... like I'm 5 years old
Imagine you're in a room that's pitch black. You can't see anything, but you know there are objects in the room because you can feel them. This is a bit like how scientists understand dark matter and dark energy.
Dark matter is an unseen substance that makes up about 27% of the universe. We know it's there because we can see its gravitational effects on stars and galaxies. It's like the invisible furniture in the room, whose presence we can infer because we bump into it.
Dark energy, on the other hand, is like a force that's pushing everything apart. It's the reason the universe is expanding at an accelerating rate. Scientists think dark energy makes up about 68% of the universe. The remaining 5% is everything we can see: stars, galaxies, planets, and so forth.
Imagine you're blowing up a balloon with dots on it. As you blow, the balloon expands and the dots move further apart. That's a bit like how dark energy is causing the universe to expand.
... like I'm in College
Dark matter and dark energy are two of the most mysterious components of our universe, primarily because they are invisible and undetectable by traditional means. However, they exert a profound influence on the cosmos.
Dark matter is thought to be made up of particles that do not interact with light or other forms of electromagnetic radiation, making it impossible to see directly. Its presence is inferred from the way galaxies rotate and cluster together, which suggests there is more mass present than we can observe.
Dark energy, on the other hand, is a hypothetical form of energy that permeates all of space and exerts a negative pressure, driving cosmic acceleration. The concept of dark energy was introduced to explain the surprising discovery in the late 1990s that the rate of the universe's expansion is increasing, not slowing down as had been assumed.
If we were to build a model of the universe using Lego bricks, the bricks themselves would represent all the matter we can see: stars, galaxies, planets, and so on. But this would only account for 5% of the bricks. The remaining 95% of the bricks, representing dark matter and dark energy, would be invisible.
For the 27% representing dark matter, imagine invisible bricks scattered throughout our model, exerting a pull on the visible bricks. This mirrors the gravitational influence dark matter has on visible matter in the universe.
For the 68% representing dark energy, imagine a constant, unseen force pushing all the bricks apart, causing our model universe to expand. This reflects how dark energy is driving the accelerating expansion of the universe.
In this way, even though we can't see dark matter and dark energy directly, we can still understand their effects on the universe.
... like I'm an expert
Dark matter, postulated to account for the discrepancy between the luminous mass and total gravitational mass in galaxies and clusters, is non-baryonic and only interacts with baryonic matter and radiation through gravity. It does not interact with electromagnetic radiation, which makes its detection and study challenging. Current theories suggest it may be composed of Weakly Interacting Massive Particles (WIMPs) or axions.
Dark energy is even more elusive. It is theorized to be a form of vacuum energy, a quantum mechanical phenomenon where empty space has an energy density. It is the leading explanation for the cosmological constant in Einstein's field equations of general relativity. Dark energy is thought to be responsible for the observed acceleration in the expansion of the universe, a conclusion drawn from redshift observations of Type Ia supernovae.