# Can there be a universe with different mathematics?

I do not know what exactly I means by other universes, but I just have a feeling that mathematics is somehow inevitable.

For example the law of "exclude in the middle". If there are aliens, can we assume they logically accept the law of "exclude in the middle"? if there are different universe, can they develop completely different mathematics?

edit: I now that there are formal systems that do not accept ltm, but what I really means is that they really think lem is a bad idea, as we think `p ^ !p` is a bad idea, they just intuitively do not think lem is right, and the canonical model do not include lem at all.

Anyway, this is just an example.

• It is law of excluded middle and it dates back to Aristole [see Wiki: "The earliest known formulation is Aristotle's principle of non-contradiction, first proposed in On Interpretation, where he says that of two contradictory propositions (i.e. where one proposition is the negation of the other) one must be true, and the other false"]. There are modern logician and mathematicians that do not accept it [again, see Wiki: "Many modern logic systems reject the law of excluded middle"]; so it is not necessary to wait for ET... – Mauro ALLEGRANZA Feb 17 '14 at 15:59
• +!: not a bad question. It shows how pervasive the idea of non-contradiction is that one has to go to another universe to think of them, which is in effect what we do when we interpret universe in the appropriate way... – Mozibur Ullah Feb 17 '14 at 18:37
• Yes and no. Mathematics and logic are not exactly empirical, so universes with different laws can be accomodated (perhaps not most naturally) by the same mathematics and logic, see Is Logic Empirical? and Is geometry mathematical or empirical? – Conifold Dec 20 '16 at 1:46

Yes, we live in one. What was regarded as mathematics 2000 years ago is not what we regard as mathematics today. Gauss published the first acceptable proof of the Fundamental Theorem of Algebra; but Gauss's proof would not be acceptable from an undergrad today. Standards of rigor, as well as our understanding of the topology of the real line, have changed considerably since then.

Mathematics is a historically-contingent activity of humans. Not only could mathematics be different on a different planet or in another universe; which are of course unprovable one way or the other; but mathematics could and actually has been different at different eras on this planet.

Just consider the rise of computers, experimental mathematics, machine proof systems, and computatibility theory. It's likely that math in 100 years will be very different than math is now. Zermelo-Fraenkel set theory is less than 100 years old. What if on some other planet they never discovered it, but rather skipped to some other framework?

Now, you may be referring not to the mathematics as a historically and culturally contingent human activity; but rather as some sort of Platonic thing that is "out there" that we can discover. To which I'd ask: Where is your evidence that such a thing exists? And if it does, then which human mathematics is the one, true mathematics? The math of 1000 years ago? The math of today? Or the math of 1000 years from now?

I do realize that you're asking if it's possible that in some other universe, 2 + 2 is 3. I have no idea. I don't think the question is meaningful. I think I'm wearing my formalist hat today.

• If you presume that the Universe is "natural" then I doubt there can be much different math from one place to another. If however we are living in, say, a simulation (A) you might expect that the head gamer can do as he pleases with the rules. In another simulation (B) it could be set up so that if you physically add two apples to two apples you always end up with three apples. We in simulation A would ask, "Where did the missing apple go". In B it always happens like that so they would likely formulate their mathematics accordingly even if they notice the peculiarity of the missing apple. – Scott Dec 19 '16 at 20:29

The interesting issue is not if somewhere somebody can "think of" a contradictory mathematics.

In this world, there are alredy researches about inconsistent mathematics (see SEP Inconsistent Mathematics.

The relevant issue is : how they works ? what we can do with them ?