Hi, Please could someone give me an accurate description of why, for example, a table is solid? What I mean is that if you calculate the amount of empty space in an atom, it is 99.999% empty space so why can't your hand go through the table (like a ghost)? I have looked on lots of, what I think, are reliable sources that say conflicting things. The ideas I have come across are: 1) Matter is almost entirely empty space. The reason you can't put your hand through a solid object is because of electrostatic repulsion of the electrons. 2) Matter is not empty space but according to QM it is filled with wavefunctions so thinking of this hand through the table idea wouldn't be suitable to address since matter is not empty at all. The problem with this is that lots of sources say the wavefunction is not a physical object but just a mathematical model to find the probability of certain quantum events like the position of a particle so how can it be full of wavefunctions if a wavefunction is not a physical entity? 3) The Pauli Exclusion Principle is the reason your hand doesn't go through the table. No two fermions can occupy the same quantum state so, although matter is mostly empty space, the PEP prevents this from happening. 4) I have found a fourth source saying source 3 is wrong because the PEP only applies to isolated atoms and not for multiple atomic system coming together and that the solidity illusion is caused by electrostatic repulsion like in explanation 1. 5) I found a physics stackexchange thread that seems to get 200 likes! This seems to be mainly aimed at explanation 2 (https://physics.stackexchange.com/q...-other-matter-if-atoms-are-99-999-empty-space). So please could someone kindly tell me which explanation is the most accurate and modern way of looking at solidity. Is it good to think of solidity as an illusion? Is it wrong to think of the atom as empty space? Lots of university lecturers talk about the atom being mostly empty space but then other talk about it being full of wavefunctions whilst other say a wavefunction is not a physical thing! Some guidance would be very much appreciated, Thanks!