The Drake equation is closely related to the Fermi paradox in that Drake suggested that a large number of extraterrestrial civilizations would form, but that the lack of evidence of such civilizations ( the Fermi paradox ) suggests that technological civilizations tend to disappear rather quickly.

* Fermi paradox

The Fermi paradox ( or Fermi's paradox ) is the apparent contradiction between high estimates of the probability of the existence of extraterrestrial civilization and humanity's lack of contact with, or evidence for, such civilizations.

A more detailed examination of the implications of the topic began with a paper by Michael H. Hart in 1975, and it is sometimes referred to as the Fermi – Hart paradox.

There have been attempts to resolve the Fermi paradox by locating evidence of extraterrestrial civilizations, along with proposals that such life could exist without human knowledge.

Starting with Hart, a great deal of effort has gone into developing scientific theories about, and possible models of, extraterrestrial life, and the Fermi paradox has become a theoretical reference point in much of this work.

The emerging field of astrobiology has brought an interdisciplinary approach to the Fermi paradox and the question of extraterrestrial life.

The second cornerstone of the Fermi paradox is a rejoinder to the argument by scale: given intelligent life's ability to overcome scarcity, and its tendency to colonize new habitats, it seems likely that at least some civilizations would be technologically advanced, seek out new resources in space and then colonize first their own star system and subsequently the surrounding star systems.

The Fermi paradox can be asked in two ways.

While numerous theories and principles are related to the Fermi paradox, the most closely related is the Drake equation.

Frank Drake himself has commented that the Drake equation is unlikely to settle the Fermi paradox ; instead it is just a way of " organizing our ignorance " on the subject.

One obvious way to resolve the Fermi paradox would be to find conclusive evidence of extraterrestrial intelligence.

The other way astronomy might settle the Fermi paradox is through a search specifically dedicated to finding evidence of life.

The Fermi paradox can be stated more completely as follows:

The two books show at least one solution to the Fermi paradox, with electromagnetically noisy civilisations being snuffed out by the arrival of self-replicating machines designed to destroy any potential threat to their ( possibly long-dead ) creators.

The Prime Directive closely mirrors the zoo hypothesis explanation for the Fermi paradox.

Stephen Hawking once suggested that the absence of tourists from the future constitutes a strong argument against the existence of time travel — a variant of the Fermi paradox, with time travelers instead of alien visitors.

* Fermi paradox, typical example of a Fermi problem pertaining to extraterrestrial civilizations

# redirect Fermi paradox

One model that estimates the properties of an electron gas at absolute zero in metals is the Fermi gas.

The maximum energy that an electrons can have at absolute zero is called the Fermi energy.

The Fermi temperature is defined as this maximum energy divided by Boltzmann's constant, and is of the order of 80, 000 K for typical electron densities found in metals.

Note that the above formula is only applicable to classical ideal gases and not Bose – Einstein or Fermi gases.

Furthermore, it describes how the density of states is changed on entering the superconducting state, where there are no electronic states any more at the Fermi energy.

: Here N ( 0 ) is the electronic density of states at the Fermi energy.

Baryons are strongly interacting fermions — that is, they experience the strong nuclear force and are described by Fermi − Dirac statistics, which apply to all particles obeying the Pauli exclusion principle.

The green curve uses the general pressure law for an ideal Fermi gas, while the blue curve is for a non-relativistic ideal Fermi gas.

Fermi is widely regarded as one of the leading scientists of the 20th century, highly accomplished in both theory and experiment.

If this sounds like hyperbole, anything about Fermi is likely to sound like hyperbole ".

He also mused about a proposition which is now referred to as the " Fermi Paradox ".

* Fermi Court in Deep River, Ontario is named in his honor.

is: Enrico Fermi

In particle physics, a fermion ( a name coined by Paul Dirac from the surname of Enrico Fermi ) is any particle characterized by Fermi – Dirac statistics and following the Pauli exclusion principle ; fermions include all quarks and leptons, as well as any composite particle made of an odd number of these, such as all baryons and many atoms and nuclei.

In an informal discussion in 1950, the physicist Enrico Fermi questioned why, if a multitude of advanced extraterrestrial civilizations exists in the Milky Way galaxy, evidence such as spacecraft or probes is not seen.

There are important differences between the statistical behavior of bosons and fermions, which are described by Bose – Einstein statistics and Fermi – Dirac statistics respectively.

The equilibrium between electromagnetic forces and Pauli repulsion of electrons ( they are fermions obeying Fermi statistics ) is slightly violated resulting in a small returning force.

Where two regions with different Fermi levels are in contact, charge carriers will flow between the two regions until the Fermi level is aligned across the interface.

One can sum the probability over energies between E < sub > f </ sub > − eV and E < sub > f </ sub > to get the number of states available in this energy range per unit volume, thereby finding the local density of states ( LDOS ) near the Fermi level.

However, in semiconductors the position of the Fermi level is within the band gap, approximately half-way between the conduction band minimum and valence band maximum for intrinsic ( undoped ) semiconductors.

Which results in a relationship between the Fermi energy and the number of particles per volume ( when we replace L < sup > 2 </ sup > with V < sup > 2 / 3 </ sup >):

Thus, there is a one-to-one correspondence between the elementary excitations of a Fermi gas system and a Fermi liquid system.

The quadratic terms correspond to a sort of " mean-field " interaction between quasiparticles, which is parameterized by so-called Landau Fermi liquid parameters and determines the behaviour of density oscillations ( and spin-density oscillations ) in the Fermi liquid.

In two-dimensional systems, however, quasiparticles can be observed which obey statistics ranging continuously between Fermi – Dirac and Bose – Einstein statistics, as was first shown by Jon Magne Leinaas and Jan Myrheim of the University of Oslo in 1977.

Cooper showed that an arbitrarily small attraction between electrons in a metal can cause a paired state of electrons to have a lower energy than the Fermi energy, which implies that the pair is bound.

Remarkably, it could be said that there was a grain of truth in this idea, because it was later shown that the Pauli exclusion principle results in a " Fermi hole " of decreased repulsion between a pair of electrons with opposite spins in the same orbital.

However, picturing density of states to be filled to the Fermi energy helps scientists understand different behaviors between insulators, metals, and intrinsic and extrinsic semiconductors.

The work function of a material is the energy difference between the Fermi energy ( chemical equilibrium energy ) and the vacuum level ( where electron removal occurs ).

In 1940 he brokered a meeting between Fermi and the US Navy at which the prospect of an atomic bomb was raised with the military for the first time.

) At this point, the Fermi levels for the two metals are equal, and there is no voltage difference between them.

This explains the equivalence between parastatistics and the more familiar Bose – Einstein / Fermi – Dirac statistics.

It lies about half-way between the walled plains Fermi to the northeast and Milne to the southwest.

It lies within the southwestern interior floor of the huge walled plain Fermi, about midway between the basin midpoint and the southwest rim.

In theory, the maximum voltage generated by such a cell is simply the difference between the ( quasi -) Fermi level of the TiO < sub > 2 </ sub > and the redox potential of the electrolyte, about 0. 7 V under solar illumination conditions ( V < sub > oc </ sub >).

where is the Fermi distribution function, and are the density of states ( DOS ) in the sample and tip, respectively, and is the tunneling matrix element between the modified wavefunctions of the tip and the sample surface.