Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

The Dark Model of Cosmology!

  1. Jul 16, 2010 #1
    What exactly is going on in physics and with the standard model of cosmology?

    We had a model that seemed to describe in absolute perfection the workings of the universe, but over the last few decades observations have been made that explicitly counter what's expected from general relativity and the overall standard model of cosmology.

    From the discovery that Stars at the edge of galaxies travel as fast as the ones closer to the center, to the discovery that the universe is only not slowing down, but accelerating it's expansion, to several unpredictable gravitational anomalies that cannot be explained by any model currently used by scientists, to the recently mysterious "Dark Flow" in which a entire cluster of thousands of galaxies seems to be moving into a "invisible" point in space, and this are just the most commonly known problems with physics.

    Since it's development, the standard model relied strongly on predictions made by general relativity, which is used to describe the effect of gravitation, so in my view there is a huge discrepancy here, yes, it is true that the standard model correctly predicts many situations and events in cosmology, but since science is supposed to be what correctly describes everything absolutely, since the moment so many problems were found that the standard model couldn't explain it ceased to be science in my opinion.

    We kept adding constants and variables to keep our standard model, but the things we added up were just invented from nothing, dark matter, dark energy, there is no foundation in reality to assume they're there, isn't it much more likely that it is the standard model that is inherently flawed or even incorrect?

    Like mentioned above the standard model derives heavily from general relativity, but we don't even know exactly what gravity is!

    We just know the effects it causes in matter and energy!

    So, in a nutshell, our model or the universe is based on something we don't fully understand, and every time some new observational paradox that contradicts what we would expect from this model appears on the horizon, we just make new stuff up to keep the model working.

    The standard model at this point is almost like a religion, it cannot be discredited in any way, and if nature itself disagrees with it, we invent new rules to keep it from becoming obsolete.

    Does anyone else agrees with me on this?
     
  2. jcsd
  3. Jul 16, 2010 #2

    phyzguy

    User Avatar
    Science Advisor

    Where was the "absolute perfection" you referred to? Zwicky's paper on the need for dark matter to explain galactic rotation curves dates to 1934. Since Hubble only realized the existence of galaxies as systems of stars in the mid 1920's, it didn't take long to realize that something was amiss.

    Before a few decades ago, cosmology was a qualitative science. Any model works when you don't have data to compare it to. I think the absolute perfection you referred to never existed. As cosmology has become more quantitative, the need for dark matter and dark energy/cosmological constant has become apparent.

    I hear these kinds of complaints all of the time, mostly from people who haven't looked at the data. I challenge you to look at the data and come up with a better explanation of the observations than the accepted Lambda-CDM standard model of cosmology.
     
  4. Jul 16, 2010 #3
    That was the exact point I was trying to address, we have a model that is flawed, broken or even wrong, yet, people prefer to have a flawed model that sometimes it works, sometimes it doesn't, rather than having no model at all until we actually find out why all this anomalies and observational inconsistecies are happening!

    Religion reigned, and still reigns in the world because most people prefer a answer (whatever it may be) than having no answer at all, and sincerely, in my view, the same is happening with our current cosmological model.
     
  5. Jul 16, 2010 #4

    phyzguy

    User Avatar
    Science Advisor

    So what is your point exactly? That a simple model that doesn't fit the data is better than a more complex model that does fit the data?

    I think this is how science works - if the model doesn't fit the data, we make hypotheses for what is wrong and test them out. The Lambda-CDM model fits a wide range of observations quite well. In what way is it "flawed"?

    A good analogy was Fermi's postulating of the neutrino in order to "save" the law of conservation of energy. It sounds like you would have abandoned the law of conservation of energy and thrown up your hands rather than make the "messy" assumption of an unseen new particle. Of course, Fermi's insight was eventually borne out as correct, and today we have ample evidence that neutrinos exist. I suspect that the same thing will happen with dark matter - we will eventually discover the particles that it is made out of. However, time will tell.
     
  6. Jul 16, 2010 #5
    My point is that there are still many observations that contradict the Lamba CDM model, to name give you an example, the gravitational anomalies observed in the pioneer spacecrafts which cannot be explained with that model, which is happening right in our doorstep, right in our solar system, but the most important incosistecy found to date is the one called "dark flow" where a huge cluster of galaxies spanning almost 1 billion years light years across, is moving or orbitting an unseen spot in a way that apparently contradicts what would be expected using the model.

    This is a huge event, it is not a miscalculation, this is a discovery as big as the discovery that the universe was expanding, therefore, if there is something happening that contradicts the model, perhaps it's time to stop accepting it as a model.
     
  7. Jul 16, 2010 #6

    phyzguy

    User Avatar
    Science Advisor

    I don't think either of these effects require any new physics to explain. Let's take them one at a time:

    (1) Pioneer anomaly. This is an extremely tiny effect, which has many possible explanations. I refer you to the excellent summary by Turyshev at http://arxiv.org/abs/1001.3686v1. To quote one of the many possible explanations from this paper:

    "The mass of the Pioneer spacecraft was ∼250 kg. An acceleration of 8.74 × 10−10 m/s2 is
    equivalent to a force of ∼ 0.22 μN acting on a ∼ 250 kg object. This is the amount of recoil force
    produced by a 65 W collimated beam of photons. In comparison with the available thermal inven-
    tory of 2500 W, a fore-aft anisotropy of less than 3% can account for the anomalous acceleration
    in its entirety. Given the complex shape of the Pioneer spacecraft, it is certainly conceivable that
    an anisotropy of this magnitude is present in the spacecrafts’ thermal radiation pattern."

    This gives you an idea of how small the effect is. How confident are you that anyone understands the thermal properties of a spacecraft that was launched in the 1970's to better than 3%?

    (2) Dark flow: The universe is highly inhomogeneous everywhere we look, with large clumps of matter and large voids. Why should this clumpiness end at our cosmological horizon? An inhomogeneity outside of our horizon is all that is required to explain the dark flow. I don't see that it even comes close to the discovery that the universe is expanding. The following paper by Kashlinsky, et.al. (at http://arxiv.org/abs/0809.3734v1) says:

    "Our findings imply that the Universe has a surprisingly coherent bulk motion out to at least ≃ 300h−1 Mpc and with a fairly high amplitude of > 600-1000 km/sec, necessary to produce the measured amplitude of the dipole signal of ≃2-3μK. Such a motion is difficult to account for by gravitational instability within the framework of the standard concordance ΛCDM cosmology but could be explained by the gravitational pull of pre-inflationary remnants located well outside the present-day horizon."
     
  8. Jul 17, 2010 #7

    Chalnoth

    User Avatar
    Science Advisor

    What you describe here would be a little absurd. It would be the equivalent of saying, "Well, because we don't know everything, we should just throw up our hands and not claim to know anything until we do know everything."

    The way that science works, instead, is that we have a model which we know isn't completely correct, but is instead an approximation to the true behavior of reality. We then progress forward by finding out where this model breaks down. Having a model is essential here because it allows scientists to focus their attention on where reality deviates from said model. When such deviations are found and confirmed, that's when science is its most interesting. Scientists live for those sorts of discoveries.

    But as yet, no deviations from the standard model of cosmology have been confirmed. Yes, there are things like the Pioneer anomaly, but these deviations are sporadic and could yet be due to systematic errors. We don't have any sort of red flag that really demonstrates where the standard model breaks down (as we know it must at some point).

    When scientists stop testing the standard model of cosmology, then you might have a point. But as long as the testing continues, what is being done in the field of cosmology is essentially the diametric opposite of religion's approach to truth.
     
  9. Jul 17, 2010 #8

    Chronos

    User Avatar
    Science Advisor
    Gold Member

    All 'models' are 'flawed' by definition. This no great revelation until you propose a superior model of the universe. Complaints that current models do not predict everything observed in the universe speaks more of measurement sensitivity than theoretical deficiencies.
     
  10. Aug 3, 2010 #9
    BN

    A short physics parable:

    I open the door of a room and see a cardboard box on a scale.

    The scale reads 1.5 Kg but from experience of cardboard boxes of a similar size and shape I conclude that, by itself, the box could weigh no more than 500 grams as an absolute maximum.

    At this point I think there are 3 main possibilities:

    1. The scale is flawed.
    2. There is Mass in the box I can't observe.
    3. There is something wrong with our understanding of Gravity and we need new Physics to fix it.

    I happen to have a 1Kg weight on my person. The mass was confirmed by me by multiple tests before I entered the room. There is space for it on the scale so I put it beside the box without opening the box and the scale now reads 2.5Kg.

    I now abandon possibility 1. as highly unlikely.

    At this point am leaning towards hypothesis 2. as I think it is more likely than 3. Maybe I don't accept that 2. is proven, but I'm comfortable with the thought that it has a higher probability than 3. and if I needed to rely on it as an assumption in further physics I would be comfortable doing so, although I should state that I was relying on the "there is something in the box" hypothesis in any paper I might submit.

    At this point in the parable are you happy that I am adopting more constructive position than saying "the scale disagrees with our model of gravity, we would have to invent something to explain it without any further evidence that any such thing exists, so let’s throw out the model and wait until we have a new model before we do any more physics"?

    Next I see the box move. In a series of jerks it falls off the scale and the scale now reads 1Kg.

    I now have additional evidence that the scale is accurate, but I have a new problem. Unless I assume that something energetic exists inside the box I now need new physics to explain the fact that it moved.

    I'm still confident that new physics is not required so I plump for another hypothesis: "there is something energetic inside the box".

    I still can't really call this proven, but I still consider that it is more useful than not having a model at all.

    Finally I hear a "meow" coming from inside the box. Now I can promote my 2 hypotheses to "proven theories" in the scientific sense. I open the box, grab the cat, and run before the phial of poison breaks!
     
  11. Aug 17, 2010 #10
    Complaints that current models do not predict everything observed in the universe may indicate an increase in measurement sensitivity uncovering theoretical deficiencies.
     
  12. Aug 17, 2010 #11

    Chalnoth

    User Avatar
    Science Advisor

    While this is in principle true, the primary problem is that right now, the only complaints that hold up under the most cursory scrutiny have to do with systems where we aren't even certain how to compute the right behavior just given the physics that we know.

    Primarily this means that if you're interested in how stars or galaxies work, this is an exceedingly rich area of research right now. If, by contrast, you wish to use our observations of stars and the inner regions of galaxies to determine the nature of fundamental physics, you're really barking up the wrong tree. When we have a better handle on the physics that we know in these regions, then we may be able to start making statements about fundamental physics with these systems. But for now it remains a poor choice.
     
  13. Aug 17, 2010 #12

    Chronos

    User Avatar
    Science Advisor
    Gold Member

    'New' physics are introduced only on the basis of numerous very good, and well confirmed observational evidence. Why is that an issue? Finding a few inconsistent examples is less certain than the body of good evidence. The 'inconsistent' examples are invariably marked by large error bars and less certainty than the body of evidence favoring accepted model.
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook




Similar Discussions: The Dark Model of Cosmology!
  1. Cosmological models (Replies: 4)

Loading...