Building the Universe: Cold Dark Matter Theory Quiz

In this context, cold means that the particles move slowly compared to the speed of light. Because they are non-relativistic, they can easily clump together under the influence of gravity. This slow motion allowed for the formation of small-scale structures in the early universe, which eventually grew into the galaxies we observe today.

It is false because CDM theory follows a "bottom-up" model of structure formation. Small fluctuations in density allowed smaller objects, like sub-galactic clumps, to form first. These smaller entities then merged over billions of years to create larger structures, such as galaxies and massive clusters, driven by the gravitational pull of slow-moving dark matter.

CDM particles are described as collisionless. This means they do not experience the electromagnetic forces that cause normal atoms to bounce off one another or emit heat. They can pass through stars, planets, and even other dark matter particles, interacting almost exclusively through gravitational attraction, which simplifies how they cluster in space.

WIMPs are the primary candidates for CDM. These hypothetical particles have significant mass but only interact through gravity and the weak nuclear force. Their existence would perfectly explain the "missing mass" in galaxies and the specific way that cosmic structures evolved from the density ripples seen in the early universe's radiation.

Small-scale clustering, the cosmic web, and gravitational lensing are all supported by CDM. The theory accurately predicts the "web-like" distribution of matter across the cosmos. While planetary volcanism is a geological process, the distribution of entire galaxies is dictated by the scaffolding provided by the slow-moving, invisible mass described in CDM.

CDM is significantly slower than Hot Dark Matter. Hot Dark Matter consists of lightweight particles, like neutrinos, that move at relativistic speeds. Because Hot Dark Matter moves so fast, it would "stream" out of small regions, preventing small galaxies from forming early on. CDM’s slower speed allows for the dense clumping observed in our universe.

It is true because the Lambda-CDM model is the most widely accepted mathematical framework for the universe. "Lambda" represents dark energy, while "CDM" represents Cold Dark Matter. Together, these components explain how the universe expanded and how matter organized itself into the complex patterns of galaxies and voids we see through modern telescopes.

The universe is crisscrossed by filaments. These are long, thin strands of dark matter that act as the skeleton of the universe. Normal baryonic matter is drawn into these filaments by gravity, leading to the formation of galaxies along these paths, creating a structure often compared to a giant cosmic spiderweb.

If dark matter were hot, small galaxies would not have formed early in cosmic history. Fast-moving particles would have stayed spread out, only allowing the very largest structures to collapse. Since we observe many small, old galaxies, the Cold Dark Matter theory is much better supported by our actual astronomical observations of the deep sky.

It is difficult because they do not emit light and rarely interact with atoms. Laboratory detectors look for the tiny "kick" an atom receives when a dark matter particle hits it. Because these interactions are extremely rare and involve no electromagnetic signals, scientists must build detectors deep underground to block out other types of interference.

Temperature fluctuations provide the blueprints. These tiny differences in the heat of the early universe represent areas that were slightly more dense than others. Cold Dark Matter began clumping in these dense spots immediately, creating the gravitational wells that eventually pulled in enough gas to ignite the very first stars.

Gravity is the primary force. Unlike normal matter, which is pushed around by light pressure and heat, Cold Dark Matter only feels gravity. This allows it to start forming structures much earlier than normal matter could, effectively winning the "race" to build the foundations of the galaxies that we live in today.

It is false because CDM particles cannot emit radiation. To settle into a small, dense object like a planet, matter must be able to shed energy and cool down. Since CDM does not interact with light, it cannot cool off, which is why it remains in large, diffuse halos around galaxies rather than forming solid objects.

They provide evidence that mass is extended far into space. The flat rotation curves show that there is a massive amount of invisible matter extending well beyond the visible stars. This matches the CDM prediction of a large "halo" that provides the gravity necessary to keep distant stars orbiting at high speeds.

The ingredients are Dark Energy, Cold Dark Matter, and Normal Matter. This "cosmic recipe" accounts for the expansion rate of the universe (Dark Energy), the gravitational structure (CDM), and the visible stars and planets (Baryonic Matter). This combination is currently the most successful model for describing the evolution of the cosmos from the Big Bang.

The theory predicts many satellite galaxies. Because CDM forms structures from the bottom up, larger galaxies should be surrounded by smaller clumps of dark matter and stars. While we see many of these satellites around the Milky Way, the "missing satellite problem" is an area where scientists continue to refine the CDM model.

CDM bends the light via gravity. Even though we cannot see the dark matter itself, its mass warps the space around it. When light from a distant quasar passes through a dark matter concentration, it follows that warped path, creating multiple images or distorted arcs that scientists use to calculate the amount of CDM present.

It is false because the term refers to its invisibility, not its color. Unlike dust or rocks, which can be seen when light hits them, dark matter is completely transparent. It does not reflect or block light at all, meaning it is "dark" in the sense that it is entirely undetectable by any form of electromagnetic observation.

It is considered "bottom-up" because small pieces merge into larger ones. In the early universe, CDM allowed small clumps to form first. Over time, gravity pulled these small clumps together to form galaxies, and then pulled galaxies together to form clusters. This sequence is a fundamental prediction of the Cold Dark Matter theory.

The main goal is to find the particle responsible for CDM. By smashing atoms together at high speeds, scientists hope to produce WIMPs or other dark matter candidates in a controlled environment. Confirming the identity of this particle would be one of the greatest discoveries in the history of science and the US schooling system's physics curriculum.