# It is possible to generalize the “real” line to be able to embed $\omega_1$ or any uncountable ordinal into a finite segment of it?

This question is motivated from a previous question, but is in itself independent of it.
So, I understand that it is not possible to embed $\omega_1$ or any uncountable ordinal into the real line, since every cut in the reals has countable cofinality. So one cannot undertake an uncountable process in a real-number of seconds, if every step is to take some nonzero real-number amount of time. But is it possible to generalize the concept of real line, in the sense that we could embed $\omega_1$ or any uncountable ordinal into a finite segment of it? I know that the reals fill the real line, so you cannot add more numbers into it, but I am not completely sure if you cannot define a more general "line" so that the number of a finite segment of points within it can have any arbitrary cardinality. And if this were possible, is there any reason why we could not think of physical time or space as having these generalized properties rather than those of the real line?

As rightly suggested by one of the comments, the actual question should be if whether or not there is a generalized concept of a valued ordered space. The body of the question apparently talks about metric spaces, but my intention is to see if it is possible to generalize this concept (and, in addition, if such concept could be also be, in principle, a model of physical space or physical time)

Caveats: For instance, take a Hilbert space (which is a metric space) with an orthonormal basis indexed by B. The Hilbert dimension is the cardinality of B (which may be a finite integer, or any countable or uncountable cardinal number). Do this mean that a neighborhood of a point in Hilbert space also have a set of points of cardinality B? If we define a "line" on a Hilbert space of uncountable cardinality B, will this line have also a number of points of cardinality B?

-
You may find this construction, suitably generalized, answers at least some of your questions. – Cameron Buie Apr 7 '13 at 16:16
thanks, I already knew about it, but its local properties are still those of the real line, an I cannot figure it out if that could be changed. – Wolphram jonny Apr 7 '13 at 16:19
You do realize that metric spaces are deeply connected with the real numbers (i.e. a metric function is always into the real numbers); so you might want to ask whether or not there is a generalized concept of a valued ordered space. – Asaf Karagila Apr 7 '13 at 16:26
@Asaf thanks for the suggestion, so should I change the title? – Wolphram jonny Apr 7 '13 at 16:28
Actually the title is fine, it talks about generalizing the real line. The body of your question, however, talks about metric spaces. – Asaf Karagila Apr 7 '13 at 16:30

The surreal numbers. They include the hyperreal numbers as well as the ordinals. The surreal numbers are the largest possible ordered field. Because they are a field, for any uncountable ordinal $\omega_{\alpha}$ you can define 1/$\omega_{\alpha}$, which lies within [0,1]. So the interval [0,1] contains a set of points that are larger in number than any cardinality (it would have the "cardinality" of the proper class of all ordinals). Regarding the issue of why physical space is considered a real field and not a surreal field, I have no idea!
To your last sentence, the surreal numbers are an invention of the 1970's or so; modeling the physical reality in $\Bbb R^3$ is something that started several centuries ago. – Asaf Karagila Apr 8 '13 at 12:07
It would be somewhat troublesome, because we can't do analysis over the surreal numbers properly in $\sf ZFC$, because we would have to talk about classes of classes. I don't know whether or not it would make too much difference. Think that if you switch to a class-friendly set theory, e.g. $\sf MK$, maybe even $\sf MK$ with $2$-classes; then you will run into other limitation. – Asaf Karagila Apr 8 '13 at 17:31
Also, all physical measurements are only of finite precision. The surreal numbers provide for infinitesimals, things smaller than any finite real but not zero. There would be no hope of measuring something down to infinitesimal distances or times due to the quantum (Planck) limits, even if they existed. Also, all of our measuring technologies are limited in precision anyways -- to a finite amount of precision. So there would seem no advantage to using $\mathbf{No}$ over $\mathbb{R}$ anyways. – mike4ty4 Sep 15 '13 at 11:10
Also, another big stumbling block to analysis over $\mathbf{No}$ is that $\mathbf{No}$ is not Dedekind-complete. Much of what makes real analysis, and so also calculus, work is the Dedekind completeness property of the reals. And physics uses calculus extensively, even in non-classical physics. – mike4ty4 Sep 15 '13 at 11:14