# In truth, only atoms and the void

In truth, only atoms and the void.

Can you explain what this sentence means? My interpretation is that the sentence does not makes sense because in physics, "atom" has multiple meanings, the same goes for "void". These words have so many meanings that, used without qualification, they mean nothing. The word truth is also a notoriously loaded and undefined word. Does he mean the absolute truth (which has no place in physics) or is he using it colloquially, we don't know.

Let's assume that he is using "atom" to mean "absolutely indivisible unit" and "void" to mean "absolutely empty space that contains nothing but atoms". This view is absurd because defines "void" to be "empty" and "not-empty" at the same time. But besides that, if in truth, there is nothing but atoms and the void, does Sean Carroll deny the existence of fields?

Here are a few meanings that physicists give to "void" (a search of titles in arxiv containing "void"): rigid void, relativistic void, magnetic fields in voids, empty voids, nano void, dynamics of void and so on. So, in physics void can mean anything but "void".

Then, what does "In truth, only atoms and the void" mean? Does it really have such a deep meaning to included as a motto of a blog?

The phrase is a translation of a quote from Democritus, an ancient Greek philosopher. The quote is not intended to refer literally to the details of modern physics. It is simply an example of an early expression of the naturalistic viewpoint. Carroll's general philosophy is that the universe can be understood in terms of natural laws. There is nothing supernatural or anthropomorphic about how the universe works. Everything we see, from the motion of ocean waves to human consciousness, emerges from simple physical laws without teleology of any sort.

• Trying to literally map this expression to modern physics is the same kind of error made by religious fundamentalists, though going in the opposite direction: attempting to read modern scientific meaning (correct or not) into an ancient non-scientific text, an exercise which does justice to neither the science nor the text when read in its original context. – Michael Brown Oct 13 '13 at 12:44
• Yes, it seems Democritus: stanford.edu/~jsabol/sophia/democritus.html. Is this so well known a quote that he uses it without attribution? – Zeynel Oct 13 '13 at 12:52
• @MichaelBrown The theory was the science of its time, so it was scientific, though I agree that one should not overaly modern on ancient. If you read on Demokritos' world view his insights were amazing for the times he lived. He postulated that the milky way was stars far away, for example, and that other worlds existed. He gave shapes to the atoms that made them stick together etc. – anna v Oct 13 '13 at 13:26
• @annav do you think you can add an answer with your interpretation of what Sean Carroll means by including this as his motto on his blog? – Zeynel Oct 13 '13 at 14:42
• @Zeynel Sorry, I do not read his blog so cannot interpret him. Why can you not ask him? – anna v Oct 13 '13 at 16:46

As Mark Eichenlaub's Answer states, this is a quote from one of Carrol's admired forerunners.

You actually hit nearer the mark with your own words:

So, in physics void can mean anything but "void".

In modern physics there are only quantum fields, a handful of them: the photon field, electron/ positron field, quark field, gluon field and so forth. In many ways these are unitary (in its meaning of being sets of one member, not in the sense of norm-conserving "unitary operators") objects, with discrete states: "one electron" state means the electron positron field in a particular state where the number operator is certain to return the eigenvalue 1, two photon state means the same where the number operator is certain to return the eigenvalue 2 and so forth. In this sense, there aren't really particles at all: when we say that there are $n$ electrons in a reaction, we mean that the unitary electron/positron field is the sole and only actor in this scenario, and it is in a state "$n$ notches above its ground state". This standpoint also shows why "particles" are indistinguishable: there is a "transaction" where, say, the light field interacts with the electron positron field: the former drops two notches, losing one "left handed photon" and one "right handed photon" and, as a result of the transaction, the electron positron field rises from the ground state to a raised state, up one electron and up one positron notch from the ground state. This "event" we call, as a shorthand, "pair production", but there are only two actors in this event beforehand and two actors afterwards and two actors in between: the two quantum fields involved. It doesn't matter how a quantum field reaches a particular state from another state, the "particles" simply label the discrete "notches" in the state space, so to ask "which two photons" excited the electron-positron field is meaningless. What we mean when we say "stuff happens" in the World is that quantum fields interact, thus mutually changing each other's states.

Modern physics has no need for the needless complication of a "void" or "empty space" further to the quantum fields. "Empty space" simply means that the fields are in their ground state in the region in question. "Space and time" are made of quantum fields in a particular state - the ground state - and they're not immersed in any "void".

Look at H, the simplest atom. One neutron and one electron. If your imagination can put H in perspective, it would be the Empire State Building as the nucleus and a grapefruit racing around it at 500 yards. This model is composed mostly of SPACE or VOID!!

• Or maybe you can explain to me how the earths magnetic field has swapped NINE times in the last 6.3 billion years? – Tom Hampton Jun 20 '15 at 1:36
• The hydrogen atom has a proton too. And our classical notion of particles breaks at the quantum level – Kyle Kanos Jun 20 '15 at 2:00
• H is composed by a proton ( not neutron) and electron – anna v Jun 20 '15 at 5:07

Empty space inside an atom is not empty. What was thought to be void inside an atom is NOT void. It is not even 0,9999999999% empty, it's full of quantum foams, etc. But between you and an object, it's full 999999999999% empty. So yes, it's full foams,etc inside an atom, and 999999999% VOID (which is outside it)

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