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perizade
2014-Nov-06, 01:15 AM
Anyone got a [language] answer for a dumbass question?

If the multiverse has many universes with their own laws of physics, is there an expected range for how varied they can be? I should imagine there's a spectrum but not truly an infinite number of possibilities. Otherwise we'd have universes with Greek gods ruling just as they did in mythology. Worse still, every fantasy novel ever written, along with their fan fiction, would essentially be real, just not in this universe. So is there something that stops the fabulous from being possible in *any* universe?

Ken G
2014-Nov-06, 04:16 AM
You've put your finger on the main problem with regarding the multiverse as a scientific theory-- how do you constrain the probability distribution if you only observe one? You can set up the distribution such that the attributes we find in our universe are relatively common among the ones that contain life, but how is it a testable theory if we set it up to seem plausible right from the outset? I don't see the predictions there, and science is supposed to be more than just a sense of plausibility.

Solfe
2014-Nov-06, 04:38 AM
If you are into fiction, "The Number of the Beast" nails this topic. Every sci-fi world is apart of the story, even if not implicitly named. Good reading.

Don't take this as science, this is the science fiction buff post. Personally, I can't wrap my mind around a multiverse with different rules for each universe. It would seem to me that there would be a lot of universes with absolutely little happening. Again, this is my bias as a science buff/sci-fi buff. My understanding is seriously limited.

MVAgusta1078RR
2014-Nov-06, 05:04 AM
http://space.mit.edu/home/tegmark/main_crazy.html#levels

http://en.wikipedia.org/wiki/Multiverse#Max_Tegmark.27s_four_levels

There's different ways that parallel universes can exist. If our universe was proven to be infinite for example it would mean other copies of the Earth and us exist somewhere out there in space. M-theory or quantum mechanics where the laws of physics could be different or other universes branching of off ours.

You are right though if these parallel universes existed then we would come full circle and every mythology would be true somewhere. Even Star Wars, Terminator or Jurassic Park would exist in some universe. Basically every movie you ever watched or book actually happened. There is no spectrum when you're dealing with infinity. Infinity is math not philosophy.

Are you familiar with Niels Bohr's quote: "Your theory is crazy, but it's not crazy enough to be true."

slang
2014-Nov-06, 09:27 AM
perizade, welcome to Cosmoquest. Please take some time to have a look at the forum rules, linked below. Using bad language here may trigger filtering software at schools, making the forum unavailable to some students.

Ken G
2014-Nov-06, 11:26 AM
Personally, I can't wrap my mind around a multiverse with different rules for each universe. It would seem to me that there would be a lot of universes with absolutely little happening. Then you can wrap your mind around it just fine, that is indeed the whole point of the multiverse. You may ask, what could be the benefit of imagining this vast number of universes with nothing happening? The flip side of all those wasted universes is that they allow us a way to "understand" (and I put that in scare quotes because it is not obvious if this rises to the level of a scientific understanding) why so much can be happening in ours (such as, life and advanced intelligence). It's a bit like wondering why there are so vastly many planets in our galaxy if it seems that so few have intelligent life on them, why not just have one planet if that's where all the action is? Having the many allows for the possibility of the few special ones, that's the idea behind the multiverse as well. Of course, we actually observe those other planets...

Cougar
2014-Nov-06, 01:01 PM
If the multiverse has many universes with their own laws of physics, is there an expected range for how varied they can be? I should imagine there's a spectrum but not truly an infinite number of possibilities. Otherwise we'd have universes with Greek gods ruling just as they did in mythology....

First of all, it's a hugely big "if" to speculate that there are many universes to begin with. A massively big, entirely unsupported "if". But OK, if there are "many universes with their own laws of physics," what conjectural theorists like Smolin mean by this is that the various universes take on different values of the physical constants. (http://en.wikipedia.org/wiki/Physical_constant#Anthropic_principle) The strength of gravity might be greater in some and lesser in others, for example. The range can be quite varied. Gravity might be so high in one universe that the whole thing recollapses shortly after it's formed. Or it might be so weak that stars and galaxies never form. Only the right mix of physical constants with certain values will produce a universe with stars, galaxies, black holes, and eventually intelligent life. I don't think any mix would yield a universe that is actually directed by Greek gods, although the intelligent life might think that's what happening for a time.

MVAgusta1078RR
2014-Nov-07, 07:48 PM
First of all, it's a hugely big "if" to speculate that there are many universes to begin with.

It would only be a huge "if" if many physicists and leading physicists didn't take it seriously and pursue it and the subject wasn't constantly being published in scientific journals and publications. People like Richard Feynman, Brian Green, Stephen Hawking...

Solfe
2014-Nov-07, 08:14 PM
It would only be a huge "if" if many physicists and leading physicists didn't take it seriously and pursue it and the subject wasn't constantly being published in scientific journals and publications. People like Richard Feynman, Brian Green, Stephen Hawking...

Multiverses are what smart people consider for fun. Basically a brain flexing exercise. There have been several experiment/observations to detect other universes, but they have been refuted so far. The test-ability of certain types of multiverses keeps it in the realm of science.

I don't really know if scientists look for fun things to test, but I know of a few idea or proposals that look "very fun" - String theory, Nemesis star (a companion to the sun that causes bombardment of Earth by comets every couple of million years), as search of stars for a IR signature from Dyson Spheres, a giant diamond as the core of <insert planet here>, etc. These sorts of "fun" ideas either end up to be impossible to test or get a slam dunk negative.

I would imagine that a lot of these things are dreamed up because with we have some knowledge or capability for observation, and the answer is interesting. The Nemesis star idea came up at just the right time to say "nope, can't happen", so the capability to test and the completion of some data set of observations allowed for the refutation of the idea from the get go. I suspect that if certain types of observations are made and there is the impetuous to ask "Ok, what do we know now?" and tick off a bunch of ideas, no matter how outlandish.

ShinAce
2014-Nov-07, 08:15 PM
Without Feynman to speak for himself, I think he would be against the multiverse as we understand it. He favoured testable theories that conform to experiment. The multiverse is not one of them. At least not yet.

At any rate, I do believe there would be an infinite number of possible universes. Yet I can't see how varying the fundamental constants(and/or mixing angles) of nature can lead to Greek gods. If we humans someday learn to manipulate spacetime and matter-energy on the level of a Greek god, will we be considered Greek gods? In that sense, yes. In the usual sense of a god prior to creation, not that I can see.

Amber Robot
2014-Nov-07, 08:28 PM
I still can't get past the idea that there should be an infinite number of universes that are identical to this one and will only differ by some minute detail at some infinite point in the future.

mkline55
2014-Nov-07, 09:14 PM
What always amused me about this conjecture is that if there were an infinite number of universes, then why does that not result in an absolute certainty that an infinite number of them would have interacted with and destroyed this one an infinite number of times?

MVAgusta1078RR
2014-Nov-08, 04:02 AM
Without Feynman to speak for himself, I think he would be against the multiverse as we understand it. He favoured testable theories that conform to experiment. The multiverse is not one of them. At least not yet.

Yea he sure would...
"This concept was introduced by Richard Feynman, whose Feynman path integral is integrated over the set of all possible histories"
http://en.wikipedia.org/wiki/Multiple_histories


Multiverses are what smart people consider for fun. Basically a brain flexing exercise.
"Parallel worlds are standard fare for sci-fi, but the idea originates from quantum physics where the seemingly bizarre notion of alternative universes is taken very seriously."
-Cosmos Magazine


"Dr Hall says the “Many-Interacting Worlds” theory may even create the extraordinary possibility of testing for the existence of other worlds."
-Griffith University

https://app.griffith.edu.au/news/2014/10/27/new-quantum-theory-is-out-of-this-parallel-world/

ShinAce
2014-Nov-08, 04:27 AM
Yea he sure would...
"This concept was introduced by Richard Feynman, whose Feynman path integral is integrated over the set of all possible histories"
http://en.wikipedia.org/wiki/Multiple_histories


I do not agree.

As you can see in you text, Feynman worked on the path integral formulation of quantum mechanics.

It loosely says: "for a particle(electron) to go from point A to B, we must add up the 'amplitude' of all possible ways of getting from A to B. To get the final answer, the probability, square the total amplitude you found."

Here, square means 'mod squared'.

It's a beautiful, unintuitive version of the principle of least action. Why does light bounce off a mirror at the same angle it came in? Because it bounces at all places on the mirror at all angles.

The difference, like I said before, is testability. Feynman's theory makes testable predictions. And those predictions are right.

The multiverse makes loose predictions at best, which are disfavoured. One of them was the Higgs boson mass. The multiverse proponents predicted a Higgs mass higher than what we found. Of course, it is such an unpolished theory that you can always include a fudge factor. But that's the problem.

A good theory makes good predictions.

Multiverse is a cute theory, not a good one.

MVAgusta1078RR
2014-Nov-08, 04:52 AM
For starters the multiverse is just one theory out of a few of parallel universes. Secondly that's why I mention Richard Feynman exactly because of his many histories theory.
The theory is cute enough to use $6 billion equipment to test for it. I'm well aware of how cute it is why everybody from Leonard Susskind to Stephen Hawking to Michio Kaku take it seriously.

Nature is not obliged to do anything that anyone considers simple or nonfantastical. Black holes are one example and like parallel universes were thought to be absurd for decades. I don't know if the theory is correct but I see why and do take it seriously.

This is what Richard Feynman believed in: "The imagination of nature is far, far greater than the imagination of man."

So good luck making sense of everything in nature.

ShinAce
2014-Nov-08, 05:11 AM
Don't get me wrong. I like the theory, but that means absolutely nothing. There are 'versions' which may be testable. One of them comes from Linde, followed by the recent observation made by BICEP2.

I'll refer to universe as the galaxies we see. I'll refer to cosmos as the galaxies we see plus those we don't see.

Linde proposes that the cosmos before inflation had some size. Our universe started inflation at some time(call it t=0), and ended shortly thereafter. Other parts of the cosmos could have inflated later, or earlier. They could have ceased inflation earlier, or later. All cosmological 'fields' we know of are scalar fields, save one. Gravity gives rise to a tensor field. So if you detect a tensor field in the relic radiation, you detect gravitational radiation. They call the ratio of the two fields the r-ratio. If we allow for space to be bigger than our universe, and gravity to be present at the very beginning, you can get an r ratio which isn't zero. This is what BICEP2 claims.

This is cool because when you combine it with the anthropic principle, you get a possible answer for "why are we here at all?". Well, the universe is bigger than we imagine, and if there is a part that can support life, guess where you'll find us.

Name dropping doesn't make a theory more solid. No one has invested $6 billion to test this theory. And you're right, Nature is not obliged to do anything. However, physics is obliged to avoid errors like appealing to authority.

Susskind has also helped promote the holographic principle, which appears to deny us the possibility to test the many worlds hypothesis in the universe we live in.

Lastly, quantum mechanics does in fact work better when you allow all possibilities to contribute. But what you measure is a single outcome. This is called wavefunction collapse. A process which is still debated, and in my opinion, poorly understood. It does not necessarily imply a multiverse.

If you want to quote Susskind, you can find one of his relevant papers here:
http://arxiv.org/abs/1105.3796

MVAgusta1078RR
2014-Nov-08, 05:32 AM
I believe that's the level 1 universe that Max Tegmark and Brian Green refer to trying to categorize the different theories of parallel universes.

http://en.wikipedia.org/wiki/Multiverse#Max_Tegmark.27s_four_levels

And whether the universe is infinite or closed: http://map.gsfc.nasa.gov/universe/uni_shape.html

I was only name dropping to point out this isn't some kind of closet science.

I was referring to the LHC about using $6 billion to test some of these parallel universe theories:
"Arkani-Hamed has proposed alternative theories that the Large Hadron Collider will test when it comes back online in 2015, and he said he is optimistic that new discoveries will be made soon."
http://www.livescience.com/48651-quantum-mechanics-lecture-watch-live.html
I know there's other teams at the LHC too that are testing for parallel universes. Even before the LHC came online years ago I knew they'd be testing for some of those theories and not just the Higgs and other particle physics. I was like how much do you want to bet it'll be more than just these conservative theories.


Lastly, quantum mechanics does in fact work better when you allow all possibilities to contribute. But what you measure is a single outcome. This is called wavefunction collapse.

"According to Wiseman and his team this interaction between parallel worlds leads to just the type of interference patterns observed – implying electrons are not waves after all. They have supported their theory by running computer simulations of the two-slit experiment using up to 41 interacting worlds. “It certainly captured the essential features of peaks and troughs in the right places,” says Wiseman."
https://cosmosmagazine.com/physical-sciences/can-we-test-parallel-worlds

Ken G
2014-Nov-08, 06:36 AM
It looks to me like what this "interacting worlds" picture is saying is, take Feynman path integrals, interpret them literally in terms of real interacting subsets of a universe, which by themselves would not rise to the level of their own universes because they look nothing like ours. Then you elevate them to the level of their own universes, that do have the basic laws of ours though not the same observables, by in some sense "fleshing them out" in ways that don't affect the observables we get in our universe. In other words, each term in a Feynman path integral in our universe may also appear in other universes, but with different weights or different degrees of consistency with the facts of that other universe. It should probably take Tegmarks level III and split it into two possibilities, say IIIa and IIIb, where IIIa is Everett's branching worlds, and IIIb is Wiseman's parallel worlds, the difference being that Wiseman's worlds are always there, they are not increasing in number and do not require re-calculating the probabilities by re-assessing the total number of possibilities at every turn and culling out the ones that are inconsistent with the observations. In Wiseman's picture, the "sterile" versions are culled out simply because they interact less and less with our universe as they deviate more and more from the facts of our universe.

What I don't like about it is the same thing I don't like about the multiverse-- the weightings we use to get the statistical distribution used in the path integrals are arbitrary and can be set to give the results we need after the fact. We need the equivalent of the Schroedinger equation to apply to the amplitudes we assign to the interactions between the universes. In so doing, we seem to be caught between a rock and a hard place. The "rock" is to just use the amplitudes we find in the wave function as the amplitudes we associate with each different universe, but then those contributing "universes" are not like our universe at all-- in particular they don't have a Schroedinger equation themselves, that equation only appears when you interact the universes. The "hard place" is to say that the contributing universes do each have their own Schroedinger equation, which represents how they interact with other neighboring universes. Then all the interacting universes do act like our own (and this is Wiseman's approach), because the other universes are also interactions, but then, how does this scheme achieve a definite closure that is not infinitely flexible to get anything we want?

Copernicus
2014-Nov-08, 06:53 AM
Anyone got a [language] answer for a dumbass question?

If the multiverse has many universes with their own laws of physics, is there an expected range for how varied they can be? I should imagine there's a spectrum but not truly an infinite number of possibilities. Otherwise we'd have universes with Greek gods ruling just as they did in mythology. Worse still, every fantasy novel ever written, along with their fan fiction, would essentially be real, just not in this universe. So is there something that stops the fabulous from being possible in *any* universe?

One end of the range for variability could be zero, another range is that could be a number of repeating ones, another range would be all over the place. I personally think that since particle physics is quantum, that extra universes would act like fractals.

WayneFrancis
2014-Nov-11, 01:30 AM
Then you can wrap your mind around it just fine, that is indeed the whole point of the multiverse. You may ask, what could be the benefit of imagining this vast number of universes with nothing happening? The flip side of all those wasted universes is that they allow us a way to "understand" (and I put that in scare quotes because it is not obvious if this rises to the level of a scientific understanding) why so much can be happening in ours (such as, life and advanced intelligence). It's a bit like wondering why there are so vastly many planets in our galaxy if it seems that so few have intelligent life on them, why not just have one planet if that's where all the action is? Having the many allows for the possibility of the few special ones, that's the idea behind the multiverse as well. Of course, we actually observe those other planets...

Another way to think of it is just life within our solar system or even our planet. You and I live in a very privileged part of our solar system/planet. We could not live in most of our solar system. So you might say there is a lot of wasted space compared to where we live.
Accepting the multiverse scenario, where there is like 10500 odd solutions, most would be sterile to life as we know it. Most would be sterile to life as we can even conceive it.
Now that said do I personally believe that, if there is a multiverse, there are universes almost like ours but with magic? No. Personally I don't believe that because magic implies a supernatural realm. I don't know how any tweaking of the parameters that lead to the 10500 different universes would support "magic" It isn't like if you tweak the strong force that a universe could then produce beings that can use "magic".

The key is that anything that can happen will happen not that anything can happen so everything will happen.

So while there may be another universe out there exactly like ours except one small detail including a duplicate of you I don't think in any universe there would be a you or me that powers like Elminster.

But my understanding of the mutliverse is very limited and I could be wrong.

Cougar
2014-Nov-14, 05:19 PM
It would only be a huge "if" if many physicists and leading physicists didn't take it seriously and pursue it and the subject wasn't constantly being published in scientific journals and publications. People like Richard Feynman, Brian Green, Stephen Hawking...

Well, even though physicists are investigating the idea, I'd still say it's a really big "if". For quite some time, there has been the question of our Universe being "fine-tuned," such that if any of several fundamental constants were only slightly different, the Universe would be unlikely to be conducive to the establishment and development of matter, astronomical structures, etc. This remained a curiosity. Then string theory began to be developed. It was hoped that the theory would lead to a single solution that would explain why the fundamental constants in our Universe had to be what they are. The opposite happened. String theorists eventually estimated that there were 10500 viable solutions. Apparently using human imagination only, Susskind suggested this must mean there are 10500 different Universes.... AND, as Ken notes, "Having the many allows for the possibility of the few special ones," IOW, that takes care of the fine tuning problem. Like with inflation, physicists really like it when a particular conjecture tends to explain another, different long-standing conundrum.

But where does this 10500 figure come from? As you know, string theory requires a 10-dimensional framework. We recognize only 3 spatial dimensions and 1 of time. From whither come 6 extra dimensions? Well, someone noticed that mathematician Shing Tung Yau was working on multi-dimensional manifolds, one of which seemed to fit the bill - the 6-dimensional Calabi-Yau manifold. This was embraced by the physics community as a possible solution to the missing dimensions - at least something they could work with. It's the number of possible configurations of Calabi-Yau manifolds that yields the 10500 estimate, and from there to Susskind's conjectural string landscape.

While Fields Medalist Yau's mathematical work is undoubtedly valuable in the field of contemporary mathematics, its apparently tacked-on application to string theory strikes me as significantly arbitrary. AFAIK, there is nothing that dictates that the 6 extra dimensions must be represented by a single 6-dimensional manifold. It certainly makes the string theorists' calculations easier to work with, but that's a questionable quality upon which to base far-reaching conclusions. Clearly this is not "fringe physics," but it is physicists working out on the fringes of what is known, seeking answers to what is unknown. As Timothy Ferris wrote:


"Making a model of the universe is like trying to pitch a tent on a moonless night in a howling Arctic wind. The tent is theory. The wind is experiment. When one gets to the precipice, where the secure lands of the known have been left behind and the dark canyons of the unknown fill one's field of view, it becomes very difficult to guess just where to set the tent pegs and to predict which ones will hold once the wind comes up."

MazeHatter
2014-Dec-08, 06:21 PM
Anyone got a [language] answer for a dumbass question?

If the multiverse has many universes with their own laws of physics, is there an expected range for how varied they can be?

According to the theory, there is only one law of physics, the Schrodinger Wave Equation, and the Multiverse is the wave function to which that law is applied.

There are (allegedly) many different outcomes, when a measurement happens, but there aren't different laws of physics for each set of outcomes.

Ken G
2014-Dec-09, 02:07 AM
Actually, that's not the "multiverse", that's the "many worlds." They sound kind of similar, but they are quite different-- the multiverse comprises of separate universes that, in some versions, can have different laws. In other versions, they have the same laws with different fundamental constants, etc. Basically, the idea behind the multiverse is that any theory that can fall under the general heading of a "string theory" is fair game for a whole universe. The purpose is to help explain why our universe seems "specially suited" for us to be able to be here, without invoking some special preparation. Whether or not that is science is quite unclear. The many-worlds, on the other hand, is an interpretation of the Schroedinger equation. Those many worlds are also not observable by us, but they are necessary to interpret the Schroedinger equation as the actual description of reality. If one holds it is just an equation, whose results we are free to interpret as we like, then no such requirement exists.

Cougar
2014-Dec-09, 02:25 PM
It would only be a huge "if" if many physicists and leading physicists didn't take it seriously and pursue it....

Having just started reading Max Tegmark's Our Mathematical Universe, My Quest for the Ultimate Nature of Reality, I can certainly see where you're coming from. I should point out, however, that after covering 118 pages of "mostly mainstream and well accepted" science, and before launching into the subsequent 280 pages of his "four levels" of possible universes, Tegmark at least makes it clear that....



"The science we've explored so far in this book has by now become mostly mainstream and well accepted. We now enter the controversial, which many of my physics colleagues will argue passionately either for or against."



I don't know if that's an understatement or not. Cosmic inflation is fairly mainstream since there are observations that support it -- first the e-mode polarization patterns in the CMB in 2002, and more recently the b-mode polarization, which Linde called the smoking gun. However, Tegmark then takes Linde and Vilenkin's "eternal inflation" idea as well established. It's an interesting idea, but AFAIK, it's far from well established, and it's unclear if or how it can gain any observational support. Tegmark's "Level 2" universe is entirely dependent on eternal inflation, where faster-than-light inflation is postulated to continue everywhere outside our own "pocket universe," with other pocket universes similar to ours decaying out of the ongoing inflation. Like Susskind has claimed, such a scenario "explains" why our pocket universe appears to be "fine-tuned," and also why the string theorists have come up with not one viable solution, but 10500 viable solutions in their mathematical workings. Problem is, unlike the horizon problem and the flatness problem, which are observable problems, I'm not so sure that the fine-tuning problem is a bonafide "problem." And string theory, well, it's not really a theory yet, and it's obviously got a lot of physicists scratching their heads.

In other words, there are good reasons that many of Tegmark's physics colleagues argue passionately against his conjectures.

Ken G
2014-Dec-09, 07:21 PM
Indeed I think the word "passionately" in Tegmark's quote puts the situation into good perspective. The one thing you can be sure about is that when two people are arguing passionately, it is not science that they are arguing. When we are doing science, we don't need passion, we need evidence.