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.

[datricker]

I would argue that time is not a dimension but a vector that can only be traveled in one direction.

I agree I don't believe in change, it's an illusion. Rather, there are only successions of causally-linked immutable values, and time is derived from the perception of these successions.

Causally-linked means the future is a function of the past; life applies reality to us to derive a new immutable us and we assign identity to these chains of values, and perceive change where there is none.

I'm going to bed

[datricker]

Odd that a scientific journal would still be stuck in just four dimensions when matrix string theory says there are 11

I believe that theory has mathematical errors from line one could be wrong but I think thats all proven junk.

[Migraine]

You got that right: bigbang is based on red-shift, i.e., galaxies appear redder than they ought to, which would indicate they are receding from our perspective. “Redder than they ‘ought’ to be”? In whose lexicon?

The premise was, when I read it in 1963, that the assumption was, that the most prevalent metallic element in all galaxies ought to be, iron; therefore, its characteristic orange-ish glow should be orange-ish; but in distant galaxies, the glow was redder than that, hence those galaxies (by Doppler-ish contexts) must be receding, hence an expanding universe, hence, there must have been an initial point, hence, big bang.

Critical variable, unexplained yet assumed, who says galaxies should glow one color or another?

[TexasTransplant]

See 95

At the beginning of the linked vid they were discussing a theory of Entropy as simultaneous creation and destruction (matter vs anti-matter) of the space between the nucleus and electrons of an atom.
The way it was pictured in my mind (I’m listening while reading FR so I don’t know what they were using as visuals) was that there is two simultaneous things existing in the same space and time, energy used to balance is slowly consumed which is Entropy.
I am not a Scientist I just love watching and listening to these shows and was a fan of Feynman back in the day.

[Nifster]

Reminds me of Abbot’s Flatland

[faithhopecharity]

I could be wrong I believe it was the 26- dimension theory that failed. I understand that the 11 dimension model remains viable (the 10 original string theory dimensions plus one more spatial dimension to incorporate gravity into the model). Maybe a better expert can add more than me, though. Thanks.

[Hoosier-Daddy]

So say you, Sebastian Cabot

[Crucial]

Because you need space for atoms to bounce around? What kind of question is this?

[Arthur McGowan]

Actually, I made a big mistake. I forgot Forward and Back.

[who_would_fardels_bear]

Here's a link to a video talking about infinite sums...

Astounding

The way this problem is related to non-integer dimensions (maybe only in my mind) is that crazy math and crazy physics somehow support each other.

I believe that the concept of non-integer dimensions is crazy math, and if physicists claim that there was a time when there were non-integer dimensions then that is crazy physics.

Crazy math is OK because it is all hypothetical. However, crazy physics seems counterproductive. It no longer gives us insight into how things are, it just makes it easy to solve physics problems.

[Kickass Conservative]

You will never know as much as you don’t know.

You may quote me.

[moose07]

Ahhhh, another quote from the Great Book of Python.
:)

[RoosterRedux]

bfl

[exDemMom]

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).

If you look at it that way, in order to measure something, there must be a beginning and endpoint to each directional axis: (x1-x2), (y1-y2), (z1-z2), (t1-t2). That does not introduce extra dimensions, but only blocks off sections of essentially infinite properties.

[Pecos]

Obviously, the shoreline is just long enough to reach from port to port, after which it becomes a collection of piers, before turning into shoreline again.

[Yes, I do understand fractals.]

[MV=PY]

Thanks!

“Crazy math is OK because it is all hypothetical. However, crazy physics seems counterproductive. It no longer gives us insight into how things are, it just makes it easy to solve physics problems.”

History shows that explorations into new realms of math have revealed truths (as far as we know) about nature. It was math that led Einstein to his theories. This, to me, is miraculous.

I suppose I’m not sure what qualifies for “crazy.” Sometimes math and the world are both crazy and they happen to match. Sometimes they don’t. I’m not yet prepared to write off fractional dimensions.

Good discussion! ;)

[E. Pluribus Unum]

That’s what I said.

[kosciusko51]

A excellent comment at the link:

In Tony's article he persists in saying that the series is the Reimann zeta function, even for s=-1, which is plain wrong. The analytically continued function zeta* spliced onto the domain of convergence (of the series) does have the value -1/12 at s=-1, but it is no longer that sum in the new domain; the two functions differ substantially in that domain extension. If the physicist wants to use analytic continuation to change the result that the original mathematical model gave, which had already shown that the model didn't work for the situation that it attempted to describe, then there needs to be a justification for the change, instead of just saying "Oops, my prediction is outside its domain of validity, so I must change the rules to flatten the function out in a way that violates my actual model, while pretending that the model hasn't changed."

In layman's terms, there are rules that must be followed to do infinite sums, and the physicists violate those rules to make the sum "work" with their theory.

[SunkenCiv]

Thanks MtnClimber.

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[stig]

Space is 3 dimensional because everything we see is based on projections of matter onto a 2 dimensional surface called retina. The fact that we have stereo vision allows us to take two separate 2 dimensional images and map them into a 3 dimensional projection.

The hypercube you display is a perfect example it's a 4 dimensional object meaning all angles are 90 degrees but when projected down to 2 dimensional screen the best we can do is map it to a 3-dimensional object.

Three dimensions may be a physical constraint of our universe but since all are equations were developed to explain 3 dimension results from experiments why would we expect thermodynamics to predict anything else.