Question

What evidence makes scientists think the universe is made mostly of dark matter and dark energy, and why are these things so mysterious? Are these mysteries likely to have an impact on the question of life in the universe? Explain.

Short answer

Dark matter's gravitational effects and dark energy's influence on cosmic expansion hint at their existence, but their true nature remains unknown.

Step-by-step solution

Observational Evidence for Dark Matter

Scientists have gathered evidence for dark matter through observations of galaxies and galaxy clusters. The rotational speeds of galaxies indicate there is more mass than what we can see with visible matter. Gravitational lensing, where light from distant objects is bent by massive objects, also suggests the presence of an unseen mass, leading to the conclusion that dark matter exists.

Observational Evidence for Dark Energy

Dark energy was proposed to explain why the universe's expansion is accelerating. Observations of distant supernovae have shown that galaxies are moving away faster than expected, suggesting an unknown energy density is pushing the universe apart. These observations support the existence of dark energy.

The Mystery of Dark Matter

Dark matter is mysterious because it does not interact with electromagnetic forces, meaning it does not emit, absorb, or reflect light, making it invisible and detectable only through gravitational effects. Its composition is unknown, but candidates include Weakly Interacting Massive Particles (WIMPs) and axions.

The Mystery of Dark Energy

Dark energy is mysterious because its properties and its exact nature are unknown. It is even less understood than dark matter. Its presence in the universe affects cosmic structure and the ultimate fate of the universe, yet it is detected only through its influence on the universe's expansion.

Impact on the Question of Life in the Universe

The mysteries of dark matter and dark energy may indirectly impact the question of life in the universe by influencing cosmic evolution and structures essential for life, such as galaxies and star systems. However, their direct impact on life's existence is uncertain and remains an area of ongoing research.

Key concepts

Dark Energy

Dark energy is a mysterious and unseen force that fills our universe. It is thought to make up about 68% of the universe's total energy density. Observations imply this energy is responsible for pushing galaxies apart, causing the universe's expansion to accelerate. This was first noted from observing distant supernovae, whose light revealed galaxies are moving away faster than anticipated.
Dark energy's undisclosed nature baffles scientists. We can't see or touch it, leaving its true essence hidden from us. Yet, it plays a crucial role in shaping the cosmos.

Galaxies

Galaxies are massive systems comprised of stars, gas, dust, and dark matter, bound together by gravity. They are the fundamental building blocks of the universe's structure. Galaxies come in various shapes, sizes, and types, including spiral, elliptical, and irregular.
Understanding galaxies helps us unravel the content of the universe. The motion of stars within galaxies often suggests there's more invisible mass present than what is visible. This invisible part is often attributed to dark matter, a substance we cannot observe directly but know exists from its gravitational effects.

Gravitational Lensing

Gravitational lensing occurs when light from a distant object, like a galaxy or quasar, is bent around a massive object, such as a galaxy cluster. This creates an effect similar to a magnifying glass, often forming multiple images or stretching the light of the distant object.
It serves as a powerful tool for astronomers to infer the presence of unseen mass, including dark matter. Through gravitational lensing, we can measure the mass distribution of galaxies and galaxy clusters, providing essential clues to understanding our universe's structure and the mysterious dark components within it.

Weakly Interacting Massive Particles (WIMPs)

WIMPs are a leading theoretical candidate for explaining dark matter. As their name suggests, they are massive particles that interact very weakly with normal matter. Unlike ordinary particles, they don't react to electromagnetic forces, so they don’t emit, absorb, or reflect light. This makes them invisible and detectable primarily through their gravitational effects.
Scientists have theorized WIMPs to help answer the question of dark matter's composition. Although they have not yet been detected directly, they remain one of the best hypotheses for the dark matter puzzle.

Cosmic Expansion

The universe is not static; it is expanding. This cosmic expansion was first discovered by Edwin Hubble in the 1920s, when he observed that galaxies are moving away from us. More recent observations have shown that this expansion is happening at an accelerating pace, largely attributed to dark energy.
As space expands, galaxies move further apart. This cosmic stretching influences how we understand time, space, and the universe’s fate. The accelerated expansion raises questions about the universe's future and challenges our understanding of cosmology.

Galaxy Clusters

Galaxy clusters are collections of hundreds or thousands of galaxies bound together by gravity. They are the largest structures known in the universe, and their formation and evolution are significantly influenced by dark matter and dark energy.
The study of galaxy clusters can reveal much about the universe's structure and the unseen forces at play. They are also laboratories for observing gravitational lensing effects, offering a window into observing unseen dark matter through its gravitational interactions with visible matter.

Universe's Structure

The universe has a vast and intricate structure, composed of galaxies, clusters of galaxies, and vast voids between them. This large-scale structure is shaped significantly by dark matter and dark energy. While dark matter acts like a scaffold, forming filaments and halos where galaxies form and grow, dark energy influences the overall expansion rate and the universe's ultimate destiny.
The distribution and motion of galaxies throughout space tell a story of the universe's life over billions of years. Understanding this structure helps scientists piece together the cosmic puzzle, including the enigmatic roles of dark matter and dark energy.