Steven Weinberg discusses the mysteries of physics

A common misconception is that the major problems of physics have mostly been solved, and all that’s left is some minor sweeping-up.  I doubt that the readers here would agree, for huge surprises and mysteries continue to surface in physics. In a new piece in the New York Review of Books,Physics: What we do and don’t know” (free download), Nobel Laureate Steve Weinberg discusses these puzzles, which occur on scales both large and small.

I found a bit of the piece tough going, as if Weinberg were writing for professionals instead of science-friendly and educated people. I had trouble with this, for example:

Speculations of this sort ran into an obvious difficulty: photons have no mass, while any new particles such as W+, W-, and Z0 would have to be very heavy, or they would have been discovered decades earlier—the heavier the particle, the higher the energy needed to create it in a particle accelerator, and the more expensive the accelerator. There was also the stubborn problem of infinities. The solution lay in an idea known as broken symmetry, which had been developed and successfully applied in other areas of particle physics since 1960. The equations of a theory may possess certain simplicities, such as relations among the photon, W+, W-, and Z0, which are not present in the solutions of the equations that describe what we actually observe. In the electroweak theory there is an exact symmetry between weak and electromagnetic forces, which would make the W+, W-, and Z0 massless, if it were not that the symmetry is broken by four proposed “scalar” fields that permeate the universe, from which the W+, W-, and Z0as well as the electron get masses. A new particle discovered last year appears to be the predicted quantum of one of these scalar fields.

But the bulk of the piece is a very nice summary of what we do and don’t know, and I recommend it warmly.  Here are some of the mysteries, with Weinberg’s take indented:

1. What is dark matter?

It turns out that particles already known to us are not enough to account for the mass of the hot matter in which the sound waves must have propagated. Fully five sixths of the matter of the universe would have to be some kind of “dark matter,” which does not emit or absorb light. The existence of this much dark matter in the present universe had already been inferred from the fact that clusters of galaxies hold together gravitationally, despite the high random speeds of the galaxies in the clusters. So this is a great puzzle: What is the dark matter? Theories abound, and attempts are underway to catch ambient dark matter particles or remnants of their annihilation in detectors on Earth or to create dark matter in accelerators. But so far dark matter has not been found, and no one knows what it is.

2. What is dark energy?

In 1998, using the apparent brightness of exploding stars to measure the distance of far galaxies, two groups of astronomers found that the expansion of the universe is not slowing down at all, but rather speeding up. Within the rules of the general theory of relativity, this could only be explained by an energy that is not contained in the masses of any sort of particles, dark or otherwise, but in a “dark energy” inherent in space itself, which produces a sort of antigravity pushing the galaxies apart.

From these measurements, and also from studies of the effect of the expansion of the universe on the cosmic radiation background, it has been found that the dark energy now makes up about three quarters of the total energy of the universe.

3. How does gravity fit into the “theory of everything”? Weinberg got his Nobel (along with Abdus Salam and Sheldon Glashow) for unifying the electromagnetic and weak forces. But one “force” has so far defied unification.

Even so, the standard model is clearly not the final theory. Its equations involve a score of numbers, like the masses of quarks, that have to be taken from experiment without our understanding why they are what they are. If the standard model were the whole story, it would require neutrinos to have zero mass, while in fact their masses are merely very small, less than a millionth the mass of an electron. Further, the standard model does not include the longest-known and most familiar force, the force of gravitation. We commonly describe gravitation using a field theory, the general theory of relativity, but this is not a quantum field theory in which infinities cancel as they do in the standard model.

4. Is string theory right?

Since the 1980s a tremendous amount of mathematically sophisticated work has been devoted to the development of a quantum theory whose fundamental ingredients are not particles or fields but tiny strings, whose various modes of vibration we observe as the various kinds of elementary particle. One of these modes corresponds to the graviton, the quantum of the gravitational field. String theory if true would not invalidate field theories like the standard model or general relativity; they would just be demoted to “effective field theories,” approximations valid at the scales of distance and energy that we have been able to explore.

String theory is attractive because it incorporates gravitation, it contains no infinities, and its structure is tightly constrained by conditions of mathematical consistency, so apparently there is just one string theory. Unfortunately, although we do not yet know the exact underlying equations of string theory, there are reasons to believe that whatever these equations are, they have a vast number of solutions. I have been a fan of string theory, but it is disappointing that no one so far has succeeded in finding a solution that corresponds to the world we observe.

String theory, combined with the idea of cosmic inflation, leads naturally to the concept of multiverses, “pocket universes” in which the laws of physics would differ from those of our own universe. This possibility, if confirmed, would finally dispel the persistent theological argument for the “strong anthropic principle”: the idea that the laws of physics were designed by God to make possible sentient life that could apprehend and worship Him (i.e. humans). To my mind, that argument is the last redoubt of a natural theology that’s been eroded to virtually nothing by science.

Unfortunately, multiverses may well be impossible to observe, even though they fall naturally out of existing theories of physics. Some physicists, like Paul Davies, claim that multiverses were concocted by physicists solely to dispel the idea of God, but they’re dead wrong. It’s a serious idea that’s been around for a while.

5. Are there multiverses?

Inflation is naturally chaotic. Bubbles form in the expanding universe, each developing into a big or small bang, perhaps each with different values for what we usually call the constants of nature. The inhabitants (if any) of one bubble cannot observe other bubbles, so to them their bubble appears as the whole universe. The whole assembly of all these universes has come to be called the “multiverse.”

These bubbles may realize all the different solutions of the equations of string theory. If this is true, then the hope of finding a rational explanation for the precise values of quark masses and other constants of the standard model that we observe in our big bang is doomed, for their values would be an accident of the particular part of the multiverse in which we live. We would have to content ourselves with a crude anthropic explanation for some aspects of the universe we see: any beings like ourselves that are capable of studying the universe must be in a part of the universe in which the constants of nature allow the evolution of life and intelligence. Man may indeed be the measure of all things, though not quite in the sense intended by Protagoras.

What better way to spend a lazy Sunday than contemplating the mysteries of the cosmos?

Here’s a picture I took of Steve and Alex Rosenberg at the “Moving Naturalism Forward” meeting about a year ago:

Steve and Alex

59 Comments

  1. gbjames
    Posted October 20, 2013 at 6:48 am | Permalink

    sub

  2. Mobius
    Posted October 20, 2013 at 7:19 am | Permalink

    Thank you Jerry for bringing this article to my attention. I look forward to reading it later when I have time to sit and contemplate what Steven Weinberg is saying.

  3. Kevin
    Posted October 20, 2013 at 7:21 am | Permalink

    Steven Weinberg is one of my heros for all time.

    Someone can correct me, but I am pretty sure you do not need string theory and cosmic inflation for the concept of multiverses. Quantum field theory, the formal theory for which Weinberg played an integral part in refining, and cosmic inflation are, at minimum, needed to support the concept of multiverses.

    • Posted October 20, 2013 at 8:10 am | Permalink

      I can agree with that, and I hope I understand this correctly. Applying string theory to the multiverse is one of the strikes against fine tuning. There are other arguments against fine tuning, but the string theory argument means that different bubble universes must come out with discrete sets of physical constants due to there being a finite set of possible modes of string vibrations.

    • Michael Fisher
      Posted October 20, 2013 at 8:21 am | Permalink

      But tough to answer that one! Brian Greene the string theorist lists nine types of multiverse.

      Looking at his list I note that they aren’t all mutually exclusive. For example if the Many Worlds Interpretation [MWI] of quantum theory is *true* & *real* [whatever that might mean], then every event instantiates every possible outcome of that event as a new universe. I assume that if the MWI is *real* [not just a mathematical abstraction] it doesn’t preclude that we are also on a Brane or in one bubble of a foam of multiverses or in an infinite single universe containing inflationary bubbles.

      Going for a lie down now…

      • Kevin
        Posted October 20, 2013 at 8:33 am | Permalink

        I did not think of it like that. Basic QM+cosmic inflation can get multiverses, but it does not preclude string theory.

        Sort of like I can design a bridge with F=ma, but at ~1 part in 100000000, special relatively says my equation is no longer correct for all those motional live loads.

    • Diana MacPherson
      Posted October 20, 2013 at 8:26 am | Permalink

      I think (albeit oversimplified) if you have inflation, you theoretically have multiverses.

      I always find this stuff interesting but at the same time, I feel like I’m just on the periphery of understanding it.

      • Richard Bond
        Posted October 20, 2013 at 10:23 am | Permalink

        You are right, at least as far as recent theory goes. Alan Guth in chapters 11-15 of “The Inflationary Universe” describes how it was initally assumed that inflation would end as bubbles of inflation coelasced to a single universe. Then Andre Linde showed that they would remain as separate universes

    • Alex
      Posted October 20, 2013 at 8:46 am | Permalink

      That’s probably true, but String theory gives you an explicit framework that describes why fundamental constants and so on would differ between Sub- Universes in the Multiverse and what the mechanism for that is. You can construct ordinary 4D field theories which have different vacuum states with different laws of physics (in fact the Standard model seems to have two), but such a rich structure is automatically part of superstring theory because there are so many different ways to go from a simple theory in the full 10 Dimensions to a complicated one in our observed four dimensions.

    • Torbjörn Larsson, OM
      Posted October 20, 2013 at 10:27 am | Permalink

      That is correct. Susskind’s cosmology lectures on youtube covers that somewhat. As a local spacetime traverses the inflationary regime quantum fluctuations makes a lot of effects including volumes that stops inflating before others.

      Unless other physics appears, you are naturally left with eternal inflation: fluctuations makes enough spacetime remain inflating to source local universes indefinitely.

      The difference is that, again without new physics, those universes have the same laws. They would have (immeasurable, I think) deviations from flatness in curvature though, since the wrinkles in the original lifetime would be different and they would have inflated for different periods.

  4. Kurt Helf
    Posted October 20, 2013 at 7:41 am | Permalink

    So, it seems to me then, the answer to the oft-repeated question from d-g botherers: “Where did the rules [governing nature and the universe] come from?” can be answered by #5 above: it is one realization of a solution to the equations of string theory and an accident of our particular part of the multiverse.

    • Diana MacPherson
      Posted October 20, 2013 at 8:20 am | Permalink

      Yeah, I find it fascinating that our universe could have formed from another universe and so on. I’m sad that we probably won’t be able to observe this directly given that multi verses are causally disconnected.

      • Torbjörn Larsson, OM
        Posted October 20, 2013 at 10:35 am | Permalink

        Mind that they are not causally disconnected in all variants of inflation. For some parameter sets universes appearing out of it can collide, and that would leave imprints. Speculative, but not yet excluded. [Ref: gravityfly's comment links to some such speculations.]

    • Alex
      Posted October 20, 2013 at 8:58 am | Permalink

      Its a speculative explanation, but of course much better than theirs: it wasnt invented to explain the apparent tuning of our universe for the ability to containcomplex structures such as life, but was discovered when trying to quantize gravity. Secondly, it is a very concrete, relatively well defined proposal and exceedingly simple compared to the problem it addresses. This is even more true for many worlds quantum mechanics, which is arguably simpler than the copenhagen interpretation.

      • Alex
        Posted October 20, 2013 at 9:07 am | Permalink

        I forgot one – the proposal is in principle testable in the lab and we know how one would go about it, with mainly (albeit incredibly huge) technological barriers. Compared to this level of clarity and simplicity and philosophically scientific quality, the god solution is a nonsensical contradolictory mess.

  5. Timothy Hughbanks
    Posted October 20, 2013 at 8:10 am | Permalink

    This possibility, if confirmed, would finally dispel the persistent theological argument for the “strong anthropic principle”

    I very much doubt that! You have forgotten Twain’s principle: You can’t reason someone out of a position they weren’t reasoned into in the first place.

    • Posted October 20, 2013 at 11:06 am | Permalink

      Reminds me of a sign at a local church which I think was meant to be a comment about the economy: “Stupidity got us into this mess, why can’t it get us out?”

      • gbjames
        Posted October 20, 2013 at 11:14 am | Permalink

        I’d suggest an alternate version:

        “Stupidity got us into this mess, can irony get us out?”

      • Posted October 20, 2013 at 3:41 pm | Permalink

        Faith got us into this mess… 

        /@

        • Posted October 20, 2013 at 8:36 pm | Permalink

          Isn’t that what Mark wrote?

          b&

        • Diane G.
          Posted October 22, 2013 at 12:26 am | Permalink

          I think the original is just fine. :)

  6. Posted October 20, 2013 at 8:19 am | Permalink

    That’s an excellent summary of the boundaries of today’s understanding of the universe.

    It’s probably equally important, though, to simultaneously observe that the interior of those boundaries is overwhelmingly well mapped: the laws underlying the physics of everyday life are completely understood.

    Cheers,

    b&

    • Kevin
      Posted October 20, 2013 at 8:37 am | Permalink

      Great link to Carroll’s article. I have read it many times and wish that everyone in America would read it.

    • Torbjörn Larsson, OM
      Posted October 20, 2013 at 10:18 am | Permalink

      I was going to mention that article, since it is reflects another common misconception of having science for ever fluid and since Carroll points out that remaining physics is not affecting us today. The background of energies beyond the standard model – drifting black holes, high energy cosmic ray interaction and DM interaction (if any) – is too sparse.

      Also, we should celebrate the LHC closure of (enough of) the standard particle model!

      Speaking of LHC, to Weinberg’s dated list I would add its recent physics. The, presumably standard, Higgs mass has left us with two possible conundrums:

      - The standard model seems to be unnatural in the sense that Weinberg’s effective theories naturally lead into new physics above their energy scale. But LHC has trouble finding any.

      - With the Higgs mass we may live in a quasistable vacuum with a lifetime from anywhere between ~ 1 billion years up to ~ 10^20 years. Still a 98 % signal, and unfortunately LHC may not suffice to decide either way.

      • Torbjörn Larsson, OM
        Posted October 20, 2013 at 10:44 am | Permalink

        Oops. That was _remaining_ lifetime – or the 1 Ga figure would be tough to square with observations!

      • Alex
        Posted October 20, 2013 at 1:06 pm | Permalink

        Yes, it hinges mostly on knowing he precise value of the mass of the top quark, and to a lesser extent of the Higgs boson. There is a good chance that the japanese will build the linear collider which will achieve both to great accuracy, 10 or 20 times better than current errors.

        But, as you know, the whole conclusion about the metastability of the Higgs field is only really meaningful if there is NO significant new physics for at least 9 orders of magnitude in mass above the heaviest known particles… Supersymmetry for example, or even much simpler extensions of the Higgs model, would change the conclusion completely

  7. Kevin
    Posted October 20, 2013 at 8:24 am | Permalink

    Some predictions on solutions:

    Dark matter/Dark Energy:
    Observational astronomy will continue to help quantify the effects of DM/DE. There is a very small possibility that observations will solve these problems, i.e., phenomenological interpretations will reveal explanations which are consistent with our present, known laws of physics, without the need for new particles or fields (DM/DE works itself out). It is more likely theory or innovative experiments on earth will provide the insight into these rather disparate cosmological effects, DM and DE, respectively. Advanced in DE are more likely to come from theory, i.e., vacuum fluctuations and energy density, etc. Advances in DM may come from anywhere: bound massive neutrinos, WIMP searches on earth and in space, GUT fields (I will explain below), etc.

    GUT (gravity and “theory of everything”):
    No idea, however Tony Leggett and Phil Anderson, condensed matter theorists have always been interesting in how far, spatially and temporally, quantum entanglement can persist. One suggestion is that coherence in quantum systems might be limited to by mass, or gravitational fields…this may introduce us to a way to quantify GUT fields. I would not be surprised if areas of research that explore the limits of quantum coherence, entanglement, and teleportation would ultimately show a measurable connection between gravity and quantum mechanics.

    String Theory:
    Without observable predictions, string theory is just elegant mathematics based on quantum field theory. There are and have been proposals in the past, e.g., modification to Casimir or gravity at short distances. One of string theories best predictive areas should be DM searches. If they can propose theories that explain dark matter observations then that would help their credibility.

    Multiverses:
    This one is potentially very difficult. Comes down to ultimately devising a theory that predicts our universe is the way it is and requires the existence of other universes past, present, or future. Otherwise multiverse = agnostic physics.

  8. gravityfly
    Posted October 20, 2013 at 9:23 am | Permalink

    Apparently, we already have the first evidence that our universe possibly collided with another one in the first few moments after the Big Bang.

    It has to do with uneven temperature fluctuations in the CMB picked up by the Planck satellite

    http://www.simonsfoundation.org/features/science-news/in-lopsided-map-of-the-cosmos-a-glimmer-of-its-origins/

    • Torbjörn Larsson, OM
      Posted October 20, 2013 at 10:40 am | Permalink

      A simpler prediction is out of statistics, a fluke:

      “Some cosmologists chalk it up to a statistical fluke. The odds that quantum fluctuations at the birth of the universe could have randomly generated the observed asymmetry are between 0.1 and 1 percent — about the same as a repeatedly tossed coin coming up heads eight times in a row.

      “If I were to bet and the odds were even money, I’d bet it was just a fluke,” said Sean Carroll, a cosmologist at the California Institute of Technology. “But the point is that the odds are not even money. If it is telling us something about the early universe, it could be extremely important.””

      Mind that WMAP rejected all of this, and I think that’s where the consensus still is. AFAIK the variants of physics that tries to predict the asymmetry all have problems in one way or another, which while not conclusive makes me think that statistics is the robust answer.

      Of course, it is *easier* to live with such statistics if our universe is an actual pick from a larger set of events…

      • gravityfly
        Posted October 20, 2013 at 4:12 pm | Permalink

        “Of course, it is *easier* to live with such statistics if our universe is an actual pick from a larger set of events…”

        I agree.

  9. Lianne Byram
    Posted October 20, 2013 at 10:38 am | Permalink

    Great article;fascinating subject. I found this interview with Frank Wilczek really helpful in understanding some of the concepts that Steven Weinberg writes about (including things discussed in the troublesome paragraph mentioned above):

    http://podbay.fm/show/210064273/e/1230049260?autostart=1

    I find physics and cosmology really challenging subjects to understand, but I really enjoy making the attempt.

    • Jesper Both Pedersen
      Posted October 20, 2013 at 12:48 pm | Permalink

      I find physics and cosmology really challenging subjects to understand, but I really enjoy making the attempt.

      That makes two of us. There’s nothing more exhilarating than an armchair trip into space and back again, when time permits. :-)

    • Diana MacPherson
      Posted October 20, 2013 at 2:00 pm | Permalink

      Yeah me too. I always think I don’t know what I’m talking about but then realize I learned something….it just takes longer than with some other things.

  10. Steven Obrebski
    Posted October 20, 2013 at 11:42 am | Permalink

    I recently saw (can’t remember where), a
    cartoon where a science reporter is
    asked why esoteric and expensive particle accelerators are worth supporting and the response is that it might lead to useful applications of the science, etc etc. In
    the next panel a physicist is asked why this expense is necessary and the physicist, an unshaven man with frizzy hair hair, mouth wide open, eyes protruding cries out : “BECAUSE ITS F#&KING AWSOME!”. And that is my attitude about the subject, stimulated
    by reading Sean Carrol’s recent book about the Higgs Boson titled “The Particle at the End of the Universe”, written for the general reader. It was, for me, nevertheless hard going but compelling and I was at one point able to regurgitate a reasonable (I hope)
    version of the significance of the Higgs boson and the Higgs field to a friend. I am back in the book, making marginal notes to try to remember all the particles and their properties, etc. I remember being
    similarly challenged reading Sean B. Carroll,
    Jennifer Grenier and Scott D. Weatherbee, “From DNA to Diversity” and marvelling at the
    f$%king awsomeness of the findings of developmental genetics. We live in interesting times indeed!

  11. Stephen Barnard
    Posted October 20, 2013 at 1:08 pm | Permalink

    Weinberg is the clearest thinker in the realm of physics I know of. At the risk of offending Jerry, I suggest that Weinberg’s acknowledgement of how much we don’t know about physics casts doubt on the denial of free will based on physical determinism.

    • Posted October 20, 2013 at 1:12 pm | Permalink

      Well, at the Moving Naturalism Forward conference, Weinberg professed straight determinism on a macro scale and said, as I recall, that quantum indeterminacy is not a basis for free will. That said, he still said he had free will because he could just feel it when he made a decision. I submit (even though he’s a Nobelist and I’m a schlub) that that is not a good reason to accept free will.

      But true libertarian free will requires not just determinism, but the rejection of materialism altogether, and I doubt Steve would accept that!

      • Stephen Barnard
        Posted October 20, 2013 at 1:29 pm | Permalink

        I’m not a fan of the numinous, but when I look at the complexity of the natural world and consider the ineffable nature of qualia and consciousness I get the feeling that there’s something important that we just don’t know, yet.

        • Posted October 20, 2013 at 1:59 pm | Permalink

          Steven not only would agree with you, he outlined exactly the important things we don’t know.

          b&

        • Michael Fisher
          Posted October 20, 2013 at 2:14 pm | Permalink

          I think so too & I also think *ingredient x* will not be a god thing [not implying that you think it might be]

          It annoys me somewhat that I will be dust before the curtain is raised on x, assuming it’s something our sloppy minds could grok

          • Jesper Both Pedersen
            Posted October 20, 2013 at 2:22 pm | Permalink

            I hope there’s plenty more than one ingredient left to discover.

            Boredom would soon get the better of us if we knew all the unknowns about this place.

      • Alex
        Posted October 20, 2013 at 2:20 pm | Permalink

        With pronouncements about free will I have a similar problem as with discussions about consciousness – these terms are so notoriously difficult to define. How did the person using the word learn what the word means? In Weinberg’s case, him being Weinberg and all, he’s probably read up on some of the usual definitions. Which one was he referring to when linking it to his feelings?

  12. Sastra
    Posted October 20, 2013 at 1:58 pm | Permalink

    A Catholic member of my book discussion group once talked about a friend of his who was at University and double-majoring in Physics and Theology. He then confidently explained that this made PERFECT sense because they were really talking about the same sort of things in the same sort of language — and then he started gassing on about String Theory. I’d assumed he had also been reading Polkinghorn.

    I also assumed that he had no idea what the hell he was talking about. A parallel between String Theory and the existence of God? As Jerry might point out, in String Theory not yet being testable is a vice; in religion God’s failure to be testable and dependence on faith is a virtue.

    So I resisted my impulse to ask him to explain the math behind the God hypothesis.
    Or even set the God hypothesis out clearly. But … if he ever brings it up again…

  13. Stephen Barnard
    Posted October 20, 2013 at 4:20 pm | Permalink

    The notion of the multiverse is the ultimate Coperincan revolution. Too bad that it’s unobservable. Or is it?

  14. Chak
    Posted October 20, 2013 at 8:02 pm | Permalink

    This talk about multiverses seems premature. Most of this idea rests on inflation, but that in itself is not well understood. We think the early universe went thru an inflationary period, but there is no understanding of what caused inflation. Other “indications” for a multiverse are even worse off, like MWI or String theory solutions which are correctly “just theories” at this point.

  15. michieux
    Posted October 21, 2013 at 5:58 am | Permalink

    Have I mentioned how much I look forward to my daily emails from WEIT?

    Reading your posts, and the contributors’ posts is at once entertaining, educational, and a downright pleasure.

    I love the kitties; I love the boots; I love the nostalgia (I’m 63); and, especially, I love knowing I’m not the only “different thinker” out here.

    Than you all very much!

  16. Posted October 21, 2013 at 11:55 am | Permalink

    Firstly, a thank you to Dr. Coyne for the post. The key take home point of String Theory (Despite being elegant mathematically) is that it has yet to make a prediction that can be verified or tested by any known experiment. Which means it doesn’t fit other data either. It’s rather amazing that it has carried forward as long as it has, but if the hold out (to proving it) is for the next generation collider with even greater energies, it would seem like a theory that doesn’t really apply to reality. Is string theory basically a meme that has found its perfect environment in the ultra high budget world of particle physics? Would it exist without this environment, say if one was forced to consider a theory under more astere conditions? Instead of asking if the unievers has produced the ideal environment for intelligent life, the question might be, is there a mechanics driving these massive cumbersome unverifiable theories?

    • Posted October 21, 2013 at 12:43 pm | Permalink

      “Which means it doesn’t fit other data either.”

      Sorry: What do you mean by this? The Standard Model falls out of string theory, so string theory fits the same data that the Standard Model does… no?

      /@

      • Posted October 21, 2013 at 8:38 pm | Permalink

        Well, do you mean “falls out of” in so far as particles, photons, electrons, w+’s etc are all represented (individually) by very tiny super strings? I think that standard modelists would probably ask, that’s really elegant, BUT how do you know that there are super strings behind these particles? Maybe that’s why they are still working on it, I only base my knowledge off of what I”ve gathered from their simplified reports, but basically that’s the current problem, is not being able to prove that a string is there, or possibly that strings are needed. So i’m not sure it would fit existing data, particles energy, except theoretically, if strings exist? Because they don’t know if they do. AS indicated above, (the expansion data) there is roughly 75% of energy in the universe unaccounted for by any known particle, is it anti-gravity or is it something else? 75% is a pretty big missing piece.

    • Stephen Barnard
      Posted October 21, 2013 at 1:35 pm | Permalink

      I object to string theory being called a “theory.” It certainly doesn’t come close to the status of, say, the theory of evolution in terms of being backed up by compelling evidence. Scientists often complain, justifiably, about creationists calling evolution “just a theory” and insist that a scientific theory is something so well confirmed that it would be perverse for an educated, rational person to doubt it. That definition sure doesn’t fit string “theory.”

      • Posted October 21, 2013 at 4:13 pm | Permalink

        Well, yes. Physicists & cosmologists might not be as careful about this as evolutionary biologists as string “theory” is not called into question by Creationists (who generally can’t even get past their misunderstanding of the “modern synthesis” of the Big Bang theory) as often as the theory of evolution is.

        /@

      • Diana MacPherson
        Posted October 21, 2013 at 4:15 pm | Permalink

        Yes, others agree with you. I’m not sure how it came to be called that but it’s closer I suppose to a model or maybe hypothesis.

        • Stephen Barnard
          Posted October 21, 2013 at 7:34 pm | Permalink

          I think we have to face up to the fact that scientists sometimes play pretty fast and loose with the word theory. It seems to have at least two, and probably more connotations, ranging from a full-blown, well-validated THEORY to something little more than a hunch, as in “I have a theory that …”

      • Alex
        Posted October 21, 2013 at 11:10 pm | Permalink

        I guess it is called string theory in analogy to “quantum field theory” which is also not a theory in the creationist debunker’s favourite sense. I believe one should read it not as guess but as “a mathematical framework”, in which one can try to formulate a theory.

      • Posted October 24, 2013 at 10:26 am | Permalink

        It is absurd to call “evolution” a theory, because of the fossil evidence and now sequencing data, showing how species are descendent from others…mechanism of how that occurs is debated. The string model still has yet to show evidence for the infinitesimal strings.

        • Stephen Barnard
          Posted October 24, 2013 at 3:54 pm | Permalink

          That evolution occurred isn’t a theory. It’s a fact. That it occurred through natural selection, differential reproduction, and inherited characteristics is what’s normally referred to as the theory of evolution. It has overwhelming support from many sources (see WEIT).

          That standard physics accurately describes a great deal of the universe is a fact. That string “theory”, or at least one of the mind-bogglingly multiple versions of string theory, is in some sense compatible with standard
          physics is true, but it is supported by no empirical observations but only by appeals to mathematical elegance, so it doesn’t deserve to called a theory, yet.


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