Physicist:
(The following paragraph is wrong. Like, really wrong. There’s a redaction here: My bad: If atoms are mostly made up of empty space, why do things feel solid?)
As atoms get too close to one another their charges begin to repel each other. Once they’re close enough that they can “see” the other atom, the electrons on the near side of both atoms begin to repel each other and move more to the far side of both atoms. This leaves the positively charged nuclei facing each other.
Electrons swarm around the nuclei of their atoms (in this case Helium 4). When they're brought very close together the electron clouds shift and the atoms briefly polarize in such a way that they repel.
Basically, when two atoms come too close they behave exactly like magnets brought together with the “north” ends pointing together.
(Everything up to here has been wrong.)
This certainly isn’t the whole story. Quantum chemistry isn’t rocket science, but it’s still pretty complicated. Atoms can share electrons, or their electrons can move so that they behave like attracting magnets, and a whole mess of other things. For example, attractive van der Waal forces can show up when atoms are close, but not too close. Slight fluctuations in the arrangement of electrons in one atom induces a sympathetic arrangement in nearby atoms (this is more specifically a “London dispersion force“). As a result, the atoms end up with dipoles lined up in a “+- +-” way, instead of a “-+ +-” way, like in the picture above.
In general, the force is extremely small. But it is just strong enough to hold liquid helium to itself (otherwise it would be a gas), and hold geckos to walls.
Geckos have weird feet because they have evolved to optimize the chance of random dipole interactions between the atoms in their feet and the atoms of whatever they're climbing. As a result, they can climb vetically on materials as smooth as glass. Pictured here is a gecko excited to learn that someone remembered his birthday.
Addressing the fact that matter is mostly empty space, if you really squeeze matter you’ll find that the electrical forces can no longer hold atoms apart. Basically, they find that it’s easier for the electrons and protons to fuse together and form neutrons. Once all the charges are out of the way the atoms (now balls of neutrons) are free to collapse together. At that point the only thing holding them apart is “Pauli pressure”, which is fancy quantum physics speak for “they can’t be in the same place”.
The only time this happens in nature is in neutron stars. To get an idea for what happens when you “deflate” matter: If you were to crush a 50m Olympic size swimming pool into neutron star material, it would be about 0.05mm long, which is about the width of a single hair.
Your answer, while plausible on its face, is not correct. Electrostatic interactions have essentially nothing to do with why matter feels solid. As you point out yourself, at close distances the fluctuations in electron density result in attractive, not repulsive, forces.
The source of the ultimate “excluded volume” forces is entirely quantum mechanical: it is the fact that electrons are fermions, hence (this is the Pauli exclusion principle) cannot occupy the same volume without being in different energy states. If you attempt to push the orbital electrons of two atoms into the same volume of space, most of the electrons will need to be promoted to much higher energy states. The requirement of a great deal of energy to move the atoms closer is what we interpret as a force. You might call it an “exclusion” force, because it comes from the exclusion principle — but it has no connection at all with any of the canonical four forces, and in particular it has nothing to do with the electrostatic repulsion between electrons. It would operate even if the electrons were uncharged.
For an easy way to see this, recall that neutron stars are held up against collapse due to the force of gravity by exactly the same exclusion forces — and, of course, neutrons have no electrostatic repulsion, being uncharged.
Pingback: My bad: If atoms are mostly made up of empty space, why do things feel solid? | Ask a Mathematician / Ask a Physicist
if we consider earth than earth is composed of atom together and it is suspended in space , all matter gases dust are suspended in space , as such space is not made up of atoms , space is only a reality which has permitted to atom to stay within him whether space and time is also created is not easy to explain even by scientist . Only posibility that even space is created is possible if there is entity more special than space that could be consciouseness a creative point from where every thing is created . In answer to if atom is mostly empty space sorry atom is smallest particle a solid and within the solid is the empty space as such the atom bulk together is solid , liquid and gas but not empty space , empty space is a ocean in which atom are like fish
Mr. Physicists? … What about the scanning tunneling microscopes? They photograph atoms and the photo’s are little rows of pyramids door to door. How does that fit with the theory that you are using? (They also show a lattice structure)
The scanning tunneling microscope can’t take pictures (if it could, it would just be a microscope). What it does is very carefully runs a current between the tip of a very sharp needle and the surface in question, and measures that current. The greater the (tiny) current, the closer the surface. This technique is accurate to distances smaller than atoms, so when that surface is made of atoms (and when isn’t it?) it appears bumpy. The fact that the atoms are mostly empty doesn’t enter into it.
So you assume the current is flowing around the tiny solar system model and not through it giving images that appear to be pyramids door to door? I know that the Bohr Atom is an accepted model and that the study of chemistry works with it. But you can trouble shoot an electrical circuit with a diagram that does not look anything like the actual circuit. What makes people think that the atom looks like the Bohr model and not like the images they see? Those images could also be forces and nothing solid. Weight could be forces and not mass. With the Tunneling microscope we at least have an image instead of just our own imagination.
In the beginning logic tells us that Emptiness, the laws of God, and time was all that was present. That stands to reason that atoms do not contain anything solid and are only forces. I might sound like someone trying to make something out of nothing, … LOL … but I have reasons for asking what other people think. If you will try to stay with me it will be a big help to me.
Well, it’s not an actual direct image (readers who’d like to see what we’re talking about, here’s some images), it’s more like a painting of the bottom of a murky river made by someone who’s poked it with a stick.
The understanding of the structure of atoms (specifically their emptiness) didn’t really get off the ground until the Geiger-Marsden experiments. In those experiments alpha particles were fired at stuff, and rather than most of the alpha particles slowing down (by pushing through material), the vast majority of the alpha particles passed through without slowing down, and a tiny few bounced off of something very small, very heavy, and very charged (what we now call the nucleus).
Up until then everyone just assumed that matter was, more or less, “full”.
SOLIDLY E t h e r e a l
— James Ph. Kotsybar
We’re made of stuff that’s hardly even here
composed of atoms that are mostly space.
The solidity with which they appear
happens because their trapped electrons race
around the nucleus — near light speed fast —
and always possess a negative charge
that wont let other negative charge past.
They also make the atom appear large.
Around the nucleus, that is tiny,
electrons blur to a far distant cloud.
Were we their size, we wouldn’t even see
the nucleus we’d remotely enshroud.
The percent of empty space we define i
s ninety-nine point nine nine nine nine nine.
I like your painting of the river bottom but I noticed that you did not mention the lattice structure. Do you have any idea of what the STM is seeing in those images?
Those are atoms.
The point is that they aren’t being imaged directly. The fact that they appear solid is just an artifact of the method we use to detect them.
I know very little about this field, but it still interests me . First, could you explain this to someone that doesn’t really understand this subject. You’re saying that despite nothing being solid at an atomic and sub atomic level, things are solid because of electromagnetic reactions that fill the space with a magnetic force or maybe some sort of energy ? Also, is the “measurement problem” anything beyond a theory and does it have much validity, plus, how did they ever test a theory where an atom does not show up until it is observed? Thank you for any replies.
I fixed this post, because of its wrongness. Update here.
It’s a little more subtle, but basically yes; electromagnetic effects keep atoms from getting too close.
The “measurement problem” is, to a large extent, the “Copenhagen problem”. Ignoring the measurement problem, by assuming that wave functions never collapse, is a one-way ticket to the Many Worlds Interpretation, which seems to work just fine (without these kind of problems).
so oke im not like you guy that know every thing about this but i like to ask some thing’s.
you guys only talk about the negative and positive size of the atome like a magnet and the space between,
why is it that there is nothing that can make the same reaction than ohter atoms,
like… say get a magnet lay it on your hand,and it makes (lets say) positive energie to your hand but it wont stiky on your hand like it does to metal,
what if it have the same positive energie as a atoms than you get “+- +-”
is this how the Geko does it ?
so the Geko have the “+- +-” in his feet to climb on any thing he is on.
what if we can make some sort of machine than preduce the same energie force?
1.wil 2 atoms fuse together than and make some thing new?
2.or wil it pass through the ohter atoms?
because they have the same energie so there is nothing than wil stop the ohter atom from going through.
We have made some machines (materials) that produce the same force. The gecko’s hands and feet don’t actually produce a force, but instead just optimize the forces already present. It’s a subtle distinction.
Two atoms fusing is a nuclear reaction, and two atoms bonding together is a chemical reaction, and the van der waals force (what geckos use), is far weaker than both.
Am almost sure that consciousness is what makes the universe ! As nothing is really solid at all and eventually if you go back beyond the big bang everything came from nothing absolutely nothing .
Motion of the atoms prevents anything from passing through it. Like if u walk past a chain link fence with a 3/4 inch steel bar and try to put it through the fence while u r walking it wont go through the links in the fence. If u stop the bar fits through the fence easily.
And/Or, Anything we could try to put through an atom is to big to fit between the particles that make up an atom. Like if u try to put your whole hand through a chain link fence, it wont pass through the fence. This happens because the links (or particles) r to close together for your hand(or an object) to pass through it.
So…. I was wondering if one or both of these theories was correct??? Send me an eMail if u can answer my question. jonathans03866@gmail.com
The central idea of “solidness” is not that something is solid because it’s there, a thing is solid because it exerts a substantial force on things that come close enough. If two types of “stuff” only generate forces that the other ignores, like one generates and responds to electric force and the other generates and responds to the nuclear strong force, then they’ll seem completely insubstantial to each other.
We see this in nature. For example, neutrinos are a type of particle that is unaffected by both the electric and nuclear strong forces (the primary forces involved in ordinary matter), and as a result they may as well be ghost particles: their density and speed have no impact on whether or not they feel “solid”.