8 ms·

Universe's expansion may be understood without dark energy

28 points by joeyespo 15y ago

J3L2404 15y ago
"Annila shows that, when gravitational lensing is analyzed with this concept, it does not require dark matter to explain the results." Both dark energy and dark matter seem contrived and virtually anything would be less hand-wavy. Just for aesthetic reasons I hope these are found to be the modern equivalents of "ether" as a medium for EM waves.
- jonnathanson 15y ago
  Something's always struck me as very "ethereal" about the concepts of dark matter and dark energy, and I'd be inclined to agree with you. Sooner or later, a robust theoretical model will come along that suffices without either of these constructs, which will be the kiss of death for them.
  - badger7 15y ago
    They're ethereal by design - they're more like placeholders for gaps in our understanding than they are concepts in their own right, they're there to be removed or explained.
- bluedanieru 15y ago
  Dark energy especially so, I think. I do agree with you somewhat, but dark matter at least is not so preposterous, simply being matter that only interacts with other matter via the gravitational force.
  - J3L2404 15y ago
    Yes, I think you have a point. Galaxy rotation is going to be hard explain without some missing mass.
    - dgottlieb 15y ago
      Now I'm merely trying to raise awareness, not offer an argument, but there are alternate gravitational theories for galaxy rotation (that I believe are more elegant, but at the expense of breaking more things than it fixes) such as MOND. http://en.wikipedia.org/wiki/Modified_Newtonian_Dynamics http://en.wikipedia.org/wiki/Modified_Newtonian_Dynamics Dark matter being less elegant in the galaxy rotation problem being a) it hasn't been detected and b) if it does exist, why does it fall into the same halo distribution pattern in different galaxies to account for the same rotational observation of these aforementioned spiral galaxies. But as I said before, MOND seems to break more physics than it solves, but much smarter people that actually work in physics are trying to put those pieces together which makes it legitimate enough for me to take seriously. Edit: Actually reading who's responding to what, I learned you're more than well aware of this :) I like to believe that galaxy rotation is solved with a single theory and not a significant combination of explanations (Occam's Razor). In any event I'll leave this comment here as an awareness booster for younger dabbling cosmologists.
- splat 15y ago
  I have to disagree with you about dark matter and dark energy seeming contrived. First it's hard to call dark energy "contrived" when it hasn't really been contrived, conceived, or created at all. That is, no one has really made any strong, convincing claims as to what it actually is. The term is really just a placeholder for the fact that something is providing a long-scale repulsive force (and so probably has negative energy density). Although it can be "explained" by a cosmological constant, that just punts the question to what the cosmological constant physically is. As for dark matter, it is the simplest, most elegant way to explain the variety of observations that point to its existence. These observations include small-scale dynamics of dwarf spheroidal galaxies, the rotation curves of galaxies, gravitational lensing due to galaxy clusters, and more. All of them can be explained if there exists some unknown particle which interacts only weakly with other particles. While it's true that the standard model predicts no such particle, it's also true that it's known that the standard model is an incomplete theory. You might argue that it could just as well be that our theory of gravity is wrong. (Certainly at the quantum level we know for sure that that is the case.) But inaccuracies in our theory of gravity at large scales have difficulty explaining the dark matter problem in an elegant matter. Consider dwarf spheroidals. These are the smallest of galaxies; in terms of luminous mass, they are only slightly more massive than globular clusters. Yet globular clusters are 1000s of times smaller than dwarf spheroidals. How can they possibly remain gravitationally bound on the scale of 1000s of light-years when globular clusters are only bound on scales of a few light-years? Dark matter can explain this by simply saying that dwarf spheroidals have relatively massive dark matter halos, whereas globular clusters have almost no dark matter. (Which one would expect in standard galaxy formation scenarios.) But modified gravity theories have difficulty explaining why two systems with similar masses interact so differently. We can similarly see that galaxies of all sizes exhibit a range of dark matter fractions. If the problem was merely with our theory of gravity one would expect all galaxies of a given luminous mass to have the same dark matter fraction. Any modified theory of gravity which explained these observations would not be aesthetic. The aesthetic explanation would be some hitherto unknown weakly interacting massive particle.
  - J3L2404 15y ago
    >The term is really just a placeholder for the fact that something is providing a long-scale repulsive force How is that not contrived? >You might argue that it could just as well be that our theory of gravity is wrong. As an armchair physicist, I was rather hoping the Pioneer anomaly would lead us down that road, oh well. >Any modified theory of gravity which explained these observations would not be aesthetic. Well aesthetics do invoke subjective qualities. Relativity, modifying Newtonian physics, could have be seen as ugly by some. E = mc^2 is so elegant as to seem improbable.
- lutorm 15y ago
  "Dark energy" isn't that contrived. When Einstein formulated GR, he showed that when you set up the theory, there is an additional free parameter. People assumed that it was zero, but there was really no empirical reason for this. But it's just as much part of the equations of GR as matter-energy is. If a dark energy had been not been allowed by GR and still been observed, then the hand-waving would have started.
gjm11 15y ago
Actual paper at author's web site: http://www.helsinki.fi/~aannila/arto/light.pdf http://www.helsinki.fi/~aannila/arto/light.pdf. I have to say that a brief perusal sets off my crank alarms, although the author does appear to be a real physicist. ... Oh. On googling a bit more, I find that the author has also claimed a proof that P != NP [EDITED to add: available at http://arxiv.org/abs/0906.1084 http://arxiv.org/abs/0906.1084]. The signs aren't looking good.
- splat 15y ago
  Another good rule of thumb is not to put too much stock in any papers typeset in Microsoft Word rather than LaTeX (as this one was). Perhaps I'll give it a closer look if it ever gets any citations, but I wouldn't put much money on that happening.
  - tzs 15y ago
    Considering that some top journals (such as Nature and Science) require or recommend Word format, your rule of thumb is ridiculous.
    - deleted 15y ago
      [deleted]
    - splat 15y ago
      In astronomy, anyway, LaTeX is the default. It's probably different in other fields which is why the broader journals use Word.
- Jabbles 15y ago
  Well he starts off by considering the kinetic energy of light...
- lutorm 15y ago
  a brief perusal sets off my crank alarms That's what I was going to say, too. And I got more convinced the further down I got. The weird, convoluted wording was a big tipoff. And then this sealed it: When a star explodes and its mass is combusted into radiation, conservation requires that the number of quanta stays the same, whether in the form of matter or radiation. There is no conservation law limiting the number of photons. This is obviously observed any time you turn on a light bulb.
bh42222 15y ago
I viscerally distrust anything from physorg.com. Anyone have a better option?

28 points by joeyespo 15y ago

"Annila shows that, when gravitational lensing is analyzed with this concept, it does not require dark matter to explain the results." Both dark energy and dark matter seem contrived and virtually anything would be less hand-wavy. Just for aesthetic reasons I hope these are found to be the modern equivalents of "ether" as a medium for EM waves.

jonnathanson 15y ago
Something's always struck me as very "ethereal" about the concepts of dark matter and dark energy, and I'd be inclined to agree with you. Sooner or later, a robust theoretical model will come along that suffices without either of these constructs, which will be the kiss of death for them.
- badger7 15y ago
  They're ethereal by design - they're more like placeholders for gaps in our understanding than they are concepts in their own right, they're there to be removed or explained.
bluedanieru 15y ago
Dark energy especially so, I think. I do agree with you somewhat, but dark matter at least is not so preposterous, simply being matter that only interacts with other matter via the gravitational force.
- J3L2404 15y ago
  Yes, I think you have a point. Galaxy rotation is going to be hard explain without some missing mass.
  - dgottlieb 15y ago
    Now I'm merely trying to raise awareness, not offer an argument, but there are alternate gravitational theories for galaxy rotation (that I believe are more elegant, but at the expense of breaking more things than it fixes) such as MOND. http://en.wikipedia.org/wiki/Modified_Newtonian_Dynamics http://en.wikipedia.org/wiki/Modified_Newtonian_Dynamics Dark matter being less elegant in the galaxy rotation problem being a) it hasn't been detected and b) if it does exist, why does it fall into the same halo distribution pattern in different galaxies to account for the same rotational observation of these aforementioned spiral galaxies. But as I said before, MOND seems to break more physics than it solves, but much smarter people that actually work in physics are trying to put those pieces together which makes it legitimate enough for me to take seriously. Edit: Actually reading who's responding to what, I learned you're more than well aware of this :) I like to believe that galaxy rotation is solved with a single theory and not a significant combination of explanations (Occam's Razor). In any event I'll leave this comment here as an awareness booster for younger dabbling cosmologists.
splat 15y ago
I have to disagree with you about dark matter and dark energy seeming contrived. First it's hard to call dark energy "contrived" when it hasn't really been contrived, conceived, or created at all. That is, no one has really made any strong, convincing claims as to what it actually is. The term is really just a placeholder for the fact that something is providing a long-scale repulsive force (and so probably has negative energy density). Although it can be "explained" by a cosmological constant, that just punts the question to what the cosmological constant physically is. As for dark matter, it is the simplest, most elegant way to explain the variety of observations that point to its existence. These observations include small-scale dynamics of dwarf spheroidal galaxies, the rotation curves of galaxies, gravitational lensing due to galaxy clusters, and more. All of them can be explained if there exists some unknown particle which interacts only weakly with other particles. While it's true that the standard model predicts no such particle, it's also true that it's known that the standard model is an incomplete theory. You might argue that it could just as well be that our theory of gravity is wrong. (Certainly at the quantum level we know for sure that that is the case.) But inaccuracies in our theory of gravity at large scales have difficulty explaining the dark matter problem in an elegant matter. Consider dwarf spheroidals. These are the smallest of galaxies; in terms of luminous mass, they are only slightly more massive than globular clusters. Yet globular clusters are 1000s of times smaller than dwarf spheroidals. How can they possibly remain gravitationally bound on the scale of 1000s of light-years when globular clusters are only bound on scales of a few light-years? Dark matter can explain this by simply saying that dwarf spheroidals have relatively massive dark matter halos, whereas globular clusters have almost no dark matter. (Which one would expect in standard galaxy formation scenarios.) But modified gravity theories have difficulty explaining why two systems with similar masses interact so differently. We can similarly see that galaxies of all sizes exhibit a range of dark matter fractions. If the problem was merely with our theory of gravity one would expect all galaxies of a given luminous mass to have the same dark matter fraction. Any modified theory of gravity which explained these observations would not be aesthetic. The aesthetic explanation would be some hitherto unknown weakly interacting massive particle.
- J3L2404 15y ago
  >The term is really just a placeholder for the fact that something is providing a long-scale repulsive force How is that not contrived? >You might argue that it could just as well be that our theory of gravity is wrong. As an armchair physicist, I was rather hoping the Pioneer anomaly would lead us down that road, oh well. >Any modified theory of gravity which explained these observations would not be aesthetic. Well aesthetics do invoke subjective qualities. Relativity, modifying Newtonian physics, could have be seen as ugly by some. E = mc^2 is so elegant as to seem improbable.
lutorm 15y ago
"Dark energy" isn't that contrived. When Einstein formulated GR, he showed that when you set up the theory, there is an additional free parameter. People assumed that it was zero, but there was really no empirical reason for this. But it's just as much part of the equations of GR as matter-energy is. If a dark energy had been not been allowed by GR and still been observed, then the hand-waving would have started.

gjm11 15y ago

Actual paper at author's web site: http://www.helsinki.fi/~aannila/arto/light.pdf http://www.helsinki.fi/~aannila/arto/light.pdf. I have to say that a brief perusal sets off my crank alarms, although the author does appear to be a real physicist. ... Oh. On googling a bit more, I find that the author has also claimed a proof that P != NP [EDITED to add: available at http://arxiv.org/abs/0906.1084 http://arxiv.org/abs/0906.1084]. The signs aren't looking good.

splat 15y ago
Another good rule of thumb is not to put too much stock in any papers typeset in Microsoft Word rather than LaTeX (as this one was). Perhaps I'll give it a closer look if it ever gets any citations, but I wouldn't put much money on that happening.
- tzs 15y ago
  Considering that some top journals (such as Nature and Science) require or recommend Word format, your rule of thumb is ridiculous.
  - deleted 15y ago
    [deleted]
  - splat 15y ago
    In astronomy, anyway, LaTeX is the default. It's probably different in other fields which is why the broader journals use Word.
Jabbles 15y ago
Well he starts off by considering the kinetic energy of light...
lutorm 15y ago
a brief perusal sets off my crank alarms That's what I was going to say, too. And I got more convinced the further down I got. The weird, convoluted wording was a big tipoff. And then this sealed it: When a star explodes and its mass is combusted into radiation, conservation requires that the number of quanta stays the same, whether in the form of matter or radiation. There is no conservation law limiting the number of photons. This is obviously observed any time you turn on a light bulb.

bh42222 15y ago

I viscerally distrust anything from physorg.com. Anyone have a better option?