Physical Nothing v. Metaphysical Nothing
I was fortunate to be in the audience when Lawrence Krauss gave his terrific presentation, "A Universe from Nothing" in Burbank California in 2009. Subsequently many have asked me, "But how can something come from nothing," and Lawrence Krauss has expanded his presentation into a recently published book. Although, I am glad to direct people to his book for the details of the physics, I feel I need to add something about how we think about the subject of nothingness at the foundation.
Nothingness has been contemplated by philosophers for thousands of years, but only explored by science in any detail, recently. The old philosophical idea is easily shown by the simple example of a table with objects upon it ("things"). We can take away things one at a time until we reach a situation where there is no thing (nothing) left on the table to remove, and we say "there is nothing on the table." But of course, the physicists will tell you that there is air on the table and dust, and photons and phonons bouncing off it into your eyes and ears, and cosmic ray particles going through it, and gravity waves and virtual particles continually going in and out of existence, plus of course, space-time itself.
So, what if we keep taking away all that physical stuff? Well, experimentally we can't remove every single thing, but we can get close. Except for spontaneous pair generation, virtual particles don't hang around long enough to be "things" and space-time is also not a "thing" and we can't take out what we don't know is there ("dark matter" may be a thing we could know about, but not be able to take out). In any case, we can experimentally get closer and closer to physical nothing, but that is still in the physical world.
The metaphysical world is in our thoughts. In metaphysics "nothing" can be defined as that from which no thing comes. It is a model we use to think about the physical world. Mathematics is the scientific tool used to formalize that model and easily supplies us with the concept of "zero" but we must remember that the map is not the territory, and just because we can visualize zero in the model (metaphysical nothing), does not mean that must have a corresponding situation in the physical world. So far, we don't have justification to assert that the metaphysical nothing in our models can be, or ever was, the condition in the physical world.
This connects right into the so called "fine-tuning" problem because, again, speculation of such in the model does not necessarily correspond to the reality we see and measure with our scientific capabilities. It is the job of physicists to make a model that matches the measurements and predicts events. It is always possible to make multiple models that give the same result so the scientific community chooses to use Occam's Razor to pick the simplest. That is fine as long as you keep to understanding that the reality is driving the model, not the other way around. To assert that the reality is "fine-tuned" because of a trick you can show in the model, without experimental verification, is to be cut by the other side of a two-edged Occam.
Until you can show me the "knobs" for fine-tuning, or a physically real case of metaphysical nothing, both are just in your head, or written in fiction with ghosts, garden sprites and the tooth fairy.