I am reading Berkeley Physics Course vol. 4 (Quantum Mechanics) , chapter 4 (photons).
(1) Section 46: book says: consider a typical photon emitted by the source. It can be regarded as a a wave train of finite duration, spreading out in all directions in space and carrying a total energy $\hbar\omega$.
If this is true, a photon emitted by a star which is few light years away, would have spread over a sphere of radius of few light years. Then it is not possible to "detect" that photon using a detector.
Then why does the book say like this?
In section 47, the book gives same example of photon spreading over light years. But in this section, it says that how the people can use this as a paradox; and clarifies that paradox by saying that classical expression for "energy density" refers to a large number of photons, and not for single photon.
So does photon really spread in all directions?
(2) In Section 38 book says: almost monochromatic photons can not be split into 2 photons of the same frequency which carry only a fraction of the energy of the original photon. While in section 48, it says (with reference to double-slit diffraction experiment) photon came through BOTH the slits.
Does a photon REALLY goes through both the slits?
Doesn't it indicate that a single photon can be split into two photons of same frequency ?
Any help will be appreciated. Thanks