Final answer:
Heat transfer always occurs from a hotter object to a colder object, in accordance with the second law of thermodynamics. This spontaneous flow of heat is unidirectional and fundamental to the principles of thermodynamics.
Step-by-step explanation:
The question asks about the direction in which heat transfer occurs between objects of different temperatures. According to the second law of thermodynamics, heat always flows spontaneously from a hotter object to a colder object. This is a fundamental concept in physics, particularly in the study of thermodynamics. The second law specifies that such heat flow in the reverse direction, from a cold object to a hot one, is never observed to occur spontaneously. This principle is crucial for understanding not only heat transfer but also the operation of heat engines and refrigerators, which are designed to utilize this one-way flow of heat.