What is nothing? Kuhn's nine levels of nothing

I would probably have been about 8 years old when a question popped into my head that would cause me sleepless nights for a long time. A question so perplexing that I didn't even know how to phrase it. Why does anything exist? Why is there anything at all?

I wasn't imagining an empty universe. I was thinking of no universe at all, and absolutely nothing else either. And that was a mind-boggling idea.

Of course, now I know that this is a common question, and it is often phrased as "Why is there something rather than nothing".

This article isn't about that question, but instead, it is about a more fundamental question - what exactly is nothing? This is a question Robert Lawrence Kuhn (who runs the excellent Closer to truth Youtube channel) attempted to answer by defining nine levels of nothingness. Sabine Hossenfelder covered these in another video. Below is my take on the nine levels.

Many will disagree with either the levels themselves, or their ordering, but I still find it is quite an interesting topic, I hope you do too.

Level 1 - an empty room

If you walk into a room with no furniture, carpets, curtains, or any other visible objects, you might say that the room has "nothing" in it.

This is the most basic idea of nothing. The room itself exists, and everything outside it, and of course, the room is full of air. But the room contains nothing you can see. It could be thought of as a childish or pre-science view of nothing, but also an everyday description that most of us would use.

Level 2 - remove the air

Of course, a room full of air is not empty, so we would need to pump all the air out of the room to make it truly empty. This would create a vacuum, at least according to classical physics.

This would leave us with a room that a 19th-century physicist might say was empty of all matter.

Level 3 - remove all other matter

So far we have removed all the molecules from the room. All the visible objects, and the various gas molecules that form the air.

Of course, there are other forms of matter. For example, neutrinos and dark matter particles. Our room will be flooded with a constant stream of neutrinos, mainly from the Sun. And although neutrinos are almost undetectable because they hardly interact with other particles, our room is still full of them so we can't call it empty.

Although this is only a thought experiment, there is a serious practical problem if we want to keep neutrinos out of our room. Neutrinos don't stop for anything. Most of the neutrinos hitting the Earth will pass straight through the whole planet as if it were a vacuum. If we surrounded our room with a solid lead wall that was one light-year thick (about ten trillion kilometres) half the neutrinos would still get through!

There is no remotely feasible way to shield our room from neutrinos.

So at this point, we need to stop thinking about a room and think about the universe. Level 3 imagines our entire universe without any matter at all, including neutrinos.

Level 4 - remove all radiation and fields

Our universe could still contain electromagnetic radiation and magnetic fields. Those things are not material, but they still physically exist, so to have nothing we would also have to remove them

There would be no matter to create these effects, of course, so maybe our level 3 universe would already be devoid of those things. But it is conceivable, for example, that something equivalent to the Big Bang had somehow created a pulse of electromagnetic radiation without creating any matter. That radiation would still be moving outwards. To be sure, we will not allow that in our level 4 universe.

Level 5 - going beyond the quantum vacuum

Quantum theory tells us that, even in a total vacuum, space would be bubbling with virtual particles. These are pairs consisting of a particle (of any kind) and its antiparticle. They typically exist for extremely short periods before recombining and annihilating each other.

One predicted effect of this is Hawking radiation. This happens when a pair of particles is created close to the event horizon of a black hole. One particle is absorbed into the black hole, leaving the other particle free to radiate away from the black hole. This is predicted but hasn't been observed so far.

The previous level 4 would be described as a quantum vacuum - a universe with no particles, and in its lowest energy quantum state. But even then, with particles popping in and out of existence, it couldn't be described as truly empty.

Level 5 would be a universe with no quantum field at all. Essentially, the rules of quantum mechanics would not apply so no particles could ever be created (at least not via the laws of quantum mechanics).

Level 6 - no space, time, or laws of physics

At this level, our universe would not exist in any form. Time and space would not exist, and the laws that govern our universe would be irrelevant as they wouldn't have anything to apply themselves to.

Although there is an argument that space and time can exist without mass, so we might already have lost space and time a couple of steps ago.

Carl Sagan defined the Cosmos as "all that is or was or ever will be". In other words, it is our entire universe and absolutely anything else that exists beyond our universe. If you believe that our universe itself is all that is or was or ever will be, you might almost be at the end of the line at level 6 (although level 9 might still be relevant).

But many people, whether for emotional or logical reasons, believe that our universe is part of something bigger - the Cosmos. Level 6 imagines the Cosmos but without our universe.

Level 7 - no gods

Level 7 addresses whatever you might think exists beyond our universe. There are many beliefs about what might exist in this realm:

• A deist or theist might consider this to be the domain of some or other god(s).
• Those who believe in the multiverse might think, for example, that this is the outer realm where all the universes live, popping in and out of existence, perhaps each with its own unique laws of physics.
• Some believe that consciousness is primary and that the physical world is just a dream that we all share in a more or less consistent way. This level would be the home of that collective consciousness.
• Others speculate that our own universe is a computer simulation, so this outer realm would be where we might find the computer and the spotty teenager who programmed it.

There are many different ideas and, of course, in reality, nobody has a clue which might be correct. But one thing we shouldn't assume is that this outer realm (if it exists) shares the same rules as our universe. If you ask a theist "Who created your god" they might well object that it isn't a valid question because their particular god is eternal. While I am an atheist myself I agree with the general point. Saying that our universe is explained by a wider containing Cosmos does not necessarily imply an infinite regression. Maybe in that outer realm, it makes perfect sense for eternal beings to just exist, or for entire universes to pop into existence. Perhaps the question "Why does anything exist?" has a perfectly good answer.

Level 8 - no abstract ideas

The notion that certain ideas might transcend everyday reality was well-known as long ago as the ancient Greek era. It is sometimes called Platonism, after the philosopher Plato.

He believed that certain ideas (Platonic ideas) existed in a different realm, separate from the physical world and separate from the realm of conscious thought. These ideas include numbers, mathematical propositions, and logic.

So the fact that 2 + 2 equals 4 is an abstract truth, and it would still be true even if there were no intelligent minds to understand addition, and if there were no physical objects to count. Similarly, the angles in a triangle would still add up to a full turn even if there was no material in existence to create triangles. Also, the statement that "NOT (A AND B) is logically equivalent to (NOT A) OR (NOT B)" would still be true even if there were no logical true or false conditions to apply it to.

But we are making a big assumption here. If we are saying that these ideas would still be true even if absolutely nothing else existed, then that implies that they would also be true in absolutely any possible universe that did exist. Is that justifiable, or is it just a failure of our human imagination?

Level 9 - no possibilities

Finally, if we had a universe where nothing existed, not even the basic laws of mathematics and logic, there is one thing that might remain. That is the possibility of something existing.

Without that, then nothing could exist. And we know something does exist. At the very least, I know my own consciousness exists, even if everything else is a hallucination. Since something exists, if there was ever a point when nothing existed, it must have been possible for something to exist.

Summary

This is just one possible hierarchy, and you might well object to some of the levels or their ordering. In particular, some might reject the existence of certain levels.

Bertrand Russell famously said, "I should say that the universe is just there, and that's all". He regarded the universe as a brute fact, that is he stopped at level 6. Not to say that lower levels might not exist, just that there is no real way of knowing anything about them.

A theist in the Abrahamic tradition might stop at level 7. God is eternal, again a brute fact, but this time they do regard this brute fact as being the final word.

What do you think?

See also

• How carbon dating works