
In Fake Universes, Evidence for String Theory - digital55
https://www.quantamagazine.org/20150218-string-theory-only-game-in-town/
======
mirimir

        Because the strings that are said to quiver at the
        core of elementary particles are too small to detect —
        probably ever — the theory cannot be experimentally
        confirmed. Nor can it be disproven: Almost any
        observed feature of the universe jibes with the
        strings’ endless repertoire of tunes.
    

In that case, it's not science. At most, mathematics.

~~~
pfortuny
Yes, that is what Peter Woight at Columbia keeps saying on and on:
[http://www.math.columbia.edu/~woit/wordpress/](http://www.math.columbia.edu/~woit/wordpress/).
It is a sad world in which scientists dare (in the XXI Century) call "science"
something which cannot be either verified of falsified...

~~~
coliveira
Very true. At most we can say that these guys found a mathematical theory that
is consistent with what the universe looks like. I imagine that there could be
an infinite number of such theories, if you are creative (and good at math)
enough.

~~~
mcherm
Maybe.

What if you considered (mathematically) the set of ALL theories that satisfied
certain basic criteria (requires a small number of assumptions compared to the
number of outputs it produces, doesn't change "arbitrarily" at some point in
time... things like that) and which also matched the currently accepted
physics of general relativity (in the limit of large sizes) and the currently
accepted physics of quantum mechanics (in the limit of small sizes). And what
if, when considering that set of theories, you were able to prove that any
theory matching those criteria had to be equivalent (isomorphic) to a certain
theory.

(This is like saying that the theory of basic algebra using equations and the
theory of curves on graphs using geometry can be proved equivalent
(isomorphic) by defining how to graph an equation and how to derive the
equation for a graph. Once you've done that, it hardly matters whether you
think the algebra is the "real theory" or the graphs... they are both
equivalent and thus both equally "real".)

Suppose you found that, and thus proved (mathematically) that string theory
was isomorphic (in certain key ways) to any theory that could apply to our
universe, assuming that quantum mechanics and general relativity are roughly
accurate. Why, then you WOULD actually have demonstrated that string theory
isn't a "waste of time", that it is a useful way to make predictions about our
universe.

And if I understand the article, this proof is precisely what these
researchers are attempting to do. So far, they have constructed such proofs
for much simpler universes than ours and a way of slowly working their way up
to proving it for our universe.

~~~
coliveira
That seems unlikely, because for that to hold they also need to show that
there is nothing better than relativity and QM to describe the known universe.
Then, you are back to square one, finding a better unifying theory, or even
worse, proving that no such theory exists.

~~~
Steuard
I don't think that you've really understood the sort of limits that the
previous commenter (and the original article) were trying to describe. To a
very good approximation, QM _does_ describe our universe: any "better" theory
must necessarily be equivalent in the appropriate limits (to many decimal
places of precision, I might add). In the same way, relativity _does_ describe
our universe, and any "better" theory must be equivalent in the (different)
appropriate limits. As I understand it, that is the level at which those are
being assumed in this argument. The whole point of the theorems that these
groups are trying to prove is that _any_ "better" theory that matches both of
these limits must be equivalent to string theory.

~~~
coliveira
I think that would be even harder to achieve than a simple unification of QM
and Relativity. Who knows what kind of phenomena we don't know about? There
could be millions of theories that are consistent with current physics and
still possible, given particular observations. In a few words, nobody can
anticipate the kind of phenomena that could be observed by future physicists.

------
JohnHammersley
I used to work with Mukund (Rangamani) and Veronika when I was doing my PhD at
Durham Uni (2004-2008) -- it's great to see the work they and others are
continuing to do on this. It formed the basis for my thesis
([http://etheses.dur.ac.uk/2906/](http://etheses.dur.ac.uk/2906/)), and Anti
de-Sitter spacetimes allow for some great visualizations (I spent much time
working in Mathematica to produce the one shown in the slide here:
[http://bethnalgreenventures.com/2013/08/05/guest-blog-
from-m...](http://bethnalgreenventures.com/2013/08/05/guest-blog-from-moon-
landings-to-collaborative-science/)).

You also learn something new everyday - I'd never come across the term
"Fisheye Universe" for AdS space before! :)

