Monday, January 31, 2011

The Deep Laws of the Cosmos, or Hope Springs Eternal

After my disappointment with a recent read on multiple universes and M-theory, I was hopeful that Brian Greene's latest offering, The Hidden Reality, would soothe the ruffled feathers. Thankfully, I wasn't disappointed (how can you be with statements like "gravity is matter's sugar daddy"?).

Greene has a way about him that is at once knowledgeable and endearing; he starts his description of parallel universes with a story from his childhood. It isn't forced or unnatural. He wants you to understand.

Though Greene has substantially more space to take tangents (141 more pages than Hawking, though I can't attest to the font sizes or line spacing being the same...), he stays on topic. No random digressions into Newton's church attendance or arguments against philosophy or religion (he does tell some funny side-stories, including one about Gamow's notorious sense of humor, but they are all couched in the point at hand: he introduces a person before introducing that person's key insight into the scientific theory being described), no vehement arguments over free will or aversion to individual scientists due to their beliefs (in fact, Greene even describes some groundbreaking work by Weinberg, among others, who used as his motivation the so-called "anthropic principle"). Greene uses amusing anecdotes, relevant references to popular culture (Cartman makes what may be his scientific debut), and his own insight from years of personal experience to describe what would otherwise be completely inaccessible to anyone without a graduate degree in mean field theory. And despite being more in-depth than the recent Hawking publication, he doesn't mince words or add fluff. There's nothing wasted in that extra volume.

Nine versions of possible multiverses (multiple/parallel universes) are presented, each with appropriate historical and scientific background, as well as - gasp! - possible scientific experiments which could test for each of them (not much can be done with the current level of technology, but the future is bright and the possibilities copious). In Greene's terminology, they are: the Quilted Multiverse, Inflationary Multiverse, Brane Multiverse, Cyclic Multiverse, Landscape Multiverse, Quantum Multiverse, Holographic Multiverse, Simulated Multiverse and Ultimate Multiverse (parts a and b). Briefly - and really, you should read the book - they can be explained as follows:
  1. Quilted Multiverse: if the universe is infinite (in space), conditions will necessarily repeat across space, which yields an infinite number of parallel worlds. We wouldn't "see" these parallel universes-within-the-universe, because they'd fall outside of our cosmic horizon (the distance limit we're able to observe due to the finite speed of light). This multiverse proposal arises mainly from general relativity, which doesn't require that the universe be finite.
  2. Inflationary (or Bubble) Multiverse: with the advent of inflationary theory, with its "inflaton" field (it can essentially be thought of as an antigravity field), to describe the beginnings of our own universe, an interesting tangent arose. The inflaton field could yield different areas of inflation (due to quantum fluctuations; this is how Cartman got involved, believe it or not), each forming a "bubble" within which a universe would form.
  3. Brane Multiverse: our first true string theory contender, "branes" are higher-dimensional objects within the string theory framework. A universe like ours could exist on a three-dimensional brane (for reasons he explains, the universe is essentially "trapped" on the brane), but more branes could exist elsewhere in the multi-dimensional space which carried their own universes.
  4. Cyclic Multiverse: the "braneworlds" from the Brane Multiverse, since they can move, have the potential to collide within the larger-dimensional space. If and when they do, the universes on each are completely annihilated and begin anew. Since branes are gravitationally attracted like any massive object, they could be pulled in and collide over and over, creating many new universes.
  5. Landscape Multiverse: delving deeper into string theory and adding in inflationary theory, we find that the multiple dimensions allowed by string theory subsequently allow an entire N-dimensional "landscape" upon which an infinite number of inflationary bubble universes could form.
  6. Quantum Multiverse: this may be the most familiar of the list. It refers to the Many Worlds interpretation of quantum mechanics, which flew in the face of the historical Copenhagen interpretation. In essence, each quantum possibility (is the electron here or there?) is actually manifested in a parallel universe (in our universe, it's here, but simultaneously in a parallel universe, it's there).
  7. Holographic Multiverse: strange, cutting edge science from string theory, quantum field theory and black holes suggests that our universe may just be a mirrored or projected "image" from a distant, differently-dimensioned (2D instead of 3D?) but physically equivalent parallel universe.
  8. Simulated Multiverse: the most banal but perhaps most immediately relevant, technological growth may make it possible for entire, self-consistent, self-aware and self-propagating simulated universes to be created.
  9. Ultimate Multiverse: Part (a), if you will, is actually philosophical - the "principle of fecundity" asserts that every possible universe is a real universe (even the ones made entirely of gorgonzola or the ones made of nothing), thereby nullifying the question of why our particular universe is the one which exists. Part (b) trims this slightly by introducing a level of self-consistency, proposing that every possible mathematically consistent universe is a universe, or, more correctly, that "these universes instantiate all possible mathematical equations."
What struck me most of all, however, wasn't Greene's incredible ability to explain string theory (I almost found myself believing it... don't tell my string theorist friends!), or his encyclopedic knowledge, but his belief in the future of science. Completely contrary to the conclusions drawn by Hawking and Mlodinow in their text, which amount to "we have a bunch of piecemeal theories which describe our universe, but our universe is only one of many, and therefore we can't achieve some beautiful mathematical description of the universe and our piecemeal theories are the best we're going to do," Greene candidly admits that not only does he believe we may still discover a true Grand Unified Theory, he hopes we will.
"The breadth of multiverse proposals... might suggest a panorama of hidden realities [essentially, what Hawking/Mlodinow were suggesting]. But I've titled this book in the singular [The Hidden Reality] to reflect the unique and uniquely powerful theme that underlies them all: the capacity of mathematics to reveal secreted truths about the workings of the world. Centuries of discovery have made this abundantly evident; monumental upheavals in physics have emerged time and again from vigorously following mathematics' lead.... [The] multiverse proposals similarly rely on a belief that mathematics is tightly stitched into the fabric of reality."
However, he continues:
"Our universe is not the only one possible [if these theories are true]. Its properties could have been different.... In turn, seeking a fundamental explanation for why certain things are the way they are would be pointless....
I don't know if this is how things will turn out. No one does. But it's only through fearless engagement that we can learn our own limits. It's only through the rational pursuit of theories, even those that whisk us into strange and unfamiliar domains, that we stand a chance of revealing the expanse of reality."
Lastly, on a bit of a schadenfreude note, I wished to make a point about philosophy. Unlike Hawking and Mlodinow, who seem to believe that philosophy is dead, Greene takes a far more reasonable standpoint. During a philosophy course as a freshman at Harvard, he was challenged by his professor: "Let's say you find the unified theory," he said. "Would that really provide the answers you're looking for?" The answer is, of course, no. The philosophy professor was right, and Greene knew it. It was this encounter which prompted Greene to consider the concept of the Ultimate Multiverse - proving, it would seem, that instead of philosophy being dead, it is alive and well and helping to push forward the frontiers of science.

And one last poke, at those Dawkins-ites:
"I understand well the impulse to tether scientific investigations to those propositions that can be tested now, or in the near future; this is, after all, how we built the scientific edifice. But I find it parochial to bound our thinking by the arbitrary limits imposed by where we are, when we are, and who we are. Reality transcends these limits, so it's to be expected that sooner or later the search for deep truths will too.... Sometimes [science] challenges us to reexamine our views of science itself."


  1. Thanks for the review and meditation. I'd agree that sheer speculation is an important and sometimes fruitful endeavor.

    But on the other hand, we shouldn't give it more credence than it deserves. From what I understand, mathematics is a matter of human invention. We can invent all sorts of axioms and mathematical systems, and whether any of them match up to reality is a matter for empiricism to sort out.

    Mathematics presents us with (hopefully) consistent systems built upon the axioms du jour. Many of these axioms are obviously true to nature, and thus the mathematics can be rigorously descriptive. But that can not be guaranteed beforehand.

    So the possibility of these various multiverses being consistent with various mathematical systems certainly helps their credibility, the other option being that even given non-empirical axioms, they are internally inconsistent. But as the many options indicate, this fails to tell us anything certain before the reality of the premises and conditions has been worked out.

    It would be great, for instance, if string theory obtained some specific empirical support, over its competitors. From what I read, the chances of that are mixed in the foreseeable future. Is that fair to say?

  2. Burk, you're right in saying that (for instance) string theory's experimental future is mixed. But reading Greene's explanations gives me hope that there are ways we can test these theories in the future - independent parallel universes can, surprisingly, leave tell-tale marks on one another.

  3. Thanks for the great review, Kelly!

    I like Greene's perspective on (was it Colbert or Terri Gross?) when he said something like, "It is worthwhile to pursue mathematical thinking here, because it is our best tool to understand reality and make educated guesses about it [then he gives numerous examples]. But if our mathematics does not correspond to reality....then all bets are off!"

  4. An interesting and related post can be found over on NPR's science blog 13.7: link here (they agree with my assessment that philosophy is hardly dead!). "Hard problems sometimes have simple solutions. But no service is rendered when smart people pretend that hard problems are simple."

  5. Sorry - note that the aforementioned link is related to Hawking and Mlodinow's new book (which I mention in this post as well as the previous one), not Greene's.

  6. I have some doubt as to whether multiverse theory can be true. Scientists say that total energy of the universe is zero. If total energy is zero then total mass will also be zero due to mass-energy equivalence. Scientists have also shown that anything having mass will always occupy some space. So anything that fails to occupy any space cannot have any mass. Our universe perhaps fails to occupy any space, and that is why its mass is zero. But if multiverse theory is true, then our universe will definitely occupy some space within the multiverse, and thus in that case its mass cannot be zero. But as this mass is zero, therefore multiverse theory cannot be true.

    Here it may be argued that radiation occupies space but its mass is zero. So here is an example that something occupying space can still be without mass. So our universe can also be without mass even if it occupies some space within the multiverse. In reply we will say that the example cited here is a bad example, because our universe is not any kind of radiation. So if it is without mass, then that can only be due to its not occupying any space, and not due to its being some sort of radiation.

    However, if total energy of the universe cannot be taken to be zero, then the conclusion drawn here will not stand.

  7. Uchitrakar, thanks for the comment. I think we have to be careful in dismissing multiverse theories so quickly - if they were impossible due to some very rudimentary law of thermodynamics, then they would not have been pursued scientifically.

    Take, for instance, the statement that if total energy is zero, then total mass must be zero, by energy-mass equivalence. But doesn't this ignore that it's the total that has to be zero? You can (and I believe this is the case in a few current cosmological theories, such as Hawking's) have positive mass which is balanced by negative energy, making the sum zero (and without invoking radiation). This also assumes that the sum needs to be zero, which isn't necessarily true (it depends on your model of the universe). And if the universe is static - in other words, if it has zero sum energy-mass - then it can take up as much volume (space) as it wants without requiring more energy to be input. This would be equally true in a single universe or a multiverse.

    So just because Hawking and Greene don't agree doesn't mean one is right and the other wrong (and especially when we don't yet have enough empirical evidence to say which hypothesis is more likely). Nor should we dismiss either of them out-of-hand.

  8. Multiverse theories are persued scientifically mostly because with these theories fine-tuning of certain parameters can be easily explained away without invoking any kind of God. But there are others (Peter Woit is one of them) whose opinion is that multiverse theories are not proper science, but pseudo-science.

  9. U, another good point. Some people would argue that, in fact, the whole of cosmology is simply pseudoscience (or, more kindly, philosophy). It certainly isn't a scientific field in the same way atomic physics or organic chemistry or even sociology is - we can't run test experiments of the universe beginning. (Incidentally, it appears that Woit agrees with my earlier assessment of Hawking's newest book!)

    As for multiverse theories being pursued merely because they do not invoke God, I'd beg to differ. The idea of infinite universes or infinite dimensions is something that comes up quite often, without religious context. Certainly one version of the multiverse is a direct consequence of the mathematics of quantum mechanics. But it needn't be that difficult. As a fifteen-year-old student, I approached my physics teacher with what I felt was a totally novel one-page discussion of infinite dimensions; he replied by saying, "congrats, you've independently re-derived the hypersphere."

  10. Gravity is the force by means of which any two masses in the universe attract each other. Gravity operating on mass cannot have any effect on light, light being pure energy. But still we know that gravity can bend light (experimentally verified). Why? This is because light being energy it will have certain corresponding equivalent mass, and due to this equivalent mass of light energy gravity can bend light. If total energy of the universe is taken to be zero, then its corresponding equivalent mass can only be zero, it cannot have any other value. So for a zero-energy universe multiverse theory will always be false. Therefore
    1)Either total energy of the universe is not zero, in which case multiverse theory may be true, but we cannot say whether it will be necessarily true. But in that case scientists will also have to stop saying that universes can, and will, originate spontaneously from nothing.
    2) Or total energy of the universe is zero, in which case multiverse theory will definitely be false, and scientists will have to find a suitable explanation for fine-tuning of certain parameters.

    We cannot eat both ends of the cake at the same time unless we bend it suitably to our own advantage.

  11. I feel like we're getting a bit off-track. Let me explain why.

    Gravity operating on mass cannot have any effect on light, light being pure energy.
    This isn't true - according to general relativity, gravity is the curvature of spacetime. Anything - massless or otherwise - traveling along a path in curved spacetime will experience a corresponding curvature of its own motion. In general relativity, mass is what causes this spacetime curvature (the common image is akin to a bowling ball on a trampoline), and light (even though photons are massless) will travel curved paths along this warped spacetime by necessity. It's not because light has an "effective mass" that is subject to gravitation, it's because gravitation is the curvature of spacetime itself, which by default has to affect the objects moving through it.

    If total energy of the universe is taken to be zero, then its corresponding equivalent mass can only be zero, it cannot have any other value.
    I mentioned this already - this is also not the case. For a zero-energy (flat) universe, it is the sum of mass and energy that is zero. Mass and energy are only equivalent insofar as they can be converted from one to the other - this isn't at all the same as saying that, because total energy is zero, total mass must be as well.

    So for a zero-energy universe multiverse theory will always be false.
    Again, this doesn't necessarily follow. A flat universe could exist within a multiverse.

    Either total energy of the universe is not zero, in which case multiverse theory may be true, but we cannot say whether it will be necessarily true. But in that case scientists will also have to stop saying that universes can, and will, originate spontaneously from nothing.
    Of course we can't say yet whether it is necessarily true, but this is hardly a reason to stop looking into it as a theory. Additionally, if one universe can "originate spontaneously from nothing," then any number can. It's not exclusive to a universe or multiverse, and there is nothing to suggest that it needn't be the case for either.

    Or total energy of the universe is zero, in which case multiverse theory will definitely be false, and scientists will have to find a suitable explanation for fine-tuning of certain parameters.
    Again, just because the universe is flat doesn't mean it's singular. Nor does it matter - scientists are still looking for a grand unified theory to explain why our universe (regardless of other universes) exists the way it does.

    Basically, as I said previously, both theories (GUT of a single universe or a multiverse of some kind) are, at the moment, (essentially) equally valid. We need more observational and experimental evidence to say anything about either hypothesis - neither can be dismissed through hand-waving. One goes off-track by trying to use one hypothesis to nullify the other, when either are equally valid (or, as is the case here, when one uses small pieces of one or the other theory, and not the entire coherent theory).
    The point of science is not to try and "eat from both ends of the cake." We're coming up with ideas, testing them for self-coherence (is it internally consistent?) and testing them against empirical evidence. Only after this can we really say anything about which of several hypotheses might be more valid or effective.

  12. If one electron and one positron meet, then both of them are annihilated, and we get two photons (pure energy) in place of them. Here total mass of electron and positron is converted into energy. As mass can be converted into energy, so similarly energy can also be converted into mass. If two particles can be collided with each other at very very high speed, then after collision it will be found that new particles have appeared. Here very high kinetic energy of the two particles has been converted into particle mass. Now how has Stephen Hawking arrived at the zero value of the total energy of the universe? Matter is having mass, and this mass can be converted into its equivalent energy. This matter energy is treated as positive energy, and gravitational energy is treated as negative energy. Positive matter energy and negative gravitational energy cancel each other, and we get zero value for the total energy of the universe. Now suppose instead of converting mass into energy we convert energy into mass. Then what will happen? Gravitational energy will be converted into its equivalent mass, and this mass will be treated as negative mass. This negative gravitational mass and positive matter mass will cancel each other and total mass of the universe will be zero. So I cannot understand why you do raise objection when I write that if total energy of the universe is zero, then its total mass will also be zero. Total mass of the universe being zero it cannot occupy any space, and in that case multiverse theory will be false.

  13. If positive matter energy of the universe is exactly equal to its negative gravitational energy, then there is no reason as to why positive matter mass of the universe cannot be exactly equal to its negative gravitational mass. If the first one is true, then the other one will also be true. So if total energy of the universe is zero, then its total mass will also be zero.

  14. Ok... as I said, and as you describe initially when discussing electron-positron annihilation, in physics, mass and energy are only equivalent, not identical. Thus, statements like "[g]ravitational energy will be converted into its equivalent mass, and this mass will be treated as negative mass" are physically meaningless (a case of philosophy misrepresenting a scientific idea). There is, first of all, no reason to argue for a 'gravitationally equivalent mass' because mass creates the curved spacetime which is, in practice, gravity (so it's like over-defining something); nor is there any rule which would state that it is negative. You can't really have negative mass. It's a physically meaningless concept. The opposite of mass is not negative mass. Antiparticles have mass. Like in a simple system such as a weight on a spring, the opposite of the weight's kinetic energy isn't negative kinetic energy. The opposite of kinetic energy is potential energy, and their sum is always the same. If you say the total mass of the universe is zero, it would mean the universe is devoid of energy. At worst, to say that "because the total energy is zero, the total mass is zero" is philosophically equivalent to saying that "because 1=1, 1=1." It's a meaningless statement.

    Again, however, this assumes that you need a flat universe. Which depends on your model. And the flat-universe model isn't any better or worse than the open- or closed-universe model, or the multiverse model. I've explained this already.

    And as I've also already explained, the argument that "[t]otal mass of the universe being zero it cannot occupy any space" is false. Even if the universe is flat, it can take up as much volume as it wants.

    Lastly, again as I've mentioned before, a multiverse can exist regardless of whether the universe we happen to find ourselves in is open, closed or flat. The particulars of one universe would not dictate the general parameters of the multiverse, just as the personality of one human being doesn't create the rule for all human personality.

    I suggest reading up on the underlying physics before spending too much time arguing the semantics: zero energy universe, zero-point energy, mass-energy equivalence, multiverses, etc.

  15. To sum up the key points:

    Zero-energy universes can have any volume.

    Zero-energy universes are only one of several theoretical universes, and are not yet verified or required by empirical evidence.

    The multiverse could exist regardless of the state (open, closed, flat) of any individual universe within it.

    Lastly, the nature of our Universe may be a question open to both philosophical and scientific debate, but I feel it is a detriment to both philosophy and science to use cherry-picked pieces of scientific hypotheses as philosophical justifications.

  16. I have never written that multiverse theory can never be true. I have only written that for a zero-energy umiverse this theory cannot be true. That is all. And so, we should end our debate here, because I think it is quite unnecessary to prolong it any further.

  17. Uchitrakar, I didn't intend to argue whether the multiverse is real (we don't know), or whether you said "could" or "would," and if that's the impression I gave then I apologize. My hope was to point out where your premise (that a zero-energy universe excludes the possibility of a multiverse) is potentially incorrect. For instance, some multiverse theories arise strictly from quantum mechanics, and thus cosmology (and the total energy of the universe) don't even come into play. The very definition of "space" (or volume) in these cases is totally different to what we mean by "space" within the observable universe. Thus the idea that (net) mass has to take up space has no bearing.

    In any case, I don't feel that Stephen Hawking (who has been wrong many times in the past) should be held in any higher regard than any other scientist who works honestly and thoroughly on the problem of the nature of the universe.

  18. By repeatedly saying that total energy of the universe has always remained fixed at zero value, scientists have expressed one deep and profound truth, and perhaps they are not aware of it. It is that nothing can come from nothing, and that something can come from something only. That is why not an iota of extra energy has been added afterwards to the universe from any outside source, and its total energy has always remained fixed to the initial zero value. If scientists do not accept my analysis as correct here, then they will have to answer the following questions: What explanation will they give for the fact that total energy of the universe throughout remained zero? What were the constraints that prevented any energy from being added to it from nowhere, or, from nothing? If something can really come from nothing, then we do not find any reason as to why its total energy did not increase by any swelling amount at any time, because that energy could have simply appeared from nothing. But in reality we find nothing of the sort, and the total energy of the universe always remained fixed at zero. So, if scientists fail to give any satisfactory answer to the above two questions, then I will presume that my analysis here is correct that nothing can actually come from nothing, and that only something can give birth to something. Keeping these in mind I will proceed further.

    If the universe has originated from a source having zero energy, zero mass, zero space and zero time, then we can draw the following conclusions:
    1) Sum total energy of the universe will always remain fixed at zero value,
    2) Sum total mass of the universe will always remain fixed at zero value,
    3) Sum total space of the universe will always remain fixed at zero value, and
    4) Sum total time of the universe will always remain fixed at zero value.
    The first conclusion above does not mean that there will be no energy within the universe. There will be all forms of energy that we can conceive of, but sum total of all these energies will always be zero, and in consequence universe as a whole will always have zero energy. Similarly the third conclusion above will not mean that there will be no space within the universe. Universe will definitely have space within it, but sum total of all this space will always be zero, and in consequence universe as a whole will have zero space. Universe will have zero space means it will have no space for it to occupy. But if universe fails to occupy any space, then multiverse theory cannot be true, because in case multiverse theory is true, then the universe will definitely occupy some space within the multiverse.

    Multiverse theory may be true in case our universe has originated from a source having non-zero value of space. But the source having non-zero value of space cannot be called a “nothing”.

    If nothing can come from nothing, and if multiverse theory is also true, then in that case scientists will have to explain whence the extra space of the multiverse has originated.

  19. Many scientists think that they have successfully demonstrated that something can appear from nothing. But actually they have demonstrated just the opposite, that nothing can appear from nothing. No energy has appeared from nothing. What energy was there at the beginning was at the end also, no energy has been added in between. That nothing can really come from nothing may have some very disturbing implications also. One such possible implication is that if the universe has originated from a source having no life, mind and consciousness, then no life, mind and consciousness can appear anywhere in the universe.

  20. I think a valid answer to your first question (What explanation will they give for the fact that total energy of the universe throughout remained zero?) is simply to say that perhaps the total energy of the universe isn't zero. As I mentioned before, this conclusion depends on your model, and there are several competing models. We just don't know if the total energy of the universe is zero (or not). The fact that we don't know which model is closer to reality also means we don't know the answer to the second question (What were the constraints that prevented any energy from being added to it from nowhere, or, from nothing?). All of your arguments which proceed from the aforementioned premises are therefore valid only within the model you have chosen, and cannot (because they are model-specific) negate any other model.

  21. Quote: I think a valid answer to your first question (What explanation will they give for the fact that total energy of the universe throughout remained zero?) is simply to say that perhaps the total energy of the universe isn't zero.

    But I think you will fail to convince any modern cosmologist by saying that total energy of the universe is not zero. They will simply refuse to believe that this energy is not zero. It is their pet theory that total energy of the universe being zero, it can simply originate from nothing, and so no God is necessary for creating the universe. And I think that there is reason to believe that they are correct. Please remember the first law of thermodynamics that states that energy can neither be created nor destroyed, but that it can be transformed from one form of energy to another form. Therefore if the universe has started its life with zero energy input, then its total energy afterwards will also remain constant at its initial zero value, because no new energy can be created that can be added to its initial input.

  22. I agree that "most" cosmologists tend to believe the universe has zero sum energy (at least, the most vocal cosmologists), but that 1) doesn't discount theories which involve non-zero energy, and 2) doesn't discount multiverse theory, either, as I've mentioned several times.
    In addition, true scientific hypotheses should have nothing to do with God or the miraculous (either for or against), so to believe the zero-energy universe hypothesis is correct merely because one doesn't want to believe in a god or creation is, to be blunt, totally unscientific (Hawking may be a brilliant man, but he has a rather poor track record as a philosopher).
    If the evidence from observation eventually weighs too heavy in favor of the zero-energy hypothesis, then we will adopt it as a scientific theory; until then (and even after), we can't discount other hypotheses. Which was, I think, the entire point of Greene's book.

  23. It has become almost a trend among some scientists that they are more eager to prove that God does not exist than to find out how the universe has actually originated. It is heartening to know that you are against this trend.

  24. Uchitrakar, I'm pretty sure that true spirituality and true science are both driven by the same human desires (just as adherence to dogma, in either spirituality or science, is also driven by the same human emotions). Anyone willing to trade one dogma for another isn't being truly scientific, or truly spiritual. And I'm also pretty sure that Hawking won't be the one to have the last word in the cosmology debate... there's still too much we don't know!


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