Artist concept of the cyclic universe.

If We Live in a Multiverse, How Many Are There?

15 Oct , 2009 by

[/caption]
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 (and more – see their paper here) 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.

The number of multiverses the human brain could distinguish. Credit: Linde and Vanchurin

The number of multiverses the human brain could distinguish. Credit: Linde and Vanchurin

“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.

Sources: ArXiv, Technology Review Blog

,



Sort by:   newest | oldest | most voted
tacitus
Member
October 15, 2009 3:36 PM

I prefer the term multi-cosmologies, which exist in a universe — the universe consisting of everything which exists, including other spacetime cosmologies.

You’re on a loser there, Lawrence. I doubt the word universe will ever come to encompass anything more than our classical “universe,” even if multiverses are proven to exist smile

Mason Kelsey
Member
Mason Kelsey
October 15, 2009 9:02 AM

This sort of “news” is tiresome. It is NOT science, it is science imaginagion or fiction. People read this sort of stuff and think that scientist KNOW there are multiuniverses. They do not know anything about the existence of multiuniverses. This is just a hypothesis and most likely completely untestable. If it is untestable it will NEVER be science and is only a belief or wish.

Put this stuff in the fantasy forum. And stop misleading the readers.

Gavin Polhemus
Member
Gavin Polhemus
October 15, 2009 9:57 AM

Thanks for posting the occasional article from the theoretical extremes. The multiverse is speculative science based on rather reasonable physical assumptions which may explain some rather surprising properties of our universe, like fine tuning. Definitely a topic worth watching (with health skepticism, of course).

Jorge
Member
Jorge
October 15, 2009 10:03 AM
Mason, I’d avise you to take a tranquilizer and think about the following for a while: Strange ideas are not science? Well, I beg to differ. You see, provided a given idea does not contradict any data, i.e., provided you don’t need to use “selectively” the available data to find a way to support your theory, like crackpots like to do, any idea that may be put forward IS science. Why? Because one person may come up with an idea but be unable to imagine a way to test it, while someone else, despite not being imaginative enough to come up with the idea in the first place, can look at the original work and expand on it… Read more »
Lawrence B. Crowell
Member
Lawrence B. Crowell
October 15, 2009 10:45 AM
I say one cheer for the multiverse, but not three and I doubt even two. There are some reasons to raise questions with this idea. Maybe I should say these ideas. On top if it I really dislike the term multiverse. I prefer the term multi-cosmologies, which exist in a universe — the universe consisting of everything which exists, including other spacetime cosmologies. There are four basic levels or versions of the multiverse, each one having a different level of characterization. I will try to outline each of these levels. The first level is the so called pocket universe. These occur because the inflaton field, a Higgs-like field which induces inflationary cosmology, assumes different values in different regions… Read more »
Manu
Member
Manu
October 15, 2009 11:55 AM

“To the Universe and Beyond!”: suddenly takes a new meaning…

I totally agree that we need theoretical, speculative physics. As long anyone is clear about the speculative part.

It’s necessary to pave the way for future observations.

When Lemaitre invented the Big-Bang and black holes, I doubt he very much believed in their testability.

tacitus
Member
October 15, 2009 10:46 PM

Don’t knock MWI!!

At least not until I have written and published my killer scifi trilogy set in a world where the technology to open wormholes between realities is not only possible but dangerously easy…

Well, if I don’t get it written in this reality — perhaps there’s a parallel me whose already raking in the big bucks after selling the movie rights…!

microverses
Member
microverses
October 15, 2009 3:51 PM

Jorge – you lost me when I skimmed and saw ‘crack pots’ in your response.

That kind of thinking reminds me of the idiots that thought the earth was flat and not round and fought the idea.

That kind of ‘holier than thou – too smart to engage in discussion of possibilities’ attitude.

I say – hey it’s plausible – since we actually know so little about what’s really going on. Our observations will ALWAYS be confined to what our human senses can detect.

I find the possible explanation in Elegant Universe to be interesting, giant particles stretched out into branes colliding and creating big bangs on a regular basis.

Just keeping an open mind.

Jorge
Member
Jorge
October 15, 2009 3:56 PM

Try not skimming and actually reading what’s written for a change. You haven’t the slightest idea of what’s “that kind of thinking” unless you actually read what’s written, see?

William928
Member
William928
October 15, 2009 4:09 PM

@Jorge: I couldn’t have responded to Mason’s criticism any better. It always amazes me how incensed some of these commenters get when something doesn’t conform to their known universe ideas. If these theories are so bothersome, then DON”T READ THEM. I’d rather keep an open mind, as I was taught that this is the basis for learning.

Astrofiend
Member
Astrofiend
October 15, 2009 4:54 PM

Untestable? Possibly, and certainly if it remains untestable for all time, then yes, it can only ever be philosophy. But never doubt the ingenuity of the human mind when it comes to devising methods to test hypotheses – even hypotheses than are supposedly ‘theoretically’ untestable.

At the moment though, it will just remain an idea – a possible explanation for our situation. I say cudos to Andre Linde for staking his entire career on such ideas, because there’s better than even chance they’ll turn out to be incorrect…

Lawrence B. Crowell
Member
Lawrence B. Crowell
October 15, 2009 4:58 PM
Tacitus: Sure the term multi-verse is here to stay. I still don’t like the term. A caveat I do have on these multi-verse ideas is that I prefer to think according to systematics that explain our observable universe with a minimal referece to the physical state of other universes. We might be able to measure their influence on physics in our universe. Detecting black hole-like amplitudes at high energy are a sort of Casimir detection of the vacuum state influenced by D-branes tied to other cosmologies (universes). Yet the one problem with fine-tuning arguments is that these involve incomputable and unobservable aspects of the internal states of these universes. Computing the conditions for fine tuning based on landscape… Read more »
Vanamonde
Guest
Vanamonde
October 15, 2009 7:22 PM

Mr. Crowell, you beat me to the punch with MWI. Man, my head STILL hurts from trying to wrap it around that one!

Dr. Max Tagmark has a wonderful page with discussion of different kinds of multiuniverse.

As for pocket universes, I KNEW Sailor Moon had some place to hide her magic wand!!!

Vanamonde
Guest
Vanamonde
October 15, 2009 7:26 PM

….oh, yeah, on testability, that is where the MWI really loses. It postulates that there can never be any information transfer between the separate universes after the split.

A circular argument, common in mental hospitals, I think.

Lawrence B. Crowell
Member
Lawrence B. Crowell
October 15, 2009 7:53 PM
Yeah, when it comes to MWI I “don’t get it.” The idea is not really that hard to understand, and the mathematics for it is not hard either. But when it comes to the “why MWI?” I don’t get it. There are people who go googoo over Bohm’s interpretation as well — again I don’t get it. You can’t test these ideas! They are not effective. It is not that they are wrong, but that these things are metaphysical notions that are wrapped around quantum physics to make it look pretty. BTW, people all wound up about the strangeness of quantum physics have the question upside down. Quantum mechanics involves nice linear wave equations, they are perfectly deterministic… Read more »
Astrofiend
Member
Astrofiend
October 15, 2009 9:44 PM

“BTW, people all wound up about the strangeness of quantum physics have the question upside down. Quantum mechanics involves nice linear wave equations, they are perfectly deterministic — I mean sheesh, what could be simpler? What is odd is the existence of the macroscopic or thermal and classical physical world we ordinarily experience. Why or by what means does that come about? Those pictures of dunes on Mars, or the dynamics of galaxy collisions, that stuff is nonlinear and bat-s**t crazy compared to nice integral wave motion of quantum fields.”

Beautifully put.

Anaconda
Member
Anaconda
October 15, 2009 10:09 PM

It’s incredible that this kind of gobledygook gets serious attention in astronomy. And it’s prima facie evidence that astronomy is in crisis.

It is not just theoretically untestable. It is physically untestable and never will be testable by the authors own admission.

This is navel gazing, not star gazing.

Nexus
Member
October 15, 2009 11:42 PM

Is Max Tegmark the guy who hypothesizes that every conceivable universe that is not logically inconsistent is objectively real?

Anyways, I don’t like the idea of postulating a gajillion universes that can never be observed, even in principle, just to explain ours. If you’re going to do that, why not just say “Because God made it that way” and be done with it?

Badger1
Member
Badger1
October 16, 2009 12:41 AM

Doesn’t matter how many universes there are (although it’s a shame we’ll never know or visit!). We are still faced with those all important questions of where they came from, why, and what existed before. I know the physicists tell us there was nothing before the Big Bang but that concept is impossible for us humans to get our heads round.

thegreenspan
Member
thegreenspan
October 16, 2009 3:42 AM

It’s not as crazy or fantasy as you think….we have known about this for over 3000 years….

Kabbalists have known about many different universes or dimensions or other worlds since the giving of the Torah on Mt Sinai.

Not to mention Black Arts and sorcery doesn’t just pull stuff from this universe, but it invokes different dimensions…

You can’t be just one sided and only look at the field through one perspective, it takes a multi-faceted integration of theories to try to understand the whole puzzle…not just physics but biology, metaphysics, etc…

wpDiscuz