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Comment by mnemonicsloth | Hacker News Reader

infinity doesn't exist because we can't observe it

Presumably, you are accessing this website using a some kind of personal computer and some communications infrastructure. The engineers who designed these systems all made frequent use of the notion of infinity, particularly in their use of limits and calculus, when these systems were designed.

I am sure that those engineers would love to hear about the equivalent (but necessarily much more complex), infinity-free versions of calculus and limit processes that you have obviously developed. Since infinity is the only simplifying assumption the average engineer is ever forced to make, I'm sure that as a group, they will be very eager to take your advice, even if it means they have to do twice as much work.

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Infinity doesn't "exist" because the notion of "existence" doesn't apply to mathematical constructs. We don't find them in nature; we use them to describe things we find in nature. The number two doesn't "exist", though there are plenty of things it models well.

There are, of course, things that are described by infinity: the energy required to accelerate a mass to the speed of light, the number of points at which a magnetic field can travel through a surface, etc.

The notion of existence is applied to mathematical constructs so long as these constructs are abstractions/generalizations of things that exist in the physical world.

The number two is a generalization of quantity. We know there may be two apples or two birds on the wire, and at one point we are taught quantity can be applied to virtually antyhing.

Now, what's infinity? Another abstraction of quantity, which has many definitions. However, every definition you take involves infinite time, e.g. you add 1 to a number ad infinitum or you accelerate a particle to the speed of light, and because reaching precise speed of light is not possible, you will be doing it infinitely.

So even "we use them to describe things we find in nature" - even that is not true. You can't find infinity in nature, neither anything that can be described with infinities.

Care to show an example how the notion of infinity can make a programmer's job easier? Particularly in the field of Internet protocols and web applications.

This is akin to entering room room full of engineers and shouting "I can fly! Prove I can't!", what do you mean, prove you can.

Take any serious book on modeling bus and routing infrastructure (and not vocational guide on using protocols designed by someone else) and you will see plenty of partial differential equations.

Just one example please. Ideally, a theory based on which engineers built something, but not the other way around, i.e. when something exists and some theorists are trying to build a de facto model of it.

Edit: a theory that involves infinities.

Edit: I'd like to warn you though, that because I'm more or less familiar with the subject, I think it will be very difficult to find what I'm asking for.

" I'd like to warn you though, that because I'm more or less familiar with the subject, I think it will be very difficult to find what I'm asking for."

Cool. Rather than posted challenges, how about educating us to why we are wrong. If you know this area well I'd be interested to learn more.

A few comments earlier there was a challenge:

The engineers who designed these systems all made frequent use of the notion of infinity

and I'm yet to see the proof.

My exact words were:

The engineers who designed these systems all made frequent use of the notion of infinity, particularly in their use of limits and calculus.

Do you disbelieve that engineers make frequent use of limits and calculus?

Do you disbelieve that notions of limit, derivative, and integral are contingent on the idea of infinity?

Why should anyone answer your questions while you continue to ignore mine?

Programming languages, compiler design and construction, operating systems, networking on all levels including protocol design, traffic analysis, etc; multithreading, games, browsers, document management systems, financial applications, telephony, CAD's, a lot of web development - are among the areas I worked in during my career. (I never touched signal processing though.)

Although in some narrow areas I've seen non-trivial calculus, but I barely remember anything that involves infinities and is significant for the solution.

You're still not answering my questions. Do you believe that no engineers use limits or calculus? Do you believe that limits and calculus are unrelated to the idea of infinity?

Now you seem to be saying: "I have never, myself, seen the concept of infinity used to solve a problem in a way I deem significant. Therefore, infinity does not exist and is not useful to anybody."

If I said the same thing about the number 65536, would it force you to program only 8-bit processors for the rest of your life?

Based on some of your earlier statements, I'm going to guess that we're using different definitions of the word "infinity." I'd guess that to you, the word "infinity" means something like "the largest possible number, denoted ∞." I'd also guess that, in your claim about calculus above, you mean something like "I have never seen a calculus problem whose solution required you to write down an ∞." Am I right?

Fourier Transform as applied to MRI. The underlying theory of Fourier Transforms involves integrating from -inf to inf. The transform is used to extract the underlying waveforms from the signal received by the MRI machine.

Since the MRI machine only samples the signal coming in it uses a DFT, but that doesn't negate the fact that the theory of Fourier Transforms involves the notion of infinity and that engineers used that body of mathematics to build a real machine.

No, he asked about protocol design.

Ideally, a theory based on which engineers built something, but not the other way around, i.e. when something exists and some theorists are trying to build a de facto model of it. Edit: a theory that involves infinities.

Spot the contradiction in this sentence. Even if I would like to argue with you on unedefined problem you have, I can't satisfy your requirements when they're contradictory.

I see PDE's in TCP papers, I don't know what's your problem.

Of course I expect you will dismiss that as too "astral" of an example, but ask Vint Cerf if he did not need any calculus. And then ask him (or Lloyd Wood) again about his new suite of protocols designed for guaranteed connectivity in spite of enormous latencies in orbital and interplanetary internet (with cisco routers with PDE-optimized buffer sizes orbiting already on several satellites).

No, he asked about protocol design.

Why didn't he just ask about discrete mathematics, then?

> Edit: a theory that involves infinities.

Asymptotic analysis of the computational complexity of algorithms.

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