Dark Matter and Dark Energy - Report Example

ESSAY: DARK MATTER AND DARK ENERGY Lecturer: due: Dark Matter and Dark Energy Expansion of the universe is a concept that was conversed in the early 1990s. It was suggested that due to gravitational force, the growth of the universe would be unhurried as time elapsed, but contrary to established opinion, and using the Hubble Space Telescope (HST), it proved that the expansion seemed to be accelerating. It was evident that an entity was causing the expansion speed, but there was inadequate information on the cause of the effect. Suggestions explaining this concept incorporated long discarded theories such as Einstein’s gravitational theory that proposed a cosmological constant; there was another suggestion of space being filled with an energy fluid, or some flaws in theories on gravity (Bertone, Hooper, & Silk 2005: 281). The solution to the challenge was the existence of a phenomenon called dark energy. Dark Energy Dark energy is a concept that has more unknown than known. The evidence of the concept is the effect on the universe’s expansion, but beyond that the energy is a mystery. It is reported that about 68% of the universe is occupied by dark energy, and dark matter occupies 27%, while what current science has observed accounts for a mere 5%. With little known about dark energy, several approaches are proposed to account for the energy in efforts of demystifying and characterizing it. The definition of an element cannot solely rely on the effect, or evidence; data has to be obtained regarding it, such as what are the element’s components. One of the proposals for dark energy is defining it as a property of space (Henry-Couannier 2005: 2341). This follows the hypothesis by Einstein that space has some particles (elements) in it; it does not represent absence of matter or nothing. Space as a scientific concept is yet to be understood, and its properties are just being refined. The first attribute of space that was stated by Einstein is the ability of space to duplicate so that more space can come to existence. Secondly, following the cosmological constant theory, space has the ability to possess its own energy and following energy as a property of space, it is not destroyed with the expansion of space. This approach suggests that with the expansion of space, more space energy would exist as well. This type of energy in the space would be the result of the expansion in the universe, and as it increases so would the rate of expansion. The deficit in this theory is that there is no understanding as to why there exists a cosmological constant, or even why the space energy it possesses would result in an increase in the expansion of the universe from having adequate energy to cause a change in the acceleration of the universe’s expansion. The quantum theory of matter provides another explanation to the existence of energy in space. This theory hypothesizes the process by which space obtains energy. The theory claims that space contains temporary (virtual) particles, which undergo a formation and disappearance cycle resulting in the generation of energy. Physicists who tried to calculate the amount of energy that would generate empty space disputed the theory, and the resulting answer was off the charts, as the answer was wrong by a factor of 10 to the 120th power (10120). The shortfall in computation of space energy and content has resulted in the continued mystery of space and space energy. Dark energy seems to defy all that we know of matter and energy, and a theory based on the abnormality of the energy tried to explain the phenomenon. The theory classifies dark energy as a dynamic energy fluid or field with the ability to inhabit space and whose effect can only be seen by the enlargement of the universe systems, but opposes the normality of both matter and energy (Bertone, Hooper, & Silk 2005: 294). This concept is named after the fifth Greek philosopher; “quintessence” (Henry-Couannier 2005: 2341). This theory fails to hold since quintessence is another mystery, following no data on its form, appearance, likeness, interactions, relationships with other elements, or even reason for its existence. A final theory on dark energy follows the idea that Einstein’s gravitational theory is wrong. This theory would only cover the expansion of the universe, but, as a result, affect how we have come to understand normal matter in the galaxies, as well as galaxy clusters. This approach provides the physicists an opportunity to answer if the dark energy can be explained in a new approach and concept in the definition of the gravitational force theory. Assessment of how galaxies come together is another approach that may provide answers to the concept of dark energy. Questions on the motion of the Solar System as currently understood via the Einstein gravity theory would need a revision (Bertone, Hooper, & Silk 2005: 296). This continuously contributes to the idea that there are so many theories explaining the existence of dark matter, but without any one that is compelling enough, thereby continuing the mystery. From the suggested theories of dark energy, two main approaches are popular with the physicists. Einstein’s approach that considers the energy a cosmological constant and existence as a scalar field in the form of quintessence and/or dynamic moduli with variances in their energy densities through time and space. The cosmological explanation is widely popular since it is based on vacuum energy. The approach of the scalar field suggests that the fields do not change provided they are in space, but have a high similarity to the cosmological constant, as the rate of change is extremely low. Dark energy is best explained by a supernova. This concept is the brainchild of Edwin Hubble, an astronomer, who was interested in studying exploding stars (supernovae) and the relationship they have to expansion of the universe (Bertone 2010: 391). The supernovas are an important contributor to the study of cosmology as they act as candles in studying distant galaxies, thus acting as gauges. Using the supernovas allows astronomers to study the expansion of the universe following the distance measured and the redshift, therefore determining the velocity in which the supernovae recede from the earth. This is a linear relationship that is developed by considering the intrinsic brightness and absolute magnitude. Dark Matter From the composition of space, where 27% is considered dark matter, it can be theorized that cosmological observations are an essential factor in defining the components of space. It can be argued that what we consider “normal matter” is not matter to the universe as it only occupies 5% (Bertone, Hooper, & Silk, 2005: 279). Since we only understand that what we call matter, the 5%, it is a challenge to define what dark matter is and what it entails, although there have been several proposals that seek to explain what dark matter really is. A major challenge to the physicists is the unavailability of evidence, and/or means of collecting the evidence that is to be used in the definition of dark matter, let alone prove that it exists. Dark matter as a concept has been mainly explored in the fields of astronomy and cosmology. The two fields suggest that it is a type of matter that influences the existence of gravitational effect from matter that is invisible. The matter is not directly visible even when powerful telescopes are used. In addition, the matter does not seem to neither absorb nor emit any light as well as electromagnetic radiation if the matter does it is at an insignificant level. The argument of the matter’s existence follows the effect that it has on the universe and galaxies. The existence of dark matter is inferred from the effect it has on the visible matter, radiation, and large-scale structures in the universe. The discovered of dark matter arose from the existence of discrepancies that are encompassed in large astronomic objects and their relation to gravitational force as well as the mass that is derived from the luminous matter (stars, gas, and dust). The proposal of such matter followed Jan Oort’s explanation of the Milky Way starts orbital velocities, as well as the missing mass in the clusters of galaxies while factoring in their velocities (Bertone, Hooper, & Silk, 2005: 300). Scientifically speaking, the evidence that has been garnered, thus far, only helps in establishing what is not dark matter, rather than what it is. From the nomenclature of the matter, it is expected to be dark, meaning that it does not encompass the visible array of stars, planets, galaxies, or any source of light in the universe. It is by this description that the visible elements in space are not encompassed in the definition of dark matter. It has been suggested that the matter seen using the likes of the HST does not amount to 27% of space, thereby nullifying claims of the observable matter being dark matter. The second derivative to the establishment of what dark matter is follows the argument that it is not captured by the dark clouds that are composed of normal matter, which in the case of the clouds is referred to as baryons. The baryonic clouds are detectable from the radiation absorbance, and fall in the range of particles and elements we define as matter (Exirifard, 2010: 102). The clouds also follow the first argument that it is detectable, thus cannot be dark matter, just as the percentage of the clouds cannot measure to the 27% of space. Since the clouds are composed of normal matter, they are easily detected by existing systems, though they do not fit the description and characteristics of dark matter. The third argument follows proposals that dark matter cannot be anti-matter. This refers to the absence of unique gamma rays that have been scientifically proven to be generated when antimatter collides with normal matter. Since science has proven the antimatter concept, it would be easy to establish the existence of antimatter in space, but the deviation from the concept follows that dark matter exists, but not in the form of antimatter. This approach would further be argued that antimatter and matter collisions would be frequent such that gamma radiation would be a component in the composition of space (Bertone, Hooper, & Silk 2005: 347), as with annihilation, matter such as space rocks would constantly be in contact with matter occupying 27% of space. The theories that have been suggested to expound on the existence of dark matter have an affiliation to the gravitational laws of Newton and Einstein. Modifications to the existing gravitational laws introduce concepts that account for the extremities of the gravitational behavior of the planets and universe. The MOND (Mordehai Milgrom’s Modified Newtonian Dynamics) (Henry-Couannier 2005: 2341) suggests that there are stronger gravitational forces in the center of the galaxy as the gravitational field gets stronger with tinier accelerations. The theory had some degree of success in explaining the occurrences of the elliptical galaxies’ rotational velocity at the ellipses curves, and dwarf galaxies that have assumed the elliptical shape. The shortfall of the theory was in the failed explanation of gravitational lensing that is exhibited by galaxy clusters. The theory relies mainly on the Newtonian approach to gravity but does not encompass the aspect of general relativity as proposed by Einstein. Developments that are more recent are still yet to demystify dark matter; Moffat’s proposal of a modified gravitational model that was founded in the Nonsymmetrical Gravitational Theory (NGT) in 2007 suggested the behavior of the planets, universe and cosmos to be from a collision of galaxies (Moffat 2005: 3; Tsagas 2011: 063503). This approach demands the presence of non-relativistic neutrinos, and/or the presence of cold matter entities to have the results as stipulated by the theory. The approach also incorporates gravitational force as a factor, but as a source of increased velocities in the galaxy extremities are founded on extra energy from collisions. To sum this discussion up, other theories, such as the back reaction theory, are being developed to explain the gravitational effect between two objects. Astrophysicists are experimenting on the relationship between two objects having their own gravitational pull. The back reaction theory has introduced a third component to the action-reaction concept, resulting into an action-reaction-back reaction relationship. The theory introduces the concept of loops in the action-reaction relationship, by suggesting that the objects react to the action, which also includes a reaction to the previous reaction. Bibliography BERTONE, G. (2010). The Moment of Truth for WIMP Dark Matter. Nature, 468 (7322): 389–393. BERTONE, G., HOOPER, D., & SILK, J. (2005). Particle Dark Matter: Evidence, candidates and constraints. Physics Reports, 405 (5–6): 279–390. EXIRIFARD, Q. (2010). Phenomenological Covariant Approach to Gravity. General Relativity and Gravitation, 43 (1): 93–106. HENRY-COUANNIER, F. (2005). International Journal of Modern Physics, A 20 (11): 2341. MOFFAT, J. W. (2005). Gravitational theory, galaxy rotation curves and cosmology without dark matter. Journal of Cosmology and Astroparticle Physics, 2005(05), 003. TSAGAS, C. G. (2011). Peculiar Motions, Accelerated Expansion, and the Cosmological Axis. Physical Review, D 84: 063503. Read More