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Nonstandard analysis is a way of doing calculus and analysis with infinitesimals. The historical approach of Leibniz, Euler, and others to infinitesimal calculus was gradually replaced by epsilon, delta techniques in the context of a real continuum, in the 19th century. It was not until the 1960s that Abraham Robinson developed a theory of a hyperreal continuum that allows for a development of analysis procedurally akin to that of its founders.

8 votes

In hyperreal field, can ln(ε) and ln(ω) be expressed as infinite sums?

To help avoid any misunderstanding that may arise for readers of this question, let me say that when understood in the usual sense, there are no nontrivial convergent sequences or series at all in the …
Joel David Hamkins's user avatar
45 votes
Accepted

Does every series of hyperreal numbers converge to some hyperreal number?

The answer is strongly negative. Arbitrary extensions. The first thing to say is that whenever one extends $\newcommand\R{\mathbb{R}}\R$ to a larger ordered field $F$, one has immediately destroyed (e …
Joel David Hamkins's user avatar
31 votes

Why does CH imply that there is a unique ultrapower of $\mathbb{N}$?

The point is that the ultrapower of any structure $\mathcal{M}$ by a nonprincipal ultrafilter $\mu$ on $\mathbb{N}$ is countably saturated, that is, it realizes any finitely satisfiable $n$-type with …
Joel David Hamkins's user avatar
56 votes

How helpful is non-standard analysis?

The other answers are excellent, but let me add a few points. First, with a historical perspective, all the early fundamental theorems of calculus were first proved via methods using infinitesimals, r …
Martin Sleziak's user avatar
70 votes
Accepted

A remark of Connes on non-standard analysis

...as soon as you have a non-standard number, you get a non-measurable set. Every nonstandard natural number $N$ gives rise to a nonprincipal ultrafilter $U$ on $\mathbb{N}$, by saying that a set $X …
Glorfindel's user avatar
  • 2,821
4 votes

Turing degree of a turing machine with access to an (arbitrary) nonstandard integer

I shall give two different interpretations of the question. (The second interpretation using true arithmetic is modified in this update.) Using arbitrary nonstandard models of PA. Let us say that a T …
Joel David Hamkins's user avatar
10 votes

Automorphisms of the hyperreals over the rationals and nontrivial automorphism groups

As a general principle, every first-order theory with infinite models, such as the theory of real-closed fields, will have models with rich automorphism groups. The general reason is that one can ta …
Joel David Hamkins's user avatar
2 votes

Compactness and omega models

There is no property of $T$ alone that will ensure that $T+S$ always has an $\omega$ model in the circumstances you describe. In fact, there is no computably axiomatizable theory $T$ with the property …
Joel David Hamkins's user avatar
29 votes
Accepted

What are the advantages of the more abstract approaches to nonstandard analysis?

To my way of thinking, there are at least three distinct perspectives one can naturally take on when undertaking work in nonstandard analysis. In addition, each of these perspectives can be varied on …
Mikhail Katz's user avatar
  • 16.6k
3 votes

"Lebesgue-measurable" cardinals and real-closed fields

You say that $\kappa$ admits a $[0,1]$-valued measure, but actually, it is a $\{0,1\}$-valued measure; every subset of $\kappa$ has measure $0$ or $1$. If I am understanding your suggestion, you inten …
Joel David Hamkins's user avatar
12 votes

Are hyperreal numbers isomorphic to formal power series?

I would like to point out that it is not true that every every hyperreal can be represented by a Laurent series in the way you describe. (Let me assume that by the term "hyperreals", you mean a nonst …
Joel David Hamkins's user avatar
31 votes
Accepted

Is non-existence of the hyperreals consistent with ZF?

The answer is yes, provided ZF itself is consistent. The reason is that the existence of the hyperreals, in a context with the transfer principle, implies that there is a nonprincipal ultrafilter on $ …
Community's user avatar
  • 1
10 votes
Accepted

Surreal numbers, ultrapowers of $\Bbb R$, ordinal-valued functions and the slow-growing hier...

This kind of analysis is very well understood in ultrapowers, and one often sees this kind of thinking with ultrapowers, where one performs calculations with the representing function for an object. W …
Joel David Hamkins's user avatar
6 votes

tennenbaum phenomena for the reals?

This is a very interesting question! One way to interpret the question is like this: we have the structure $\langle\mathbb{R},{+},{\cdot},{\lt}\rangle$, which is a real-closed field, and Tarski prove …
Joel David Hamkins's user avatar
5 votes
Accepted

Star-transfer of powerset

$\cal{P}({}^\ast\mathbb{R})$ is the full standard power set of the nonstandard reals, the set of all subsets of ${}^\ast\mathbb{R}$. This power set includes the subsets consisting solely of infinites …
Joel David Hamkins's user avatar

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