A measure for the multiverse

[n2doc]

03 March 2010 by Amanda Gefter

WHEN cosmologist George Ellis turned 70 last year, his friends held a party to celebrate. There were speeches and drinks and canapés aplenty to honour the theorist from the University of Cape Town, South Africa, who is regarded as one of the world's leading experts on general relativity. But there the similarity to most parties ends.

For a start, Ellis's celebration at the University of Oxford lasted for three days and the guest list was made up entirely of physicists, astronomers and philosophers of science. They had gathered to debate what Ellis considers the most dangerous idea in science: the suggestion that our universe is but a tiny part of an unimaginably large and diverse multiverse.

To the dismay of Ellis and many of his colleagues, the multiverse has developed rapidly from a being merely a speculative idea to a theory verging on respectability. There are good reasons why. Several strands of theoretical physics - quantum mechanics, string theory and cosmic inflation - seem to converge on the idea that our universe is only one among an infinite and ever-growing assemblage of disconnected bubble universes.

What's more, the multiverse offers a plausible answer to what has become an infuriatingly slippery question: why does the quantity of dark energy in the universe have the extraordinarily unlikely value that it does? No theory of our universe has been able to explain it. But if there are countless universes out there beyond our cosmic horizon, each with its own value for the quantity of dark energy it contains, the value we observe becomes not just probable but inevitable.

more

http://www.newscientist.com/article/mg20527501.100-a-measure-for-the-multiverse.html

[villager]

1. It might explain why we're living in the "evil mirror universe"

And why the good denizens of "Earth One" -- who respect their planet, each other, never vote for liars (or buy their products) etc. -- are living some parallel where else...

[DKRC]

2. Where all the women are strong,

all the men are good looking, and all the children are above average ...

[AlecBGreen]

4. sounds like Lake Woebegon has met the reqs for NCLB

everyone else can learn from their success :)

[Orsino]

3. Skinner--your agonizer, please.

I, for one, welcome our goateed masters.

[IndianaGreen]

5. Fascinating article

K&R

[Fumesucker]

6. If there are an infinite number of disconnected bubble universes..

Then the number cannot be "ever growing"..

At least not the way I understand "infinite number"..

[TheMadMonk]

7. Actually there are an infinite number of infinities.

So yes, you can have an ever growing infinite number of universes.

[Fumesucker]

8. It seems to me that if infinity + 1 > infinity ..

Or infinity * infinity > infinity..

Then infinity wasn't actually infinity to start with..

[TheMadMonk]

9. While it may seem counterintuitive, there are entire systems of mathematics...

...devoted to infinities that work and have real applications.

The most trivial example is that the set of integer numbers is infinitely large but by definition the set of real numbers is infinitely larger. We can also toss in the idea that between any two integers there exists an infinite set of real numbers, which is itself an infintesimal subset of the set of all real numbers and further that this infinity is exactly equal in size to the set of all positive integers. And from there we can posit the axiom that the set of all integers is twice as large as the set of positive integers plus 1 (for zero).

Then beyond that it gets really wierd.

[Jim__]

10. It's not that infinity + 1 > infinity.

It's that, say, the real numbers cannot be mapped (1 to 1) onto the integers. There are an infinite number of integers (you can just keep adding +1) but there are more real numbers - as clearly shown by Cantor.

Using the normal mathematical notation: ∞ + 1 = ∞

But, using ω to represent the transfinite numbers,
then ω0 + 1 = ω1
while 1 + ω0 = ω0

And, as noted in the previous post, there are an infinite number of ω's

[pokerfan]

11. Imagine a hotel with an infinite number of rooms and they are all occupied...

You show up and want to check in.

“No problem!” says the manager, "You can stay in room #1." He then gets on the intercom and tells every guest to move into the next highest numbered room. #1 moves to #2, #2 moves to #3, #237 moves to #238 and so on. Now Room #1 is empty and you move in. This works because there is no absolute largest number.

Now imagine that an infinitely large bus shows up with an infinite number of people and they all want to check in.

"No problem!" says the manager. He simply tells every guest to move into the room whose number is twice their current number. #1 moves to #2, #2 moves to #4, #237 moves to #474 and so on. Now all of the odd numbered rooms are empty, and there are infinitely many odd numbered rooms, so you can accommodate the whole bus.

AKA as Hilbert's paradox of the Grand Hotel.