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The galaxy rotation curves and gravitational lensing should not be too hard to understand though.
We have not ruled out the possibility of dark matter in our solar system but even if it's at the expected density it's too small to detect because on a galactic scale, the 93 million mines from Earth to the sun is a tiny distance and cosmically speaking it contains a tiny amount of dark matter. On a human scale the 93 million mile radius around the sun could be expected to contain a "large" amount of dark matter, something like 2.3 billion tons! That sounds like a lot, so how could we not detect that? The reason is because the mass of the sun is roughly a billion times a billion times larger than that and we don't have any measurement methods precise enough to detect something that's a billionth of a billionth of the sun's mass
originally posted by: Arbitrageur
The two alternative ideas being debated to discuss observations have been these. Either:
A. There some kind of matter we can't see causing galaxies that are rotating so fast they would fly apart without it, or
B. Our model of gravity which seems to work at the scale of our solar system is completely broken at larger scales like galaxies.
Can anybody think of a third option?
Black holes as doorways
Popławski's approach is based on the Einstein–Cartan theory of gravity which extends general relativity to matter with intrinsic angular momentum (spin). Spin in curved spacetime requires that the affine connection cannot be constrained to zero and its antisymmetric part, the torsion tensor, must be a variable in Hamilton's principle of stationary action which gives the field equations. Torsion gives the correct generalization of the conservation law for the total (orbital plus intrinsic) angular momentum to the presence of the gravitational field, but also modifies the Dirac equation for fermions.
Gravitational effects of torsion on fermionic matter are significant at extremely high densities which exist inside black holes and at the beginning of the Universe. Popławski theorizes that torsion manifests itself as a repulsive force which causes fermions to be spatially extended and prevents the formation of a gravitational singularity within the black hole's event horizon.[12] Because of torsion, the collapsing matter on the other side of the horizon reaches an enormous but finite density, explodes and rebounds, forming an Einstein-Rosen bridge (wormhole) to a new, closed, expanding universe.[13][14] Analogously, the Big Bang is replaced by the Big Bounce before which the Universe was the interior of a black hole.[15] This scenario generates cosmic inflation, which explains why the present Universe at largest scales appears spatially flat, homogeneous and isotropic.[16][17] It may explain the arrow of time, solve the black hole information paradox, and explain the nature of dark matter.[18] Torsion may also be responsible for the observed asymmetry between matter and antimatter in the Universe.[19] The rotation of a black hole could influence the spacetime on the other side of its event horizon and result in a preferred direction in the new universe. Popławski suggests that the observed fluctuations in the cosmic microwave background might provide evidence for his hypothesis.[20]
Did you watch the video in the OP yet?
originally posted by: MarioOnTheFly
Is it fair to say that this Dark matter mass is rather small to be holding galaxies together ?
Figure 4: An example of 3D distribution of dark matter reconstructed via tomographic methods using the weak lensing technique combined with the redshift estimates of the background galaxies.
Who said they know how gravity works? You are mistaken, we are not saying we know how gravity works, we say we can predict the effects of gravity which is different. We have fantastic proof that our gravity models work in our solar system when we can land a spacecraft on Mars with a high degree of accuracy.
originally posted by: zatara
They say they have found out how gravity works but I just do not believe it.
UNIVERSE IN A BLACK HOLE IN EINSTEIN–CARTAN GRAVITY (PDF)
The Astrophysical Journal, 832:96 (8pp), 2016 December 1
ABSTRACT
The conservation law for the angular momentum in curved spacetime, consistent with relativistic quantum mechanics, requires that the antisymmetric part of the affine connection (torsion tensor) is a variable in the principle of least action. The coupling between the spin of elementary particles and torsion in the Einstein–Cartan theory of gravity generates gravitational repulsion at extremely high densities in fermionic matter, approximated as a spin fluid, and thus avoids the formation of singularities in black holes. The collapsing matter in a black hole should therefore bounce at a finite density and then expand into a new region of space on the other side of the event horizon, which may be regarded as a nonsingular, closed universe. We show that quantum particle production caused by an extremely high curvature near a bounce can create enormous amounts of matter, produce entropy, and generate a finite period of exponential expansion (inflation) of this universe. This scenario can thus explain inflation without a scalar field and reheating. We show that, depending on the particle production rate, such a universe may undergo several nonsingular bounces until it has enough matter to reach a size at which the cosmological constant starts cosmic acceleration. The last bounce can be regarded as the big bang of this universe.
Matter-antimatter asymmetry and dark matter from torsion
PHYSICAL REVIEW D 83, 084033 (2011)
We propose a simple scenario which explains the observed matter-antimatter imbalance and the origin of dark matter in the Universe. We use the Einstein-Cartan-Sciama-Kibble theory of gravity which naturally extends general relativity to include the intrinsic spin of matter. Spacetime torsion produced by spin generates, in the classical Dirac equation, the Hehl-Datta term which is cubic in spinor fields. We show that under a charge-conjugation transformation this term changes sign relative to the mass term. A classical Dirac spinor and its charge conjugate therefore satisfy different field equations. Fermions in the presence of torsion have higher energy levels than antifermions, which leads to their decay asymmetry.
Such a difference is significant only at extremely high densities that existed in the very early Universe. We propose that this difference caused a mechanism, according to which heavy fermions existing in such a Universe and carrying the baryon number decayed mostly to normal matter, whereas their antiparticles decayed mostly to hidden antimatter which forms dark matter. The conserved total baryon number of the Universe remained zero.
Yes, I asked if there was a third option because I would like to know if there is. I still don't.
originally posted by: Majic
One possibility for where "dark matter" would potentially fit into all this is considered here:
Matter-antimatter asymmetry and dark matter from torsion
Ultimately, however, whether any of this is right or wrong, my intention is not to prove anything specific to a given theory. Rather, it is to point out that when you ask if anybody can think of a third option regarding possible explanations for the phenomenon of "dark matter", the answer is "yes".
originally posted by: Arbitrageur
a reply to: Majic
If you don't have a paper representing a third option to explain dark matter observations, can we say there is no third option that anybody has written a peer reviewed paper about yet?
Evidence from the depths of the Universe has ruled out a number of models for what the mysterious dark matter might be, but one candidate that fits so far is the lightest supersymmetric particle (LSP) otherwise known as the “neutralino”, the lightest of a whole range of new particles suggested by a theory called supersymmetry.
If the neutralino exists it will likely be stable, heavy, neutral, and will not interact electromagnetically. This makes it a perfect candidate for a substance that pervades the universe without being spotted. If supersymmetric particles exist, they are very likely to be produced in collisions in the LHC. The heavy particles will decay into combinations of leptons (like electrons and muons) and quarks (which will cause sprays of particles called jets) as well as into neutralinos that will not decay any further. Therefore many neutralinos will pass through the CMS detector, without depositing any energy or leaving a trail.
So how do you detect an “invisible” particle? CMS will be able to find the neutralino indirectly – by identifying when the energy used to make it goes missing.
Momentum in equals momentum out…
One of the most fundamental laws of physics is that ‘momentum is conserved’. In other words, the total momentum before a collision is equal to the total momentum after. If the total momentum of the observed particles that emerge from a proton-proton collision does not equal the momentum of the two protons, we can deduce there must be an invisible particle somewhere that carried away that missing momentum.
As we collect all the particles we can also add up their momenta and energies (in the “transverse” direction, i.e. at right angles to the beam line) and reconstruct the entire collision; like building a giant jigsaw puzzle. When a neutralino is formed and we can’t detect it we see an imbalance in the collision, with particles flying out one side but not the other and the energy not adding up. This shows up as a hole in the jigsaw puzzle: a missing particle seen through its missing energy or momentum.
The CMS is “hermetic” when it comes to finding missing particles. This means that, to the extent possible, it catches every detectable particle emerging from a collision. Large detectors have “channels for escape”, regions where particles cannot be detected because of cables or other mechanical support. These regions must be minimised to ensure that standard particles can't slip by undetected. This way, if the energy or momentum is "missing", it really is due to an invisible particle.
To search for this missing energy, it is important that the CMS has a good hadron calorimeter as well as detectors at every angle around the beam line. To ensure that particles flying from all directions will be detected, this includes the very shallow angles known as the “forward region”. Tags / keywords: Dark Matter
I can be too long-winded myself sometimes.
originally posted by: Majic
So if the prospect of an under-edited multi-post blast of stilted, conjectural prose isn't too off-putting, I'm willing to flesh it out and post it probably in the next few days or so, time permitting. A more concise summary would probably take longer to pare down without begging an excessive number of questions and possibly being even less helpful.
Thus I figure I should ask if you're okay with the long-winded version before continuing.
We observe that energy always seems to be conserved in physics, but measuring the exact energy in and exact energy out can be a challenge. For example if the LHC proton-proton collision is exactly head on it's the highest possible energy but what if it's not perfectly head on?
originally posted by: Phantom423
I came across this article on the cms.cern website. Unfortunately, there's no date or references. Have any experiments detected the "neutralino" yet?
Question for you and Eros if he's around about the collider - the article states: "So how do you detect an “invisible” particle? CMS will be able to find the neutralino indirectly – by identifying when the energy used to make it goes missing." In general, when a collision experiment is performed, does the energy in always equal the energy out?
If there is an energy deficit, and assuming it is measurable, how would they know whether it was the result of one, two or more particles being produced by the collision?
Would appreciate a link to a publication if there is one. Thanks.
Neutral weakly interacting particles, such as neutrinos, escape from typical collider detectors without producing any direct response in the detector elements. The presence of such particles must be inferred from the imbalance of total momentum. The vector momentum imbalance in the plane perpendicular to the beam direction is particularly useful in pp and p¯ p colliders, and is known as missing transverse momentum...Its magnitude is called missing transverse energy...
originally posted by: Arbitrageur
How many multi-posts are we talking about?
Can anybody think of a third option?