With the coming into view of a quantum mechanical picture of matter and of all that exists,
many of the traditional ways in which physicists were thinking about nature had to change.
In the pre-quantum world, Newton thought of objects as being made of particles,
and the particles had mass, they had size, they had motion,
then they had other attributes that later were added on, like electric charge.
So the object, and all of these could be measured, so that in a Newtonian picture of physics,
everything was made out of particles and the particles could all be measured,
every aspect of them could be measured, so that the object or the matter was identical to its observables.
Everything you could think about, you could measure.
Quantum mechanics changed that in a profound way.
Quantum mechanics began to show us that whereas matter obviously exists,
the things that are available for us to know about it are limited.
For example, the position and velocity of an object are not simultaneously knowable
with arbitrary precision in the same direction.
So in these ways, quantum mechanics gave us a sense of humility about our level of knowledge.
matter exists, but what it presents to us is limited.
There is only so much we can know about it.
But there has been a very long-standing, and in fact ongoing, question in the field of quantum foundations
as to what is actually going on, what is really happening to matter, so that it behaves in the ways that we see.
For example, there is this simple experiment that people often use to describe quantum mechanics.
They talk about a double-slit experiment.
So in a double-slit experiment, you consider a situation where you have a source of particles,
you have a wall, and the wall are, let's say, two holes.
You close one hole, you look back behind the wall, and you have a detector.
And from this source, you shoot off, let's say, bullets.
Eventually, on this back surface, you see a pileup of incidents, of hits, of events.
When you look at that distribution, you see a hump.
Now you do the experiment again. You open this hole, and you close the other hole.
Now from this one, you do the same thing. You see the same thing. It's just another distribution.
Now the strange thing is that when you open both holes, you expect to see just the sum of the two distributions.
In other words, you know, they would add up together.
But in fact, you see a pattern that looks like an interference, looks like as if a wave went through.
And in some places, what you see is less with both holes open than with one hole open.
How is it that I open the second hole and some go away here?
And this was the first hint that something very mysterious or something very strange is happening.
That there seems to be a wave nature involved as well.
Now the question is, how do we then have a coherent, consistent ontology, which means a description of existence,
that is consistent with both this particle nature and the wave nature?
And that's been a subject of great debate in quantum mechanics.
And I would say at this point, there is not a definite answer.
And this is an area which is still needing a lot of work.
Whereas we know enough about the quantum world to predict the results of experiments extremely well,
we don't have a clear understanding of the underlying things that are going on.
One philosopher and mathematician by the name of Wolfgang Schmidt is proposing a picture these days of quantum mechanics
in which he's invoking essentially a classical ancient picture,
in which it kind of goes back to, for example, what the Greeks would have called the hylomorphic conception of nature.
Whereas the hyla, which is the substrate of matter, and then morph, which is the shape of the matter.
So if you think of a piece of marble, the marble, a big chunk of marble, there is, you can think of a statue as in there.
But until the sculptor actually puts that shape in, carves that shape out of the marble, there is none of that statue in there.
The statue is in there, but it's not really in there.
It's really in the form that the statue is.
But the form without the marble is also not a statue.
So the hyla and the morph need to come together.
So Wolfgang Schmidt kind of uses this to say that in reality there seems to be, at one level, a corporeal world,
in which it's the world of objects we see and sense and touch.
But then in another level there is the world of the physics, of the physicist,
which is something in between sort of this corporeal world and this sort of the highly kind of space,
this Greek highly concept.
And that there is the potentiality that quantum mechanics talks about is really in this in-between state,
which Schmidt calls the physical world.
It makes for a difficult ontology.
It's one that I don't feel like I fully grasp.
But also I can tell you that it tells us there is still a lot of exciting work ahead.
That even understanding the very basic nature of matter is still something that's not fully grasped.
It's a humbling thing.
It says that God created the world with much more depth and detail than our simple approximations
can just dispatch and make it look like, oh yeah, we know everything.
No, there is a lot more to learn.