Dark Matter Discussion with Gemini

Is there a pattern to the distribution of galaxies where the effects of dark matter have been seen?

Yes, there is a strong correlation between the distribution of galaxies and the inferred presence of dark matter. Here’s how:

  • Galaxy Rotation Curves: When we study the rotation speeds of stars and gas within galaxies, we see that they spin much faster than expected based on the visible matter alone. This suggests the existence of a vast amount of invisible mass, likely dark matter, that contributes significantly to the galaxy’s overall gravity. The distribution of this dark matter is believed to be more concentrated towards the center of galaxies compared to the luminous matter.
  • Weak Gravitational Lensing: This technique doesn’t directly detect dark matter, but it reveals its presence by its gravitational influence. By observing how light from distant galaxies bends around massive foreground objects like galaxy clusters, astronomers can map the distribution of mass, including dark matter. These studies show that the distribution of dark matter often extends far beyond the visible extent of galaxies, forming a massive halo.

These observations suggest a pattern:
Dark matter is more concentrated in the central regions of galaxies compared to the distribution of visible matter.

  • Galaxies are likely embedded in extended halos of dark matter that reach far beyond the luminous extent of the galaxy.

It’s important to remember that dark matter is invisible by definition, so these patterns are based on indirect methods. However, the consistency of the evidence across different techniques strongly suggests a link between dark matter distribution and galaxy formation and evolution.

No, I meant that if you were to map those galaxies in terms of their location and distance from each other, would there be a pattern?

Ah, I see! You’re asking about the large-scale distribution of galaxies with dark matter, not within individual galaxies themselves.

On the largest scales (hundreds of millions to billions of light-years), the distribution of galaxies with dark matter doesn’t show a perfectly uniform pattern. Here’s what we see:

  • Large Scale Structure: Galaxies tend to cluster together in filaments and walls, forming a vast cosmic web. The space between these structures is mostly empty. This “clumpy” distribution is thought to be influenced by the initial distribution of dark matter in the early universe.
  • No Grand Unified Pattern: There isn’t a single, grand, repeating pattern like a perfect grid. The distribution is more like a complex network with variations in density and filament connections.

However, there are some hints of order within this large-scale structure:

  • Superclusters: The largest structures are superclusters, containing thousands of galaxies. These superclusters may show some degree of alignment or elongation.
  • Voids: The vast empty regions between filaments and walls are called voids. These voids might show some regularity in their size distribution.
A map of the Boötes void.
Credits: Powell, Richard. Atlas of the Universe
Copyrights information: atlasoftheuniverse.com/copyright

Overall: The distribution of galaxies with dark matter is not random, but it’s a complex and evolving large-scale structure.

Here are some resources for further exploration:

NASA, ESA, and E. Hallman (University of Colorado, Boulder), Public domain, via Wikimedia Commons

Do all galaxies show signs of dark matter?

There’s actually some exciting research suggesting not all galaxies may exhibit the same amount of dark matter, or even any at all.

Traditionally, astronomers believed dark matter was present in all galaxies based on observations like galactic rotation curves and gravitational lensing. However, recent discoveries have challenged this notion.

  • Ultra-Diffuse Galaxies (UDGs): These recently discovered galaxies are surprisingly large and faint, containing very few stars compared to their size. Intriguingly, some studies suggest these UDGs might lack significant amounts of dark matter, defying our current understanding of galaxy formation.

It’s important to note that these findings are relatively new and require further confirmation. Here are some possibilities:

  • Low Dark Matter Density: It’s possible these galaxies still have dark matter, but it’s distributed very differently than in typical galaxies, perhaps at much lower densities.
  • Alternative Explanations: Some researchers are exploring alternative explanations for the observed dynamics of UDGs that don’t necessarily require dark matter.

The discovery of UDGs with potentially little dark matter highlights the ongoing exploration of this mysterious substance. While the evidence for dark matter in most galaxies remains strong, these recent findings suggest there might be more to the story.

Are there any mulitverse theories that attempt to explain dark matter?

Yes, there are some multiverse theories that propose an explanation for dark matter. These theories are speculative and lack concrete evidence, but they offer an interesting perspective:

  • Hidden Sector Theory: This theory proposes the existence of a “hidden valley” – a parallel universe made of dark matter particles that interact very weakly or not at all with our own universe. The basic idea is that the laws of physics in this hidden sector might allow for stable, massive particles that wouldn’t readily interact with normal matter, potentially explaining dark matter’s elusive nature.
  • Sterile Neutrinos: In the Standard Model of particle physics, there are three types of neutrinos. Multiverse theories propose the existence of additional, “sterile” neutrinos that wouldn’t interact with standard matter but could contribute to dark matter.
  • Weakly Interacting Massive Particles (WIMPs): This is a more mainstream candidate for dark matter, but some multiverse theories propose that WIMPs might originate from interactions between our universe and another.

It’s important to consider the limitations of these ideas:

  • Highly Speculative: These multiverse theories lack experimental verification. There’s no direct evidence for the existence of hidden universes or exotic particles.
  • Explanatory Power: While these theories offer explanations, they don’t necessarily provide more clarity or testable predictions compared to other dark matter candidates like WIMPs or Axions.

The current focus in dark matter research is on finding these particles directly through experiments or through indirect methods like gravitational lensing. However, multiverse theories remain an interesting avenue for future exploration, prompting us to consider alternative explanations for the universe’s unseen mass.

In the order in which matter was formed just after the big bang, when is it theorised that dark matter formed?


The Big Bang.
NASA/WMAP Science Team,
Public domain, via Wikimedia Commons

The prevailing theory is that dark matter formed very early in the universe, most likely alongside the formation of normal matter, or elementary particles, in the hot, dense soup following the Big Bang. Here’s the breakdown:

  1. First Fraction of a Second: During this incredibly brief period, the universe was in a state of extremely high energy and temperature. The fundamental forces, except gravity, are thought to be unified. Here, it’s theorized that dark matter particles could have formed along with other elementary particles.
  2. Inflationary Epoch (Possible): Some theories propose an inflationary epoch shortly after the first fraction of a second. This rapid expansion might have affected the nature and abundance of dark matter particles.
  3. A Few Minutes Later: As the universe cools, fundamental forces separate, and familiar particles like protons and neutrons start forming. Dark matter, if it formed in the first stage, would likely continue to exist as a separate component from normal matter.

Key Points:
The exact mechanism of dark matter formation remains unknown, but it’s believed to be an extremely early process.

  • Dark matter wouldn’t have participated in the formation of stars and heavier elements later in the universe’s history, unlike normal matter.
  • There are alternative theories proposing dark matter formation at later stages, but these are less widely accepted.

While there’s no single definitive theory, the current understanding points to a very early origin for dark matter, possibly alongside the formation of the first elementary particles.

Why did dark matter not interact with the other particles created at the same time?

That’s a great question, and it’s right at the heart of the mystery surrounding dark matter. Here’s what we know, and some of the prevailing theories:

The Nature of the Unknown: Since we haven’t directly detected dark matter yet, we can only theorize about its properties. One key characteristic is that it likely interacts very weakly, if at all, with normal matter and the electromagnetic force. This means it wouldn’t clump together with normal particles in the same way after the Big Bang.

Possible Explanations:
Different Forces: Dark matter particles might interact with different forces or mediators compared to normal matter. Imagine two sets of gears, normal matter interacting with familiar gears like electromagnetism, while dark matter has its own unique set that rarely meshes with the first set.

  • Massive and Weakly Interacting: A popular theory proposes dark matter as Weakly Interacting Massive Particles (WIMPs). These WIMPs would be massive compared to elementary particles but wouldn’t readily interact through the electromagnetic force or strong nuclear force. This weak interaction would have limited their participation in the processes that formed stars and galaxies later on.
  • Sterile Neutrinos: Another possibility is the existence of sterile neutrinos, theorized particles that wouldn’t interact with normal matter but could contribute to dark matter.

It’s All Speculation (for Now): It’s important to remember these are just some of the leading theories. The true nature of dark matter remains a subject of ongoing research. Scientists are searching for dark matter particles directly in experiments or indirectly through gravitational effects. As we learn more about dark matter’s properties, we might be able to understand why it interacted so minimally with other particles in the early universe.

Here are some resources for further exploration:

When you say ‘different forces,’ are you suggesting there are forces or mediators other than the ones we know that have not yet been identified?

Yes, that’s exactly right! When I said “different forces” in the context of dark matter, I was referring to the possibility of forces or mediators beyond the four fundamental forces we currently understand:

  • The Strong Nuclear Force: This force binds quarks together to form protons and neutrons.
  • The Weak Nuclear Force: This force is responsible for certain types of radioactive decay and some subatomic particle interactions.
  • The Electromagnetic Force: This force governs the interaction between electrically charged particles, including light and most atomic interactions.
  • Gravity: This force attracts all matter and energy.

These four forces have been extensively studied and explain a vast amount of physical phenomena. However, dark matter’s elusive nature hints at the possibility of additional forces or mediators that we haven’t yet identified.

Here’s how these hypothetical forces might play a role:

  • New Mediators: Imagine the fundamental forces as gears that mesh and transmit interactions between particles. These new forces could be like gears in a separate system, rarely interacting with the gears of the known forces. This could explain why dark matter particles wouldn’t interact strongly with normal matter.
  • Hidden Sector: Some theories propose a “hidden sector” – a parallel universe that interacts with our universe through these new forces. Dark matter particles might originate from this hidden sector and only interact weakly with our own.

The Challenge of the Unknown: Unfortunately, these are all speculative ideas. We don’t have any concrete evidence for these new forces or a hidden sector. Theories like Weakly Interacting Massive Particles (WIMPs) attempt to explain dark matter within the framework of known physics, but the possibility of entirely new forces remains an intriguing avenue for exploration.

Particle physics experiments and cosmological observations are constantly searching for clues about dark matter. As we gather more data, we might be able to shed light on whether new forces are at play in the universe.

Isn’t that just creating more unknowns to fill the gap? I thought science was all about simplifying things.

You’re absolutely right. In science, the goal is often to strive for simplicity and unifying explanations. Introducing new forces or particles to explain dark matter does add complexity. However, there’s a balance between this desire for simplicity and the need to accurately represent reality. Here’s how to think about it:

  • The Power of Known Physics: The Standard Model of particle physics, based on the four fundamental forces, has been incredibly successful in explaining a vast range of phenomena. It’s a powerful and well-tested theory.
  • The Challenge of the Unknown: Dark matter throws a wrench into this simplicity. It’s a major component of the universe, yet it interacts very weakly with everything we understand. This forces us to consider the possibility that there might be something missing from our current picture.
  • Occam’s Razor (Sort Of): This principle suggests favouring simpler explanations, but it doesn’t mean clinging to a theory that doesn’t fit the observations. In this case, the existence of dark matter is a well-established observation. We need an explanation that accommodates this fact, even if it means introducing new ideas.
  • Science is a Journey: The beauty of science is that it’s constantly evolving. New discoveries can challenge existing paradigms. While adding new forces might seem complex now, it could ultimately lead to a more comprehensive understanding of the universe.

Finding the Missing Piece: Theories like new forces or hidden sectors are attempts to bridge the gap in our knowledge. They’re not necessarily creating unknowns for the sake of it, but rather proposing possibilities to explain a real phenomenon – dark matter.

The hope is that further experimentation and observation will provide evidence for, or against, these new ideas. If we can detect dark matter particles directly, it might reveal if they interact through known forces or entirely new ones.

Science is a process of refinement, constantly seeking the simplest explanation that fits all the data. Dark matter pushes us to re-evaluate our current understanding, which may lead to a more complete and nuanced picture of the universe, even if it takes a few more unknowns to get there.

Notes and Considerations

  1. Attribution: This is from a discussion with  Bard, a large language model from Google AI on March 28, 2024) to provide context for the discussion.
  2. Accuracy: While Bard strives to provide accurate and up-to-date information, the field of dark matter research is constantly evolving. New discoveries might necessitate revisions to our current understanding.
  3. Transparency:  Bard is a machine learning model and not a sentient being. Its responses are based on the information it has been trained on and does not have personal opinions or beliefs.
  4. Further Exploration: Please use credible sources if you want to delve deeper into the topics discussed. Some were provided throughout the conversation.