Is Nibbana devoid of a permanent and eternal substance?
So the phrasing of this question makes it slightly difficult to answer, but I will do my best. I would answer in this way.
Nibbana is devoid of anything but itself. Nibbana is eternally present, but it is often described as “empty” or “devoid” because once it is experienced alone for the first time, the practitioner realizes that every day of their life they have experiencing Nibbana, but never noticed it due to it being “full” of other experiences. Hopefully my answer to your next question will clear up what I mean by this.
Also, is Nibbana a mere projection of human consciousness?
This is how I like to describe the structure of Nibbana, and how it fits in to our experience. This explanation is incomplete, but I think it accurately conveys its structure.
You can think of Nibbana as the totality of the universe. It is the only thing that actually exists. First Nibbana exists. Then, within Nibbana experiences appear. We call these experiences seeing, hearing, tasting, touching, smelling, and thinking. From these experiences, form is conceptualized, and the “physical” universe we believe to exist is born.
Nibbana is like a television. When a television is turned off, you could describe it as “empty”. Devoid of any content. When it is turned on, it does not create anything. The beings that exist within a TV do not physically exist. The sights it produces could not possibly exist outside of the TV, for the images themselves are the TV. The only thing that ever exists is the Television, and the forms that appear within it are still the TV, simply pixels modulating that we interpret as something more meaningful.
Have you ever been so focused on the content of a movie or show, the presence of the TV melts into the background? Have you ever had the experience of suddenly being pulled out of the show and realizing “oh yea, I’m just looking at a screen”? This experience is much like the feeling that occurs when you see Nibbana for the first time.
Nibbana is like a tv, modulating, taking the form of an image that we interpret as mental phenomena. Then we conceptualize the image/mental phenomena as form, and falsely believe the form has some independent (physical) existence outside of its mental appearance.
I would not say Nibbana is a projection of human consciousness. I would say human consciousness is a projection within Nibbana.
Also, are all things "mere names"?
I would say “all things are nothing more than concepts”. Trees, your mother, sadness, and mathematics all are the same thing. Nibbana. But with the appearance of thought usually comes also conceptualization. We single out a sight and sound we heard before and label that group of sense experiences as “Mother”. Everything you have a name for is conceptualized. What makes Nibbana so difficult to describe, is that Nibbana is what exists when no conceptualization is occurring. It’s logically impossible to describe such a thing, so we fall on words like “empty” as a poor attempt to describe what it’s like when no one is describing.
Although these questions are virtually impossible to answer outside of your own personal experience, I hope my very poor explanations have at least pointed you towards the answers you seek.