Jesse

Seraphim:
Even IF he did, I don't think it is possible for another doppelganger to think the same way as I do. My way of thinking is based on my experience and unless the dopplerganger has the same experience as I did in another world (which is very unlikely), I don't see how the other Me could share anything similar.

Well, if one believes that experiences affect your current self because of the physical traces they leave in the brain (like memories), then a physically-identical copy would act like it had exactly the same experiences as you. If not, then the math that was used to calculate a physically-identical copy of you would probably be within a certain distance could also be used to calculate the most likely distance to the nearest region of space that not only is a perfect copy of earth now, but also has been a perfect copy of earth for the last X years.

Answerer:
Anyway, I'm also skeptical about the article's predictions. I wonder what math did the scientists use to predict another identical twin?

Just combinatorics. They estimated the number of particles in the visible universe, and the volume of the visible universe, and then they calculated the total number of ways to arrange this number of particles in a volume of this size. If you assume that in a randomly-volume of space, any of these arrangements is equally likely, you can estimate the likely distance to a region with an identical arrangment in an infinite universe of uniform average density.

That's my memory anyway--I was looking through the article in a bookstore, and it had a little sidebar about how they came up with the estimate.

edit: just noticed there's a link to this sidebar in the online article--here it is:

Sidebar: How Far Away is a Duplicate Universe?

It looks like they didn't actually assume a uniform density, they actually looked at all possible arrangements of particles in a volume, from 0 particles to the maximum number that could fit in that volume (which they give as 10^118, which means the number of possible arrangements is 2^10^118, which is close to 10^10^118).

Wounded King

Dear Seraphim,

Which particular multiverse scenarion did you have a problem with? The many worlds QM interpretation doesnt suppose that there exist people in other universes who just happen to look like you, they were you up until the quantum event that made their universe diverge from yours.

As for the argument based upon the supposition that the universe is infinite and has an equal distribution of matter throughout, these seem to be rather large assumptions.

DBrant

Well, the article was very interesting... but what evidence did they present that the parallel universes actually exist? Did I miss something? The front page of the magazine clearly states that "parallel universes really do exist." I guess I was expecting something a bit more conclusive.
Sure, the parallel universes are possible mathematically, but what is the evidence that they're actually out there (other than creative use of Occam's razor)? And which of the four multiverse models does the magazine want us to believe in?

Jesse

I think the front page was a bit of hyperbole designed to reel people into buying the magazine. However, I would guess they're referring to the fact that the current cosmological evidence suggests we live in an "open universe", which should theoretically be infinite in extent. That would mean we have evidence for at least the first multiverse model, in which a perfect duplicate of the observable universe would probably exist around 10^10^118 meters away.

Wounded King

There seemed to be a number of different angles the writer reffered to, although he himself seemed inclined to think that all of these levels of multiverse were operative.

His main line of reasoning for the existence of a multiverse was that sice the chances of our universe having formed and had its history progress exactly as it has are almost infinitely small, and that consequently ther must be an almost infinite number of other universes out there for it to have happened at all.

There seem to be a number of rather large assumptions in a lot of the reasoning, especially with regard to speculation on conditions existing outwith our universes light cone.

sullster

I am very glad that this topic was brought up, since I have read the article and it made me want to ask some of you science people a question or two.

Is the main point, the acceptance of infinity? I never realized before that there was a feeling that the universe is finite and many ideas came from this. Acceptance of infinity must open up the possibilities of what is out there.

Am I mistaken to view the article's underlying thrust as being that once infinity is accepted, then you can fill it with universes of all types as long as they don't contradict mathematical axioms from our local universe?

The first time I read the article, I felt a very strange feeling, when contemplating infinity. It strains the mind to think that space goes on forever. Forever in all directions. Who needs silly religious ideas when you have infinity beginning just before you.

Infinity has always freaked me out. Not that religious crap, but the real thing, when you look out at night. It goes on forever!

Does it really help to think that there are infinite universes in all directions? Yeah, maybe. It is nice to know there is something out there and not total nothing forever.

I am getting a headache.

Marduk

“Infinity has always freaked me out. Not that religious crap, but the real thing, when you look out at night. It goes on forever!”
“I am getting a headache.”

Me to, I’ve also read there may be infinite infinities, an infinite variety of this universe, some empty with operating laws that don’t allow stars to form, some just like this one with minor differences like the spin of one particle being different, to extreme differences like WWII being one by the Germans, Japanese Egyptians etc. ad infinitum. Some universes as close as 1 mm. In another dimension, if two collide a big bang occurs making yet another universe, a star collapses into a black hole creating another universe, an infinitely small universe where a billion years is a billionth of a second to an infinitely large universe, and so on and so on. It all sounds very Hindu, the Vedas go on and on about this sort of thing, and how beings who live there travel here, how an hour here is a million years somewhere else.

Answerer

Sorry, I thought we are living in a 'flat universe' when does it become an 'open universe'?

Answerer

I think you read too much books on superstring and parallel universe theory.

Jesse

Answerer:
Sorry, I thought we are living in a 'flat universe' when does it become an 'open universe'?

Well, I had thought "open" referred to both negative curvature (hyperbolic) and zero curvature (flat), but I may be wrong about that. According to this page, the term "open universe" is "sometimes applied strictly to the hyperbolic Friedmann model, though both the hyperbolic and flat models are open in the sense of expanding forever." Looking at some other pages, it does look like most people just use "open" to refer to hyperbolic geometry.

Another question this made me think of is whether "open" and "closed" refer to the curvature of spacetime or just space--if the cosmological constant is zero, positive spatial curvature means a big crunch and zero or negative spatial curvature means expanding forever, but with a nonzero cosmological constant this is not necessarily true. Based on this page, it seems that "open" and "closed" refer only to the spatial curvature, not to the question of whether the universe will expand forever or collapse: