Base class and derived class

/*Created 5 derived objects*/

Derived derived(5);

   

/*reference to object*/

Derived &rDerived = derived;

/*Pointer to object*/   

Derived *pDerived = &derived;

since Derived has a Base part, a more interesting question is whether C++ will let us set a Base pointer or reference to a Derived object

// These are both legal!

    Base &rBase = derived;

    Base *pBase = &derived;

A Base Class pointer can point to a derived class object. Why is the vice-versa not true without casting? Logically a base class would not have enough information of the derived class but a derived class should have the information of the base class as well. I am missing some basics here.