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The 5 truths about dark matter that everybody must know

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The 5 truths about dark matter that everybody must know

The 5 truths about dark matter that everybody must know Sometimes, supporters of a fringe belief system that doesn’t match the facts and evidence or the established theory attempt to revive the theory.

Sometimes, new evidence comes to the surface, challenging the dominant theory and forcing alternative theories to be reviewed.

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Sometimes a random sequence of evidence confirms a once discredited theory, which brings it back into the spotlight.

At other times it is a false story that is at play in the case of disingenuous arguments deemed untrue by mainstream professionals taking root in a new generation of untrained individuals.

If you’re not a person with the expertise to recognize the information being displayed precisely and in-depth, It’s nearly impossible to distinguish these two scenarios.

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Recently, someone suggested in both video and text in a manner that follows the example of perhaps the most dishonest person in the field of contrarians that the state of the dark matter phenomenon has changed and that modified gravity is worthy of the same consideration.

Unless you’re in charge of not paying attention to the bulk of cosmic evidence, it’s just not the scenario. When you understand these five facts, they can aid in identifying the false assumptions made by those who want to create doubt amid the most important cosmological puzzles.

dark matter

Distant sources of light – from galaxies, quasars, and even the cosmic microwave background – must pass through clouds of gas. The absorption features we see enable us to measure many features about the intervening gas clouds, including the abundances of the light elements inside. ED JANSSEN, ESO

1.) A large amount of matter in the Universe is well-known. One could look around the Universe, which is full of galaxies, stars, dust, plasma, black holes, and so on, and ask yourself whether there’s more of this “known stuff” out there.

If there are other gravitational effects beyond the ones, we can explain that maybe there’s an unknown mass to be responsible for. This notion of “normal matter that’s just dark” was one of the main theories that stood in the direction of dark matter becoming an accepted part of cosmology during the 20th century.

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In the end, plenty of plasma and gas exists in the Universe. It’s easy to think that if there were plenty of them, we’d never require a fundamentally new kind of matter in the first place.

If neutrinos were large enough, they could manage to handle the problem. Perhaps If the Universe was made up of more matter than it could handle and some were able to collapse into black holes at an early stage, this could resolve the cosmic imbalance we observe.

None of those possibilities is possible, given that the volume of ordinary matter within the Universe is well-known: 4.9% of the critical density, and the uncertainty is just +-0.1 percent within that range.

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dark matter

The predicted abundances of helium-4, deuterium, helium-3 and lithium-7 as predicted by Big Bang Nucleosynthesis, with observations shown in the red circles. This corresponds to a Universe where ~4-5% of the critical density is in the form of normal matter. With another ~25-28% in the form of dark matter, only about 15% of the total matter in the Universe can be normal, with 85% in the form of dark matter. NASA / WMAP SCIENCE TEAM

The most important observational limitation is the apparent abundance of light elements, such as hydrogen-deuterium and helium-3. lithium-7, and helium-4. Within the first 4 seconds of the Big Bang, these light elements were formed during the Universe’s first nuclear explosions.

The quantity of each element is directly related to the amount of normal matter present during those initial moments.

Nowadays, we can analyze these abundances directly through spectroscopic measurements of gas clouds and indirectly through precise observations of the background of cosmic microwaves. Both kinds of observations point to the same conclusion: 4.9 percent + 0.1 percent of the Universe’s energy is composed of normal matter.

It’s too fast for black holes; therefore, they aren’t in. Big Bang Nucleosynthesis relies on neutrinos, and three types of them -muon, electron tau, and electron is the only one permitted and aren’t dark matter, either. There is nothing in the Standard Model that can perform the task.

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However, this fact can’t be disputed. Given the amount of normal matter we’ve identified, an entirely new fundamental component must be present to correspond with our observations of the cosmological world. We refer to this ingredient as “dark matter,” and it has to exist.

dark matter

The largest-scale observations in the Universe, from the cosmic microwave background to the cosmic web to galaxy clusters to individual galaxies, all require dark matter to explain what we observe. The large scale structure requires it, but the seeds of that structure, from the Cosmic Microwave Background, require it too. CHRIS BLAKE AND SAM MOORFIELD

2.) You can’t explain the cosmic microwave background nor the structures that is the Universe without dark matter. Imagine the Universe at the beginning: hot, dense, and almost uniform, expanding and cooling throughout the process.

Certain regions, born with slightly higher density than others, will start to draw matter towards them, attempting to increase their size gravitationally.

As gravitation starts to play as it does, the density rises, and the radiation pressure inside it grows too. This leads to the density reaching its peak and causes the flow of photons out, which then falls back.

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As time progresses, the larger regions will expand via collapse as smaller regions shrink before becoming more rarified, finally fall back down, etc. This can lead to cracks in the temperature of the glow left from the Big Bang and, eventually, will create the seeds of structure, transforming into stars, galaxies, and the cosmic web.

However, you’ll see a different pattern of behavior in the background of cosmic microwaves and the Universe’s vast scale structure, based on whether you’re dealing with normal and dark matter or normal matter by itself.

dark matter

As our satellites have improved in their capabilities, they’ve probes smaller scales, more frequency bands, and smaller temperature differences in the cosmic microwave background. The temperature imperfections help teach us what the Universe is made of and how it evolved, painting a picture that requires dark matter to make sense. NASA/ESA AND THE COBE, WMAP AND PLANCK TEAMS; PLANCK 2018 RESULTS. VI. COSMOLOGICAL PARAMETERS; PLANCK COLLABORATION (2018)

The reason is that Physics is different. Normal matter and dark matter gravitate. Both causes increases in radiation pressure, and the radiation flows from dense regions regardless of whether it’s composed of dark matter or both. Normal matter is also in contact with other ordinary matter and interacts with light, while dark matter is inaccessible to the rest.

In the end, dark matter in a Universe with dark matter contains double the amount of fluctuation peak-and-valleys both in the spectrum of the cosmic microwave background and its power spectrum for large-scale structures in comparison to the Universe that is dominated by normal matter.

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In all certainty, the dark matter requirement is clear and unambiguously. In particular, it must be non-combatable, cold, and impervious to electromagnetic radiation.

This means it is not a normal matter. Suppose you’re looking to increase the sensitivity on your skepticism meter and keep an eye out for papers attempting to explain the background of cosmic microwaves or the power spectrum of matter with no dark matter.

Chances are they’ll include something — such as the massive neutrino, a neutral neutrino that is sterile, or an additional field tuned for a specific coupling that performs as a distinct entity from dark matter.

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dark matter

The formation of cosmic structure, on both large scales and small scales, is highly dependent on how dark matter and normal matter interact. Despite the indirect evidence for dark matter, we’d love to be able to detect it directly, which is something that can only happen if there’s a non-zero cross-section between normal matter and dark matter. ILLUSTRIS COLLABORATION / ILLUSTRIS SIMULATION

3.) Dark matter behaves like particles, distinct from something that acts as a field. Another falsehood has been propagated by people who would like to dispel doubt on dark matter: that since particles are merely excitations for quantum fields, the addition of an additional quantum field (or altering the field of gravitational) could be the same as creating the new (dark matter) particles.

This is the shadiest type of argument with an element of scientific truth however is misleading about the essence of the argument.

This is the most important point: Fields are universal and are pervasive across every inch of the space. They could be homogeneous (identical all over the world) or clumpy.

They may be isotropic (identical in all directions) or possess a preferred direction. On the other hand, particles are not non-massive, which means they’ll behave like radiation. They can also be massive, and in that, they will behave similarly to conventional particles. In the case of the latter, they will behave as if:

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  • clump,
  • gravitate,
  • Have the known, well-understood connections between potential and kinetic energy.
  • They are characterized by particle properties, such as the cross-sections of particles, scattering amplitudes, and couplings, and behave following (at minimum) the physical laws.
  • This is why — for all the characteristics of dark matter we’ve discovered by observing astrophysical phenomena alone, and we can conclude that it is particle-like the nature of things.
dark matter

This snippet from a structure-formation simulation, with the expansion of the Universe scaled out, represents billions of years of gravitational growth in a dark matter-rich Universe. Note that filaments and rich clusters, which form at the intersection of filaments, arise primarily due to dark matter; normal matter plays only a minor role. RALF KÄHLER AND TOM ABEL (KIPAC)/OLIVER HAHN

It doesn’t mean that it can’t be a fluid that isn’t pressureless, clumpy dust or that its cross-section is a zillionth of an inch in all interactions, except for gravity.

It indicates that if you prefer replacing dark matter with the field, it should behave in a manner that is, from an astrophysical viewpoint, can’t be distinguished as the behavior of a huge collection composed of large particles.

Dark matter doesn’t necessarily have the characteristics of a particle but to say that “it can be a field just as easily as it can be a particle” is a lie the dark matter can behave precisely the way we’d imagine a new species of the massive, cold non-scattering particle to behave.

Particularly at large cosmic scales, i.e., the size of clusters of galaxies (about 10-20 million light-years) and higher particles, this particle behavior is only possible to substitute by an indistinguishable field from the dark matter particle behaves.

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dark matter

Star formation in tiny dwarf galaxies can slowly “heat up” the dark matter, pushing it outwards. The left image shows the hydrogen gas density of a simulated dwarf galaxy, viewed from above. The right image shows the same for a real dwarf galaxy, IC 1613. In the simulation, repeated gas inflow and outflow causes the gravitational field strength at the centre of the dwarf to fluctuate. The dark matter responds to this by migrating out from the centre of the galaxy, an effect known as ‘dark matter heating’. J. I. READ, M. G. WALKER, & P. STEGER (2019), MNRAS 484, 1

4.) The effects of physics at a small scale are very real, like dynamical heating feedback and star formation, and nonlinear effects need to be figured out. Dark matter’s issues (in other words, the instances in which dark matter that is cold and collision-free creates predictions that conflict with observations occur on smaller cosmic scales. These are scales of massive galaxies as individual galaxies and smaller.

There is a good reason why certain adjustments to gravity may better align with the observations made on these scales. However, there’s a dark secret: sloppy physical physics in these tiny dimensions has not been adequately explained.

Without a way to take them into account, we’re not sure whether we should call dark matter and modified gravity approaches to be successful or not.

It’s hard work! When the matter is sucked into the middle of a massive object it:

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  • The angular momentum is released,
  • heats up,
  • could trigger star formation
  • that can cause Ionizing radiation
  • which pulls the normal matter to the outside,
  • That gravityally “heats” the dark matter that is in the center

All of this requires to be considered. In addition, we’re only thinking about the most simple dark matter model: pure inert and non-combatable without inter- or intra-personal interactions.

It is possible to alter gravity, adding cold, collision-free dark matter, or consider, “what interaction properties could dark matter have that would lead to the small-scale structure we observe?” These methods are equally valid. However, both require the existence of dark matter and have to deal with these real consequences.

dark matter

A galaxy cluster can have its mass reconstructed from the gravitational lensing data available. Most of the mass is found not inside the individual galaxies, shown as peaks here, but from the intergalactic medium within the cluster, where dark matter appears to reside. More granular simulations and observations can reveal dark matter substructure as well. A. E. EVRARD. NATURE 394, 122–123 (09 JULY 1998)

5.) You need to present the complete range of evidence from cosmology; otherwise, you’re cherry-picking and not conducting scientifically valid research. This is a crucial fact that is not stressed enough that we have all this data on the Universe and must consider it all when drawing our conclusions.

This includes the following instances:

  • it is essential to take a look at the seven acoustic peaks of the background of cosmic microwaves and not only the two first ones,
  • You must be truthful about whether you’re honest about whether the “thing” you’re adding (instead of dark matter) is similar to dark matter.
  • It would be incredibly useful on the off chance that you would be able not to change your gravity law in a manner that helps explain small-scale phenomena at the expense of not describing large-scale features,
  • It would be best if you did not choose statistically unprobable outcomes that are occurring (but they aren’t prohibited) to use as “evidence” that the leading theory is not true (see this low-quadrupole/octupole found in the CMB for years of ineffective effort on this subject),
  • You mustn’t overstate and undervalue the theory’s strengths that your alternative approach aims to replace.

To displace and overthrow an old science concept, the first hurdle to conquer is replicating the success of the previous theory. We may require a new law that explains gravity to understand the nature of our Universe, but you cannot create it in an approach that dark matter doesn’t get needed.

dark matter

The data points from our observed galaxies (red points) and the predictions from a cosmology with dark matter (black line) line up incredibly well. The blue lines, with and without modifications to gravity, cannot reproduce this observation without dark matter. S. DODELSON, FROM HTTP://ARXIV.ORG/ABS/1112.1320

There are a few crucial things you must not overlook when it comes to the issue of Dark matter as well as modified gravity on large and small scales.

On larger scales, gravitational phenomena are the only one that is relevant and constitute a “cleanest” astrophysical laboratory for testing cosmological physical theories. In smaller sizes, star radiation, gas, and other effects resulting from the physics that comprise normal matter play an important function, and the simulations are constantly improving.

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We are not yet at the point at which we can perform physics at a small scale in a clear manner. Yet, large-scale Physics has been in place for quite a while and is a clear path toward dark matter.

The most effective method for you to deceive yourself is to create things that give you the correct answer but don’t take the entire range of factors at stake into account.

You can get the right answer for the wrong reasons (especially if you can verify that the answer is correct -it is the most reliable method of convincing you that you’re on to something significant even if the only thing you’ve gotten is the results of the physics that you’ve not considered.

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Although we don’t know if gravity’s law needs to be altered, we are certain that in the case of matters of our Universe, around 90% of it is dark.

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