How can we be sure this is reality?

[Confused Ape]

atheists will just invent something else, just as they did when spontaneous generation got kicked to the curb

I'm not sure what you mean here. Atheists didn't invent spontaneous generation and it was accepted into Christianity.

Spntaneous Generation - Adoption In Christianity

From the fall of the Roman Empire in 5th century to the East-West Schism in 1054, the influence of Greek science declined, although spontaneous generation generally went unchallenged. New descriptions were made. Of the numerous beliefs, some had doctrinal implications outside of the Book of Genesis. For example, the idea that a variety of bird known as the Barnacle Goose emerged from a crustacean known as the Goose Barnacle, had implications on the practice of fasting during Lent. In 1188, Gerald of Wales, after having traveled in Ireland, argued that the "unnatural" generation of barnacle geese was evidence for the Immaculate Conception.[18] Where the practice of fasting during Lent allowed fish, but prohibited fowl, the idea that the goose was in fact a fish suggested that its consumption be permitted during Lent. The practice was eventually prohibited by decree of Pope Innocent III in 1215.[19]

Louis Pasteur was the one who finally put the idea to rest.

his son-in-law, in perhaps the most complete biography of Louis Pasteur, writes:

Absolute faith in God and in Eternity, and a conviction that the power for good given to us in this world will be continued beyond it, were feelings which pervaded his whole life; the virtues of the gospel had ever been present to him. Full of respect for the form of religion which had been that of his forefathers, he came simply to it and naturally for spiritual help in these last weeks of his life.[18]