- #1
Lisa!
Gold Member
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I want to know more about dark matter.
Please tell me:
Why do scientists think that there should be dark matter?
Please tell me:
Why do scientists think that there should be dark matter?
wolram said:Try this article Lisa
[URL]http://en.wikipedia.org/wiki/Dark_matter[/u.[/QUOTE]
I couldn't go through that.
Lisa! said:Thanks both of you.
I couldn't go through that.
Neried, I have followed your posts on the subject and I have been grateful for your considered criticism of baryonic DM. However, exactly why can this rich cluster DM not be baryonic?Nereid said:I've written on this numerous times - both here in PF and elsewhere - and I really don't want to repeat myself ... BUT:
a) if there is DM, then there's far, far more in the (local) universe in rich galaxy clusters than anywhere else (including the halos of spirals)
b) there are multiple, independent lines of investigation - yielding approx equal results - that the DM in rich clusters is very real, and very non-baryonic (note in passing, mostly to Garth - this is one set of good observational data which the SCC fans have yet to address, unless I have missed a key paper or three)
Garth,Garth said:Neried, I have followed your posts on the subject and I have been grateful for your considered criticism of baryonic DM. However, exactly why can this rich cluster DM not be baryonic?
O.K. so it is not observed, but has this ruled out all baryonic possibilities?
Oh thank you but you know it was my browser problem.I couldn't go through the link and read it at all.?(I'll give it a try again)wolram said:Lisa don't worry, as you read more your understanding will increase, believe
me i am a numb skull, but please read, read, read, and eventually it will not
be difficult
Thank you Nereid for that considered reply.Nereid said:Garth,
........
Have I missed anything significant?
Can you supply a time-line (approximate epochs) for items 3-7? The reason I ask is that as far back as we have been able to see (z~6.5) quasars and their host galaxies exhibit metallicities similar to or higher than that of our own galaxy. There has been no observed evolution in metallicity with redshift. This is a happy circumstance for an infinite steady-state universe, but puts some constraints on the Big Bang model (galaxies of super-solar metallicity form in less than a billion years). I know that your freely coasting model gets some extra breathing room in this regard (>13.7Gy), but at what point would you regard this metallicity as a constraint on your model? If the Webb or the LBT can push these observations back to z~7, 7.5, 8, etc, with no evolution of metallicity, where do we start questioning the validity of the BB model in SCC?Garth said:My scenario:
1. Out of the freely coasting BB emerges a dense plasma of H He and high metallicity.
2. A series of over-dense inhomogeneities condense into a series of objects with a ~linear log-log mass function.
3. A few super-massive BHs (106 – 109)MSolar form.
4. Massive PopIII stars quickly consume their fuel and go SN. They re-ionise the IGM and leave many intermediate mass BH’s (10 – 105)MSolar.
5. Finally a dense high metal IGM permeates space.
6. The super-massive and massive BHs form the nuclei for galaxy formation, which leads to PopII star formation and further metallicity.
7. Finally PopI stars with planetary systems form. And here we are.
Thank you matt.o Hi! Indeed what would we observe?matt.o said:Hi Garth, one thing you need to remember is the hierarchical fromation methods involving Lambda CDM models mimick what we observe very closely. Since baryons collapse in a very different manner to CDM, it would be difficult to derive models that describe what we observe in large scale structure.
you also need to ask yourself; what would we observe if there were ~10^9 intermediate mass black holes residing in a cluster (since dark matter makes up around 10^14-10^15Msolar in a rich cluster, you would need around 10^9 to account for the unobserved mass)?
Hi turbo-1 I won't engage in any more 'hand waving' in terms of putting ages to these epochs without doing the calculations. However the linearly expanding model gives considerably more breathing space in the earliest PopIII star and galaxy forming epochs.turbo-1 said:Can you supply a time-line (approximate epochs) for items 3-7? The reason I ask is that as far back as we have been able to see (z~6.5) quasars and their host galaxies exhibit metallicities similar to or higher than that of our own galaxy. There has been no observed evolution in metallicity with redshift. This is a happy circumstance for an infinite steady-state universe, but puts some constraints on the Big Bang model (galaxies of super-solar metallicity form in less than a billion years). I know that your freely coasting model gets some extra breathing room in this regard (>13.7Gy), but at what point would you regard this metallicity as a constraint on your model? If the Webb or the LBT can push these observations back to z~7, 7.5, 8, etc, with no evolution of metallicity, where do we start questioning the validity of the BB model in SCC?
The problem it has is deuterium, which has to be produced by spallation in this model. Spallation occurs anyway and contaminates the results of the standard model - but that is not often acknowledged!It turns out that for baryon entropy ratio eta~
5×10−9, there would just be enough neutrons produced, after nucleosynthesis commences, to give ~ 23.9% Helium and metallicity some 108 times the metallicity produced in the early universe in the standard scenario. This metallicity is of the same order of magnitude as seen in lowest metallicity objects.
There is another viable candidate for the missing mass, although most people are probably sick of hearing me talk about it by now. It is commonly accepted by quantum physicists that the gravitational potential expressed by the energies of the vacuum field would be able to collapse the visible universe to a size smaller than the orbit of the moon, if they were not very finely balanced to about 120 OOM. I believe that this does not happen because of the Pauli exclusion principle. These virtual particle-antiparticle pairs are fermions and they resist occupying the same states as their neighbors, so there is always a dynamical balance between their gravitational attraction and their mutual repulsion. In white dwarves and neutron stars the Pauli exclusion principle provides the pressure to prevent further collapse, and I believe the same dynamical balance holds true in less-degenerate gravity realms.Garth said:That there is some IGM gas is well accepted, and the Lyman alpha forest shows that it has high metallicity, but I'm not relying on it to supply much of the total baryonic mass. It does however require some explaining as only 20% or so can be accounted for from stellar nucleosynthesis and galactic outgassing.
Is there a way of assigning a force-distance relationship to this Pauli exclusion principle on interstellar material? Thanks.turbo-1 said:There is another viable candidate for the missing mass, although most people are probably sick of hearing me talk about it by now. It is commonly accepted by quantum physicists that the gravitational potential expressed by the energies of the vacuum field would be able to collapse the visible universe to a size smaller than the orbit of the moon, if they were not very finely balanced to about 120 OOM. I believe that this does not happen because of the Pauli exlusion principle. These virtual particle-antiparticle pairs are fermions and they resist occupying the same states as their neighbors, so there is always a dynamical balance between their gravitational attraction and their mutual repulsion. In white dwarves and neutron stars the Pauli exclusion principle provides the pressure to prevent further collapse, and I believe the same dynamical balance holds true in less-degenerate gravity realms.
I'm sure someone could explain this in such terms, but in non-technical terms, fermions resist being forced into the same quantum states with other fermions of similar spin. As I understand it, the Pauli exclusion principle is a balance beween the position and momentum of the fermions in accordance with the Heisenberg uncertainty principle. The more tightly compacted the fermions, the more certainly their positions are defined, and the less certainly their momentums are defined. Naively, one would expect that in a domain of very low gravitation (not very densely packed) the fermions would have well-defined energies but very poorly defined positions (broad range of possible locations). The more densely they are packed the more uncertain their momenta would become. The vacuum fields in the absence of matter will be very diffuse, and in the presence of large masses of matter, they will be densely compacted.Mike2 said:Is there a way of assigning a force-distance relationship to this Pauli exclusion principle on interstellar material? Thanks.
Maybe, maybe not ... an interesting topic (anyone want to start a separate thread? - what does the Lyman forest tell us? about the size and nature of the gas clouds the quasar photons went through to get to us? about their space density and proximity to galaxies and clusters?), but let's let this red finned critter swim away too.That there is some IGM gas is well accepted, and the Lyman alpha forest shows that it has high metallicity, but I'm not relying on it to supply much of the total baryonic mass. It does however require some explaining as only 20% or so can be accounted for from stellar nucleosynthesis and galactic outgassing.
We could play around with this, within the Local Group and Milky Way ... your call Garth, to what extent would our local environment be typical of that in a rich cluster (in terms of IMBHs)?Is there a IMBH within a thousand parsecs?
It's potentially an interesting idea turbo-1, but until you can give us something to work with - i.e. numbers, equations, or OOM calculations - the most respectful thing we could say is something like 'nice idea, please get back to us when you can model the (apparent) missing mass in rich clusters' ... or have I missed something significant?turbo-1 said:There is another viable candidate for the missing mass, although most people are probably sick of hearing me talk about it by now. It is commonly accepted by quantum physicists that the gravitational potential expressed by the energies of the vacuum field would be able to collapse the visible universe to a size smaller than the orbit of the moon, if they were not very finely balanced to about 120 OOM. I believe that this does not happen because of the Pauli exlusion principle. These virtual particle-antiparticle pairs are fermions and they resist occupying the same states as their neighbors, so there is always a dynamical balance between their gravitational attraction and their mutual repulsion. In white dwarves and neutron stars the Pauli exclusion principle provides the pressure to prevent further collapse, and I believe the same dynamical balance holds true in less-degenerate gravity realms.
Hi juju,juju said:It may be that both dark matter and dark energy considerations may be heandled by the appropriate modification of general relativity.
I'd be happy to explore this, Nereid. You know that I'll give you headaches with regard to gravitational redshift effects, but I look forward to the discussion.Nereid said:Maybe, maybe not ... an interesting topic (anyone want to start a separate thread? - what does the Lyman forest tell us? about the size and nature of the gas clouds the quasar photons went through to get to us? about their space density and proximity to galaxies and clusters?), but let's let this red finned critter swim away too.
You may have missed somthing that I have been trying to get you to pay attention to for at least a year. For the gravitational energy of the vacuum fields to be exquisitely (and dynamically) fine-tuned (to 120 OOM) the forces involved must necessarily arise from the SAME field. They cannot arise from the fortuitous conspiracy of two fields, because any tiny imbalance would already have led to a disastrous collapse (or explosion) of the universe. For this reason the gravitational attraction AND the balancing repulsion must of necessity both be characteristics of the same field.Nereid said:It's potentially an interesting idea turbo-1, but until you can give us something to work with - i.e. numbers, equations, or OOM calculations - the most respectful thing we could say is something like 'nice idea, please get back to us when you can model the (apparent) missing mass in rich clusters' ... or have I missed something significant?
Space Tiger has already started one - maybe you could start another? Something like 'what is the interpretation of the Lyman forest in QSO spectra, according to folk like Arp, Ari Brynjolfsson (and other plasma cosmologists), the CREIL crowd, etc'?turbo-1 said:I'd be happy to explore this, Nereid. You know that I'll give you headaches with regard to gravitational redshift effects, but I look forward to the discussion.
Sorry, it seems I wasn't clear turbo-1.turbo-1 said:You may have missed somthing that I have been trying to get you to pay attention to for at least a year. For the gravitational energy of the vacuum fields to be exquisitely (and dynamically) fine-tuned (to 120 OOM) the forces involved must necessarily arise from the SAME field. They cannot arise from the fortuitous conspiracy of two fields, because any tiny imbalance would already have led to a disastrous collapse (or explosion) of the universe. For this reason the gravitational attraction AND the balancing repulsion must of necessity both be characteristics of the same field.
Dark matter is a type of matter that makes up about 85% of the total mass of the universe. It does not emit or absorb light, making it invisible to telescopes and other instruments. Its presence is inferred by its gravitational effects on visible matter.
Scientists study dark matter through its gravitational effects on visible matter, such as stars and galaxies. They also use various methods such as gravitational lensing, where the bending of light by dark matter can be observed, and particle accelerators to try and detect dark matter particles.
Understanding dark matter is crucial for understanding the formation and evolution of the universe. It also helps us understand the distribution of matter in the universe and the behavior of galaxies. Additionally, understanding dark matter could potentially lead to new breakthroughs in physics and technology.
Dark matter is different from regular matter in that it does not interact with light or other forms of electromagnetic radiation. It also does not interact with itself or regular matter through the strong or weak nuclear forces, only through gravity. This makes it much more difficult to detect and study.
There are several theories about the nature of dark matter, including the possibility that it is made up of yet-undiscovered particles, such as weakly interacting massive particles (WIMPs) or axions. Other theories propose modifications to the laws of gravity, such as modified Newtonian dynamics (MOND), to explain the observed effects of dark matter. However, the exact nature of dark matter is still a mystery and continues to be an active area of research.