WIMP Wars: People Disagree About the Existence of Dark Matter and Dark Energy

WIMP Wars: People Disagree About the Existence of Dark Matter and Dark Energy

The universe is composed of many things, including stars, galaxies, dust, gas, moons, planets and other cosmic debris. Stars tend to cluster themselves into groups known as galaxies, and these galaxies can contain billions of stars. Several galaxies can also cluster together to form what is called a cluster. The stars in these clusters produce energy that travels throughout the universe, perceived in x-rays and as light. However, observable phenomena in the universe, such as stars and planets, only make up approximately 4% of the known universe. The rest of the universe is made up of dark matter (21%) and dark energy (74%).

Dark matter and energy are so difficult to measure because they are invisible. But, scientists know that both exist because they exert force, and the type of force exerted distinguishes dark matter from dark energy. Dark matter has a gravitational pull that attracts visible matter. In contrast, dark energy repels items with visible matter by exerting an outward push. While studying the Milky Way, it was discovered that dark matter exerts a gravitational pull on the universe, as well as individual galaxies. Dark energy however, can only be seen on a large scale by looking at clusters in the cosmos. 

Scientists discovered dark matter when they noticed that all the stars in the Milky Way were orbiting at the same speed around the center of the galaxy, despite there being nothing visible to hold the stars in place; dark matter was the invisible force stabilizing the stars. Dark matter is so vast and powerful that it is calculated to be stronger than all the stars and gas clouds within the galaxies. In addition to the Milky Way, dark matter has been found in numerous other galaxies and galaxy clusters. It is hypothesized that dark matter is composed of subatomic particles, and some scientists believe that dark energy, too, has its own distinct particles. In fact, most research shows that more is unknown than known about dark matter and energy.

Dark Matter

Dark Matter vs Dark Energy

Dark Energy, Dark Matter

Einstein understood that empty space was not “empty”, that such space contained its own energy, and that it was possible for more space to form. In fact, Albert Einstein stumbled across the possibility of the existence of dark matter and dark energy as he developed his theory of relativity. Although Einstein was the first scientist to propose dark matter and dark energy's existence over eighty years ago, he quickly abandoned the theory, considering it to be his biggest blunder. In 1934, Fritz Zwicky accounted for the dark matter present in the orbitational velocity of galaxies and star clusters, but termed it "missing mass". While the origins of black matter theories are attributed to Einstein, it is Stephen Hawking that developed the theories. Hawking theorized that light elementary particles called neutrinos or axions, and other exotic particles may be at the heart of dark matter. Yet, despite Hawking's widely publicized theoretical propositions, much about dark matter remains unobservable and unproven.

Birth of Ordinary Matter

Numerous experiments attempt to detect dark matter, both directly and indirectly. Direct experiments are carried out in underground laboratories in order to decrease background noise caused by cosmic rays. Labs engaged in direct experiments include: the Deep Underground Science and Engineering Laboratory in South Dakota, US, the Boulby Underground Laboratory in the UK, the Gran Sasso National Laboratory in Italy the Soudan mine, and the SNOLAB underground laboratory in Ontario, Canada.

The two main types of detection used in direct experiments rely upon noble liquids and cryogenics. Noble liquid detectors measure the light emissions produced when particles collide in liquid argon or xenon. LUX, WARP, ArDM, DEAP, XENON and ZEPLIN are all examples of noble liquid detectors. Cryogenic detectors operate at extremely low temperatures by measuring the heat produced when a particle hits the atoms present in a crystal absorber- which is typically composed of Germanium. CRESST, EURECA, EDELWEISS and CDMS systems all utilize cryogenic detectors. 

Indirect experiments attempt to trace the products resulting from the collision of special particles, known as WIMPs, or weakly interacting massive particles. WIMPs destruct upon collision, producing gamma rays or positrons, and behave most like light dark matter particles. Gamma ray telescopes, such as the EGRET, are used to observe excessive amounts of gamma rays. The Fermi Gamma-ray Space Telescope, launched in 2008, is looking for gamma rays produced from the destruction of dark matter. However, the difficulty of the aforementioned telescope is the occurrence of other events in space that generate gamma rays and positrons, such as pulsars.

Scientists postulate that there are several different types of dark matter; cold, hot, light, self-interacting, mirror, warm and WIMPs. Cold dark matter (CDM) is an exceptionally slow-moving material that emits electromagnetic radiation. This slow or cold movement of CDM is thought to be responsible for the big bang that created our universe. Hot dark matter (HDM) is still hypothetical, and particles like neutrinos- that may comprise HDM- move at very fast speeds, described as ultraleativistic speeds. Warm dark matter (WDM) is defined as dark matter with properties that fit somewhere between cold and hot dark matter. Gravitinos and sterile neutrinos are believed to be warm dark matter particles. Light dark matter are thought to be particles that have a mass that is less than 1 GeV, which are heavier than warm and hot dark matter, but lighter than cold dark matter. Mirror matter (or shadow matter), is called such because its particles have mirror symmetry, rotation, reflection and translation of ordinary matter, save for the weak interactions that could occur. Self-interacting dark matter is another theoretical possibility, as particles tend to exhibit strong interactions with other dark matter particles. WIMPs interact through gravity and weak forces, and do not interact with electromagnetism and other strong nuclear forces.

While many scientists believe in the presence of dark matter, others remain skeptic and deny its existence due to the lack of visible proof for this “invisible” material. The estimated abundance of dark matter is so vast and varied because the nature of the particles creating such matter is so contested. Contemporaries of Physics and Astronomy have yet to identify the source of dark matter particles. If the particles were from white dwarfs or failed stars, then many would have been detected in large quantities, but scientists have discovered only a few, which is certainly not enough to create the abundance of dark matter to maintain the fabric of our universe. Current dark matter detection mechanisms illustrate the conundrum where for any given set of data, the dark matter theory can explain the results on one hand, yet on the other hand, particle physics can verify the results but cannot account for the dark matter. The MACHO experiments illustrate the aforementioned catch-22, in which data interpretation has proven controversial within the scientific community. The technology and methods presently available to scientists are far from the capabilities needed to determine precisely what dark matter is composed of, and with research results being mixed at best, the issues surrounding the validity of dark matter appear light years from being either proven or disproven.

Einstein Dilemma

Doubtful Dark Matter “Proof”

No Dark Matter?

Evidence of Dark Matter