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Dynamics of flows and maps (continuous and discrete time), including infinite-dimensional dynamics, Hamiltonian dynamics, ergodic theory.

3 votes
Accepted

Uniquely ergodicity and polynomial ergodic average

This is indeed true for some "nice systems", for example one can show this theorem (for say $L^{2}$-functions) for Kronecker systems simply by van-der-Corput trick. In general, those averages converg …
Asaf's user avatar
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6 votes

Examples of transformations that are totally ergodic but not weakly mixing?

Totally ergodic is equivalent to not having rational eigenvalues (I guess a suitable reference for this is Eli's book). Hence basically the Kronecker factor of such a system will be "essentially" the …
Asaf's user avatar
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1 vote
Accepted

An angle between two vectors in Oseledets theorem

Ok, let take $v$ in the bundle at $x$. We may decompose $v=v^{u}+v^{s}\in E^{u}\oplus E^{s}$. Assume without loss of generality that $\lVert v\rVert=1$. Applying $A^{i}$, using equivariance and Osceld …
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0 votes
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Help in understanding the singular system of linear forms and non escape of mass

Okay, these are just basic technical tidbits. Unsure if anything here is of research level. $SO(n)$ acts transitively on the sphere of $\mathbb{R}^{n}$ (there's a slight ambiguity about $0$, but I gue …
Asaf's user avatar
  • 2,459
5 votes

Book recommendation for ergodic theory and/or topological dynamics?

I second Siming Tu's recommendation for E-W book. It is a well balanced book (regarding theory vs applications), it has nice appendix contains relevant theory from functional analysis, and it contains …
26 votes
Accepted

If there is a dense geodesic, are almost all geodesics equidistributed? Dense?

The first question is false as stated. By Artin's encoding, geodesics on $SL_{2}(\mathbb{R})/SL_{2}(\mathbb{Z})$ corresponding to continued fractions, and the geodesic flow corresponds to the shift. I …
Asaf's user avatar
  • 2,459
1 vote

Some puzzles about the three conditions in a paper of D.Berend

For a start, I guess that one should be very familiar of the proofs of Furstenberg's diophantine result, as this paper generalizes this theorem. Secondly, it might be of interest that Zhiren Wang in h …
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  • 2,459
1 vote

The identity element of a compact group is a limit point of any "polynomial sequence"

For getting the every-point statement, at-least in the compact abelian case (see Tao's comment above), one can either prove it by harmonic analytic approach (Weyl's equi. criterion + van der corput tr …
Asaf's user avatar
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2 votes
Accepted

Basic question on minimal flows

Your question is about a theorem of Furstenberg. About the definitions - obviously every periodic orbit is minimal, if exists, hence in the case the action is minimal, you won't have any periodic orb …
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  • 2,459
2 votes

Ratner's orbit closure for a unipotent semigroup

$\DeclareMathOperator\supp{supp}$The theorem holds for semigroups as well (well, in the finite volume setting! in the infinite volume setting there are subtleties between two-sided and one-sided avera …
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  • 2,459
1 vote
Accepted

Compact group extension of a zero entropy system.

[I'm assuming G means K] In case the elements of K are not measure preserving, I doubt that the question is correct. In general, one can easily show that entropy decrease by moving into factors. Her …
Asaf's user avatar
  • 2,459
3 votes
Accepted

Furstenberg-Zimmer theorem: non-invertible systems

Posted as requested - consult the book by Manfred Einsiedler and Tom Ward - "Ergodic Theory with a view towards number theory" - published in GTM, especially in ch 7.
Asaf's user avatar
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11 votes
Accepted

Furstenberg $\times 2 \times 3$ conjecture, bibliography

Well that will be some lengthy answer. The first article that was published after the famous disjointness paper is another paper by Hillel called "Intersections of Cantor sets", it's related to the m …
1 vote
Accepted

Entropy equals zero?

EDIT - The answer below deals with an ergodic m.p.s As this question got up-voted, I've decided to fuly write a solution, based on the sketch I've made in the comments. Fix some $\varepsilon>0$ smal …
Asaf's user avatar
  • 2,459
2 votes

Geodesics on hyperbolic surfaces whose closures have arbitrary Hausdorff dimension

Show that for a Bernoulli system, there exists ergodic (Bernoulli) measures of any given entropy (between 0 and full entropy). Pick such a measure with appropriate entropy as you would like. Recall t …
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