Anti-Matter vs. Dark Matter

The Collison Annihlation of Matter and Anti-matter

The Collison Annihlation of Matter and Anti-matter

What is the difference between anti-matter and dark matter? Is there anything anti-matter and dark matter have in common?

Anti-matter is the idea of negative matter, or matter with the same mass but opposite an charge and quantum spin than that of normal matter. Anti-matter is just like normal matter with different properties. The antimatter of the electron (e-)  is the positron (e+); similarly, the antimatter of the proton is the anti-proton (p-). When normal matter and anti-matter collide, the two annihilate each other. Scientists speculate that anti-matter and matter existed in equal quantities in the early Universe.  The apparent asymmetry of high quantities of matter and very low quantities of anti-matter is a great unsolved problem in physics. Anti-matter is only found through radioactive decay, lightning, and cosmic rays (high-energy particles from supernovae) and very expensive to produce. Practical uses of anti-matter include the positron emission tomography (PET) used for medical imaging and as triggers to nuclear weapons.

Dark matter cannot be seen and is hard to detect, because dark matter interacts by gravity and weak atomic force, not with strong atomic forces (nuclear force: holds subatomic particles, electrons, neutrons, and protons, together in an atom) or electromagnetism. Dark matter constitutes about 22.7% of the Universe. On April 3, 2013, the International Space Station’s Alpha Magnetic Spectrometer (AMS) found the first evidence of dark matter. [AMS was carried out by the Endeavor in 2011 in one of NASA’s last space shuttle flights.] Normally, detectors are blocked by Earth’s atmosphere, but by orbiting Earth above its atmosphere,  the AMS can monitor cosmos rays (have an excess of anti-matter, discovered two decades ago) without hindrance. The AMS will tell scientists whether the abundance of positrons signal the presence of dark matter.  One theory scientists are testing is supersymmetry, which speculates that the collision and annihilation of two dark matter particles could produce positrons. Another instrument that could help the dark matter hunt is the Large Underground Xenon Experiment (LUX).

References

Anderson, Natali. “Antimatter Hunter aboard International Space Station Detects Hints of Dark Matter.” Sci-News.com. Sci-News.com, 4 Apr 2013. Web. 4 Apr 2013.

Boyle, Alan. “Space station’s antimatter detector finds its first evidence of dark matter.” NBCnews.com. NBC News, 3 Apr 2013. Web. 4 Apr 2013.

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Temperature of the Universe

What is the universe’s temperature? How has it changed and evolved? What causes the temperature to change? How is the temperature estimated? Is it continuously cooling or constant? –Pcelsus

Black Body Curve of the Cosmic Microwave Background

13.75 billion years ago, the Universe was much smaller and hotter. In the 1960s, Robert Dicke predicted a remnant “glow” from the Big Bang. In 1965 at the Bell Labs, radio astronomers Amo Penzias and Robert Wilson discovered that glow, named the cosmic microwave background radiation. The CBR was seen in all directions in empty space, with a black body curve (temperature ~3K in every direction). About 1 second after the Big Bang, the Universe was very hot, at ~1 billion K. At 3 minutes, protons and neutrons combine to form the nuclei of atoms. As space cooled, material condensed and atomic particles, then elements, molecules, stars, and galaxies formed. The hydrogen/ helium ratio (3:1) found today is about the same as what’s expected after the Big Bang. Atoms were “ionized” with electrons roaming free without being bound. At 300,000 years after the Big Bang, the Universe becomes transparent with a temperature of 3,000K. Light red-shifted by a factor of 1000, and the expansion of the Universe ensued.

Today, the Universe is 2.73K, or 2.73°C above absolute zero, but at the beginning of space and time, the Big Bang, the Universe reached over one billion degrees. From a single pinpoint, the Universe emerged as a scorching hot primordial soup of subatomic particles moving at high velocities. As the Universe expanded, the temperature cooled as more space was created and density decreased. The Universe is continuously cooling as it expands.

Measuring the temperature isn’t as simple as sticking a thermometer in space and waiting until it stabilizes at a certain temperature. Instead, scientists measure indirectly using the cosmic microwave background, or leftover radiation emitted by hot plasma 38,000 years after the Big Bang. As the Universe expanded, the electromagnetic waves of the CMR elongated and decreased in energy, leading to cooler temperatures. Using Planck’s law, scientists measured the black body radiation of the Universe. Planck’s law states that every object radiates electromagnetic energy according to temperature. Black body curves are lopsided, with the curve peaking at different wavelengths depending on the object. In fact, space has a nearly perfect black body curve, since physical objects tend to absorb and reflect light in certain wavelengths.

Albert Einstein’s Legacy

ALBERT EINSTEIN (1879-1955)

Albert Einstein

Legacy

  • Reformulated the concept of time and space (E = mc² => special relativity)
    • Time is not an absolute quantity but appears to flow at a different rate depending on relative motion
  • Opened the road to quantum mechanics
    • Light “hits” like a particle
    • Light waves have “quantized” and “discrete” energies, depending on their wavelengths
  • Presented a revised theory of relativity
    • General relativity: space is curved
    • Foundation of modern cosmology

Einstein’s World

  • Reality of atoms and molecules in hot debate
  • Light poorly understood: “What was the medium light traveled in?”
  • Phenomena of radiation
  • Absorption lines in the Sun were observed, but could not be explained

Einstein helped clear these mysteries and began the era of modern physics.

Einstein’s Early Life and Career

Born in Ulm, German Empire in 1879, Albert Einstein excelled in physics and mathematics but failed in other subjects. Einstein dropped out of high school in 1895 and restarted school in Aarau, Switzerland, where he studied Maxwell’s works (~1870), which stated that electricity and magnetism obeyed the same set of physical laws — hence, electromagnetism. Einstein discovered that the velocity of light remained constant no matter the media. Although Einstein was brilliant, he irritated professors as he was too independent. In 1902, Einstein became a patent office clerk at the Swiss Patent Office in Bern. By 1905, Einstein had written six scientific papers, three of which explored the existence of molecules and the “kinetic theory.” For his other three papers, one published in March explained his light-quantum hypothesis (light hits like a particle), a fundamental step of quantum mechanics. For this, Einstein received a Nobel Prize in 1921. Another paper published in June was Einstein’s first paper on Special Relativity that explored light contraction and time dilation approaching the speed of light. In September of 1905, Einstein published his second paper on special relativity, in which he included the famous equation E = mc².

* General relativity includes gravity, while special relativity does not.

General Relativity and Special Relativity

Special Relativity

  1. The laws of physics are the same in all uniformly moving reference frames, or in all directions
  2. In any uniformly moving reference frame, the velocity of light (c) is the same whether emitted by a body at rest or a body in motion

Time Dilation and Length Contraction

Time Dilation: Time itself doesn’t tick at the same rate approaching the speed of light; instead, the time synchronization veers off; so approaching the speed of light, time appears to tick much slower.

Length Contraction: The lengths of moving objects are contracted when viewed by a stationary viewer

Mass and Energy

  • The mass of a moving body increases compared to its “rest mass” because it takes a bigger force to accelerate
  1. Acceleration: speed gained in a given time
  2. An object accelerating up is smaller because of time dilation; acceleration is harder the more massive the object is
  • Energy is responsible for powering stars, nuclear decay, and nuclear energy

Einstein’s Impact

  • At first, the scientific community met Einstein’s special relativity theory with silence, but Max Planck, who won the Nobel Prize for explaining black body radiation, realized the importance of Einstein’s work and publicized it; from 1906, scientists took notice and visited Einstein to talk about science
  • Einstein’s scientific circles grew stating 1908; became associate professor in 1911 and a professor of the Swiss Federal Institute of Technology in 1912
  • Einstein’s findings demanded a new way of thinking as Newton’s Law of Gravity was only valid from speeds much smaller than light
  • Einstein named the “birth of special relativity” “The Step”
  • 1907: The Equivalence Principle – gravity corresponds to acceleration
  • 1911: Bending of light in a gravitational field, a consequence of the Equivalence Principle, could be checked with astronomical observations
  • 1912-1915: Extend relativity to objects moving in an arbitrary way with respect to one another
  • 1915: General Relativity “Gravity curves space”: there’s no need for the “force” of gravity; all motion is along “straight lines” in curved space-time and matter tells space how to move
    • Evidence: starlight bends around the Sun; Mercury’s orbit will precede at a different rate than Newton predicted
  • 1919: Arthur Eddington leaders solar eclipse expedition and confirms special relativity
  • 1929: Edwin Hubble observes expansion of the Universe
    • Friedmann said that Einstein’s equations supported an expanding Universe, but Einstein proposed the “cosmological constant” to keep the Universe static

In Remembrance: Sally Ride (1951-2012)

SALLY RIDE (May 26, 1951 – July 23, 2012)

Sally Ride, First Woman Astronaut in Space

Sally Ride, the first woman astronaut to travel to space, passed away today at the age of 61 from her 17-month battle with pancreatic cancer. At Stanford University, Ride earned her master’s degree and Ph.D in physics. Ride joined NASA in 1978 and rode the Challenger to space on June 18, 1978 at the age of 32 and again in 1984. She spent 14 days in space!  After NASA, Sally Ride worked at the Stanford University International Security and Arms Control and taught physics at the University of California, San Diego. She later became the director of the California Space Institute and the founder and CEO of Sally Ride Science. Today, President Obama remembered Sally Ride as “a national hero and a powerful role model.”

References

Borenstein, Seth, and Alicia Chang. “Sally Ride, first US woman in space, dies at 61.” Boston.com. Boston.com, 23 July 2012. Web. 23 July 2012.