Our universe is controlled by complex and unseen forms of matter and energy that are still unknown. The vast majority of our universe is hidden from plain sight. Many scientists believe that dark matter and dark energy make up the majority of the universe, although we can't see or touch it. It's unimaginable to think that only 5% of the universe is made up of normal matter. This involves the atoms that make up everything that is visible, from vehicles to living beings to planets and stars. Dark energy and dark matter make up the remaining 95%. What exactly do these two intriguing words imply? What exactly is the difference between dark matter and dark energy?
Until the late 1990s, scientists assumed that the universe's expansion was slowing down due to gravity's attractive force. However, measuring the speed at which distant supernovae receded produced an unexpected result in 1998: the universe's expansion was accelerating. This gave rise to the concept of dark energy, which was said to have a repulsive force greater than gravity and also slightly stretched space. Dark energy, unfortunately, remains a mysterious concept because scientists are unsure of its nature and origin. Some assume it is a fifth fundamental force, while others compare it to a stronger version of Einstein's cosmological constant, which was essentially a zero space's energy and supposedly counterbalanced gravity's influence to achieve a static universe.
Furthermore, until around 7 billion years after the big bang, the expansion was found to be decelerating, after which it began to accelerate for unknown reasons. Dark energy is a significant concept since it has the potential to determine the universe's destiny. Scientists are uncertain if the accelerated expansion can continue forever, but if it does, it could lead to the Big Rip, a terrifying scenario in which acceleration overcomes the universe's forces of attraction, causing all matter to be ripped apart. Alternatively, the universe's accelerated expansion could cool it to the point that heat no longer exists, resulting in the Big Freeze.
Dark matter, on the other hand, has a gravitational force. astronomer Fritz Zwicky first proposed the concept of dark matter when he found that the total mass of all stars in the Coma cluster was less than 1% of the mass needed to prevent the galaxies from escaping the cluster's gravitational pull. Vera Rubin, another astronomer, stated that despite the distance from the galaxy's center, orbital velocity – the minimum velocity needed to hold a body in orbit remains constant. This was in direct contradiction to Newton's law of gravitation, which states that gravitational force is inversely proportional to the square of the distance between two masses, leading to the assumption that there must be another attractive force at work, one exerted by dark matter. Because of discoveries in gravitational lensing, the cosmic microwave background, and galactic collisions, there is now even more evidence for the existence of dark matter, and its widespread acceptance is emphasized by the fact that it is a part of the standard model of cosmology.
Despite this, since dark matter does not interfere with electromagnetic radiation, its origin remains unknown. It is not directly visible, that is why it is called "dark". We do know, however, that it is "cold" and electrically neutral. There have been several theories proposed as to what dark matter is.Many scientists say it is made up of weakly interacting massive particles (WIMPs) that are yet to be discovered. Others assume dark matter is made up of an axion, a hypothetical particle. Other hypotheses include Gravitationally Interacting Massive Particles (GIMPs) and sterile neutrinos. Despite having similar properties, non-sterile neutrinos cannot be dark matter since they could only be “hot” dark matter, which moves near to or at the speed of light. However, there is strong evidence that there is no “hot” dark matter, simply since it would be insufficient to explain the formation of galaxies and clusters.
There are also a few astronomers who fully reject the concept of dark matter in support of a concept known as Modified Newtonian dynamics (MOND). This assumes that gravity behaves differently over long distances than it does over short distances. However, since it matches observational data of galaxy clusters, this concept has attracted a lot of criticism. WIMPs are currently the most common explanation, and many attempts to detect them are continuing, but none have been effective so far. Dark matter research is important because it can help clarify the creation of galaxies and enhance our understanding of the universe's shape.
In conclusion, despite their similar sounding names, dark matter and dark energy are actually opposites: the former attracts, while the latter repels. Dark matter has an impact on individual galaxies, while dark energy has an impact on the whole universe. Furthermore, dark energy is clearly stronger because it can overpower attractive forces and cause rapid expansion. Even though dark matter and dark energy make up almost all of the universe, we know very little about them. However, various studies are being carried out around the world, and scientists are hopeful that a breakthrough will be made in the coming years. Some theoretical physicists believe that there is a vast unknown realm of particles and forces waiting to be discovered. Whatever dark energy and dark matter are made of, they seem to be tugging at the structure of our universe, keeping it together but still ripping it apart.
Image Credit: All images is from Pixabay, except for the cover image. The cover image is created by the author using Canva.
References
- Dark Matter and Dark Energy: Only five percent of the universe is visible. What is the rest made up of?
- Dark Energy, Dark Matter
- Dark energy: new experiment may solve one of the universe's greatest mysteries
- What are dark matter and dark energy, and how are they affecting the universe?
- Searching for Dark Matter with the ATLAS detector
- What's the difference between dark matter and dark energy? Our universe is dominated by mysterious and invisible forms of matter and energy
- Invisible dark matter makes up most of the universe – but we can only detect it from its gravitational effects
- Dark matter: What is it, how do we know it's there and will we find it?