About 39years ago when I did o-level physics, I learnt that E=mc2. a book lately said E=+or-mc2. anybody knows

Question

science

Answer 1

This is just a semantics question.

The derivation gives you

E^2 = m^2c^4 + p^2c^2

If you assume no momentum, this results in

E = plus or minus mc^2

We used to (like back in the 30s and 40s) interpret the negative energy solutions as the cause of antiparticles. Dirac imagined that there were all these negative energy states (the Dirac sea) that were filled. Because they were everywhere we didn't notice them. But with enough energy, you could pop an electron out of the negative energy state and into a positive one. This would look like pair production. You had nothing (except some energy--maybe a gamma) and suddenly you've got an electron and a positive hole--a positron.

Current notation, though, is to treat matter and antimatter as positive energy solutions. This is really just a semantics question, nothing to get all wrapped up about.

Answer 2

Can't work that way. The value of "c" is a constant that determines the basis of our existence, and defines what reality is according to that speed. That speed is why all forms of mass and energy move from the present into becoming that of the past at the same rate of speed. Were that value to have a plus or minus factor, time itself would dilate.

http://360.yahoo.com/noddarc "Concepts Concerning Time, Gravity, and Energy" may be of interest. It is short and easy to read.

Answer 3

Zero point energies
E = + mo c^2 (for electrons)
E = - mo c^2 (for HOLES - the vacancy created by ejected or transferred or shifting electrons due to various causalities/reasons)
the rest mass energy state ( - moc^2) is also reffered to as the MIRROR image of rest mass energy of electron

Holes are due to PM DIRAC - physicist

when potential difference id applied and electron moves is the expected direction - its counterpart (vacancy) moves in the opposite direction as successive stages get renewed in space/time.

read more - i also read it long back

in depth reference to working of photovoltaic cells may give the first hand info

Answer 4

I read Only E=mc2

Answer 5

the book is wrong!