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mattbrowne's avatar

If we live in a multiverse, how many are there?

Asked by mattbrowne (31735points) October 16th, 2009

The topic isn’t new, but I found an interesting new article I’d like to share:

Theoretical physics has brought us the notion that our single universe is not necessarily the only game in town. Satellite data from WMAP, along with string theory and its 11— dimensional hyperspace idea has produced the concept of the multiverse, where the Big Bang could have produced many different universes instead of a single uniform universe. The idea has gained popularity recently, so it was only a matter of time until someone asked the question of how many multiverses could possibly exist. The number, according to two physicists, could be “humongous.”

Andrei Linde and Vitaly Vanchurin at Stanford University in California, did a few back-of- the- envelope calculations, starting with the idea that the Big Bang was essentially a quantum process which generated quantum fluctuations in the state of the early universe. The universe then underwent a period of rapid growth called inflation during which these perturbations were “frozen,” creating different initial classical conditions in different parts of the cosmos. Since each of these regions would have a different set of laws of low energy physics, they can be thought of as different universes. Linde and Vanchurin then estimated how many different universes could have appeared as a result of this effect. Their answer is that this number must be proportional to the effect that caused the perturbations in the first place, a process called slow roll inflation, — the solution Linde came up with previously to answer the problem of the bubbles of universes colliding in the early inflation period. In this model, inflation occurred from a scalar field rolling down a potential energy hill. When the field rolls very slowly compared to the expansion of the universe, inflation occurs and collisions end up being rare.

Using all of this Linde and Vanchurin calculate that the number of universes in the multiverse and could be at least 10^10^10^7, a number which is definitely “humungous,” as they described it. The next question, then, is how many universes could we actually see? Linde and Vanchurin say they had to invoke the Bekenstein limit, where the properties of the observer become an important factor because of a limit to the amount of information that can be contained within any given volume of space, and by the limits of the human brain.

The total amount of information that can be absorbed by one individual during a lifetime is about 10^16 bits. So a typical human brain can have 10^10^16 configurations and so could never distinguish more than that number of different universes. “So, the total number of possibilities accessible to any given observer is limited not only by the entropy of perturbations of metric produced by inflation and by the size of the cosmological horizon, but also by the number of degrees of freedom of an observer,” the physicists write. “We have found that the strongest limit on the number of different locally distinguishable geometries is determined mostly by our abilities to distinguish between different universes and to remember our results,” wrote Linde and Vanchurin. “Potentially it may become very important that when we analyze the probability of existencse of a universe of a given type, we should be talking about a consistent pair: the universe and an observer who makes the rest of the universe “alive” and the wave function of the rest of the universe time-dependant.”

So their conclusion is that the limit does not depend on the properties of the multiverse itself, but on the properties of the observer. They hope to further study this concept to see if this probability if proportional to the observable entropy of inflation.

http://www.universetoday.com/2009/10/15/if-we-live-in-a-multiverse-how-many-are-there/

http://en.wikipedia.org/wiki/Multiverse

What are your thoughts? Does the concept of a multiverse scare you? Do you feel comfortable co-existing with all the trillion copies of you?

When do you expect the multiverse to become mainstream science? A confirmed theory like general relativity? At the moment the multiverse is just a hypothesis.

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18 Answers

Cartman's avatar

Removed by me. Brain freeze.

nisse's avatar

I feel this is truly a metaphysical question, and that i dont have the scientific knowledge (despite 5+ years of college) to appreciate the evidence laid forth for the hypothesis of multiverses. Also i belive there are alot more pertinent unanswered questions in our immediate reality. As presented this just feels like metaphysical mumbo jumbo.

If you are interested in the limits of knowledge from a scientific standpoint i suggest some study of Gödels theorem of uncertainty (the book Gödel Escher Bach is a great start, and enjoyable easy reading too).

mattbrowne's avatar

@nisse – Well, many would argue that it’s beyond metaphysics, because quantum interference is a real phenomenon, see double-slit experiment. Max Tegmark uses this to postulate the level 3 multiverse.

nisse's avatar

It may well just be my limited capacity for absorbing information (10^16 bits) that’s blocking me from fully comprehending the concept. :)

ragingloli's avatar

So a typical human brain can have 10^10^16 configurations and so could never distinguish more than that number of different universes.

but it doesn’t follow that there can only be 10^10^16 different universes. It only means a human can’t distinguish more. The universe could very well be different (like a few different atoms at the other end of the galaxy) and the human could not tell the difference.

kevbo's avatar

Idk, but the third ‘verse is the same as the first.

proXXi's avatar

Violent Femmes Lurve @kevbo

Shuttle128's avatar

I’m fairly certain the Many Worlds interpretation of Quantum Physics came long before String Theory. If the many worlds interpretation is correct, it is possible that there are infinite parallel universes.

I’ve accepted that we are in a multiverse for quite some time. If there can be a large number of universes created from “frozen” initial conditions caused by quantum fluctuations, what of the ludicrously large number of fluctuations that have occurred since then? At each moment in time the Schrödinger equation shows that quantum decoherence occurs. I don’t think it is possible to put a limit on the number of universes that may exist, and I certainly think that 10^10^10^7 is far too small a number to represent all possible universes.

El_Cadejo's avatar

i dont fully understand everything that was written above, but i find all of this highly fascinating. I just watched an episode of “The Universe” about the multiverse possibilities last week.

dpworkin's avatar

Let me know when string theory garners some empirical data. Until then, it’s just Scholastics arguing over angels dancing upon the heads of pins.

Austinlad's avatar

Personally, I’d like to see us focus our energy and brainpower on THIS beleagured little planet.

ratboy's avatar

My counterpart in Universe 173 sent me his picture by TransUniversal Express; it seems to suggest that estimates based on the size of the human brain ought to be taken with a grain of salt.

ratboy's avatar

@mattbrowne: If we live in ”a multiverse,” it would seem that there is one.

Cartman's avatar

Does this mean that there is a universe where life is great and everything in dandy?

And a universe where I have a million Lurve – wow!?!

mattbrowne's avatar

@Austinlad – There was a recent documentary on German television about earthquake prediction using quasars. Sounds far fetched? Unfortunately I couldn’t find anything on the web except for a scanned newspaper article, but it’s still quite interesting

http://news.google.com/newspapers?nid=348&dat=19740901&id=WbEFAAAAIBAJ&sjid=LjMDAAAAIBAJ&pg=7063,43952

Quasars belong to some of the most distant objects in our universe and if they have something to do with THIS beleagured little planet, why not investigate the multiverse, or multiverses. @ratboy – I’m also a bit puzzled by this distinction.

Shuttle128's avatar

It’s not that they have anything to do with us, its that they are so far away that the difference between the distance two rays of light travel is so small that the difference in the radio tower’s altitude outweighs it. Having a basically stationary measuring point is ideal to measure relative crust heights extremely precisely.

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