# Bumpy-free CD/DVD

When you drive on a bumpy road, your CD music plays normally and smoothly while your body bumps up and down in your car?

Why CD disk can be bumpy-free ?
Thanks to Galois, the 19-year-old French Math genius and tragic victim of the X Concours. Galois invented the whole Abstract Algebra with two revolutionary ideas: Group and Field.
Galois Group explains why symmetry is a Math structure which plays the role of Quintic equation with no radical solutions.
Galois Field is used in the cryptography coding for computers, digital music in CD / DVD.
————–
Galois Field Theorem: the only one in Field Theory
There is EXACTLY ONE such system whenever the number of element is a power of any prime number p.
<=>
Fp contains EXACTLY 1 sub-Field with pⁿ elements. (n ≥1)
<=>
For p prime, n ≥1
|Fp | = pⁿ unique
Example:
p=2 n =1
=> Galois Field = {0,1} with pⁿ = 2 elements

Galois Field {0,1}
1+1 = 0 = 0+0
1+0 = 1 = 0 + 1

Reed-Solomon codes for CD, DVD
(1960) using binary Galois Field {0,1}
Error correcting codes based on algebraic properties of Polynomials, whose coefficients are taken from a Galois Field.
255 bytes block = 223 + 32
223 = encode the signal
32 bytes = parity codes
When the car bumps and so the CD player’s laser beam on the CD disk, digital music code errors can be auto-corrected using Reed-Solomon code Algorithm, so you don’t hear any jerking disruption.