From the site of Anne Reith, Ph.D.:
Ascension is the process of increasing your cells' vibrational levels. If looked at under an electron microscope, you can see that the cells of all living things vibrate. It is believed that spiritual energy also vibrates, but it does so at a much faster speed than those of us on the Earth plane. Through the process of developing spiritual skills, the vibrational level of our cells increases, and we consequently ascend to a higher level of spiritual understanding and connectedness.