cosmology Cosmology () is a branch of physics and metaphysics dealing with the nature of the universe, the cosmos. The term ''cosmology'' was first used in English in 1656 in Thomas Blount's ''Glossographia'', with the meaning of "a speaking of the wo ...

, phantom dark energy is a hypothetical form of

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. It also slows the rate of structure format ...

. It possesses negative kinetic energy, and predicts expansion of the universe in excess of that predicted by a

cosmological constant In cosmology, the cosmological constant (usually denoted by the Greek capital letter lambda: ), alternatively called Einstein's cosmological constant, is a coefficient that Albert Einstein initially added to his field equations of general rel ...

, which leads to a

Big Rip In physical cosmology, the Big Rip is a hypothetical cosmological model concerning the ultimate fate of the universe, in which the matter of the universe, from stars and galaxies to atoms and subatomic particles, and even spacetime itself, is p ...

. The idea of phantom dark energy is often dismissed, as it would suggest that the

vacuum A vacuum (: vacuums or vacua) is space devoid of matter. The word is derived from the Latin adjective (neuter ) meaning "vacant" or "void". An approximation to such vacuum is a region with a gaseous pressure much less than atmospheric pressur ...

unstable In dynamical systems instability means that some of the outputs or internal state (controls), states increase with time, without bounds. Not all systems that are not Stability theory, stable are unstable; systems can also be marginal stability ...

with

negative mass In theoretical physics, negative mass is a hypothetical type of exotic matter whose mass is of opposite sign to the mass of normal matter, e.g. −1 kg. Such matter would violate one or more energy conditions and exhibit strange properties ...

particles bursting into existence. The concept is hence tied to emerging theories of a continuously created negative mass dark fluid, in which the

can vary as a function of time. It is a special type of quintessence. The term was coined by Robert R. Caldwell in 1999.

Equation of state

In cosmology, the

equation of state In physics and chemistry, an equation of state is a thermodynamic equation relating state variables, which describe the state of matter under a given set of physical conditions, such as pressure, volume, temperature, or internal energy. Most mo ...

of a

perfect fluid In physics, a perfect fluid or ideal fluid is a fluid that can be completely characterized by its rest frame mass density \rho_m and ''isotropic'' pressure . Real fluids are viscous ("sticky") and contain (and conduct) heat. Perfect fluids are id ...

is given by

p = w \rho,

where is the pressure, is the energy density and is the ratio between the two. For normal baryonic matter

w = 0

and for a cosmological constant

w = -1

. Phantom dark energy is defined as having

w <-1

Big Rip mechanism

The existence of phantom dark energy could cause the expansion of the universe to accelerate so quickly that a scenario known as the

, a possible end to the universe, occurs. The

expansion of the universe The expansion of the universe is the increase in proper length, distance between Gravitational binding energy, gravitationally unbound parts of the observable universe with time. It is an intrinsic and extrinsic properties (philosophy), intrins ...

reaches an infinite degree in finite time, causing expansion to accelerate without bounds. This acceleration necessarily passes the speed of light (since it involves expansion of the universe itself, not particles moving within it), causing more and more objects to leave our

observable universe The observable universe is a Ball (mathematics), spherical region of the universe consisting of all matter that can be observation, observed from Earth; the electromagnetic radiation from these astronomical object, objects has had time to reach t ...

faster than its expansion, as light and information emitted from distant stars and other cosmic sources cannot "catch up" with the expansion. As the observable universe expands, objects will be unable to interact with each other via fundamental forces, and eventually, the expansion will prevent any action of forces between any particles, even within atoms, "ripping apart" the universe, making distances between individual particles infinite. One application of phantom dark energy in 2007 was to a

cyclic model A cyclic model (or oscillating model) is any of several cosmological models in which the universe follows infinite, or indefinite, self-sustaining cycles. For example, the oscillating universe theory briefly considered by Albert Einstein in 1930 ...

of the universe, which reverses its expansion extremely shortly before the would-be Big Rip. This cyclic model can be more complicated if the mass–energy of every point in the universe is dense enough to collapse into black hole core substance that will bounce after reaching a maximum threshold of compression causing the next big bang (the overall scenario is highly unlikely).

Possible evidence

In 2025, the Dark Energy Spectroscopic Instrument (DESI) collaboration, published a survey on baryon acoustic oscillations. They found violations of the standard model of cosmology, the

Lambda-CDM model The Lambda-CDM, Lambda cold dark matter, or ΛCDM model is a mathematical model of the Big Bang theory with three major components: # a cosmological constant, denoted by lambda (Λ), associated with dark energy; # the postulated cold dark mat ...

, within 4

standard deviations In statistics, the standard deviation is a measure of the amount of variation of the values of a variable about its mean. A low standard deviation indicates that the values tend to be close to the mean (also called the expected value) of the ...

. They reported acceleration of the universe that was stronger in the past, suggesting the presence of phantom dark energy in the early universe.

Equation of state

Big Rip mechanism

Possible evidence

See also

References

Further reading