In 1913, using this formula as a basis, Albert Einstein and Otto Stern published a paper of great significance in which they suggested for the first time the existence of a residual energy that all oscillators have at absolute zero. They called this "residual energy" and then Nullpunktsenergie (in German), which later became translated as zero-point energy. They carried out an analysis of the specific heat of hydrogen gas at low temperature, and concluded that the data are best represented if the vibrational energy is taken to have the form:
Thus, according to this expression, even at absolute zero the energy of an atomic system has the value ½hν. Although the term zero-point energy applies to all three of these interactions in nature, customarily it is used in reference only to the electromagnetic case. Because the zero-point field has the property of being Lorentz invariant, the zero-point field becomes detectable only when a body is accelerated through space.
Some experiments in 1992 have demonstrated experimentally that the familiar spontaneous emission process in atoms may be regarded as stimulated emission by zero-point field radiation. In recent years, it has been suggested that the electromagnetic zero-point field is not merely an artifact of quantum mechanics, but a real entity with major implications for gravity, astrophysics and technology. This view is shared by a number of researchers, including Boyer (1980), McCrea (1986), Puthoff (1987) and Rueda and Haisch (1998).
However, the historical analysis of the zpf energy density just described appears to contradict the first law of thermodynamics and our understanding of the cosmology of the universe. The physical evidence is extensive that the universe has expanded from an origin containing essentially no space and infinite energy density in the event called the Big Bang. If our universe is defined as all that has the potential of being known to us and interacted with, then it is defined as a "closed system". A closed system retains causality because its total energy is finite and always conserved. This is not a contradiction with the universe at time (t) = 0 because the concept of infinite energy "density" in "zero" occupied space does not equal "infinite energy" for the universe. The historical analysis of the zpf energy density used in the example of energy in one cubic meter of space does not account for the expansion of the universe. It simply increments this expanding space over time and assigns each new additional quantum space with the maximum energy density.
There is a major drive in physics to create a more realistic zpf energy density model that still allows for causality and conservation of energy in the universe. There is substantial evidence in quantum physics, via the de Broglie relations, the Casimir effect, and the Zitterbewegung action of electrons that this field of energy acts as an energy intermediary in the dynamic actions of all particles. Electrons orbiting a nucleus, as one specific example, may use this energy source to move up in an orbit, and then contribute back to this energy source when they relax back into a lower orbit around the nucleus. The de Broglie relations show that the wavelength is inversely proportional to the momentum of an electron and that the frequency is directly proportional to the electron's kinetic energy. As long as the electron does not increase its average kinetic energy over time through acceleration or heating of the atom as a whole, then this wave-like movement of electrons can be seen as a direct interaction of electrons with the zpf.
A potentially promising area for research is the fact that if particles become more energetic as they are heated or accelerated their gravitational field increases. Changes in gravity can perhaps be attributed to a change in a spherical zpf energy density gradient surrounding an accelerated or decelerated massive particle. This dynamic action is just an extension of the static orbiting electron wave model to a dynamic model in which the "average" kinetic energy of a particle no longer remains constant over time and energy is drawn in from the quantum vacuum but not returned. If a massive particle's ground state is defined as it's reference frame at the instant of its creation, then when a particle or body returns to this reference frame, or ground state, from an accelerated state that energy is returned to the quantum vacuum as a decrease in gravity surrounding the particle. This would be in accord with the rules of gravity on accelerated bodies as we know them, and most importantly, maintains conservation of the combined energy of both particles and the zpf, while still allowing for dynamic interaction between the two.
A static, but plastic quantum foam is a better analogy to the character of the quantum vacuum, and not the kind of foam Wheeler described. It should be remembered that each quantum space represents the sum of quantum harmonic oscillator energy in each of the three spatial degrees of freedom, and that each of these three degrees of freedom can act separately, but in coordination with the other two to provide a total energy for that quantum space which is always conserved. If a photon with a specific energy and direction enters and then exits a quantum space these three degrees of freedom allow for a change in the magnitude of the energy in each of the three spatial directions while conserving the total magnitude of harmonic energy in that space - an increase in magnitude of harmonic energy in one dimension can be compensated by a decrease in the other two dimensions. The orientation and size of these changes will correlate to the direction and energy of any particle passing through that quantum space. Similarly, any particle encountering a quantum space which has recently had a particle pass through it will be affected by that previous particle, even though they are not coincident in time.
For example, in the cold reaches of space between galaxies photons from distant galaxies arrive rarely. If by chance a rare photon passes through one of these cold dark spaces it will leave a quantum signature on the oscillatory energy of each quantum space it passes through. If a quantum space has experienced a photon passing through it and no further photons pass through, then that area of space will retain a memory of the last photon it experienced. That space will then exhibit a residual force which has a magnitude and a direction that resides in the memory of that space. This force can be observed in the Zitterbewegung, or jittery action of electrons, which in principle can be extended to all particles. In effect, a pathway has been produced by this single photon. The fact that this pathway cannot be maintained in its unaltered form after measuring it, as the Heisenberg Uncertainty Principle predicts, does not alter the fact that this pathway is retained in space until the next photon passing through creates an interference with this pathway. Acts of measurement represent an exchange of photons between the "observer" and the "observed" and are synonymous with local changes in energy. The "observed" can be an actual particle or just the pathway in space created by the particle. The appearance of fluctuation is actually the transformation of energy and information as it travels through space, but the total energy and information of the universe are always maintained. So it is seen that this quantum foam is not the kind of foam that springs back, but is more like milk foam on top of a cup of cappuccino - a straw can be pushed through the foam and a hole in the foam will remain for a time after the straw is withdrawn. But in the case of quantum foam the impression left behind is not of a hole, but rather the impression of the photon or particle with mass that passed through it..
In the West the scientific description of gravity remains centered on Einstein's original conception as described in General Relativity, i.e. gravity is the geometry of space, or geometrodynamics. In this description space can curve not only around a large massive object but it can also be made to curve similarly around a much, much less massive object that has been accelerated close to the speed of light. This is a perfectly accurate description, but "space" in this description is an amorphous element that is similar to the classical elements of earth, water, fire, and air, as described by early Greek, Japanese, and Hindu civilizations - there is no granularity or definition of what that space represents.
Sakharov was able to see that the geometrodynamics of gravity could just as easily be subsumed within a larger description of the geometry of the energy density of the zpf. This geometry refers to a framework in which the total energy density for each quantum space can actually change and does not refer to residual electromagnetic forces represented by past history of particle trajectories referred to earlier. Rather than being viewed as process in which a photon is both entering and exiting a quantum space it should be viewed as a photon exiting the space only and leaving the total energy of the quantum space at a reduced magnitude. In this way gravity can be described similarly to the geometry of isobaric lines of equal air pressure in the atmosphere, but in the case of gravity these lines would instead be spherical surfaces of equal zpf energy density around a massive object. In this conception the spherical surfaces of lowest zpf energy density would be those closest to the massive object or particle and the energy density in space would increase at the rate equal to , where is the distance from the massive object or particle. (The gravitational constant, , and the specific mass, , are left out as they do not effect the "rate" at which gravitational force changes with distance.) Here would be the average density of the zpf over the entire universe at any given moment in the life of the universe. At sufficient distances in open space from the massive body would approximate .
The Planck length defines the shortest wavelength quantum oscillator that is possible. The summation of energy of all possible wavelengths for each of the three dimensional degrees of freedom up to this limit has historically defined the energy for each quantum space. The Planck length is:
If the zpf energy density decreases as the volume of the universe expands then, by definition, the upper bound for each quantum oscillator must be reduced and consequently the "average" total energy for each quantum space in the universe must be reduced correspondingly. Perhaps the Planck length is not a constant but stretches out as the universe expands? There would be some precedence for this in the stretching out of light in the cosmic microwave background radiation. There are three constants used to create the Planck length constant, as shown above. Is it possible that the gravitational constant, always assumed to be constant throughout the expansion of the universe, is not a constant? This seems plausible, in view of structural changes that would occur in the universe as the fabric of space becomes less dense as it expands. Of the three constants included in the Planck length the gravitational constant seems to be most directly correlated with the expansion of this primordial field.
If one considers fundamentally altering the status of one the three constants then altering the gravitational constant would be preferable to altering the constancy of the speed of light or changing Planck's constant. Planck's constant and the speed of light fundamentally underlie all current calculations of physical properties. The constancy of the speed of light may also be directly tied to the interaction of matter with the local density of the zpf. As the zpf density changes within gravitational fields and as the universe expands then the length measurements, which are time dependent, change along with locally changing rates of passage of time. The direct correlation of changes in both measurement of distance and measurement of time as this density changes create the constancy of the speed of light. While the gravitational constant also underlies many fundamental properties of physics, the properties affected by the gravitational constant seem to be more directly tied to contradictions that already exist between gravitational physics and quantum physics.
Only future experience will tell if more problems are "solved" or if more problems are "created" by allowing for changes in the gravitational constant during the evolution of the universe. One thing is certain though: If the Planck length stretches out as the universe expands then the zpf energy density is not even close to what it is currently assumed to be.
It is a fact that Albert Einstein's equation in General Relativity for the geometrodynamics of space is one of the most beautiful equations in physics. Unfortunately, its beauty has resulted in a fixation in the West on the mathematics of geometry, including the geometry of hyper-dimensional space. This focus has resulted in Western mainstream physics ignoring the need for a mathematical definition that connects the classical General Relativity 4-dimensional and Kaluza-Klein 5-dimensional theories of the geometry of space with new quantum mechanical derived ideas that will better correlate with them. Until an explicit mathematical equation is robustly proven to link these two disparate interpretations of physics the first law of thermodynamics for our universe appears to be conceptually violated.
Andrei Sakharov's conception of the elasticity of space, though incomplete, seems to point towards an ultimate resolution of this problem. In his cosmological model space is elastic like the surface of a balloon and thins out as the volume of the universe expands over time. If the 3-dimensional volume of the universe is represented as a 3-dimensional surface of a balloon, then in its collapsed state at the beginning of time the zpf energy density of the universe is greatest. In approximately the first pico-pico second in the life of the universe the zpf energy density would be extremely high, high enough to create the proton in the hydrogen atom. The proton represents approximately 99.9 percent of the mass of the entire hydrogen atom. The estimated energy density of the physical vacuum at the instant of the proton creation would then represent approximately the amount of energy density recently calculated for the hydrogen atom using stochastic electrodynamics. However, in this conceptual framework this zpf energy density would only exist at precisely this one moment in the life of the universe. Sakharov conceived that at the instant of the creation of fundamental massive particles that the elastic zpf energy required for their mass was transformed into inelastic energy.
Though Sakharov didn't know this when he conceptualized this idea, today our experimental knowledge indicates the proton, which itself is made up of three quarks, is the only fundamental massive particle that does not undergo transformation through radioactive decay if given a long enough time of observation or a large enough quantity of protons being observed.(In the case of neutrinos, they simply transform into other kinds of neutrinos). So his idea seems to fit in with the idea of a type of "absolute" inelasticity that the Standard Model cannot account for.
So a question similar to the question Einstein proposed concerning the non-collapse of the electron into the hydrogen nucleus can be posed for the proton: Why doesn't the proton radioactively decay if the energy density of the physical vacuum is now a tiny fraction of what it was when the proton was created? The principle of asking why is exactly the same even though they apply to different processes. If the zpf energy density decreases over time the statistical probability of both processes occurring should increase. If the proton composes 99.9 percent of the energy of the hydrogen atom, is itself a composite elementary particle, an even more pertinent question would be to ask why the proton doesn't radioactively decay?
Sakharov imagined that spin and its associated angular momentum provided this inelasticity. Spin, and specifically inelastic spin, is a part of 5-dimensional definition that directly correlates with gravity in Kaluza-Klein theory. If one maintains the balloon metaphor then we sew in a round piece of inelastic material into our balloon while it is still in its collapsed state. We are careful to select a piece of inelastic material that has exactly the same density as the same equivalent elastic material surrounding it at that point in its expansion. As we continue to blow up the balloon its elastic material thins out symmetrically except where the inelastic patch is located. Because the area of the inelastic patch does not stretch and thin out the elastic material surrounding it must compensate by stretching and thinning even more than it otherwise would. The greatest thinning will be right on the periphery of the patch in the elastic material because this is the part of the elastic material that has the greatest concentration of stress. If we translate this idea to physics the greatest zpf stress, or thinning out, will be right on the periphery of any massive body and this is where gravity is greatest.
One now returns to the question of where the missing energy went to that is required to support the proton in today's greatly expanded universe. Using pure logic it appears that the proton still has it in the form of energy pulled in from the surrounding physical vacuum. Though the inelasticity between a proton's quarks can by no means account for all the gravity in the universe it certainly can account for nearly all the gravity of nucleons, i.e., protons and neutrons. (A neutron can be included in this because it has very slightly more energy than a proton and will decay into a proton after fifteen minutes if separated from protons.) It seems that the energy density in the universe from that first pico-pico second, at least for protons, is equal to 99.9 percent of the original energy density calculated for the hydrogen atom from stochastic electrodynamics and the Casimir effect. If one accounts only for the gravity of nucleons, which is a very large proportion of the gravity implicitly assigned within the cosmological constant, then a significant proportion of the 10^120 difference between it and the traditional vacuum energy can be resolved simply by allowing for a decrease in energy density as the finite zpf energy expands into an ever increasing volume, and by subtracting that energy in nucleons from the vacuum energy. Gravity seems to be created by that subtraction. This is not gravity as we are used to understanding it, but gravity as an energy density gradient in the vacuum spreading out smoothly around any massive object. So it can be seen that the reason the proton does not decay in today's universe is because energy is pulled in from the surrounding physical vacuum. We experience that reduction in energy as gravity.
Such views are not without controversy. Some see such discussion as pseudoscience. However, physicist David Bohm and other respected scientists, have found some utility in looking at the relationship of the zero point field to matter. Bohm posited, for example, that the field might be the force from which all life unfolds. He also stated that the "nonlocality" of quantum physics might be explained through interconnections allowable via the zero point field.