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First we had Newton's laws of gravity. It worked quite well in the solar system scale and everyone was happy. Then Einstein formulated the special theory of rel

by gh1 10y ago

First we had Newton's laws of gravity. It worked quite well in the solar system scale and everyone was happy. Then Einstein formulated the special theory of relativity and Newtonian gravity was found to be incompatible with that. So Einstein formulated the General Theory of Relativity (Einsteinian Gravity) which solves that problem. As a bonus, his theory could also explain the eccentric behavior of Mercury's orbits, which Newtonian Gravity couldn't. It also predicted that galaxies should be able to bend light (lensing) and this was confirmed by Arthur Eddington. However, for many galaxies, the amount of lensing is way off from what the Einsteinian theory predicts. Similarly, rotational velocities of stars in a galaxy are also way off from what is predicted by both Einsteinian and Newtonian theory. In addition, when you apply the Einsteinian theory to the entire universe, you can't explain the observable geometry of the universe. That is also way off. Dark matter and Dark Energy are just a very clever way of saying "we have no idea what's going on with gravity in the large scale (beyond solar system scales)". No one has ever observed any dark matter or dark energy so far. It is entirely possible that Einsteinian theory of Gravity is just an approximation that works well for small scales and that we need a new theory of gravity at the galactic scale or the scale of the universe. It is also entirely possible that Dark Matter and Energy don't actually exist.

danharaj 10y ago
> In addition, when you apply the Einsteinian theory to the entire universe, you can't explain the observable geometry of the universe. https://en.wikipedia.org/wiki/Friedmann%E2%80%93Lema%C3%AEtre%E2%80%93Robertson%E2%80%93Walker_metric https://en.wikipedia.org/wiki/Friedmann%E2%80%93Lema%C3%AEtr... "The Friedmann–Lemaître–Robertson–Walker (FLRW) metric is an exact solution of Einstein's field equations of general relativity; it describes a homogeneous, isotropic expanding or contracting universe that is path connected, but not necessarily simply connected." > No one has ever observed any dark matter http://chandra.harvard.edu/press/06_releases/press_082106.html http://chandra.harvard.edu/press/06_releases/press_082106.ht... "NASA finds direct proof of Dark Matter" > or dark energy so far. This is probably the only part of your post that actually came close to the truth. Dark energy is far more of a placeholder than dark matter at this point.
- gh1 10y ago
  1. I was referring to the fact that the observable matter of the universe is not enough to generate the nearly flat and accelerating universe. 2. I am quoting from the article. "In addition to the Chandra observation, the Hubble Space Telescope, the European Southern Observatory's Very Large Telescope and the Magellan optical telescopes were used to determine the location of the mass in the clusters. This was done by measuring the effect of gravitational lensing, where gravity from the clusters distorts light from background galaxies as predicted by Einstein's theory of general relativity." Since they are calculating the mass by using General Theory of Relativity (indirect measurement, you have to trust the theory for this), I don't see how this can be called direct detection. 3. We don't seem to disagree on this :)
  - smallnamespace 10y ago
    https://en.wikipedia.org/wiki/Modified_Newtonian_dynamics#Attempts_to_explain_MOND_phenomenology_using_dark_matter https://en.wikipedia.org/wiki/Modified_Newtonian_dynamics#At... 'The most serious problem facing Milgrom's law is that it cannot completely eliminate the need for dark matter in all astrophysical systems: galaxy clusters show a residual mass discrepancy even when analysed using MOND.' 'Besides these observational issues, MOND and its generalisations are plagued by theoretical difficulties. Several ad-hoc and inelegant additions to general relativity are required to create a theory with a non-Newtonian non-relativistic limit, the plethora of different versions of the theory offer diverging predictions in simple physical situations and thus make it difficult to test the framework conclusively, and some formulations (most prominently those based on modified inertia) have long suffered from poor compatibility with cherished physical principles such as conservation laws.' Basically, people have tried to fiddle with the laws as you suggested, but none of actually managed to fit the data better than GR + dark matter, plus the fiddling often just looked like curve-fitting without any good theoretical justification. Of course, the jury's still out.
conistonwater 10y ago
It's the precession of Mercury's perihelion, not the eccentricity of its orbit: apart from the perihelion precession issue for Mercury and, to a lesser extent, Venus, the solar system is quite Newtonian. Also, the first lensing experiment measured the amount of light deflection by the sun, not galaxies.
- gh1 10y ago
  Thanks. I actually meant eccentricity = craziness, not in the mathematical sense. You are absolutely right about the Eddington experiment.
  - conistonwater 10y ago
    That's seriously confusing, then, it's such a standard mathematical term: https://en.wikipedia.org/wiki/Orbital_eccentricity https://en.wikipedia.org/wiki/Orbital_eccentricity
    - gh1 10y ago
      You are right. I changed it. Hopefully, its not confusing any more.
StanislavPetrov 10y ago
>It is also entirely possible that Dark Matter and Energy don't actually exist. Exactly. The whole basis for belief in "dark matter" and "dark energy" is basically: "our theories on how the universe works don't compute, so there must be some invisible things (dark matter & energy) we cannot detect since our theories can't be wrong."
- XorNot 10y ago
  Except for the slight problem that observations of the bullet cluster show gravitational lensing inconsistent with the observed mass of physical matter. MOND has no explanation for this.
- Avshalom 10y ago
  No our theories were wrong, that was obvious, dark matter and dark energy are (part of) the new theory We're going with them because all the other new theories end up requiring fractional dimensions or some similarly bizarre space time and still don't end up explaining things as well as "I dunno guys maybe there's just some stuff we can't see". We already know there's a bunch of stuff we can't see, dark matter is just some other kind of stuff we can't see. Dark matter is on the correct side of the razor.
  - sdenton4 10y ago
    The shift here is that dark matter is detected only in aggregate. And massive aggregates at that. What are the properties of dark matter? Where does it come from? How does it interact with other matter, light or dark? No idea, because it's only detected as a correction term.
    - Avshalom 10y ago
      https://en.wikipedia.org/wiki/Bullet_Cluster https://en.wikipedia.org/wiki/Bullet_Cluster We know there's a bunch of mass we can't see: https://en.wikipedia.org/wiki/MACS_J0025.4-1222 https://en.wikipedia.org/wiki/MACS_J0025.4-1222 https://en.wikipedia.org/wiki/Dragonfly_44 https://en.wikipedia.org/wiki/Dragonfly_44 We have had direct detection of dark matter since the 50s https://en.wikipedia.org/wiki/Neutrino https://en.wikipedia.org/wiki/Neutrino And the generally successful standard model predicts several possible additional forms of dark matter e.g. https://en.wikipedia.org/wiki/Neutralino https://en.wikipedia.org/wiki/Neutralino I mean no shit there are in answered questions. We aren't omniscient. this is how it works.
aaron695 10y ago
Einstein made a small improvement to Newton. People seem think think this allows our current theories to be wrong..... Perhaps there might be small issues with Einstein theories, personally I doubt it, but, to me, I really don't think small fixes to the theory will explain this stuff away.
- fibo 10y ago
  Even if Einstein theory need a fix, some math achievements would keep valid: for example the Bianchi identities Einstein used.
- madaxe_again 10y ago
  It's not actually clear that there is any problem with current theory - it may just be that our understanding and application of it is incorrect. You can have a perfect mathematical model, but if just one of your premises is incorrect, the output can be nonsensical. I am a physicist (well, I studied as one, before going technology entrepreneur), and have always sat in the "dark matter is bullshit" camp - so my opinion is likely tainted. I think a far more likely explanation, as this paper could suggest, is that something far more mundane is happening. For instance, we already understand tidal forces - that bodies can become tidally locked, that there is an inertial frame shear that drags bodies along around a rotating centre of mass, and exchanges energy between an orbiting body and the centre.... So why is it infeasible that galaxies are tidally locked, and the lack of fall-off in radial velocity is down to the gravitational shear from the galactic core being far more intense than we anticipate, causing the behaviour we see. It doesn't require a rewrite of relativity, "just" of galactic evolution. Either that, or galaxies are sprites, and lazily rendered ones, at that.
  - dnautics 10y ago
    I've half joked that dark matter might be cumulative IEEE floating point rounding errors.
    - adrianN 10y ago
      I hope God doesn't use IEEE floats.
zamalek 10y ago
> Dark matter and Dark Energy are just a very clever way of saying "we have no idea what's going on with gravity in the large scale (beyond solar system scales)". While I agree with definition of dark matter that you provided, keep in mind that there are hypothesis that try and explain it as something that exists. For example: WIMPs.
- dnautics 10y ago
  This result could suggest a MACHO, however.
ilogik 10y ago
Didn't eddington prove lensing caused by the sun? By measuring the positions of stars during a solar eclipse in Africa

by gh1 10y ago

danharaj 10y ago

> In addition, when you apply the Einsteinian theory to the entire universe, you can't explain the observable geometry of the universe. https://en.wikipedia.org/wiki/Friedmann%E2%80%93Lema%C3%AEtre%E2%80%93Robertson%E2%80%93Walker_metric https://en.wikipedia.org/wiki/Friedmann%E2%80%93Lema%C3%AEtr... "The Friedmann–Lemaître–Robertson–Walker (FLRW) metric is an exact solution of Einstein's field equations of general relativity; it describes a homogeneous, isotropic expanding or contracting universe that is path connected, but not necessarily simply connected." > No one has ever observed any dark matter http://chandra.harvard.edu/press/06_releases/press_082106.html http://chandra.harvard.edu/press/06_releases/press_082106.ht... "NASA finds direct proof of Dark Matter" > or dark energy so far. This is probably the only part of your post that actually came close to the truth. Dark energy is far more of a placeholder than dark matter at this point.

gh1 10y ago
1. I was referring to the fact that the observable matter of the universe is not enough to generate the nearly flat and accelerating universe. 2. I am quoting from the article. "In addition to the Chandra observation, the Hubble Space Telescope, the European Southern Observatory's Very Large Telescope and the Magellan optical telescopes were used to determine the location of the mass in the clusters. This was done by measuring the effect of gravitational lensing, where gravity from the clusters distorts light from background galaxies as predicted by Einstein's theory of general relativity." Since they are calculating the mass by using General Theory of Relativity (indirect measurement, you have to trust the theory for this), I don't see how this can be called direct detection. 3. We don't seem to disagree on this :)
- smallnamespace 10y ago
  https://en.wikipedia.org/wiki/Modified_Newtonian_dynamics#Attempts_to_explain_MOND_phenomenology_using_dark_matter https://en.wikipedia.org/wiki/Modified_Newtonian_dynamics#At... 'The most serious problem facing Milgrom's law is that it cannot completely eliminate the need for dark matter in all astrophysical systems: galaxy clusters show a residual mass discrepancy even when analysed using MOND.' 'Besides these observational issues, MOND and its generalisations are plagued by theoretical difficulties. Several ad-hoc and inelegant additions to general relativity are required to create a theory with a non-Newtonian non-relativistic limit, the plethora of different versions of the theory offer diverging predictions in simple physical situations and thus make it difficult to test the framework conclusively, and some formulations (most prominently those based on modified inertia) have long suffered from poor compatibility with cherished physical principles such as conservation laws.' Basically, people have tried to fiddle with the laws as you suggested, but none of actually managed to fit the data better than GR + dark matter, plus the fiddling often just looked like curve-fitting without any good theoretical justification. Of course, the jury's still out.

conistonwater 10y ago

It's the precession of Mercury's perihelion, not the eccentricity of its orbit: apart from the perihelion precession issue for Mercury and, to a lesser extent, Venus, the solar system is quite Newtonian. Also, the first lensing experiment measured the amount of light deflection by the sun, not galaxies.

gh1 10y ago
Thanks. I actually meant eccentricity = craziness, not in the mathematical sense. You are absolutely right about the Eddington experiment.
- conistonwater 10y ago
  That's seriously confusing, then, it's such a standard mathematical term: https://en.wikipedia.org/wiki/Orbital_eccentricity https://en.wikipedia.org/wiki/Orbital_eccentricity
  - gh1 10y ago
    You are right. I changed it. Hopefully, its not confusing any more.

StanislavPetrov 10y ago

>It is also entirely possible that Dark Matter and Energy don't actually exist. Exactly. The whole basis for belief in "dark matter" and "dark energy" is basically: "our theories on how the universe works don't compute, so there must be some invisible things (dark matter & energy) we cannot detect since our theories can't be wrong."

XorNot 10y ago
Except for the slight problem that observations of the bullet cluster show gravitational lensing inconsistent with the observed mass of physical matter. MOND has no explanation for this.
Avshalom 10y ago
No our theories were wrong, that was obvious, dark matter and dark energy are (part of) the new theory We're going with them because all the other new theories end up requiring fractional dimensions or some similarly bizarre space time and still don't end up explaining things as well as "I dunno guys maybe there's just some stuff we can't see". We already know there's a bunch of stuff we can't see, dark matter is just some other kind of stuff we can't see. Dark matter is on the correct side of the razor.
- sdenton4 10y ago
  The shift here is that dark matter is detected only in aggregate. And massive aggregates at that. What are the properties of dark matter? Where does it come from? How does it interact with other matter, light or dark? No idea, because it's only detected as a correction term.
  - Avshalom 10y ago
    https://en.wikipedia.org/wiki/Bullet_Cluster https://en.wikipedia.org/wiki/Bullet_Cluster We know there's a bunch of mass we can't see: https://en.wikipedia.org/wiki/MACS_J0025.4-1222 https://en.wikipedia.org/wiki/MACS_J0025.4-1222 https://en.wikipedia.org/wiki/Dragonfly_44 https://en.wikipedia.org/wiki/Dragonfly_44 We have had direct detection of dark matter since the 50s https://en.wikipedia.org/wiki/Neutrino https://en.wikipedia.org/wiki/Neutrino And the generally successful standard model predicts several possible additional forms of dark matter e.g. https://en.wikipedia.org/wiki/Neutralino https://en.wikipedia.org/wiki/Neutralino I mean no shit there are in answered questions. We aren't omniscient. this is how it works.

aaron695 10y ago

Einstein made a small improvement to Newton. People seem think think this allows our current theories to be wrong..... Perhaps there might be small issues with Einstein theories, personally I doubt it, but, to me, I really don't think small fixes to the theory will explain this stuff away.

fibo 10y ago
Even if Einstein theory need a fix, some math achievements would keep valid: for example the Bianchi identities Einstein used.
madaxe_again 10y ago
It's not actually clear that there is any problem with current theory - it may just be that our understanding and application of it is incorrect. You can have a perfect mathematical model, but if just one of your premises is incorrect, the output can be nonsensical. I am a physicist (well, I studied as one, before going technology entrepreneur), and have always sat in the "dark matter is bullshit" camp - so my opinion is likely tainted. I think a far more likely explanation, as this paper could suggest, is that something far more mundane is happening. For instance, we already understand tidal forces - that bodies can become tidally locked, that there is an inertial frame shear that drags bodies along around a rotating centre of mass, and exchanges energy between an orbiting body and the centre.... So why is it infeasible that galaxies are tidally locked, and the lack of fall-off in radial velocity is down to the gravitational shear from the galactic core being far more intense than we anticipate, causing the behaviour we see. It doesn't require a rewrite of relativity, "just" of galactic evolution. Either that, or galaxies are sprites, and lazily rendered ones, at that.
- dnautics 10y ago
  I've half joked that dark matter might be cumulative IEEE floating point rounding errors.
  - adrianN 10y ago
    I hope God doesn't use IEEE floats.

zamalek 10y ago

> Dark matter and Dark Energy are just a very clever way of saying "we have no idea what's going on with gravity in the large scale (beyond solar system scales)". While I agree with definition of dark matter that you provided, keep in mind that there are hypothesis that try and explain it as something that exists. For example: WIMPs.

dnautics 10y ago
This result could suggest a MACHO, however.

ilogik 10y ago

Didn't eddington prove lensing caused by the sun? By measuring the positions of stars during a solar eclipse in Africa