What does E=mc2 mean?

Hi crazydog,

E=mc2 
http://www.geocities.com/Athens/Academy/1929/einsteinquiz.htm

"The most famous of Einstein's equations, E=mc2 says that energy (E) and 
mass (m) are equivalent. In other words, mass can be converted to energy 
and vice versa. The conversion factor is the speed of light (c) squared, an 
enormous number when you consider that the speed of light itself is a 
whopping 186,000 miles per second." 

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"Proof" of E=mc2
http://www.drphysics.com/syllabus/energy/energy.html

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E=mc2 Explained
http://www.geocities.com/thesciencefiles/emc2/emc2.html



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Best regards,
tlspiegel

E=mc2 -- Energy (E) is equal to the mass (m) multiplied by the square
of the speed of light (represented by "c2"). Einstein thought that the
speed of light remains constant whether you are going away from the
light source or towards it, thus the symbol "c".

The supposition that "c", the velocity of light, is always constant is
still mind-blowing to me and I realised how little I understood until
Brian Greene explained it.  Which just left me with more questions.

The strangest part is the following example:

Let's say you and I are standing near each other, and I throw a
baseball at you at about 20mph.  If you stand still, you see the ball
approaching at 20mph.  Easy.  Now I throw another ball at you at 20
mph, but you move away from me at 10mph.  You now see the ball
approaching at 10 mph (20-10=10).  This is basic relativity.  Relative
to me, the ball travels at 20mph, relative to you it travels at 10mph.

Okay, now let's say I have a laser gun.  I fire it at you and you
stand still.  The laser approaches you at close to 186 000mps.  You
see the laser approaching at 186 000 mps.  I fire it at you again, but
this time you are moving away from me at 90 000mps.  Relative to me,
the laser is going 186 000 mph.  And due to the constant speed of
light, relative to you, the laser approaches at 186 000 mps.  The old
186000-90000 trick doesn't work here because light always travels at
approx 186000mps.  Never faster and never slower.

This is where we introduce time dilation and other fun things.  

If you are interested in finding out more about Einstein's
contributions to the world of Physics, and then going further and
looking at Quantum Mechanics and then further on to Superstring
Theory, there is a heap of good information at
http://www.pbs.org/wgbh/nova/elegant/ which is the home page for "The
Elegant Universe" a PBS show that goes a good way to explaining some
of these concepts in layman's terms.

Unfortunately, it also shows that we are no closer to the answer of
"Life, the Universe and Everything" but it's excellent food for
thought.