If atoms are mostly empty space, why doesn't light pass through everything?


They taught me that in high school too (i.e., that matter is "mostly empty space.") Only thing is, it's not true.

Solid matter is mostly filled with electrons. Yeah, the mass is all concentrated in the relatively tiny nucleii, but the mass is not what photons interact with, and the mass is not what defines the physical and chemical properties of ordinary matter. The electrons are responsible for all of that, and the electrons pretty much fill the space.


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Updated on August 01, 2022


  • Tdonut
    Tdonut over 1 year

    Atoms are mostly empty space, and although I now understand why matter doesn't pass through other matter, why don't photons pass through the empty space of the atoms? Is it the same sort of idea as matter passing through other matter?

    • CuriousOne
      CuriousOne over 8 years
      For the purpose of your questions photons do not interact with the empty space inside matter but with the electrons that are in it. How strong that interaction is depends on the quantum mechanical state of the electrons. In some materials a few hundred nm of material will absorb almost all photons, in others photons can go trough hundreds of meters without being absorbed. To understand the details one has to dig deep into atomic, molecular and solid state physics.
    • dmckee --- ex-moderator kitten
      dmckee --- ex-moderator kitten over 8 years
      "Atoms are mostly empty space" This sits right near the top of my list of "Unhelpful Science Factoids That Aren't Really So". It depends on a half-assed understanding of the Bohr model which is wrong in a lot of ways, but is still taught because it is a easy stepping stone toward a real understand of atoms. However, as the de facto single thing that non-scientists "know" about atoms it is just awful and is wrong, wrong, wrong!
    • The Photon
      The Photon over 8 years
      Chicken wire is mostly empty space, but that doesn't mean you can walk right through it.
    • 299792458
      299792458 over 8 years
  • Mike Dunlavey
    Mike Dunlavey over 8 years
    True, if you keep in mind that where an electron "is" is uncertain - it is a wave function that is spread out. So is a photon.