Vacuum energy

For articles related to vacuum energy, seeQuantum vacuum (disambiguation).

Vacuum energyis an underlying backgroundenergythat exists inspacethroughout the entireuniverse.The vacuum energy is a special case ofzero-point energythat relates to thequantum vacuum.

Unsolved problem in physics:

Why does thezero-point energyof the vacuum not cause a largecosmological constant?What cancels it out?

(more unsolved problems in physics)

The effects of vacuum energy can be experimentally observed in various phenomena such asspontaneous emission,theCasimir effect,and theLamb shift,and are thought to influence the behavior of the Universe oncosmological scales.Using the upper limit of thecosmological constant,the vacuum energy of free space has been estimated to be 10⁻⁹joules(10⁻²ergs), or ~5GeVper cubic meter.However, inquantum electrodynamics,consistency with the principle ofLorentz covarianceand with the magnitude of thePlanck constantsuggests a much larger value of 10¹¹³joules per cubic meter. This huge discrepancy is known as thecosmological constant problemor, colloquially, the "vacuum catastrophe."

Origin

Quantum field theorystates that all fundamentalfields,such as theelectromagnetic field,must bequantizedat every point in space. A field in physics may be envisioned as if space were filled with interconnected vibrating balls and springs, and the strength of the field is like the displacement of a ball from its rest position. The theory requires "vibrations" in, or more accurately changes in the strength of, such a field to propagate as per the appropriatewave equationfor the particular field in question. Thesecond quantizationof quantum field theory requires that each such ball–spring combination be quantized, that is, that the strength of the field be quantized at each point in space. Canonically, if the field at each point in space is asimple harmonic oscillator,its quantization places aquantum harmonic oscillatorat each point. Excitations of the field correspond to theelementary particlesofparticle physics.Thus, according to the theory, even thevacuumhas a vastly complex structure and all calculations of quantum field theory must be made in relation to this model of the vacuum.

The theory considers vacuum to implicitly have the same properties as a particle, such asspinorpolarizationin the case oflight,energy, and so on. According to the theory, most of these properties cancel out on average leaving the vacuum empty in the literal sense of the word. One important exception, however, is the vacuum energy or thevacuum expectation valueof the energy. The quantization of a simple harmonic oscillator requires the lowest possible energy, orzero-point energyof such an oscillator to be

${E}={\frac {1}{2}}h\nu.$

Summing over all possible oscillators at all points in space gives an infinite quantity. To remove this infinity, one may argue that only differences in energy are physically measurable, much as the concept ofpotential energyhas been treated inclassical mechanicsfor centuries. This argument is the underpinning of the theory ofrenormalization.In all practical calculations, this is how the infinity is handled.

Vacuum energy can also be thought of in terms ofvirtual particles(also known as vacuum fluctuations) which are created and destroyed out of the vacuum. These particles are always created out of the vacuum in particle–antiparticlepairs, which in most cases shortly annihilate each other and disappear. However, these particles and antiparticles may interact with others before disappearing, a process which can be mapped usingFeynman diagrams.Note that this method of computing vacuum energy is mathematically equivalent to having aquantum harmonic oscillatorat each point and, therefore, suffers the same renormalization problems.

Additional contributions to the vacuum energy come fromspontaneous symmetry breakinginquantum field theory.

Implications

The Casimir effect is a physical force affecting macro-size objects and arises from vacuum energy, which are quantized oscillations in the electromagnetic field permeating every microscopic crevice of the Universe that give that field a non-zero energy. When two conductive flat plates of the same material are less than about 1000 nanometers apart (about twice the width of a common bacterium), they begin to form an electromagnetic cavity that excludes larger-wavelength components of vacuum energy. This reduces the energy between the plates, creating a pressure imbalance that pushes them together. Here, the gap permits only excitations with wavelengths no greater those shown in green color to pop into existence between the plates, excluding yellow, orange, red wavelengths.

Vacuum energy has a number of consequences. In 1948,DutchphysicistsHendrik B. G. CasimirandDirk Polderpredicted the existence of a tiny attractive force between closely placed metal plates due toresonancesin the vacuum energy in the space between them. This is now known as theCasimir effectand has since been extensively experimentally verified.It is therefore believed that the vacuum energy is "real" in the same sense that more familiar conceptual objects such as electrons, magnetic fields, etc., are real. However, alternative explanations for the Casimir effect have since been proposed.

Other predictions are harder to verify. Vacuum fluctuations are always created as particle–antiparticle pairs. The creation of these virtual particles near theevent horizonof ablack holehas been hypothesized by physicistStephen Hawkingto be a mechanism for the eventual"evaporation" of black holes.If one of the pair is pulled into the black hole before this, then the other particle becomes "real" and energy/mass is essentially radiated into space from the black hole. This loss is cumulative and could result in the black hole's disappearance over time. The time required is dependent on the mass of the black hole (the equations indicate that the smaller the black hole, the more rapidly it evaporates) but could be on the order of10⁶⁰years for large solar-mass black holes.

The vacuum energy also has important consequences forphysical cosmology.General relativitypredicts that energy is equivalent to mass, and therefore, if the vacuum energy is "really there", it should exert agravitationalforce. Essentially, a non-zero vacuum energy is expected to contribute to thecosmological constant,which affects theexpansion of the universe.

Field strength of vacuum energy

The field strength of vacuum energy is a concept proposed in a theoretical study that explores the nature of the vacuum and its relationship to gravitational interactions. The study derived a mathematical framework that uses the field strength of vacuum energy as an indicator of the bulk (spacetime) resistance to localized curvature. It illustrates the association of the field strength of vacuum energy to the curvature of the background, where this concept challenges the traditional understanding of gravity and suggests that the gravitational constant, G, may not be a universal constant, but rather a parameter dependent on the field strength of vacuum energy.

Determination of the value of G has been a topic of extensive research, with numerous experiments conducted over the years in an attempt to measure its precise value. These experiments, often employing high-precision techniques, have aimed to provide accurate measurements of G and establish a consensus on its exact value. However, the outcomes of these experiments have shown significant inconsistencies, making it difficult to reach a definitive conclusion regarding the value of G. This lack of consensus has puzzled scientists and called for alternative explanations.

To test the theoretical predictions regarding the field strength of vacuum energy, specific experimental conditions involving the position of the moon are recommended in the theoretical study. These conditions aim to achieve consistent outcomes in precision measurements of G. The ultimate goal of such experiments is to either falsify or provide confirmations to the proposed theoretical framework. The significance of exploring the field strength of vacuum energy lies in its potential to revolutionize our understanding of gravity and its interactions.

History

In 1934,Georges Lemaîtreused an unusualperfect-fluidequation of stateto interpret the cosmological constant as due to vacuum energy. In 1948, theCasimir effectprovided an experimental method for a verification of the existence of vacuum energy; in 1955, however,Evgeny Lifshitzoffered a different origin for the Casimir effect. In 1957,LeeandYangproved the concepts of broken symmetry andparity violation,for which they won the Nobel prize. In 1973,Edward Tryonproposed thezero-energy universehypothesis: that the Universe may be a large-scale quantum-mechanical vacuum fluctuation where positivemass–energy is balanced by negativegravitational potential energy.During the 1980s, there were many attempts to relate the fields that generate the vacuum energy to specific fields that were predicted by attempts at aGrand Unified Theoryand to use observations of the Universe to confirm one or another version. However, the exact nature of the particles (or fields) that generate vacuum energy, with a density such as that required by inflation theory, remains a mystery.

Vacuum energy in fiction

• Arthur C. Clarke's novelThe Songs of Distant Earthfeatures a starship powered by a "quantum drive" based on aspects of this theory.
• In the sci-fi television/film franchiseStargate,a Zero Point Module (ZPM) is a power source that extractszero-point energyfrom amicro parallel universe.
• The bookStar Trek: Deep Space Nine Technical Manualdescribes the operating principle of the so-calledquantum torpedo.In this fictional weapon, an antimatter reaction is used to create a multi-dimensional membrane in a vacuum that releases at its decomposition more energy than was needed to produce it. The missing energy is removed from the vacuum. Usually about twice as much energy is released in the explosion as would correspond to the initial antimatter matter annihilation.
• In the video gameHalf-Life 2,the item generally known as the "gravity gun" is referred to as both the "zero point field energy manipulator" and the "zero point energy field manipulator."

See also

• Cosmic microwave background
• Dark energy
• False vacuum
• Normal ordering
• Quantum fluctuation
• Sunyaev–Zeldovich effect
• Vacuum state

External articles and references

• Free PDF copy ofThe Structured Vacuum – thinking about nothingbyJohann Rafelskiand Berndt Muller (1985);ISBN3-87144-889-3.
• Saunders, S., & Brown, H. R. (1991).The Philosophy of Vacuum.Oxford [England]: Clarendon Press.
• Poincaré Seminar, Duplantier, B., & Rivasseau, V. (2003). "Poincaré Seminar 2002: vacuum energy-renormalization".Progress in mathematical physics,v. 30. Basel: Birkhäuser Verlag.
• Futamase & YoshidaPossible measurement of vacuum energy.
• Study of Vacuum Energy Physics for Breakthrough Propulsion2004, NASA Glenn Technical Reports Server (PDF, 57 pages, Retrieved 2013-09-18).