"In science, "fact" can only mean "confirmed to such a degree that it would be perverse to withhold provisional assent." I suppose that apples might start to rise tomorrow, but the possibility does not merit equal time in physics classrooms"

This quote by Stephen Jay Gould is highlighting the significance of scientific realities and the need to identify them from simple possibilities. He is saying that in science, a truth is something that has actually been validated to such a degree that it would be unreasonable to deny it. He then goes on to give an example of something that is not a scientific truth, such as apples increasing tomorrow, and discusses that this possibility does not benefit equivalent time in physics classrooms. This quote is emphasizing the significance of clinical truths and the requirement to differentiate them from simple possibilities. It is likewise highlighting the importance of scientific proof and the need to be critical of what is accepted as fact. Gould is emphasizing that science needs to be based upon truths that have actually been verified through rigorous testing and research study, and not on simple speculation or possibilities.