@rikuyamaha: Countable infinities refer to all the natural numbers. Like 1 2 3...etc. To understand higher infinities you need to understand cardinal set theory logic.
To be clear, higher infinities only apply to infinite sets aka groups of things such as: Oranges, universes, etc. You can't apply it to discrete stuff like weight or energy.
To understand set theory, we need to understand how to compare sets. When we say two sets of objects are equal, we put them into correspondence on a one-by-one basis. For example, if I claim I have the same number of fingers as toes, I mean that for every one finger there corresponds one toe, with no toes left over and no fingers left unmatched at the finish.
Now do the same for natural numbers and even numbers: pair 1 with 2, 2 with 4, 3 with 6, and so on. There will be exactly one even number for every natural number. The fact that each series forms an infinite set means the sets of numbers are the same size, even though one set is contained within the other. This result gives a definition of infinity: an infinite set of objects is so big it isn’t made any bigger by adding to it or doubling it; nor is it made any smaller by subtracting from it or halving it. This is known as a "weakly inaccessible cardinal" meaning you can't "reach" it via additions or multiplications.
In spite of this, it would be wrong to think of the infinity of natural numbers – which mathematicians refer to as a ‘countably’ infinite set, because you can count the members one by one – as the biggest conceivable number. Between 1 and 2, for example, lie an infinite number of numbers, such as 3/5 and 7917/384431. There is no limit to how many digits we can add to the numerator and denominator to make more fractions. Nevertheless, it won’t surprise you to learn that the set of all fractions is in fact no bigger than the set of natural numbers: they form a countably infinite set too.
But not all numbers between 1 and 2 are fractions: some decimals (with infinite numbers of digits after the point) cannot be expressed as fractions. For example, the square root of 2 is one such number. It is known as an ‘irrational’ number because it cannot be expressed as the ratio of two integers. This is best understood by envisaging a continuous line, labelled by equally spaced natural numbers: 1, 2, 3 and so on. There will be an infinite number of points between 1 and 2, for example, with each point corresponding to a decimal number. No matter how small an interval on that line and how much you magnify it, there will still be an infinite number of points corresponding to an infinite number of decimals.
It turns out that the set of all points on a continuous line is a bigger infinity than the natural numbers; mathematicians say there is an uncountably infinite number of points on the line (and in three-dimensional space). You simply can’t match up each point on the line with the natural numbers in a one-to-one correspondence. We know that the positive whole numbers (the natural numbers) are countably infinite. The positive and negative whole numbers (aka the integers) are also countably infinite, because there’s still a way to count them. The order would look something like this: 0, 1, -1, 2, -2, 3, -3… There is still a way to count the integers. However, there’s no possible method or rule to count the real numbers in this way. Even looking at the real numbers between 0 and 1, how would you start counting them? Would you start with… 0.0000001? Well what about 0.0000000001 instead? Hopefully it makes some intuitive sense here that the real numbers are a different kind of set in this way, that there’s no way to actually count the real numbers.
Georg Cantor went even further and wrote formal proofs that the real numbers are uncountable, the most famous being Cantor’s diagonal argument. Here’s the rough idea: let’s say we want to show that the set of all real numbers between 0 and 1 is uncountable (this is true by the way). Let’s pretend we have listed all the numbers in this set, every single number between 0 and 1. This would look like a big list of decimals, many of which go on for ridiculous lengths. It would look something like this:
0.00185674...
0.73527994...
0.47575958...
0.27527595...
0.28355596...
.
.
Cantor would then say “Oh yeah? That’s your list of all the real numbers between 0 and 1? I bet I can find a number that’s not in your list,” which would prove that there’s no way we can ever list (or count) all of these numbers. Cantor then slammed his drink on the table (I think) and said something like, “Make a new number which is equal to the first digit of the first number plus 1, and then the second digit of the second number plus 1, and so on until we’ve gotten through all the numbers in your list.” In other words we go down the diagonal of our list and modify each number by 1:
So the value we get is: 0.7755...
Now, this new string of numbers we made will never appear in the list above. Why? Well it is clearly different from the first number in our list, because we defined it as differing by the first number in that first digit. Similarly, the string of numbers differs from every number in the list by at least one digit, because that’s how it is defined. So it can’t possibly be in the list, which would mean our “complete list” of all the real numbers between 0 and 1 was actually incomplete, making that set uncountable. As all the natural numbers have already been used up mapping the values above, leaving this new string of value without a (natural) partner.
So while both the naturals and numbers between 0 and 1 are infinite, one is larger than the other. As the naturals cannot map all the values between 0 and 1.
Now to explain why an infinite-D multiverse > baseline infinite multiverse.
So let's assume that an infinite multiverse is infinite universes where each universe is infinite. So the math here would be infinity x infinity = Aleph Null (smallest/countable infinity).
An infinite-D multiverse will be also assumed to have infinite universes (each universe being infinite) in each one of its spatial axes. So it would be infinite x infinite ^ Aleph Null = Aleph 1. We know from Cantor that the power set of a number is strictly larger than the number itself. So the power set of Aleph Null > Aleph Null. And according to the Continuum Hypothesis, there is nothing between Aleph Null and Aleph 1, so the power set of Aleph Null = Aleph 1. I hope my uber long post is enough to explain higher infinities to you.
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