Is it true that you are never actually touching something?

  • #51
ZapperZ
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I can't say too much about quantum field theory and quantum mechanics because I just recently got interested in the subject. But these electron clouds are not really "clouds," they are just the space which an electron may or may not occupy at any given time. The electron itself can only be in one place at one time.
That is totally incorrect. It is at a particular location when you make a position measurement of it, but before that, it is really spread out. That's the whole point of the principle of superposition that resulted in the Schrodinger Cat scenario! Things CAN be in many places at once! If it is only at one particular location at a particular time, you will not have bonding/antibonding states, etc. in molecules.

This is a clear example where one cannot simply learn about physics in bits and pieces, because a lot of things are involved in many of these phenomena.

Zz.
 
  • #52
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It is at a particular location when you make a position measurement of it, but before that, it is really spread out.
Of course the question then is "what is really spread out, and exactly how do we know that?".

That's the whole point of the principle of superposition that resulted in the Schrodinger Cat scenario! Things CAN be in many places at once!
But this is only the case when we don't know (ie., haven't made a measurement). Because when a measurement is made, then the possibilities of the superposition are localized/collapsed to a specific position/outcome.

If it is only at one particular location at a particular time, you will not have bonding/antibonding states, etc. in molecules.
Ok, so it isn't at a particular location at a particular time, but you said above that "it is at a particular location when you make a position measurement of it".

Please clarify.
 
  • #53
A. Neumaier
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Of course the question then is "what is really spread out, and exactly how do we know that?".
The electron _field_ is spread out, and we know it since quantum electrodynamics (from which everything is derived, with very high accuracy in some cases) is primarily a field theory. Electrons behaving as particles (in the sense of being localized at approximately one place) only exist if you consider the field theory in the limit of geometric optics - which is an essentially macroscopic view not applicable inside atoms or small molecules.

But this is only the case when we don't know (ie., haven't made a measurement). Because when a measurement is made, then the possibilities of the superposition are localized/collapsed to a specific position/outcome.
It is impossible to make a measurement of an electron bound in a molecule. What one can measure there is only the charge distribution. To measure the position of a single electron, you need to make it reach a localized detector such as a Geiger counter.

Ok, so it isn't at a particular location at a particular time, but you said above that "it is at a particular location when you make a position measurement of it".
Namely when the Geiger counter clicks. But it doesn't measure of the many bound electrons in its material but only clicks when essentially free electrons reach it.
 
  • #54
ZapperZ
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Of course the question then is "what is really spread out, and exactly how do we know that?".

But this is only the case when we don't know (ie., haven't made a measurement). Because when a measurement is made, then the possibilities of the superposition are localized/collapsed to a specific position/outcome.

Ok, so it isn't at a particular location at a particular time, but you said above that "it is at a particular location when you make a position measurement of it".

Please clarify.
I don't have to make a position measurement to detect such superposition. You are forgetting that I can detect such a thing by measuring either a non-commuting observable, or a non-contextual observable.

For example, if A and B do not commute, then measurement of A does not collapses the observable for B. Similar things can be done in trying to detect such superposition. This is what has been done in the Delft/Stony Brook SQUID experiments in detecting the coherence gap. The coherence gap exists because of the superposition of the supercurrent in BOTH directions at the same time!

Zz.
 
  • #55
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Ok, thanks ZapperZ and A. Neumaier.
 
  • #56
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The nucleus of an atom makes up only a tiny fraction of the entire atom. The electrons make up an even smaller portion. How is it possible that there is no empty space within the atom? If the nucleus makes up 1/(insert large number) of the atom, and the electrons make up another 1/(insert larger number) of the atoms mass, how is it possible for these fractions to add up to equal 1? There is a large field where the electron(s) of an atom may be at any given time, but that doesn't mean that they are there nor that they are making full "touching" contact with other nearby electrons.
The electrons make up a tiny proportion of the mass of an atom, while the nucleus makes up the rest. These proportions add up to 100%.

The nucleus makes up a tiny proportion of the space occupied by an atom, while the electrons make up the rest. Again things add up to 100%.

The picture of an atom being mostly empty stems from the childhood of atomic structure analysis, where most of the atom's extension was found to be transparent for alpha rays,
and the early models explained that by pointlike nuclei and electrons. http://en.wikipedia.org/wiki/Rutherford_model

But we don't think glass doesn't occupy space because it is transparent for light, or that only the bones of our bodies occupy space because the remainder is transparent for X-rays. So why should we think of the electronic fluid surrounding nuclei not to occupy space simply because it is transparent to alpha rays?
 
  • #57
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I really apologize for bumping an old topic, but I have a pretty significant question:

Thus touching is real. The nuclei don't touch each other but the atoms and molecules do.
How often does this happen? When my skin touches the surface of a desk, or my wife's skin, are the atoms (or the electron fields of the atoms) touching then? Or does this happen only under specific circumstances?
 
  • #58
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How often does this happen? When my skin touches the surface of a desk, or my wife's skin, are the atoms (or the electron fields of the atoms) touching then? Or does this happen only under specific circumstances?
Electrical conduction will require some overlap of the electron clouds, and you can get conduction with a rather light touch. So I would say you are pretty much guaranteed to have some significant overlap whenever you are touching something.

At how many points that actually happens is a different question, and it will depend greatly on the surface in question.
 
  • #59
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I really apologize for bumping an old topic, but I have a pretty significant question:



How often does this happen? When my skin touches the surface of a desk, or my wife's skin, are the atoms (or the electron fields of the atoms) touching then? Or does this happen only under specific circumstances?
It always occurs. Whatever we feel is ultimately just the electron field.

Think of the electron field as a kind of glue. If two surfaces with glue on them touch, the glue merges, until the surfaces separate again. The change in the glue field is ''noticeable'' by both surfaces.

In the same way, when we touch something, the electron fields merge, and are changed by that enough that the nerves register contact.
 
  • #60
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is it true that you are never actually touching something? i keep hearing that this is true but why is it that we can feel the texture of things?
In all serious, this is not a difficult question to answer, even philosophically. The way it is presented immediately defines it as a psychophysical question. It is every bit the same as the question: "If a tree falls in the woods and no one is around to hear it, does it make a sound." The answer to that question is obviously NO. Why? because "sound" is defined as the vibration of molecules in a medium (usually air) purturbing a human's basilar membrane which sends a signal to the brain causing the conscious perception of the vibrating medium. No basilar membrane around? No sound.

It is exactly the same with the idea of "touching." The OP said, "you" are never actually touching something. When we think of what it means to know we are touching something, it means that we have a conscious perception of our bodies making contact with another object. It is that experiential sense that the sense organ gives our awareness of a tactile sensation that defines "touching." It actually has little or nothing to do with whether two objects actually make physical contact with one another, and from a QM perspective, you can't even prove that ever happens. But that wasn't even the question, it wasn't about "contact," it was about "you touching" something. In short, whether or not you are actually making contact with an object, if you feel its texture or feel like you are touching it at all, then YES, Millie! You are actually touching it. That's the real deal.
 
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  • #61
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It always occurs. Whatever we feel is ultimately just the electron field.
E-field can significantly extend past the electron density, though. Yes, I know the actual interactions are going to be much shorter range due to charges almost completely balancing, Van der Waals, etc., but the above seems like an over generalization.
 
  • #62
A. Neumaier
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E-field can significantly extend past the electron density, though. Yes, I know the actual interactions are going to be much shorter range due to charges almost completely balancing, Van der Waals, etc., but the above seems like an over generalization.
We have no sensors for the e/m field (except for vision), thus its longer range does not count.
All touching is based on contact, which is governed by the electron field.
 
  • #63
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Our touch receptors are sensitive enough to pick up minute movements caused by an E-field from charged object. It's much better picked up by hairs, but if you move your hand past a charged object, you should still be able to feel it.

But more importantly, the actual interaction of "touch" is an electrostatic interaction. You are still responding to an E field. Not to electron densities. Not directly.
 
  • #64
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But more importantly, the actual interaction of "touch" is an electrostatic interaction.
All this talk about electrostatic interactions involved in our sense perception I don't think advances an understanding of the OP's question. Why not just make the statement,"it all has to do with atoms." ALL sensory perception relates to electrostatic interactions. I don't think all of this discussion about electric fields, van der waal forces, etc. is advancing any insight into the psychophysiology of touch.

Touch receptors are mechanoreceptors in the deeper layers of the integument. They produce action potentials that travel toward the brain when they are "bent" or mechanically altered by a pressure on the superficial layers of skin. There can be a pressure there that is subliminal to conscious perception even though the mechanoreceptors are issuing pulses. Similarly, there can be pressure or contact on the skin that is insufficient to generate action potentials because the pressure is not great enough to deform the receptor in such a manner as to trigger action potentials.

That triggering is accomplished via the bending of the receptor allowing the transfer of Na+ and K+ ions to traverse the neuronal membrane triggering the potential. Yes, it is electrostratic, but then again, so is everything in human physiology.
 
  • #65
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I guess my point is that it seems to me the OP's question has already been answered--if you feel like you're touching something, then yes you are touching it. That could be a baseball you grip in your hand, a raindrop on your forearm, a laser beam pointed at your forehead, or a resistive magnetic force on a metal plate in your head when you're taking an MRI.

It seems to me that this discussion of the physics of overlapping electron clouds, etc., is now off-topic for this discussion. I just don't see the relevance. Maybe that conversation should be taken up in a new thread.
 
  • #66
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No, it is entirely relevant. We're not discussing the sensation of touch per se (that would be more off-topic, if anything), we're discussing the physical definition - i.e. if we clasp two sponges together, are those sponges touching? Is there merely empty space between the atoms of those sponges? OP's question was probably raised in response to the popular notion brought up by certain physicists like Michio Kaku that say we're actually hovering over our chairs when we sit on them. Fortunately, the question in that context has been answered in this thread.
 
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  • #67
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i.e. if we clasp two sponges together, are those sponges touching? Is there merely empty space between the atoms of those sponges?
Doesn't this get down to an epistemological question, though, at its foundation? I mean, if we continue to look deeper and deeper into the problem, don't we just come up with superpositions of states and wave functions? If these wave functions, as many do, extend out to infinity, albeit at negligible values for large radius's, how can we say where "contact" ends and inter-particle space begins? I think analysis at this level is qualitatively distinct from the psychophysics of sentient experience that seemed to be the OP's central concern.
 
  • #68
A. Neumaier
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All this talk about electrostatic interactions involved in our sense perception I don't think advances an understanding of the OP's question. Why not just make the statement,"it all has to do with atoms." ALL sensory perception relates to electrostatic interactions. I don't think all of this discussion about electric fields, van der waal forces, etc. is advancing any insight into the psychophysiology of touch.

Touch receptors are mechanoreceptors in the deeper layers of the integument.
It is this level that is addressed in question and answer. The question was not about how the receptors and the transmission work, but what causes the receptors to signal.

The signal is caused by a mechanical force on the skin, not by an electromagnetic one, since our skin is comnpletely insensitive to small electromagnetic fields unless these casue some mechanical or thermal effect first.

And the mechanical effect is a force caused by touching. Touching is the contact of electron clouds to an extent significant enough to change the macroscopic force field.
 

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