# When will euclidean geometry become ?

## Main Question or Discussion Point

Hello everybody,
Based of some information that I recently learnt(which I don't know if they are right or wrong), I start asking myself this question about the euclidean geometry.
Ok, this geometry is basically founded on straight lines, and what I have learnt is there is no such a thing as a straight line in our planet.So.alot of human activities is based on this geometry,and it does really work after all but only for our eyes , so there must be some mistakes but very little one that we can't observe,because they very tiny .So ,my question is , when will the euclidean geometry become useless ? I mean if it is making some little mistakes some where ,then there must be cases which the mistakes can no longer be hidden
Or I am just talking randomly and all this question is based on mistaken information, please do enlighten me.

Of course, we use Euclidean geometry where it's applicable. And that is: on small scales. So if we want to build a house, then our notions of parallel and perpendicular work, because the scales are so small.

However, if we start to go to larger scales (like: larger distances), then Euclidean geometry breaks down. A classical and historical example is for a ship to find the shortest distance between two points. Here, the curvature of the earth comes into play and things are much more difficult than in Euclidean geometry.

Of course, we use Euclidean geometry where it's applicable. And that is: on small scales. So if we want to build a house, then our notions of parallel and perpendicular work, because the scales are so small.

However, if we start to go to larger scales (like: larger distances), then Euclidean geometry breaks down. A classical and historical example is for a ship to find the shortest distance between two points. Here, the curvature of the earth comes into play and things are much more difficult than in Euclidean geometry.
Ok, so let's assme that we want to build on very large scale ,what will we use in the place of euclidean geometry,since it will break down ?

I guess we would use some kind of spherical geometry. Do you have any concrete example of such a structure?

I guess we would use some kind of spherical geometry. Do you have any concrete example of such a structure?
No,I am just quoting your words .Ok ,so would you give some exemples on constructions work based on spherical geometry.

No,I am just quoting your words .Ok ,so would you give some exemples on constructions work based on spherical geometry.
I don't know any. But I'm pretty ignorant of these things. You should ask in the engineering forums.

verty
Homework Helper
An example is microwave towers. How do you know where to point the microwave dish? You can't just point it parallel to the ground, it won't find the other tower.

coolul007
Gold Member
An example is microwave towers. How do you know where to point the microwave dish? You can't just point it parallel to the ground, it won't find the other tower.
Microwave towers are line of sight. Theoretically they are pointed parallel to the tangent of the midpoint curve between the two towers.

coolul007
Gold Member
Euclidean Geometry's usefulness is not its application to real world solutions, necessarily. It's beauty lies in the mathematical structure it created and the concept of proof. The rigor of the geometric proof, sadly, is not taught anymore in schools. Just because the politics in control of schools see no use for it does not mean it is not a worthwhile endeavor. It is a great foundation for all things mathematical.

AlephZero
Homework Helper
There is nothing wrong with the "math" in the examples in #2 an #7, but in my view they are both Euclidean geometry. Euclid's "Elements" is not just about "straight lines". The second book (out of 13) is mostly about circles, and it progresses to 3-D geometry.

Engineers use Euclidean geometry every day in situations that are much mode complicated than just the surface of a sphere (i.e. the earth, in the two examples).

IMO the only applications of non-Euclidean geometry in Physics would involve special or general relativity.

I think the OP (and others) may be confusing "Euclidean geometry" with "geometry of a two dimensional plane".

symbolipoint
Homework Helper
Gold Member
The rigor of the geometric proof, sadly, is not taught anymore in schools. Just because the politics in control of schools see no use for it does not mean it is not a worthwhile endeavor.
That is not universally true everywhere. Some education secondary (and college) systems teach Geometry and with proofs included as a big part of instruction.

coolul007
Gold Member
That is not universally true everywhere. Some education secondary (and college) systems teach Geometry and with proofs included as a big part of instruction.
I would love to know where. Everything I have seen uses either Algebra, or Cartesian coordinates as part of the curriculum.

Geometry was refined by Hilbert to those essential Postulates and Theorems necessary for geometric proofs. In all of the geometric proofs numbers never appear as the measure of anything. Only references to right angles or n times an object. as in surface of a sphere is 4 times that of a great circle.

verty
Homework Helper
I would love to know where. Everything I have seen uses either Algebra, or Cartesian coordinates as part of the curriculum.

Geometry was refined by Hilbert to those essential Postulates and Theorems necessary for geometric proofs. In all of the geometric proofs numbers never appear as the measure of anything. Only references to right angles or n times an object. as in surface of a sphere is 4 times that of a great circle.
But... many proofs are easier with coordinates, especially those with sides in some ratio, those with midpoints, those relying on gradients. Some are just down-right infeasible in purely synthetic form, hence why you see geometry problems so often in math competitions.