# When you touch something there isn't really any physical contact

1. Aug 27, 2007

### Oblef

When you touch something there isn't really any "physical" contact

When you touch something there isn't really any "physical" contact, it's just the electromagnetic forces that repel each other. So if I try to touch a table, no particles from my hand actually touches any particles from the table, right?

So if we imagine my fingers where made of particles without any charge and I was trying to pick up a brick made out of particles without any charge with my fingers, then what would happen? Would I be able to touch the brick? If not, what would it look like if I tried? If yes, what would that look like?

(A more realistic example could be 2 neutron stars colliding.)

And second, can you see a hand made out of particles with no charge?

Regards.

Last edited: Aug 27, 2007
2. Aug 27, 2007

### scarecrow

An electromagnetic interaction is a physical interaction. Your definition of "physical" is just misinterpreted.

No. An atom is an assembly of charges, therefore it carries an electromagnetic "space" that is a part of the whole atom. Therefore an electromagnetic interaction (or touch) constitutes a "physical touching" of particles.

3. Aug 27, 2007

### Oblef

So if I touch a table the electrons and protons etc. in the atoms in my hand touch the electrons and protons etc. in the atoms in the table?

4. Aug 27, 2007

### Oblef

I mean physically touch. Like one electron bumping into another..!

5. Aug 27, 2007

### scarecrow

No because then you'd be chemically reacting with the table...lol. But, you're right when you say that the EM forces repel each other and that's what you consider to be "touching".

6. Aug 27, 2007

### Oblef

Alright, so there is in fact no _real_ physical touching. What about my other question?

7. Aug 28, 2007

### Billygoat

Well OK - If you were made up of neutral particles, but these particles could interact with each other some way besides electromagnetically so you could hold together, but if they didn't interact with the brick you are trying to lift, your hand would simply pass through the brick. Very ghost like. You probably couldn't even see you hand because light, with which you see, interacts almost totally electromagnetically, and so wouldn't interact with you stuff, whatever it is. So if your hand would pass through the brick, light would probably pas through you.

A very interesting question worth looking into, if it hasn't already been studied is to ask how far into a neutron star light could travel. Could it go all the way through? Probably not since neutrons are unstable, and in a neutron star they are decaying and reforming. This would mean that there are some electrons and protons within the star to interact with the photon.

8. Aug 28, 2007

### Oblef

So would the same thing happen if 2 neutron stars hit each other. The same thing that happened to my fingers and the brick - pass right through?

9. Aug 28, 2007

### Nesk

This premise is false; the repelling is mainly explained by the Pauli exclusion principle. When the electron distributions at the tip of your hand get so close to those of the table surface that the distributions start to overlap each other, they are deflected, i.e. your finger and the table, and to some extent all entities supporting either part, are elastically deformed. That requires a force, and at some point you'll either be unable to apply more force (you cannot push harder), or a permanent deformation occours (something breaks - don't do that).

EDIT: As for the neutron stars, since neutrons are fermions just like electrons they'll repel each other when they get close enough. If they didn't, the neutron stars would collapse into themselves under their own gravity.

10. Aug 28, 2007

### Pythagorean

There is a physical "touch". The simple view is that if you touch a counter, your electrons repel it's electrons and they don't actually make physical contact, but that's not how we humans define touch anyway: we define touch by texture, warmth, and intensity.

When our electrons make contact with the counter's electrons, they conduct heat, which is part of the experience of touching something. We also detect texture, which is the geometrical arrangement of the many electrons and they're variable heights creating different pressures and intensities across all of the electrons in our finger touching it.

Our neurons don't detect each electron individually, they are made up of electrons themselves. So how we interpret a touch is a very physical, macro-scale thing with several quantum physical processes involved. You're looking to closely at one component of "touching" (the electron charge repelling) and not considering the whole dynamic of it. Quantum physics can hardly be applied to human experience.

11. Aug 29, 2007

### Oblef

Pythagorean - I completely agree with you, thank you.

Nesk - What is a fermion?

12. Aug 29, 2007

### scarecrow

A fermion is a particle with spin S = 1/2 such as a proton or an electron.

13. Aug 29, 2007

### Oblef

al right - Could you tell me about spin and what S = 1/2 means. Or is that to much to ask for? :)

14. Aug 29, 2007

### Loren Booda

I believe it means that a particle with such spin as 1/2 (e. g., a fermion) can take on the angular momentum (h-bar)/2 or -(h-bar)/2. h-bar is Planck's constant. Spin here is not what we visualize macroscopically as a rotating object, but a microscopically conserved phenomenon with similar units.

15. Aug 29, 2007

### Nesk

It certainly is a lot, though not necessarily too much.

It has been experimentally show that electrons posses an intrinsic magnetic moment which can take two distinct values: $$+\frac{1}{2}\mu _b$$ or $$-\frac{1}{2}\mu _b$$. A magnetic moment usually arises from an orbiting charge (clasically), but electrons are generally considered to be elementary particles. As such, it cannot have a fine structure, i.e. it is not made up of anything smaller, and therefore the classical idea of an orbiting charge being the origin of the magnetic moment collapses in this case.

All particles have some kind of spin, and this has profound consequences for how they act. It can be shown theoretically that the probability that two identical particles with half integer spin occupy the same point in space equals zero. Such particles are called fermions. On the other hand, it can be shown that particles with integer spin can easily occupy the same piece of space. Such particles are called bosons.

Fermions include electrons and quarks. Protons and neutrons are each made of three quarks, the combination of which decides which of the two you get. Since quarks have half integer spin, so do protons and neutrons (try adding three half numbers to get a whole, it isn't easy!).

Bosons include so-called field particles, of which the photon is the one that most people are fairly familiar with. Other bosons include gluons and a variety of more exotic particles.

The properties of bosons is the reason why you can shine two rays of light through each other without photon collisions. Instead the photons may interfere through superposition.

Anyway, back to the fermions: Since they cannot occupy the same point in space, they appear to repel each other. *That* is what you feel when pressing the table.

I hope this clarifies things a bit.

--Nesk.

16. Aug 30, 2007

### Oblef

Thank you :)

17. Sep 1, 2007

### django

oblef
Wrong! You should actually be in a forum dealing with medical sciences! When you touch something, the nervous sytem in your hand activates neurons within the brain that inform you of the kind of substance that you are 'touching'. So what we are dealing with here is not physics, it is the interaction of your neurons, with what they are coming into contact with. That, I am sure you will agree with, is different from the physics of what is actually happening. django

18. Sep 1, 2007

### Oblef

Django - yeah but what I meant by touching was just matter itself applying force to matter. Don't know how else to describe what I meant.. :/

19. Sep 1, 2007

### django

oblef
Yeah! But what you are forgetting is that you yourself are a very complicated aggreagation of matter, that just happens to classify what is happening as a sense of touch! django

20. Sep 1, 2007

### Oblef

I got my question answered before I believe, and that's all I wanted.