Where does cosmic radiation matter and light come from? Physicists have had ideas about this since the early 1960s and these ideas are not unrelated to black hole radiation. Some of the leads derived from quantum field theory in curved space-time have now been tested for cosmology with a Bose-Einstein capacitor in a laboratory on Earth.

The theory of big bangbig bang The 21st is a solid record of opening^{e} century But by the Big Bang theory, it means that the observable universe, not all that exists, was a much denser and hotter state without atoms and atoms. StarsStarsLet’s say 10 to 20 billion years ago. So our visible universe is only a part universeuniverse A day in infinite space and time collapsed gravitationally, like a star giving birth to a black hole, before jumping back into an expansion phase after reaching a finite but finite density.

However, one may ask the question of its origin mattermatter And the light of cosmic radiation that we observe all around us. Developments in Quantum MechanicsQuantum Mechanics And in particular quantum field theory from 1925 to 1935 made it possible to imagine processes that not only produce quanta of light but also quanta of matter. ElectronsElectrons Atoms and QuarksQuarks creating ProtonsProtons And this NeutronsNeutrons Being relatives then PhotonsPhotons.

These processes can be used in part CosmologyCosmology Einstein’s relativism to explain the origin of matter?

## Creation of matter through dynamic space-times

The answer is yes and paradoxically, these are actually processes described by a quantum field theory space timespace time The unscaled curve, as we have known it since the 1960s Stephen HawkingStephen Hawking It was not until the beginning of the next decade that this theory was applied to detect the production of particles by Black holesBlack holes Now the topic of Hawking radiation bears his name.

We owe the discovery of the quantum formation of particles in cosmology to his thesis in 1962, under the direction of the famous Sidney Coleman, who began working on this question.See the Futura article about Jean-Pierre Luminet’s recent book on black holes) the physicist in question is called Leonard Parker And you can find out *arXiv, *A fascinating history, in the form of an interview Quantum theory of particles in curved space-time. For example, we know that the first quantum calculations of these effects date back to 1939 and we owe them. Erwin Schrödinger !

Leonard Parker also explains that after completing his thesis, he spoke with Fred Hoyle about his discovery of the production of particles by expanding the spacetimes described by a family of famous solutions. EquationsEquations Said about Einstein Friedman-Lemaître-Robertson-Walker (FLRW) cosmological models IsotropicIsotropic and homogeneous (so appear identical to any observer everywhere and looking in different directions depending on the average particle density SpeedSpeed expansion at some point in the history of the observable universe).

Fred Hoyle, at the time Britain’s greatest cosmological theorist Stephen Hawking’s star was beginning to shine, became known as co-author in 1948 with Herman Bondy and Thomas Gould. Standard cosmological modelA model that refutes Lemaitre and Gamow’s big bang theory.

Hoyle, Bondi, and Gold proposed this model, which dominated cosmology before its discovery. QuasarsQuasars And above all from fossil radiation, the cosmos was infinite in time and space, yet paradoxically expanding. Since no matter where or what time an observer makes measurements, he will always see the same things on average without evolution, so it is perfectly uniform in space and time. GalaxiesGalaxies Or the thing is really noticeable.

But for that, Hoyle must have assumed that continuous creation of matter must occur, leading to an equally continuous birth of galaxies. Without this assumption, the universe would dilute itself with further expansion.

Hoyle developed some equations to account for some aspects of the formation of this material, but they were more or less basic. Parker’s work gave a more accurate description and unfortunately, as he explained to Hoyle, did not allow him to create enough material with a measured expansion rate. But everything changed during a very rapid primitive expansion phase.

Quantum field theory in curved spacetime developed rapidly in the 1970s under the inspiration of many researchers in England and Russia for cosmology, particularly due to the discovery of Hawking radiation. A second impetus would come with the discovery of the theory of cosmological inflation in the early 1980s, which would make it possible to construct a scenario of the formation of matter that makes up the observable universe today and lead to the prediction of production. Attraction, in generalGravitational wavesGravitational wavesIn inflationary theory by the exponentially exponentially expanding phase of the universe’s early history.

These gravitational waves may have left traces in fossil radiation that can be seen today.

Can we test the mechanisms of particle production due to the expansion of the universe proposed by Parker and his colleagues?

## Spacetime simulators with Bose-Einstein condensates

Directly, it is not known, but as with indirect tests of Hawking radiation, Canadian physicist William Unrue, who discovered the radiative cousin of black holes, showed the “Unrue effect” in the early 1980s. The equations of quantum field theory in curved spacetime had analogies with phenomena in fluids, so one could test ideas and calculations in the laboratory that could not actually reproduce the formation of particles in relativistic spacetime. .

In fact, for more than a decade, we have actually obtained in the laboratory, particularly so-called sonic black holes, Not only analogies of Hawking radiation ButThe Unrue effect. Famous examples have been obtained in Bose-Einstein capacitors. So we wouldn’t be surprised to see the latest release *nature,* and can be found freely *arXiv,* Precisely heralds a breakthrough in the field that allows us to investigate the formation of particles in cosmology.

The article talks about the work done Markus Oberthaler of the University of Heidelberg, Germany, with his colleagues Started by getting about 20,000 ultracold atoms PotassiumPotassium 39 uses LasersLasers to slow their speed and reduce their temperature to about 60 nanokelvins, or 60 billionths of a degree KelvinKelvin Above absolute zero.

These atoms then a phase transitionphase transition This makes them behave like a quantum wave and more precisely A Bose-Einstein capacitor. This ensemble of atoms can be manipulated to produce processes described by equations analogous to those governing the creation of quantum particles through the curved spacetime of the expanding FLRW family, more precisely a spacetime infinity. Kind of hyperbolic to use the phrase PhysicistsPhysicists Relatives.

Of course, the BE capacitor is not infinite, but a part of it is described by what is called the relevant equations Poincaré disc, i.e. the set of points on a disk by a mathematical transformation with points in space with a hyperbolic geometry. So there is a kind of dictionary between the two spaces, which allows us to accurately translate quantum field theory to quantum theory in hyperbolic space. Sound wavesSound waves Quantification of photons with relatives, Phonons.

In doing so, the researchers have performed the first experiment using ultracold atoms to simulate a curved and expanding universe. Quantum acoustic waves in the BE capacitor reveal an analogue of the formation of particle pairs predicted by the work of Parker and his colleagues, strengthening confidence in the theory of quantum fields in curved spacetime.

As a bonus, we now have a laboratory to explore unknown effects of the equations of this theory, which we could not yet find in the equations through calculation and reasoning.