Dark Matter Revisited

[shellyhe]

Hello folks, After a short hiatus, but always reading new commentary from respected astrophysicists and space jounalists, I proudly remain in the camp that Dark Matter is nothing more than gravity behaving differently at long distances and closely resembles the Modified Dynamics (MOND) theory line. The only discrepancy is that the equations for MOND do not emulate gravity exactly. Other forces in the universe also are affecting the appearance of the galaxies by JWST and other telescopes. This holds true in the cases of Bullet Clusters and Gravitational Lensing examples where MOND is getting so much ridicule. The research for the right answers is continuing, but right now, I am holding form that Dark Matter is not a real substance. And for those other believers that Dark Matter can be something from another universe or dimension that pops in and out of our universe, that will forever remain a mythical event.

 

[Ed Stauffer]

I believe that dark matter is what makes up the fabric of spacetime and we won’t find it until we figure out how to look outside of spacetime. If in the early universe the dark matter all condensed at the same time this would have resulted in black holes appearing much larger and gravity wells much deeper. In these wells time would pass more slowly relative to use which would match the slower pulsars and to us faster galaxy developement. Pulsar timing also shows a possible phase transition in the early universe. Over time as the ratio of liquid to gaseous dark matter dropped which reduced the time differential across the universe. Not taking into account the redshift due to climbing out of those gravity wells biases our distance calculations making us think the universe is expanding. It would be interesting to calculate the neutrino mass without the assumption of an expanding universe.

 

[amateur astronomer Jeff]

Trying to understand Dark Matter

I am not an astrophysics but consider myself relatively intelligent. I am finding it very difficult to understand the concept of dark matter.

In simplistic terms, as I understand it, astrophysics currently believe that there is far more mass in the universe than can be explained by the visually observable universe (visible, infrared, x-ray and gamma ray light). The observed effects of gravity in distant galaxies is claimed to show far more rotational speed that would be based on the visually observed mass. Based on these assumptions it is stated that 85% of this calculated mass is something we cannot see or indirectly detect. “Dark Matter” is the placeholder name for this “unknown excess” mass that cannot or has not been observed or explained.

It is also my understanding that there are many things of mass that we expect exist which we cannot visually observe. Rogue moons, planets, failed stars, brown dwarfs, interstellar asteroids are just being found within our Milky-way galaxy. Scientists say there are likely millions of stellar-mass black holes in our galaxy. Multiply that by the billons of galaxies, along with the speculated microscopic blackholes and many other possible not yet know items of mass in the universe. Voyager 1 has detected a faint, monotonous hum from plasma (ionized gas) in interstellar space. Therefore, it could be said that all of space contains plasma which has mass.

All of the above could account for the assumed mass within the current known universe.

I must therefore question the 85% estimated Dark Matter hypothesis.

Would someone please address this issue providing a detailed explanation which a non-astrophysicist/quantum physicist could understand.

 

[Jim Franklin]

Trying to understand Dark Matter

I am not an astrophysics but consider myself relatively intelligent. I am finding it very difficult to understand the concept of dark matter.

In simplistic terms, as I understand it, astrophysics currently believe that there is far more mass in the universe than can be explained by the visually observable universe (visible, infrared, x-ray and gamma ray light). The observed effects of gravity in distant galaxies is claimed to show far more rotational speed that would be based on the visually observed mass. Based on these assumptions it is stated that 85% of this calculated mass is something we cannot see or indirectly detect. “Dark Matter” is the placeholder name for this “unknown excess” mass that cannot or has not been observed or explained.

It is also my understanding that there are many things of mass that we expect exist which we cannot visually observe. Rogue moons, planets, failed stars, brown dwarfs, interstellar asteroids are just being found within our Milky-way galaxy. Scientists say there are likely millions of stellar-mass black holes in our galaxy. Multiply that by the billons of galaxies, along with the speculated microscopic blackholes and many other possible not yet know items of mass in the universe. Voyager 1 has detected a faint, monotonous hum from plasma (ionized gas) in interstellar space. Therefore, it could be said that all of space contains plasma which has mass.

All of the above could account for the assumed mass within the current known universe.

I must therefore question the 85% estimated Dark Matter hypothesis.

Would someone please address this issue providing a detailed explanation which a non-astrophysicist/quantum physicist could understand.

Jeff, you have a basic misunderstanding here, we can account for around 15% of all energy in the observable Universe, this includes all baryonic matter as mass and energy are interchangeable.

The 85% you mentioned is not all Dark Matter - take a look at this graphic.

Now, as you can see, in this graphic, Dark Matter only makes up around 26% of the matter in the Observable Universe, some 63% is believed to be Dark Energy, however, this assumptions has been called into question lately due to the publication in The Monthly Notices of the Royal Astronomical Society, of a paper by Antonia Seifert, Zachary G Lane, Marco Galoppo, Ryan Ridden-Harper, David L Wiltshire called Supernovae evidence for foundational change to cosmological models.

The new evidence supports the "timescape" model of cosmic expansion, which doesn't have a need for dark energy because the differences in stretching light aren't the result of an accelerating Universe but instead a consequence of how we calibrate time and distance. It takes into account that gravity slows time, so an ideal clock in empty space ticks faster than inside a galaxy.

The model suggests that a clock in the Milky Way would be about 35 per cent slower than the same one at an average position in large cosmic voids, meaning billions more years would have passed in voids. This would in turn allow more expansion of space, making it seem like the expansion is getting faster when such vast empty voids grow to dominate the Universe.

With regards Dark Matter, despite being invisible, its presence is inferred through its gravitational effects on visible matter, radiation, and the large-scale structure of the Universe.

So what is dark matter?
Dark Matter refers to a form of matter that does not emit, absorb, or reflect light, making it undetectable through electromagnetic radiation. It interacts primarily through gravity, and its existence is postulated to explain several astronomical observations that cannot be accounted for by visible matter alone.
How Do We Know Dark Matter Exists?
1. Galaxy Rotation Curves:

• Observations of spiral galaxies show that stars at their edges orbit faster than predicted by the visible mass (stars, gas, and dust). This discrepancy implies the presence of unseen mass extending beyond the visible galaxy.

2. Gravitational Lensing

• Massive objects, such as galaxy clusters, bend light from background objects. The amount of bending often exceeds what can be attributed to visible matter, suggesting the presence of additional invisible mass.

3. Cosmic Microwave Background (CMB) Radiation

• The CMB, a relic of the Big Bang, shows patterns that can only be explained if there is much more matter than we can see, with Dark Matter being a significant contributor.

4. Large-Scale Structure of the Universe

• The distribution and formation of galaxies and galaxy clusters over time require a gravitational framework provided by Dark Matter to clump and form structures.

5. Galaxy Clusters and Missing Mass

• Measurements of galaxy cluster masses via the motion of galaxies, hot gas observed in X-rays, and gravitational lensing reveal far more mass than visible matter accounts for.

Effects of Dark Matter on Normal Matter
Dark Matter affects the Universe in several profound ways:

• Gravitational Binding - It provides the gravitational "scaffolding" that holds galaxies and galaxy clusters together. Without it, galaxies would disperse.
• Formation of Structures - During the early Universe, Dark Matter clumped under gravity, forming the seeds for galaxies and larger structures.
• Motion of Stars and Gas - It influences the dynamics within galaxies, explaining their flat rotation curves.
• Cosmological Evolution - It impacts the expansion rate and structure of the Universe, interacting indirectly with normal matter through gravity.

What Might Dark Matter Be?
The nature of Dark Matter remains unknown, but several hypotheses exist:

1. WIMPs (Weakly Interacting Massive Particles)

• Hypothetical particles that interact only via gravity and weak nuclear forces. They are a popular candidate and are sought through particle physics experiments.

2. Axions

• Ultralight particles predicted by extensions of quantum field theory. They might form a diffuse field that permeates the Universe.

3. Sterile Neutrinos

• Hypothetical heavier versions of neutrinos that do not interact via normal weak nuclear forces, only through gravity.

4. MACHOs (Massive Compact Halo Objects)

• These include objects like black holes, neutron stars, or brown dwarfs. However, they are not sufficient to explain the observed effects.

5. Modified Gravity

• Some theories suggest modifying our understanding of gravity (e.g., MOND—Modified Newtonian Dynamics) to explain the observations without invoking Dark Matter. However, these fail to account for all evidence. This has been largely disproved in recent months with one of its biggest proponents now actively speaking out against the theory. I have included it for completeness.

How Might We Detect Dark Matter?
1. Direct Detection

• Experiments aim to observe rare interactions between Dark Matter particles and normal matter. Facilities like LUX-ZEPLIN (LZ) and XENON use ultra-sensitive detectors to look for WIMP interactions.

2. Indirect Detection

• Dark Matter annihilations or decays might produce high-energy gamma rays, neutrinos, or other particles. Observatories like the Fermi Gamma-ray Space Telescope search for these signals.

3. Collider Experiments

• High-energy particle colliders, like the Large Hadron Collider (LHC), may produce Dark Matter particles that escape detection, inferred through missing energy in particle collisions.

4. Astrophysical Observations

• Improved telescopes and gravitational wave detectors might provide additional indirect evidence by studying the effects of Dark Matter on cosmic structures.

5. Axion Detection

• Experiments like ADMX (Axion Dark Matter Experiment) use resonant cavities to search for the conversion of axions into photons in a magnetic field.

The search for Dark Matter is challenging due to its weak interactions. However, upcoming projects, such as the Vera C. Rubin Observatory, Euclid mission, and advanced particle detectors, aim to unravel its nature. Breakthroughs in theoretical physics, including quantum gravity and supersymmetry, may also provide clues.

In essence, Dark Matter remains one of the Universe's greatest mysteries, with its discovery promising to revolutionize our understanding of physics and cosmology.

I hope this helps you get a better understanding of Dark Matter and do not confuse it with Dark Energy.

 

[shellyhe]

Trying to understand Dark Matter

I am not an astrophysics but consider myself relatively intelligent. I am finding it very difficult to understand the concept of dark matter.

In simplistic terms, as I understand it, astrophysics currently believe that there is far more mass in the universe than can be explained by the visually observable universe (visible, infrared, x-ray and gamma ray light). The observed effects of gravity in distant galaxies is claimed to show far more rotational speed that would be based on the visually observed mass. Based on these assumptions it is stated that 85% of this calculated mass is something we cannot see or indirectly detect. “Dark Matter” is the placeholder name for this “unknown excess” mass that cannot or has not been observed or explained.

It is also my understanding that there are many things of mass that we expect exist which we cannot visually observe. Rogue moons, planets, failed stars, brown dwarfs, interstellar asteroids are just being found within our Milky-way galaxy. Scientists say there are likely millions of stellar-mass black holes in our galaxy. Multiply that by the billons of galaxies, along with the speculated microscopic blackholes and many other possible not yet know items of mass in the universe. Voyager 1 has detected a faint, monotonous hum from plasma (ionized gas) in interstellar space. Therefore, it could be said that all of space contains plasma which has mass.

All of the above could account for the assumed mass within the current known universe.

I must therefore question the 85% estimated Dark Matter hypothesis.

Would someone please address this issue providing a detailed explanation which a non-astrophysicist/quantum physicist could understand.

I like your answer but just don't think that the objects mentioned is enough to keep any particular galaxy from falling apart. For example, if there were many black holes near a large visible galaxy, there would be some visible evidence. Maybe it could be a combination of unseen matter, as you mentioned, plus the MOND gravity adjustment and some other unseen forces in the universe. Just no pure dark matter.