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Parallel universes: I'm so confused

Paul C. Anagnostopoulos

Nap, interrupted.
Paul C. Anagnostopoulos
Joined
Aug 3, 2001
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19,141
Referring again to Max Tegmark's article in the May Sci Am, "Parallel Universes": I'm really confused now. For all these years we've been careful to describe the Big Bang as creating space and time, so there is no "space" beyond the universe. We've debated whether the universe is expanding or collapsing, and at what rate. We've talked about it as if it is the surface of a balloon.

Tegmark, without so much as a by your leave, tells us that there is infinite space full of an infinite number of Hubble-volume-sized universes. All this from one Big Bang? How does an expansion create an infinite-sized space? Or is it one Big Bang per universe? He says:
The Level I multiverse framework is used routinely to evaluate theories in modern cosmology, although this procedure is rarely spelled out explicitly.
Click to expand...
Really?

Any clarification will be most welcome.

~~ Paul
 
I haven't read the article, could he be refering to Guth's conjecture that inflationary universes can spawn more inflationary universes?

Peace
dancing david
 
DD:"Enough about parallel universes. What about perpendicular universes?"

Shouldn't that be orthogonal universes? Seems to me I know a few people at right angles to reality.:p
 
Paul C. Anagnostopoulos said:
Tegmark, without so much as a by your leave, tells us that there is infinite space full of an infinite number of Hubble-volume-sized universes. All this from one Big Bang? How does an expansion create an infinite-sized space? Or is it one Big Bang per universe?

~~ Paul
Click to expand...

Maybe I mis-read the article, but I thought that the Level I multiverse was finite but just very large, arising from a single Big Bang event. The significance of the multiple Hubble volume is simply that, at any given point in this "multiverse", there will only be a limited amount of space that is observable. The fact that we can see galaxies 48 light-years away despite the fact that light has only been travelling for 12 billion years suggests that it is possible that there is a lot more galaxies out there whose light has not reached us yet -- so many, that it's within probability that an identical planet to Earth exists in it somewhere.

The Level II model posits multiple multiverses, each with its own Big Bang event. This allows a infinite number of multiverses, each with finite (but very large) volume.
 
It sounded to me like these universes were more independent than that, Aggle, but the article certainly confused me. Typical Sci Am article: Wow them out, but don't actually explain things well.

~~ Paul
 
ar:"...so many, that it's within probability that an identical planet to Earth exists in it somewhere. "

This conclusion has been reached in other threads (with some interesting elaborations and conclusions being drawn, as well). But, looking at it, I was struck with an idea, and I need help seeing whether it is reasonable or not.

Consider the area under any given curve; the area of a segment between two points is calculated, and that proportion (over 1.00, the are of the curve itself) is the probability of a value of that population being in that segment. As the points grow closer, the area of the corresponding segment decreases, until we see that, by definition, any single point (no length between the 2 points on the curve) is infinitesimally small.

When we look at the question of life arising on other planets, "life" is a particular subset of "stuff" (I'm so technical here): we would certainly find all kinds of "stuff" hither, thither and yon throughout the universe, and some of that "stuff" would have the characteristics that allow us to call it "life". The various possible permutations of "life" allow us to (mostly through conjecture, I think--if anyone knows better, please tell me) calculate a probability of life arising, given assumptions about the size of the universe.

Now, let's take "life" and move the points closer together. I would think that if we specify "carbon-based life", that is--logically--less probable than simply "life". Let's make a gigantic leap and go for "humanoid carbon-based life"; we know from our experience on this planet that this is only a tiny fraction (either in numbers or in time, on this planet) of "life". To make an even greater leap, and suppose that there is a Mercutio2 (who would call me Mercutio2 and himself just plain Mercutio) sitting with an I-Book, contemplating the existence of the other...(you get my drift), I think we have slammed that segment of a curve down to infinitessimally small.

Given the number of physical and behavioral (including social, cultural) variables, and given the effects of even minute changes in these variables, and given the amount of time that truly random changes can accumulate, I would think that an exact copy earth, while theoretically possible, is by no means guaranteed, even by an infinite universe. (Of course, if everything else is the same, but Merc2 calls himself Tybalt, only the most hardened skeptic would really call that a "miss.")

So anyway, that was my line of thinking. I'd be interested in seeing where I screwed this up, if I have.
 
Paul- I suspect this is some of the "Quantum froth" we keep hearing about.
 
As for the probability of a planet identical to Earth in one of these multiverses of any level; calculating that requires an equation with a whole lot of unknowns, so just filling in values is meaningless. Sort of like the Drake equation.
 
Wait - if you read the article, on the first page, the author goes right ahead and states that the calculations, similar to the Drake equation, are dependent on an infinite universe. Isn't this a little bit of a leap, to just quickly mumble "in an infinite universe," and then go on deriving things from there? I think this guy is a kook, but I'm confused as to why this is a feature article at Scientific American.

By the way, earth's twin is not within 12 billion light-years from us - it's within 10^(10^28) meters from us! That number is so large, I'm not sure how to refer to it. And how would you express it in light years? 10 ^ ((10^28)-13)? This number is so large, that it doesn't matter whether you're talking meters or light-years!
 
hello...gread board!

Paul,

Paul C. Anagnostopoulos said:
Typical Sci Am article: Wow them out, but don't actually explain things well.

~~ Paul
Click to expand...

that was my impression as well (and i actually took general relativity in grad school!) after thumbing through that article at the bookstore. there are a few questionable assumptions underlying the Level 1 multiverse: 1) the universe is infinite (current observations indicate that it is, but cosmologists have been stunningly wrong in the past), 2) matter in the infinite universe is uniformly distributed, 3) the probability distribution of sub-universes within the separate Hubble volumes is such that every possible configuration of matter is at least possible (no configurations are strictly forbidden).

i can certainly imagine an infinite string of numbers where a particular pattern never repeats itself so that its probability of occurrence within the string is zero.

with regard to the Level 2 and 3 multiverses...those are much more interesting, IMO. has anyone read the Larry Niven story ``All the Myriad Ways'', which takes place in that particular Level 3 universe in which everyone acts on various violent impulses (murder, suicide, etc.) truly a disturbing possibility.

--Gianni
 
Welcome to the forum, Giovanni!

The universe is infinite? What's with all the recent chit-chat about how it's expanding at an ever-increasing rate? I suppose it could be both.

If it's infinite, how come it has a finite age? Or is that just the part we can see?

I'm still confoozed.

~~ Paul
 
Off the topic:
Alternate universes are not acsessible, whether they are infationary or what have you, they are speculation at this time.
It seems to be the equivalent of speculationg that there are so many angels in heaven that one must be like me.

I thought that the universe was bounded by the speed of light times the age of the universe times the rate of expansion, did I miss something? THe universe is huge but not infinite.

Peace
dancing David
 
Paul,

Paul C. Anagnostopoulos said:
Aha! We need to be careful when we speak of the universe vs. the known universe.

~~ Paul
Click to expand...

that's right. it's possible for spacetime to be infinite and still have a beginning in time (a singularity). think of the usual infinite rubber sheet analogy where the density of the sheet is infinite at the singularity. in an infinite expanding universe, the finite speed of light implies that only a finite volume of the universe is observable from any given point in spacetime.

if you think classical cosmology is confusing, read up on quantum cosmology (Wheeler-DeWitt equation), which attempts to define the wavefunction of the universe describing the probabilities of various alternative ``space-like'' surfaces within a ``superspace'' without a well defined notion of time evolution from one surface to another. my brain overheats whenever i attempt to understand that stuff....but, luckily, somwhere in that superspace, there's a parallel ``me'' for which it all makes perfect sense. :)

-Gianni
 
Paul C. Anagnostopoulos said:


Any clarification will be most welcome.

~~ Paul
Click to expand...

Think of it this way. In a universe very near here, there is a Paul who understands this completely. You are merely unfortunate enough to be one of an infinity of alternate Pauls that don't understand.
 
CurtC said:
Wait - if you read the article, on the first page, the author goes right ahead and states that the calculations, similar to the Drake equation, are dependent on an infinite universe.
Click to expand...

Yeah, but who wants to read the damn thing? :)

By the way, earth's twin is not within 12 billion light-years from us - it's within 10^(10^28) meters from us! That number is so large, I'm not sure how to refer to it. And how would you express it in light years? 10 ^ ((10^28)-13)? This number is so large, that it doesn't matter whether you're talking meters or light-years!
Click to expand...

The article describes the distance as "beyond astronomical". I think that's an understatement.
 
Giovanni Jensen said:
Paul,



that's right. it's possible for spacetime to be infinite and still have a beginning in time (a singularity). think of the usual infinite rubber sheet analogy where the density of the sheet is infinite at the singularity. in an infinite expanding universe, the finite speed of light implies that only a finite volume of the universe is observable from any given point in spacetime.
Click to expand...
So WHAT did the anisotropy probe take a picture of?

Yes, I know it's the microwave background radiation, which is the red-shifted first observable "flash" of photons originally visible once the universe became transparant to photons, but we did map it all around, and I think it's supposed to represent what the universe looked like a very long time ago, when it was much smaller.

What I mean is, since we can see the MBR in every direction, and now we've mapped it in pretty fair detail, how can we not, in some sense, be seeing the ENTIRE universe?
 
Giovanni Jensen said:


that's right. it's possible for spacetime to be infinite and still have a beginning in time (a singularity). think of the usual infinite rubber sheet analogy where the density of the sheet is infinite at the singularity. in an infinite expanding universe, the finite speed of light implies that only a finite volume of the universe is observable from any given point in spacetime.

-Gianni
Click to expand...

Ooops I stand corrected, however I thought that it also depended on lambda , and that it still up in the air. I still wonder if the age of the objects in the seen universe sets a bound.

Peace
dancing david
 
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