Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Touching at atomic and macro scale

  1. Apr 23, 2015 #1
    I asked a question here in the forum, in the topic "Many Worlds Interpretation", things do touch in atomic scale? and in the macro scale? what defines "touching" ? Some members answered me..

    Rodrigo Cesar said:
    in this video: watch?v=P0TNJrTlbBQ Professor Philip Moriarty explains it perfectly "Do Atoms Ever Touch?"
    "Professor Moriarty's definition of contact is also the definition of contact that we all use for the Newtonian world. The attractive & repulsive forces balancing out."

    Bhobba said:
    he defines contact as forces balancing ie the Van Der Walls attractive force and the repulsive force of the Pauli Exclusion Principle that is the origin of solidity. This is a LOT different from the usual conception of contact.

    What Bhobba means with " a LOT different from the usual conception of contact"?

    I'm creating this topic, because I was advised to create another topic to not disturb the main subject
  2. jcsd
  3. Apr 23, 2015 #2
    It could be that the Pauli exclusion principle is born out of quantum mechanics, and is therefore far removed from anything we might consider 'usual'. It relies not on particles being kept apart by forces as in the Newtonian picture, but by the very nature of their wavefunctions.
  4. Apr 23, 2015 #3


    Staff: Mentor

    I thought it was obvious. The usual concept of touching is you have some kind of solid surface (with what solid exactly means deliberately left vague eg the dictionary defines it as hard or firm; not in the form of a liquid or gas - its unstated implication being its impenetrable - like I said - rather vague) and they touch like in those problems you did at school about blocks sliding down inclined planes.

    The view the physical chemist gave was not like that - it was of objects having forces that originated in QM (van der walls force and the pauli exclusion principle force from electron degeneracy) associated with them and touching is when they are in balance.

    Its the difference between everyday pictures of the world and what science says is really going on.

    You should read the early chapters of the Feynman Lectures where this is discussed:

    Last edited: Apr 23, 2015
  5. Apr 23, 2015 #4
    So, we do touch things on macro scale?
  6. Apr 23, 2015 #5
    I need to add: it would be VERY useful for you to post the whole link to a Youtube video, not the just the part after .com/
  7. Apr 24, 2015 #6


    Staff: Mentor

    It depends on what you mean by touch.

  8. Apr 25, 2015 #7
    So, It's just matter of semantics? Biology?
  9. Apr 25, 2015 #8


    Staff: Mentor

    It simply means if you want a scientific answer you need to be exact in the question you are asking.

    What do you mean by touch? The concept of contact espoused by the physical chemist is different to its everyday use. Touch means in everyday use, from the Oxford dictionary, 'Come into or be in contact with'.

    The answer depends, obviously, on your conception of contact. Is it the everyday one or is it the scientific one. Either way its obvious.

  10. Apr 26, 2015 #9


    User Avatar
    Staff Emeritus
    Science Advisor
    Education Advisor

  11. Apr 27, 2015 #10
    and what about this video??

    I think this guy just wanted audience?
  12. Apr 27, 2015 #11


    Staff: Mentor

    Without viewing it I can say 100% for sure semantics about what touching is, is a dead end.

    You have the correct scientific explanation of what touching is. Beyond that isn't really what this forum is about.

Share this great discussion with others via Reddit, Google+, Twitter, or Facebook