Probability of stars in a multiverse

[jimjohnson]

Having recently read two books (Just Six Numbers by Martin Rees and The Fallacy of Fine-Tuning by Victor Stenger) I am confused on one issue. Assuming a multiverse, what is the probability that stars and galaxies would form in a universe. Stenger would say it is high but Rees would say it is low. Based on the clarity of arguments, my vote would be with Rees. What do others think?

 

[Cybalicist]

In any system where the individual parts still act on each other with gravity it would only be a matter of time. Especially when you know how the early stars were formed.

 

[Chronos]

I'm no fan of multiverse theories, but, assuming it is correct, we still have no clue how probable structure formation [stars, galaxies, etc.] may be. Assuming the fundamental constants of nature are free to arbitrarily choose any value at the beginning of any given universe, I agree the probability appears vanishingly small. But, using the infinitude of alternate universes as an excuse to dismiss the odd coincidence our universe happens to be just right for structure formation sounds a little hand wavy to me.

 

[jimjohnson]

I agree with your comment but wanted to clarify the authors positions. Of the six numbers in Rees' book, all appear to be critical for the formation of stars and galaxies: N - the ratio of gravitation and electromagnetic forces (1039); ε -the percent of energy released in hydrogen to helium conversion (0.7%); Ω - the ratio of actual density to critical density (0.3); λ -the cosmological constant (0.7); Q - proportion of galaxy rest mass needed to disperse galaxies (10-5); and D - the number of dimensions (3). The first two are basic forces. The second two are relate to energy and expansion. The last two are properties of space. Rees says that changing anyone of these independently would not produce stars as we know them. Stenger says changing two or more may produce a stable environment because of the way they interact. Analysis appears to be very technical physics. Anyway, something to think about.

 

[Chronos]

My suspicion is the fundamental constants of nature are somehow intimately related, not free to arbitrarily assume random values. On that basis, I would hazard to guess structure formation is more likely than not in most 'multiverses'.

 

[Naty1]

Stenger says changing two or more may produce a stable environment because of the way they interact.

I have the Reese book. I have not seen Stenger's view...which seems interesting. Either our universe is 'one a kind never to be repeated' or we are in just one of perhaps an infinite number of universes, some habitable, some not. A related view which I have seen and find appealing is that from the universes which are born only those universes that can evolve do so, and of those, only the ones that can lead to new universes survive in the long run. If you can't have babies, your species dies out.

 

[Chalnoth]

My suspicion is the fundamental constants of nature are somehow intimately related, not free to arbitrarily assume random values. On that basis, I would hazard to guess structure formation is more likely than not in most 'multiverses'.

There's no real reason to suspect that. And everything we learn about the universe is pushing us in the other direction entirely. Though granted it is true that what we know now about the necessary physics is far too little to make a strong determination, what little we do know seems to be pushing in the direction of no such relationship that makes structure formation (or life) likely.

Also, we can infer nothing whatsoever about the likelihood of structure formation from the fact that we observe it: the probability that intelligent observers will observe structure formation is precisely equal to one, because without structure formation there can be no intelligent observers in the first place.

As far as what fraction of the universe beyond our cosmological horizon has structure formation? Well, we don't know. I suspect that fraction is very small indeed, based upon the very little that we do know about the topic.

 

[Naty1]

Chalnoth:

As far as what fraction of the universe beyond our cosmological horizon has structure formation? Well, we don't know. I suspect that fraction is very small indeed, based upon the very little that we do know about the topic.

I get the first two sentences, but not the last... Why might that be? Too young to have evolved much??

 

[Sayajin]

"Multiverse" theories are really speculative atm. There is no way to tell if something is going to happen when you don't know anything about it. Structure formulation would depend on the laws of physics.
If you believe that the laws of physics and all the constants except the cosmological constant are the same in the "multiverse" then our universe would be exception because if you change the cosmological constant by a little it affects the structure formulation in the universe by a lot.
However if you believe that some other constants or laws of physics are not the same then you can't say that because you can achieve other combination of values of the constants such that the universe has galaxies and stars even if it has much different cosmological constant.

 

[julcab12]

First, Let's put the speculation on one side and 'ASSUME' it is true. As per chaotic inflation theory. Multiverse tend to stop stretching in some region. Different bubbles may experience different spontaneous symmetry breaking resulting in different properties such as different physical constants. Acc. to WIKI. "Linde and Vanchurin calculated the number of these universes to be on the scale of 10^10^10,000,000. I don't know the probability of stars forming due to fact that we can't be sure of the variation of constants/factors for star formation as mentioned by Chronos.

 

[Chalnoth]

Chalnoth: I get the first two sentences, but not the last... Why might that be? Too young to have evolved much??

With slightly stronger gravity relative to the other forces, you get nothing but black holes. With slightly weaker gravity or a slightly larger cosmological constant no structures form at all. We don't know how likely these things are, but if these numbers vary much at all, star-bearing regions are probably extremely rare.

 

[Chalnoth]

"Multiverse" theories are really speculative atm. There is no way to tell if something is going to happen when you don't know anything about it. Structure formulation would depend on the laws of physics.
If you believe that the laws of physics and all the constants except the cosmological constant are the same in the "multiverse" then our universe would be exception because if you change the cosmological constant by a little it affects the structure formulation in the universe by a lot.
However if you believe that some other constants or laws of physics are not the same then you can't say that because you can achieve other combination of values of the constants such that the universe has galaxies and stars even if it has much different cosmological constant.

This is why proper comparisons use only dimensionless numbers that aren't prone to these problems.

 

[rbj]

"Multiverse" theories are really speculative atm. There is no way to tell if something is going to happen when you don't know anything about it. Structure formulation would depend on the laws of physics.
If you believe that the laws of physics and all the constants except the cosmological constant are the same in the "multiverse" then our universe would be exception because if you change the cosmological constant by a little it affects the structure formulation in the universe by a lot.
However if you believe that some other constants or laws of physics are not the same then you can't say that because you can achieve other combination of values of the constants such that the universe has galaxies and stars even if it has much different cosmological constant.

This is why proper comparisons use only dimensionless numbers that aren't prone to these problems.

i realize why we need to consider only dimensionless values for the fundamental constants of the universe to compare to other possibilities. but i do not understand why the need to consider dimensionless numbers has anything to do with what Sayajin wrote. he/she said nothing about units or the like.

but i do sort of object to saying that the Cosmological Constant is 0.7 . it is not 0.7 .

also, i thought that the whole idea of the concept of multiple universes is so that even if it is unlikely for some universal parameter to take on some necessary value for structure to form and eventually life that is intelligent enough to behold that structure, even if that is highly unlikely, it is not remarkable that we see such structure and such values for those universal parameters in the universe we behold. it's called selection bias, or specifically in this case, the Anthropic principle.

 

[Chronos]

Im no more a fan of the anthropic principle than the multiverse conjecture. Both go to great [and rather fantastic] lengths to explain the universe we observe - and resist any observational constraints. I think there must be a simpler, less 'finely tuned' expanation.

 

[jimjohnson]

I found two references addressing opposite views on the probability that stars/galaxies form. In the first, page 151 in The Hidden Realities, Greene quotes Weinberg on his argument for galaxy formation based on the value of the cosmological constant. His conclusion is that if it were a few hundred times larger there would be no galaxies. Using analogy he concludes that if E124 universes existed in a multiverse, then one like ours would be likely. The second reference is from Stenger's book page 227 and is based on the Principle of Mediocrity: " This implies that when we use physics to compute the possible range of a parameter, the value of that parameter should not be at the edges of that range but somewhere in the mediocre in-between." Not sure we will ever know.

 

[Chalnoth]

Im no more a fan of the anthropic principle than the multiverse conjecture. Both go to great [and rather fantastic] lengths to explain the universe we observe - and resist any observational constraints.

The weak anthropic principle is necessarily true. It makes as much sense to object to it as to object to the statement that 2+2=4. To not take it into account when considering questions of, "Why these laws?" is foolish: it's a selection effect that must be considered to have a chance at arriving at the correct answer.

I think there must be a simpler, less 'finely tuned' expanation.

Why?

 

[Chalnoth]

i realize why we need to consider only dimensionless values for the fundamental constants of the universe to compare to other possibilities. but i do not understand why the need to consider dimensionless numbers has anything to do with what Sayajin wrote. he/she said nothing about units or the like.

No, it actually does. For example, the reason why you don't get nothing but black holes now is not because of the absolute value of G, but rather of G's strength relative to the other forces: as long as gravity is weak enough that there is a regime where stable compact matter can exist without forming a black hole, we can have structure.

Gravity's strength compared to the other forces is around 10^{-40}. If it were around 10^{-39} or so weaker, it would overwhelm the other forces and we'd have nothing but black holes.

but i do sort of object to saying that the Cosmological Constant is 0.7 . it is not 0.7 .

Sure. The 0.7 number is based on convenience, and is particular to our period of time. A more sensible number is the one based on its ratio compared to the Planck scale, approximately 10^{-120}. If the dark energy were much higher, around 10^{-119} or so, the universe would expand too rapidly and no structures could form.

Anyway, my point is that if we take the space of all possible laws that we know of, the space in which structures can form only comprises a teeny, tiny subset of that space. Now, it is possible that there are details of the universe that we don't know which disallow or disfavor certain parts of the whole space. It's also possible that the fundamental laws of physics are richer and more varied than we currently imagine, leading to a much larger parameter space than a naive analysis based on the standard model would predict. Either way, work in high energy physics seems to be pushing that there probably isn't anything that really makes the low-energy laws we see the preferred ones in any sense.

 

[rbj]

No, it actually does. For example, the reason why you don't get nothing but black holes now is not because of the absolute value of G, but rather of G's strength relative to the other forces: as long as gravity is weak enough that there is a regime where stable compact matter can exist without forming a black hole, we can have structure.

Gravity's strength compared to the other forces is around 10^{-40}. If it were around 10^{-39} or so weaker, it would overwhelm the other forces and we'd have nothing but black holes.Sure. The 0.7 number is based on convenience, and is particular to our period of time. A more sensible number is the one based on its ratio compared to the Planck scale, approximately 10^{-120}. If the dark energy were much higher, around 10^{-119} or so, the universe would expand too rapidly and no structures could form.

i think actually we agree on substance and are differing with semantics.

i would say that there is no comparison of G (or c or \hbar or \epsilon_0) to any other situation. they're all just 1. including G (actually, i think it's 4 \pi G = 1).

what makes gravity so much weaker, from the POV of subatomic particles, is that the electric charge of any of these particles (if charged) is in the ballpark of the Planck charge, or the rationalized Planck charge, where e = \sqrt{4 \pi \alpha} while the masses of any of these particles is far, far less than the Planck mass, like something like 10^-19 or something like that.

i do not believe that there is some intrinsic parameter of free space that is G. the parameter G is only a manifestation of the units we choose to measure things.

 

[Chronos]

I agree the weak anthropic principle is undeniably true - the universe cannot possesses properties that forbid the existence of observers [i.e., us]. But, that does not explain why the measured properties of the universe possesses the values they do. To wave it off as a statistical fluke in an infinite sea of alternative universes with different properties is just a little too convenient, IMO. In my mind, there are only four fundamental forces in the universe and all of existence is and was determined by these four forces. Presumably they were all combined as a single force in the beginning. That at least suggests the existence of some unknown principle that encourages the individual forces to emerge with well behaved values, or proportionality of values, similar to those we observe. The trick, obviously, is figuring out the interdependence between all the forces. Thus far we've only solved the puzzle for electromagnetism. Many scientists still hold out hope for a grand unified theory [EM, strong and weak force], and some ponder an even grander theory that includes the black sheep [gravity]. Armed with such a theory, I believe we could assert alternative universes substantially unlike our own demand a primordial unified force substantially unlike that from which our universe emerged.

 

[Chalnoth]

I agree the weak anthropic principle is undeniably true - the universe cannot possesses properties that forbid the existence of observers [i.e., us]. But, that does not explain why the measured properties of the universe possesses the values they do. To wave it off as a statistical fluke in an infinite sea of alternative universes with different properties is just a little too convenient, IMO.

Why is it too convenient?

In my mind, there are only four fundamental forces in the universe and all of existence is and was determined by these four forces. Presumably they were all combined as a single force in the beginning. That at least suggests the existence of some unknown principle that encourages the individual forces to emerge with well behaved values, or proportionality of values, similar to those we observe.

Many high-energy physicists have been going down this route for decades without success.

 

[rbj]

I agree the weak anthropic principle is undeniably true - the universe cannot possesses properties that forbid the existence of observers [i.e., us]. But, that does not explain why the measured properties of the universe possesses the values they do. To wave it off as a statistical fluke in an infinite sea of alternative universes with different properties is just a little too convenient, IMO.

Why is it too convenient?

perhaps because there is about as much evidence of the existence of these other universes as there is evidence of a transcendent God or of a flying spaghetti monster. no physical experiment is going to make a God-detecting device nor one that detects other universes.

fine-tuning of the universe begs the teleological question and I'm afraid that explaining it away with other universes that may or may not exist is just making a faith statement.

In my mind, there are only four fundamental forces in the universe and all of existence is and was determined by these four forces.

there were forces and there was stuff. just having laws of interaction doesn't mean you have stuff to interact.

Presumably they were all combined as a single force in the beginning.

some hope of that.

but i think there needed to be more than just the forces (or the big unified force), there had to be the physical quantities of stuff for the forces to act on. unless, i guess it all gets to pop into existence as a mondo "quantum fluctuation" which some might describe the big bang as. perhaps that's the reason that there is something rather than nothing.

i dunno.

 

[Chronos]

The current idea of 'stuff' is that it was produced as a consequence of the big bang - i.e., a consequence of the initial, primordial energy state of the universe - thus, not fundamental.

 

[Chalnoth]

perhaps because there is about as much evidence of the existence of these other universes as there is evidence of a transcendent God or of a flying spaghetti monster.

That is completely and utterly false. The evidence for the existence of regions of space-time with different physical laws is the fact that spontaneous symmetry breaking resulted in the precise low-energy physical laws that we experience. We don't yet know how much spontaneous symmetry breaking played a part, but we know it did play a part. Quantum mechanics guarantees that all possible spontaneous symmetry breaking results occurred.

So the evidence for some level of multiverse with different physical laws is pretty significant, based upon what we know of quantum mechanics. We don't know just how much physical laws vary, or what the distribution is. But we know that there is some variation.

If you want to try to get around this, you have to make additional unevidenced assumptions (e.g. some unknown potential drove the symmetry breaking to be precisely the one we see).

A multiverse includes fewer assumptions, and because of this should be the default unless some strong evidence pushes us in another direction.

 

[rbj]

... there is about as much evidence of the existence of these other universes as there is evidence of a transcendent God or of a flying spaghetti monster.

That is completely and utterly false.

and that is a matter of opinion. your opinion. and i am sure that it is an opinion shared by others.

there were forces and there was stuff. just having laws of interaction doesn't mean you have stuff to interact.

The current idea of 'stuff' is that it was produced as a consequence of the big bang - i.e., a consequence of the initial, primordial energy state of the universe - thus, not fundamental.

well, the primordial energy of the universe at t=0 is not "stuff"?

 

[Chalnoth]

and that is a matter of opinion. your opinion. and i am sure that it is an opinion shared by others.

Hardly. There simply isn't any comparison. One is a solid conclusion based upon broadly-supported scientific theory (in this case the standard model of particle physics). The others are completely made-up with no connection to any scientific theory or evidence, or even any known way they could fit with current scientific theories.

 

[rbj]

Hardly. There simply isn't any comparison. One is a solid conclusion based upon broadly-supported scientific theory (in this case the standard model of particle physics).

multiverse is a conjecture. there is no evidence for it, nor is there evidence that precludes it.

The others are completely made-up with no connection to any scientific theory or evidence, or even any known way they could fit with current scientific theories.

never said there was a connection to any scientific theory. but there are those who have made such a connection, like Amit Goswami.

but, a safer philosophical ground to stand on is that science doesn't speak directly to the supernatural or non-materialistic notions, Gould's Non-overlapping magisteria. the theists have to admit that science does speak to the issue of the intersection of the supernatural with nature (these are sometimes called "miracles"). anyone who claims that some miraculous event they believe happened in reality is not disputed by science also has their head in the sand.

personally, i am more impressed by folks like John Polkinghorne or Freeman Dyson or Owen Gingerich than i am of Goswami. at least at present. Chalnoth, if you insist that your authority to the facts and the interpretation of the facts exceeds theirs, i just have to say, "sorry, it doesn't". (where is your wikipedia page?)

Chalnoth, i think that your error (just an error in my POV, it's very well if you don't see it as an error), is that you think that, in the sphere of philosophy, that the material and that physics trumps every other line of thinking and that's that. i consider it short-sighted (physics isn't everything), but i don't know everything. and because i don't know everything and i recognize it, i look at what other persons of recognized authority have to say, i try to learn from them, and i try to discern myself what to believe. just because they are a recognized authority doesn't mean that i take everything they say for granted. because you will find persons of credible authority on either side or of multiple sides with diametric or nearly diametrically opposite conclusions.

your simplistic categorization of the POV that is not your own is just that: simplistic. Dawkins makes the same mistake, so you have company.

 

[Chalnoth]

multiverse is a conjecture. there is no evidence for it, nor is there evidence that precludes it.

You keep saying that, but it just isn't true. As I've already pointed out, evidence for spontaneous symmetry breaking is evidence for a multiverse.

Chalnoth, if you insist that your authority to the facts and the interpretation of the facts exceeds theirs, i just have to say, "sorry, it doesn't". (where is your wikipedia page?)

I'm not insisting any authority on anything. I'm simply pointing out that a necessary conclusion of spontaneous symmetry breaking is a multiverse. Exactly how diverse that multiverse is we don't yet know. But it is quite clear that there is one.

Chalnoth, i think that your error (just an error in my POV, it's very well if you don't see it as an error), is that you think that, in the sphere of philosophy, that the material and that physics trumps every other line of thinking and that's that.

Uh, what? When it comes to questions like this, physics is the relevant field of study.

your simplistic categorization of the POV that is not your own is just that: simplistic.

Simple arguments are the best arguments. They are easier to analyze for fallacies and more difficult to brush aside when lacking said fallacies.

 

[rbj]

Chalnoth, i think that your error (just an error in my POV, it's very well if you don't see it as an error), is that you think that, in the sphere of philosophy, that the material and that physics trumps every other line of thinking and that's that.

Uh, what? When it comes to questions like this, physics is the relevant field of study.

just confirming what i said.

Simple arguments are the best arguments. They are easier to analyze for fallacies and more difficult to brush aside when lacking said fallacies.

"simplistic" is not the same as "simple". the latter might mean that there's some elegance or profundity in it.

 

[Chronos]

I think we are all on the same page here, guys, so let's play nice. I agree with Chalnoth to the extent there is theoretical support for the multiverse idea. I also question if it is possible to observationally confirm or reject. That provokes me to great cynicism.

 

[jimjohnson]

I wanted to add Brian Greene's perspective from The Hidden Reality. Quoting from pages 8/9: "So my point in writing this book is not to convince you that we're part of a multiverse. I'm not convinced- and, speaking generally, no one should be convinced - of anything not supported by hard data. That said, I find it both curious and compelling that numerous developments in physics, if followed sufficiently far, bump into some variation on the parallel-universe theme…. all of the parallel-universe proposals that we take seriously emerge unbidden from the mathematics of theories developed to explain conventional data and observations."

 

[Chalnoth]

I wanted to add Brian Greene's perspective from The Hidden Reality. Quoting from pages 8/9: "So my point in writing this book is not to convince you that we're part of a multiverse. I'm not convinced- and, speaking generally, no one should be convinced - of anything not supported by hard data. That said, I find it both curious and compelling that numerous developments in physics, if followed sufficiently far, bump into some variation on the parallel-universe theme…. all of the parallel-universe proposals that we take seriously emerge unbidden from the mathematics of theories developed to explain conventional data and observations."

Honestly, I think he's hedging way too much.

Given what we know of physics, what has been tested, a multiverse should be the default assumption because it requires fewer assumptions.

 

[rbj]

Honestly, I think he's hedging way too much.

and you have every right to think that.

Given what we know of physics, what has been tested,

so what properties or any physical manifestation of a universe other than the one we exist in has been tested? how did that experiment turn out?

i'll tell you about my God-measuring experiment after you settle that.

a multiverse should be the default assumption because it requires fewer assumptions.

"should" is a value judgment. you are welcome to have your own values, Noth.

what requires whatever assumptions is, again, a matter of opinion. and how to value and count the assumptions is, also, a matter of opinion.

Chalnoth, you just seem to not be able to understand that just because you believe something or believe in something that others might have very good reason to believe otherwise. you seem to insist that your sensibilities are the only sensible sensibilities; that everyone in the world should believe exactly as you do. ain't that a bit presumptuous?

i mean, if i read someone else insist that everyone else accept his or her faith-statement in what is not seen, nor measured, nor even possibly measured, i would call that person to task also. but you seem to think you are immune to that.

it might not be the case, but i would associate that with a hard-core fundamentalist of the faith of Materialism or Physicalism. you're certainly free to adhere to such a faith, but to insist that every thinking person, whether a scholar or not, adhere to the same is, to say the least, a bit pushy.

 

[julcab12]

You keep saying that, but it just isn't true. As I've already pointed out, evidence for spontaneous symmetry breaking is evidence for a multiverse.
.

I'll keep an open view on the matter. We have to be careful. I'm not keen to say that multiverse is the only interpretation for SSB. It's somewhat simple, slightly convincing notion. Simple in a sense that it is viewed directly as a possible outcome and often ignores some other basic possibilities not to mention the less unfounded nature of that idea. It 'can' be just a effect of radiative correction found in massless gauge theories were it can induce spontaneous symmetry breaking as a consequence of relationship between the masses of the scalar and vector mesons, predicting (for small coupling constants) that the scalar mesons are much lighter. (http://arxiv.org/abs/hep-th/0507214).

 

[julcab12]

Chalnoth, you just seem to not be able to understand that just because you believe something or believe in something that others might have very good reason to believe otherwise. you seem to insist that your sensibilities are the only sensible sensibilities; that everyone in the world should believe exactly as you do. ain't that a bit presumptuous?


it might not be the case, but i would associate that with a hard-core fundamentalist of the faith of Materialism or Physicalism. you're certainly free to adhere to such a faith, but to insist that every thinking person, whether a scholar or not, adhere to the same is, to say the least, a bit pushy.

Lets keep it clean guys. I believe point is already taken. No more rendundant 'god and spaghettis (I'm beginning to feel hungry). Needs attenuation and be more direct. hehe

 

[jimjohnson]

Honestly, I think he's hedging way too much.

Given what we know of physics, what has been tested, a multiverse should be the default assumption because it requires fewer assumptions.

Yes, Greene is definately hedging in the introduction; the purpose of the book is to describe 7 multverses each developed via different logic.

 

[Chalnoth]

so what properties or any physical manifestation of a universe other than the one we exist in has been tested? how did that experiment turn out?

How do you know humans descended from apes? You weren't there! Nobody has done an experiment showing an ape give birth to a human!

Arbitrary restrictions on what sorts of conclusions we can draw based upon evidence are fundamentally anti-science.

 

[Chalnoth]

I'll keep an open view on the matter. We have to be careful. I'm not keen to say that multiverse is the only interpretation for SSB. It's somewhat simple, slightly convincing notion. Simple in a sense that it is viewed directly as a possible outcome and often ignores some other basic possibilities not to mention the less unfounded nature of that idea. It 'can' be just a effect of radiative correction found in massless gauge theories were it can induce spontaneous symmetry breaking as a consequence of relationship between the masses of the scalar and vector mesons, predicting (for small coupling constants) that the scalar mesons are much lighter. (http://arxiv.org/abs/hep-th/0507214).

Well, right. For each symmetry breaking event it is possible that there was some interesting physical phenomenon that forced the symmetry breaking to happen in a very specific way. I wouldn't be horribly surprised if a few things, such as the electroweak symmetry breaking event, turned out to do this.

But I don't buy for an instant that this sort of thing can possibly explain how we go from E8xE8 down to SU(3)xSU(2)xU(1), for instance (or whatever the fundamental symmetry group happens to be).

 

[rbj]

How do you know humans descended from apes? You weren't there! Nobody has done an experiment showing an ape give birth to a human!

not answering the question.

Noth, even when the theory is there, and even when the theory makes sense, when there are holes in the evidence, you have to be prepared for surprizes. like Homo floresiensis.

you're problem is, again, that you're so enamored by a theory, versions of which are quite elegant (i think the string landscape theory of other universes is pretty elegant), that you are confusing that with evidence. i like elegance, too, but Nature doesn't necessarily give a rat's @ss about elegance.

Arbitrary restrictions on what sorts of conclusions we can draw based upon evidence are fundamentally anti-science.

that's called "strawman".

so what would have happened to special relativity if experiments like the Rossi-Hall (muon decay time is dilated) or the many that followed had turned out differently? or what would have happened to GR if Eddington's trip to measure the perihelion precession of Mercury (or the many subsequent experiments or observations supporting GR) turned out differently?

you know as well as anyone else what the meaning of "falsifiable" is and we're waiting patiently for you to describe a falsifiable physical experiment that would turn out one way if another universe exists and would turn out another way if no other universe exists.

 

[Chalnoth]

you know as well as anyone else what the meaning of "falsifiable" is

So, you think reality will just play nice and only present itself so that every single aspect of it will be neatly-falsifiable in a trivial manner?

 

[rbj]

So, you think reality will just play nice and only present itself so that every single aspect of it will be neatly-falsifiable in a trivial manner?

never said anything of the sort. so i am at a loss to why you would conclude that i think that.

please stop propping up strawmen and just answer the question posed to you.

 

[julcab12]

Well, right. For each symmetry breaking event it is possible that there was some interesting physical phenomenon that forced the symmetry breaking to happen in a very specific way.
.

We can handle that. Its not even clear whether the product of such breaking can fully constitute to a whole new set of physical laws moreover an entire zoo of universes. When a quantum particle becomes larger, the symmetry of the system as a whole becomes more unstable against small perturbations signaled by a set of noncommuting limits. It led to the particles with nonzero masses remains symmetrical but appears to be/'could be' hidden by default observation. Besides, it is pointing towards a form of indirect mechanism that hides EWSB. And one thing is certain. The specific mechanism that hides EWSB remains an open question but they have reasons to believe that a positive suspect is 'much' closer to home^^.

 

[Chalnoth]

We can handle that. Its not even clear whether the product of such breaking can fully constitute to a whole new set of physical laws moreover an entire zoo of universes.

It depends upon what you mean by, "a whole new set of physical laws." There's not really any question that having the electroweak symmetry breaking event occur somewhat differently would have impact on the properties of the weak force, and maybe also the electromagnetic force. This would likely result in different particles having different masses, and various reactions having rather different cross sections or decay times.

But that's only the tip of the iceberg: there were also symmetry breaking events earlier that transformed from a higher-order symmetry down to the standard model. We don't know what those were yet, but those may also have resulted in significant differences. I think it will be interesting to see where high energy physics goes in the next few decades, to see if we make any significant progress towards uncovering this part of the mystery.

All that said, yes, quantum mechanics guarantees that every possible result of a symmetry breaking event occurs. And even if you have trouble buying that, all you need is a universe that is larger than the typical size of a domain with a typical value of the broken symmetry, and that is trivially easy to produce in most inflation models, and perhaps even easier given that the original event that started inflation is highly unlikely to be a unique, one-off event.

 

[Chalnoth]

never said anything of the sort. so i am at a loss to why you would conclude that i think that.

please stop propping up strawmen and just answer the question posed to you.

My point is that you're making up legalistic restrictions on what sorts of things we should and should not conclude, but perhaps even worse you're jumping to the conclusion (without even bothering to argue the point) that the default assumption should be a unique universe.

But that's nonsensical: a unique universe requires more assumptions than a prolific one. Even if we knew nothing at all about physical law, but just knew a little bit about how math behaves, the default assumption should clearly be a prolific universe. To take a simple example, consider the following two situations:

1. The set of all integers with addition, negation, and multiplication operations defined. The set of all integers is closed under these operations.
2. A set of the integers from [0,5], with addition, negation, and multiplication operations defined, with the set of integers [0,5] closed under these operations.

Which of the two above requires fewer assumptions? Clearly the second: it requires all of the rules of the first set, but it also requires additional rules to determine how to deal with the fact that it only includes six numbers.

 

[rbj]

... you're jumping to the conclusion (without even bothering to argue the point) that the default assumption should be a unique universe.

citation, please.

My point is that you're making up legalistic restrictions on what sorts of things we should and should not conclude

i am making the same requirement about what it means for something to be "science" that Woit and Smolin and these guys that are fond of the phrase "Not even wrong". I'm not a big fan of Wikipedia, but i'll quote it :

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

The scientific method requires observations of nature to formulate and test hypotheses.[1] It consists of these steps:[2][3]

1. Asking a question about a natural phenomenon
2. Making observations of the phenomenon
3. Hypothesizing an explanation for the phenomenon
4. Predicting a logical consequence of the hypothesis
5. Testing the hypothesis by an experiment, an observational study, or a field study
6. Creating a conclusion with data gathered in the experiment

Observation plays a role in the second and fifth steps of the Scientific Method. ...

how do you plan to deal with step 5? or are you saying that at least one of these multiverse theories is immune to that requirement? that somehow your scientific theory need not be subject to falsifiable empirical testing? if it does not ever subject itself to such, then what difference does it make? (and my question is how long does it retain the status of "science"? Smolin and Woit would say the same thing about string theory, which is also nice and elegant, on paper.)

But that's nonsensical: a unique universe requires more assumptions than a prolific one.

not for theists. i don't even know that this claim is true for materialists or physicalists, and i suspect there are even those who disagree with you.

Even if we knew nothing at all about physical law, but just knew a little bit about how math behaves, the default assumption should clearly be a prolific universe.

the issue is not whether or not we know nothing about the physical law, but whether or not we know everything about it (and we don't, of course). you don't know what will be discovered or derived by our descendants 400 years into the future. but you are writing as if you do.

To take a simple example, consider the following two situations:

1. The set of all integers with addition, negation, and multiplication operations defined. The set of all integers is closed under these operations.
2. A set of the integers from [0,5], with addition, negation, and multiplication operations defined, with the set of integers [0,5] closed under these operations.

the reality regarding other universes does not give a rat's patootie about it.

Which of the two above requires fewer assumptions? Clearly the second:

i think you meant the first. but the greater reality (about the multiverse or lack thereof) still is unaffected by the argument.

 

[julcab12]

It depends upon what you mean by, "a whole new set of physical laws."

I'm referring to SSB resulting to different physical constant.

quantum mechanics guarantees that every possible result of a symmetry breaking event occurs. And even if you have trouble buying that, all you need is a universe that is larger than the typical size of a domain with a typical value of the broken symmetry, and that is trivially easy to produce in most inflation models, and perhaps even easier given that the original event that started inflation is highly unlikely to be a unique, one-off event.

Well .I don't have any problem with explicit or spontaneous symmetry breaking occurring because it did happen in nature. Some scientists can 'agree' on the multiverse theory, they can't always agree on how the multiverse actually works. I also see possibilities on mutiverse as a clear/direct consequence (The best we could think of or/ the only thing we could postulate for now) but i'll remain skeptic of multiverse until sufficient evidence is presented. The multiverse scenario right now is problematic. It can neither be verified nor falsified as per standard. Given our current universe as basis. No form of selection process can be invoked. Maintaining a plausible hypothesis, a universe generating mechanism is needed. In conclusion, without a scientifically rigorous means by which a multiverse (not SB)can exist. The concept remains a conjecture and less satisfactory. On the other hand it is 'exciting'. They've taken a great deal of speculation in attaining an answer to fine tuning but i do hope they'll find something more cohesive Or it is!? We don't know..

 

[Chronos]

I feel constrained by observational evidence - which does not yet favor the multiverse conjecture. Until that changes, I remain skeptical.

 

[Chalnoth]

citation, please.

You don't see how continually demanding to see evidence for a multiverse is, by default, assuming a unique universe?

I demand you present evidence that a unique universe is the preferred conclusion.

 

[Chalnoth]

I feel constrained by observational evidence - which does not yet favor the multiverse conjecture. Until that changes, I remain skeptical.

Why be more skeptical about a multiverse than a unique universe?

 

[rbj]

... you're jumping to the conclusion (without even bothering to argue the point) that the default assumption should be a unique universe.

citation, please.

You don't see how continually demanding to see evidence for a multiverse is, by default, assuming a unique universe?

i don't see that. it is, in fact, not the case. i do not assume a single universe and i also do not assume there are other universes out there. and settling that question (which cannot be settled for mortals) does not affect my worldview. i don't require a single universe to support my worldview, nor do i require multiple universes. i guess i cannot wrap my head around it if the number of universes is not a real integer greater than zero, unless the reality we apparently live in is really a simulation in a universeless existence (but i don't give that any credibility).

I demand you present evidence that a unique universe is the preferred conclusion.

well, i cannot. nor do i say it's the preferred conclusion.

i will say this: the universe we're in is pretty big and quite old. and we can see it pretty deeply (e.g. Hubble deep space). it could be all that there is (and there is no evidence and no hope for evidence that it's not all that there is, materially), and if that is the case, the teleological question regarding fine tuning remains. anthropic reasoning and selection bias does not cut the mustard in explaining fine tuning of a single universe from a solely materialist POV.

if the universe is one of many (some have speculated as many as 10^{10^{10000}}), just having math that is compatible with such an existence does not, in itself, make for a mechanism for the generation of all these universes. physical law is not "stuff", but it governs the stuff that exists or emerged into existence. all adding the multiverse concept does is add another layer of turtles. from a material POV, it's still "turtles all the way down". just another step in this problem of infinite regress.

perhaps there is a multi-multiverse. that the multiverse we live in is just one of many multiverses. maybe it's even another layer deeper than that. perhaps our multiverse that has some reasonable set of common physical law (but different parameters for the different universes) is one of many multiverses where the other multiverses have a reality of magic, wizards, and pink unicorns. we don't know.

you might object and say that such a reality is ridiculous, and i might agree. but if, in order to avoid (in your mind) the teleological question, you construct the necessity of a gazillion other universes, just to answer the question for how is it that our universe seems so finely-tuned (both in fundamental constants and in initial conditions) for the existence of matter, astronomical structures, elemental diversity, or life as we understand it, and yet criticize theists as being silly for suggesting that maybe it's the consequence of design, i think that open-minded philosophers would be quite dubious of your position.

but there are both open-minded and close-minded philosophers. just as there are open-minded and close-minded comologists, physicists, electrical engineers, musicians, and parents.

 

[Chalnoth]

i don't see that. it is, in fact, not the case. i do not assume a single universe and i also do not assume there are other universes out there.

You say that, and yet you continually demand that people present evidence for one (and only one) of those options. Furthermore, you won't listen to evidence that isn't of your specific desired type.

Why do you act as if you have already assumed there is only one universe if you don't believe it?