Of Particular Significance

Dark Matter Around the Corner?

POSTED BY Matt Strassler

POSTED BY Matt Strassler

ON 11/29/2012

The meaning of the title of Clara Moskowitz’s new article for the public, “Dark Matter Mystery May Soon Be Solved“, all lies in the word “may”.  It may.  It may not.

According to the article, “the answer to this cosmic mystery could come within the next three or four years, scientists say.”

I have to admit that this kind of phraseology, which one often sees in the press in reports about science, drives me a bit nuts.  Which scientists? How many of them?  You can’t tell from this line whether this is something that a group of three or four mavericks are claiming, or whether it is conventional wisdom shared by most of the community.   And “the answer… could come…”? Interpreted literally it is content-free: yes, the answer could come in the next few years, or not — but you don’t need any scientists to tell you that.  If one interprets it more optimistically — that it is intended to imply that the answer will very likely come within the next three or four years — then I think it is far from clear what fraction of the experts will agree with that statement.

Rather than debate the claim, let’s start with the physics.  What will determine how long it takes to discover what dark matter is made from?

Well, it is possible this has already started to happen; remember this hint of a discovery of dark matter?  This is still alive; here’s a recent update from the Resonaances blog.  Whether this is a real signal of dark matter or an experimental problem or subtlety, only time will tell. But such a discovery could occur, in the optimistic scenario that dark matter particles are abundant and that, when they find each other near the center of the galaxy, they often annihilate in spectacular fashion, to a pair of photons.  It would almost be — and it may be — too good to be true.

Alternatively, an extremely pessimistic scenario is possible: that dark matter is made from something that only interacts with ordinary matter via gravitational forces, which are exceedingly weak.  In this case there is no possibility that any of the on-going searches for dark matter particles will turn up anything, because all of them assume, by necessity, that the particles they are looking for do interact with ordinary matter in some much stronger, non-gravitational fashion.

And even if dark matter is made from particles that do interact with ordinary matter in a non-gravitational way, how long it takes to find them will depend on how rare they are, and on how strong those non-gravitational forces are.  We know roughly how much dark matter there is out in the universe, but (assuming it is even made from particles, which we don’t know for sure) it might be made from a great abundance of low-mass particles or a lesser abundance of particles with a large mass.  All other things being equal, it’s harder to find the particles if there are fewer of them around.  And we can infer how these particles will interact with ordinary matter only by making certain simplifying assumptions about how the dark matter particles were left behind as the universe cooled during the Big Bang.  These assumptions are just that: assumptions, ones which are intelligent but not necessarily correct.

So we can’t guess whether insights into the nature of dark matter have already been obtained, whether they won’t be obtained for centuries, or whether the next few years will dramatically change our knowledge.

What is true — and this is really the content, properly interpreted, of the article I referenced at the beginning — is that the next few years will allow for some of the most popular possibilities for the nature of dark matter to be ruled out or confirmed.  (If you read the last half of the article, you’ll find this is actually its meaning, despite the optimistic words in the first half of the article.) Of course, just because something is popular doesn’t mean it is more likely.  And that means that when you’ve ruled out the popular options, you can’t assume the unpopular options are wrong; you still have to go check.  [You’ve heard me say this, even recently, about supersymmetry, extra dimensions, and the like; that’s because it’s always true when you’re searching.  Notice what Lance Dixon says in the article accords with this point of view.]  So although one can be hopeful, the stark reality is that this process could take a few years, decades, or millenia.

As Dan Bauer says at the end of the article, “I guess it’s the natural optimism of physicists to think [dark matter] is something we might actually be able to find.”  I have nothing against optimism, as long as we don’t confuse our own optimism that nature behaves in such and such a way for high likelihood that nature behaves that way. Optimism is a good thing: most of the things we look for — decay of the proton, neutrino oscillations, dark matter, etc. — don’t come with a guarantee that they are discoverable.  [The Higgs particle was very unusual; we had a very strong reason to believe it or something like it had to be discoverable at the Large Hadron Collider, because without it our equations for the already-known particles were inconsistent.  We are rarely so confident.]  Pessimism would keep us from doing these experiments; and although most such experiments do come up empty (proton decay, for instance — at least so far), a few exceptional ones do not (neutrino oscillations) and they permanently change our understanding of the world.  Maybe dark matter will be discovered soon, maybe it won’t; but it is a good thing that we’re looking for it.   And maybe a better title for Ms. Moskowitz’s article would have been “Searchers for Dark Matter Optimistic About Near Term.”  That at least would have been undeniable.

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58 Responses

  1. Say Dr. Strassler, what do you think of the production numbers shown in Figure 5 on page 1808 of Columbia’s Takamitsu Tanaka and Zoltán Haiman (2009) “The Assembly of Supermassive Black Holes at High Redshifts” Astrophysical Journal 696:1798-822? They suggest why such an IMBH population would stop growing in their Monthly Notices of the Royal Astronomical Society paper from this September which I mentioned above.

    1. I’m really not the right expert for this question, I am afraid; I really can’t evaluate this kind of paper, and would call up experts if I wanted to do so. Also we’re too close to the end of the term and I just don’t have time to think about it; maybe you could raise this again in the new year.

        1. Matt, the NuSTAR team remains absurdly mum and essentially punted on any preliminary black hole census that they still say in several places left over from before calibration is their top priority. But if they release data in “Spring 2013” as promised, these guys will be all over it.

          1. I’ve been corresponding with one of the authors of that paper, and I’m very excited. There’s probably enough spectral resolution from NuSTAR to exclude redshifted iron lines (6.4 keV) for anything too faint to be in SIMBAD as a nearish galaxy, so there is a very good chance of not only getting a reasonable statistical census of Milky Way sources, but also of being able to characterize the 20-60 keV envelope which is the only thing likely to distinguish stellar mass black holes from larger ones accreting only from the low density interstellar medium, all from the data they’ve already collected.

            The NuSTAR team was corresponding with me frequently and promptly, about every month up until I asked them why they weren’t doing such a survey themselves when it became apparent that they weren’t just before AAS last week, after which I have not received a single reply.

  2. If a = b and a = c , is there any way that a = b + c ?
    In other b and c can be converted back to a , but can both b and c get converted but to a as well? Assumption being all three are quantum states.

  3. I meant to type “resolve the objections to DM from MOND”. What I am trying to say is that McGaugh, Kroupa, and a few dozen other experts are convinced that Newton-Einstein gravitational theory is either significantly wrong or appears to be significantly wrong for some unknown reason. What Prof. Strassler suggests about my incompetence is probably right on the money. I still think McGaugh and Kroupa are correct — they have looked at the evidence as much as anyone.

    1. Enough. Enough already, please. You made your point; there is no need to reiterate it repeatedly. The evidence is against MOND; should the evidence swing in its favor you will see the community swing round with it. The real issue is always about acquiring better data.

  4. “… why must particles be prevented from lumping?” The way I understand the evidence, the particles might lump according to Newton-Einstein gravity as most physicists expect, but, if so, some extremely weird phenomenon makes it appear that the prevention occurs to some extent.
    According to Milgrom:
    “The new physics entailed by MOND shows up in full force only in galactic systems, whose dynamics is governed by gravity.” (p. 3 of “MD or DM?”)
    “Contrary to MOND, DM does not predict the rotation curves of individual galaxies from the baryon distribution.” (p. 10 of “MD or DM?”)
    http://arxiv.org/pdf/1101.5122v1.pdf “MD or DM? Modified dynamics at low accelerations versus dark matter”, 2010
    According to McGaugh and Kroupa, black holes and WIMPs cannot resolve the objections to MOND. The experts have complicated computer simulations that embody the biases of the experts. So far as I know, the Wolf prize winner Bekenstein is the most prestigious physicist to back MOND. To me the evidence proves that Milgrom is the Kepler of contemporary cosmology because MOND is here to stay.

  5. My point is this: (A) non-relativistic MOND is approximately correct. (B) If DM particles explain MOND, then some weird unknown fifth force (or something else) MUST prevent the DM particles from lumping.

    1. David, why must particles be prevented from lumping? If dark started out as WIMPs and lumped into black holes, that would be consistent with the other black hole evidence above, be consistent with the big bang nucleosynthesis element ratios from plain vanilla inflation, and be consistent with the lack of WIMP detection results except from one lab in Italy from which no attempted replications have been successful.

  6. It is true the effect of the moon on the ocean is purely gravitational, but it is quite possible to measure the inertia of the moon. I claim the empirical evidence shows that non-relativistic MOND is approximately correct. I claim that the counter-MONDists are wrong. There might be lumpy areas consistent with MOND. The question of lumpiness is somewhat dependent on relativistic MOND, whatever that theory might. be.

  7. According to McGaugh, dark matter particles cannot resolve the cuspy halo problem. I quote Prof. Dr. Pavel Kroupa from a (Nov. 1, 2011) e-mail,
    “My criticism is not based on me not liking dark matter, but is a result of rigorous hypothesis testing such that, from a strictly logical and scientific point of view, LCDM is definitely not a viable model of cosmological reality. I do not write such statements because I do not like LCDM and its ingredients, but because every test I have been involved with falsifies LCDM. At the same time, the tests of MOND we performed were done on the same footing as the LCDM tests. The MOND tests yield consistency so far. I am not more “fond” of MOND or any other alternative, but the scientific evidence and the logical conclusions cannot be avoided. And it is true, I must concede, that MOND has an inherent beauty which must be pointing at a deeper description of space time and possibly associated quantum mechanical effects which we do not yet understand (compare with Kepler laws and the later Newtonian dynamics).” According to both McGaugh and Kroupa there are only 2 possibilities:
    (1) Newton-Einstein gravitational theory is really correct, but some unknown phenomenon makes it appear that the theory is significantly wrong and Milgrom is mostly correct for fortuitous reasons.
    (2) Newton-Einstein gravitational theory is significantly wrong, and Milgrom is basically correct.

  8. I can understand that there might be a difference between purely gravitational dark matter and MOND, but to say that dark matter particles do not exist seems, to me at least, empirically compatible with the statement that dark matter particles are purely gravitational. How could experimentalists distinguish between modified gravitational theory and purely gravitational dark matter particles? They might be able to, but would they necessarily be able to? If yes, then why?

    1. I already told you that MOND makes different predictions than dark matter for CMB, large scale structure, lyman alpha forrest, bullet cluster, and this has killed it. So why do you keep asking the same questions again and again?

    2. Because you don’t understand physics, Mr. Brown. Your statement is silly. The effect of the moon on the ocean is purely gravitational; do you say that replacing the moon and its gravitational effects with your modified form of gravity [but no moon] would give the same tides?

      If dark matter exists and is made from particles, those particles will form clumpy areas, lumps in the distribution of dark matter that are not necessarily at locations where there is a large amount of ordinary matter. MOND, however, always puts the dark-matter-like effects centered at locations where there is ordinary matter. I am not expert enough to tell you the best way to distinguish these two things through astronomical observations, but they certainly are physically different. Honestly, your attempt to claim they are the same is foolish, and has lowered your reputation on this site.

  9. The electron spin:
    Historically, one distinguishes between the “normal” and an anomalous Zeeman effect that appears on transitions where the net spin of the electrons is not 0, the number of Zeeman sub-levels being even instead of odd if there’s an uneven number of electrons involved.

    Spin angular momentum is real angular momentum.
    Switching the state of two particles, though, is mathematically related to rotating the two spins by 360 degrees. And as we just saw, when you rotate a spin-1/2 particle by 360 degrees, it picks up a factor of -1. Thus, when you are dealing with spin-1/2 particles, swapping any two of them has to give you the same wavefunction you started with, multiplied by -1.

    This also gives you features like the cancellation described in the topological insulator post, where there’s an interference between the part of an electron’s wavefunction that sees its spin rotate clockwise by 180 degrees, and the part that sees its spin rotate counter-clockwise by 180 degrees. If you think about it a little, you can see that getting from one of those states to the other involves a 360 degree rotation, which means that one is just a factor of -1 from the other.

    in the below video, he is not continuously rotating his kid’s hand. He left a interval between two rotations. Only the mathematical logic connect between these two rotations.

    So, quantum mechanics is magic?
    In this limited sense, yes. For reasons that I can’t really explain, electron spins have the property that when you rotate them by 360 degrees, you get back to where you started, only with a negative sign in front of the wavefunction.

    Anyway, the take-home message from all of this is that when you include spin in the calculation, you can make a material that has the properties of a topological insulator: it does not allow electrons to flow through the middle of a solid chunk of material, but will allow electrons to flow along the surface of the material. Moreover, the flow of electrons along the surface will be unaffected by defects and impurities on the surface (within reason, anyway– if you put enough impurities in, you effectively make it a surface of a different material, and then everything changes).

    What’s topological about this, again? You haven’t said anything about coffee cups and donuts yet, so I don’t see where topology comes into it.

    It’s a little difficult to explain in a picture involving real particles moving around. When you move to the more abstract “band structure” picture, it turns out that the band structure of a topological insulator has features that cannot be changed by allowable distortions of the band structure, in much the same way that you can turn a doughnut into a coffee cup with simple stretching operations, but can’t make either one into a sphere. The mathematical structure of these things is identical to some of the math you find in topology, so they’re “topological insulators.”

    www .youtube.com/watch?feature=player_embedded&v=hJO0mi3w81s

  10. The Moskowitz’s article was actually very well written and captured the situation quite well. As a dark matter expert myself, I can attest to this. On the other hand, Strassler is not a dark matter expert, so his aggressiveness was quite unecessary. The worst thing scientists can do is to continually criticize and shout at journalists when they don’t 100% agree with the wording. The journalist is ultimately responsible for what they write, and has no obligation to go around polling all physicists on every word that is used in the article, just as a physicist wouldn’t take a poll to decide the title of his/her paper. This is the opposite of how science should be conducted.

    1. I don’t agree with you. I don’t know who you are (you might reveal yourself, since you are obviously one of my colleagues.) I am not perhaps as much an expert as you (though you haven’t stated what your expertise is) but I am certainly an expert on various theories that predict dark matter, including those quoted in the article, and I certainly know how to calculate the amount of dark matter that remains in a given theory after the Big Bang, and also how to calculate the rate at which dark matter will be observed in a given experiment, such as LUX and XENON. What additional expertise is essential here? So if you are going to criticize my point of view, please do so on the science, not by vaguely claiming that your expertise gives you greater authority. What makes you think any of the statements I have made are false? Give me something specific to respond to, and I’ll show you the justification for my statements.

      Incidentally, would you take the point of view that Lance Dixon is an expert on dark matter? He is quoted extensively.

      Furthermore, journalists *do* have a responsibility not to mislead the public about what is happening in science. This is for many reasons. And I consider it part of my job as a scientist to make sure the public knows what’s happening in the field. If you and I disagree publicly about this, that’s fine with me — let the public see that disagreement. That is exactly how science should be conducted. For my part, I’m very upset with seeing journalists regularly creating a belief in the public that something spectacular has happened, or is about to happen, in science, and then when nothing comes of it the public ends up deeply jaded about science. I find that many in the public are no more likely to believe in scientific results than they are in any pronouncement from a politician; it’s all headlines and spin, as far as they are concerned. It bothers me to see as good a journalist as Ms. Moskowitz playing into this unfortunate process, which needs to be changed, in my opinion.

  11. “What do you think we have been doing for the last thirty years?” I think that physicists and astronomers have been ignoring the work of Milgrom for the last thirty years. I think that the empirical evidence shows that Milgrom is the Kepler of contemporary cosmology. Even if all my other ideas are wrong (a real possibility) I say that I am correct about Milgrom. The evidence has been steadily accumulating in favor of Milgrom for 30 years.

    1. You can say that the evidence has been accumulating for milgrom for 30 years, but i don’t think you have actually studied it. CMB, large scale structure, lyman alpha forrest, bullet cluster, etc, have all killed mond, and have supported dark matter. Also, mond suffers from deep theoretical inconsistencies, which always made it highly dubious, but now the data has killed it once and for all.

  12. Hello Prof,

    Getting of on topic for a change, 🙂 …

    Is it possible that we have not yet deciphered dark matter (nor dark energy) because we are using the wrong camera?

    All our physics, thus far, is derived from using Schrodinger and/or Heisenberg pictures (cameras). Maybe it is just not sufficient to see dark matter. In my view, Heisenberg picture would be the correct approach (time-independent, well almost independent, the “shutter speed” frequency to change from one state to the next, the energy-time uncertainty principle), if only we learn how to use it properly.

    So, would it be quicker if we use the Dirac picture, so that we can get a clear understanding as to how to manipulate the density matrix and deal with mixed states, which is what, I believe, dark matter comprises. My reasoning for this approach is that the interaction between dark matter and ordinary, “visible” matter could be through quantum entanglement.

    I don’t believe time is a natural variable, like Einstein once wrote, it is we, physicists, that embedded the time variable in the equations for our convenience (lack of visualization). Of course it took Einstein (the genius) to decipher that one, 🙂 … I do, though, accept that there must be order (as opposed to chaos and not in the spacial sense of direction , vector). So, in keeping my line of reasoning that higher order leads to consciousness (my post above, “the universe expands like the brain”) then ordinary matter would be the stuff that is being spewed out of the fissures of dark energy at much higher eigenstates, more “stable”, than dark matter. One of the most beautiful function I have even seen is the hydrogen wave function with all those beautiful states.

    There is no doubt in my mind that we are at the higher end of the spectrum, we with consciousness, and that we are not at the top either. We are only in existence for a mere 2.0 – 2.5 million years, think of what a conscious Being could be and do Who is in existence for billions of years?

  13. Think about this: if dark matter particles interact solely through gravitation then what is the empirical difference between modified gravity and alleged dark matter particles that cannot be detected in terms of relating these particles to inertial reference frames? How could Milgrom be proven wrong concerning dark matter particles?

    1. The empirical difference is significant. That’s why so many people claim Milgrom’s theory is already ruled out by evidence in data. It is all done using the gravitational forces that dark matter exerts — and nothing else.

      You must really think we’re truly stupid. “Think about this:”. What do you think we’ve been doing for the last thirty years?

  14. Actually a surprising advance came from the bullet cluster, and now we’ve learned that there are lots and lots more of the collisions out in the sky like the bullet cluster’s. Seems like an optimistic situation, in that case.

    Concerning direct detection, the situation is rather more fertile than caused optimism for new physics to be discovered at the LHC (the Higgs is likely to be old physics, although sure, a surprise might be lurking). Nice article, actually, with the mention of ADMX, LUX, in addition to others.

    There difference between LHC and the dark matter groups is that there is a larger variety of approaches to the dark matter problem. Not a big dinosaur, but a lot of smaller creatures still mutating and adapting. Sure, it could all add up to a big fat zero, but so could all hopes for anything other than the SM Higgs at the LHC.

  15. If just 1% of all known black holes are intermediate mass (~100,000 solar masses) that would explain all dark matter. There are no reasons to believe this is unlikely. Microlensing studies don’t rule out MACHOs over 15 solar masses because of the low number of lensing events observed. For a few years last decade some people thought the orbits of wide binary stars ruled out black hole dark matter but those assertions have been withdrawn. There is no theory of supermassive black hole formation which does not result in a much more abundant quantity of intermediate mass black holes being produced, and plenty of reason to believe that they would stop growing after being produced. Big bang nucleosynthesis does not rule out black holes because we don’t know enough about how inflation occurred . If dark matter is intermediate mass black holes the interstellar medium isn’t dense enough to make them look different than stellar mass black holes.

    1. I sincerely appreciate the fact that (in contrast to some past exchanges we’ve had) this time you limited yourself to stating the scientific arguments in favor of your position, and refrained from insulting the people who disagree with it. If your point of view is correct, time will reveal it.

      Incidentally you’ll note I explicitly said that we do not know that dark matter is made from particles.

      1. Thank you! My correspondence with NuSTAR observers has convinced me that there is no longer any reason to argue against WIMPs while arguing for black hole dark matter. I hope they release their initial black hole survey results at AAS in early January as planned.

        Here’s an interesting question which needs a far more experienced physicist than I to answer: this paper says dark matter has a self-interaction cross section of about 7cm^2/g. Are intermediate mass black holes small and dense enough to fit that bill?

  16. “Alternatively, an extremely pessimistic scenario is possible: that dark matter is made from something that only interacts with ordinary matter via gravitational forces, which are exceedingly weak.” In my opinion, it the preceding scenario is true, then Milgrom is basically correct, and Newton-Einstein gravitational theory is significantly wrong. Are we in agreement on this point?

  17. Phenomenological or Logos?: The necessity of introducing half-integral spin goes back experimentally to the results of the Stern–Gerlach experiment.
    It is dark matter or anti matter, the mathematics involved to connect them with intuition is tricky and historical.

    E = ± √p²c² + m² c^4 :
    In 1928, Paul Dirac solved the problem: he wrote down an equation, which combined quantum theory and special relativity, to describe the behaviour of the electron. Dirac’s equation won him a Nobel Prize in 1933, but also posed another problem: just as the equation x2=4 can have two possible solutions (x=2 OR x=-2), so Dirac’s equation could have two solutions, one for an electron with positive energy, and one for an electron with negative energy. But in classical physics (and common sense!), the energy of a particle must always be a positive number!

    The equation also implied the existence of a new form of matter, antimatter, hitherto unsuspected and unobserved, and actually predated its experimental discovery. It also provided a theoretical justification for the introduction of several-component wave functions in Pauli’s phenomenological theory of spin. Although Dirac did not at first fully appreciate what his own equation was telling him, …

    “his resolute faith in the logic of mathematics as a means to physical reasoning”,

    ….. his explanation of spin as a consequence of the union of quantum mechanics and relativity, and the eventual discovery of the positron, represents one of the great triumphs of theoretical physics, fully on a par with the work of Newton, Maxwell, and Einstein before him.


    1. Where did you get this information from???? The history is completely and utterly inaccurate!!!

      Spin was introduced by Goudsmit and Uhlenbeck in 1925, to explain features of the spectrum of hydrogen in the presence of a magnetic field (“Zeeman splitting”). Here is an article about it by the physicist and historian Abram Pais: http://www.rowdyboeyink.org/ehrenfest/images/Uhlenbeck.pdf This was before quantum mechanics was really formulated in its modern form, and well before the Dirac equation. See also http://www.lorentz.leidenuniv.nl/history/spin/goudsmit.html for Goudsmit’s account and http://download.springer.com/static/pdf/436/art%253A10.1007%252FBF01558878.pdf?auth66=1354472553_29c456a98e7fc3ca94cb26fd7786fab5&ext=.pdf for the paper (in German).

      Dirac’s equation *did* combine quantum mechanics, relativity and spin, and the equation, properly interpreted, did predict anti-electrons, yes. Though it took a while for it to be interpreted correctly; initially the positively charged particle it implies was assumed incorrectly to be the proton, until it was understood that the anti-particle had to have the same mass as the particle. And that wasn’t all figured out by Dirac himself.

      1. In quantum mechanics the basis for a spectroscopic selection rule is the value of the transition moment integral. The wave function of a single electron is the product of a space-dependent wave function and a spin wave function. In Raman spectroscopy the laser light interacts with molecular vibrations, phonons or other excitations in the system, resulting in the energy of the laser photons being shifted up or down(Rotational symmetry).

        The mathematics here, applied to wave function as molecular vibration. If the value of the integral is zero the transition is forbidden. So the point group unites the quantum symmetry and simple symmetry. In formal terms, only states with the same total spin quantum number are “spin-allowed”.
        But if electron orbit, function like an Atmosphere, how this mathematics possible?.
        “Perhaps there exists a quantized rotation of the electrons”- but It is again merely a linear transformation(Morphism) ?
        Goudsmit was a genius. He founded a formula for the doublets in the spectra. He worked on the intensities in the Zeeman effect and founded the exact expressions.
        It was quite different from today; there was no quantum mechanics at the time, don’t forget that this did not yet exist! One had to guess these little formulae; one developed a feeling for them. It is just as with veterinary and human medicine. People can tell one where it hurts, but a veterinary doctor has to guess where it hurts. A horse or a cow cannot tell that. And so it is with these little formulae. It is really curious …… it was a kind of numerology, and it is a miracle that we arrived at the correct expressions which later could be derived by quantum mechanics. Now, when it is derived it becomes quite simple. If one knows some mathematics, then one can derive all those things. We had to guess at them; I had a feeling for that. And that is the way Kronig and I did those things.

        Very ENLIGHTENING, thank you Professor.

    1. Yes, though (a) the existence of dark matter filaments was expected from basic considerations and computer simulations, and (b) the article keeps saying “we found the filaments!!” but if you read carefully they found one filament, by being clever about where they looked. So that’s a long way from saying they’ve shown observationally that “it’s all connected”.

  18. P.S. :
    Before accepting such fantasies , they must first prove that fields and forces can generate consciousness , will , feelings……
    How can we respect any one who proclaiming the un-provable ?

  19. To Oaktree :
    Why this PANIC of the reality of GOD ?
    Before saying such ……… please think of just one point ; it is impossible in principle to even imagine a materialistic mechanism to generate laws of nature and consciousness , notice that ALL cosmic fact free fantasies talk about forces and fields only , never any one even imagined how nature can generate meta-material realities like consciousness…..
    How can human gift of reason and rationality be so flooded with fantasies to the degree of losing all touch with logic and understanding so talking about the ultimate absurd ??

  20. One day, I’m sure, the dark matter mystery will be solved. But what about dark energy? How is it possible to find out where it comes from?

    1. There’s no question “dark energy” (discovered more recently and much more difficult to study than dark matter) seems more difficult to study. I really have no guesses as to what will happen there. Theoretical insights may be needed to suggest experimental pathways we haven’t thought of.

  21. So if I understand you correctly, dark matter particles that interact with matter only via gravity cannot be produced say via particle-antiparticle annihilation? there’s no way they’d show up as missing energy in particle collisions?

    1. Oh, sure, they can be produced. Unfortunately, this would occur with a probability that is so small that it would likely take the Large Hadron Collider longer than the age of the universe to produce even one pair.

      Unless gravity is greatly modified from the simplest expectations, the rate for producing particles that interact with matter only via gravity is suppressed by a factor of (E/M_planck)^4, where E is the energy of the collision and M_planck is about 10^18 GeV, in other words 10^15 TeV. Since typical quark-anti-quark collisions at the LHC have an energy of less than a TeV… oh well.

  22. Hello Prof,
    I am very curious to know if you feel the same way about a recent publish study, research, that the universe may grow like a giant brain.

    “The universe may grow like a giant brain, according to a new computer simulation.

    The results, published Nov. 16 in the journal Nature’s Scientific Reports, suggest that some undiscovered, fundamental laws may govern the growth of systems large and small, from the electrical firing between brain cells and growth of social networks to the expansion of galaxies.

    [“Natural growth dynamics are the same for different real networks, like the Internet or the brain or social networks,”]said study co-author Dmitri Krioukov, a physicist at the University of California San Diego. ” … NBC news.com

    A few months ago I posted this same observation but with a twist, that may have caused a negative impression, GOD. Of course, this is not what Dr. Krioukov is suggesting but he does like it open to conjecture.

    He is my post …

    If the is God then did God create the universe or did the universe create God?

    If God created the universe then that would be very problematic w.r.t. causality, what caused God? However, if the universe created God then that would be well within the realm of our real universe all our questions both from evolutionism and creationism would lead to a common goal.

    Given all that we know about our universe and ourselves:
    1. What could God be?
    2. Why would there be a need for God in the first place?
    3. How could God control the universe, which created Him?

    A curious observation is as the structures, atoms and molecules, become more complex the outcome, evolution of the universe, tends to life and beyond to consciousness, (we are very high up in the overall scheme of existence).

    We have a consciousness which is very difficult to define and formulate with the same math we use to formulate physical phenomena. Below is a very interesting video of a 3D formulation of what the known universe looks like. As you can see it has a striking resemblance to the structure of our brain, the structure that gives us consciousness.

    1. Do you believe that a universal consciousness (God) can exist given this data?

    2. Like our own consciousness can control our brain’s motor functions and hence our body functions, could the universal consciousness (once it “turned on”) create the more complex physical fields from the fundamental field (gravity or something else to the strong field) and hence drove the primordial chaotic universe to one of order and expanding, i.e. the expansion of the universe is not related to the initial conditions at the big bang but rather the universal consciousness is reinforcing and evolving to a higher and higher state. A principle of conscious advancement as the driving force for everything. No conservation laws need to be violated or invalidated.

    Is God the universal consciousness created by the magnificent structures of our universe, see the video below.

    http: //www.youtube.com/watch?feature=player_embedded&v=74IsySs3RGU

  23. Prof. Strassler :
    Does our physics allow a real particles — not ripples — with no charges , no forces , no interactions to exist ? ,
    Please do not allow insults in your website from some void minds.

    1. Yes. Those are called ghosts and turn up pretty generically. Thing is, they’re irrelevant by definition.

      1. I am curious about these, do you know of any good material on them? It’s hard to pry them apart from people speaking colloquially of neutrinos or woo theories.

        1. Looking around the Internet, there don’t appear to be layman-level discussions. The most relatable example out there is probably the missing “longitudinal polarization” for massless spin 1 fields. For example, as you may know, light can be left polarized or right polarized, but a spin 1 particle like the photon “should” have 3 polarizations (-1, 0, +1). For a massless field, though, the 0 polarization has no interactions with anything–it’s a ghost. So, does the 0 polarization “exist”? Meh, take your pick; it’s truly an issue of mathematical aesthetics and not physics. I suspect this is something Prof. Strassler will add an article on eventually; I don’t see one dealing with it.

  24. This is again a very nice, reasonable, and interesting article 🙂

    (I only hope that the comment section will not be flooded by crazy anti – dark matter zealots, who feel the need to express their disagreement with Prof. Strassler’s nice explanations and reasonable attitude …)

  25. Nigel Calder relates an anecdote in _The Key to the Universe_. A committee of angels is convened when experimentalists fire up a new instrument. “See what they’re doing now? We never dreamed they’d get so far into the teravolt range. What do we do now?”

    “All in favor of a new particle, please raise your wing.”

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A decay of a Higgs boson, as reconstructed by the CMS experiment at the LHC


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