What is the smallest theoretical building block of the universe?

[Logical Adolecent]

From what I learned, the smallest thing we have an idea of are planks and string. And no, I'm not talking about wooden planks and thread. But, is there anything that we know of that is smaller than these things? Possibly anything to do with dark matter? I'm just curious about this.

[Anomalocaris]

You mean Planck?

Planck is not one thing, as in "the Planck", unless you are talking about the physicist.

There are separate entities, presumed to be smallest and indivisible quantities of time, length, and energy, which are named in honor of Planck and called Planck time, Planck length and Planck mass. If these exist they would be building blocks of reality. But their theoretical size is too small to be probed by existing technology, so they are still theoretical. If they are too small to probe, then obviously we would have no idea if anything exists that is even smaller.

The String is a thing, but it is also only theoretical thing. Many people would fervently like to believe they exist, because if they do, then the universe would seem much more comprehensible. But string theory has been reticent in producing unique and practically falsifiable predictions, and as a result no one has managed to devise a test that can be performed with available or foreseeable technology that can definitively determine whether string exists or not.

There is no requirement that string must all be small. Some strings have been theorized to span the entire universe. So obviously it is possible things smaller than some string can exist if these strings can be shown to exist.

[Heywood]

From what I learned, the smallest thing we have an idea of are planks and string. And no, I'm not talking about wooden planks and thread. But, is there anything that we know of that is smaller than these things? Possibly anything to do with dark matter? I'm just curious about this.

The following is a link which allows you examine how different things relate to each other in terms of scale. At one end is the smallest things and the other is the largest things. You have to watch a 30 second ad(probably about world of warcraft) and then the play button will appear. Its pretty cool and is updated all the time as new information becomes available.

http://www.scaleoftheuniverse.com/

Curiously, it turns out that in terms of scale, human existence is right in the middle(human egg to adult human).