The Conversation has published an article of mine, co-authored with Geraint Lewis, titled “Have cosmologists lost their minds in the multiverse?“. It’s a quick introduction to the multiverse in light of the recent BICEP2 results. Comments welcome!
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Hi Luke. Great article! Have you seen Sean Carroll’s blog post and paper? I’d be very interested in your views on this “reality of fluctuations ” question. In particular, I suspect that Carroll is right but – as I commented there (in agreement with a comment by Andy Charman) – wrong to give exclusive or priority credit to the psi-ontic MWI for the insight.
Overall a very good article, but there are a few points I would have added.
The inflationary multiverse is not a reality if (1) inflation did not happen and (2) inflation doesn’t lead to a multiverse.
BICEP 2 makes 1 more likely if confirmed but does not affect 2.
Before talking about (2) I do think one needs to stress the importance of confirmation , BICEP’s results are in slight conflict with Planck’s but Planck hasn’t released its polarisation data yet, when it does so we will get a very good picture of whether or not BICEP results are real. I’ve spoken to people on Planck and they told me they would have the data around June when I saw them at the beginning of this year when I saw other Planck people before Easter they said November. This data will be key. There are other ground and balloon experiments as well.
Even if B modes are confirmed there is more to learn from the data that can make us more or less confident that inflation in particular: what is the tilt of the gravity waves spectrum? There are non inflationary theories that predict gravity waves but a blue tilted spectrum,inflation predicts red tilt. So this discovery if confirmed can rule out some rivals to inflation (the ekpyrotic springs to mind) but not all.
On the issue of 2, according to Guth inflation is not a theory but a class of theories but virtually all the have the generic property of being eternal http://arxiv.org/abs/hep-th/0702178
This includes chaotic inflation but is not limited to it.
So the probability of there being a multiverse on the back of that and if some form of inflation is confirmed seems higher than many people I think are led to believe.
I would also point out the famous quote of Comte:
“On the subject of stars, all investigations which are not ultimately reducible to simple visual observations are…necessarily denied to us… We shall never be able by any means to study their chemical composition.”
Writing in a time before spectroscopy this may have seemed like a very reasonable statement. But human ingenuity is an impressive thing. I recall everyone saying a multiverse was impossible to detect even in principle then people found it was not impossible. That there’s a chance we could have a bubble collision and that may have led to an imprint in the CMB. So far no such signal has been confirmed but alas that doesn’t falsify the multiverse, it was a long shot to begin with. But I think the lesson is don’t be too quick to say something is unobservable. If our universe was born of a process that generated others we may be able to find a signal of it.
I am not convinced there is enough data to make a reasonable calculation about the probability of a boltzman brain forming in a multiverse rather than a universe like ours forming. We know a brain is an unimaginably unlikely thing to spring into existence through a fluctuation because we understand the process by which some event like that might happen and what chance does it have to survive in the vacuum of space? I’m not convinced we have a similar understanding of how constants of nature are chosen as a universe forms. Perhaps it’s a random process, but perhaps not. Perhaps they are both infinite and hence comparing the probability of the two simply depends upon a measure.
Again that stupid argument of Collins 😦
How can’t one see that even if Boltzmann brains are scattered throughout multiverse then it is still possible that per unit of volume there is more “biological” brains than “Boltzmann” ones…..
If the probability of BB (Boltzmann brain) popping up is small enough then it may be that only a single BB exists per huge number of universes at specific point of time. If the probability is small enough then this number of universes may be big enough to be likely to host at least one life permitting universe which itself can host billions to gazillions “biological” brains.. Therefore it may be still so that per number of “typical” universes in multiverse ( or per unit of “volume” of multiverse) there is much more biological brains than Boltzman ones. This in turn assures that a single brain is more likely to be biological brain than Boltzmannn one……And, if so our being biological brains is to be expected given multiverse existence so it can not be argument against this existence…..
Collins argument can only work under scientific premise that the probability of single BB per unit of spacetime is bigger than the probability of single “biological brain” in the same unit. This premise must be true for conclusion to be established. Unless this premise is warranted by some scientific inquiry (and I doubt it have been warranted yet or can be warranted in near future) the argument is not conclusive.
But here lies the real puzzle – Luke how can it be you do not see it? And if you do, why are you putting this shaky argument in scientific paper? And if you have a reply for my objection why it is not in the article -I’ve found nothing in Collin’s book which would allow this argument to stand and as I said I doubt it can be done (How can you calculate the probability of the BB or life permitting universe -we seem to have insufficient data to calculate these probabilities).
“Collins argument can only work under scientific premise that the probability of single BB per unit of spacetime is bigger than the probability of single “biological brain” in the same unit.”
Hence why I said “[freaks] could be common in the almost unending time and space of the entire multiverse.” Could, not would.
“shaky argument in scientific paper” – it’s not a scientific paper. Its an op-ed.
Calculations of what a typical multiverse observer would observe are common in the scientific literature. E.g.
– Tegmark et al 2006, figure 9 http://journals.aps.org/prd/pdf/10.1103/PhysRevD.73.023505
– Bousso and Leichenauer, 2010 http://adsabs.harvard.edu/abs/2010PhRvD..81f3524B
– and many more.
The point that Boltzmann brains can rule out multiverses is not original to Collins. It was first deployed, as far as I can tell, by Eddington in response to Boltzmann’s multiverse – the universe as a whole is in equilibrium and we are in a statistically improbable low entropy fluctuation. The premise is warranted in that case by entropy considerations, i.e. by comparing the entropy of the entire observable universe to that of a single Boltzmann brain. Penrose has applied exactly the same argument to inflationary multiverses, with similar results. Cosmologists are well aware of the Boltzmann brain problem: http://arxiv.org/pdf/1308.4686v1.pdf , http://arxiv.org/pdf/hep-th/0405270v2.pdf.
It is justified more generally by fine-tuning itself. The more fine-tuned biological life is, the more likely it is that an observer in the multiverse will be a freak rather than a biological life form.
“I’ve found nothing in Collin’s book”. He hasn’t written a book on fine-tuning. Collins’ argument is here: http://home.messiah.edu/~rcollins/Fine-tuning/Modern%20Cosmology%20in%20Philosophical%20and%20Theological%20Perspective.pdf
The whole point of my article is that such considerations are ways of testing multiverses. I didn’t say that they definitively rule out all multiverses. I explicitly said that “there is much much more to be done.”
All right, maybe I’ve overreacted, but I. m still suspicious, so I’ll explain
My doubt concerns the very comparison of BB to “bigger” chunks of matter like star, galaxy of universe. The arguments presented by the articles you posted assume that BB is more likely because it is “smaller” than star or universe.Hence more of entropy and bigger probability. The thing is that the particles of brain must be arranged in much more definite way than that of star.
Consider the spontaneous creations of star by gazilions of particles appearing randomly in space -all they have to do is to appear in some region of space -after that gravity and fusion will do the rest by binding that hydrogen into sphere and igniting them (I know there may be scientific inaccuracies in this picture but the priniple should be correct)
With the brain situation is different. Because particles ( in less quantity of course) must not only appear here in one place but they have to accidentally arange thmselves into microstrctures. : neurons, glial cellls, specific proteins arranged that so that contain all your knowledge memories etc and so on..
Therefore in case of BB less matter is to be arranged, but in a much more definite way….
Now, of course I doubt you are unfamiliar with this but my suspicion is that Collins neglects that issue On page 5 of the article you linked he seems to compare BB vs universe to monkey’s writing single meaningful world to monkey writing “Hamlet”
My point is is that the analogy is inaccurate is more like monkey writing a Bible vs big cosmic demiurge Hamster making a dot on giant cosmic piece of paper. The latter is is much bigger than the former but much les “sophisticated” in his action , nervous system and also much more likely to produce the result (Hamster will never write a single word but dot it can made :D)
It is of course possible that I am wrong but Collins arguments seem to assume “-word-Hamlet” analogy whereas they should operate on “small bible-big dot” analogy and this make them shaky in my opinion.
But my chief interest are considerations of respected physicists. Do the think like Collins or is there more?
Therefore two Questions to you Luke:
1. How exactly can you tell that Entropy of a universe with single BB and random interstellar gas (or whatever) is bigger than our universe? How it is calculated?
2. IF this entropy is in fact bigger, doesi t really enables us to predict the higher probability of BB? How would you answer to my “small bible- big dot ” analogy?
Regards
Clarification: If i’ve not put it clearly -above I ‘ve tried to argue that BB is less probable than a star because it is arranged in more definite way requiring its particles to be in more definite relations to each other which decreases probability of such a spontaneous arrangemnt even if BB has les particles than the star….or universe…
Hey, are you going to weigh in on the Boltzmann Brain debate between Carroll and Craig? Craig recently posted a Q an A defending it.
@Ceres
I allow myself to assume that you asked me (not Luke) to weigh on Craig. Therefore I ‘ll do it. First of all, apologies for any mistakes in spelling and grammar and/or syntax –I’m not a native speaker. Also I apologise for vitriol and some prejudices – I may not know the whole philosophy of WLC –nevertheless –after reading his cosmological arguments I consider him a charlatan. This is however the matter for different debate. (parts of why I think so can be found in my response to Luke’s post in Carroll vs Craig(4) here on LtN). However here I’ll do my best to be honest in judgment, even so I think his theses are bollocks..(or at least they seem so to me)
I’ve read the WLC posts concerning Boltzmann brains problem and it seems to me that the whole case is based on SINGLE argument. If i’m wrong, feel free to criticise me. However, assuming this, my job amounts to reconstructing this single argument and criticising it. What the WLC does in his posts is merely complaining that Carroll is not responding to his argument.
So what is the WLC ‘s argument? It can be summarized like this If there is multiverse, there are many ( possibly infinite number of) universes in it. Now , because of random distribution, some of these universes are “chaotic” or better “random” (which seems to prohibit) life. Others (a minority as the order is less probable then the random arrangement) are ordered. They seem to be universes however, that are partially ordered – a fragment of it is ordered the rest is not. The degree of ordering makes the universe less probable –the more ordered universe –the less probable it is. And less probable universes are less common. Thus the Universe where only Solar System is “ordered” ( spherical bodies dance along each other 😀 ) is much more likely and common in multiverse than universes which is ordered as a whole like us. And universe in which there is almost only a single brain that floates in nebula’s for a short time is even more likely and common –much more actually(tens of orders or magnitude). From this it is inferred that universes like ours are small minority in MV (multiverse) And because the difference is in orders of magnitude the majority of sentient brains in presumed to be “brains in space” i. E. Boltzmann brains (BB). Now this conclusion is used in the following reductio ad absurdum. If multiverse spawns more BB than biological brains (biB) we should expects us to be BBs instead biBs which is not the case. Therefore multiverse theory must be false cause it gives us wrong predictions about the world. QED.
What are the problems with this argument.
First of all, simple question arises : why the arrangement of Solar System is considered random? After all it is a result of laws of physics, I presume,at least to certain extent. WLC would probably respond that the laws themselves are part of order of universe are result of random distribution among universes and subjected to probability laws. But this reveals his important assumption: he seems to be some kind of nominalist regarding laws of physics: it is like he believes only some particles exists and their arrangement is either accidental or ruled by absolute..Laws are merely descriptions of facts found in minority of well ordered universes where most-all of facts seem to be uniform or description of events which are uniform due to supernatural command. If in our universe 10^80 of protons seem to obey Einstein equations it is merely either the big fucking stroke of luck or result of god’s will. The former leads to paradox specified above so the latter must be true.
Unfortunately they may be other options, laws for example may be held to be universals or some consequences of thereof (as David Mallet Armstrong , native of Luke’s suggested). The point is that WLC assumes Humean account of laws of physics, like many/most naturalists do. But they are non-humean accounts, and NO they are no antinaturalist. Armstrong seemed to believed that his account was naturalistic if I understand him correctly.
Why this matters?
Because if Armstrong is right we have much less to arrange than Craig presumes. We do not need “arrange” all 10^80 nucleons or so :D…We may need to arrange universals of types of particles of Standard Model, maybe also some constants (if they can be understood as having corresponding universals. But this leaves us with dozens or hundreds of SEPARATE beings to arrange NOT some freaky number like 10^80 or so) And if arrangement produces order and life it does it among the whole universe. One may conceive other universe to have different universals and -respectively –different constants. But if in our universe one electron has certain spin of charge –others have it too..
This greatly changes the situation. If those dozens or hundreds beings are arranged the beginning of life in universe may be even a necessity. On the other head spontaneous creation of BB in life permitting and especially life-prohibiting universes may much less probable, because creation of brain without necessary enviroment still requires accidental arrangement of some particles which generates low probability of this fact. There are much more neurons in brain then there are constants and types of particles. If so , it is possible that the probability of single BB per “volume” of multiverse is smaller than probability biB in such “volume”. Which solves our problem without resorting to supernatural ,as universals are naturalistic.
Of course do not provide arguments in favour of Armstrong’s theory, I only present it. I do not have. It’s WLC that makes the case and onus probandi is on him. He is obliged to close the loophole that Armstrong’s hypothesis creates to proceed…
However there is more….Even if Humean account of laws of physics (merely descriptions) is true…still we can doubt WLC
2. Second objection can be stated as follows: WLC assumes that laws or physics must be explained somehow. Either by MV or absolute. Laws constitute order of universe which is nothing more that nonrandom and intelligible distribution of matter. If it were not for some reason ( absolute or MV) the distribution of matter would be random ,as we can presume reading his argument.
But why “random” means “not arranged” ?
Random distribution assumes conformity with probability theory ,which has ITS OWN LAWS that “govern” reality as much as physical laws. If physical laws require explanations why not probability laws?
But there is problem: any distribution of matter in space and probably any physical process is either random or follows some pattern (and is thus governed by some laws). But if randomness is lso some kind of “pattern” then there is really no difference. Any distribution of matter is thus ruled by some laws. Hence existence of SOME (but non-specific) physical laws is a LOGICAL necessity. This invalidate the question: “who created laws of physics?” as meaningless. Tautology does not require explanation and justification.
This affects the whole Craig’s case which Boltzmann’s brain argument is a part. However it specifically raises doubt as to why we should assume that distribution of matter in it is probabilistic. There is no reason to assume it should have. Such a distribution is no more “obvious”, “spontaneous” than the alternative. Hence the basis of WLC conclusion is no more arbitrary than Carrol’s. And WLC errs if he thinks that Carrol is obliged to explain why he assumes different probabilities than WLC.
3. But there is one more thing. Even granting that random distribution is “prima facie plausible” given naturalism, one can still infer laws of physics from principle of conservation of mass/energy and mass energy convertibility and the former may be understood as instantiation of. “ex nihilo nihil fit”. In short. If nothing cannot come from nothing , matter is particulate and can be converted to energy and vice versa then the ratio of conversion has to be constant. Why? Because in other case there would be possible for us to change x nucleons into energy and then use this energy to make x+1 nucleons which would amount to creating one nucleon from nothing, which may be deemed to impossible. However similar ratios of conversion must apply not only to matter/ energy conversions but also to various types of energy conversions (heat to kinetic etc). But these constant ratios constitute most if not all laws or physics as physics as physical processes are probably transformations of one form of matter and energy into other (at least majority of them seems so).
Why this is important? If this is true ,then in given universe, laws should be constant throughout it NOT BY VIRTUE of universals or god but by virtue of principle of energy conservation. Of course there is a problem with different universes having different sets of laws but the point is that contrary to WLC it ‘s not the order and uniformity that begs the question –rather the opposite of it….IN EVERY universe that obeys principle of conservation of energy we should expect existence of laws or physics and of order. And such an order should be uniform throughout it thus freeing us from necessity to “arrange” every possible nucleon independently. (just as in case of Armstrong’s theory) And even if principle of causation is violated it is enough that it would not be likely for us to see violation to ensure we perceive the order. This solution again makes the life permitting universe possible more likely than BB’s.
Ending note: Wiki says that David Mallet Armstrong about whom I’ve wrote died today. May he be remembered for his achievements.
@trollmonster
I meant Luke actually. 😦 Sorry.
As to (1) and (2) I honestly don’t see much relation between what Luke and Craig have said about Boltzmann Brains arising from quantum fluctuations and what you said.
(3) Are you saying all the laws of nature can be derived from conserveration of energy? This seems false. Can’t there be other universes with different constants and laws consistent with energy conservation.
@Ceres Ok I ‘ll abandon discussion then
however clarification
in (3) I have not said that conservation of energy entails SPECIFIC SET of LAWS. I said it entails SOME SET OF LAWS :D…Universe with conservation of energy different sets of laws are possible but the point is that it can not be “lawless” i.e. there must be some order there….And given my analysis of WLC it is enough…..because it suggest that every universe with CoE is ordered “as a whole”. As a result any ciological brain will experience universe ordered as a whole….
As for (1) and (2) it is an answer to my reading of WLC I presented in the beginning. Is this reading bad? Why? If not (1) and (2) should apply to it…..