Matter as we know it, atoms, stars and galaxies, planets and trees, rocks and us(human), this matter accounts for less than 5% of the known universe. About 25% is dark matter and 70% is dark energy, both of each are invisible. It is very hard to observe these particles as they do not emit or reflect light that can be detected in the electromagnetic spectrum. Although the scientists have not directly observe dark matter particles, but there are many suspects that dark matter and dark energy exist. http://ww3.haverford.edu/physics-astro/course_materials/astr152i/Rubin-Dark-Matter.pdf
What is Dark Matter
Dark matter is not just clouds of normal matter, because it would emit particles we could detect. It is not anti-matter because anti-matter produces unique gamma rays when it reacts with normal matter. Also, dark matter is not made up of black holes which categorize as compact objects that violently affect their surroundings, while dark matter seems to be scattered all over the place. https://science.nasa.gov/astrophysics/focus-areas/what-is-dark-energyMany people have speculated dark matter is a category of dark objects called MACHOs. These are things like brown dwarfs, white dwarfs, or black holes which are made of ordinary matter such as protons, neutrons and electrons. Some of the missing mass might be these MACHOs, but cosmological models of the early universe have shown that we should not see more than this 5% level of baryonic matter.
As the search continued for dark matter, previously discovered exotic particles like neutrinos, axions and neutralinos were reconsidered. These particles are the prime candidates of WIMPs( Weakly Interacting Massive Particles) which are not made up of ordinary matter and are able to pass through ordinary matter without any effects. Like dark matter neutrinos are passing through the earth millions of particles at a time but they are too light to account for dark matters effect an gravity and scientists can recreate neutrinos in particle colliders. They also come from the sun. https://imagine.gsfc.nasa.gov/educators/galaxies/imagine/dark_matter.html
Axion is also another possible dark matter candidate, they were invented to explain a particular glitch in the particle physics and astronomy theories. Axions are very light and are believed to have been created at the moment of big bang just like dark matter but theories suggest that they could convert into microwave photons while dark matter is stable. https://phys.org/news/2017-02-axion-dark-device.html
After exhausting all the usual suspects, many scientists believe dark matter is a new exotic particle unlike anything on earth and billions are passing through us every second.
To be a perfect dark matter candidate it must have a certain properties, for example dark matter must not be fast moving particles as fast moving particles would not clump together in the universe. https://imagine.gsfc.nasa.gov/educators/galaxies/imagine/dark_matter.html
The moment of the big bang, dark matter was created. Scientist believed that dark matter was pulled together by gravity very slowly over time and it played a critical role in helping ordinary matter clump together to form stars and planets. http://curious.astro.cornell.edu/about-us/95-the-universe/galaxies/general-questions/508-are-there-any-dark-stars-or-dark-galaxies-made-of-dark-matter-advancedAs
Initial evidence of existence of dark matter
Dark matter was first posited by Fritz Zwicky, when he was studying the motions of galaxies in the Coma Cluster. He estimated the mass of the Coma Cluster by determining the galactic velocities then he compared it to how much mass he could actually get by measuring the galaxies light output. He found that the galaxies were moving too fast within the cluster for the amount of illuminated stuff he could see, by his calculations there should have be a hundred and sixty times more illuminated mass to account for the random speeds of galaxies in the cluster. He analyzed their motions and concluded that the cluster could not be stable unless there was a large amount of dark matter present. Dark matter was present in the galaxies and it had enough mass to keep the rotation speed constant. http://www.learner.org/courses/physics/unit/text.html?unit=10&secNum=2
Astronomers realized that dark matter exposed itself by bending light that passes through it ,called gravitational lensing. A light ray can be deflected in its path by dark matter. By tracing the lights path, gravitational lensing detected dark matter concentrated in the Halos of galaxies. Measure the distortion of the light rays passing through the dark matter. By looking at the distortion of light a2s it goes through galaxies, we have maps of dark matter. http://ww3.haverford.edu/physics-astro/course_materials/astr152i/Rubin-Dark-Matter.pdf
What is Dark Energy
Science believes dark energy was created along with dark matter at the moment of the big bang. Dark energy seems to be some kind of energy intrinsic to empty space. Energy that is stronger than anything else and it keeps getting stronger as time passes by. There are multiple ideas about what dark energy might be. Firstly, the Dark energy is not a thing, but just a property of the space. According to Albert Einstein, empty space is not nothing, it has its own energy. It can generate more space and is quite active. So, as the universe expands, it could be that just more and more space appears to fill the gaps and this leads to a faster expanding universe. https://science.nasa.gov/astrophysics/focus-areas/what-is-dark-energyThis idea is close to an idea that Einstein had back in 1917 of a concept of a cosmological constant, a force that counteracted the force of gravity. Dark energy is the energy of vacuum and it pushes the galaxies apart creating a runaway universe. http://www.astro.ucla.edu/~wright/cosmo_constant.html The only problem is, that when we tried to calculate the amount of this energy the result was so wrong and weird, that it only added to the confusion. Another idea is that empty space is actually full of temporary, virtual particles that spontaneously and continually form from nothing and then disappear into nothing again. The energy from those particles could be dark energy. Lastly, maybe dark energy is an unknown kind of dynamic energy fluid or field which permeates the entire universe. https://science.nasa.gov/astrophysics/focus-areas/what-is-dark-energy
– Scientists have discovered a new mysterious dark energy was dominating space and it’s repulsive energy is driving the galaxies apart .
– Science always assumed that although the universe continues to grow in size it wuld eventually slow in its expansion or perphaps even collapse on itself. Gravity would overcome any momentum it had but while measuring the expansion history of the universe ,scientists realize that was not slowing down it was speeding up
Difference between dark matter and dark energy
In short, there are about 70% of the total mass of the universe consists of dark energy, and about 25% is dark matter. They have different effects on the acceleration of expansion of the Universe. Dark matter decelerates the universe expansion and it plays important role in helping gravity to holds galaxies together. In the early universe, small fluctuations in the Cosmic Microwave Background is amplified by the dark matter in order to build a massive structure in the universe today.
Dark energy is described by the cosmological constant in the equation of general relativity. While measuring the expansion history of the universe, scientists realized that there is presence of dark energy that causes the universe to not only expand, but it also has a negative pressure that speeds up the expansion. Due to the larger quantity of the dark energy, the impact caused by it on the acceleration of the expansion is 5.5 times bigger. http://curious.astro.cornell.edu/about-us/108-the-universe/cosmology-and-the-big-bang/dark-matter/658-what-s-the-difference-between-dark-matter-and-dark-energy-intermediate http://curious.astro.cornell.edu/about-us/101-the-universe/cosmology-and-the-big-bang/general-questions/569-how-can-we-compare-dark-matter-and-dark-energy-intermediate
Evidence of existence of dark energy
– Edward hubble first discovered galaxies were moving away from the Milky Way in 1929 by realizing the more distant galaxies move faster away from us than the nearby ones. He realiesed he could measure thir velocities by studying their vwavelength through a prism called measuring the redshift and is still used to measure distances in space and he found that in fact the greater the distances of a galaxy right now the greater the speed with which it’s ,moving away from us that is the grater its redshift
– Few year ago astronomers decided to use red shift measurement s to measure the expansion history if the universe
– In 1929, Edward Hubble examined how the wavelength of light emitted by distant galaxies, shifts towards the red end of the electromagnetic spectrum as it travels through the space, He found that fainter, more distant galaxies showed a large degree of red shift. Hubble determined that this was because the universe itself is expanding. The red shift occurs, because the wavelengths of light are stretched as the universe expands. More recent discoveries have shown that, the expansion of the universe is accelerating. Before that, it was thought that the pull of gravity would cause the expansion to either slow down or even retract and collapse in on itself at some point. Space doesn’t change its properties as it expands, there is just more of it. New space is constantly created everywhere, galaxies are tight bound clusters of stuff held together by gravity so we don’t experience this expansion in our daily lives but we see it everywhere around us. Wherever there is empty space in the universe, more is forming every second.