Zero-point energy

<p>Zero-point energy (ZPE) is the lowest possible <a href="/facts/Energy/wd8PrQM7">energy</a> that a <a href="/facts/Quantum_mechanical/BRc3Mzgr">quantum mechanical</a> system may have. Unlike in <a href="/facts/Classical_mechanics/ykG8upsN">classical mechanics</a>, quantum systems constantly <a href="/facts/Quantum_fluctuation/qKRsNId0">fluctuate</a> in their lowest energy state as described by the <a href="/facts/Heisenberg_uncertainty_principle/UUSoSp4T">Heisenberg uncertainty principle</a>. Therefore, even at <a href="/facts/Absolute_zero/U3UyPl2K">absolute zero</a>, atoms and molecules retain some vibrational motion. Apart from <a href="/facts/Atom/69syB8dH">atoms</a> and <a href="/facts/Molecule/N9ljSfFq">molecules</a>, the empty space of <a href="/facts/Vacuum_state/dTvXYPad">the vacuum</a> also has these properties. According to <a href="/facts/Quantum_field_theory/VoewsNJV">quantum field theory</a>, the universe can be thought of not as isolated particles but continuous fluctuating <a href="/facts/Field_(physics)/FJdAKeRA">fields</a>: <a href="/facts/Matter/osyc04UN">matter</a> fields, whose <a href="/facts/Quantum/4x5QTxGB">quanta</a> are <a href="/facts/Fermions/LEckdDsR">fermions</a> (i.e., <a href="/facts/Lepton/X4a6MGop">leptons</a> and <a href="/facts/Quark/hwuuVkV5">quarks</a>), and <a href="/facts/Force_field_(physics)/Mz782ame">force fields</a>, whose quanta are <a href="/facts/Boson/XtPFcjb5">bosons</a> (e.g., <a href="/facts/Photon/mFNhAEzA">photons</a> and <a href="/facts/Gluon/t6YH8I21">gluons</a>). All these fields have zero-point energy. These fluctuating zero-point fields lead to a kind of reintroduction of an <a href="/facts/Luminiferous_aether/UzRf78a2">aether</a> in physics since some systems can detect the existence of this energy. However, this aether cannot be thought of as a physical medium if it is to be <a href="/facts/Lorentz_invariant/K5AEuGKg">Lorentz invariant</a> such that there is no contradiction with <a href="/facts/Albert_Einstein/CNTet8qu">Albert Einstein</a>’s theory of <a href="/facts/Special_relativity/vsFFc63E">special relativity</a>.
</p><p>The notion of a zero-point energy is also important for <a href="/facts/Cosmology/yM19zM7Y">cosmology</a>, and physics currently lacks a full theoretical model for understanding zero-point energy in this context; in particular, the discrepancy between theorized and observed vacuum energy in the universe is a source of major contention. Yet according to Einstein's theory of <a href="/facts/General_relativity/jVsoIg8X">general relativity</a>, any such energy would gravitate, and the experimental evidence from the <a href="/facts/Expansion_of_the_universe/f6Uvt79B">expansion of the universe</a>, <a href="/facts/Dark_energy/6bWIYewA">dark energy</a> and the <a href="/facts/Casimir_effect/xRhpDH6T">Casimir effect</a> shows any such energy to be exceptionally weak. One proposal that attempts to address this issue is to say that the <a href="/facts/Fermion_field/KKaGVgX6">fermion field</a> has a negative zero-point energy, while the <a href="/facts/Boson_field/rMKo9HWw">boson field</a> has positive zero-point energy and thus these energies somehow cancel out each other. This idea would be true if <a href="/facts/Supersymmetry/hkWGrMet">supersymmetry</a> were an exact <a href="/facts/Symmetry_(physics)/gJmgsooI">symmetry of nature</a>; however, the <a href="/facts/LHC/XWJCFSqT">Large Hadron Collider</a> at <a href="/facts/CERN/y1gwRchm">CERN</a> has so far found no evidence to support it. Moreover, it is known that if supersymmetry is valid at all, it is at most a <a href="/facts/Symmetry_breaking/q3yqVlNQ">broken symmetry</a>, only true at very high energies, and no one has been able to show a theory where zero-point cancellations occur in the low-energy universe we observe today. This discrepancy is known as the <a href="/facts/Cosmological_constant_problem/odjlvwLL">cosmological constant problem</a> and it is one of the greatest <a href="/facts/List_of_unsolved_problems_in_physics/vJ3d1A83">unsolved mysteries in physics</a>. Many physicists believe that "the vacuum holds the key to a full understanding of nature".
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Zero-point energy open-in-new

Zero-point energy