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Question
Dear Brother,

Help me in the subject of Matters in Universe.

What is Anti-Matter? How can we believe it exists?

Regards
Mohammed Tharik F

Answer
Hello,

"Anti-matter" refers to particles which bear the exact opposite electric charge (or baryon number in the case of neutrons) to the normal matter particles. For example, hydrogen has one proton (+ charge) and one electron (- charge) but anti-hydrogen has one anti-proton (negatively charged proton) and one positron (positively charged electron - instead of negative.)

Antimatter is detected both in laboratory experiments - e.g. using the Wilson cloud chamber, see e.g.

http://en.wikipedia.org/wiki/Positron

and also, more recently, via space-based observations.

In the case of the latter, I refer to the orbiting spectrometer dubbed PAMELA, which is designed to detect charged particle of antimatter - whether positrons (e+, positive electrons) or antiprotons (p -).

PAMELA ('Payload for Antimatter-Matter Exploration and Light-nuclei Astrophysics') uses a tracking magnetic spectrometer as its principal component and it's half a meter long. To learn much more about the craft, the instruments and mission you can check the PAMELA site here:

http://pamela.roma2.infn.it/index.php


Basically, entering particles take a curved path in the spectrometer's magnetic (B-)field since the field measures the particles' momentum per unit charge and the charge's sign. What gets plotted then is the particle flux through the local (x-y-z) plane whose orientation maximizes said flux. Generally this plane also includes the associated magnetic field line (i.e. around which the charged particle is expected to spiral)

Relevant to PAMELA's discovery  there is the detection of a significant population of antiprotons magnetically trapped in the inner Van Allen radiation belt.(Which you can Google)  The flux of the trapped antiprotons spiraling around the inner belt's geomagnetic lines turns out to be a thousand times greater than the flux of cosmic ray antiprotons entering the atmosphere

Now, how to distinguish trapped protons from antiprotons? Well, the first will always spiral left-handedly around a magnetic field line, and the latter right handedly. (Since they are negatively charged.) Trapped protons do this spiraling about the magnetic field lines from Earth's dipole field, bouncing back and forth between the north and south magnetic poles or mirror points.

(-L)--------------!--------------
---------------- 0----------- B = (L)

<--------- L ------------ -->

The mathematical basis for a typical plasma "mirror machine" is shown above, but we make the adjustment that the end points (at B = ± L) are “pinched” and thus of narrower bore than at the midpoint. (This is hard to show in a sketch so I leave it to you to do it mentally!)

In the case of the terrestrial mirror machine, the pinching is done most at the north and south magnetic poles. What we are saying then, is that charged particles - say protons OR *antiprotons*, will tend to bounce back and forth between L and (-L) which denote the pole locations with the magnetic mirror length = L.

Antiprotons entering the inner belt become similarly trapped. The existence of a resident trapped population of antiprotons invokes the mechanism shown below:

p + p -> p + p + n' + n

where anti-neutrons (n') are created in the pair-production process. (Note: By anti-neutrons I mean they have the same mass as the neutron and still no net electric charge (i.e. neutral), but have opposite "baryon number" to the normal matter neutron. So have (-1) baryon number while the ordinary matter neutron has +1.

It is surmised that the process above is initiated in atmospheric nuclei via cosmic ray protons with energies > 7 GeV. Like a free neutron, an anti-neutron decays into its opposite baryon number partner with a half life of ~ 10 mins. The trapped anti- proton population is thus created from the n-n' population.

The basic principle underlying these pair production processes is the energy-time uncertainty principle:

(delta E )(delta t) < h/ 2π

where h is the Planck constant of action. Thus, a brief fluctuation occurring over time dt can produce a change in energy dE, which may be sufficient to produce particles., i.e. n' -> p- + e-.

Hopefully this makes sense, but if you have further points that need clarification, please ask!  

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Philip A. Stahl

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I specialize in stellar and solar astrophysics. Can answer questions pertaining to these areas, including: stellar structure and evolution, HR diagrams, binary systems, collapsars (black holes, neutron stars) stellar atmospheres and the spectroscopic analysis of stars – as well as the magnetohydrodynamics of sunspots and solar flares. Sorry – No homework problems done or research projects! I will provide hints on solutions. No nonsense questions accepted, i.e. pertaining to astrology, or 'UFOs' or overly speculative questions: 'traveling through or near black holes, worm holes, time travel etc. Absolutely NO questions based on the twaddle at this Canadian site: http://members.shaw.ca/warmbeach/FAQ.htm purporting to show a "new physics". Do not waste my time or yours by wasting bandwidith with reference to such bunkum.

Experience

Have constructed computerized stellar models; MHD research. Gave workshops in astrophysics (stellar spectroscopy, analysis) at Harry Bayley Observatory, Barbados. More than twenty years spent in solar physics research, including discovery of SID flares. Developed first ever consistent magnetic arcade model for solar flares incorporating energy dissipation and accumulation. Developed first ever loop-based solar flare model using double layers and incorporating cavity resonators. (Paper presented at Joint AGU/AAS Meeting in Baltimore, MD, May 1994)

Organizations
American Astronomical Society (Solar physics and Dynamical astronomy divisions), American Geophysical Union, American Mathematical Society, Intertel.

Publications
Papers appearing in Solar Physics, Journal of the Royal Astronomical Society of Canada, Journal of the Barbados Astronomical Society, Meudon Solar Flare Proceedings (Meudon, France). Books: 'Fundamentals of Solar Physics', 'Selected Analyses in Solar Flare Plasma Dynamics', 'Physics Notes for Advanced Level', 'Astronomy & Astrophysics: Notes, Problems and Solutions', 'Modern Physics: Notes, Problems and Solutions'

Education/Credentials
B.A. degree in Astronomy; M.Phil. degree in Physics - specializing in solar physics.

Awards and Honors
Postgraduate research award- Barbados government; Studentship Award in Solar Physics - American Astronomical Society. Barbados Astronomical Society award for service (1977-91) as Journal editor.

Past/Present Clients
Caribbean Examinations Council (as advisor, examiner), Barbados Astronomical Society (as Journal Editor 1977-91), Trinidad & Tobago Astronomical Society (as consultant on courses, methods of instruction, and guest speaker).

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