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# Astrophysics/Curious

Question
Hi there,  it is said that if - hypothetically - a space craft moved almost at  the speed of light the space craft would somehow become larger & larger to the point that it's size would be infinite. Can you exPlain [why] that is? - sounds baffling...

Hello,

Actually in terms of special relativity it is the mass that is critical not the size. (Which is more related to spatial volume)

The relativistic relation of a moving mass, m, to its rest mass m(0) is:

m = m(o)c^2 / [1 – {v/c)^2] ^1/2

and m(o) is the rest mass.

Now, let the velocity v of the mass be = c, the speed of light. Then we can use basic algebra to show what would occur.  Then:

m = m(o)c^2/ [1 - c^2/c^2]^1/2 = m(o)c^2/ 0 = oo

In other words, the moving mass would be "infinite", i.e. have infinite inertia.

This is just another way of saying that no mass can attain the speed of light  since that would require all the mass in the existing universe to be converted into energy and even that would not allow a speed of c.

Astrophysics

Volunteer

#### 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).