Reason why the chair can support me

[pivoxa15]

A physicist said that the reason why the chair is able to hold my weight is because of Heisenberg's Uncertainty principle. His reasoning was that when the atoms of my body are in contact with that of the chair, the electrons in the my body push against the electrons in the chair. Thereby forcing the electrons to a smaller region of space. Due to HU princple the more accurately we can determine the position of particles, the more wide ranging their momentum. Therefore when I sit on a chair, the electrons in the chair due to their high momentum push against my electrons hence providing pressure to hold me up. That is the reason why the chair is able to support me.

I am not fully comfortable with this explanation but that is due only to my basic understanding of QM

My inital reaction would be simply that when I sit on a chair, the electrons in my body will repel that in the chair due to the electromagnetic force. It is this repelsion that provides the reason why the chair is able to support me. The protons in my body and that of the chair are on average too far away to exert any attractive force.

It seems that my idea and that of the physicist is completely different. Can someone offer some insight here?

 

[masudr]

When you say a "physicist," what exactly do you mean? The reason the chair does support you is due to the fact that the "vacuum" field of electromagnetism generates enough virtual photons, especially in the presence of the electrons of you and the chair, so as to transfer enough momentum so as to keep you from falling into it.

 

[pivoxa15]

When you say a "physicist," what exactly do you mean?

A professional physicist and a good one because he was interviewed (that is where I got the infomation from) in a software about physics that contained two physics nobel prizewinners. The CD was called 'The mystery of the universe' or something like that.

 

[LURCH]

My inital reaction would be simply that when I sit on a chair, the electrons in my body will repel that in the chair due to the electromagnetic force. It is this repelsion that provides the reason why the chair is able to support me. The protons in my body and that of the chair are on average too far away to exert any attractive force.

It seems that my idea and that of the physicist is completely different. Can someone offer some insight here?

I do not think it is true that your idea is "completely different" from that of the physicist you have quoted. It is indeed the repulsion of like charges between the electrons in your butt and those in your chair that hold you up. But that is only the direct cause. The next obvious question is, "then why don't my electronics simply push the chair's electrons out of their way, and keep going?". The fellow on the CD was answering that question.

 

[Galileo]

There's another purely quantum mechanical effect which looks very different from the above two, and this comes from Pauli's exclusion principle. I believe it's called 'degeneracy pressure' and is unrelated to electric repulsion and thermal motion.

 

[Gokul43201]

A physicist said that the reason why the chair is able to hold my weight is because of Heisenberg's Uncertainty principle. His reasoning was that when the atoms of my body are in contact with that of the chair, the electrons in the my body push against the electrons in the chair. Thereby forcing the electrons to a smaller region of space. Due to HU princple the more accurately we can determine the position of particles, the more wide ranging their momentum. Therefore when I sit on a chair, the electrons in the chair due to their high momentum push against my electrons hence providing pressure to hold me up. That is the reason why the chair is able to support me

Either you are misquoting the "physicist" or he's not really one. Does he have a name ?

 

[Locrian]

This is all backwards. You don't say "what reason does physics give that the chair can support me?" Physics doesn't make the rules, the rules are already there. You've already proven many times that chairs usually support you.

The real question is, "What predictive system can I suppose that describes why the chair supports me." The answer will be unlike anything listed here, since describing macro-scale obviously classical phenomena with quantum mechanics is a dismal waste of time.

What you might be really asking is how you can get from quantum mechanical systems to classical ones. The answer is, as I pointed out in another thread, that you really can't, or at least not in a complete way. You can make some general statements, but they are just assertions, and can't be proven.

 

[pivoxa15]

Either you are misquoting the "physicist" or he's not really one. Does he have a name ?

The physicist's name is Jean Dalibard. The software's name is called 'Secrets of the Universe'.

So you don't like the HU principle as an explantion for the reason why people don't fall through a chair?

 

[pivoxa15]

This is all backwards. You don't say "what reason does physics give that the chair can support me?" Physics doesn't make the rules, the rules are already there. You've already proven many times that chairs usually support you.
The real question is, "What predictive system can I suppose that describes why the chair supports me." The answer will be unlike anything listed here, since describing macro-scale obviously classical phenomena with quantum mechanics is a dismal waste of time.
What you might be really asking is how you can get from quantum mechanical systems to classical ones. The answer is, as I pointed out in another thread, that you really can't, or at least not in a complete way. You can make some general statements, but they are just assertions, and can't be proven.

What I said which was "what reason does physics give that the chair can support me?" and what you say "What predictive system can I suppose that describes why the chair supports me." are to me, the same thing. Physics does not give laws to nature but merely tries to find them which I have assumed all along. But because of their close connection I might sound as if physics actually determines the law of nature. So you have stated my thoughts in a clearer way.

The quantum and classical do not mix but what I was assuming was coming up with what microscopic things tend to behave on average. And it is this averge state that dictates or contributes to the macroscopic level. I read this from Erwin's Schrodinger's "What is life?"

 

[Locrian]

What I said which was "what reason does physics give that the chair can support me?" and what you say "What predictive system can I suppose that describes why the chair supports me." are to me, the same thing. Physics does not give laws to nature but merely tries to find them which I have assumed all along.

But they aren't the same at all! The reason they seem so to you is revealed at the end of the above quote - you feel that physics finds laws of nature. I said nothing about laws of nature, but instead wrote of predictive systems, which are entirely man-made. How closely those describe "laws of nature" (whatever that is! I would argue there is only one law, and it cannot be fully described mathematically) is another question entirely.

You also speak of microscopic things on average. My argument is that you cannot deduce macroscopic phenomena by averaging microscopic phenomena. Note that this is primarily a philosophical discussion, as there is no definitive proof either way.

As a counter example to your physicist's argument, I remember a chair I used to use as my computer chair. Your physicist's argument (because it is qualitative, and not even a good qualitative argument) would suggest that that chair would support me just as this one does. Of course, it didn't; it broke in two and I ended up on the floor. The strength of materials is just one of many things that you should (by such reductionist ideals) be able to produce using QM, but cannot. The reason the chair holds your weight is not adequately described by the HUP.

I like the above example because it illustrates the philosophical lackings of such reductionist arguments while at the same time making their absurd uselessness obvious.

 

[pivoxa15]

But they aren't the same at all! The reason they seem so to you is revealed at the end of the above quote - you feel that physics finds laws of nature. I said nothing about laws of nature, but instead wrote of predictive systems, which are entirely man-made. How closely those describe "laws of nature" (whatever that is! I would argue there is only one law, and it cannot be fully described mathematically) is another question entirely.

I never said that physicsts will find what nature or reality 'really' is. I wanted to say that physicsts try their best to find it by theorising which from experiments looks like a pretty good way of going about it but they are all approximations to reality. Your predictive systems are what I would call theories. So actually we share the same view.

You also speak of microscopic things on average. My argument is that you cannot deduce macroscopic phenomena by averaging microscopic phenomena. Note that this is primarily a philosophical discussion, as there is no definitive proof either way.
As a counter example to your physicist's argument, I remember a chair I used to use as my computer chair. Your physicist's argument (because it is qualitative, and not even a good qualitative argument) would suggest that that chair would support me just as this one does. Of course, it didn't; it broke in two and I ended up on the floor. The strength of materials is just one of many things that you should (by such reductionist ideals) be able to produce using QM, but cannot. The reason the chair holds your weight is not adequately described by the HUP.
I like the above example because it illustrates the philosophical lackings of such reductionist arguments while at the same time making their absurd uselessness obvious.

So you are saying that there are emergent properties that arise from microscopic systems when looked at macroscopically and these properties cannot be described by the microscopic laws. Maybe if you model the atoms in the chair classically such as how classical thermodynamics models the physical systems than you might get a result that matches your experiment. But that is cheating a bit because you are soley using macroscopic laws.

 

[Son Goku]

As a counter example to your physicist's argument, I remember a chair I used to use as my computer chair. Your physicist's argument (because it is qualitative, and not even a good qualitative argument) would suggest that that chair would support me just as this one does. Of course, it didn't; it broke in two and I ended up on the floor. The strength of materials is just one of many things that you should (by such reductionist ideals) be able to produce using QM, but cannot. The reason the chair holds your weight is not adequately described by the HUP.
I like the above example because it illustrates the philosophical lackings of such reductionist arguments while at the same time making their absurd uselessness obvious.

That doesn't really seem to be a counter proof. The example used by the physicist is probably the standard "Assuming a chair where strucural weakness can be ignored". Even so the chair broke into two, you didn't pass through the chair as if it were immaterial.

 

[Locrian]

That doesn't really seem to be a counter proof. The example used by the physicist is probably the standard "Assuming a chair where strucural weakness can be ignored".

I was waiting for that! No, see, that's the whole point - how do you think you can possibly show you cannot pass through the chair without making a case for its structural integrity? Every argument listed in this thread (HUP, electron repulsion, etc) so far could be applied to air, and yet it doesn't support anyone most of the time. You must try and describe the physical properties of the material - and you can't do that using strict reductionism.

 

[Locrian]

Maybe if you model the atoms in the chair classically such as how classical thermodynamics models the physical systems than you might get a result that matches your experiment. But that is cheating a bit because you are soley using macroscopic laws.

Exactly! It's worth mentioning that studies of very low-level systems (atomic structure, etc) are essential to properly understanding some higher level systems. They just aren't enough. You end up having to take measurements at whatever larger scale you are operating at.

 

[pivoxa15]

I guess my main question is how, if at all, does the triangle between HU principle, electromagnetic repulsion and with Paul's exclusion principle connect together. What relationship exists between the three physical theories. I gather that Paul's exclusion principle includes the charge so the electromagnetic repulsion and Paul's princple are more similar than the HU principle, which seems to stand on its own.

The three all explain why broadly speaking, matter are structured and organised in some way.

 

[Locrian]

What?

Can you hit us with that again, worded differently?

 

[pivoxa15]

What?

Can you hit us with that again, worded differently?

Sorry about that. I have fixed post 15 and have made it make sense, hopefully.

 

[Galileo]

I gather that Paul's exclusion principle includes the charge so the electromagnetic repulsion and Paul's princple are more similar than the HU principle, which seems to stand on its own.

No. That pressure has nothing to do with electron-electron repulsion. It's a purely quantum mechanical effect that arises from the antisymmetrization of the wavefunctions.

 

[Son Goku]

I was waiting for that! No, see, that's the whole point - how do you think you can possibly show you cannot pass through the chair without making a case for its structural integrity? Every argument listed in this thread (HUP, electron repulsion, etc) so far could be applied to air, and yet it doesn't support anyone most of the time. You must try and describe the physical properties of the material - and you can't do that using strict reductionism.

Heh, true. It is macroscopic properties of the chair that prevent you from going through it.

 

[Gokul43201]

Every argument listed in this thread (HUP, electron repulsion, etc) so far could be applied to air, and yet it doesn't support anyone most of the time.

Exactly ! That's why (among other reasons), I said the original argument was essentially gibberish.

 

[LURCH]

I'm afraid the final answer here is going to be more philosophical than quantum mechanical. In philosophy, it is taught that there are many different kinds of "cause"; sufficient, efficient, necessary, etc. The explanation from HUP is a necessary cause, but not a sufficient cause. That is to say, this phenomenon can be said to be the "reason" that the chair holds you up in so much as, without this quantum principal, the chair would not hold you up. However, this property of quantum systems is not enough, on its own, to keep your backside off the floor. It requires a host of other necessary causes like the repulsion of like charges (probably the most direct cause), and the ionic bonding in the polymers, if it is a plastic chair (the most immediate indirect cause), and many others.

Any one of these can be plugged into the statement, "the reason the chair holds you up is...", to make a true statement.

 

[pivoxa15]

I'm afraid the final answer here is going to be more philosophical than quantum mechanical. In philosophy, it is taught that there are many different kinds of "cause"; sufficient, efficient, necessary, etc. The explanation from HUP is a necessary cause, but not a sufficient cause. That is to say, this phenomenon can be said to be the "reason" that the chair holds you up in so much as, without this quantum principal, the chair would not hold you up. However, this property of quantum systems is not enough, on its own, to keep your backside off the floor. It requires a host of other necessary causes like the repulsion of like charges (probably the most direct cause), and the ionic bonding in the polymers, if it is a plastic chair (the most immediate indirect cause), and many others.
Any one of these can be plugged into the statement, "the reason the chair holds you up is...", to make a true statement.

So you are saying that if I don't fall through the chair imply I know the HU principle is true. However, I cannot say that if HU principle is true imply I won't fall through the chair.

Since the CD was made for the layman, maybe Jean Dalibard was trying to illustrate one general applicability of the HU principle.

 

[Haelfix]

Its funny you mention this, Brian Greene brought this up once at a dinner conversation.

Yes the fundamental reason why you can sit in the chair is the EM force. That is the answer.

Otoh, if the chair was made of say bosons, and your butt was made of bosons, well it wouldn't be a pretty sight, and let's just say you wouldn't leave with everything quite the same, if you know what I mean.

 

[Gokul43201]

So you are saying that if I don't fall through the chair imply I know the HU principle is true. However, I cannot say that if HU principle is true imply I won't fall through the chair.

I think it's most unnecessary to bring up the HUP here. It plays as much a role in holding up my butt as does say, the nature of the strong force - it may be at the basis of things more fundamental, but has no direct relevence by itself. The direct cause is simply regular electrostatics (as pointed out by Haelfix, above).

Besides, the explanation involving the HUP's role (in the OP) is just wrong.

 

[Locrian]

Its funny you mention this, Brian Greene brought this up once at a dinner conversation.

Yes the fundamental reason why you can sit in the chair is the EM force. That is the answer.

I'm interested - was that Greene's answer to the question? It would make sense. That answer is physically unprovable, scientifically unfalsifiable, philosophically uninteresting and allows for only the most general and useless of predictions.

Which pretty much fits everything Greene's been working on for a decade.

As I've already said, these vague, hand waving arguments are not scientifically sound. You can use that electromagnetic repulsion idea to argue that metal, water, glass and fractured glass all would make a chair that would support a person. But as we all know, those don't all do that.

I've been biting my tounge for a long time in this thread now, but I am finally going to refer the initial poster to a branch of people who can answer their question better than anyone has yet answered it here. If you want an unassailable, meaningful, predictive and useful argument for why a chair supports a person,

ask a carpenter.

 

[LURCH]

But unless the carpentor has an understanding of ellectromagnetic repulsion, he cannot explain why a chair that is principly made of empty space can repell your body, which is also mostly made of empty space. Without ellectromagnetic repulsion, your body would pass right through the chair.

 

[Locrian]

You didn't even read the post. You didn't read the ones before that, either. Electromagnetic repulsion explains nothing about why a chair holds up your body. It's a mathematically unprovable, scientifically unfalsifiable, philosophically uninteresting idea that predicts nothing at all. You can keep repeating it, but it won't make it true.

It's bad philosophy and bad science.

 

[Haelfix]

Umm, its not unfalsifiable its pretty much obvious to anyone with any education in physics. Look, we're not talking about how much EM repulsion is required to keep someone's ass in the chair, that will quickly degenerate into molecular physics and how best to arrange a lattice of molecules for the maximum rigidity and so forth.

But at the end of the day all this is, is a simple statement about EM forces (in some shape or another) that gives the normal force required to keep someone in their seat. Its nothing mysterious like weird neutron degeneracy like in a neutron star, or the strong force or the weak force. Its pure atomic and molecular physics which has been known for 150 years.

The original author wanted to make a point that chemistry is more or less made possible by the pauli exclusion principle, which is true. Otherwise your butt and the chair would have a certain amount of elements that would randomly fall into some sort of weird quantum condensate. But at the end of the day, the fundamental *force* supporting you is made possible by electrons pushing against one another, that's it. Details of course are more complicated.

 

[inha]

Umm, its not unfalsifiable its pretty much obvious to anyone with any education in physics. Look, we're not talking about how much EM repulsion is required to keep someone's ass in the chair, that will quickly degenerate into molecular physics and how best to arrange a lattice of molecules for the maximum rigidity and so forth.
But at the end of the day all this is, is a simple statement about EM forces (in some shape or another) that gives the normal force required to keep someone in their seat. Its nothing mysterious like weird neutron degeneracy like in a neutron star, or the strong force or the weak force. Its pure atomic and molecular physics which has been known for 150 years.
The original author wanted to make a point that chemistry is more or less made possible by the pauli exclusion principle, which is true. Otherwise your butt and the chair would have a certain amount of elements that would randomly fall into some sort of weird quantum condensate. But at the end of the day, the fundamental *force* supporting you is made possible by electrons pushing against one another, that's it. Details of course are more complicated.

On your main point I agree 100% but atomic and molecular physics being 150 years old?!? Was that a typo perhaps? And this is also more of a condensed matter physics issue than atomic or molecular physics.

An illustrative view on the complex details is that Pauli tells the chair how to organize it's contents(with the help of EM) and the EM interaction keeps ones ass from falling to into it as you stated. Pounding someone in the head with Ashcroft&Mermin is also highly illustrative but unfortunately painful.

 

[Locrian]

Umm, its not unfalsifiable its pretty much obvious to anyone with any education in physics.

No, it's actually the exact opposite. The idea that electromagnetic repulsion is a suitable explanation for why a chair supports a person is only something that someone who hasn't worked in materials science would argue. The reason it is unfalsifiable is because no one can use it to produce properties of macroscopic objects. To produce these macroscopic properties you have to take macroscopic measurements - which any furniture maker has, ad nauseum.

A chair supports a person because of the strength and mechanical organization of the stuff it is made out of. You cannot produce information about that using fundamental properties of its constituents, and therefore you cannot produce a working theory of why a chair supports a person. I already gave examples of why this is very poor reasoning above:

As I've already said, these vague, hand waving arguments are not scientifically sound. You can use that electromagnetic repulsion idea to argue that metal, water, glass and fractured glass all would make a chair that would support a person. But as we all know, those don't all do that.

No one here has, and no one here can, refute the above statement. This is because everyone here is making simplistic and absurd reductionist assumptions that are not supported by reality.

I've given concrete examples of why this thinking is backwards, and no one has made any attempt to confront them - instead, they merely repeat unprovable assertions over again. If you have some personal need for this type of reductionist crutch that's fine, but just understand it is unscientific in nature and philosophically suspect.

 

[masudr]

Locrian,

I felt that the OP didn't ask "why would a wooden chair support me but not a chair made of water support me?" So your point about glass and water chairs is largely irrelevant.

I also think that inha has more or less hit the button with his/her most recent post in this thread.

 

[Locrian]

Locrian,

I felt that the OP didn't ask "why would a wooden chair support me but not a chair made of water support me?" So your point about glass and water chairs is largely irrelevant.

Yes they did ask that! That question is one of many that are asked by the more general question "Why does a chair support me?" I of course knew that people would cry foul when I pointed this issue out, but you won't be in a more comfortable position when you rephrase the question (which you haven't fully done). On the contrary, the harder you try to narrow your focus, the more plain it will be that the reason a chair supports a person is a property that is not predictable by subatomic rules.

I do apprecite your actually moving the issue forward slightly, so please rephrase the question and I'll continue to show you why the answer given here is unacceptable.

Saying something like "the EM force is the reason you don't fall through a chair" is like saying "sound is the reason we listen to music." Sure, it might be necessary, but all you're doing is making an incomplete list of the constituents, and in no way can it be shown that the phenomena you're describing can be predicted from that list.

 

[Locrian]

I felt that the OP didn't ask "why would a wooden chair support me but not a chair made of water support me?" So your point about glass and water chairs is largely irrelevant.

The more I think about this the more it amuses me! The OP asked a question. The answer they were given are so general and unpredictive, that even if you accept them they suggest absurd conclusions!

Why would anyone accept an answer that was so obviously flawed? The question of why water, which contains molecules under the same laws of E&M as wood, doesn't support someone and wood may, is the obvious counter argument to the backwards statement that E&M is the reason you don't fall through the chair!

 

[Locrian]

Pivoxa,

I would like to give you the first correct answer to your question so far submitted in this thread. It is very unlike every other answer you've been given.

A chair supports a person because the material it is made out of exhibits properties of strength and hardness. Neither of these properties is something you can predict from electrons, protons and EM fields. Some will tell you this is merely because of our computational limits, and you should accept that the way you accept someone telling you they could jump the moon, if only they had really bouncy shoes.

Not just any material will do to make a chair. You have to choose materials whose strength and hardness are sufficient, and this is always a question, especially if you want to make many of them. Your base material will probably (but not necessarily) have good strength and high hardness. If you would like to be kind to the poor person sitting in your chair, you could also cover parts of your chair with a material whose hardness is very low, such that someone's buttox would not be offended by prolonged sitting.

Once you've acquired your materials, you must then arrange them in a way that takes advantage of the properties of your materials, and will produce a sitting surface. There are many potential methods of arranging your materials, and people have been doing this for many, many years. I once again refer you to a furniture maker.

No doubt it will once again be argued that I've missed the point. You didn't speak of material strengths or hardnesses in your post, you talked of the HUP! However, the reason I sound off topic is merely because the oringal answer you were given by that physicist is so rediculously wrong that the correct answer bears no resemblance.

I give myself an "A" for producing the correct answer,

and a "D-" in the area of humility.

 

[pivoxa15]

Locrian, I see what you are getting at and for all practical purposes, your answer is the best. But I made the thread because I was curious between the relationship between fundalmental physics and everyday life.

I also like to see things from a reductionist point of view (although I am not sure everything can be explained by fundalmental laws due to the fact that some things emerge from lots of fundalmental things - i.e. how could you predict how a cell functions even if you knew all the matter that makees it?) . Even though you say that 'Neither of these properties is something you can predict from electrons, protons and EM fields.' I am sure all the fundalmental laws of physics contribute to the properties of strength and hardness. If they contribute a little bit. I also find it interesting whether the micro laws are consistent with the macro properties which is a good thing that they are, with the HUP and electromagnetic repulsion.