# Euler's Equation: A sign from god?

Jin314159
The first time I saw Euler's equation, it blew my mind.

$$e^{i\pi}+1 \equal 0$$

Here, we have three of the most important numbers in math, all related to each other in such a remarkably compact equation. Does anyone know what this means? I think you can prove this through Taylor Series, but that's not what I'm asking for. Is there some underlying, intuitive reason for why Euler's equation is true? Or is it just a big fat coincidence (hence sign from god)?

Edit: Why is there a stupid dash over my zero? This is why I hate Latex. Stupid, unexplained stuff always happens.

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ahrkron
Staff Emeritus
Gold Member
Instead of "\equal", just use "="

$$e^{i\pi}+1 = 0$$

I don't see any divine influence on the equation, but it is definitely a wonderful one. I think of it as a brief, yet elegant, summary of some of our most powerful and beautiful math (algebra, complex numbers and calculus).

In terms of the underlying reason, the proof is basically the reason you are looking for. Think of exponentiation in terms of the Taylor series (i.e., picture ("e^x" as a short notation for the series), and of complex numbers in terms of their intimate relation with rotations, which naturally bring pi to the arena. Instead of an unexplained coincidence, I see it as an inevitable result of the structure of math, lying in an unavoidable intersection of various branches of it.

Jin314159 said:
The first time I saw Euler's equation, it blew my mind.

$$e^{i\pi}+1 \equal 0$$

Here, we have three of the most important numbers in math, all related to each other in such a remarkably compact equation. Does anyone know what this means? I think you can prove this through Taylor Series, but that's not what I'm asking for. Is there some underlying, intuitive reason for why Euler's equation is true? Or is it just a big fat coincidence (hence sign from god)?

Edit: Why is there a stupid dash over my zero? This is why I hate Latex. Stupid, unexplained stuff always happens.

It's from the definition of $e^z$ = $e^x(Cos(y) - i Sin(y))$ for complex z = x + iy. And yes, this definition does come about because if you use the Taylor Series expansion for $e^z$ you can separate the resultant series into two which represent the trigonometric functions. However, such rearrangement of infinite series with changing signs is very dangerous, as this can change the resultant sum (as in conditionally convergent series). But Euler often played fast and loose with such unrigorous methods, and got away with it! In any case, having done that, setting x to 0 and y to $\pi$ gives you $e^{i\pi}$ = -1 which is a most ugly form. I much prefer it when the identity elements of addition and multiplication show in the equation.

But I'm not so sure it proves there's a God. Perhaps it proves that Euler was in league with the devil! :)

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Hm?

"Is there some underlying, intuitive reason for why Euler's equation is true? Or is it just a big fat coincidence (hence sign from god)?"

Since when did coincidences imply a sign from God?

HallsofIvy
Homework Helper
Are you saying that you consider any "coincidence" a sign from God? You are truly blessed!

Staff Emeritus
Gold Member
Dearly Missed
According to the vector interpretation of complex numbers $$e^{i\pi} = -1$$ just says that if you turn through 180o you will be facing the other way. Another way to look at it is that $$e^{i\theta}$$ generates a circle in the complex plane, and of course $$\pi$$ has its well-known relationship to a circle.

And why does $$e^{i\theta}$$ generate a circle? Basically because if you multiply two complex numbers with magnitude and argument, the magnitude of the product will be the product of the magnitudes and the argument of the product will be the sum of th arguments, so the argument, or angle of a complex number behaves like a natural logarithm, and e is the basis of the natural logarithms.

And why does the product of complex numbers work that way? It comes out of the distributive law of multiplication and the representation of the complex numbers in components as $$m cos \theta + i sin \theta$$ which brings us back to Euler's series.

It hangs together because the plane has this rotation property. Whether you take that as a mystical sign or not is of course up to you.

philosophking said:
"Is there some underlying, intuitive reason for why Euler's equation is true? Or is it just a big fat coincidence (hence sign from god)?"

Since when did coincidences imply a sign from God?

you can use taylor expansion to proof this equation

Janitor
John Baez has a lot of interesting stuff at his website. Complex numbers, and their "higher dimensional" analog, the quaternions, are pet topics of his. I took the liberty of pasting this from there:

There are very few dimensions in which the unit sphere is also a group. It happens only in dimensions 1, 2, and 4! In 1 dimensions the unit sphere is just two points, which we can think of as the unit real numbers, -1 and 1. In 2 dimensions we can think of the unit sphere as the unit complex numbers, exp(i theta). In 4 dimensions we can think of the unit sphere as the unit quaternions.

Only in these dimensions do we get polytopes that are also groups in a natural way. In 2 dimensions all the regular n-gons correspond to groups consisting of the unit complex numbers exp(2 pi i / n). In 4 dimensions things are more subtle and interesting. It's especially interesting because the group of unit quaternions, also known as SU(2), happens to be the `double cover' of the rotation group in 3 dimensions. Roughly speaking, this means that there is a nice function sending 2 elements of SU(2) to each rotation in 3 dimensions.

Richard Feynmann, in his lectures at Caltech (available in book form), referred to the underlying relation that produced the referenced equation as the "crown jewel of algebra", I think.

Icebreaker
Jin314159 said:
Or is it just a big fat coincidence (hence sign from god)?
Perhaps you should be a little less humble; it is an achievement of human intellect: we did it.

Pengwuino
Gold Member
Icebreaker said:
Perhaps you should be a little less humble; it is an achievement of human intellect: we did it.

since when did humans invent math? Did math not exist before us?

I'm still rather (extremely) confused as to how this relates to God. What's so important about this equation?

Icebreaker

Icebreaker, math existed before we discovered it, and it will exist long after we're gone.

Pengwuino
Gold Member
Unless of course, you follow that "If I believe it's true, then it's true" line of thinking.

i think euler himself thought that his equation was so perfect that it proved the existence of God.

Tide
Homework Helper
thecolor11 said:
Icebreaker, math existed before we discovered it, and it will exist long after we're gone.

Unless you are assuming there are/were other intelligent species in the Universe, how could that possibly be?

Pengwuino
Gold Member
Tide said:
Unless you are assuming there are/were other intelligent species in the Universe, how could that possibly be?

1 + 1 = 2 existed before humans did. We didn't invent math, we discovered it.

Tide
Homework Helper
Pengwuino said:
1 + 1 = 2 existed before humans did. We didn't invent math, we discovered it.

I don't think so! Number is a concept and you cannot have concepts without mind. There may have been a "number" of things before the mind existed but the numbers require realization in order to exist.

Euler Formula: http://mathworld.wolfram.com/EulerFormula.html

Gauss is reported to have commented that if this formula was not immediately obvious, the reader would never be a first-class mathematician (Derbyshire 2004, p. 202).

I doubt most of us are in that class, but, according to Gauss, so much for mystification of the formula. (It might be added that Gauss was a hard master who cared little for his students, and did absolutely nothing to help Galois or Able.)

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Tide: I don't think so! Number is a concept and you cannot have concepts without mind. There may have been a "number" of things before the mind existed but the numbers require realization in order to exist.

Does a tree falling in the forest make a sound if there is no one to hear it?

Pengwuino
Gold Member
robert Ihnot said:
Does a tree falling in the forest make a sound if there is no one to hear it?

I think the argument here is that does the forest even exist if no one is around to hear it.

Pengwuino: I think the argument here is that does the forest even exist if no one is around to hear it.

Correct, if you want to put the argument that way.

Tide
Homework Helper
robert Ihnot said:
Tide: I don't think so! Number is a concept and you cannot have concepts without mind. There may have been a "number" of things before the mind existed but the numbers require realization in order to exist.
Does a tree falling in the forest make a sound if there is no one to hear it?

How, exactly, do you know a tree is falling in the forest?

Icebreaker
Saying mathematics is discovered and that it somehow trascends us only serves to add grandeur to where it's not really needed.

George Jones
Staff Emeritus
Gold Member
Tide said:
Number is a concept and you cannot have concepts without mind.

This is not a fact, it is a personal philosophy of mathematics held by some. Others believe that mathematics exists independently of the human mind. There is no way to "prove" that one philosophy is more true than the other.

As I have said before, I personally am a whole-hearted enough Platonist that I like:

"... and there is no sort of agreement about the nature of mathematical reality among either mathematicians or philosophers. Some hold that it is 'mental' and that in some sense we construct it, others that it is outside and independent of us ... I believe that mathematical reality lies outside of us, that our function is to discover or observe it, and that the theorems which we prove, and which we describe grandiloquently as our 'creations', are simply our notes of our observations."

G. H. Hardy

Regards,
George