
How many fundamental constants does it take to describe our Universe? - ni-c
https://medium.com/starts-with-a-bang/throwback-thursday-the-fundamental-constants-behind-our-universe-a95de09f9a46
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orbifold
Perturbative String theory reduces those ~20 constants to one (the string
coupling constant), plus a choice of vacuum, which is then of course the crux
of the problem, as the effective field theories we observe don't map uniquely
to a particular high energy string theory vacuum (as far as we know). It
should also be obvious that while those constants are indeed important, the
initial conditions are potentially more important and a great deal of effort
has been put into explaining why from fairly generic initial conditions we
would expect the universe as we observe it to arise (inflation theory).

~~~
jerf
How many dimensions are there in choice of vacuum? My understanding was that
it was still "many", in which case this merely reframes the problem rather
than solving it.

~~~
orbifold
The answer to this question has changed over time. My knowledge of the history
is incomplete to say the least. During the first super string revolution, when
it was understood that perturbative string theory would give a description of
perturbative quantum gravity, the goal was to demonstrate that there were only
a few choices of compactification manifolds available from consistency
arguments (anomaly cancellation and unbroken super symmetry in four
dimensions, probably the most well known paper is "Vacuum configurations for
superstrings" by Candelas et. al.)

Ignoring heaps of details, the result was that the vacuum manifold (that is a
solution to the 10d vacuum Einstein Equations) had to be some 4 dimensional
symmetric space (usually taken to be Minkowsky Space) times a Calabi-Yau
manifold, those are Kaehler manifolds with vanishing Ricci curvature (those
have non-vanishing constant spinors, which you need for unbroken
supersymmetry).

Initially it was believed that with additional physical consistency conditions
and by relating the geometry of the Calabi-Yau manifold to known physical
parameters, like the number of generations of particles, it would be possible
to narrow down the number of "stable" vacua to a limited number.

While there were discovered a fair amount of dualities between different
string theories, with the discovery of D-Branes and Flux Compactifications
(which stabilize the moduli of a huge number of potential vacua, the general
idea is that the space of calabi-yau manifolds can locally be paramterized as
a finite dimensional manifold and those paramters would show up as massless
fields that aren't observed, if there weren't any fluxes they couple to), the
number of potentially stable vacua is now sometimes quoted as 10^500.

In itself this is not too concerning, if you think about the fact that there
is a infinite number of solutions to the Einstein Field equations and general
relativity is still a very predictive theory. In practice this means that you
carefully engineer the vacua you study, for example with F-theory techniques
in order to relate them to observed phenomena.

You are right that it just reframes the question, the low energy effective
field coupling constants turn up as vacuum expectation values of certain
fields, but in an interesting way. The idea is then to use relations and
identities discovered in string theory (for example AdS-CFT) to study the low
energy theories.

~~~
jerf
Yes, by no means let me be interpreted as claiming that it's not an
interesting reformulation. I'm just saying that for example trading 20
arbitrary parameters for 20 differently-inter-related arbitrary parameters is
still just a reformulation of the question of where those 20 dimensions of
information came from for our universe.

(And when I put it that way, in information theoretic terms, one notices that
we must also take as parameters the description of the system that consumes
those 20-some parameters in the first place. Even if one did come up with an
answer for the parameters that question would remain below it. Of course in
the end you eventually and inevitably are going to hit some form of "Just
Because".)

------
gradys
Numerical constants alone don't fully specify the universe. They don't account
for the laws that relate numerical constants to each other. What's missing is
a sort of structural constant -- a minimal set of laws that describe all
physical phenomena.

If the universe were the execution of a program, knowing these numerical
constants would be like knowing all the... well... constants, in the source
code, but missing all the code that binds them together.

~~~
cLeEOGPw
You are viewing into these constants as numbers in memory in programming
language. In physics, a constant actually means a law that describes
unchanging way of how things interact. Think of these constants not as of
simple numbers (1, 0, -1, etc.), but as of constant ways things interact (1
always attract -1, etc).

------
amelius
Is anybody here familiar with the book by Peter Rowlands? [1]

> Unique in its field, this book uses a methodology that is entirely new,
> creating the simplest and most abstract foundations for physics to date. The
> author proposes a fundamental description of process in a universal
> computational rewrite system, leading to an irreducible form of relativistic
> quantum mechanics from a single operator. This is not only simpler, and more
> fundamental, but also seemingly more powerful than any other quantum
> mechanics formalism available. The methodology finds immediate applications
> in particle physics, theoretical physics and theoretical computing. In
> addition, taking the rewrite structure more generally as a description of
> process, the book shows how it can be applied to large-scale structures
> beyond the realm of fundamental physics

There is also a video lecture series [2]

[1] Peter Rowlands, Zero to Infinity, The Foundations of Physics,
[http://www.worldscientific.com/worldscibooks/10.1142/6544](http://www.worldscientific.com/worldscibooks/10.1142/6544)

[2]
[http://www.youtube.com/watch?v=W2XdhzCORbo](http://www.youtube.com/watch?v=W2XdhzCORbo)

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joshvm
My undergraduate supervisor was the lead author on the paper about Tri-
Bimaximal Mixing, a parametisation for the PMNS matrix.

[https://en.wikipedia.org/wiki/Tribimaximal_mixing](https://en.wikipedia.org/wiki/Tribimaximal_mixing)

I attemtped to do something similar with the CKM matrix for my undergraduate
thesis. Didn't really work, but it was fun.

The CKM matrix is annoyingly _almost_ symmetric, the off diagonal elements are
_almost_ the same magnitude. But they're not, so bah! Basically you spend a
lot of time trying to come up with simple first order relations for the
various quantities. Ideally you should be able to eliminate fundamental
constants by writing them in terms of one another.

------
fit2rule
I'm sort of disappointed that the answer to this question is not: "All of
them."

Ah well.

------
karmakaze
So let me get this straight--we live in a giant condom?

------
Navarr
stupid undocumented magic numbers...

------
typedweb
1 - phi. It's quite shocking to see how many places it turns up and how many
constants can be derived from it.

~~~
nemothekid
Is this from the article? I'm not sure how phi relates to the speed of light,
Newton's G, Planks constant or the numerous other force & energy constants
described in the article.

~~~
meric
I suppose his answer might be more philosophical. All things in this universe
are shards of the same one universe. Shards of this one universe thinking
about what this universe is itself made of. As far as we know from the fact
the constants cannot be derived from any other principle and must be measured
directly, the universe is made of itself. The universe is one.

Also an interesting read, if you're feeling philosophical about the number 1.
[http://en.wikipedia.org/wiki/One-
electron_universe](http://en.wikipedia.org/wiki/One-electron_universe)

EDIT: I'm tempted to give myself a downvote, totally missed phi was an actual
constant in itself.
[http://en.wikipedia.org/wiki/Golden_ratio](http://en.wikipedia.org/wiki/Golden_ratio)

~~~
czbond
The one electron wiki entry literally blew my mind. I read the first sentence
and thought "absolutely not". Then as I read into it thinking "give it a
chance". My logic tells me this can't be the case ..... but man this is a wild
theory to me.

~~~
darkmighty
The theory is more an amusement than anything, but as the article points out,
it seems it led to a major impact with the exposition of CPT symmetry. It
makes sense if you know of Feynman's earlier work with Wheeler
([http://en.wikipedia.org/wiki/Wheeler%E2%80%93Feynman_absorbe...](http://en.wikipedia.org/wiki/Wheeler%E2%80%93Feynman_absorber_theory))
which is actually a consistent theory of classical electrodynamics (i.e. half
the electromagnetic interactions are "coming from the future").

