# Space and particles

1. Jan 15, 2009

### wolram

It seems the consensus is that space is just a metric, but what is the metric when, we consider (solid) objects, i mean we think of objects as solid, but they are mostly by volume just space, can we say that some un physical stuff constrains particles at some distance apart? or that particles (live) in a metric, without even knowing what this metric is.

2. Jan 16, 2009

### Demystifier

I wonder if anybody understands this question.

3. Jan 16, 2009

### malawi_glenn

No it is a mystery, I don't understand a thing

4. Jan 16, 2009

### thenewmans

OK, fine. I’ll take a crack at it even though I’m a complete amateur. Wolram is a contributor with 3k posts. I haven’t heard of space referred to as a metric. To me a metric is a way of measuring things. So I’ll assume our standard units of measure are suitable for measuring space. Do particles maintain a certain distance from each other? Yes! Look up the exclusion principal and the fundamental forces. Protons and neutrons are close but still don’t occupy the same location. They keep a certain distance not because of their size but because of the forces. Electrons are a little farther away due mostly to electromagnetic forces. Beyond that, it’s nearly all about electromagnetics. Quantum Electrodynamics is a great read for that.

Mostly Space
By space I think you mean empty and non-empty contains solid particles with a certain size and mass. But when you get down to that level, that kind of thinking doesn’t work so well. I’ve managed to stop thinking of particles having a size. I don’t even think of them as points. Instead I only think of the forces they have on other particles.

• Particles produce forces.
• Forces control the shape of fields (like space).
• Fields control the movement of particles.

Solid
There’s usually some thermodynamic explanation involved when comparing solids to non-solids. Let’s use a diamond, which is kind of like a really large molecule in that every atom has a covalent bond with its neighbor. You can see through it but you can’t put your finger through it. The bonds in your finger are electromagnetic but not as strong as covalence. When they collide, these bonds don’t break and no bonds are formed between your finger and the diamond. So they stay separated.

Un-Physical
If it has an effect then it’s physical. I think you mean unknown. I’m sure there’s plenty we haven’t learned about all that why there is an exclusion principal at all. But we have testable theories that make very accurate predictions. So that’s a good start.

5. Jan 16, 2009

### thenewmans

When you hear scientists say “Mostly Space” that’s because an atom could be compressed. A neutron star is far more dense. Using that as a "metric", then yes, our atoms are mostly space.

6. Jan 16, 2009

### jnorman

hmmm - it is ALL space. eg, electrons are point particles - they have no volume, they do not take up any space. nucleons are made up of quarks, which are, again, point particles with no volume. photons have no volume. it is fields that permeate space, interactions of which result in all that we see.

7. Jan 16, 2009

### thenewmans

I know there are interpretations like that but I don’t know of any testable theories. Are there?

8. Jan 16, 2009

### DrChinese

The theory is that any fundamental particle, when observed as to position, can be isolated to a volume of space that is arbitrarily small. (You won't see its wave nature at that time.) Experiments confirm this to the limits of current technology. So there is an upper limit on the size of an electron, one which is very small indeed. So experiment is, so far, consistent with theory.

I would agree with the comments that ordinary matter around us, when considered as to its particle nature, is nearly a perfect vacuum. Regardless of how you consider it, all of the matter in the Milky Way at one time was compressed into a volume much smaller than a grain of salt. (Of course it was not organized into atoms at that time.)

9. Jan 16, 2009

### wolram

AFAIK no one has said space is a physical entity lately, so to me it is un physical.
And if particles can be reduced to all most nothing, it seems crazy that i am sitting on a
chair that is all most nothing, and even i am all most nothing.

Thanks for the help.

10. Jan 16, 2009

### Dmitry67

Particles can repel each other even being pointlike.
In order to interact, they dont need to actually *touch* each other.
So there is nothing strange that you are sitting on a chair made of zero-sized particles

11. Jan 16, 2009

### thenewmans

The "Metric expansion of space" does not mean space is a metric. It just means it can be measured. Quote: "The metric expansion of space is the averaged increase of metric (i.e. measured) distance between objects in the universe with time."

OK but saying it that way is a little confusing. Un-physical sounds like no physics. And physical entity sounds like it takes up space.

Yeah, I'm with ya on that one. But keep in mind, taking up space has a whole different meaning down there at the QM level. To us it's just one thing bumping into another. Down there, it's repelling electromagnetic forces.

12. Jan 17, 2009

### debra

All particles are probably just mathematical models with properties and ways of behaving, but otherwise not the usual small piece of rock or dust as you may believe. How large is a heap of equations and parameters?

Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?