Infinitely large times the infinitesimally small

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Discussion Overview

The discussion revolves around the mathematical concepts of "infinitely large" and "infinitesimally small," particularly in the context of limits, hyperreal numbers, and their implications in physics, such as the behavior of an infinite wing and the forces acting on it. Participants explore the definitions and applications of these terms, questioning their mathematical validity and relevance.

Discussion Character

  • Debate/contested
  • Technical explanation
  • Conceptual clarification

Main Points Raised

  • Some participants assert that terms like "infinitive" and "infinitely small" are not well-defined in standard calculus.
  • One participant illustrates that expressions like ##\frac{1}{n}## become infinitesimal as ##n \rightarrow \infty##, but others challenge this by stating that these are well-defined positive numbers.
  • There is a discussion about the implications of an infinite wing using an infinite amount of air, with some arguing that such physical concepts do not exist in reality.
  • Participants introduce hyperreal numbers, explaining that while there are no infinite or infinitesimal real numbers, hyperreals allow for such concepts, leading to various outcomes when multiplied.
  • Some participants express confusion about the meaning of the symbol ##\infty## and its use in arithmetic expressions, with claims that dividing by infinity yields zero being described as a simplification.
  • There is a debate over the validity of teaching that dividing a number by infinity results in zero, with some participants defending the teaching methods and others criticizing them.

Areas of Agreement / Disagreement

Participants do not reach a consensus on the definitions and implications of "infinitely large" and "infinitesimally small." Multiple competing views remain regarding the mathematical validity of these concepts and their physical interpretations.

Contextual Notes

Limitations include the ambiguity of terms like "infinitive" and "infinitely small," the dependence on definitions of infinity and infinitesimals, and the unresolved nature of the mathematical steps involved in the discussion.

  • #31
jbriggs444 said:
IEEE floating point contains two signed infinities and is algebraicly complete. Although I have not been able to Google up an explicit statement, this strongly implies that ##\frac{1}{+\text{inf}}## yields a result of 0.

Note, however, that IEEE floating point is not an algebraic field. It has behaviors that violate other axioms that the real numbers (for instance) adhere to.
So when I asked the OP what ##\infty## is then one reasonable response would have been that it is the IEEE floating point signed infinity. And if you are right then the statement would be true there.

But then the problem is that the question in the OP cannot be asked because there is no infinitesimal number in the IEEE floating point.
 
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  • #32
user079622 said:
Mentor note: changed the thread title so readers don't mistake this for a question about verb forms.
What is result of infinitive times infinitive small?
Infinitive?
Rearrange A*B to A/(1/B) then try L'Hopital's Rule.
 
  • #33
jbriggs444 said:
IEEE floating point contains two signed infinities and is algebraicly complete. Although I have not been able to Google up an explicit statement, this strongly implies that ##\frac{1}{+\text{inf}}## yields a result of 0.

Note, however, that IEEE floating point is not an algebraic field. It has behaviors that violate other axioms that the real numbers (for instance) adhere to.
This is really all a bit of a non-sequiter The set of numbers used in floating point arithmetic is defined to deal with values that are encountered in 'real' life. in my Maths Analysis course we were told to be scrupulous about open and closed intervals and the use of continuous and differentiable.

To get this properly sorted out, you need to go much deeper into 'proper' Maths. You can't rxpect a group of Engineers to come up with a working rule that behaves itself outside the range of experience. The term +inf is pragmatic. Without it, they. would still be arguing about what zero and infinity mean. That's the job of Mathematicians. The concept of the limit is not too hard to get on top of and it gets you through a lot of Maths but there are many processes that can't be dealt with so simply.
 

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