Dimensions of our physical world

[LightningInAJar]

TL;DR Summary

Are there things of lesser dimensions?

Is there anything we know of in this physical world that is less than 3 spatial and 1 time dimension? Or is that pretty much everything, no more, no less?

 

[DaveC426913]

Summary:: Are there things of lesser dimensions?

Is there anything we know of in this physical world that is less than 3 spatial and 1 time dimension? Or is that pretty much everything, no more, no less?

I guess that depends on how picky you get about what constitutes 'this physical world'.

The surface of a balloon is 2-dimensional. The coastline of a continent is somewhere between 1- and 2-dimensional.

 

[Baluncore]

The speed of light is two dimensional. Length per Time.

 

[Drakkith]

Nothing that most people consider to be 'physical' such as desks, chairs, rocks, etc are less than 3 dimensional. Even fundamental particles are considered to occupy three dimensional volumes of space, though the concept of size for a fundamental particle is... complicated.

 

[anorlunda]

Death and taxes.

 

[LightningInAJar]

I guess that depends on how picky you get about what constitutes 'this physical world'.

The surface of a balloon is 2-dimensional. The coastline of a continent is somewhere between 1- and 2-dimensional.

Well I mean even a single layer of atoms has measurable thickness. I mean more in a literal sense.

 

[Ibix]

Well I mean even a single layer of atoms has measurable thickness. I mean more in a literal sense.

I think you may be missing @DaveC426913's point here. The surface of a balloon is not a layer of atoms. It's the boundary between the region of space where there are atoms of the balloon and the region where there are none. That's literally two dimensional. The question is whether or not it's what you think of as part of the physical world.

 

[PeroK]

I mean more in a literal sense.

Rather than a littoral sense?

The coastline of a continent is somewhere between 1- and 2-dimensional.

 

[LightningInAJar]

I think you may be missing @DaveC426913's point here. The surface of a balloon is not a layer of atoms. It's the boundary between the region of space where there are atoms of the balloon and the region where there are none. That's literally two dimensional. The question is whether or not it's what you think of as part of the physical world.

Sorry. Still escapes me. Balloon wall still has thickness right? And it's thickness takes away a little space from the inside and outside regions? It is an imperfect boundary as a wall 2 feet thick?

 

[Ibix]

Sorry. Still escapes me. Balloon wall still has thickness right?

Yes. So there are two boundaries between balloon and not-balloon, which are 2d surfaces. Perhaps simpler, a 3d solid cube has six 2d faces, which divide space into regions inside the cube and regions outside. Are those 2d faces part of the physical world?

 

[DaveC426913]

Well I mean even a single layer of atoms has measurable thickness.

I was about to counter, but it looks like several others got my back.

 

[DaveC426913]

So, what people are pointing out is examples of a general case: boundaries between two regions do not necessarily have 3 dimensions, yet they are still physical.

 

[LightningInAJar]

Yes. So there are two boundaries between balloon and not-balloon, which are 2d surfaces. Perhaps simpler, a 3d solid cube has six 2d faces, which divide space into regions inside the cube and regions outside. Are those 2d faces part of the physical world?

The boundary is more conceptual than actual? Like I think a hockey goal counts only after puck breaks plane of second boundary of the line?

 

[DaveC426913]

The boundary is more conceptual than actual? Like I think a hockey goal counts only after puck breaks plane of second boundary of the line?

What makes you think it's merely conceptual? It's a real, physical boundary.

 

[Baluncore]

We live in a universe of incompatible interfaces. We only see the surfaces where there is a change of impedance.

What makes you think it's merely conceptual? It's a real, physical boundary.

When it comes to wavefronts encountering real boundary surfaces, such as a lens or reflector, the boundary needs to be defined in 3D position with a specified orientation, such as the normal to the surface at each 3D point, which requires two more numbers or dimensions.
That depends on what is really meant by dimension.

 

[russ_watters]

My commute to work has a [spatial] length dimension and a time dimension and there is no corellation between them.

 

[jbriggs444]

What makes you think it's merely conceptual? It's a real, physical boundary.

Like many concepts, the words "real" and "physical" stop meaning as much when you start looking closely.

The imaginary plane at the mouth of a hockey goal is an abstraction. So not physical. But the red light does go on and the number on the score board does increment, so something measurable and real did occur.

Perhaps we can agree that arguing over whether the plane at the mouth of the goal is or is not physical will not get anyone's team any closer to the Stanley Cup.

 

[Ibix]

The boundary is more conceptual than actual?

Arguable. Boundaries are not abstract concepts like "justice", for example. They are defined solely with respect to physical objects. I think you'd say that "the interior of the cube" was an actual thing and so is "the region outside the cube". So why not the boundary?

Essentially what we have here is an argument about what counts as "actual", so it's pretty pointless. You could rephrase the question to "is there anything made of matter or radiation that has lower dimension", to which the answer would be no.