The Vacuum as Ether in the last Century

Scientific Paper
Title	The Vacuum as Ether in the last Century
Read in full	Link to paper
Author(s)	Michele Barone
Keywords	Ether, QM, QED, QCD, Cosmology
Published	2004
Journal	Foundations of Physics
Volume	34
Number	12
No. of pages	10
Pages	1973-1982

Read the full paper here

Abstract

In this paper we review the evolution of the concept of ?vacuum? according to different theories formulated in the last century, like Quantum Mechanics, Quantum Electrodynamics, Quantum Chromodynamics in Particle Physics and Cosmology. In all these theories a metastable vacuum state is considered which transforms from one state to another according to the energy taken into consideration. It is a ?fluid? made up by matter and radiation present in the whole Universe, which may be identified with a modern definition of ether.

Overview

This ten-page review, published in Foundations of Physics in December 2004 and written for the seventieth birthday of Franco Selleri, makes a single sustained point: that twentieth-century physics did not abolish the ether so much as rename it. Barone, a CERN-associated experimental particle physicist, walks through the vacuum as it appears in quantum mechanics, quantum electrodynamics, quantum chromodynamics and cosmology, and argues that in each of these the "vacuum" is a structured, energetic, polarizable, state-changing medium — "a 'fluid' made up by matter and radiation present in the whole Universe, which may be identified with a modern definition of ether."

The argument is unusual among the ether papers catalogued on this wiki in that it is made almost entirely from orthodox physics. Barone does not propose a new theory or dispute any standard calculation; he takes the Standard Model and concordance cosmology at their word and observes what they say the vacuum is. The dissident content lies in the conclusion drawn: that a medium with a permittivity, a permeability, a polarization, a zero-point pressure, phase transitions and a state of rest is an ether by any reasonable definition, and that the historical rejection of the ether was therefore premature rather than final.

Barone frames this against the pre-history. In Lorentz's theory — which appeared a year before Einstein's 1905 paper — the luminiferous ether is a preferred reference system to which all laws should be referred, with the Lorentz transformations carrying description from one inertial system to another. Einstein removed the need for it by postulating the equivalence of all inertial systems; but, Barone notes, "after 1916 and till his death, Einstein reintroduced the concepts of ether which he intended as physical space or field."

The review

The vacuum in quantum mechanics and QED

Barone begins with the uncertainty relation ΔE·Δt ≥ h/4π. Applied to the electromagnetic field, it forbids the electric and magnetic fields being simultaneously zero, so the vacuum is subject to fluctuations and "cannot be considered a static and empty entity as in classical physics, but it is a complex and dynamic one."

In second quantization a field is a sum over its quanta, equivalent to an infinite collection of harmonic oscillators — "a series of springs with masses attached"; exciting one oscillator produces a particle. The QED vacuum is then the state in which no quanta are excited, the zero energy level or ground state. Barone stresses that its perturbations are hard to observe precisely because there is no lower-energy state to compare against. The exception he singles out is the Casimir effect: Casimir's 1948 prediction, experimentally verified in 1958, that two clean neutral parallel metal plates attract with a force varying as the inverse fourth power of their separation, because zero-point modes with wavelengths longer than the gap are suppressed between the plates so the external zero-point pressure exceeds the internal. At separations below 10⁻⁵ m the Casimir force exceeds gravitation and is a real engineering concern in nanotechnology. He also reports a then-recent prediction that a dielectric body in crossed electric and magnetic fields will extract linear momentum from the vacuum and begin to move — about 50 nm s⁻¹ for 17 T and 100,000 V m⁻¹, which unlike the Casimir effect depends on the high-frequency cut-off.

The virtual photon in electron–positron annihilation is used to make the point sharply: it is virtual precisely because it does not satisfy E² = p²c² + m²c⁴. And yet the resulting theory is spectacularly accurate — Barone quotes the electron g-factor as g/2 = 1.00115965238 ± 0.00000000026 theoretically against 1.00115965241 ± 0.00000000202 measured. The vacuum, in other words, is not a philosophical embarrassment attached to a shaky theory; it is a load-bearing part of the most precisely confirmed theory in physics.

Vacuum polarization, QCD and mass

The heart of the paper is the analogy between the vacuum and ordinary polarizable matter, which Barone develops carefully. Insulators have a dielectric constant ε > 1 because bound electrons shift to shield an introduced charge; magnetic substances have a permeability μ > 1 (paramagnets, pulled into stronger fields) or μ < 1 (diamagnets such as bismuth, expelled). In QED the analogy holds: over short intervals virtual pairs of opposite charge exist in the vacuum and can be polarized like the molecules of a gas or a liquid, so the bare electron charge is screened and its effect weakened at large distance.

Barone then notes where the analogy strains. The speed of light in a medium is c/(εμ)^1/2, and special relativity requires c in vacuum, so the vacuum must have εμ = 1: if it is dielectric with ε increasing with distance it must be diamagnetic with μ decreasing. But that holds only for spinless virtual particles, whereas QED deals in e⁺ and e⁻, which have spin and are magnetic — so one expects a paramagnetic vacuum instead. He records the tension rather than resolving it.

In QCD the same picture runs with opposite sign. A quark introduced into the vacuum interacts with virtual quark–antiquark pairs carrying colour charge; the cloud of different colours reduces the effective charge at short distance rather than at long, giving asymptotic freedom, with the turn-around near 10⁻¹³ cm, the proton diameter. Free quarks and free gluons have never been detected — their evidence is always indirect, as hadrons and as jets — and the QCD vacuum has ε decreasing and μ increasing with distance, so it is paramagnetic. Barone reports the suggestion that the QCD vacuum is analogous to a superconducting state with two phases and a non-sharp transition between them, at distances of order 10⁻¹⁵ m.

Mass itself is attributed to the vacuum: "the masses of all particles are generated by the action of empty space (vacuum) on each single particle," through a Higgs field pervading all space, with different couplings producing the variety of masses. Barone's illustration is a balloon of steam that is perfectly symmetric until cooled, whereupon liquid and ice appear at the bottom and the symmetry is broken by nothing more than cooling. He notes the hunt for the boson then under way at LEP, the Tevatron and the LHC.

The vacuum in cosmology

The cosmological sections supply Barone's most direct claim of an ether-like preferred frame. The cosmic background radiation discovered by Penzias and Wilson in 1965 at 3.5 ± 1 K and 7.3 cm is almost isotropic and homogeneous, but shows a dipole at the level of ΔI/I = 10⁻³, attributed to the Earth's motion at about 350 km s⁻¹ relative to an isotropic frame. He compounds the Sun's 220 km s⁻¹ motion in the Galaxy, the Galaxy's roughly 200 km s⁻¹ motion in the Local Group, and the Local Group's motion within the Local Supercluster, all referred to the frame in which the CBR is fully isotropic, and concludes: "Therefore CBR can be considered a good candidate to ether."

He then reviews the WMAP-era picture — an age of 13.7 billion years with 1% error, first stars about 200 million years after the big bang, light from 380,000 years after it, H₀ = 71 km s⁻¹ Mpc⁻¹ with 5% error — and the composition split he quotes as 4% ordinary matter with the remainder dark. Dark matter is inferred indirectly, chiefly from spiral galaxy rotation; Dark energy has an antigravity effect and drives accelerated expansion, and there is no firm evidence it is made of particles at all.

The candidate he dwells on is vacuum energy, and the difficulty is stated plainly: a zero-point estimate gives a vacuum energy density 120 orders of magnitude greater than the energy density of all the matter in the universe, which would rip apart every electrostatic and nuclear bond. Some mechanism must cancel it — not to exactly zero, but "to 120 decimal places after zero," leaving precisely the missing two-thirds of critical density. Since a dark energy density that changed with time could not be vacuum energy, the alternative is quintessence: a dynamic, time-evolving, spatially dependent form of energy with negative pressure, a fifth kind of matter best modelled by scalar fields and — unlike the quantum vacuum — subject to classical laws. The two are separable observationally through the ratio w of pressure to energy density (more negative w giving greater acceleration), by precise supernova measurements over a longer span of distance, and by small differences in the angular size of hot and cold spots in the microwave background. Quintessence too, Barone concludes, "can be considered a new form of ether."

Assessment

The paper's strength is its restraint. Barone is an experimentalist writing from inside the establishment — a CERN liaison and CMS collaborator — and he grants mainstream physics all of its successes, including the electron g-factor agreement that is normally deployed against ether talk. The argument then becomes hard to dismiss on the usual grounds, because it does not require any orthodox result to be wrong. What it asks is a question about naming and about consistency: a medium with permittivity and permeability, with a polarizable content, with phase transitions, with a zero-point pressure that pushes plates together, and with a frame in which it is isotropic, is being denied a name it manifestly answers to. The cosmological-constant problem is presented in the same spirit — as orthodoxy's own admission, not as an outside accusation.

The limits are equally clear. This is a review, not a derivation: nothing new is calculated, and the identification of the vacuum with an ether is asserted at the end of each section rather than made to do any work. The crucial gap is between a preferred frame and a Lorentzian ether. The CBR rest frame is a preferred frame only in the weak sense that a particular distribution of matter and radiation happens to be at rest in it — which is true of the air in a room and does not make air a violation of relativity. Nothing in the paper shows that the local laws of physics pick out that frame, and special relativity's own experimental record — including the null results that motivated it — is not addressed. Barone himself does not claim otherwise; he says the vacuum "may be identified with a modern definition of ether," and the qualifier is doing real work.

Two smaller points should be noted for accuracy. The internal tension Barone raises over vacuum ε and μ is left standing rather than resolved, and he is candid that the paramagnetic-versus-diamagnetic conclusion flips depending on whether the virtual particles carry spin. And the paper is a 2004 snapshot: the Higgs boson was still being hunted — it was observed at the LHC in 2012, after publication. That dates the survey without touching its central argument, which concerns the ontology of the vacuum rather than any particular particle's mass.