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Comment by jebarker | Hacker News Reader

I'm not a physicist. An idea from physics that I recently learned and found very unnerving was that the solid objects we see and feel in the world are actually mostly empty space. We just see them as solid because of the way light interacts with the particles. So in a sense our visual and tactile perception of the world is just one representation of the underlying reality and you can imagine there being infinitely many other possible representations.

I'm just crudely saying the same thing as the author I think, but I wanted to emphasize how uncomfortable this makes me. In some sense it feels like being a prisoner in a perceptual cell you can't escape from surrounded by a reality you'll never know.

Having philosophy as a counterpoint (in my case dabbling in Buddhism) has been essential to keep me calm and relaxed.

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"Solid" doesn't really have meaning at the sub-molecular level. All space has something in it, even if it's just vacuum energy. Virtual particle pairs come and go all the time. Some space has particles with electromagnetic charge. Each of these has some interaction radius. Technically, this is infinite. Electric field reaches everywhere, but thanks to inverse square law, only other particles within some much smaller radius than infinity will interact with enough force to change velocity noticeably. Gather together a large enough collection of these into chemically bonded distinct macroscopic objects, and there you go. The radius at which particles are repelled from each other is smaller than the distance between these bonds. That's all "solid" means.

Whether particles truly have any material extent at all, or are simply literal points representing the center of various interaction radii, is unknown and probably unknowable. It's not even clear what the difference would mean. Can a particle somehow "take up space" and prevent another particle from occupying that space if it interacted with no force at all? I'm not a physicist and kind of talking out of my ass here, but I think the Pauli exclusion principle implies maybe, but it doesn't apply to all particles.

Human perception relies entirely upon electromagnetism. Once you get down to distances less than the wavelength of the highest frequency photons and electrons, we can probe and describe the relationships mathematically, but I don't think it makes sense to try and conceive of what these things "are" in some greater ontological sense. We inherently analogize to what things look and feel like, but looking and feeling like anything is a higher-level emergent phenomenon of electromagnetic interactions.

This is more of an intellectual parlor trick than anything else. Like literally what else could "solid" mean besides "that which we call solid based on our perception." When you say that matter is "mostly empty space" you are really writing is a sentence which implicitly uses two definitions of solid in one place without distinguishing between them.

But we have a common understanding of what "mostly empty space" looks like and what we perceive as solid objects don't look like it.

Solid objects look exactly like what we perceive solid objects to look like. That is kind of the point.

I think I can be more clear. When you refer to what something looks like you are referring to the way we perceive things, which is with electromagnetic waves. In a very real sense, with respect to that, (that is, with respect to the electromagnetic field), solid objects really aren't "full of empty space," they are chock full of electromagnetic fields. Like the idea of "empty" is actually just sort of not a great way of thinking about small stuff. In fact, if we want to operationalize our notion of full or empty, we'd probably end up back at our intuitive notion of the idea.

For example. We might say that a helium atom is "mostly empty space" because if we measured the position of one of the electrons it would tend to be far away from the other one (maybe the right way to think of this is to look at the spread of coherent position states). But, in fact, around a helium atom the electrons interact pretty strongly (enough to distort their wave functions substantially) so in that sense the region around a helium atom is significantly less empty than the space around the sun between (say) mercury and venus, which have very little effect on one another. What I am getting at is that all this idea of "atoms are mostly empty space" gets at is that our definition of "empty space" is pretty vague. Vague enough to do some silly word gymnastics.

Thanks! This is helpful. It seems like I took an overly-simplistic explanation of the small scale and took it too literally. There's still a nugget of truth to the idea that our perceptions only partially tell us what the universe is really like, but it's not as disturbing as my initial thought that I was somehow observing something ghost-like as if it were solid.

Electrons meaningfully fill up the space in materials at low frequencies but not at high frequencies. So you can be... half calm?

You're a brain in a bucket. What is the nature of the bucket is up for debate

Your brain is part of a nervous system that extends throughout the "bucket". Body and brain aren't really separate.

I think the bucket is bigger than just your body.

why is this unnerving? fog isnt transparent while air is and since these are gases they are "emptier" than solid things. the emptiness properties is disconnected from visual or tactile properties.

i cant understand what you mean by knowing reality. reality is sui generis and knowledge is a relational concept.

Fog is a great analogy here and indeed much less unnerving. I think what I mean is that I'm unnerved by the fact that our perception only gives us a partial view on what really makes up the universe.

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