Sit back. Close your eyes. Relax your body.

Take note, for a moment, of the sounds around you. Try to hear them all at once, paying attention to them without really listening to any one of them.

Now, just like you were looking at that goofy optical illusion which can look like a vase or two faces and you were shifting your focus from seeing one to seeing the other, shift your focus from the sounds around you to the silence around you.

Don't think you can't hear it. The more noise there is, the more silence there is, too. Silence is the dark matter of sound; the Yin of it, if you will. You will notice the silence between the sounds you hear, and also around them, underneath them. Focus on it. Try to let it get really loud. See if you can drown out the noise with silence (in your perception, of course).

Now. Wrap your mind around the following:

Silence is, for want of a better word, the opposite of sound. It is the non-thing to which sound is the thing. For every thing, there is a corresponding non-thing, a Yin for every Yang, an is-not for every is.

The trick is, while there are myriad things, there can by definition only be one not-thing. Nothingness can not be divided up into parts; it is all one and the same nothing. So that silence you are listening to is not just the absence of sound, it is the empty space around every material thing that allows it to be (because of course, you can't have anything if you don't have room for it to exist; that is, empty space). It is also the famous No-Mind, for as you will notice eventually, when hearing silence, your brain grinds to a halt.

One Void is all void, without which there could be No Thing. Got it?

So, in theory, what is the One Eternal Thingy that all those spiritualists are always out looking for?

Why, No Thingy, of course.

Mu.