We take a look of a very important equation. Relativistic quantum mechanics is the way to make quantum mechanics consistents with Lorentz’s invariance. Dirac proposed his equation due to ‘the fail’ of the Klein-Gordon equation. This fail ocurred in two ways:

  1. The solutions of the Klein-Gordon equation accept both possitive and negative energy solutions. Maybe you don’t see any issue on this, but if you think about a free particle, you would not expect this negative energy type solutions.
  2. The other reason for the fail was that the probability density seems to be negative which is inconsistent with a probability definition.

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Bienvenue!

febrero 5, 2012

Aujourd’hui est arrivé ma très chère cousine, elle habite à Madrid et il y a sept ans que je ne l’avais vu pas. Elle sourit et moi aussi. Ne t’elle pas belle?

Bienvenue!

Teaching General Physics

febrero 4, 2012

Some friends say to me: “You have a gift Gabriel, when you teach something, you become like a old, warm and wise grandfather, it’s impossible do not learn with you”.

Last weeks, I’ve been working as a teacher physics in my pretty loved Universidad Central de Venezuela. It has been a therapeutical experience because of several reasons that I will not explain in this note. Yesterday, I was talking to my students about differentials equations and how they enter in the newtonian mechanics. Of course this was done in a really introductory and informal way because it’s the very first physics course that this students take at the university.

Well, I wished to show them how totally useless is learn by heart all the physics formulae learned in the past. To do that, I solved the simple problem of motion with constant aceleration, the solution of this problem make arise all the kinematics formulae of high school.

When I was finishing something happen never happened to me: I saw the astonished face of my students, all the class. I saw their beautiful yet innocents and shiny eyes wide open and also their mouth. They couldn’t believe what they watched. I didn’t lie to them… “It’s really useless learn by heart all this formulae. Physics are ideas, not the maths”. And then they gave me an applause. I saw and smiled to them, afterwards I became serious and said loudly: Don’t sabotage the class! They smiled too and I continued giving the class.

Really, teaching, music, physics, love, dislove, some friends (in whatever order) make me feel so fortunate! Thanks all of them for this fantastic week.