Should physicists have a new word to describe things of an unlimited extent?

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Offline Soul Surfer

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Infinity is essentially a mathematical concept and its mathematical use leads to many problems of understanding when it is applied ad hoc to the physical world.  Many awkward questions on these pages are caused by the rigorous application of mathematical concepts of infinity to physical situations.

There is a television programme on infinity in the BBC horizon series starting in a few minutes time that will probably illustrate these quite well.

When I deal with infinities in a physical sense I tend to use the term indefinite rather than infinite because the true situation is usually that something will bridge the gap even though we may not fully understand it at the moment.

What do you think about infinity?
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Offline yor_on

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What do you think of larger and lesser infinities.
Now, that's a strange subject :)
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Offline JP

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Many awkward questions on these pages are caused by the rigorous application of mathematical concepts of infinity to physical situations.

I know I've seen these before, but I can't recall one at the moment.  Can you give an example?

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Offline namaan

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What do you think of larger and lesser infinities.
Now, that's a strange subject :)

Haha, yes, different sized infinities has always been a bit of a no-no for me. I mean, sure, there are a lot of things in physics that are neither simple nor intuitive just because they reflect a complex and abstract world...but seriously? This one just goes beyond not being intuitive for me.
Take it with a grain or two of salt...

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Offline LeeE

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Many awkward questions on these pages are caused by the rigorous application of mathematical concepts of infinity to physical situations.

I know I've seen these before, but I can't recall one at the moment.  Can you give an example?

The most common that comes to mind is describing The Universe as 'infinite', when 'open' or 'unbounded' may be better descriptions.
...And its claws are as big as cups, and for some reason it's got a tremendous fear of stamps! And Mrs Doyle was telling me it's got magnets on its tail, so if you're made out of metal it can attach itself to you! And instead of a mouth it's got four arses!

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Offline Geezer

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Many awkward questions on these pages are caused by the rigorous application of mathematical concepts of infinity to physical situations.

I know I've seen these before, but I can't recall one at the moment.  Can you give an example?

The most common that comes to mind is describing The Universe as 'infinite', when 'open' or 'unbounded' may be better descriptions.

"Unquantifiable" perhaps? (Doesn't exactly "trip off the tongue")

or "Defies quantification" if there is a way to make a single word out of it.
There ain'ta no sanity clause, and there ain'ta no centrifugal force Šther.

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Offline JP

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Ah.  I think using the proper word in each context would be clearest, then.  Of course, the word "unbounded" is less intuitive than infinite, which might be why people tend to substitute infinity for the concept.  There's also the case of infinity appearing in singularities, which has a different physical meaning as well as infinity appearing in a lot of equations as an approximation to "something really big." 

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Offline techmind

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One a related topic, you will have noticed that the word "exponential" is increasingly abused in the media and by politicians, to mean anything that increases faster than linear.

On the smarter programmes (Radio 4) we're now beginning to hear the word "geometrical" in the context of growth or expansion - meaning exactly what exponential used to mean.  [;)]
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Offline Farsight

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What do I think about infinity? There are no infinities in nature. It's a mathematical concept, that's all.

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Offline Geezer

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One a related topic, you will have noticed that the word "exponential" is increasingly abused in the media and by politicians, to mean anything that increases faster than linear.

On the smarter programmes (Radio 4) we're now beginning to hear the word "geometrical" in the context of growth or expansion - meaning exactly what exponential used to mean.  [;)]

Quite right! We need to train them to use "nonlinear" instead.

I once worked for an outfit that had a rather temperamental CEO (Managing Director). The engineers were careful to point out that the CEO's response to unfavorable events was nonlinear. As in;

"Old wotsizname went freekin' nonlinear on hearing we would not be able to ship the product for at least 18 months."
There ain'ta no sanity clause, and there ain'ta no centrifugal force Šther.

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Offline fontwell

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I not a mathematician but in any maths at high school level I don't like it when people use phrases that make it sound like infinity is just a big number, such as 'to infinity' or the real killer, 'an infinite number'. To my ears that is an oxymoron.

In my head I always replace these words with something like 'going on forever'  or 'without end'. It has always seemed to me that infinity plus one doesn't even make sense because it treats infinity as a number.

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Offline Bored chemist

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Many awkward questions on these pages are caused by the rigorous application of mathematical concepts of infinity to physical situations.

I know I've seen these before, but I can't recall one at the moment.  Can you give an example?

The most common that comes to mind is describing The Universe as 'infinite', when 'open' or 'unbounded' may be better descriptions.
The problem is that something can be finite, but unbounded. The two terms have different meanings.
From our point of view the Earth's surface is unbounded - you can set off in any direction and keep going. You never hit a boundary. But the Earth is also finite.
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Offline LeeE

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Many awkward questions on these pages are caused by the rigorous application of mathematical concepts of infinity to physical situations.

I know I've seen these before, but I can't recall one at the moment.  Can you give an example?

The most common that comes to mind is describing The Universe as 'infinite', when 'open' or 'unbounded' may be better descriptions.
The problem is that something can be finite, but unbounded. The two terms have different meanings.
From our point of view the Earth's surface is unbounded - you can set off in any direction and keep going. You never hit a boundary. But the Earth is also finite.


Yes, this it true, if you try to separate space from time.  In space-time though, the surface of the Earth would be both unbounded and infinite (as time hasn't stopped yet) and your space-time coordinates require all four values to be identical to be able to come back to exactly the same place (in space-time).
...And its claws are as big as cups, and for some reason it's got a tremendous fear of stamps! And Mrs Doyle was telling me it's got magnets on its tail, so if you're made out of metal it can attach itself to you! And instead of a mouth it's got four arses!

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Offline Bored chemist

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True, but the words still have different meanings so you can't use one in place of the other.
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Offline LeeE

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Ah, but the point about space-time is that either is meaningless without the other [;)]
...And its claws are as big as cups, and for some reason it's got a tremendous fear of stamps! And Mrs Doyle was telling me it's got magnets on its tail, so if you're made out of metal it can attach itself to you! And instead of a mouth it's got four arses!

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Offline yor_on

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I think Geezer is on to something there.
"Defies quantification"

How about Defqua?
Or does that sound to military?

"Well Sir, we spotted this defqua trying to take over our limited resources, so we attacked with our larger Defqua. But, alas, it refused to surrender insisting that is was just as much a defqua as the one taking over."
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Offline Geezer

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I think Geezer is on to something there.
"Defies quantification"

How about Defqua?
Or does that sound to military?

"Well Sir, we spotted this defqua trying to take over our limited resources, so we attacked with our larger Defqua. But, alas, it refused to surrender insisting that is was just as much a defqua as the one taking over."

The military would likely abbreviate it to "DQ". Wait a minute - I think that's already taken! It's disqualified. (or even DairyQueen)
There ain'ta no sanity clause, and there ain'ta no centrifugal force Šther.