Why is space three-dimensional?

Phys.org ^ | 3 May, 2016 | Lisa Zyga

[MtnClimber]

The question of why space is three-dimensional (3D) and not some other number of dimensions has puzzled philosophers and scientists since ancient Greece. Space-time overall is four-dimensional, or (3 + 1)-dimensional, where time is the fourth dimension. It's well-known that the time dimension is related to the second law of thermodynamics: time has one direction (forward) because entropy (a measure of disorder) never decreases in a closed system such as the universe.

In a new paper published in EPL, researchers have proposed that the second law of thermodynamics may also explain why space is 3D.

"A number of researchers in the fields of science and philosophy have addressed the problem of the (3+1)-dimensional nature of space-time by justifying the suitable choice of its dimensionality in order to maintain life, stability and complexity," coauthor Julian Gonzalez-Ayala, at the National Polytechnic Institute in Mexico and the University of Salamanca in Spain, told Phys.org.

..... The scientists propose that space is 3D because of a thermodynamic quantity called the Helmholtz free energy density. In a universe filled with radiation, this density can be thought of as a kind of pressure on all of space, which depends on the universe's temperature and its number of spatial dimensions.

Here the researchers showed that, as the universe began cooling from the moment after the big bang, the Helmholtz density reached its first maximum value at a very high temperature corresponding to when the universe was just a fraction of a second old, and when the number of spatial dimensions was approximately three. The key idea is that 3D space was "frozen in" at this point when the Helmholtz density reached its first maximum value, prohibiting 3D space from transitioning to other dimensions.

[frithguild]

You are Tim?

[Larry Lucido]

And if you crash and an airbag goes off, it could destroy the universe.

[MtnClimber]

I agree. With Time/entropt that is four dimensions. But time only goes in one, not two directions.

[PhiloBedo]

They likely think this is the dawning of the age of aquarius.

[Electric Graffiti]

'You’ve been reading too much Parmenides or Plotinus.'

Haven't you read tao of physics or the dancing wu li masters?

[grey_whiskers]

There are some who call me... Tim.

Follow! But! follow only if ye be men of valor, for the entrance to The White House is guarded by a Hildabeeast so foul, so cruel that no man yet has fought with it and lived! Bones of four fifty men lie strewn about its lair. So, brave knights, if you do doubt your courage or your strength, come no further, for death awaits you all with nasty big pointy teeth.

[tinyowl]

Never heard of them!?

When I was a kid in Texas I found myself staring at a fence, and realizing, though I didn't have words for it at the time, that the verb 'to be' is the fundamental misapprehension underlying the entire illusion. By 'illusion' I don't mean a bad thing ... it is what it is ... but it is an illusion. And that's not say I understand and have mastered the illusion - I live and behave as if it's real all day long, I just don't treat it as if it's really real.

But I have intruded, I'm not here to say questions of the nature of dimensions don't matter ... although in the context of the bigger question, it's totally irrelevant, a symptom of the misunderstanding. The origin of the universe is mind. The question is, what is mind? It could be said that it's the 'container of the dimensions' ... if you had to say anything at all. But it's not the other way around. Mind contains dimensions, the mind does not exist within the dimensions.

[HandyDandy]

Have you ever been in Plato’s cave?

[who_would_fardels_bear]

With fractals, mathematicians seem to have come up with an idea that allows them to assign a more meaningful number to some physical phenomenon such as the total length of a coastline.

However it doesn't constitute something like a partial dimension in an orthogonal direction like the full x, y, and z dimensions of 3-space.

This seems like a similar case to what happens with infinite sums and String Theory:

Mathematically you can arrange for 1 + 2 + 3 + 4 + ... = -1/12

Physically you can use that "equality" to determine the number of curved dimensions in String Theory.

Because the crazy math seems to have an analog in crazy physics then somehow they both must be right.

So because some fun math with fractals can be analogized with the dense plasma soon after the Big Bang we can supposedly talk about fractional dimensions without giggling.

Two insanities don't constitute sanity. This seems like another case of "Just shut up and do the math," i.e. physics isn't telling us what there is out there in the real world, it is merely telling us what math equations we can write out to predict what mathematical values we will see when we conduct certain experiments.

[Cruising Speed]

There is only one space, one dimension. For convenience, we use a three-coordinate system to uniquely identify any point in that dimension.

Btw, all this talk about extra dimensions 'rolled up' too small to see is wild speculation based on a mathematical quirk. And don't get me started on 'branes'.

[tinyowl]

No! But I just read what it is. OK, here's what I say: Plato went from being chained against the cave wall facing it to being permanently impregnated into the rock and yelling 'now I understand - freedom at last!'

Socrates was once asked 'do you know yourself'. He replied 'no, but I understand this not-knowing.'

There are no dimensions. Not 4, not 3, not 2, not 1, not even 0. You could say, though, that 'no dimensions are missing.'

[TexasTransplant]

https://www.youtube.com/watch?v=gQgWa9htDso

[MV=PY]

Wow. I was simply thinking about a coastline that continued to be “complex” as one zoomed in. It would, in fact, be infinite, yet somehow less than two dimensional.

I’m not that familiar with string theory so I don’t see the similarity in patterns you describe. Will you point me to a good starting point?

[Organic Panic]

How else would we blow up balloons?

[TexasTransplant]

Seriously folks ... I was thinking about what makes up the “nothing” space between the nucleus of an atom and the electrons, thinking about that I was made of energy then I remembered Richard Feynman and ended up watching this
https://www.youtube.com/watch?v=gQgWa9htDso
actually listening to it while I was reading FR

Coincidence?

[Moonman62]

time has one direction (forward) because entropy (a measure of disorder) never decreases in a closed system such as the universe.

...

Thermodynamic entropy is not a measure of disorder.

http://entropysimple.oxy.edu/content.htm

[skr]

Okay, good, was thinking time would be a fourth.

[datricker]

Four dimensions, actually, including time.

would you not then need 5 or 6 dimensions if you include time so as to have a beginning and ending element in your field set other (x, y, z, t0, time_start, time_end).

Thankfully linear algebra doesn't care about the number of dimensions in the so the whole premise of the question is probably wrong.

[Migraine]

Time does not exist in and of itself. It is a by-product of matter, in motion.

Put that in your pipe and smoke it.

Neither qualitatively, nor quantitatively, can time be said to exist independently.

So I only know of 3 dimensions.

[minnesota_bound]

Why is space three-dimensional?
It is not. Go too far out and spacecraft will fall off the edge of space and be lost!