Captain Obvious headlines

WBahn

Joined Mar 31, 2012
32,829
and it proves how divorced mathematics is from reality.
I wouldn't go that far -- there are some quite profound results that come out of this, such as rigorous proofs about several aspects of what is, and what is not, computationally possible.
 

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nsaspook

Joined Aug 27, 2009
16,322
I wouldn't go that far -- there are some quite profound results that come out of this, such as rigorous proofs about several aspects of what is, and what is not, computationally possible.
Sure, there are rigorous proofs but a proof is not a physical fact or physical evidence of anything other than mathematical correctness.
 

WBahn

Joined Mar 31, 2012
32,829
Sure, there are rigorous proofs but a proof is not a physical fact or physical evidence of anything other than mathematical correctness.
And yet those mathematical results have had profound impact on our understanding of, and ability to interact with, the physical world. Relativity and quantum mechanics come immediately to mind, in which the mathematical implications of accepting some very simple observed phenomena, such as the observed speed of light in a vacuum being independent of the motion of the observer, have resulting in many discoveries as those implications where tested and confirmed to hold in the physical world.
 

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nsaspook

Joined Aug 27, 2009
16,322
And yet those mathematical results have had profound impact on our understanding of, and ability to interact with, the physical world. Relativity and quantum mechanics come immediately to mind, in which the mathematical implications of accepting some very simple observed phenomena, such as the observed speed of light in a vacuum being independent of the motion of the observer, have resulting in many discoveries as those implications where tested and confirmed to hold in the physical world.
Absolutely but as you noted, physical evidence was absolutely needed for it to be scientifically valid. Vast numbers of the previous results with beautiful proofs are rightly in the trash bin when evidence decided what was fact and what as fiction.
 

djsfantasi

Joined Apr 11, 2010
9,237
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BobTPH

Joined Jun 5, 2013
11,515
Actually the rational numbers is the same cardinality as integers, whereas real numbers are not. The test is whether you can map the two sets one to one.
 

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nsaspook

Joined Aug 27, 2009
16,322
Ok


The most obvious example is to ask yourself how many integers there are? And how many rational numbers? If the answer to the both question are infinite, how can that be, since integers are a subset of rational numbers?
First, that's not a physical reality in nature. Second, see the post below yours.
 
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WBahn

Joined Mar 31, 2012
32,829
Ok


The most obvious example is to ask yourself how many integers there are? And how many rational numbers? If the answer to the both question are infinite, how can that be, since integers are a subset of rational numbers?
This has some serious shortcomings, since it implies either that a set that is a subset of another set must be smaller than that set, or that two sets that are infinite in size are always the same size. Neither of these claims is true. You can establish a one-to-one and onto mapping (a.k.a., correspondence) between the set of natural numbers and the set of rational numbers, meaning that each member of one set can be paired up with exactly one distinct member of the other set, thus establishing that the size of both sets is, in a very fundamental way, the same.

The same can be done between the set of natural numbers and the set of positive integers that are divisible by ten, even though the second set is a proper subset of the first.

Any set that is either finite, or can be placed in correspondence with the natural numbers is said to be "countable". All infinite countable sets are the same size.

However, you cannot establish a correspondence between the set of natural numbers and the set of real numbers (even if you restrict it to the positive real numbers). No matter what mapping you come up with, you can always construct a real number that is not mapped to from any natural number. Thus, in a very fundamental way, the set of real numbers is larger than the set of natural numbers and is said to be uncountable. Uncountable sets are strictly larger than countable sets.

These are only two of the type of infinities that mathematics deals with. In general, the behavior of infinite concepts (whether it be the size of sets, or the magnitudes of values) is tricky and very non-intuitive.
 
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