Can real numbers and infinity coexist in all number systems?

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Discussion Overview

The discussion revolves around the coexistence of real numbers and infinity within various number systems. Participants explore the implications of performing operations involving infinity and the distinctions between different mathematical frameworks that incorporate infinity.

Discussion Character

  • Debate/contested
  • Technical explanation
  • Conceptual clarification

Main Points Raised

  • Some participants assert that in the usual real number system, operations involving infinity are not valid since infinity is not considered a real number.
  • Others propose that there are different number systems where infinity can be treated as a number, suggesting that operations with infinity may make sense in those contexts.
  • One participant mentions specific examples of number systems, such as the affine real line and the projective real line, to illustrate how operations involving infinity can vary in validity depending on the system used.
  • Concerns are raised regarding the relevance of certain exponential identities, such as exp(0) = 1, in the context of discussing infinity.
  • There is a suggestion that while infinity may behave like a number in some respects, it does not fully qualify as a real number.
  • Participants express a desire for additional resources or links related to the topic of infinity in different number systems.

Areas of Agreement / Disagreement

Participants generally disagree on the validity of operations involving infinity, with some asserting that such operations are not permissible in the standard real number system, while others argue that they can be valid in alternative number systems. The discussion remains unresolved regarding the specific contexts in which these operations may or may not hold true.

Contextual Notes

Participants highlight the importance of specifying the number system in question when discussing operations involving infinity, as different systems yield different results and interpretations.

Jhenrique
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Is correct to state that:

##x \infty = \text{sgn}(x) \infty##

##\infty^x = \infty^{\text{sgn}(x)}##

?
 
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If you are talking about the "usual" real number system, the are NO "operations with infinity" because "infinity" is not a real number. And there are several different ways to create number systems which include "infinity" as a number. Which are you talking about?
 
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HallsofIvy said:
If you are talking about the "usual" real number system, the are NO "operations with infinity" because "infinity" is not a real number. And there are several different ways to create number systems which include "infinity" as a number. Which are you talking about?

Your answer complicated more the things... look, exp(-∞) = 0, exp(0) = 1, exp(∞) = ∞... appears make sense make operation with ∞...
 
Not with the usual real number system, they don't- except a short hand for limits.
(Not "exp(0)= 1". I have no problem with that and I don't know why you included it here.)
 
HallsofIvy said:
(Not "exp(0)= 1". I have no problem with that and I don't know why you included it here.)

For shows that infinity acts like a number...
 
Jhenrique said:
Your answer complicated more the things... look, exp(-∞) = 0, exp(0) = 1, exp(∞) = ∞... appears make sense make operation with ∞...

They make sense in some number systems equipped with infinity, but not in others. For example, on the affine real line, the above operations are true, see http://en.wikipedia.org/wiki/Extended_real_number_line
But on the projective real line, they are false: http://en.wikipedia.org/wiki/Real_projective_line
There are many other systems which allow an infinity and where the above might make sense or not, so you need to specify.


Jhenrique said:
For shows that infinity acts like a number...

I don't see what ##e^0 = 1## has to do with infinity.

And infinity is certainly not a real number. It might act like on in some ways, but not in others.
 
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micromass said:
They make sense in some number systems equipped with infinity, but not in others. For example, on the affine real line, the above operations are true, see http://en.wikipedia.org/wiki/Extended_real_number_line
But on the projective real line, they are false: http://en.wikipedia.org/wiki/Real_projective_line
There are many other systems which allow an infinity and where the above might make sense or not, so you need to specify.




I don't see what ##e^0 = 1## has to do with infinity.

And infinity is certainly not a real number. It might act like on in some ways, but not in others.

Hummm, you have more links about this subject?
 

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