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101-482: The Supernova Legacy Survey Program is a project designed to investigate dark energy , by detecting and monitoring approximately 2000 high- redshift supernovae between 2003 and 2008, using MegaPrime , a large CCD mosaic at the Canada-France-Hawaii Telescope . It also carries out detailed spectroscopy of a subsample of distant supernovae . This astronomy -related article is

202-413: A ). This can be understood intuitively: for an ordinary particle in a cube-shaped box, doubling the length of an edge of the box decreases the density (and hence energy density) by a factor of eight (2 ). For radiation, the decrease in energy density is greater, because an increase in spatial distance also causes a redshift. The final component is dark energy: it is an intrinsic property of space and has

303-480: A free electron gas (see Figure 2 ). The negative mass appears as a result of vibration of a metallic particle with a frequency of ω {\displaystyle \omega } which is close the frequency of the plasma oscillations of the electron gas m 2 {\displaystyle m_{2}}  relatively to the ionic lattice m 1 {\displaystyle m_{1}} . The plasma oscillations are represented with

404-407: A stub . You can help Misplaced Pages by expanding it . Dark energy In physical cosmology and astronomy , dark energy is a proposed form of energy that affects the universe on the largest scales. Its primary effect is to drive the accelerating expansion of the universe . Assuming that the lambda-CDM model of cosmology is correct, dark energy dominates the universe, contributing 68% of

505-481: A time machine . For energy eigenstates of the Schrödinger equation , the wavefunction is wavelike wherever the particle's energy is greater than the local potential, and exponential-like (evanescent) wherever it is less. Naively, this would imply kinetic energy is negative in evanescent regions (to cancel the local potential). However, kinetic energy is an operator in quantum mechanics , and its expectation value

606-433: A wormhole . Cramer et al. argue that such wormholes might have been created in the early universe, stabilized by negative-mass loops of cosmic string . Stephen Hawking has argued that negative energy is a necessary condition for the creation of a closed timelike curve by manipulation of gravitational fields within a finite region of space; this implies, for example, that a finite Tipler cylinder cannot be used as

707-647: A "negative mass" can be of three kinds: whether the inertial mass is negative, the gravitational mass, or both. In his 4th-prize essay for the 1951 Gravity Research Foundation competition, Joaquin Mazdak Luttinger considered the possibility of negative mass and how it would behave under gravitational and other forces. In 1957, following Luttinger's idea, Hermann Bondi suggested in a paper in Reviews of Modern Physics that mass might be negative as well as positive. He pointed out that this does not entail

808-616: A constant energy density, regardless of the dimensions of the volume under consideration ( ρ  ∝  a ). Thus, unlike ordinary matter, it is not diluted by the expansion of space. The evidence for dark energy is indirect but comes from three independent sources: In 1998, the High-Z Supernova Search Team published observations of Type Ia ("one-A") supernovae . In 1999, the Supernova Cosmology Project followed by suggesting that

909-552: A design for spacecraft propulsion using negative mass that requires no energy input and no reaction mass to achieve arbitrarily high acceleration. Forward also coined a term, "nullification", to describe what happens when ordinary matter and negative matter meet: they are expected to be able to cancel out or nullify each other's existence. An interaction between equal quantities of positive mass matter (hence of positive energy E = mc ) and negative mass matter (of negative energy − E = − mc ) would release no energy, but because

1010-533: A direct estimate of the Hubble parameter The reliance on a differential quantity, ⁠ Δ z / Δ t ⁠ , brings more information and is appealing for computation: It can minimize many common issues and systematic effects. Analyses of supernovae and baryon acoustic oscillations (BAO) are based on integrals of the Hubble parameter, whereas ⁠ Δ z / Δ t ⁠ measures it directly. For these reasons, this method has been widely used to examine

1111-453: A logical contradiction, as long as all three forms of mass are negative, but that the assumption of negative mass involves some counter-intuitive form of motion. For example, an object with negative inertial mass would be expected to accelerate in the opposite direction to that in which it was pushed (non-gravitationally). There have been several other analyses of negative mass, such as the studies conducted by R. M. Price, though none addressed

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1212-502: A mystery, and possible explanations abound. The main candidates are a cosmological constant (representing a constant energy density filling space homogeneously) and scalar fields (dynamic quantities having energy densities that vary in time and space) such as quintessence or moduli . A cosmological constant would remain constant across time and space, while scalar fields can vary. Yet other possibilities are interacting dark energy, an observational effect, and cosmological coupling (see

1313-503: A non-standard form of kinetic energy such as a negative kinetic energy . They can have unusual properties: phantom energy , for example, can cause a Big Rip . A group of researchers argued in 2021 that observations of the Hubble tension may imply that only quintessence models with a nonzero coupling constant are viable. This class of theories attempts to come up with an all-encompassing theory of both dark matter and dark energy as

1414-508: A profound effect on the universe, making up 68% of universal density in spite of being so dilute, is that it is believed to uniformly fill otherwise empty space. The vacuum energy , that is, the particle-antiparticle pairs generated and mutually annihilated within a time frame in accord with Heisenberg's uncertainty principle in the energy-time formulation, has been often invoked as the main contribution to dark energy. The mass–energy equivalence postulated by general relativity implies that

1515-606: A single effective mass m eff {\displaystyle m_{\text{eff}}}  we obtain: m eff = m 1 + m 2 ω 0 2 ω 0 2 − ω 2 , {\displaystyle m_{\text{eff}}=m_{1}+{{m_{2}\omega _{0}^{2}} \over {\omega _{0}^{2}-\omega ^{2}}},} where ω 0 = k 2 m 2 {\displaystyle \omega _{0}={\sqrt {k_{2} \over m_{2}}}} . When

1616-430: A single phenomenon that modifies the laws of gravity at various scales. This could, for example, treat dark energy and dark matter as different facets of the same unknown substance, or postulate that cold dark matter decays into dark energy. Another class of theories that unifies dark matter and dark energy are suggested to be covariant theories of modified gravities. These theories alter the dynamics of spacetime such that

1717-435: A universe which contracts slightly will continue contracting. According to Einstein, "empty space" can possess its own energy. Because this energy is a property of space itself, it would not be diluted as space expands. As more space comes into existence, more of this energy-of-space would appear, thereby causing accelerated expansion. These sorts of disturbances are inevitable, due to the uneven distribution of matter throughout

1818-411: Is a push that repels the positive mass from the negative mass, and a pull that attracts the negative mass towards the positive one at the same time. Hence Bondi pointed out that two objects of equal and opposite mass would produce a constant acceleration of the system towards the positive-mass object, an effect called "runaway motion" by Bonnor who disregarded its physical existence, stating: I regard

1919-520: Is always positive, summing with the expectation value of the potential energy to yield the energy eigenvalue. For wavefunctions of particles with zero rest mass (such as photons ), this means that any evanescent portions of the wavefunction would be associated with a local negative mass–energy. However, the Schrödinger equation does not apply to massless particles; instead the Klein–Gordon equation

2020-401: Is called "cosmological coupling" because the black holes couple to a cosmological requirement. Other astrophysicists are skeptical, with a variety of papers claiming that the theory fails to explain other observations. The evidence for dark energy is heavily dependent on the theory of general relativity. Therefore, it is conceivable that a modification to general relativity also eliminates

2121-414: Is close to flat . For the shape of the universe to be flat, the mass–energy density of the universe must be equal to the critical density . The total amount of matter in the universe (including baryons and dark matter ), as measured from the cosmic microwave background spectrum, accounts for only about 30% of the critical density. This implies the existence of an additional form of energy to account for

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2222-452: Is in fact possible to obtain the required deformation through the introduction of the energy–momentum of a perfect fluid. Although no particles are known to have negative mass, physicists (primarily Hermann Bondi in 1957, William B. Bonnor in 1964 and 1989, then Robert L. Forward ) have been able to describe some of the anticipated properties such particles may have. Assuming that all three concepts of mass are equivalent according to

2323-478: Is known. This allows the object's distance to be measured from its actual observed brightness, or apparent magnitude . Type Ia supernovae are the best-known standard candles across cosmological distances because of their extreme and consistent luminosity . Recent observations of supernovae are consistent with a universe made up 71.3% of dark energy and 27.4% of a combination of dark matter and baryonic matter . The theory of large-scale structure , which governs

2424-409: Is measured as a function of cosmological redshift . OHD directly tracks the expansion history of the universe by taking passively evolving early-type galaxies as "cosmic chronometers". From this point, this approach provides standard clocks in the universe. The core of this idea is the measurement of the differential age evolution as a function of redshift of these cosmic chronometers. Thus, it provides

2525-468: Is measured to be negative. This may occur due to a region of space in which the sum of the three normal stress components (pressure on each of three axes) of the Einstein stress–energy tensor is larger in magnitude than the mass density. All of these are violations of one or another variant of the positive energy condition of Einstein's general theory of relativity; however, the positive energy condition

2626-434: Is minimally coupled to gravity, and does not feature higher order operations in its Lagrangian. No evidence of quintessence is yet available, nor has it been ruled out. It generally predicts a slightly slower acceleration of the expansion of the universe than the cosmological constant. Some scientists think that the best evidence for quintessence would come from violations of Einstein's equivalence principle and variation of

2727-417: Is more hypothetical than that of dark matter, and many things about it remain in the realm of speculation. Dark energy is thought to be very homogeneous and not dense , and is not known to interact through any of the fundamental forces other than gravity . Since it is rarefied and un-massive—roughly 10  kg/m —it is unlikely to be detectable in laboratory experiments. The reason dark energy can have such

2828-606: Is not a required condition for the mathematical consistency of the theory. In considering negative mass, it is important to consider which of these concepts of mass are negative. Ever since Newton first formulated his theory of gravity , there have been at least three conceptually distinct quantities called mass : The law of conservation of momentum requires that active and passive gravitational mass be identical. Einstein's equivalence principle postulates that inertial mass must equal passive gravitational mass, and all experimental evidence to date has found these are, indeed, always

2929-500: Is possible to investigate the effect of dark energy in the history of the universe, and constrain parameters of the equation of state of dark energy. To that end, several models have been proposed. One of the most popular models is the Chevallier–Polarski–Linder model (CPL). Some other common models are Barboza & Alcaniz (2008), Jassal et al. (2005), Wetterich. (2004), and Oztas et al. (2018). Researchers using

3030-465: Is required. The mechanical model giving rise to the negative effective mass effect is depicted in Figure 1 . A core with mass m 2 {\displaystyle m_{2}} is connected internally through the spring with constant k 2 {\displaystyle k_{2}}  to a shell with mass m 1 {\displaystyle m_{1}} . The system

3131-400: Is sometimes labeled "gravitational repulsion". In standard cosmology, there are three components of the universe: matter, radiation, and dark energy. This matter is anything whose energy density scales with the inverse cube of the scale factor, i.e., ρ  ∝  a , while radiation is anything whose energy density scales to the inverse fourth power of the scale factor ( ρ  ∝ 

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3232-416: Is subjected to the external sinusoidal force F ( t ) = F 0 sin ⁡ ω t {\displaystyle F(t)=F_{0}\sin \omega t} . If we solve the equations of motion for the masses m 1 {\displaystyle m_{1}}  and m 2 {\displaystyle m_{2}}  and replace the entire system with

3333-462: Is that it is an intrinsic, fundamental energy of space. This is the cosmological constant, usually represented by the Greek letter Λ (Lambda, hence the name Lambda-CDM model ). Since energy and mass are related according to the equation E = mc , Einstein's theory of general relativity predicts that this energy will have a gravitational effect. It is sometimes called vacuum energy because it

3434-525: Is the stress–energy tensor , which contains both the energy (or matter) density of a substance and its pressure. In the Friedmann–Lemaître–Robertson–Walker metric , it can be shown that a strong constant negative pressure ( i.e., tension) in all the universe causes an acceleration in the expansion if the universe is already expanding, or a deceleration in contraction if the universe is already contracting. This accelerating expansion effect

3535-415: Is the energy density of empty space – of vacuum . A major outstanding problem is that the same quantum field theories predict a huge cosmological constant , about 120  orders of magnitude too large. This would need to be almost, but not exactly, cancelled by an equally large term of the opposite sign. Some supersymmetric theories require a cosmological constant that is exactly zero. Also, it

3636-414: Is thought to have completely ended when the universe was just a fraction of a second old. It is unclear what relation, if any, exists between dark energy and inflation. Even after inflationary models became accepted, the cosmological constant was thought to be irrelevant to the current universe. Nearly all inflation models predict that the total (matter+energy) density of the universe should be very close to

3737-399: Is unknown whether there is a metastable vacuum state in string theory with a positive cosmological constant, and it has been conjectured by Ulf Danielsson et al. that no such state exists. This conjecture would not rule out other models of dark energy, such as quintessence, that could be compatible with string theory. In quintessence models of dark energy, the observed acceleration of

3838-580: The Australian Astronomical Observatory scanned the galaxies to determine their redshift. Then, by exploiting the fact that baryon acoustic oscillations have left voids regularly of ≈150 Mpc diameter, surrounded by the galaxies, the voids were used as standard rulers to estimate distances to galaxies as far as 2,000 Mpc (redshift 0.6), allowing for accurate estimate of the speeds of galaxies from their redshift and distance. The data confirmed cosmic acceleration up to half of

3939-647: The Dark Energy Spectroscopic Instrument (DESI) to make the largest 3-D map of the universe as of 2024, have obtained an expansion history that has greater than 1% precision. From this level of detail, DESI Director Michael Levi stated: We're also seeing some potentially interesting differences that could indicate that dark energy is evolving over time. Those may or may not go away with more data, so we're excited to start analyzing our three-year dataset soon. Some alternatives to dark energy, such as inhomogeneous cosmology , aim to explain

4040-534: The Friedmann-Robertson-Walker metric (which describes the isotropic and homogeneous universe that is the basic assumption of modern cosmology), then one finds that black holes gain mass as the universe expands. The rate is measured to be ∝ a , where a is the scale factor . This particular rate means that the energy density of black holes remains constant over time, mimicking dark energy (see Dark_energy#Technical_definition ). The theory

4141-635: The Lambda-CDM model . Some people argue that the only indications for the existence of dark energy are observations of distance measurements and their associated redshifts. Cosmic microwave background anisotropies and baryon acoustic oscillations serve only to demonstrate that distances to a given redshift are larger than would be expected from a "dusty" Friedmann–Lemaître universe and the local measured Hubble constant. Supernovae are useful for cosmology because they are excellent standard candles across cosmological distances. They allow researchers to measure

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4242-715: The Planck spacecraft and the Supernova Legacy Survey. First results from the SNLS reveal that the average behavior (i.e., equation of state) of dark energy behaves like Einstein's cosmological constant to a precision of 10%. Recent results from the Hubble Space Telescope Higher-Z Team indicate that dark energy has been present for at least 9 billion years and during the period preceding cosmic acceleration. The nature of dark energy

4343-582: The Standard Model , already included negative solutions. The Standard Model is a generalization of quantum electrodynamics (QED) and negative mass is already built into the theory. Morris , Thorne and Yurtsever pointed out that the quantum mechanics of the Casimir effect can be used to produce a locally energy-negative region of space–time. In this article, and subsequent work by others, they showed that negative matter could be used to stabilize

4444-461: The University of Oxford proposed a " dark fluid " theory, related, in part, to notions of gravitationally repulsive negative masses, presented earlier by Albert Einstein , that may help better understand, in a testable manner, the considerable amounts of unknown dark matter and dark energy in the cosmos . Negative mass is any region of space in which for some observers the mass density

4545-436: The critical density . During the 1980s, most cosmological research focused on models with critical density in matter only, usually 95% cold dark matter (CDM) and 5% ordinary matter (baryons). These models were found to be successful at forming realistic galaxies and clusters, but some problems appeared in the late 1980s: in particular, the model required a value for the Hubble constant lower than preferred by observations, and

4646-442: The dominant energy condition . This is because if the energy and momentum satisfies the dominant energy condition within a spacetime that is asymptotically flat, which would be the case of smoothing out the singular negative mass Schwarzschild solution, then it must satisfy the positive energy theorem , i.e. its ADM mass must be positive, which is of course not the case. However, it was noticed by Belletête and Paranjape that since

4747-471: The equation of state had possibly crossed the cosmological constant boundary (w = −1) from above to below. A no-go theorem has been proved that this scenario requires models with at least two types of quintessence. This scenario is the so-called Quintom scenario . Some special cases of quintessence are phantom energy , in which the energy density of quintessence actually increases with time, and k-essence (short for kinetic quintessence) which has

4848-548: The equivalence principle , the gravitational interactions between masses of arbitrary sign can be explored, based on the Newtonian approximation of the Einstein field equations . The interaction laws are then: For two positive masses, nothing changes and there is a gravitational pull on each other causing an attraction. Two negative masses would repel because of their negative inertial masses. For different signs however, there

4949-400: The expansion of the universe are required to understand how the expansion rate changes over time and space. In general relativity, the evolution of the expansion rate is estimated from the curvature of the universe and the cosmological equation of state (the relationship between temperature, pressure, and combined matter, energy, and vacuum energy density for any region of space). Measuring

5050-416: The universe's expansion is accelerating . Prior to this observation, scientists thought that the gravitational attraction of matter and energy in the universe would cause the universe's expansion to slow over time. Since the discovery of accelerating expansion, several independent lines of evidence have been discovered that support the existence of dark energy. The exact nature of dark energy remains

5151-540: The Lambda-CDM model then became the leading model. Soon after, dark energy was supported by independent observations: in 2000, the BOOMERanG and Maxima cosmic microwave background experiments observed the first acoustic peak in the cosmic microwave background, showing that the total (matter+energy) density is close to 100% of critical density. Then in 2001, the 2dF Galaxy Redshift Survey gave strong evidence that

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5252-473: The Universe began when it did. If acceleration began earlier in the universe, structures such as galaxies would never have had time to form, and life, at least as we know it, would never have had a chance to exist. Proponents of the anthropic principle view this as support for their arguments. However, many models of quintessence have a so-called "tracker" behavior, which solves this problem. In these models,

5353-464: The accelerated cosmic expansion and study properties of dark energy. Dark energy's status as a hypothetical force with unknown properties makes it an active target of research. The problem is attacked from a variety of angles, such as modifying the prevailing theory of gravity (general relativity), attempting to pin down the properties of dark energy, and finding alternative ways to explain the observational data. The simplest explanation for dark energy

5454-411: The age of the universe (7 billion years) and constrain its inhomogeneity to 1 part in 10. This provides a confirmation to cosmic acceleration independent of supernovae. The existence of dark energy, in whatever form, is needed to reconcile the measured geometry of space with the total amount of matter in the universe. Measurements of cosmic microwave background anisotropies indicate that the universe

5555-418: The competing theories successfully explain observations to the same level of precision as standard dark energy. Cosmologists estimate that the acceleration began roughly 5 billion years ago. Before that, it is thought that the expansion was decelerating, due to the attractive influence of matter. The density of dark matter in an expanding universe decreases more quickly than dark energy, and eventually

5656-447: The conservation laws remain unbroken. This is true even when relativistic effects are considered, so long as inertial mass, not rest mass, is equal to gravitational mass. This behaviour can produce bizarre results: for instance, a gas containing a mixture of positive and negative matter particles will have the positive matter portion increase in temperature without bound. However, the negative matter portion gains negative temperature at

5757-508: The cosmic microwave background aligned with vast supervoids and superclusters. This so-called late-time Integrated Sachs–Wolfe effect (ISW) is a direct signal of dark energy in a flat universe. It was reported at high significance in 2008 by Ho et al. and Giannantonio et al. A new approach to test evidence of dark energy through observational Hubble constant data (OHD), also known as cosmic chronometers, has gained significant attention in recent years. The Hubble constant, H ( z ),

5858-437: The dark energy dominates. Specifically, when the volume of the universe doubles, the density of dark matter is halved, but the density of dark energy is nearly unchanged (it is exactly constant in the case of a cosmological constant). Projections into the future can differ radically for different models of dark energy. For a cosmological constant, or any other model that predicts that the acceleration will continue indefinitely,

5959-405: The elastic spring k 2 = ω p 2 m 2 {\displaystyle k_{2}=\omega _{p}^{2}m_{2}} , where ω p {\displaystyle \omega _{p}}  is the plasma frequency. Thus, the metallic particle vibrated with the external frequency ω is described by the effective mass which is negative when

6060-446: The equation of state for dark energy is one of the biggest efforts in observational cosmology today. Adding the cosmological constant to cosmology's standard FLRW metric leads to the Lambda-CDM model, which has been referred to as the " standard model of cosmology " because of its precise agreement with observations. As of 2013, the Lambda-CDM model is consistent with a series of increasingly rigorous cosmological observations, including

6161-490: The existence of negative matter. Some bimetric theories of the universe propose that two parallel universes with an opposite arrow of time may exist instead of one, linked together by the Big Bang and interacting only through gravitation . The universe is then described as a manifold associated to two Riemannian metrics (one with positive mass matter and the other with negative mass matter). According to group theory,

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6262-444: The expansion history of the universe by looking at the relationship between the distance to an object and its redshift , which gives how fast it is receding from us. The relationship is roughly linear, according to Hubble's law . It is relatively easy to measure redshift, but finding the distance to an object is more difficult. Usually, astronomers use standard candles: objects for which the intrinsic brightness, or absolute magnitude ,

6363-538: The expansion of the universe is accelerating . The 2011 Nobel Prize in Physics was awarded to Saul Perlmutter , Brian P. Schmidt , and Adam G. Riess for their leadership in the discovery. Since then, these observations have been corroborated by several independent sources. Measurements of the cosmic microwave background , gravitational lensing , and the large-scale structure of the cosmos , as well as improved measurements of supernovae, have been consistent with

6464-451: The explanation of dark matter , dark energy , cosmic inflation and an accelerating universe . The gravitational interaction of antimatter with matter has been observed by physicists. As was the consensus among physicists previously, it was experimentally confirmed that gravity attracts both matter and antimatter at the same rate within experimental error. Bubble chamber experiments provide further evidence that antiparticles have

6565-477: The formation of structures in the universe ( stars , quasars , galaxies and galaxy groups and clusters ), also suggests that the density of matter in the universe is only 30% of the critical density. A 2011 survey, the WiggleZ galaxy survey of more than 200,000 galaxies, provided further evidence towards the existence of dark energy, although the exact physics behind it remains unknown. The WiggleZ survey from

6666-441: The frequency ω {\displaystyle \omega }  approaches ω 0 {\displaystyle \omega _{0}}  from above the effective mass m eff {\displaystyle m_{\text{eff}}}  will be negative. The negative effective mass (density) becomes also possible based on the electro-mechanical coupling exploiting plasma oscillations of

6767-417: The fundamental constants in space or time. Scalar fields are predicted by the Standard Model of particle physics and string theory , but an analogous problem to the cosmological constant problem (or the problem of constructing models of cosmological inflation ) occurs: renormalization theory predicts that scalar fields should acquire large masses. The coincidence problem asks why the acceleration of

6868-413: The interstellar space'. The mechanism was an example of fine-tuning , and it was later realized that Einstein's static universe would not be stable: local inhomogeneities would ultimately lead to either the runaway expansion or contraction of the universe. The equilibrium is unstable: if the universe expands slightly, then the expansion releases vacuum energy, which causes yet more expansion. Likewise,

6969-471: The matter density is around 30% of critical. The large difference between these two supports a smooth component of dark energy making up the difference. Much more precise measurements from WMAP in 2003–2010 have continued to support the standard model and give more accurate measurements of the key parameters. The term "dark energy", echoing Fritz Zwicky 's "dark matter" from the 1930s, was coined by Michael S. Turner in 1998. High-precision measurements of

7070-418: The matter of the conjugated metric would appear to the matter of the other metric as having opposite mass and arrow of time (though its proper time would remain positive). The coupled metrics have their own geodesics and are solutions of two coupled field equations. The negative matter of the coupled metric, interacting with the matter of the other metric via gravity, could be an alternative candidate for

7171-694: The model under-predicted observations of large-scale galaxy clustering. These difficulties became stronger after the discovery of anisotropy in the cosmic microwave background by the COBE spacecraft in 1992, and several modified CDM models came under active study through the mid-1990s: these included the Lambda-CDM model and a mixed cold/hot dark matter model. The first direct evidence for dark energy came from supernova observations in 1998 of accelerated expansion in Riess et al. and in Perlmutter et al. , and

7272-428: The modified dynamics stems to what have been assigned to the presence of dark energy and dark matter. Dark energy could in principle interact not only with the rest of the dark sector, but also with ordinary matter. However, cosmology alone is not sufficient to effectively constrain the strength of the coupling between dark energy and baryons, so that other indirect techniques or laboratory searches have to be adopted. It

7373-407: The momentum of the system remains zero if they both travel together and accelerate together, no matter what their speed: And equivalently for the kinetic energy : However, this is perhaps not exactly valid if the energy in the gravitational field is taken into account. Forward extended Bondi's analysis to additional cases, and showed that even if the two masses m and m are not the same,

7474-475: The need for dark energy. There are many such theories, and research is ongoing. The measurement of the speed of gravity in the first gravitational wave measured by non-gravitational means ( GW170817 ) ruled out many modified gravity theories as explanations to dark energy. Astrophysicist Ethan Siegel states that, while such alternatives gain mainstream press coverage, almost all professional astrophysicists are confident that dark energy exists and that none of

7575-481: The observational data by a more refined use of established theories. In this scenario, dark energy does not actually exist, and is merely a measurement artifact. For example, if we are located in an emptier-than-average region of space, the observed cosmic expansion rate could be mistaken for a variation in time, or acceleration. A different approach uses a cosmological extension of the equivalence principle to show how space might appear to be expanding more rapidly in

7676-415: The only configuration of such particles that has zero momentum (both particles moving with the same velocity in the same direction) does not produce a collision, such interactions would leave a surplus of momentum. In general relativity , the universe is described as a Riemannian manifold associated to a metric tensor solution of Einstein's field equations. In such a framework, the runaway motion forbids

7777-521: The original paper. Another study questioning the essential assumption that the luminosity of Type Ia supernovae does not vary with stellar population age was also swiftly rebutted by other cosmologists. This theory was formulated by researchers of the University of Hawaiʻi at Mānoa in February 2023. The idea is that if one requires the Kerr metric (which describes rotating black holes) to asymptote to

7878-438: The positive energy theorem does not apply to asymptotic de Sitter spacetime, it would actually be possible to smooth out, with energy–momentum that does satisfy the dominant energy condition, the singularity of the corresponding exact solution of negative mass Schwarzschild–de Sitter, which is the singular, exact solution of Einstein's equations with cosmological constant. In a subsequent article, Mbarek and Paranjape showed that it

7979-456: The problem remains unresolved. Independently of its actual nature, dark energy would need to have a strong negative pressure to explain the observed acceleration of the expansion of the universe . According to general relativity, the pressure within a substance contributes to its gravitational attraction for other objects just as its mass density does. This happens because the physical quantity that causes matter to generate gravitational effects

8080-492: The question of what kind of energy and momentum would be necessary to describe non-singular negative mass. Indeed, the Schwarzschild solution for negative mass parameter has a naked singularity at a fixed spatial position. The question that immediately comes up is, would it not be possible to smooth out the singularity with some kind of negative mass density. The answer is yes, but not with energy and momentum that satisfies

8181-400: The quintessence field has a density which closely tracks (but is less than) the radiation density until matter–radiation equality , which triggers quintessence to start behaving as dark energy, eventually dominating the universe. This naturally sets the low energy scale of the dark energy. In 2004, when scientists fit the evolution of dark energy with the cosmological data, they found that

8282-484: The ratios differ only in sign; but this does not indicate whether it is the charge or the inertial mass that is inverted. However, particle–antiparticle pairs are observed to electrically attract one another. This behavior implies that both have positive inertial mass and opposite charges; if the reverse were true, then the particle with positive inertial mass would be repelled from its antiparticle partner. In 1928, Paul Dirac 's theory of elementary particles , now part of

8383-557: The remaining 70%. The Wilkinson Microwave Anisotropy Probe (WMAP) spacecraft seven-year analysis estimated a universe made up of 72.8% dark energy, 22.7% dark matter, and 4.5% ordinary matter. Work done in 2013 based on the Planck spacecraft observations of the cosmic microwave background gave a more accurate estimate of 68.3% dark energy, 26.8% dark matter, and 4.9% ordinary matter. Accelerated cosmic expansion causes gravitational potential wells and hills to flatten as photons pass through them, producing cold spots and hot spots on

8484-466: The runaway (or self-accelerating) motion […] so preposterous that I prefer to rule it out by supposing that inertial mass is all positive or all negative. Such a couple of objects would accelerate without limit (except a relativistic one); however, the total mass, momentum and energy of the system would remain zero. This behavior is completely inconsistent with a common-sense approach and the expected behavior of "normal" matter. Thomas Gold even hinted that

8585-458: The runaway linear motion could be used in a perpetual motion machine if converted to circular motion: What happens if one attaches a negative and positive mass pair to the rim of a wheel? This is incompatible with general relativity, for the device gets more massive. But Forward showed that the phenomenon is mathematically consistent and introduces no violation of conservation laws . If the masses are equal in magnitude but opposite in sign, then

8686-401: The same inertial mass as their normal counterparts. In these experiments, the chamber is subjected to a constant magnetic field that causes charged particles to travel in helical paths, the radius and direction of which correspond to the ratio of electric charge to inertial mass. Particle–antiparticle pairs are seen to travel in helices with opposite directions but identical radii, implying that

8787-403: The same rate, again balancing out. Geoffrey A. Landis pointed out other implications of Forward's analysis, including noting that although negative mass particles would repel each other gravitationally, the electrostatic force would be attractive for like charges and repulsive for opposite charges. Forward used the properties of negative-mass matter to create the concept of diametric drive,

8888-402: The same. In most analyses of negative mass, it is assumed that the equivalence principle and conservation of momentum continue to apply without using any matter in the process, and therefore all three forms of mass are still the same, leading to the study of "negative mass". But the equivalence principle is simply an observational fact, and is not necessarily valid. If such a distinction is made,

8989-417: The scale factor is caused by the potential energy of a dynamical field , referred to as quintessence field. Quintessence differs from the cosmological constant in that it can vary in space and time. In order for it not to clump and form structure like matter, the field must be very light so that it has a large Compton wavelength . In the simplest scenarios, the quintessence field has a canonical kinetic term,

9090-407: The section Dark energy § Theories of dark energy ). The " cosmological constant " is a constant term that can be added to Einstein field equations of general relativity . If considered as a "source term" in the field equation, it can be viewed as equivalent to the mass of empty space (which conceptually could be either positive or negative), or " vacuum energy ". The cosmological constant

9191-450: The speed of light for any massive object (see Uses of the proper distance for a discussion of the subtleties of defining any notion of relative velocity in cosmology). Because the Hubble parameter is decreasing with time, there can actually be cases where a galaxy that is receding from us faster than light does manage to emit a signal which reaches us eventually. Negative mass In December 2018, astrophysicist Jamie Farnes from

9292-428: The statistical methods employed were flawed. A laboratory direct detection attempt failed to detect any force associated with dark energy. Observational skepticism explanations of dark energy have generally not gained much traction among cosmologists. For example, a paper that suggested the anisotropy of the local Universe has been misrepresented as dark energy was quickly countered by another paper claiming errors in

9393-427: The total energy in the present-day observable universe while dark matter and ordinary (baryonic) matter contribute 26% and 5%, respectively, and other components such as neutrinos and photons are nearly negligible. Dark energy's density is very low: 7 × 10  g/cm ( 6 × 10  J/m in mass-energy ), much less than the density of ordinary matter or dark matter within galaxies. However, it dominates

9494-458: The ultimate result will be that galaxies outside the Local Group will have a line-of-sight velocity that continually increases with time, eventually far exceeding the speed of light. This is not a violation of special relativity because the notion of "velocity" used here is different from that of velocity in a local inertial frame of reference , which is still constrained to be less than

9595-403: The universe's mass–energy content because it is uniform across space. The first observational evidence for dark energy's existence came from measurements of supernovae . Type Ia supernovae have constant luminosity, which means that they can be used as accurate distance measures. Comparing this distance to the redshift (which measures the speed at which the supernova is receding) shows that

9696-438: The universe. Further, observations made by Edwin Hubble in 1929 showed that the universe appears to be expanding and is not static. Einstein reportedly referred to his failure to predict the idea of a dynamic universe, in contrast to a static universe, as his greatest blunder. Alan Guth and Alexei Starobinsky proposed in 1980 that a negative pressure field, similar in concept to dark energy, could drive cosmic inflation in

9797-438: The vacuum energy should exert a gravitational force. Hence, the vacuum energy is expected to contribute to the cosmological constant , which in turn impinges on the accelerated expansion of the universe . However, the cosmological constant problem asserts that there is a huge disagreement between the observed values of vacuum energy density and the theoretical large value of zero-point energy obtained by quantum field theory ;

9898-476: The very early universe. Inflation postulates that some repulsive force, qualitatively similar to dark energy, resulted in an enormous and exponential expansion of the universe slightly after the Big Bang . Such expansion is an essential feature of most current models of the Big Bang. However, inflation must have occurred at a much higher (negative) energy density than the dark energy we observe today, and inflation

9999-409: The voids surrounding our local cluster. While weak, such effects considered cumulatively over billions of years could become significant, creating the illusion of cosmic acceleration, and making it appear as if we live in a Hubble bubble . Yet other possibilities are that the accelerated expansion of the universe is an illusion caused by the relative motion of us to the rest of the universe, or that

10100-532: Was briefly theorized in the early 2020s that excess observed in the XENON1T detector in Italy may have been caused by a chameleon model of dark energy, but further experiments disproved this possibility. The density of dark energy might have varied in time during the history of the universe. Modern observational data allows us to estimate the present density of dark energy. Using baryon acoustic oscillations , it

10201-419: Was first proposed by Einstein as a mechanism to obtain a solution to the gravitational field equation that would lead to a static universe, effectively using dark energy to balance gravity. Einstein gave the cosmological constant the symbol Λ (capital lambda). Einstein stated that the cosmological constant required that 'empty space takes the role of gravitating negative masses which are distributed all over

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