes and dimensions in that blog.