God Feeds the Ravens
- Reaction score
Very well expressed. So I have pulled out some main bits for people who will not read the whole thing.
I go with number 4:
Four Scientific Meanings of Nothing
1) A time when your "thing" of interest didn't exist. How did the Universe make planets? How about stars? How about a matter asymmetry? These things didn't always exist, but rather had to be created. When the mechanism is known, we normally say that our "thing" was created from something, rather than nothing … According to some, this means that the matter we have today arose from nothing, although others who adhere strictly to one of the other definitions dispute this.
2) Empty space. Think of all the "things" that exist in the Universe today. Think of every fundamental constituent of matter; every quantum of radiation; every black hole; every mass; every particle and antiparticle. Now, imagine removing them all. Imagine somehow taking them out of the Universe, leaving nothing but empty space behind. What would you have left? Some call that "nothing," and are quite happy with that definition. The entity known as spacetime is still there, as are the laws of physics.
3) Empty spacetime in the lowest-energy state possible. What if the zero-point energy of the Universe were reduced to its true ground state? … If you reached whatever the true ground state is and expelled all the matter, energy, radiation, and spacetime ripples from your Universe, what would you be left with? That is, perhaps, the ultimate idea of what "physical nothingness" can be: where you still have a stage for the Universe to play out on. There may be no players, no cast, no script and no scene, but in the great abyss of nothingness, you still have a stage.
4) Whatever you're left with when you take away the entire Universe and the laws governing it. At last, you can conceive of removing everything, including space, time, and the rules that govern any sort of particles or quanta of energy. This creates a type of "nothing" that physicists have no definition for. This goes beyond "nothing" as it exists in the Universe, instead realizing some sort of philosophical, absolute nothingness. But in the context of physics, we cannot make sense of this sort of nothingness. We'd have to assume that there is such a thing as a state outside of space and time, where you can have the emergence of spacetime from this hypothesized state of true nothingness.
But is that possible? How does spacetime emerge at a particular location, when there's no such thing as space? How can you create the beginning of time if there's no concept of something like "before" without time already existing? And where, then, would the rules governing particles and their interactions arise from? Does this final definition of "nothing" even mean anything at all, or is it just a logical construct with no physical meaning of its own?
If something fundamentally arose where there was no such thing before, you can call it nothing, but not everyone will agree. If you take all the matter, antimatter, radiation, and even spatial curvature away, you can certainly lay a claim to that being what "nothing" is all about, but there are some "things" that are still around.
If you then take away any energy inherent to space itself, leaving only spacetime and the laws of nature, you can call that "nothing" as well. But ... Only by taking away that as well will some finally acquiesce to calling such an entity "nothing."