What is the Difference Between Dark Matter and Anti-matter?

25/12/2010 19:27

Dark matter and antimatter are separate but similarly mysterious concepts in physics which each present their own vexing questions for scientists. Perhaps the most fundamental difference between the two is that much of what we know about dark matter comes from observations of the very large, while much of what we know about antimatter comes from observations at the particle level.

Dark matter

Scientists believe dark matter exists throughout the universe because based on our best calculations using Einstein’s equations of gravity, the universe should be much more massive than what all the observable stars and other bright objects would weigh; therefore, scientists believe that there must be more matter out there, we just can’t see it. Thus the name dark matter, and its mysterious nature, since our only tool for observing distant matter is light, so if matter does not emit light, we can only make indirect observations and inferences about its properties.

One specific way we’ve observed dark matter is through a phenomenon called gravitational lensing, in which large gravitational forces actually bend light as it travels through space - we can observe this happening throughout the universe and therefore infer the existence of matter which is creating the large gravitational forces. How much of the universe is comprised of dark matter? Scientists estimate that we can only see 4% of the real mass and energy in the universe. Also, 22% of the universe’s mass and energy is estimated to be dark matter, while the remaining 74% is thought to be a related concept, dark energy. Similar to dark matter, dark energy’s existence is inferred from indirect observation, but dark energy is thought to contribute to the outward pushing force which is causing the universe to expand.

Antimatter

Antimatter is another strange concept in physics - but unlike dark matter, it’s one which we’ve actually observed in labs. In a nutshell, antimatter is matter that has the opposite charge of matter. For example, an electron is a matter particle which has a negative charge, while a positron (also called an antielectron) is an anti-matter particle which has a positive charge. The cool part about this is that when these two things come into contact with each other, they annihilate each other and release massive amounts of energy. In fact, this interaction is the pure conversion of matter into energy. It is estimated that energy created from matter / anti-matter annihilation would yield 10,000,000,000 times the maximum energy created by chemical energy and 100 times the energy possible through nuclear fusion. The potential applications for antimatter energy are exciting, although far off in terms of feasibility. For example, it would take only a few grams of antimatter to propel a rocket ship from Earth to Mars and it would only take a few minutes. Scientists and fiction writers alike have high hopes for possibilities in interplanetary and interstellar travel based on antimatter energy. Scientists at CERN and Fermilab have created minute amounts of anti-matter in particle accelerators - but with current technologies it takes vastly more energy to create anti-matter than the energy that would be produced by it. So dark matter exists at the large scale, beyond what we can see with our telescopes, while antimatter we know exists based on antimatter particles we’ve created and observed in labs. There is no direct relationship between the two that we know of. More detailed reading:

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