Why not detect dark matter in our own galaxy?

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  • #1
alejandromeira

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Wikipedia dixit:
The standard model of cosmology indicates that the total mass–energy of the universe contains 4.9% ordinary matter, 26.8% dark matter and 68.3% dark energy
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According to this, dark matter must be everywhere.
Why then do we look for dark matter in distant galaxies?
Would not it be better to look for it in our own galaxy?
Or in our own ground laboratories?
:rolleyes::rolleyes::rolleyes::rolleyes:
 

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  • #2
Orodruin
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Why then do we look for dark matter in distant galaxies?
Would not it be better to look for it in our own galaxy?
Or in our own ground laboratories?
The premise of your question is flawed. We do look for dark matter in our ground laboratories.
 
  • #3
alejandromeira
Perhaps in the empty space the density is very small and difficult to detect.

But if space is isotropic, and this matter acts gravitationally, it should be present in the gas cloud that formed our solar system.
But now we do not detect it on the earth, or the solar system, and we feel any gravitational interaction (in the Earth or the solar system) because of it.

It is rare.
 
  • #4
Orodruin
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Perhaps in the empty space the density is very small and difficult to detect.

But if space is isotropic, and this matter acts gravitationally, it should be present in the gas cloud that formed our solar system.
Dark matter interacts very weakly. This means it is not distributed as normal matter. The dark matter density is not going to be significantly higher in the solar system than in the interstellar medium. However, dark matter does form halos seeding the galaxy formation. These halos are generally larger than the galaxies they host.

But now we do not detect it on the earth, or the solar system, and we feel any gravitational interaction (in the Eart or the solar system) because of it.

It is rare.
It is unclear what you mean by this. The amount of dark matter in the solar system is much smaller than the amount of ordinary matter. The gravitational effects in the solar system are well explained by those of ordinary matter.
 
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  • #5
alejandromeira
I apologize me, I did not know that it interacted differently than ordinary matter.

What you say means that when dark matter is used to predict the rotation of galaxies, the laws used are different from the laws of Newton (with different mean of mass) or those of general relativity? Sorry i'm profane on the subject.

Another question. It looks like the standard model is pretty full, and it works great. (No new fundamental particles at CERN are now detected). So the particles of dark matter are some of the known ones?
 
  • #6
Orodruin
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I did not know that it interacted differently than ordinary matter.
If it did not it would be visible.

What you say means that when dark matter is used to predict the rotation of galaxies, the laws used are different from the laws of Newton (with different mean of mass) or those of general relativity? Sorry i'm profane on the subject.
No. Dark matter interacts gravitationally. However, a key ingredient in forming solar systems and planets is the ability for the system to get rid of energy through radiation. Dark matter does not do this.

Another question. It looks like the standard model is pretty full, and it works great. (No new fundamental particles at CERN are now detected). So the particles of dark matter are some of the known ones?
No. The particle nature of dark matter is unknown. It cannot be any of the SM particles.
 
  • #7
alejandromeira
To me, the standard model, inspires me a lot of confidence. Perhaps it is easier to investigate something we have here than something that is very distant in space ... and in time. Now I'm going to say a lot of nonsense: what if no new fundamental particles are detected at CERN? I think this could happen.

Ok, I am a scientist, and therefore I must be very skeptical about my beliefs. Or at least have an open mind to other possibilities.
One of the things I often think: why should atoms, and other particles, be in the distant past, the same as now?

Okay, thanks for your constructive conversation :ok::ok:
 
  • #8
Janus
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To me, the standard model, inspires me a lot of confidence. Perhaps it is easier to investigate something we have here than something that is very distant in space ... and in time. Now I'm going to say a lot of nonsense: what if no new fundamental particles are detected at CERN? I think this could happen.

Ok, I am a scientist, and therefore I must be very skeptical about my beliefs. Or at least have an open mind to other possibilities.
One of the things I often think: why should atoms, and other particles, be in the distant past, the same as now?
Well, for one thing, when we examine really distant galaxies, we are in effect looking back at the early universe. We are seeing them as they were billions of years ago. The information we get from these galaxies shows no indication that matter behaved any differently then than it does now.
 
  • #9
alejandromeira
Yes. But the spectra are redshifted and stretched. I know that the Lambda_CDM model explains this as an expansion of the FLRW metric, but I am very classic in physics, and to think that the speed of expansion of the metric can diverge ... it is very hard for my mind.

I tried this summer, with data from Fraunhofer's H K lines, for Ca_II, to find a model in which by varying the 'constants' inside Rydberg constant, (yes, I know what that means), did not diverge the expansion of the metric. I used Redshift data up to 1.6 taken from: https://dr13.sdss.org/optical/spectrum/search

But the model failed, when it tried to explain other spectra (In addition the metric continued to diverge). So I didn't even send it to any scientific paper, this model is wrong evidently. I'm sad, because I don't like that the expansion of the metric diverge, but there is nothing else at the moment.

I don't know, in the standard model of particles, I feel like stepping on solid ground (maybe too much), but in cosmology I seem to be walking down a muddy road.
 
  • #10
Chronos
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As I'm sure you are aware, it might be instructive to note the body of evidence supporting DM as a principal component in the matter budget of the universe is overwhelming, despite its success in eluding detection by means other than gravimetric effects.. Phenomenon like the bullet cluster and CMB data pretty much insist most of it must be non-baryonic..
 
  • #11
Orodruin
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it is very hard for my mind.
Physics is about describing how the Universe behaves, not about being easy on your mind.
 
  • #12
PeterDonis
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I tried this summer...to find a model
PF is not for discussion of personal speculation or research. If you are unable to accept the mainstream cosmological models, that's your choice, but those are the models we are focused on discussing here at PF.
 
  • #13
PeterDonis
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The OP question has been answered. Thread closed.
 

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