Materialism isn’t the statement that the world consists of matter, ‘substance’. This includes energies, the movement of and ‘within’ matter. This is obvious.
Materialism is the philosophical statement that any statement – including this one –, thought, language, conscience, consciousness, moral value, subject or personality is material. It is not a thing in itself, but has to get the necessary attribute of meaning (sense). It has to exist in a material process over time in some substrate that can connect it with other statements. Before the development of AI, the only substrate that could develop and use statements was the human brain. All these statements, these ‘mental constructs’ are virtual. They only exist for a longer (memory) or shorter (reading, speaking, writing, thinking) time in the brain.
When a brain stops functioning, that particular statement or thought ceases to exist. Any statement, even 1+1=2, loses its meaning when there is no brain left that knows its meaning: when all the brains that hold an adequate consciousness have stopped existing. Simply said: all humans who can make additions have died. It is possible that at some point in time, a new form of consciousness can come into existence that discovers addition, and maybe this consciousness will discover that in ancient times there was a civilization that could make additions.
The most important feature of thoughts, better called memes, is that they can and need to be transferred from brain to brain. This is the social process called communication. When an individual brain dies or gets out of order, memes continue to multiply in other brains. This way a cluster of human beïngs form a living social being: a culture or civilization. The individual members die, but the civilization lives on, although it also can die. Note that this cultural being is not humanity as a whole. Humanity is made up of different (sub)cultures.
Modern materialism was first described by Spinoza.
Second Foundation is the title of the third part of the 
