I am a physics student and don't know very much about dark matter nor cosmology. But today I went to a talk in which the speaker showed us this image (or a very similar one):    showing how the predictions of the standard model of cosmology having to do with background radiation vary when the ratio of dark matter is modified. I don't know what is the meaning of that plot but it seem that varying the ratio of dark mater produces a very important change in it.  My question is: how is that something that does not interact with electromagnetic radiation (as dark matter) has such a drastic effect in CMB?
122669
After the data from the cosmic microwave background has been collected by WMAP or Planck, what types of analysis is needed to conduct in order to deduce the cold dark matter density and the distribution of matter in the universe? In other words - How the CMB anisotropy measurements giving us evidence for the existence of dark matter/energy? (Any further explanation on the analysis of data is also welcomed.)
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As short as possible: From what I understand the Cosmic Microwave Background was predicted by multiple people as a theoretical consequence of the Big Bang theory, and hence today, is evidence for the Big Bang. So of course there was also a prediction of the age of the CMB, because it was predicted to have occurred at a certain point in time.  Now, is that the only reason cosmology dates the CMB to 13.8 billion years ago, i.e. is the dating inferred by the theory? I assume there must be many types of measurements that somehow connect to this so as to infer the exact age of what we are seeing there.
123038
Most of the dark matter in the Universe is cold or nonrelativistic which rules out neutrinos as dark matter candidate as they are hot or relativistic. But why do physicists think that the dark matter is cold? How cold (i.e., how heavy) do these dark matter particles have to be?
122275
Why is absolute zero considered to be ? Wouldn't regions such as massive gaps between galaxy clusters have temperatures of absolute zero?  I just do not see why our model must work the way that it does. I mean there have to be regions with no thermal energy out there, the universe is massive.
84678
The LHCb has recently  the observation of $B_s \rightarrow \mu^+ \mu^-$ with a branching ratio that agrees with the Standard Model (SM). There are many blog posts about it (See: ).  The result initiated a debate over its implication on Supersymmetry in general, which I don't want to discuss here. But it certainly affects some Supersymmetric models that may have a different prediction than that of the SM.   My questions are,   Which models in particular are affected (or variants of models)? What is the MSSM status? The NMSSM? Does the result affect some of the parameter space of a particular model, or does it rule out an entire model/or variant of a model?
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As far as my understanding goes, dark matter is nothing but an amount of gravitational force, from yet unresolved/undiscovered source(s), needed to explain some observed attributes of our universe. Then, is it called "Matter" only because of gravity? Because other properties of matter like occupation of some space, mass etc is not found in this case. And, can it be some new kind of force other than gravity?
29955
Dark matter is said to be present in the galaxies which helped galaxies to exist in the first place forming the glue to attach all the matter in the galaxies.  Given that dark matter never been seen or detected and only effect of which could be felt why do we believe it would be a particle? We have universe (almost) equally distributed in all directions with dark matter forming the skeleton for all the matter that could be seen. Can the dark matter be a illusion of gravitational waves interfering with each other forming this uniform interference pattern of galaxies/matter that is seen by us?  That would also explain the repulsive dark energy which would be the troughs in the gravitational waves indicating desructive interference in the gravitational waves.  Can we hope to simulating the above to come to the possible conclusion of source(two or many) of these gravitational waves that could give rise to skeleton of dark matter and dark energy which may be present in some higher dimentions?
90001
Our galaxies are speeding apart from each other and that is because of dark energy, but we don't know where it comes from right? If I'm not mistaken could dark matter have dark energy? (If they are the same thing please correct me.) Matter has gravity so could  have , so sense there is more dark matter is that why our galaxies are being pushed apart?
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Due to the mass-energy equivalence, both matter and EM radiation bend spacetime, and both are capable of forming singularities (black hole, white hole/kugelblitz). In light of this, why do photons traveling from the most distant reaches of the observable universe not lose energy due to the gravitational radiation they must emit? Furthermore, mustn't cosmic rays (e.g. protons) slow down or stop as they lose energy through the same mechanism?
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In the past days it was announced that the lastest results of the muon $g-2$ experiment indicates some discrepancies with the standard model. As an outsider in particle physics, I don't understand exactly what's happening and my only sources have been some online newspapers such as the new york times. Could someone explain to a non-expert like me what is going on and what are the consequences of such results?
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Recently I found out this  about nuclear decay rates somehow showing seasonal variations with a high correlation with sun activity.   Has this been experimentally confirmed/disproved? An experiment using neutrinos from a fission reactor would be awesome, although probably a couple orders of magnitude below the required luminosity (at least to be comparable with solar sources) Could the standard model possibly allow neutrinos to modulate decay rates in this way? Or do we need new physics?   Link to the .  Another paper about this, but now the SuperKamiokande data is compared with data from Brookhaven:  They also propose a model of the effect called neutrino "resonant spin-flavor precession".
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My question is: if we write Einstein field equations in this form:  $$R_{\mu\nu} - \dfrac{1}{2}g_{\mu\nu}R=8\pi \dfrac{G}{c^4}T_{\mu\nu}$$  Then the left hand side is one statement about the geometry of space-time and the right hand side is one statment about the distribution of momentun and energy right? My point is: what if we use the electromagnetic stress-energy tensor as the energy-momentum tensor?   My thought was: if I understood correctly, does this says that electromagnetic fields can also change the geometry of space-time making it bend as does the presence of matter?  Sorry if it makes no sense, or if it's completely nonsense, it's just a thought that came out, I'm just starting to study those things.
15829
As of this writing it has been made clear to me that classical physics' Luminiferous aether was a terriblly poor discriptor of space. With the advent of Special Relativity and General Relativity, that aether ceased to be applicable. Today I began reading on the Higgs boson, and the Higgs field. How are those theories different from or similar to the seemingly irrational Luminiferous aether?  P.S. I am a first year student at Bakersfield Community College. If this question seems naive, you now have an explanation.  (EDIT) To me the similarity rests upon their fundamental influences regarding static positions in space. I currently only accept models in which static spacial positions are impossible. Contrastingly relative positions seem quite reasonable. In my humble opinion my naivatisms inhibit me from absorbing and understanding the Higgs boson. If they actually are similar, public protest would probably be more apparant. However, I have put forth my best effort to pose an direct question here.  P.S. The questions Where does space go when it falls? and What happens to time lost when matter accelerates? come much earlier in my studies, and they seem relevant.
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When I look at electric or magnetic fields, each of them has a constant that defines how a field affects or is affected by a medium. For example, electric fields in vacuum have a permittivity constant $ϵ_0$ embedded in the electric field expression of a point charge: $E = q/4π ϵ_0r^2$. However, if I put this point charge in some dielectric that has a different  permittivity constant $ϵ$, the value of the electric field changes. On a similar note, magnetic fields behave very similar but have the permeability constant $μ_0$ instead.   From my understanding, I believe that this is not the case for gravitational fields since the universal gravitational constant $G$ is consider to be a fundamental constant. So I am assuming that even though gravitational fields do operate in different types of mediums, this somehow doesn’t affect the gravitational field value. My question is why is this the case, that is, why isn’t there a permittivity-type constant for gravitation?
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I understand that dark matter does not collapse into dense objects like stars apparently because it is non-interacting or radiating and thus cannot lose energy as it collapses. However why then does it form galactic halos? Isn't that also an example of gravitational collapse?
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How does a   outside a galaxy help to explain a ?  Suppose for simplicity we use a model of a star rotating about a more massive star in a fixed circular orbit. For another star at larger radius, the velocity should be smaller but observationally for spiral galaxies, the opposite happens (moves at even more speed or at least at the same speed as the closer star).  People hypothesize that dark matter halo may be present “surrounding” the system (i.e., halo exists outside the system) to account for such observation. I feel that exactly the opposite should be the case that is, dark matter halo should be inside the galaxy rather than outside. Reason being, if dark matter is outside the galaxy then the effective gravitational pull on the rotating star towards the center will be reduced due to outward attraction on the star exerted by dark matter existing outside. Thus, its speed of rotation should be reduced; but we observe the opposite. So how does dark matter halo "surrounding" a galaxy help to explain galaxy rotation curve? Where am I making mistake in argument?
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Title speaks for itself.  Dark matter: We see extra attractive force, and we posit that there are particles which create such a force, and use the measure of that force to guess their locations.  Dark Energy: We see extra repulsive force.   Only thing is, dark energy is uniform. So I suppose the stuff would have to be (at least somewhat) uniformly distributed throughout the universe. How uniform do we know it to be? Could the "stuff" be somehow a part of empty space itself?