How come we can't walk through walls?

  • Thread starter Wellsi
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In summary, the conversation discusses the concept of solidity and the ability to pass through objects. It is mentioned that science does not actually state that atoms are mostly free space, but rather the probability distributions of quantum particles fill all space. The conversation also touches on the Heisenberg Uncertainty Principle and the Pauli exclusion principle in relation to this topic. It is suggested that the reason why we cannot pass through objects is due to electron repulsion and the EM force. The conversation also mentions an experiment by Rutherford involving shooting helium through a sheet of gold, which challenges the previous notion of matter as a smooth, rigid continuum.
  • #1
Wellsi
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Hey all...
im still at school and doing the IB diploma, and for Theory of Knowledge subject i have to write an essay, the topic being
"Our sense say that a table is solid, yet science tells us it is mainly empty space, so how come we can't put our hand through it?"
I have been looking and it seems it has something to do with electron repulsion and the Heisenburg Uncertainty Principle can someone help me please! Why can't we put our hands through tables or walk through walls?
 
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  • #2
  • #3
Because tunneling is a QM phenomenon and the physics that describes humands colliding onto a wall is not valid on atmic scale : ie classical physics.

marlon
 
  • #4
Wellsi said:
Hey all...
im still at school and doing the IB diploma, and for Theory of Knowledge subject i have to write an essay, the topic being
"Our sense say that a table is solid, yet science tells us it is mainly empty space, so how come we can't put our hand through it?"
"...science tells us it is mainly empty space..." ! Does it, really? I think not, and I wish high school textbooks would stop propagating this ill-formed idea.
 
  • #5
Gokul43201 said:
"...science tells us it is mainly empty space..." ! Does it, really? I think not, and I wish high school textbooks would stop propagating this ill-formed idea.

Why is this idea ill-formed? Because the probability distributions of quantum particles fill all space? Or is there some classical reason why the idea is flawed?
 
  • #6
Think of it like this. When your ceiling fan is off, you can easily put your hand through it and touch the ceiling. Now when it's on full blast, the blades start looking almost like 1 object, and if you put your hand in there, it's going to stop you.

Now think about atoms and electrons and such orbiting at light speeds. It may give the appereance of being 100% solid, but I doubt that's even possible. Anyways, I hardly know what I'm talking about, just referring to an example my chemistry teacher gave me way back in high school, maybe it'll help.
 
  • #7
Gokul43201 said:
"...science tells us it is mainly empty space..." ! Does it, really? I think not, and I wish high school textbooks would stop propagating this ill-formed idea.

Agreed 100%.

To the OP, you should consider challenging this statement in your essay, provided of course that you are able to use arguments grounded in physics.

Claude.
 
  • #8
so what grounds do i challenge it on? The fact that "science" in general does not state that atoms are mostly free space so therefore the hypothesis is wrong?
thanks for the fan analagy that helped a lot :)
check this url for some deductive reasoning about the subject:
http://everything2.com/index.pl?node_id=919472&lastnode_id=0
i mean, theoretically, it must be possible to walk through a wall?
 
  • #9
Wellsi said:
so what grounds do i challenge it on? The fact that "science" in general does not state that atoms are mostly free space so therefore the hypothesis is wrong?
thanks for the fan analagy that helped a lot :)
check this url for some deductive reasoning about the subject:
http://everything2.com/index.pl?node_id=919472&lastnode_id=0
i mean, theoretically, it must be possible to walk through a wall?

Theoretically yes, the probability is just really low...
 
  • #10
Wellsi said:
Hey all...
im still at school and doing the IB diploma, and for Theory of Knowledge subject i have to write an essay, the topic being
"Our sense say that a table is solid, yet science tells us it is mainly empty space, so how come we can't put our hand through it?"
I have been looking and it seems it has something to do with electron repulsion and the Heisenburg Uncertainty Principle can someone help me please! Why can't we put our hands through tables or walk through walls?

Electrons 'repel' other things with the EM force. This makes it so your particles and a table's particles repel each other to a point where you cannot go through the table itself.
 
  • #11
ok so the outer most electrons repel each other with the EM force... that's all good. So it means that we never actually touch something? its only the force between the outer most electrons? how can we then tell something is rough or smooth, and why do different things "feel" different?
wasnt there an experiment before done about quantum tunnelling and proved it worked?
 
  • #12
Then how do you explain Rutherfords experiment where he was able to shoot helium through a sheet of gold. QM definitely tells us that what was previously thought as solid i.e. a smooth rigid continuum is not entirely true. In fact, QM can show us that our previous notion of the phases of matter, primarily say Solid, liquid and gas, although macroscopically having very different properties, on the microscopic scale they look almost identical (there are many ways to characterise this difference, correlation lengths, order parameters etc), however this is a very different notion than what was previously believed about matter.
 
  • #13
things are all the same on a microscopic level? How come a helium atom can go through when say an atom on my hand cant?
 
  • #14
The gold foil was pretty thin, but the point of the experiment was that if the 'size' of nuclei were what they were supposed, the scattering angle would have been much larger. Instead of you hand let's talk about making the gold thicker and thicker. Forget all that crap about tunnelling through walls and the like, its one of those popular physics notions which frustrates the hell out me and others I know. If a solid was a continuum then if I was to take an infinitesimal slice, nothing would be able to pass through it without breaking it. However if the slice is made out say a single sheet of atoms (think of filling a plane with equilateral triangles, at each vertex is placed an atom), then there will be 'space' between the atoms (regions where there is most likely little or nothing to impede the motion of a projectile) and an object will pass through. Let us say that statistically if we randomly shoot projectiles at this sheet, the probabilty that it will pass through is

[tex]
Pr(passing through 1 sheet)=\frac{1}{q}
[/tex]

Now if I build up a 3d solid by adding layers to this sheet, the probability of passing through the solid will be a function of the number of layers

[tex]
Pr(passing through n sheets)=\frac{1}{q^{n}}
[/tex]

Now say a sheet of gold is effectively 5.0 Angstrom thick (mean plane separation in fcc structured gold), and the transition probability is nearly one, let's say [tex]\frac{99}{100}[/tex] for some particular momentum projectile (it will be different for a whole lot of parameters). Now take a slab of gold to be 1cm thick, that's approximately [tex] 10^{9}[/tex] layers of gold, such that the transition probability will be

[tex]
Pr(passing through 1cm gold)=\frac{99}{100}^{10^{9}}
[/tex]

which is an incredibly small number, although it is still theoretically possible.
 
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  • #15
"Forget all that crap about tunnelling through walls and the like, its one of those popular physics notions which frustrates the hell out me and others I know."

thanks for that, it makes sense there. These popular physics notions? They would help to know so i can use them in the essay about generalisations (see the original post)
Can u explain the one i just used (about the tunneling?) what really happens there?
 
  • #16
You might appeal to the Pauli Exclusion Principle. The reason that your hand stops when you slam it on the table-top is that the electrons in the molecules making up your hand refuse to be forced into the same quantum state as the same-spin electrons in the molecules that make up the table. Of course, the PEP could be entirely wrong, and then it would be your job to explain why you can't walk through walls... ;)
 
  • #17
is PEP proved? Or is it one of those things we use to explain something that we don't quite understand properly?
 
  • #18
The Pauli exclusion principle is phenomenoligical. However the mathematics behind such mechanisms is well understood in that if we say

'If a type of particle has the propertu that only one particle is able to any particular state'

then we can go quite a long way. However no one really knows why some particles (half integer spin, fermions) can only singularly occupy states and others (integer spin, bosons)may all occupy the same state. This is one of the open problems in physics
 
  • #19
Wellsi said:
things are all the same on a microscopic level? How come a helium atom can go through when say an atom on my hand cant?

Because the "atoms" in your hand are molecules and even at the smallest size are 4-5 times bigger than a helium atom. Not to mention pseudo-surface tension in the phospholipid bilayer and the spacing between the individual units as described by the fluid mosaic model dictate what can/cannot pass through it.
 
  • #20
Epicurus said:
Forget all that crap about tunnelling through walls and the like, its one of those popular physics notions which frustrates the hell out me and others I know.

indeed, it is annoying but how else are quantum physicists going to get funding support from the public? :biggrin:
 
  • #21
ok that's all good and fine thanks guys :) let me clarify something thou? electrons "pop" in and out of existence within their sub orbital forming this "cloud" of varying shapes (dumbbell etc) thus appearing to be everywhere at once like the fan analagy on the previous page?
 
  • #22
Don't forget that the atoms and molecules in the table, or your car, our yourself form very tight bonds, to the point where it takes a sledgehammer, or an ax or a saw or a drill to break a table top, or simply put, to put something through it. On the other hand, putting your hand through liquid water or air is not exactly a challenge.

So, lo and behold, the real issue is what distinguishes solids from liquids and gasses. There's plenty of folks who have written on this subject, Google is certainly one place to check. some chemistry books will touch on this issue, as will books on solid state physics. (The probability of your hand tunneling through anything solid is so small that it is less likely than a snow blizzard in tropical weather.)

Regards,
Reilly Atkinson
 
  • #23
when you put your hand into liquid water or through air, your not putting your hand "through" them like i mentioned with a table or walking through the walls are you?
another question... what would happen if in rutherfords experiment, the helium atom that was fired at the sheet of gold entered into it, but became caught within, ie stopped before it could make it the whole way through. Would this have any effects on the gold or the helium?
 
  • #24
Wellsi said:
so what grounds do i challenge it on? The fact that "science" in general does not state that atoms are mostly free space so therefore the hypothesis is wrong?

Quantum physicists AFAIK have reached a consensus that the wavefunction that represents a bound electron actually represents the spatial distribution of the electron, and not the electron whizzing around behind the scenes (i.e. the electron exists everywhere within the wavefunction at anyone time).

Since the electron wavefunction occupies most of the space in the atom, you could say that an atom is filled with electrons, not empty space. Empty space has no mass and charge etc, while the space occupied by an electronic wavefunction does.

Claude.
 
  • #25
ok that's good, i needed counter arguments and arguments from the perspective of another culture... can anyone help me on that all i can find is this story about a chinese monk getting "stuck" while he was reportedly attempting to walk through a wall, and that sounds pretty absurd to me.

still to follow my last post on this topic... putting your hand through water and air is not the same as putting it through a table is it?
 
  • #26
Wellsi said:
when you put your hand into liquid water or through air, your not putting your hand "through" them like i mentioned with a table or walking through the walls are you?
another question... what would happen if in rutherfords experiment, the helium atom that was fired at the sheet of gold entered into it, but became caught within, ie stopped before it could make it the whole way through. Would this have any effects on the gold or the helium?


Answer 1. Yes -- what else could it be?

Answer 2. Yes -- the alpha particle could could indeed be "trapped" in the foil, but the probability is miniscule. (Think nuclear reaction

alpha + nucleus --> other nucleus + anything but an alpha)

If this happens, it's called inelastic scattering, and it certainly lowers the number of alphas detected relative to the no-trapping allowed situation. But, Rutherford's conclusions would not be much changed -- it's the "high" number of alphas that are scattered into large scattering angles -- like 120 degrees from the beam direction -- that suggests the nuclear atom.
Regards,
Reilly Atkinson
 
  • #27
Wellsi said:
still to follow my last post on this topic... putting your hand through water and air is not the same as putting it through a table is it?

yes it is the same
 
  • #28
So, to recap about walking thru walls...

It'd be impossible to do it in our nonquantum states (i.e., my body and the wall as we are right now) because of the electron repulsion (i.e., the like charges on the electrons on my body and on the wall, repulse the two masses).

Given the above, what is the nature of tearing open a wall at the quantum level? I.e., what bond is being broken to allow the separation of one part of the wall from the other?
 
  • #29
reilly said:
Answer 1. Yes -- what else could it be?

I think what the OP means is to leave the state of the material the hand goes through unchanged, or at least without setting it into motion.
 
  • #30
yes, when i move my hand through some air, its not going through the molecules in the air is it? like if i put my hand through a table the atoms are passing between each other, in air or water they go around?
How could you put your hand through water then?
 
  • #31
So, your question is, "How come we can't put one solid through another?"
 
  • #32
In response to masudr, that is the direct question I had in mind. But the water/air analogy mentioned above is a very good one..a solid can go through liquids and gases and remain intact. So, why is it -- at the atomic or even quantum level, is it not possible for a "solid" to go through a "solid" with each remaining intact after the passage.
 
  • #33
what would happen if the solid entered another solid, yet was unable to continue any further and was hence stuck in the other solid? would ne thing special happen there?
 
  • #34
Wellsi said:
what would happen if the solid entered another solid, yet was unable to continue any further and was hence stuck in the other solid? would ne thing special happen there?
Lets imagine that you have a block of iron and a block of copper on the desk in front of you. If you think that the nucleus and electrons of each atom are infinitesimal points, then you might imagine that each atom is mostly empty space and that you could slide one block through the other. This is not the case, though. The electrons are not little points, but are smeared over all the places where they are permitted to be, and they are already as tightly packed as permitted by the Pauli exclusion principle. Being fermions, they resist being packed any closer than they currently are (with same-spin neighbors). Because of the Pauli exclusion principle, it is impossible to superimpose the two cubes in one space at the same time. If you will Google "degenerate matter" you will find out more about how the behavior of fermions effects the properties of matter.
 
  • #35
Iron Block vs. Copper block -- why neither can go thru the other

Very well. Now, let's shift to the next scenario..I want to cut each block in half. I use a saw to do that. How is it that I can cut thru the interlinked bonds of the copper block's atoms? Perhaps put another way, how does brute force shear one copper atom's connect to the next causing them to separate?

The response to this is going to lead to my final question which is what force can be harnessed to allow the separated copper block atoms to remember their location with each other and rejoin once the "brute force" -- the saw -- leaves? Answering this will lead perhaps to the answer to the reason for my very first question (why can't we walk thru walls): Can a force be harnessed to allow the wall to part to allow our passage...This principle was shown by the "bad guy" in the sci fi movie, Terminator II.
 
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