# What is meant by “Nothing” in Physics/Quantum Physics?

I am not a phycisist, so please forgive my ignorance. This is related to my posts and this.
I am trying to understand what is meant by the term "Nothing" in physics or Quantum Field Theory (QFT) since it seems to me that this term is not used in the way we understand it in everyday language.
So QFT seems to suggest (in a nutshell) that "things pop out of nothing".
But from wiki I see the following quote:

"According to quantum theory, the vacuum contains neither matter nor energy, but it does contain fluctuations, transitions between something and nothing in which potential existence can be transformed into real existence by the addition of energy.(Energy and matter are equivalent, since all matter ultimately consists of packets of energy.) Thus, the vacuum's totally empty space is actually a seething turmoil of creation and annihilation, which to the ordinary world appears calm because the scale of fluctuations in the vacuum is tiny and the fluctuations tend to cancel each other out.

So what is "Nothing" in QFT? If this quote is correct, I can interpret it only as follows:
The "Nothing" is not in the way used in everyday speech but is composed of "transitions" i.e. something that is "about to become"
Is this correct? If yes, why is this defined as "Nothing"? Something that is "about to become" is not nothing but there is something prerequisite.
In very lame terms: Einstein was born a non-physicist but became a physicist, so if this is a correct analogy, then there

1. there is something underlying that was non-something that became something
2. A non-something came into something because something else (not nothing) permitted it to become. E.g. Einstein's talent (or Mozart's) would have been lost had he been born in Africa or in a country with no educational facilities. So he would not become a physicist (but the required talent would be present but not come into reality)

In Physics "nothing" is generally taken to be the lowest energy state of a theory. We wouldn't normally use the word "nothing" but instead describe the lowest energy state as the "vacuum". I can't think of an intuitive way to describe the QM vacuum because all the obvious analogies have "something" instead of nothing "nothing", so I'll do my best but you may still find the idea hard to grasp. That's not just you - everybody finds it hard to grasp.

Start with the classical description of an electric field (Maxwell's equations). It's not too hard to image an electric field as a field filling space. You can even feel the field: for example if you put your hand near an old style TV screen you can feel the static electricity. You can imagine turning down the electric field until it disappears completely, in which case you are left with the vacuum i.e. nothing.

Now imagine the same field, but this time we're using the quantum description of the field (Quantum Electrodynamics instead of Maxell's equations). At the classical level the field is approximately the same as the description Maxwell's equations give, but now we have fluctuations in the field due to the energy-time uncertainty principle. Just as before, imagine turning down the electric field until it disappears. Unlike the classical description, the (average) electric field may disappear but the fluctuations do not. This means the quantum vacuum is different from the classical vacuum because it contains the fluctuations even after you've turned the field down to zero.

The key point is that when I say "turn the field down" I mean reduce the energy to the lowest it will go i.e. you can't make the energy of the electric field any lower. By definition this is what we call the "vacuum" even though it isn't empty (i.e. it contains the fluctuations). It isn't possible to make the vacuum any emptier because the fluctuations are always present and you can't remove them.

• So a first conclusion I make from a first reading of your answer (thank you for your help) is that what a physicist means when says Nothing does not have an exact equivalent with the term Nothing that we ordinary people use in our everyday speech.Did I get this part? – Jim Jun 29 '12 at 10:31
• Well, physicists use the word "vacuum" when they specifically mean a quantum field theory ground state. The word "nothing" doesn't have a specific meaning in physics. However you are basically correct in that for most people "vacuum" and "nothing" are the same thing, while for physicists "vacuum" and "nothing" mean different things. – John Rennie Jun 29 '12 at 10:53
• A second point is that from "nothing" is generally taken to be the lowest energy state of a theory 1) Each "theory" has a different notion of "nothing" 2) lowest energy state is not the same as no energy state. Are these (2) also correct? – Jim Jun 29 '12 at 11:15
• Have a look at my updated answer to physics.stackexchange.com/questions/30965 as I think it addresses some of your concerns. – John Rennie Jun 29 '12 at 14:22
• I know this is the standard language but is "fluctuations" really an appropriate word? I mean the vacuum state would be an eigenstate of the Hamiltonian (and thus, would be a stationary state). I never understood why we use the word "fluctuations". – Dvij Mankad Jun 8 at 9:32

At an even more abstract level (and inspired by the John Rennie's TV analogy): you seem to think of "Nothing" as the equivalent of a black TV screen. In modern physics, "Nothing" is similar to the noise between TV channels.

If we take "nothing" to be the same as "zero", "something" to be the same as "not-zero", the vacuum state is both "nothing" and "something".

The "nothing" part of the vacuum state as a theoretical object is that the average value of a series of measurements of the field will be zero. The "something" part of the vacuum state is that the value of any single measurement will in general not be zero. When we can't predict single measurement results and how they will vary over time, we often find that we can predict average values and how the average values will vary over time.

There will most likely be technical aspects to any Physicist's answer here. In the above, "measurements of the field" must be understood to have quite theoretical connotations. John Rennie has labored heroically, but ultimately you have to work at being an intimate friend of the Math and its relationship to experiment.

You seem to be trying to make "nothing" be something vaguely different from any mathematical idea.

• a theoretical object is that the average value of a series of measurements of the field will be zero doesn't this depend on the scale?Perhaps it is because my lack of background but it seems to me that the term Nothing is a misnomer. It is actual a "handy" name for something so small that is negligible.But in reality there is "something" – Jim Jun 29 '12 at 13:49
• I think no. The average value predicted by the theory for measurements of the field in the vacuum state is zero. Not so small as to be negligible. The measurements we really record in lab books and in computer memory are never measurements of the vacuum state, however, because there's always a nontrivial environment, always thermal fluctuations, etc., all of which has to be modeled. The vacuum is the maximally symmetric starting point for an idealized theoretical model, just as the zero-valued classical field is the starting point for modeling classical systems. – Peter Morgan Jun 29 '12 at 15:36

Simple answer to the simple question Yes this is definately a mis-nomer.

Nothing has come to mean in physics the base state. I will try not to use the word "nothing" in my description.

In the simplest terms if I start with zero apples and add one apple then eat that apple before you see it(and continuously add and subtract just as fast as they are added) that is what the word is being used for there was something but when you checked you got the answer of zero whichh is just what I started with(the base state) it is just a almost accurate description of a QED Vacuum

The necessary physics part is:
“The quantum theory asserts that a vacuum, even the most perfect vacuum devoid of any matter, is not really empty. Rather the quantum vacuum can be depicted as a sea of continuously appearing and disappearing [pairs of] particles that manifest themselves in the apparent jostling of particles that is quite distinct from their thermal motions. These particles are ‘virtual’, as opposed to real, particles. ...At any given instant, the vacuum is full of such virtual pairs, which leave their signature behind, by affecting the energy levels of atoms.”

• Interesting analogy.But where do this apple you add and eat come from? – Jim Jul 3 '12 at 6:31
• If myself or anyone on this site knew that answer to that question, it would be all over the news. – Argus Jul 3 '12 at 13:41
• Fair enough.But I guess what you are saying here is that what the observation is, is that in time X there was nothing there and time X+δτ there is an apple.What I don't get is why it is believed that the apple appeared suddenly (and lost afterwards) and not that it was always there, but we couldn't detect it? Seems more reasonable to me that supporting that nothing is the "birth" of something.Does this make sense to you?I don't have your background and perhaps this seems to simplistic/dumb for you – Jim Jul 3 '12 at 13:49
• For the most part because we only detect(at this time) the effect of this vaccum as it relates to the energy of atoms. – Argus Jul 3 '12 at 13:57
• My background involves 1 week in a high school history class describing Issac newton sitting under a tree. So there is no too simplistic in my view. Lol but thank you for makeing me feel smart. – Argus Jul 3 '12 at 13:59

I'm not a physicist but based on studies I did : all types of elementary particles and forcrs also have fields in the whole universe. and fields always are there so even if we don't see any particle in a place it does't mean that there is "nothing" in that place because fields are always there. based on the uncertainty principle Since we can't accurately calculate the energy of a specific system in a specified time , the conclusion is that the energy of system can not be absolutely zero.so changes happens in the fields even in places we think that is empty. in this case virtual particles and virtual antiparticles borrow energy from system to come in existence and then after a short time they collide togheter and give back this energy to system. So actually "nothing" does not exist. Forgive me for my poor english.

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