# Singularities in minimal surfaces [closed]

There is a theorem by Jean Taylor that says that an almost minimal set in $\mathbb{R}^3$ can be locally parametrize by the only three possible minimal cones in $\mathbb{R}^3$, the plane, an $Y$ times a line and all the faces you can make from the center of a tetrahedron and its vertices.

This question has already been answered (in some sense) by Otis Chodosh as negative: Can we obtain those minimal cones by a deformation of minimal surfaces ( i.e. mean curvature = 0)?

Thanks, Mario

## closed as unclear what you're asking by Benoît Kloeckner, Joonas Ilmavirta, coudy, Stefan Kohl, Neil StricklandApr 24 '15 at 6:15

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• Your question is unclear: are you talking about minimal surfaces (which are smooth, as you say) or soap films? In the later case, there are several possible definitions, but my understanding of Jean Taylor's work is precisely that the minimal cones she classified are the infinitesimal models for soap films. Either way, it looks like you answered your own question, but I may have overlooked something. – Benoît Kloeckner Apr 23 '15 at 15:50
• Maybe a better question could be if there is a way to deform minimal surfaces (mean curvature equals zero) to obtain at the limit that list of minimal cones. Maybe by only looking at the Weierstrass-Enneper representation it shouldn't be so difficult to produce examples of minimal surfaces that deforms into those cones, I wonder if someone has already done that or if this is totally wrong. – Mario Apr 23 '15 at 17:14

On one hand, the answer to the question

Is there an analogous of this for minimal surfaces (mean curvature = 0)? I know that minimal surfaces are smooth but, are there examples where they kind of have the Y or the tetrahedron singularity?. It is easy to see in experiments that in real soap bubbles this singularities actually appears.

Is that, yes there are "minimal surfaces" in an appropriately generalized sense that have an e.g. "$Y$ times a line" singularity. The easiest example is just the $Y$ times a line! This is a minimal surface in some generalized sense.

On the other hand, the $Y$ times a line cannot arise as the limit of smooth minimal surfaces, under some reasonable assumptions! This is a consequence of the following remarkable work of Brian White: https://projecteuclid.org/euclid.dmj/1240432190. The paper might be very difficult to read, depending on your background in geometric measure theory, but the upshot is: in some loose sense, a "weak" limit of minimal surfaces must have a "mod 2" multiplicity/orientation. It's easy to see that a $Y$ times a line $L$ cannot be given such an orientation so that they cancel out at the spine $\{0\}\times L$.

On the other hand, a "cross" times a line can be given such an orientation (give each of the four half-planes the multiplicity $1$, then this cancels out at the spine. So, a natural question is, can this cross arise as a limit of smooth minimal surfaces? The answer is yes: a rescaling of Scherk's surface http://en.wikipedia.org/wiki/Scherk_surface#Scherk.27s_second_surface will do exactly this.

EDIT: One comment, based on your wording of the question I wanted to clarify one point. I'm not well versed in the theory of almost minimal sets, but it seems that Jean Taylor's theorem is not about "surfaces" but rather "sets." (see, e.g. http://www.math.u-psud.fr/~gdavid/Montreal011.pdf). So, it is not really concerned with minimal surfaces or "almost minimal surfaces." I'll remark that White's theorem that I linked above would apply to a sequence of minimal surfaces with (1) mean curvature uniformly bounded in $L^1$ and boundary length uniformly bounded. So, this seems to suggest that Taylor's theorem is really about a different sort of objects than classical "surfaces."

• I've just corrected the wording. – Mario Apr 26 '15 at 14:59