wtf wrote: ↑Wed Apr 24, 2019 5:28 am
PeteOlcott wrote: ↑Wed Apr 24, 2019 5:21 am
One is true on a plane and the other is true on a sphere.
On a sphere is triangle actually has more than 180 degrees.
http://mathworld.wolfram.com/SphericalTriangle.html
This is fudging with truth a little bit because an actual triangle is only on a plane.
A spherical triangle would actually be an object that is comparable to a plane triangle
yet on a spherical surface rather than a plane.
So I guess for this same sort of reasoning parallel lines do not really meet.
First, let's note that when you say plane, you mean Euclidean space in general. It could be a cube or a 4-cube or 5-cube or n-cube. But it's "flat."
And spheres are only a special case of non-Euclidean geometry. There are saddle shapes, torii (n-dimensional donuts), etc. And some of those can be flat too!! This subject is
differential geometry. There are many wild shapes out there.
And it can be tricky. A 2-torus (a standard donut shape) is actually flat, for technical reasons. So "flat" isn't really the word. But Euclidean versus non-Euclidean is a simple dichotomy sufficient for our needs.
But the point is that we happen to find ourselves living in a universe. And that universe has SOME geometry. Which is it? Is it Euclidean or non-Euclidean? It must be one or the other and it can't be both.
You seem to be redefining what everyone else calls validity, with the word "truth." Perhaps that's your idea of a stipulative definition. If you define '5' to mean 4, then 2 + 2 = '5'. But that doesn't make 2 + 2 = 5. It only means that you changed the meaning of a standard symbol. That's perfectly legal. But it doesn't change the meaning of the underlying objects. It only means you express the same concepts using different symbols. Syntax and semantics again. Marks on paper on the one hand; and meaning on the other.
True is what's true in the world. Is the world Euclidean or non-Euclidean? That's a matter for empirical science. Logic and math can't answer the question.
Can I ask you a personal question? We're all smart about some things and ignorant of others so no judgment. But is it really true that you never heard about non-Euclidean geometry before? Or that Einstein's great mind-blowing revelation was that we DON'T necessarily live in a Euclidean world? Gravity distorts straight lines.
Historically it was non-Euclidean geometry that got mathematicians interested in foundations, leading to set theory and Gödel. It was this very example that led to the study of axiomatic systems.
I mean Cartesian plane.
I know that there are different non-Euclidean geometries. I solve problems by making them concrete and I had concrete examples.
I am converting formal proofs to use the sound deductive inference model. https://www.iep.utm.edu/val-snd/
having connected sequence of valid deductions from true premises to a true conclusion.
I am staying away from from formalizing synthetic truth.
According to Hindu Maya reality is fictional thus truth does not actually exist in physical reality.
https://www.britannica.com/topic/maya-Indian-philosophy
In purely analytic geometry both Euclidean geometry and non-Euclidean geometry are true.
I have been pondering the nature of truth for 50 years and providing the only correct one.
(1) There are certain expression of language that are defined to be true
and connected together by deductive inference:
"dogs are mammals"
"mammals breath"
∴ "dogs breath"
Because of the problem of induction, brain-in-a-vat and five-minute ago hypothesis
https://en.wikipedia.org/wiki/Brain_in_a_vat
https://en.wikipedia.org/wiki/Omphalos_ ... hypothesis
https://stanford.library.sydney.edu.au/ ... n-problem/
nothing not fitting this model counts as true.
Another way to say this is that true statements are statements that are completely
verified as true entirely on the basis of the meaning of their words.
I did not know that non-Euclidean geometry had non-plane geometric objects as its
foundation. I thought that it simply assumed a known falsehood.
Triangles on a sphere are not really triangles because triangles are defined on a plane.
Parallel lines never meet because parallel lines are defined on a plane.
Geometric objects that are comparable to triangles and parallel lines can
be defined on a basis other than a plane.
It does not matter if physical reality disagrees with the above stipulated definitions.
Because they are stipulated they form a mutually self-defining tautology.
All of conceptual truth functions this way as long as it remains consistent.
Inconsistency forces a choice.
My stipulated axioms eliminate undecidability and incompleteness from all formal
systems that were previously insufficiently expressive to detect and reject
semantically unsound logic sentences.
Axiom(0) Stipulates this definition of Axiom:
Expressions of language defined to have the semantic value of Boolean True.
Provides the symbolic logic equivalent of true premises.
Stipulating this specification of True and False: (TRUE ↔ ⊤ ∧ FALSE ↔ ⊥)
Axiom(1) ∀F ∈ Formal_System ∀x ∈ Closed_WFF(F) (True(F, x) ↔ (F ⊢ x))
Axiom(2) ∀F ∈ Formal_System ∀x ∈ Closed_WFF(F) (False(F, x) ↔ (F ⊢ ¬x))
Thus stipulating that consequences are provable from axioms.
Stipulating that formal systems are Boolean:
Axiom(3) ∀F ∈ Formal_System ∀x ∈ Closed_WFF(F) (True(F,x) ∨ False(F,x))
Screens out semantically unsound sentences as not belonging to the formal system.
The following logic sentence is refuted on the basis of Axiom(3)
∃F ∈ Formal_System ∃x ∈ Closed_WFF(F) (G ↔ ((F ⊬ G) ∧ (F ⊬ ¬G)))
There is no sentence G of Formal System F that is neither True nor False in F.
Thus refuting the 1931 Incompleteness Theorem.