The basic concept of Quantum mechanics , from classics to quantum.

1. *
Werner Heisenberg (1901-1976)

2. *
*What is Uncertainty?
Being dependent on chance
*In classical physics
Due to limitation of apparatus
Inability of observer
Determinism
Coordinates and velocity of particle along with all forces
known the velocity and coordinates at any time could be
known.

3. *Background
In 1927 Werner Heisenberg stated that it is impossible
to know precisely where an electron is and what path
it follows—a statement called the Heisenberg
uncertainty principle.
*If momentum of a particle is precisely known the
location of the same particle is completely unknown.

4. *
“We can’t measure complementary variable of matter/particle
at same time to certainly.”
Complementary variables are :
*Energy and time
*Any two Cartesian components of angular momentum
*Position and momentum
*Spin on different axis
*Wave and particle
*Value of a field and its change (at a certain position)
*Entanglement and coherence

5. *
*In the world of very small particles, one cannot measure any
property of a particle without interacting with it in some way
and this interaction changes related property.
Measuring p and x of electron
*So to determine the position accurately
it is necessary to use
light with a short wavelength

6.  By Planck’s law E = hc/λ, a photon with
a short wavelength has a large energy
 So will give a large ‘kick’ to the electron
 But to determine its momentum
accurately,
electron must only be given a small kick
 This means using light of long
wavelength
 (Δp)(Δx) ≥ h/2π ≥ ћ

7. *Qualitatively if an identical experiment involving an
electron is performed many times and in each the position
of electron is measured then for same momentum
measurement of position will be different each time.
*If <x> is average then standard deviation gives
*If ∆x is small x=<x> is more certain
*If ∆x is large measurement of x is uncertain
* ∆x is uncertainty in x

10. Other physical quantity are also expressed in
uncertainty.

11. Classical World
*The observer is objective and passive
*Physical events happen independently of whether
there is an observer or not
*This is known as objective reality
VS
Quantum world
*The observer is not objective and passive
*The act of observation changes the physical system
irrevocably
*This is known as subjective reality

12. Thank You
Floor is open for
Questions