Q: If atoms are 99.99% space, what “kind” of space is it? Is it empty vacuum?

Physicist: This is a bit of a misnomer.

When we picture an atom we usually picture the “Bohr model”: a nucleus made of a bunch of particles packed together (protons and neutrons) with other particles zipping around it (electrons).  In this picture, if you make a guess about of the size of electrons and calculate how far they are from the nucleus, then you get that weird result about atoms being mostly empty.  But that guess is surprisingly hard to make.  The “classical electron radius” is an upper-limit guess based on the electron being nothing more than it’s own electric field, but it’s ultimately just a gross estimate.

The picture gives you an idea of more or less where things can be found in an atom, but does a terrible job conveying what those things are like.

The picture gives you an idea of more or less where things can be found in an atom, but does a terrible job conveying what those things are actually like.

However, electrons aren’t really particles (which is why it’s impossible to actually specify their size); they’re waves.  Instead of being in a particular place, they’re kinda “smeared out”.  If you ring a bell, you can say that there is a vibration in that bell but you can’t say where exactly that vibration is: it’s a wave that’s spread out all over the bell.  Parts of the bell will be vibrating more, and parts may not be vibrating at all.  Electrons are more like the “ringing” of the bell and less like a fly buzzing around the bell.

Just to be clear, this is a metaphor: atoms are not tiny bells.  The math that describes the “quantum wave function” of electrons in atoms and the math that describes vibrations in a bell have some things in common.

Where exactly is the ringing happening?

Where exactly is the ringing happening?

So, the space in atoms isn’t empty.  A more accurate thing to say is that the overwhelming majority of the matter in an atom is concentrated in the nucleus, which is tiny compared to the region where the electrons are found.  However, even in the nucleus the same “problem” crops up; protons and neutrons are just “the ringing of bells” and aren’t simply particles either.  The question “where exactly is this electron/proton/whatever?” isn’t merely difficult to answer, the question genuinely doesn’t have an answer.  In quantum physics things tend spread out between a lot of states (in this case those different states include different positions).

The atom picture is from here.

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16 Responses to Q: If atoms are 99.99% space, what “kind” of space is it? Is it empty vacuum?

  1. Peter Russell says:

    I imagine space as a gluon field. The way gluons structurally bind to form exclusion patterns means that just like you can find bubbles in water you can also find structures in gluons. Just like quarks are structures in gluons supported by the way gluons transit states and those states changes propagate. At the macroscopic level of human observation this gives rise to the temporal and spacial sense that has served the mammalian predictive survival model very well.

    In the Bohr billiard ball model, the red proton “ball” is really a collection of three stable gluon patterns in a sea of busily state transitioning gluons. There is no empty space, and space like time is just an illusion.

  2. Doug says:

    The ringing of a bell analogy still leaves us far from a connection to the reality of what matter, particles and space are as constituents of an atom. The ringing of a bell rings the bell. What does the “ringing” of an electron or proton ring, space, or the electromagnetic field?

    Then when you consider larger entities it gets less intuitive. Particles can be thought of as stacking up into something bigger, like the peg and ball models chemists use, but resonances of indeterminate size ringing nothing somehow dance together to form all that we experience. That is a great conceptual void.

  3. Joe says:

    Doesn’t the wave-particle duality say that there’s still a discrete physical entity? It’s the probability distribution that’s smeared out, and observing the particle collapses that probability (since it’s now certain where exactly it is), right?

    I didn’t think the electron itself was smeared out. If it isn’t, I think a better analogy would be a beach ball in a pool. The difference of course is that that electrons have velocity, whereas the ball is entirely at the mercy of the waves. So ok, maybe an even better analogy would be a toy motorboat in a pool, propelling itself forward, yet having a less predictable position over time.

    Interesting post!

  4. The Physicist The Physicist says:

    @Joe
    This is really subtle, and complicated enough that it would have totally derailed the post. It turns out that things being in multiple states (and positions) is fundamental. You literally can’t describe the universe in terms of things being in definite places and states (without making up a lot of weird ad hoc laws). There’s an old post here that talks about how we can know something so deeply bizarre.

  5. Sheldon says:

    So what happens to those electrons (their smearyness, or definite position-ness or lack there of) if we stop their motion? Say hypothetically drop the atom to absolute 0 K?

  6. George Clark says:

    Since all matter is just compressed energy, everything would be a wave and the particle would be nothing more than a very high energy portion of the wave.

  7. Erol B says:

    Here’s something to consider. According to quantum physics, the “empty space” here should really be filled with virtual particles, which basically appear and disappear within a very short amount of time. As far as I understand, this arises from the fundamental uncertainty of the amount of energy (interchangeable with matter) in a field. I am not a formally trained physicist, so if anyone can explain this better or correct any error I made, feel free.

  8. Miske50 says:

    If there are dark energy and dark mass, there is no such thing as “Einsteinan vacuum”, i.e. a space whereas all values of fields are zero. So, consequently, with time, the dark energy will “dissolve” even atoms in to a Big Freeze. At least this is today’s theory, as far as I understand it.

  9. Amaven says:

    Wouldn’t it be more honest to say that we don’t have the math, technology or the conceptual fortitude to accurately explain the position of all sub atomic particles? Rather than saying ‘its a smearing’? Doesn’t the Heisenberg Uncertainty principle codify our inability to fully explain the world of quantum mechanics?

  10. Swarnkar Rajesh says:

    Not sure if it is a normal space. But In my opinion it must be some exotic kind of space, we never experience in real life.

  11. bradford Thomas says:

    the electron “cloud ” fills much of this “empty” space……..

  12. Wes says:

    Why are atoms built, shaped like they are? One of the more general things about particle distribution in atoms is that they are shaped like an ongoing perpetual explosion… the heavy stuff in the middle (protons, neutrons) and the light fluffy stuff (electrons) thrown to the outside. Maybe, maybe not.

    I used this simple principle in developing a more elaborate idea I once had to improve my understanding of Einstein’s relativites and cosmology. As a bonus, it seems to help explain the logic behind the weird “spacey dust-cloud” blueprint as well. Afterall, a universe inhabited by simple little square solid-block atoms would be much more aesthetic, if it were up to me.

  13. Kaol says:

    Amaven said: “Wouldn’t it be more honest to say that we don’t have the math, technology or the conceptual fortitude to accurately explain the position of all sub atomic particles?…”

    I agree. After all, modern science is barely three hundred years old, so we cant expect to know all of the answers – or indeed even most of the answers – about the subtle levels of nature’s functioning. To quote …

    “Everything, however complicated – breaking waves, migrating birds, and tropical forests – is made of atoms and obeys the equations of quantum physics. But even if those equations could be solved, they wouldn’t offer the enlightenment that scientists seek. Each science has its own autonomous concepts and laws”.
    -Martin Rees

  14. Doug says:

    The atom has some extension. Looking at the electron as a wave rather than its character as a particle smears it out so it has extension even if the boundaries cannot be specified. This wave extends into what space within the atom to give us what is considered the size of any atom? Apart from the waviness of the electron (is that an electromagnetic waviness?) is there anything other defining the space inside the what is understood to be the volume of an atom?

  15. Doug says:

    It is curious that with all the uncertainty about electrons we have the certainty to build multitudes of devices in which we use electrons with finesse.

  16. Angel says:

    @Anaven:

    That’s not really what the Uncertainty Principle by Heisenberg states.

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