Is infinity a constant or a variable ?

In summary, the conversation discusses the concept of infinity and its properties. It is determined that infinity cannot be a constant because its value does not change when added or subtracted. However, it also cannot be a variable because it is not defined and cannot vary with respect to anything. It is mentioned that infinity is a concept and not a number, and is only useful in limits. The conversation also touches on the extended real number system and the comparison between cardinal and ordinal numbers. Finally, the conversation briefly discusses finding the limit of a sequence involving infinity, with the conclusion that the answer is 0.
  • #71
de_brook said:
In mathematics, infinity is a symbol representing an extremely very large quantity compared to the variables you are working with such that the system cannot even comprehend. Thus, we could have different infinities for different systems. An infinity for a system A may be a finite number for a system B.

What do you mean by "the system cannot...comprehend" mathematically? Please elaborate on your post.
 
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  • #72
slider142 said:
[itex]0.\bar{9} = 1[/itex]?? is a crackpot magnet as well. :D
Thank god religious threads are banned
 
  • #73
slider142 said:
What do you mean by "the system cannot...comprehend" mathematically? Please elaborate on your post.
I mean't that there are systems in which we are restricted to work with cetain variables. They could be considered as too large for our infinity or too small for a zero. For instance if you are working with a system in which most of what you encounter are infinitesimal values such as nano values and you encounter kilo-value once, you notice that there is a jump. This, we can say kilo-value is an infinity when compared to the sysytem we are working with
 
  • #74
de_brook said:
I mean't that there are systems in which we are restricted to work with cetain variables. They could be considered as too large for our infinity or too small for a zero. For instance if you are working with a system in which most of what you encounter are infinitesimal values such as nano values and you encounter kilo-value once, you notice that there is a jump. This, we can say kilo-value is an infinity when compared to the sysytem we are working with

Ah, that is definitely a physical/engineering infinity, not a mathematical one. Just checking. :)
 
  • #75
slider142 said:
Ah, that is definitely a physical/engineering infinity, not a mathematical one. Just checking. :)

Alright, what do you think it is? cos i know you quite agree that infinity is a symbol and it does not have a fixed value it just tells us about something very large
 
  • #76
There are many examples of infinities that are considered constants listed in this thread that have nothing to do with variables or allowing some variable to vary. They have precise definitions and algebraic properties and can be considered "fixed" in their respective systems.
 
  • #77
de_brook said:
Alright, what do you think it is? cos i know you quite agree that infinity is a symbol and it does not have a fixed value it just tells us about something very large
Again, that is not mathematics- it may well be some application of mathematics, but mathematics does NOT use "infinity" to mean "very large".
 
  • #78
I'll chime in with the other two here: each of the various infinite numbers have precise, fixed meanings in mathematics. It's not just a synonym for "big".
 
  • #79
Right. de brooks's definition is the Physics definition... I've heard it several times before.
 
  • #80
My explanation is quite informal, but I hope it helps.

Well it's not a constant, but roughly speaking, it's just a positive number when you approach given conditions ( usually the Weierstrass limit conditions ) that will grow bigger and bigger ... and bigger ... and bigger ... and bigger ... and bigger ...

Now if you consider the expression ∞+2, when ∞ will grow bigger and bigger as you approach given conditions, ∞+2 under the same conditions will grow bigger and bigger ... and bigger ... and bigger ... and bigger ... and bigger ...

So ∞+2 = ∞
 
  • #81
deiki: That's a fine explanation for physicists, but it won't cut it in math. Infinity isn't growing, it just it. Further, just to muddy the waters, [itex]\omega+2>\omega.[/itex]
 
  • #82
CRGreathouse said:
Further, just to muddy the waters, [itex]\omega+2>\omega.[/itex]

To make it clear, here [itex]\omega[/itex] is the first infinite ordinal.
To muddy the waters further, we also have [itex]\omega + 2 > 2 + \omega = \omega[/itex].
 
  • #83
de_brook said:
I mean't that there are systems in which we are restricted to work with cetain variables. They could be considered as too large for our infinity or too small for a zero.

What if they are not comparable?
 
  • #84
de_brook said:
For instance if you are working with a system in which most of what you encounter are infinitesimal values such as nano values and you encounter kilo-value once, you notice that there is a jump. This, we can say kilo-value is an infinity when compared to the sysytem we are working with
NO!
We never say that kilo-value here is "infinity" when compared to those Infinitesimal value.
We still say that it's too large, but we never say it is infinite compared to those Infinitesimal values.
Did you ever heard a physicist working with Schrödinger eq. and dealing in Planck numbers saying that universe started infinite years ago, NO! He will still say universe started (nearly) 13.7 billion yrs ago.
 
  • #85
de_brook said:
Alright, what do you think it is? cos i know you quite agree that infinity is a symbol and it does not have a fixed value it just tells us about something very large

I think slider and HallsofIvy gave quite appropriate answer to your question.
 
  • #86
deiki said:
that will grow bigger and bigger ... and bigger ... and bigger ... and bigger ... and bigger ...

So, Are you treating it as variable?
If it is so, then why aint it is waning rather than just waxing?
 
  • #87
deiki said:
it's just a positive number

JUST A POSITIVE NUMBER
I think you should read the whole thread before; then post something, because if you have read all the posts, you won't have said just a positive no.
 
  • #88
deiki said:
So ∞+2 = ∞

That's what I said in OP, what do you mean by repeating this?
 
  • #89
Okay everyone, I discussed it somewhere else, and there's one point I found quite interesting,
I'd like to share that one.

"It is really nothing and so something immeasurable .So it is none other than Infinity itself !It is everything and nothing too.
It is immeasurable and , boundless.It is nothing ; but something ; a being that is a non-being ! That alone is infinity.
For instance , space is emptiness. It can be filled or can be vacuum.and so something can be put into it .Something can extend into it .If there is NO SPACE , NO VACUUM for something to be put into, a thing can not exist .All things need space to exist in.But the space that things need to exist is actuallyemptinesss , vacuum, NOTHING .But if that "NOTHINGNESS" is not there , where will anything exist in this universe ?So all thatexitst , needs this space - this nothingness to exist in.But this nothingness does not existbecausee of anything else .It needs nothing to exist in! It depends on nothing for its existence ; but everything else in thisUniversee or anywhere , say in hell or heaven, needs this nothingness to exist in.Even the Gods and all Avatars needed this space , the emptiness to exist .but for this, even the Gods and their Avatars do not exist!"
 

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