Is dark matter really a meaningful hypothesis?












2












$begingroup$


This thought has been bugging me from quite some time so I decided to ask.



According to CMBR the universe was a cloud of plasma and was a perfect black body, $380,!000$ years after big bang.



But the Sun in our solar system also is in the state of plasma and yet doesn't act like a blackbody (i.e. sun radiates large amounts of its energy as electromagnetic radiation), so it is possible that the universe in its initial stage also behaved similarly. And this is the reason we find find less baryonic matter than we should. Thus making the concept of dark energy irrelevant.










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N Pranav Subhraveti is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
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  • $begingroup$
    I heard dark matter was invented because modern physics theories didnt create accurate simulations in a computer. youtube.com/watch?v=GFxPMMkhHuA
    $endgroup$
    – eromod
    4 hours ago






  • 3




    $begingroup$
    Black bodies DO radiate; dark matter is not black, because it does not radiate. Thermodynamic principles require surfaces which absorb (are black) be good radiators of light, which is a feature absent in dark matter.
    $endgroup$
    – Whit3rd
    4 hours ago






  • 1




    $begingroup$
    Dark matter and dark energy are not the same thing
    $endgroup$
    – lcv
    2 hours ago
















2












$begingroup$


This thought has been bugging me from quite some time so I decided to ask.



According to CMBR the universe was a cloud of plasma and was a perfect black body, $380,!000$ years after big bang.



But the Sun in our solar system also is in the state of plasma and yet doesn't act like a blackbody (i.e. sun radiates large amounts of its energy as electromagnetic radiation), so it is possible that the universe in its initial stage also behaved similarly. And this is the reason we find find less baryonic matter than we should. Thus making the concept of dark energy irrelevant.










share|cite|improve this question









New contributor




N Pranav Subhraveti is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.







$endgroup$












  • $begingroup$
    I heard dark matter was invented because modern physics theories didnt create accurate simulations in a computer. youtube.com/watch?v=GFxPMMkhHuA
    $endgroup$
    – eromod
    4 hours ago






  • 3




    $begingroup$
    Black bodies DO radiate; dark matter is not black, because it does not radiate. Thermodynamic principles require surfaces which absorb (are black) be good radiators of light, which is a feature absent in dark matter.
    $endgroup$
    – Whit3rd
    4 hours ago






  • 1




    $begingroup$
    Dark matter and dark energy are not the same thing
    $endgroup$
    – lcv
    2 hours ago














2












2








2





$begingroup$


This thought has been bugging me from quite some time so I decided to ask.



According to CMBR the universe was a cloud of plasma and was a perfect black body, $380,!000$ years after big bang.



But the Sun in our solar system also is in the state of plasma and yet doesn't act like a blackbody (i.e. sun radiates large amounts of its energy as electromagnetic radiation), so it is possible that the universe in its initial stage also behaved similarly. And this is the reason we find find less baryonic matter than we should. Thus making the concept of dark energy irrelevant.










share|cite|improve this question









New contributor




N Pranav Subhraveti is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.







$endgroup$




This thought has been bugging me from quite some time so I decided to ask.



According to CMBR the universe was a cloud of plasma and was a perfect black body, $380,!000$ years after big bang.



But the Sun in our solar system also is in the state of plasma and yet doesn't act like a blackbody (i.e. sun radiates large amounts of its energy as electromagnetic radiation), so it is possible that the universe in its initial stage also behaved similarly. And this is the reason we find find less baryonic matter than we should. Thus making the concept of dark energy irrelevant.







cosmology big-bang dark-matter cosmic-microwave-background baryons






share|cite|improve this question









New contributor




N Pranav Subhraveti is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.











share|cite|improve this question









New contributor




N Pranav Subhraveti is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.









share|cite|improve this question




share|cite|improve this question








edited 2 hours ago









MannyC

1,346314




1,346314






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N Pranav Subhraveti is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
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asked 5 hours ago









N Pranav SubhravetiN Pranav Subhraveti

111




111




New contributor




N Pranav Subhraveti is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
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New contributor





N Pranav Subhraveti is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.






N Pranav Subhraveti is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.












  • $begingroup$
    I heard dark matter was invented because modern physics theories didnt create accurate simulations in a computer. youtube.com/watch?v=GFxPMMkhHuA
    $endgroup$
    – eromod
    4 hours ago






  • 3




    $begingroup$
    Black bodies DO radiate; dark matter is not black, because it does not radiate. Thermodynamic principles require surfaces which absorb (are black) be good radiators of light, which is a feature absent in dark matter.
    $endgroup$
    – Whit3rd
    4 hours ago






  • 1




    $begingroup$
    Dark matter and dark energy are not the same thing
    $endgroup$
    – lcv
    2 hours ago


















  • $begingroup$
    I heard dark matter was invented because modern physics theories didnt create accurate simulations in a computer. youtube.com/watch?v=GFxPMMkhHuA
    $endgroup$
    – eromod
    4 hours ago






  • 3




    $begingroup$
    Black bodies DO radiate; dark matter is not black, because it does not radiate. Thermodynamic principles require surfaces which absorb (are black) be good radiators of light, which is a feature absent in dark matter.
    $endgroup$
    – Whit3rd
    4 hours ago






  • 1




    $begingroup$
    Dark matter and dark energy are not the same thing
    $endgroup$
    – lcv
    2 hours ago
















$begingroup$
I heard dark matter was invented because modern physics theories didnt create accurate simulations in a computer. youtube.com/watch?v=GFxPMMkhHuA
$endgroup$
– eromod
4 hours ago




$begingroup$
I heard dark matter was invented because modern physics theories didnt create accurate simulations in a computer. youtube.com/watch?v=GFxPMMkhHuA
$endgroup$
– eromod
4 hours ago




3




3




$begingroup$
Black bodies DO radiate; dark matter is not black, because it does not radiate. Thermodynamic principles require surfaces which absorb (are black) be good radiators of light, which is a feature absent in dark matter.
$endgroup$
– Whit3rd
4 hours ago




$begingroup$
Black bodies DO radiate; dark matter is not black, because it does not radiate. Thermodynamic principles require surfaces which absorb (are black) be good radiators of light, which is a feature absent in dark matter.
$endgroup$
– Whit3rd
4 hours ago




1




1




$begingroup$
Dark matter and dark energy are not the same thing
$endgroup$
– lcv
2 hours ago




$begingroup$
Dark matter and dark energy are not the same thing
$endgroup$
– lcv
2 hours ago










3 Answers
3






active

oldest

votes


















2












$begingroup$


But the Sun in our solar system also is in the state of plasma and yet doesn't act like a blackbody




Wrong, the sun radiation is approximately fitted as a black body. The word "black body" does not describe the frequencies, but the assumption that it absorbs all radiation falling on it and re-emits it.



Here is the sun, and it fits the black body formula approximately.



sunbb




Solar irradiance spectrum above atmosphere and at surface. Extreme UV and X-rays are produced (at left of wavelength range shown) but comprise very small amounts of the Sun's total output power.




Plasma is also described by black body radiation.




so it is possible that the universe in its initial stage also behaved similarly. And this is the reason we find find less baryonic matter than we should. Thus making the concept of dark energy irrelevant.




This is wrong, as seen above because your premiss is wrong, but also, dark matter is necessary to fit the newtonian rotational curves of galaxies, and more observational evidence can be found in this link..



Dark matter is a completely classical observation of newtonian and general relativity. Baryon asymmetry comes from quantum mechanical knowledge of the content of the classical masses, and does not involve dark matter in any meaningful manner.






share|cite|improve this answer











$endgroup$





















    2












    $begingroup$

    Short answer: yes.



    You should look in to the history behind the dark matter hypothesis. It started not from the examination of cosmology and the CMB, but from the motion of galaxies in clusters and stars orbiting around galaxies. See, the vast majority of ordinary matter in every galaxy is contained in the gas between the stars, not the stars themselves. Because of that, we can get a decent handle on how much ordinary matter is around by observing that. Tools for this purpose: the 21 cm line of atomic hydrogen, when the gas is cold, as much of it is in spiral galaxies, and looking at the x-ray spectrum when it is exceptionally hot, as it is between galaxies in large clusters.



    When we examine the way the parts of galaxies, and the galaxies in clusters, move, they're travelling way too fast. If the mass we can see direct evidence for is all there is, the clusters would not be able to hold on to their hot gas and galaxies, and the galaxies would not hold together, either.



    "So what? Maybe the matter is there, it just isn't giving off light." Trouble is, if it were hot enough to be a plasma, and thus lack spectral lines, we could see it directly. If it were too cold to be a plasma, it would block light from galaxies and quasars in the background more in the matter's spectral lines. So whatever is producing this extra gravity has to neither emit nor absorb light in any way we've been able to detect.



    It just so happens that adding dark matter (or something very like it) to the cosmology simulations is also essential to explain the CMB data.



    Now, you may object that the extra gravity we've observed may have some other source. For instance, maybe Newton's law of gravitation is simply wrong on the scale of galaxies and larger. The trouble that idea runs into is you're no longer able to explain the bullet cluster, where the gas between the galaxies has collided, but the dark matter and galaxies did not.



    On the subject of black body spectra. The black body is the spectrum that a gas of photons assumes if it is in thermal equilibrium (constant uniform temperature everywhere). The CMB is very very nearly a black-body because at the time the differences in temperature between any two parts of the universe were very very small. The sun, however, is surrounded by a very cold vacuum, and that lack of equilibrium will inevitably cause the spectrum to deviate from the ideal Planck function.






    share|cite|improve this answer









    $endgroup$













    • $begingroup$
      Could it be we don’t measure the mass correctly at all?
      $endgroup$
      – 0x90
      52 mins ago










    • $begingroup$
      @0x90 Not likely. The way we measure mass is based on the physics of how light interacts with matter, something we have measured extremely well here on the ground. See, if a gas is thin enough that it is unlikely to reabsorb anything it emits ("optically thin" - see the 21 cm line), then we can deduce the gas temperature from the way the shape of the line is distorted, and the amount of gas along the line of sight ("column density") from brightness. Total mass is just adding up the lines of sight. The process is similar for absorption, just inverted.
      $endgroup$
      – Sean E. Lake
      48 mins ago










    • $begingroup$
      That said, one of the dark matter candidates is known as "MACHOs" for "Massive Compact Halo Objects". Basically, the thinking is if you have enough really high concentrations of mass that don't emit light (think black holes), that could do the trick. Trouble is, you'd expect them to pass between you and a star from another galaxy from time to time, lensing the light of the background star, making it appear brighter. Searches for this phenomenon have come up short, meaning it is unlikely that MACHOs can explain all of dark matter.
      $endgroup$
      – Sean E. Lake
      44 mins ago










    • $begingroup$
      what if the matter is transparent to light (the wavelength of the light is too long). Like radio wave and our body.
      $endgroup$
      – 0x90
      43 mins ago



















    -1












    $begingroup$

    Being meaningful and being hypothetical, do not always work in hand.



    My personal opinion is, dark matter will be replaced for a better model in time. By the way, the sun is a black body, its just not a pure one. It's antithesis is the black hole, which is a near perfect black body.






    share|cite|improve this answer









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      3 Answers
      3






      active

      oldest

      votes








      3 Answers
      3






      active

      oldest

      votes









      active

      oldest

      votes






      active

      oldest

      votes









      2












      $begingroup$


      But the Sun in our solar system also is in the state of plasma and yet doesn't act like a blackbody




      Wrong, the sun radiation is approximately fitted as a black body. The word "black body" does not describe the frequencies, but the assumption that it absorbs all radiation falling on it and re-emits it.



      Here is the sun, and it fits the black body formula approximately.



      sunbb




      Solar irradiance spectrum above atmosphere and at surface. Extreme UV and X-rays are produced (at left of wavelength range shown) but comprise very small amounts of the Sun's total output power.




      Plasma is also described by black body radiation.




      so it is possible that the universe in its initial stage also behaved similarly. And this is the reason we find find less baryonic matter than we should. Thus making the concept of dark energy irrelevant.




      This is wrong, as seen above because your premiss is wrong, but also, dark matter is necessary to fit the newtonian rotational curves of galaxies, and more observational evidence can be found in this link..



      Dark matter is a completely classical observation of newtonian and general relativity. Baryon asymmetry comes from quantum mechanical knowledge of the content of the classical masses, and does not involve dark matter in any meaningful manner.






      share|cite|improve this answer











      $endgroup$


















        2












        $begingroup$


        But the Sun in our solar system also is in the state of plasma and yet doesn't act like a blackbody




        Wrong, the sun radiation is approximately fitted as a black body. The word "black body" does not describe the frequencies, but the assumption that it absorbs all radiation falling on it and re-emits it.



        Here is the sun, and it fits the black body formula approximately.



        sunbb




        Solar irradiance spectrum above atmosphere and at surface. Extreme UV and X-rays are produced (at left of wavelength range shown) but comprise very small amounts of the Sun's total output power.




        Plasma is also described by black body radiation.




        so it is possible that the universe in its initial stage also behaved similarly. And this is the reason we find find less baryonic matter than we should. Thus making the concept of dark energy irrelevant.




        This is wrong, as seen above because your premiss is wrong, but also, dark matter is necessary to fit the newtonian rotational curves of galaxies, and more observational evidence can be found in this link..



        Dark matter is a completely classical observation of newtonian and general relativity. Baryon asymmetry comes from quantum mechanical knowledge of the content of the classical masses, and does not involve dark matter in any meaningful manner.






        share|cite|improve this answer











        $endgroup$
















          2












          2








          2





          $begingroup$


          But the Sun in our solar system also is in the state of plasma and yet doesn't act like a blackbody




          Wrong, the sun radiation is approximately fitted as a black body. The word "black body" does not describe the frequencies, but the assumption that it absorbs all radiation falling on it and re-emits it.



          Here is the sun, and it fits the black body formula approximately.



          sunbb




          Solar irradiance spectrum above atmosphere and at surface. Extreme UV and X-rays are produced (at left of wavelength range shown) but comprise very small amounts of the Sun's total output power.




          Plasma is also described by black body radiation.




          so it is possible that the universe in its initial stage also behaved similarly. And this is the reason we find find less baryonic matter than we should. Thus making the concept of dark energy irrelevant.




          This is wrong, as seen above because your premiss is wrong, but also, dark matter is necessary to fit the newtonian rotational curves of galaxies, and more observational evidence can be found in this link..



          Dark matter is a completely classical observation of newtonian and general relativity. Baryon asymmetry comes from quantum mechanical knowledge of the content of the classical masses, and does not involve dark matter in any meaningful manner.






          share|cite|improve this answer











          $endgroup$




          But the Sun in our solar system also is in the state of plasma and yet doesn't act like a blackbody




          Wrong, the sun radiation is approximately fitted as a black body. The word "black body" does not describe the frequencies, but the assumption that it absorbs all radiation falling on it and re-emits it.



          Here is the sun, and it fits the black body formula approximately.



          sunbb




          Solar irradiance spectrum above atmosphere and at surface. Extreme UV and X-rays are produced (at left of wavelength range shown) but comprise very small amounts of the Sun's total output power.




          Plasma is also described by black body radiation.




          so it is possible that the universe in its initial stage also behaved similarly. And this is the reason we find find less baryonic matter than we should. Thus making the concept of dark energy irrelevant.




          This is wrong, as seen above because your premiss is wrong, but also, dark matter is necessary to fit the newtonian rotational curves of galaxies, and more observational evidence can be found in this link..



          Dark matter is a completely classical observation of newtonian and general relativity. Baryon asymmetry comes from quantum mechanical knowledge of the content of the classical masses, and does not involve dark matter in any meaningful manner.







          share|cite|improve this answer














          share|cite|improve this answer



          share|cite|improve this answer








          edited 1 hour ago

























          answered 1 hour ago









          anna vanna v

          162k8153456




          162k8153456























              2












              $begingroup$

              Short answer: yes.



              You should look in to the history behind the dark matter hypothesis. It started not from the examination of cosmology and the CMB, but from the motion of galaxies in clusters and stars orbiting around galaxies. See, the vast majority of ordinary matter in every galaxy is contained in the gas between the stars, not the stars themselves. Because of that, we can get a decent handle on how much ordinary matter is around by observing that. Tools for this purpose: the 21 cm line of atomic hydrogen, when the gas is cold, as much of it is in spiral galaxies, and looking at the x-ray spectrum when it is exceptionally hot, as it is between galaxies in large clusters.



              When we examine the way the parts of galaxies, and the galaxies in clusters, move, they're travelling way too fast. If the mass we can see direct evidence for is all there is, the clusters would not be able to hold on to their hot gas and galaxies, and the galaxies would not hold together, either.



              "So what? Maybe the matter is there, it just isn't giving off light." Trouble is, if it were hot enough to be a plasma, and thus lack spectral lines, we could see it directly. If it were too cold to be a plasma, it would block light from galaxies and quasars in the background more in the matter's spectral lines. So whatever is producing this extra gravity has to neither emit nor absorb light in any way we've been able to detect.



              It just so happens that adding dark matter (or something very like it) to the cosmology simulations is also essential to explain the CMB data.



              Now, you may object that the extra gravity we've observed may have some other source. For instance, maybe Newton's law of gravitation is simply wrong on the scale of galaxies and larger. The trouble that idea runs into is you're no longer able to explain the bullet cluster, where the gas between the galaxies has collided, but the dark matter and galaxies did not.



              On the subject of black body spectra. The black body is the spectrum that a gas of photons assumes if it is in thermal equilibrium (constant uniform temperature everywhere). The CMB is very very nearly a black-body because at the time the differences in temperature between any two parts of the universe were very very small. The sun, however, is surrounded by a very cold vacuum, and that lack of equilibrium will inevitably cause the spectrum to deviate from the ideal Planck function.






              share|cite|improve this answer









              $endgroup$













              • $begingroup$
                Could it be we don’t measure the mass correctly at all?
                $endgroup$
                – 0x90
                52 mins ago










              • $begingroup$
                @0x90 Not likely. The way we measure mass is based on the physics of how light interacts with matter, something we have measured extremely well here on the ground. See, if a gas is thin enough that it is unlikely to reabsorb anything it emits ("optically thin" - see the 21 cm line), then we can deduce the gas temperature from the way the shape of the line is distorted, and the amount of gas along the line of sight ("column density") from brightness. Total mass is just adding up the lines of sight. The process is similar for absorption, just inverted.
                $endgroup$
                – Sean E. Lake
                48 mins ago










              • $begingroup$
                That said, one of the dark matter candidates is known as "MACHOs" for "Massive Compact Halo Objects". Basically, the thinking is if you have enough really high concentrations of mass that don't emit light (think black holes), that could do the trick. Trouble is, you'd expect them to pass between you and a star from another galaxy from time to time, lensing the light of the background star, making it appear brighter. Searches for this phenomenon have come up short, meaning it is unlikely that MACHOs can explain all of dark matter.
                $endgroup$
                – Sean E. Lake
                44 mins ago










              • $begingroup$
                what if the matter is transparent to light (the wavelength of the light is too long). Like radio wave and our body.
                $endgroup$
                – 0x90
                43 mins ago
















              2












              $begingroup$

              Short answer: yes.



              You should look in to the history behind the dark matter hypothesis. It started not from the examination of cosmology and the CMB, but from the motion of galaxies in clusters and stars orbiting around galaxies. See, the vast majority of ordinary matter in every galaxy is contained in the gas between the stars, not the stars themselves. Because of that, we can get a decent handle on how much ordinary matter is around by observing that. Tools for this purpose: the 21 cm line of atomic hydrogen, when the gas is cold, as much of it is in spiral galaxies, and looking at the x-ray spectrum when it is exceptionally hot, as it is between galaxies in large clusters.



              When we examine the way the parts of galaxies, and the galaxies in clusters, move, they're travelling way too fast. If the mass we can see direct evidence for is all there is, the clusters would not be able to hold on to their hot gas and galaxies, and the galaxies would not hold together, either.



              "So what? Maybe the matter is there, it just isn't giving off light." Trouble is, if it were hot enough to be a plasma, and thus lack spectral lines, we could see it directly. If it were too cold to be a plasma, it would block light from galaxies and quasars in the background more in the matter's spectral lines. So whatever is producing this extra gravity has to neither emit nor absorb light in any way we've been able to detect.



              It just so happens that adding dark matter (or something very like it) to the cosmology simulations is also essential to explain the CMB data.



              Now, you may object that the extra gravity we've observed may have some other source. For instance, maybe Newton's law of gravitation is simply wrong on the scale of galaxies and larger. The trouble that idea runs into is you're no longer able to explain the bullet cluster, where the gas between the galaxies has collided, but the dark matter and galaxies did not.



              On the subject of black body spectra. The black body is the spectrum that a gas of photons assumes if it is in thermal equilibrium (constant uniform temperature everywhere). The CMB is very very nearly a black-body because at the time the differences in temperature between any two parts of the universe were very very small. The sun, however, is surrounded by a very cold vacuum, and that lack of equilibrium will inevitably cause the spectrum to deviate from the ideal Planck function.






              share|cite|improve this answer









              $endgroup$













              • $begingroup$
                Could it be we don’t measure the mass correctly at all?
                $endgroup$
                – 0x90
                52 mins ago










              • $begingroup$
                @0x90 Not likely. The way we measure mass is based on the physics of how light interacts with matter, something we have measured extremely well here on the ground. See, if a gas is thin enough that it is unlikely to reabsorb anything it emits ("optically thin" - see the 21 cm line), then we can deduce the gas temperature from the way the shape of the line is distorted, and the amount of gas along the line of sight ("column density") from brightness. Total mass is just adding up the lines of sight. The process is similar for absorption, just inverted.
                $endgroup$
                – Sean E. Lake
                48 mins ago










              • $begingroup$
                That said, one of the dark matter candidates is known as "MACHOs" for "Massive Compact Halo Objects". Basically, the thinking is if you have enough really high concentrations of mass that don't emit light (think black holes), that could do the trick. Trouble is, you'd expect them to pass between you and a star from another galaxy from time to time, lensing the light of the background star, making it appear brighter. Searches for this phenomenon have come up short, meaning it is unlikely that MACHOs can explain all of dark matter.
                $endgroup$
                – Sean E. Lake
                44 mins ago










              • $begingroup$
                what if the matter is transparent to light (the wavelength of the light is too long). Like radio wave and our body.
                $endgroup$
                – 0x90
                43 mins ago














              2












              2








              2





              $begingroup$

              Short answer: yes.



              You should look in to the history behind the dark matter hypothesis. It started not from the examination of cosmology and the CMB, but from the motion of galaxies in clusters and stars orbiting around galaxies. See, the vast majority of ordinary matter in every galaxy is contained in the gas between the stars, not the stars themselves. Because of that, we can get a decent handle on how much ordinary matter is around by observing that. Tools for this purpose: the 21 cm line of atomic hydrogen, when the gas is cold, as much of it is in spiral galaxies, and looking at the x-ray spectrum when it is exceptionally hot, as it is between galaxies in large clusters.



              When we examine the way the parts of galaxies, and the galaxies in clusters, move, they're travelling way too fast. If the mass we can see direct evidence for is all there is, the clusters would not be able to hold on to their hot gas and galaxies, and the galaxies would not hold together, either.



              "So what? Maybe the matter is there, it just isn't giving off light." Trouble is, if it were hot enough to be a plasma, and thus lack spectral lines, we could see it directly. If it were too cold to be a plasma, it would block light from galaxies and quasars in the background more in the matter's spectral lines. So whatever is producing this extra gravity has to neither emit nor absorb light in any way we've been able to detect.



              It just so happens that adding dark matter (or something very like it) to the cosmology simulations is also essential to explain the CMB data.



              Now, you may object that the extra gravity we've observed may have some other source. For instance, maybe Newton's law of gravitation is simply wrong on the scale of galaxies and larger. The trouble that idea runs into is you're no longer able to explain the bullet cluster, where the gas between the galaxies has collided, but the dark matter and galaxies did not.



              On the subject of black body spectra. The black body is the spectrum that a gas of photons assumes if it is in thermal equilibrium (constant uniform temperature everywhere). The CMB is very very nearly a black-body because at the time the differences in temperature between any two parts of the universe were very very small. The sun, however, is surrounded by a very cold vacuum, and that lack of equilibrium will inevitably cause the spectrum to deviate from the ideal Planck function.






              share|cite|improve this answer









              $endgroup$



              Short answer: yes.



              You should look in to the history behind the dark matter hypothesis. It started not from the examination of cosmology and the CMB, but from the motion of galaxies in clusters and stars orbiting around galaxies. See, the vast majority of ordinary matter in every galaxy is contained in the gas between the stars, not the stars themselves. Because of that, we can get a decent handle on how much ordinary matter is around by observing that. Tools for this purpose: the 21 cm line of atomic hydrogen, when the gas is cold, as much of it is in spiral galaxies, and looking at the x-ray spectrum when it is exceptionally hot, as it is between galaxies in large clusters.



              When we examine the way the parts of galaxies, and the galaxies in clusters, move, they're travelling way too fast. If the mass we can see direct evidence for is all there is, the clusters would not be able to hold on to their hot gas and galaxies, and the galaxies would not hold together, either.



              "So what? Maybe the matter is there, it just isn't giving off light." Trouble is, if it were hot enough to be a plasma, and thus lack spectral lines, we could see it directly. If it were too cold to be a plasma, it would block light from galaxies and quasars in the background more in the matter's spectral lines. So whatever is producing this extra gravity has to neither emit nor absorb light in any way we've been able to detect.



              It just so happens that adding dark matter (or something very like it) to the cosmology simulations is also essential to explain the CMB data.



              Now, you may object that the extra gravity we've observed may have some other source. For instance, maybe Newton's law of gravitation is simply wrong on the scale of galaxies and larger. The trouble that idea runs into is you're no longer able to explain the bullet cluster, where the gas between the galaxies has collided, but the dark matter and galaxies did not.



              On the subject of black body spectra. The black body is the spectrum that a gas of photons assumes if it is in thermal equilibrium (constant uniform temperature everywhere). The CMB is very very nearly a black-body because at the time the differences in temperature between any two parts of the universe were very very small. The sun, however, is surrounded by a very cold vacuum, and that lack of equilibrium will inevitably cause the spectrum to deviate from the ideal Planck function.







              share|cite|improve this answer












              share|cite|improve this answer



              share|cite|improve this answer










              answered 1 hour ago









              Sean E. LakeSean E. Lake

              14.8k12351




              14.8k12351












              • $begingroup$
                Could it be we don’t measure the mass correctly at all?
                $endgroup$
                – 0x90
                52 mins ago










              • $begingroup$
                @0x90 Not likely. The way we measure mass is based on the physics of how light interacts with matter, something we have measured extremely well here on the ground. See, if a gas is thin enough that it is unlikely to reabsorb anything it emits ("optically thin" - see the 21 cm line), then we can deduce the gas temperature from the way the shape of the line is distorted, and the amount of gas along the line of sight ("column density") from brightness. Total mass is just adding up the lines of sight. The process is similar for absorption, just inverted.
                $endgroup$
                – Sean E. Lake
                48 mins ago










              • $begingroup$
                That said, one of the dark matter candidates is known as "MACHOs" for "Massive Compact Halo Objects". Basically, the thinking is if you have enough really high concentrations of mass that don't emit light (think black holes), that could do the trick. Trouble is, you'd expect them to pass between you and a star from another galaxy from time to time, lensing the light of the background star, making it appear brighter. Searches for this phenomenon have come up short, meaning it is unlikely that MACHOs can explain all of dark matter.
                $endgroup$
                – Sean E. Lake
                44 mins ago










              • $begingroup$
                what if the matter is transparent to light (the wavelength of the light is too long). Like radio wave and our body.
                $endgroup$
                – 0x90
                43 mins ago


















              • $begingroup$
                Could it be we don’t measure the mass correctly at all?
                $endgroup$
                – 0x90
                52 mins ago










              • $begingroup$
                @0x90 Not likely. The way we measure mass is based on the physics of how light interacts with matter, something we have measured extremely well here on the ground. See, if a gas is thin enough that it is unlikely to reabsorb anything it emits ("optically thin" - see the 21 cm line), then we can deduce the gas temperature from the way the shape of the line is distorted, and the amount of gas along the line of sight ("column density") from brightness. Total mass is just adding up the lines of sight. The process is similar for absorption, just inverted.
                $endgroup$
                – Sean E. Lake
                48 mins ago










              • $begingroup$
                That said, one of the dark matter candidates is known as "MACHOs" for "Massive Compact Halo Objects". Basically, the thinking is if you have enough really high concentrations of mass that don't emit light (think black holes), that could do the trick. Trouble is, you'd expect them to pass between you and a star from another galaxy from time to time, lensing the light of the background star, making it appear brighter. Searches for this phenomenon have come up short, meaning it is unlikely that MACHOs can explain all of dark matter.
                $endgroup$
                – Sean E. Lake
                44 mins ago










              • $begingroup$
                what if the matter is transparent to light (the wavelength of the light is too long). Like radio wave and our body.
                $endgroup$
                – 0x90
                43 mins ago
















              $begingroup$
              Could it be we don’t measure the mass correctly at all?
              $endgroup$
              – 0x90
              52 mins ago




              $begingroup$
              Could it be we don’t measure the mass correctly at all?
              $endgroup$
              – 0x90
              52 mins ago












              $begingroup$
              @0x90 Not likely. The way we measure mass is based on the physics of how light interacts with matter, something we have measured extremely well here on the ground. See, if a gas is thin enough that it is unlikely to reabsorb anything it emits ("optically thin" - see the 21 cm line), then we can deduce the gas temperature from the way the shape of the line is distorted, and the amount of gas along the line of sight ("column density") from brightness. Total mass is just adding up the lines of sight. The process is similar for absorption, just inverted.
              $endgroup$
              – Sean E. Lake
              48 mins ago




              $begingroup$
              @0x90 Not likely. The way we measure mass is based on the physics of how light interacts with matter, something we have measured extremely well here on the ground. See, if a gas is thin enough that it is unlikely to reabsorb anything it emits ("optically thin" - see the 21 cm line), then we can deduce the gas temperature from the way the shape of the line is distorted, and the amount of gas along the line of sight ("column density") from brightness. Total mass is just adding up the lines of sight. The process is similar for absorption, just inverted.
              $endgroup$
              – Sean E. Lake
              48 mins ago












              $begingroup$
              That said, one of the dark matter candidates is known as "MACHOs" for "Massive Compact Halo Objects". Basically, the thinking is if you have enough really high concentrations of mass that don't emit light (think black holes), that could do the trick. Trouble is, you'd expect them to pass between you and a star from another galaxy from time to time, lensing the light of the background star, making it appear brighter. Searches for this phenomenon have come up short, meaning it is unlikely that MACHOs can explain all of dark matter.
              $endgroup$
              – Sean E. Lake
              44 mins ago




              $begingroup$
              That said, one of the dark matter candidates is known as "MACHOs" for "Massive Compact Halo Objects". Basically, the thinking is if you have enough really high concentrations of mass that don't emit light (think black holes), that could do the trick. Trouble is, you'd expect them to pass between you and a star from another galaxy from time to time, lensing the light of the background star, making it appear brighter. Searches for this phenomenon have come up short, meaning it is unlikely that MACHOs can explain all of dark matter.
              $endgroup$
              – Sean E. Lake
              44 mins ago












              $begingroup$
              what if the matter is transparent to light (the wavelength of the light is too long). Like radio wave and our body.
              $endgroup$
              – 0x90
              43 mins ago




              $begingroup$
              what if the matter is transparent to light (the wavelength of the light is too long). Like radio wave and our body.
              $endgroup$
              – 0x90
              43 mins ago











              -1












              $begingroup$

              Being meaningful and being hypothetical, do not always work in hand.



              My personal opinion is, dark matter will be replaced for a better model in time. By the way, the sun is a black body, its just not a pure one. It's antithesis is the black hole, which is a near perfect black body.






              share|cite|improve this answer









              $endgroup$


















                -1












                $begingroup$

                Being meaningful and being hypothetical, do not always work in hand.



                My personal opinion is, dark matter will be replaced for a better model in time. By the way, the sun is a black body, its just not a pure one. It's antithesis is the black hole, which is a near perfect black body.






                share|cite|improve this answer









                $endgroup$
















                  -1












                  -1








                  -1





                  $begingroup$

                  Being meaningful and being hypothetical, do not always work in hand.



                  My personal opinion is, dark matter will be replaced for a better model in time. By the way, the sun is a black body, its just not a pure one. It's antithesis is the black hole, which is a near perfect black body.






                  share|cite|improve this answer









                  $endgroup$



                  Being meaningful and being hypothetical, do not always work in hand.



                  My personal opinion is, dark matter will be replaced for a better model in time. By the way, the sun is a black body, its just not a pure one. It's antithesis is the black hole, which is a near perfect black body.







                  share|cite|improve this answer












                  share|cite|improve this answer



                  share|cite|improve this answer










                  answered 4 hours ago









                  Gareth MeredithGareth Meredith

                  374112




                  374112






















                      N Pranav Subhraveti is a new contributor. Be nice, and check out our Code of Conduct.










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                      N Pranav Subhraveti is a new contributor. Be nice, and check out our Code of Conduct.












                      N Pranav Subhraveti is a new contributor. Be nice, and check out our Code of Conduct.
















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