The multiverse as a scientific concept — part II

multiverseby Coel Hellier

[The first part of this essay can be found here.]

Inflation

The comparison of cosmological models with high-quality and detailed observations of the early universe has led to the “inflationary” version of the Big Bang. This hypothesizes that, very early in the first second after the initial quantum fluctuation, only about 10-35 seconds later, our universe started an episode of exceptionally rapid exponential expansion, growing by a huge factor of about 1030 in only a tiny fraction of a second. This “inflation” was proposed in order to explain several otherwise puzzling features of the universe, including: (1) the similarity of the universe in opposite directions in the sky; (2) the exceptional smoothness of the cosmic microwave background (CMB); (3) the fact that the universe appears to have a very close balance between the total amount of matter and energy and the expansion rate, thus giving space a near-zero “curvature” on the largest scales; and (4) the absence of heavy particles such as magnetic monopoles that would otherwise be expected to be seen.

Thus inflation is motivated by strong empirical evidence [7]. Further, after inflation had been proposed, it was used to predict the spectrum of fluctuations expected in the CMB. These temperature fluctuations originate as quantum fluctuations in the inflating field, later to be frozen into the CMB, and the inflationary model gives specific predictions of their form and power spectrum. These predictions have now been compared to the better-and-better data from the WMAP and Planck satellites, and several ground-based experiments, and the result is again an exceptional agreement, giving strong support for inflation.

Further still, the inflationary model makes specific predictions about gravitational waves generated by the rapid inflationary episode. Recently the BICEP2 experiment has reported detecting these gravitational waves, imprinted on the CMB just as predicted, which would be an additional strong confirmation of inflation. These results are new and need confirming, but at a minimum they show that the inflationary model can be directly tested. Thus the inflationary Big Bang model is robust, mainstream cosmology. The mechanism driving inflation is, however, less understood.

Modern physics explains all known interactions in terms of four forces (gravity, electromagnetism, and the strong and weak nuclear forces), and at the exceptionally high temperatures in the very early Big Bang all four forces are expected to have existed in a “symmetric” state where they all acted similarly. As the universe expanded and cooled the symmetry was broken and the four forces developed the different characteristics that we see today. This process would have been analogous to the “phase transition” from a liquid (hot) state to a crystalline (cold) state. Such a phase transition has a “latent heat of crystallization” given out during the transition. It is, though, possible for material to get stuck in a “supercooled” state where it hasn’t yet made the transition, and thus has extra energy than expected for its temperature. It is this energy — thought to be associated with the phase transition that breaks up the strong and electroweak forces — that is thought to drive the ultra-rapid expansion of the inflationary era.

The tricky bit of inflationary models is then getting the universe to drop out of the “supercooled” inflationary state (rather than being stuck in that state forever), and thus give its energy into the hot Big Bang that then produces our universe. In order to get such models to work theorists have developed a scenario in which a quantum fluctuation can cause a limited region to drop out of the inflationary state, forming an expanding bubble of normal-state universe.

Thus, overall, we have our universe originating as a quantum fluctuation in the quantum-gravity era, at a scale of 10-43 seconds, leading to the exponentially expanding inflationary-state, followed by quantum fluctuations within the inflationary state, at a scale of 10-35 seconds, leading to bubbles of normal-state universe. However, in such a scenario, the inflationary-state stuff surrounding the bubble will be expanding vastly faster than the normal-state bubble, and thus the size of the inflationary-state regions continue to increase, even as bubbles continually drop out into the normal state.

The result is called “eternal inflation,” a “Swiss cheese” mixture in which bubbles of normal universe are continually forming out of a surrounding and exponentially expanding inflationary state. One of those bubbles would be our universe, and that bubble would now have expanded to vastly larger than our observable horizon. Thus, the only things we can now see are in our bubble, our normal-state universe.

This is a multiverse scenario. It says that somewhere beyond our observable horizon there is a transition, beyond which is supercooled, inflationary-state stuff. And in that rapidly expanding vastness are other bubbles, other universes, like ours, but now separated from us by unfathomable distances. If you don’t like the idea of a multiverse extending vastly beyond our observable horizon, or consider it to be unscientific, then realize that conventional cosmological models extend to infinity in much the same way. The stuff beyond our observable horizon is real, it is just a long distance away. There is no reason to declare such stuff not “real” just because of the finite value of the speed of light, which means that we humans can never receive information from those regions (especially since the location of that observable horizon depends entirely on where you are looking from, and it also continually recedes as you look at it).

The only sensible alternative to this multiverse idea is that our universe extends vastly beyond our observable horizon (to infinity?) and is normal-state all the way. Is that really preferable? If you do prefer normal-state all the way, then you have a problem in constructing an inflationary model that correctly makes the transition from the inflationary state to a normal state everywhere, especially given that any “transition front” would have a speed limited by c.

As it is, we have strong observational and theoretical arguments that lead us to an eternal-inflation model of the Big Bang, and that eternal-inflation produces a multiverse. It is currently rather difficult to produce a model of the Big Bang that works, and that explains the observations, and which does not automatically produce a multiverse. Admittedly we cannot observe those other universes, the other normal-state bubbles continually forming in the inflationary-state multiverse, but good, sensible and scientific reasons lead us to conclude that they likely exist. And, as stated early on, it is not necessary to empirically validate every prediction of a theory in order to have good confidence in that theory. To accept a theory and its implications all one needs is to have validated some of the predictions of the theory, and to have established that overall the theory does a better job than any alternative that we know of. As a comparison, no-one disputes the validity and scientific status of laws of gravity, that do an excellent job of predicting the times of future solar eclipses, just because we cannot verify those eclipse timings indefinitely into the future; and similarly it is not grounds to reject a model as unscientific just because we cannot verify its predictions indefinitely into the far distance.

Are the “physical constants” constant?

Now let’s ask a further question. Are those other bubble-universes in the multiverse just like ours? In what ways might they be different? How much scope is there for the bubbles to differ?

Above I used the analogy of a bubble dropping out of the inflationary state being akin to a liquid freezing. Consider a snowflake freezing in a high-up cloud. The freezing of each snowflake complies with the same underlying laws of physics, and yet each snowflake is different, with a related but distinct pattern. This tells us that some aspects of what we see are local “accidents,” variations allowed by the underlying laws but contingent on local circumstance.

The transition from inflationary state to normal state is thought to be due to the fundamental forces changing from a “symmetric” state, where they acted similarly, to a broken-symmetry state where they have different strengths. Further, physical “constants” such as the masses of particles and the values of electromagnetic charges are much the same thing as the strengths of the forces, since essentially they are all telling us how particles interact with each other. Thus we can ask whether the values of the masses and charges of particles and the strengths of forces are dictated by the fundamental physical laws, or whether they are local accidents, dependent on the local contingency of symmetry breaking early on in the Big Bang.

We don’t know the answer to that, but if it is the latter then we would expect each bubble universe to be different in the same way that each snowflake is different, and thus to have different physical constants. Note that — somewhat counter-intuitively — the latter suggestion is more parsimonious. The correct interpretation of Occam’s razor is in terms of the information content needed to specify a model [8]. If you have to explicitly specify the couple-of-dozen fundamental constants of the standard model of particle physics, that takes a lot of information. It takes less information to say that values for the constants are strewn around at random. After all, no-one claims that every snowflake having a different pattern is unlikely under Occam’s razor, since everyone accepts that the individual patterns are accidents, variations allowed by deeper-level rules.

As for falsifiability, it would be unscientific to add information to a model that had no observational motivation or consequences, and thus was unfalsifiable. However, if we are simply extrapolating from an observationally motivated model, or even reducing the information content of our model, while ensuring that the remaining information is observationally motivated, then that is scientific, even if not all of the implications of the model can be tested.

Considering this idea one quickly arrives at the obvious point that we human observers could only find ourselves in a bubble that had parameters suitable to have produced us, and it may be that the vast majority of such bubbles would be too alien to support or produce us. This is an entirely normal way of thinking. No-one nowadays supposes that there is some mechanism that ensures that an Earth-size planet gets placed in an orbit at the right distance from its star to allow it to have liquid water; we now know that extra-solar planets have a huge variety of orbits. We, of course, find ourselves on a planet suitable for us, but likely there are vast numbers of similar but uninhabited planets where the conditions are not right for life.

Similarly, no-one since Darwin would argue that we find polar bears in the Arctic and camels in deserts because that was carefully and deliberately arranged; rather, we understand that the local fauna is the contingent product of the local environment — a statement that applies just as much to the multiverse.

If you still find that line of reasoning unpalatable, consider that Steven Weinberg used it to predict that the value of the “dark energy” parameter in our universe would be small but non-zero. This prediction was made a decade before the observational detection of dark energy, at a time when most cosmologists assumed there was no dark energy. Then it was found, with a value in line with Weinberg’s prediction, but which is vastly smaller than given by attempts at calculating it from fundamental physics [9].

Weinberg’s verified prediction is currently the best explanation we have of the amount of dark energy in our universe. At this point, with an infinite extent of expanding inflationary-state stuff, dotted with island-universe bubbles, with each universe having different values for the physical constants, we have a full-blown multiverse of the sort to give critics a fit of the vapors. Yet, everything above is solid scientific reasoning, motivated and supported by observational evidence, and with already-demonstrated predictive power. That does not mean that it is true or proven, but it is a fully scientific concept and, regardless of the critics, the scenario is becoming increasingly accepted and mainstream among physicists.

A last remark: if the above is correct then in all likelihood we are near the middle of such a bubble and not near its edge. Yet there is some possibility that we are near an edge, and if we are then there would be nothing to stop us observing it if we looked far enough into the distant universe. In principle, then, the scenario is directly verifiable [10].

——

Coel Hellier is a Professor of Astrophysics at Keele University in the UK. In addition to teaching physics, astrophysics, and maths he searches for exoplanets. He currently runs the WASP-South transit search, finding planets by looking for small dips in the light of stars caused when a planet transits in front of the star. Earlier in his research career Coel studied binary stars that were exchanging material, leading up to his book about Cataclysmic Variable Stars.

[7] For an account of inflation and its observational motivations read this wiki page or this pdf of a chapter of Max Tegmark’s book Our Mathematical Universe.

[8] See this article of mine for a defense of Occam’s razor as a scientific concept.

[9] Naive calculations of the amount of dark energy expected give values about 10120 too big, perhaps the biggest error in the history of physics! Why is it that the actual value is 10120 times smaller than expected?

[10] And of course cosmologists are already looking for possible effects of “colliding bubbles”, which might be visible in the CMB. See this post for an example.

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171 thoughts on “The multiverse as a scientific concept — part II

  1. I was surprised to learn that the ‘multiverse’ is really just the idea that there are some areas, even beyond our own normal-state observable universe, which we have no access to, but whose existence our cosmological theories predict. I had been under mistaken impression (perhaps others as well?) that the ‘multiverse’ was akin to ‘parallel universes’ in another dimension, which I definitely do not view as scientific.

    I don’t see any good reason to dismiss the concept of multiverse as unscientific, yet emotionally, I have a hard time with the argument that even though we have no access to it, that because it is predicted by our current cosmological models, I should therefore grant it scientific status. If something is scientific by virtue of being predicted by a model, and given that the graveyard of science is full of ideas dead and discarded, aren’t you really asking us to believe in this concept with the same intensity and confidence of previous scientists? The only way out of this, as I see it anyway, is to regard previous failures as stepping-stones towards more secure knowledge, in which case, perhaps we can assume that models become ‘better’ with time and data. Eh, I don’t know.

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  2. Hi Coel,

    I agree that talk of the inflationary universe is motivated by scientific observations, but I am not convinced that we will every be able to show or falsify that there are more than one universe. Yes, almost all inflationary models produce many universes, but there are models which don’t, and those could be true. Or there could be models we haven’t thought of. Similarly, there may never be any evidence that inflation allows the different physical constants to take different values. This seems to me to be very speculative at the moment.

    So a multiverse is a reasonable speculation, drawn from physical observations, but I do not share your confidence that it will eventually be rejected or accepted based on improving our scientific understanding of the universe. It may be, but it seems to me that it may not.

    Yet there is some possibility that we are near an edge, and if we are then there would be nothing to stop us observing it if we looked far enough into the distant universe.

    Also, while I hesitate to contradict an astrophysicist on his cosmology, I do not think your portrait of how bubble universes might work is correct. As I understand them, they would have no edge. Like black holes, general relativity allows them to be finite from an external perspective but infinite from an internal perspective, and even if they are not infinite they almost certainly have no interior border. Space would likely instead wrap around in some way. Tegmark explains this in his book, where travelling towards the edge of a bubble is equivalent to travelling back in time, and the border of a bubble is actually that bubble’s Big Bang.

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  3. Hi Massimo,

    It really is beyond me how you can possibly equate one vs many spiders with one vs many universes. If not qualitatively, at the very least quantitatively we are talking entirely different situations, with the latter warranting much more epistemic caution than the former, no?

    I agree. I am not equating spiders with universes. I am illustrating by analogy that it is not generically the case that seeing one of something is grounds to believe that only one such thing exists. There may be grounds to believe that there is only one universe (since a universe is not a spider!) but you need to articulate that argument and you have not.

    Again, I have no problem with agnosticism. The hypothesis that there is only one universe is perhaps reasonable (whereas the hypothesis that there is only one such green spider seems to be entirely baseless). My problem with what you said is that you claim that we have good evidence that n=1, which I think is a mistake. We have evidence only that n is at least one.

    “Technically, we now have evidence that one side of one sheep in New Zealand is black.” I know, to you I sound like the third philosopher…

    Not quite. I actually agree with the third philosopher. I have no problem with epistemic caution. My problem with you is that you are not being epistemically cautious: you are actually making a claim that we have good reason to believe that there are no other universes. Perhaps this is not what you meant to say, but this is what you did in fact say. You claimed we had reason to believe the universe was a singleton and that n=1. This is like a fourth philosopher on the train saying “Actually, we now have evidence that only one side of one sheep in New Zealand is flat”.

    there are plenty of instances in the history of physics where parsimony as a criterion of theory selection has failed.

    Of course. Parsimony proves nothing. Again, my only point is that in my view not even parsimony gives grounds to prefer the singleton universe hypothesis. There is no reason at all to prefer the singleton universe hypothesis as far as I can see, but of course that doesn’t mean that the singleton universe hypothesis is wrong.

    Got any non speculative candidate for such fundamental explanatory principle? No, the MUH doesn’t count, I’m talking physics

    Coel’s post here could be such a candidate, although I actually agree that it is somewhat speculative.

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  4. Dr. Hellier: Thanks for taking time out to write these articles ! As a non-physicist (and non-philosopher) but scientist with a love for physics, your two articles offer one of most accessible yet insightful summaries on inflation and the multiverse that I have read. In fact, your second part here is the first place where I have learnt some little details (perhaps insignificant to practicing theoreticians, nevertheless informative to lay fans like me) about what the inflationary model actually entails. Your active engagement in discussions in the comments section in the previous (and hopefully this one as well) are also much appreciated !

    In spite of all my prefacing about how I am not a physicist or a philosopher, I am going to go ahead and commit the folly of offering two comments. If not anything else, it may hopefully provide you and your readers with a perspective of at least how one mildly informed lay person thinks !

    Your statements:
    “And, as stated early on, it is not necessary to empirically validate every prediction of a theory in order to have good confidence in that theory. To accept a theory and its implications all one needs is to have validated some of the predictions of the theory, and to have established that overall the theory does a better job than any alternative that we know of.”
    are perhaps the most unsatisfying in these essays and at least leaves me feeling jittery. Yes, there are some discussions in this regard in the previous article’s comments section yet it seems that it isn’t a bad feeling that is easily quelled ! Again, if anything, this only points to my own shortcomings. For instance, I certainly do understand the proposition, which I first came across spelt out by Lawrence Krauss, that far into the future, many hundreds of billions of years later, when the galaxies would all have receded (red shifted) away from each other so much that for a conscious scientific observer (if any) in, say, the milky way galaxy, it would appear that the milky way is the only galaxy in the Universe and the big bang model would, alas, be completely lost out to observational evidence. Krauss, in the original form of stating this, laments how falsifiable Science would produce the wrong answer to the origin of the supposedly singleton galaxy universe to that far future observer. This could be an instance validating your claim, as I understand or reinterpret it, that the nature of reality is independent of the constraints set forth by observations and models, and sometimes when 99 out of 100 predictions of a model are empirically reinforced, the 100th one which can possibly never be tested, even in principle, may have to be taken to be true on reasonable faith. I understand all of these (or believe so) yet I find it hard to internally reconcile—grok—your quoted statement.

    My second (non expert) and short observation is that:
    “Considering this idea one quickly arrives at the obvious point that we human observers could only find ourselves in a bubble that had parameters suitable to have produced us, and it may be that the vast majority of such bubbles would be too alien to support or produce us.”
    is too much reminiscent of the anthropic principle rearing its, dare I say, ugly head in a weak weak—weaker ?—form.

    Thanks again for your writings and discussions !

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  5. is too much reminiscent of the anthropic principle rearing its, dare I say, ugly head in a weak weak—weaker ?—form.

    This is not reminiscent of the anthropic principle, it is the anthropic principle.

    And the anthropic principle is perfectly valid.

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  6. The early parts of this article are heavily-laden with hype about what inflation is, how definite its predictions are, and how strong the evidence for these is.

    But, as they say, whatever… I do agree that inflationary models are science worth thinking about, and there is some sort of evidence for the general idea. The much worse problem is the use of these models to claim evidence for a fundamental physical theory in which our tested fundamental laws are random artifacts. I see zero such evidence, and I think before you trash the successful way fundamental physics has been done for centuries, you should have some.

    Here’s a simple question: the inflationary model that you claim now has significant evidence for it (I’ll even give you BICEP2 if you want) according to you implies that the quantities determining the Standard Model could be different, according to some statistical distribution, right? What does the tested model say about this distribution? Which constants, gauge groups, fermion representations are randomly determined according to what distribution?

    Put differently, how is the tested inflationary model different than my personal model for this, which says that I have no idea what determines these things, so they’re equally likely to be anything. Note that my personal model has no free parameters at all, and is so simple that the previous single sentence covers everything. Yes, there are possible worlds in which imprints of collisions with other bubbles would be visible in the CMB. There’s also a possible world in which close examination of the CMB would find the words “Peter Woit is right” imprinted there by a higher intelligence. So, why shouldn’t I get $3 million from Milner and $1 million from Kavli for my theory?

    Of course, the last paragraph questions are rhetorical, but the previous paragraph question is the crux of the matter. I very much would like to hear an answer to it. Apologies if any future responses take a while, I’m heading off to the airport, will be traveling the next few days.

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  7. What do you mean by “perfectly valid”?

    I mean there’s no reason to say it is raising its ugly head. There’s nothing wrong with the anthropic principle, especially if we are entertaining the idea of a multiverse.

    And which version of the principle are you referring to?

    Why, the version appealed to by Coel, of course.

    This version of the anthropic principle (sometimes called the Weak Anthropic Principle) is the one which makes actually makes sense. It states that it is unsurprising that the universe is capable of supporting life (or some kind of observer) because we are observers in this universe. It couldn’t be otherwise.

    The Strong Anthropic Principle is nonsense, and holds that the purpose of the universe is to give rise to life or that life is a necessary or inevitable part of a universe. Since Coel made no such claim this has nothing to do with the discussion.

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  8. Hi Coel,
    Very interesting post once again.

    This maybe asking a lot but if you have a chance, I’m still curious as to what makes something scientific versus unscientific for you? I think having a clear understanding of that would better help to judge the question of whether or not the multiverse is in fact a scientific idea.

    I’m personally still more inclined to say that this is scientific speculation or philosophizing rather than actual scientific work. The model may seem plausible but unless we can actually empirically verify it (and it doesn’t seem we can, even in principle), I don’t think we are justified in assuming that there is a multiverse as a scientific conclusion, which others have pointed out is a extraordinary claim.

    For all we know, the picture could be completely different beyond our universe if there is anything there at all. I think the appropriate response is here are some guesses we have but ultimately at this point, we don’t know. If someone of course came along and was able to provide direct evidence or perhaps if enough indirect evidence accumulated over time that it was overwhelmingly likely that the multiverse was true, that would be another story.

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  9. Agreed, though I’ve often wondered why we raise this sort of trivially true statement to the level of “principle.”

    Because it isn’t obvious to everyone. There are people who take as evidence for a creator that the earth is just the right distance from the sun for life.

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  10. Hi Steven,

    I had been under mistaken impression (perhaps others as well?) that the ‘multiverse’ was akin to ‘parallel universes’ in another dimension, …

    This is a point I remarked on in Part 1. More than one concept has attracted the label “multiverse”. The “eternal inflation” multiverse that I expound in these articles is one that is rooted in fairly well-established cosmological models and which is now fairly mainstream among cosmologists.

    You are right that there are also speculations about higher-dimensional physics (e.g. M-theory) which can also give rise to “multiverse” concepts. These are (in my opinion) vastly more speculative and vastly less empirically grounded than the “eternal inflation multiverse” concept.

    If something is scientific by virtue of being predicted by a model, and given that the graveyard of science is full of ideas dead and discarded, aren’t you really asking us to believe in this concept with the same intensity and confidence of previous scientists?

    Saying that something is “scientific” is not at all the same as saying how confident we should be in it being right. There are lots of theories and models in science with a big range in how confident we are in them. Thus, to pick an example, various theories about what caused the Cambrian Explosion are entirely scientific, but are not secure and possibly wrong.

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  11. Hi DM,

    Space would likely instead wrap around in some way.

    This is indeed possible, and would be the case if we have a positive curvature to space. The current observations say that curvature is very close to zero (as expected for a post-inflation universe), but it could still be small and positive. (Current observational values for Omega_curvature are about 0.003 +/- 0.004, depending on which data one uses.)

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  12. You are right that there are also speculations about higher-dimensional physics (e.g. M-theory) which can also give rise to “multiverse” concepts

    Let’s not forget the Many Worlds Interpretation! It’s not quite mainstream but not far off it, and it is arguable just as grounded in standard physical models as inflation. The only way to escape from many worlds is to add ad hoc complication to the models such as objective waveform collapse, which is anything but parsimonious.

    And this is much more like the idea of parallel universes Steven mentions.

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  13. Hi Kaushik,

    Thanks for your kind words about my article. On your “bad feeling” about my statement about “accepting” a prediction of a validated theory, I reiterate that by saying we should “accept” it I do not mean that we can now consider it proven beyond doubt, but only that we should accept it in the provisional way that we accept science’s ideas as the best we humans can do, given the current data that we have available to us.

    Science is always pragmatic and is (I assert) the best we humans can do, but it is not better than we humans can do and is not infallible!

    On the weak anthropic principle: in the weak form it is entirely valid. We humans are only going to find ourselves observing the universe from a location that is suitable to have produced us.

    If we try to explain the fact that Earth is at the right distance from the Sun to have life like us, we can either assert that there is some mechanism that requires an Earth-like planet to be at a given distance from a star, or we can say that there are lots of such planets at lots of distances, and sentient life forms find themselves on the ones that are suitable to produce sentient life forms.

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  14. Sure, we might be able to see collisions between bubbles, but that wouldn’t mean there is an edge or that space inside a bubble is finite. The papers you cite talk about detecting collisions in the microwave background radiation, which is looking towards the past. This would seem to be consistent with my understanding that the edge of the bubble as seen from outside it is from a perspective inside it equivalent to the Big Bang.

    I’ve only read the abstracts though. I imagine the contents would be way too far above my head.

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  15. Hi Peter,

    Here’s a simple question: the inflationary model that you claim now has significant evidence for it (I’ll even give you BICEP2 if you want) according to you implies that the quantities determining the Standard Model could be different, according to some statistical distribution, right?

    Yes, noting the “could be”. If we establish inflation then we have established that the “laws of physics” are acting differently at different times. At that time, early in the universe, there was an “inflaton field” acting that isn’t acting now. The fact that forces were acting differently then is equivalent to the physical constants being different (since most of the physical constants are simply specifying strengths of interactions between particles).

    So, if we have established that “physical constants” were effectively different at that time, then we have established that they are not immutable results of the most fundamental laws, but are contingent on circumstance.

    That justifies the claim that you quote (again noting the “could be”). It is then legitimate to ask about the current values of the constants in the universe today, and whether they could be different in other post-inflation “bubbles”, and again noting the greater parsimony of not having to justify all the exact values of the constants that we measure today.

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  16. Hi imzasirf,

    I’m still curious as to what makes something scientific versus unscientific for you?

    Something like: we are being scientific if the information content of a model is motivated by and justified by empirical evidence. We are being unscientific if our model has information content that is not justified by empirical evidence.

    Note how this is phrased, in terms of the information content of models, rather than about “objects”, which I don’t think can be considered in a model-independent way (see comments to Part 1 for more discussion of this; for the philosophers here, note that the concept is also similar to Quine’s `web of belief’).

    The model may seem plausible but unless we can actually empirically verify it (and it doesn’t seem we can, even in principle), I don’t think we are justified in assuming that there is a multiverse as a scientific conclusion …

    The reason that we cannot “empirically verify it in principle” is simply the finite speed of light. As I said in the article, I don’t think that that is sufficient reason to discount the concept as scientific. We would still regard a prediction of future eclipse times as scientific even though we cannot verify them indefinitely into the future.

    For example, to me the statement: “There will be a solar eclipse in the year 3068 visible from America” is scientific — because it is implied by validated models — even though as we are *now* we cannot verify that statement by direct observation.

    Future humans could, of course, verify it directly in the year 3068, but we cannot verify it, even in principle, as we are now, yet I assert that it is a scientific statement *now*.

    Or, how about the claim: “There was a solar eclipse in the year 38,787,991 BC visible from some specified latitude and longitude”.* I assert that such a statement would be scientific by virtue of being implied by validated models, even if there is absolutely no way of directly verifying it.

    [*I did of course just make this year up, but our models of planetary motion are accurate enough to extrapolate to such a time.]

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  17. Interesting post, but a few observations.
    1. If our own universe dropped out of inflation after just 10^-35 seconds, why is the rest of the universe still inflating after 14 billion years? In the eternal inflation model, it would seem extraordinarily unlikely that our universe came into being so rapidly.
    2. You assume that the fundamental constants of nature are randomly selected. But equally there could be a reason for them to take the values that are measured. That’s what the history of physics teaches us – that apparently arbitrary constants are explained in terms of some more fundamental theory. Since we don’t yet have a fundamental theory, that seems like a wild assumption. Even if they do take different values in different universes, there must be something that causes them take these random values, so random allocation isn’t a theory at all.
    3. You refer several times to the idea of an infinite universe. The empirical evidence merely shows that it is extraordinarily big. Extrapolating from very big to infinite is a dangerous game.

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  18. Hi Steve,

    1. The first question is based on a misunderstanding. In eternal inflation, the past and future of the multiverse are both eternal. That figure of 10^-35 is only relative to the point where our universe began to nucleate. The multiverse as a whole has always existed and universes are being created constantly.

    2. Either random selection or selection according to some fundamental theory is fine. The point is that we are no longer left with the situation where they are simply predefined and arbitrary.

    Even if they do take different values in different universes, there must be something that causes them take these random values, so random allocation isn’t a theory at all.

    So is QM not a theory? What is it that causes measurements in QM to be allocated randomly? Mathematical models are really just descriptions, not fundamentally explanatory. Why is it that opposite charges attract? Why not opposites repel, same attract? It makes just as much sense. There is no explanation of why this is, there is only a mathematical model of what happens. Random allocation would be no different.

    3. He doesn’t assert the universe is infinite, only that it may be. Which is true. It is at least as likely to be infinite as finite, in my view.

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  19. Good posts, but I must disagree with you because of the following reasons.

    Coel Hellier: “If you don’t like the idea of a multiverse extending vastly beyond our observable horizon, or consider it to be unscientific, then realize that conventional cosmological models extend to infinity in much the same way. …and to have established that overall the theory does a better job than any alternative that we know of.”

    Instead of arguing over the ‘speculations’, I will show ‘facts’ only here, that is, all those speculations are not ‘needed’.

    The cyclic universe (C-multiverses, with different initial conditions while having the same physics laws and nature constants) is the central point in the book “Super Unified Theory; ISBN 9780916713010, US Copyright number TX 1-323-231”. That is, I only disagree with the simultaneous-coexist-multiverse (S-multiverse, with different physics laws and nature conditions). And, this S-multiverse can of course be ruled out with four points (facts) although by definition that those other universes are unobservable from ‘this’ universe.

    Point one: for the S-multiverse as a ‘fact’, it has produced a special universe which we are living in. For the S-multiverse-theory, it has failed to describe that ‘fact’, as being unable thus far to find out how ‘this’ universe came about from the S-multiverse fact. That is, the S-multiverse-theory is useless and nonsense.

    Point two: ‘all’ open issues (such as, the dark matter, dark energy, the fine-turning and the ‘string-unification’, etc.) of this universe can be addressed without the need of knowing anything about the S-multiverse. I am showing just a few such cases below.

    The most widely known open issues of today are the dark mass and the dark energy, and they are clearly outlined with the Planck data (dark energy = 69.2; dark mass = 25.8; and visible matter = 4.82).

    The current paradigm is having ‘dark matter’ (such as SUSY particles) to account for the dark mass. But, all dark particle searches are coming out empty handed thus far. Yet, both dark issues can be fully accounted for with a ‘structure’-model which describes ‘this’ universe with a set of structure number (64, 48). Then, the dark mass is accounted for with “the Pimple model (or house-address name model)” —
    1. There are 48 mass-particles, and each of these 48 has its own ‘measured’ mass-value which is different from all other mass-particles.
    2. For every mass-particle, its measured mass is only a ‘name-tag (or a Pimple)’ for its house which also encompasses all 47 other mass-particles. That is, for every visible particle, it is only a ‘part’ of the house which houses the entire 48 particles.

    With this name-tag model, only 7 of the 48 mass-particles [the first generation matter (not anti-matter)] gives out lights (excluding e-neutrino). Thus, the dark mass/visible mass ratio = [41 (100 – w) % / 7]. The *w* is the percentage of the dark matter (the ‘household’ of those 41 regular particles) which does give out lights or melted into as dark energy. According to the AMS02 data, ‘w’ is between 8 to 10%. By choosing w = 9, the d/v ratio = 5.33 (while the Planck data shows d/v ratio = 25.8/4.82 = 5.3526).

    For dark energy, this structure model is described as an iceberg model — that is, the Time, Space and Mass (dark + visible) form an iceberg system, while the mass is the iceberg. And, they three take the *equal* share.

    So, the dark mass = [(33.3 – 4.82) x (100 -w)%] = 25.91 (while the Planck data is 25.8), with d/v ratio = 5.37. The w = 9% here is the melting ratio from the dark matter (described in the above paragraph). Thus, the dark energy = 66.66 + [(33.3 – 4.82) x w%] = 66.66 + 2.56 = 69.22 (while the Planck data is 69.2).

    There are three points on this.
    a. The dark-mass target was hit twice on the bull’s-eye by this structure model.
    b. The ‘w’ is able to encompass a small (in 10%) adjustment in Planck data.
    c. ‘w’ is a physics-parameter and is measurable, that is testable.

    Of course, for every given number (as a target), one can ‘always’ reversely engineer a ‘bow and arrow’ to hit that target. Thus, it is very easy to tell whether a formula is a ‘numerology’ or not with two criteria.

    Criterion one: does the formula has a ‘preset’ framework which is not ‘directly’ connected to the target(s)?

    Criterion two: a bow/arrow set which hits one target in a ‘field’ must be able to hit the other targets in that same field (field as discipline, such as, physics, chemistry, biology, etc.).

    If one ‘bow/arrow’ is able to hit all targets in a field, it becomes a ‘base’ of a new language which describes all those targets. If the targets are true, their describing language must be ‘necessary’ true. Of course, the key is that that ‘bow/arrow’ must not be a single-shot gismo (being reverse-engineered from one target). Every structure can always be outlined with a few demarcation markers (or landmarks) which are seemingly unrelated superficially among one another. In the case of this universe, those landmarks are a set of numbers (or values). The ‘w’ bow/arrow has hit two targets. Yet, that structure-bow/arrow (64, 48) must hit all other structure targets in order to become a ‘language’ of that field. The followings are some examples of this bow/arrow/targets demonstration.

    Target three: (1/Alpha) = 137.0359 …
    Bow/arrow: the structure ‘number’ model — the structure of this universe is 100% described with two numbers (64, 48),
    Beta = 1/alpha = 64 (1 + first order mixing + sum of the higher order mixing)
    = 64 (1 + 1/Cos A (2) + .00065737 + …)
    = 137.0359 …
    A (2) is the Weinberg angle, A (2) = 28.743 degree
    The sum of the higher order mixing = 2(1/48) [(1/64) + (1/2) (1/64) ^2 + …+(1/n)(1/64)^n +…]
    = .00065737 + …

    Note: Alpha is wholly described with (64, 48), as the Weinberg angle is also wholly described only with (64, 48). That is, the total mass of this universe is equal to ‘zero’ in the Weinberg angle calculation, and that theoretical number is (Weinberg Angle = 28.5 degrees), see below. So, the ‘current’ Weinberg angle for the current measured Alpha has been compressed by the current non-zero mass of this universe. So, the measured Alpha value should also vary a bit depending on the total mass of the universe. At high energy (about 90 Gev.), the Weinberg angle can be compressed to ‘zero’, that is, the measured Alpha at that energy will be about equal to 128.

    Target four: Weinberg angle (from 28 to 30 degrees)
    Bow/arrow: the same as for the Alpha calculation. See http://prebabel.blogspot.com/2011/10/theoretical-calculation-of-cabibbo-and.html .

    Target five: Cabibbo angle (about 13 degree)
    Bow/arrow: the same as for the Weinberg angle.

    Target six: Neff (the numbers of neutrino species) => 3 and smaller than 4.
    Bow/arrow: 48/16 = 24/8 = 3 (for matter field), three known neutrino species.
    For the CMB, the dark energy can be read (or misread) as a sterile-neutrino, that is, (48 + 16)/16 = 4; thus, in the CMB reading, the Neff can be close to 4.

    Target seven: the r-ratio of B-mode in the CMB. The value is currently unknown but claimed by BICEP2 as r = 0.2
    Bow/arrow: the same set as for Cabibbo/Weinberg angles and Alpha, the structure ‘number’ model — the structure of this universe is 100% decided with two numbers (64, 48). The 48 forms the mass-field, encompassing 48 mass-particles. The 16 forms the energy-field (the dark energy). Thus, the polarized (dark energy)/scalar (total energy, E-mode + B-mode) ratio = (64 – 48)/64 = 0.25
    Note: the BICEP2 data is now in trouble, but 0.25 is the target of this bow/arrow.

    In fact, those seven targets are hit by the same bow/arrow.

    Point three: if we can show that the physics laws and nature constants of ‘this’ universe are bubble-independent (need not invoking the S-multiverse hypothesis), then the laws and constants of this universe is ‘universal’. In the second point above, all the constants of ‘this’ universe are accounted for without using any ‘bubble’-dependent variable or parameter, as they all arise from two pure numbers (64, 48). That is, S-multiverse is not needed for ‘this’ universe. Furthermore, the S-multiverse hypothesis cannot derive any of those nature constants anyway. As those numbers of this universe are precisely calculated, there is no fine-tuning issue neither. They are simple precise.

    Fourth, Coel Hellier: ” However, where one quantum fluctuation can occur so can another, and thus it is natural to suppose that there might be many other such universes. In particular, we have no strong reason to suppose that the quantum fluctuation that originated our universe was the origin of all things or of time itself — though equally we lack arguments against those possibilities, … This tells us that some aspects of what we see are local “accidents,” variations allowed by the underlying laws but contingent on local circumstance.”
    Disagree 100%.
    First, quantum fluctuation produces different vacua (different snowflakes). There is no logic, no physics law and no theorem of any kind stating that quantum fluctuation is able to produce different laws and different nature constants.

    Second, the quantum principle is in fact the direct ‘consequence’ of this universe.
    F (Force of ‘this’ universe) = K ħ/ (delta S x delta T)
    K (coupling constant, dimensionless); ħ (Planck constant); S (space); T (time).
    Then, delta P (linear momentum) = F x delta T = K ħ/ (delta S)
    So, delta P x delta S = K ħ
    When, K is near to 1 (but a bit smaller than 1), then delta P x delta S > ħ (the uncertainty principle).
    When K ħ is near to (0 ħ), the F is ‘gravity’.
    F (of ‘this’ universe) is not bubble-dependent, and the quantum principle is the consequence of this universe. More details (see http://prebabel.blogspot.com/2013/11/why-does-dark-energy-make-universe.html ).

    Not one thing in ‘this’ universe is bubble-dependent. S-multiverse is now totally ruled out from ‘this’ universe.

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  20. Thank you DM. The mathematics of eternal inflation is beyond me (I studied physics to degree level) and I will never understand it. As for why opposite charges attract and so on, these are good questions and I am confident that we will one day find out. Our current theories are clearly provisional.

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  21. Hi Steve,

    If our own universe dropped out of inflation after just 10^-35 seconds, why is the rest of the universe still inflating after 14 billion years?

    A good question, which points to a slightly sloppy way in which cosmologists talk about time. In the old days of Big Bang cosmology, people extrapolated the universe back in time to arrive at a past “singularity”, and thus talked about time since that “zero point” singularity. Nowadays, most cosmological models don’t have a singularity, and instead we extrapolate backwards to an origin of the universe in quantum fluctuations. The “time” value (and equivalent statements about lengths and energy scales) are really statements about how things have changed *since* those quantum fluctuations. One should really think of this in terms of the change in the “scale factor” of our universe since that point, and that is what the numbers really refer to. Thus that time is not about what happened *before* we dropped out of inflation, and is not a time “since the singularity”, since this model does not have any such singularity and thus does not have any zero point at which to set the clock running. Thus the “eternal inflation” would indeed by eternal, and our bubble could have dropped out of it at “any time”.

    You assume that the fundamental constants of nature are randomly selected.

    Well, that’s one possibility.

    But equally there could be a reason for them to take the values that are measured. That’s what the history of physics teaches us – that apparently arbitrary constants are explained in terms of some more fundamental theory.

    One of the the reasons that theoretical physicists have started thinking about the constants being contingent accidents is that they were actually making rather little progress in explaining the values of the constants in terms of anything more fundamental. The “standard model” depends on over 20 such constants, and at the moment they are just numbers measured observationally with no explanation of why they have those values.

    But you’re right that maybe some better model will come along that does explain and predict exactly the values that we see.

    You refer several times to the idea of an infinite universe. […] Extrapolating from very big to infinite is a dangerous game.

    True, but this is just as much an issue for any account of the universe, and is no worse in a multiverse model than in any alternative account. Thus it is not, in itself, a defect of the multiverse hypothesis.

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  22. Although a caveat is that these BICEP2 results are currently being heavily discussed, with issues about whether foreground dust has been properly accounted for, and whether the data are consistent with Planck results. We need to wait a year or two before knowing whether the BICEP2 results can be relied upon.

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  23. I’ve never quite understood why the inflaton field isn’t regarded as simply discharging itself in the expansion? If a crystal forms from a supersaturated solution, it tends to keep absorbing all the excess. And if multiple crystals form, they may interfere which each other, marring the perfection of the crystal forms. The apparent absence of any collision with another bubble is suggestive. An infinite inflaton that has enough volume that it’s dissipation is purely local with no wider effects, ,like shock waves passing through a supersaturated solution precipitating, seems at a glance to be more specific, higher information content, less parsimonious. (If I understand your version of Occam’s Razor?)

    In addition to not quite understanding how the notion explains the spatial quarrantine of the universe bubbles, I’m not quite sure why this infinite inflaton does not smooth out and continue to interact with this universe? This is a cosmological version of Olbers’ paradox I suppose, hence the notion of an expanding inflaton-space. But what powers the inflaton-space expansion? The empirical evidence for the inflaton is the cosmological evidence for an expansion. An expanding inflaton-space expansion seems a little like infinite regress.

    Double checking, Weinberg’s calculation was for the energy density of the vacuum which he identified, most do after all, with the cosmological constant and dark energy?

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  24. Hi DM,

    The multiverse as a whole has always existed and universes are being created constantly.

    It’s a bit more complicated than that, and whether the “eternal inflation” is past-eternal as well as future-eternal is something one can argue about. What is the case is that the inflating state is self-similar in that it has a constant energy (that being the main feature of the inflating state, and why it drives exponential expansion), and thus it doesn’t matter at what “time” one drops out of it, because the resulting bubble will be the same whatever.

    Thus the “time since” the possible quantum-gravity fluctuation that led to the inflating state is something that can have any value.

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  25. Hi Steven,

    I’ve never quite understood why the inflaton field isn’t regarded as simply discharging itself in the expansion?

    If the inflation is caused by a “energy density of the vacuum” — that is, an energy that is the property of the vacuum itself — then expansion produces more vacuum and thus more of the energy, and thus the “inflaton field” is not itself changed by the expansion. This is why it drives an exponential expansion (since the exponential is a self-similar curve).

    In addition to not quite understanding how the notion explains the spatial quarrantine of the universe bubbles …

    One shouldn’t think of a pre-existing space with a coordinate system locked to that space, and stuff expanding into that space. One should think of the space itself expanding “internally”. In other words, volume is not a conserved quantity, and parts of space can inflate by their “internal” volume increasing, not by encroaching into another region.

    The empirical evidence for the inflaton is the cosmological evidence for an expansion.

    No, the main empirical evidence for inflation is the structure that it then imprints onto the Cosmic Microwave Background. The current expansion of the universe, seen as the red-shift of the galaxies, is something different (indeed the galaxies only formed long after the inflationary era).

    Double checking, Weinberg’s calculation was for the energy density of the vacuum which he identified, most do after all, with the cosmological constant and dark energy?

    Yes, all of those are different names for the same thing (different names because no-one yet understands what “dark energy” is in terms of fundamental physics, and thus it is called different things depending on how one approaches it: “cosmological constant” is the term one adds to the Friedman equation, “dark energy” is the stuff we think results in that term being needed, and “energy density of the vacuum” is one possible interpretation of what dark energy actually is).

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  26. DM,
    all you are saying is we are here because we are here. It is totally trivial and can’t be used to support other lines of reasoning.

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  27. Coel, I don’t hunk you took Peter’s criticisms seriously enough, frankly. That, by the way, is Peter Woit, the author of Not Even Wrong: The Failure of String Theory and the Search for Unity in Physical Law for Unity in Physical Law

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  28. Peter,
    The much worse problem is the use of these models to claim evidence for a fundamental physical theory in which our tested fundamental laws are random artifacts.

    That is the heart of the matter. We don’t have the foggiest idea where our laws of nature come from and why they seem to have the prescriptive power they evidence. Until we understand that we have no way of knowing that they can be different, why and when they could be different. All our observations suggest they are time and space invariant and we have no reason to think otherwise.
    Multiverse proponents make this vast jump without the slightest evidence that it could be possible for the laws of nature to be different. That is what happens when ideology drives science.

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  29. Hi labnut,

    all you are saying is we are here because we are here. It is totally trivial and can’t be used to support other lines of reasoning.

    It’s trivial in the same way that the survival of the fittest is a trivial idea. It’s tautological and obvious once it is explained but it has profound implications in explaining what otherwise appears to be intelligent design. As I said to Massimo, it is not completely trivial because it is lost on some people.

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  30. Disagree. It’s trivial in a much more obvious way than the principle of natural selection. Which, of course, is also apparently beyond the comprehension of half of the American population.

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  31. Coel,
    If we establish inflation then we have established that the “laws of physics” are acting differently at different times.
    Have we? How have we established that? You are making a huge assumption without any supporting data, so how can you say ‘we have established that‘?

    Surely, establishing something requires:
    1) a well reasoned hypothesis,
    2) data that validates the hypothesis.

    You have neither, so how can you claim that it is established? We are talking about science here, which has high standards for the claim ‘established‘.

    Quite frankly, you are treading on dangerous ground. There is a swelling counter-knowledge movement that feeds on weak or flimsy claims. You have no business, as a responsible scientist, putting forward such flimsy claims since it only encourages the counter-knowledge movement to make equally extravagant claims in other, dangerous areas, on equally flimsy grounds.

    To neutralize the counter-knowledge movement we must insist on rigorous, evidence based claims, so we must hold you to that standard.

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  32. Hi Massimo,
    My reply to Peter addressed one point: do we have good reason for supposing that the physical constants are not all necessarily constant, and I think that with inflation we do have reason to think that.

    Peter’s next questions (which are, “ok then, so what is the possible distribution of these constants and why?”) I didn’t answer because I have no idea what the answer is. This isn’t something that the eternal-inflation-multiverse model makes any predictions about. At that point we really are merely speculating.

    However, not knowing that doesn’t undermine the basic idea of bubble universes within eternal inflation. Indeed, that multiverse concept holds even if every bubble has (and necessarily has) exactly the same physical constants as we do.

    By the way, I regard this cosmological stuff as vastly less speculative and more scientific than superstring and M-theory stuff, because the eternal-inflation model really does make predictions about the CMB that we can test (and indeed has made predictions that have been tested and verified). In contrast, M-theory has not done that and maybe can’t (in the reasonably forseeable future) and I would agree with Peter that there are legitimate questions to ask about it. If one judges it by appointments of young academics, it is currently a lot less fashionable than it was a while ago.

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  33. Hi labnut,

    Me: “If we establish inflation then we have established that the “laws of physics” are acting differently at different times.”
    Have we? How have we established that?

    Note the *if* in my quote. *If* we have established inflation, then we have established that (1) there was an inflaton-field acting then; and (2) that inflaton-field is not acting now. We would have established that some very major force (sufficient to dominate the universe at that time) was acting then but is not acting now.

    That is what I meant by we would have “established that the “laws of physics” are acting differently at different times”, bearing in mind that “laws of physics” are simply descriptions of how forces and such act.

    Now, one could reply that ok, but some deeper-level description (= laws) would have remained constant, and I would likely agree with you. But that is the whole proposal, that some deeper-level description (= laws) allows things like forces (= “physical constants”) to act differently in different circumstances (= allows physical constants to be different in different circumstances).

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  34. Disagree. It’s trivial in a much more obvious way than the principle of natural selection.

    I didn’t bring the whole of evolution into it. I said “the survival of the fittest”, which is the idea that those organisms that are best at surviving (and reproducing) will reproduce the most. That is pretty darn trivial, but provides the foundation for more sophisticated understanding. “We find ourselves in a place we can possibly be” is similar. It is trivial but acts as a basis for deeper thought, suggesting that there may be more than one universe, that the constants are probably not fine tuned by a creator, that there may be many other kinds of ways for life to exist than the niche earth life has evolved to fit and so on.

    Which, of course, is also apparently beyond the comprehension of half of the American population.

    And as I have said a few times now, there are still plenty of people who are blind to the anthropic principle and think that the distance of the earth from the sun etc is reason to believe in intelligent design, so this is rather a weak argument to distinguish survival of the fittest from the anthropic principle.

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  35. Hi labnut,

    all you are saying is we are here because we are here.

    No, he’s not saying that, he’s saying that the natural state is that we (as products of the universe) would see around us an environment suitable to have produced us.

    The only way this could not be the case is if we were in some sort of zoo, that we had been moved from an environment that could have produced us to an environment that could not. Thus the only way we could see around us a universe that did not appear suitable for us is intervention by an intellgient and powerful entity which had moved us to a “zoo”.

    This is one reason why the “fine tuning” argues against theism and for naturalism. The fact that we fit our surroundings (and thus that our surroundings are a fit to us) is a prediction of naturalism. It is not a prediction of theism, which could go either way.

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  36. Do you really think people don’t understand the idea that fittest organisms are more likely to survive? I seriously doubt it.

    No, I don’t think that at all. I’m not sure why you think that I do. People just don’t think about it much and don’t realise what it suggests (or at least they didn’t before Darwin).

    Besides, are you now switching to say that the survival of the fittest is more trivial than the anthropic principle? Or what? Because you attack the anthropic principle by saying it is too trivial to bother with, while at the same time you seem to be saying the same of “the survival of the fittest”. Do you not think that this was an important insight, then?

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  37. You brought up the survival of the fittest. And yes, I do think they are both trivial ideas, and I don’t believe that most people don’t grasp them. So I reiterate my point: to call a triviality a “principle” seems entirely out of proportion.

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  38. Coel,
    there is an irony that I am arguing against you about the multiverses. As it happens, I do believe in the multiverse, but on theological/philosophical grounds and not scientific grounds. However, in these posts I am leaving theology/philosophy behind and only arguing from a science viewpoint since you base your views on your understanding of science(you and I can talk about my theology in another time and place!)

    (1) there was an inflaton-field acting then; ” – Agreed
    (2) that inflaton-field is not acting now. ” – Andre Vilenkin(Many Worlds In One) does not agree with you. He maintains that new universes, small and large, are constantly bubbling into existence everywhere, even in this room as I type.

    We would have established that some very major force (sufficient to dominate the universe at that time) was acting then but is not acting now.
    What we have not established is that this very major force in anyway changed the laws of nature. How would it change the laws of nature? Can they be changed? How would we know? We don’t have the smallest iota of evidence for it. This is major guesswork and that is most emphatically not science. It is a faitheist hypothesis.

    Simply saying that a major force acted then and not now says nothing about the ‘nature’ of the laws of nature, or that they changed or how they have changed.

    There is a bigger problem that Andre Vilenkin refers to at the end of his book. If the laws of nature changed from one instantiation to the next then there must be meta-laws of nature that describe how this could happen. What are these meta-laws? Are they a master copy of the laws of nature, copied into each instantiation of a universe? We have gone so deep into the realm of guesswork that we resemble Alice in the Looking-Glass. I prefer Lewis Carroll’s account of what Alice found on the other side of the looking glass. It is more plausible.

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  39. Hi labnut,

    On (2) “that inflaton-field is not acting now”, let me clarify that to “is not acting now in our observable universe”, in that it is not affecting the observation of all the galaxies we see strewn across the observable universe out to the microwave background.

    It might indeed, as you quote Vilenkin saying, be currently acting on other spaces, but it is not acting in our observable space.

    Therefore my comment stands, that it acts some times/places but not other times/places.

    Simply saying that a major force acted then and not now says nothing about the ‘nature’ of the laws of nature, or that they changed or how they have changed.

    Yes it does! “Laws of nature” are descriptions of nature. “A force is acting” is a different “law” (= description) to “that force is not acting”. If gravity in our world suddenly started acting differently that would be different “laws of nature ” (= “descriptions of nature”).

    If the laws of nature changed from one instantiation to the next then there must be meta-laws of nature that describe how this could happen.

    That’s exactly what I said in the comment you were replying to.

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  40. Coel,
    It might indeed, as you quote Vilenkin saying, be currently acting on other spaces, but it is not acting in our observable space.
    I am afraid not, he is saying it also acts in our space. If you like I can give you the page numbers. I am not saying I agree with him. I just want to illustrate how leaders in the field can arrive at such different conclusions and if that is possible, we should assign much less weight to their conclusions. After all, who is right when we can’t appeal to real evidence to settle the matter?

    Yes it does! “Laws of nature” are descriptions of nature. “A force is acting” is a different “law” (= description) to “that force is not acting”
    That seems very confused. A force acts according to the laws of nature. That is a well established fact. What has never been established is that a force changes the laws of nature. That is a very good thing since we would otherwise live in a most arbitrary and unpredictable universe.

    The theologist hiding inside me notes your statement with wry amusement since it opens the door to explaining miracles. I am sure you don’t want to go down that route.

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  41. Hi labnut,

    That seems very confused. A force acts according to the laws of nature. That is a well established fact. What has never been established is that a force changes the laws of nature.

    That is a somewhat superficial description of the situation.

    Suppose that the actual laws of nature are unchanging and universal (something I agree with, and Coel probably does too). We can’t perceive these directly, so we propose models of these laws which explain what we see. These models are not the laws themselves, and our best models of what we see may describe only one particular kind of space where the more fundamental laws can describe a whole lot more.

    This is just like the move from Newtonian mechanics to General Relativity. At high energies, Newton’s laws no longer work. That could be loosely described as the laws of physics changing even though the fundamental laws of physics are unchanged. What Coel is proposing is that the laws we see in this universe are like Newtonian Mechanics – a convenient approximation that works for the kind of space and energies we see around us, but that there are other scenarios which are better described by a more fundamental theory (something analogous to General Relativity).

    So when we talk about the laws of nature changing, we are not really talking about changes to the underlying fundamental laws, but changes in the phase of the vacuum such that physics appears to behave differently and be described by different physical models. The confusion is that both the models and the underlying physics are both often described by the term “law” even though they are usually not the same.

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  42. Hi labnut,

    I am afraid not, he is saying it also acts in our space. If you like I can give you the page numbers.

    I’d be interested in looking it up, since I don’t see how anyone can maintain that our observable universe currently has the inflaton field acting as it did in the inflationary era.

    A force acts according to the laws of nature.

    Which means that a force acts according to the description of how it acts. Agreed.

    What has never been established is that a force changes the laws of nature.

    That is the confused statement, and is not what I’m suggesting. A “law of nature” is a *description* of the force. If the force were different then the description of it would be different and thus the “laws of nature” would be different.

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  43. Dear Coel, it seems to me that you are playing fast and loose with technical terms like “law”, “constant”, “force” and “field”. This game of words seems to allow you leap over many logical steps necessary to make a connection (which is in fact very tenuous) between evidence for inflation and evidence for “changing physical constants”. I think that in the interests of transparent argumentation you should give some precise definitions for these terms that those who are not already familiar with these terms have a chance to follow the necessary chain of logical reasoning. Feel free to be as technical as you like, but lets agree to not conflate concepts like model parameters, fields over spacetime and outcomes of physical measurements which all have important differences between then.

    Let me make my position clear. What we seem to be gathering increasing amounts of evidence for is an inflationary period in the early universe, whose underlying mechanism is unfortunately still subject to debate. However, lets grant even that the mechanism is given by the roll and decay of a scalar field, the inflaton. So the evidence that we have been collecting is telling us that the value of this field has changed between the inflationary period and today. Granted! However, from that information it does absolutely NOT follow that quantities like measured charges and masses of fundamental particles have changes between the inflationary period and today. Such a change would be implied only under very special assumptions on the physics of the inflaton field. More precisely, to be confident in the changes of physical quantities like measured charges and masses, we would have to be confident of how the inflaton field couples to all other matter fields (the form of the specific interactions terms in the fundamental Lagrangian which depend both on the inflaton field and other matter fields). But, and it’s a big one, at the moment there is essentially no information about these couplings, though please correct me if I’m wrong. So the logical leap to conclude that we have amassed (even indirect) evidence for possibly different values of measured physical constants in unobservable patches of the universe requires that we have at least amassed some evidence for these physical constants to have changed within our own observed patch. But this is precisely where the evidence is weakest!

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