How was it when Dark Energy invaded the universe?

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Looking further and further away, we find that objects are moving away not only from us at apparently greater speeds, but that every distant galaxy, individual, has begun to accelerate, there are about 6 billion years. Two of the most distant quasars, illustrated in the box, also corroborate this picture.Illustration: NASA / CXC / M.Weiss; X-Ray: NASA / CXC / Univ. from Florence / G.Risaliti & amp; E.Lusso

When we observe the ultra-distant Universe, billions of light years away, we see it as well. At that time, the Universe was warmer, denser, and filled with smaller, younger, and less evolved galaxies. The light we see from afar in the history of our universe only comes to our eyes after traveling these vast cosmic distances, where it is stretched by the expanding fabric of the universe. space.

It is these early signals and how this light extends over longer wavelengths – that is, the red shift – as a function of distance, allows us to deduce how Universe has developed throughout its history. That's how we discovered that the Universe was not just expanding, but accelerating. This is how we discovered black energy and measured its properties. Our image of the universe will never be the same again. This is what the first dark energy looked like.

Our entire cosmic history is theoretically well understood, but only qualitatively. This is by confirming and revealing through observation various stages of the past of our universe that had to happen, such as during the formation of the first stars and galaxies and the expansion of the 39 universe over time, that we can truly understand our cosmos.Nicole Rager Fuller / National Science Foundation

If you were still alive at the time of the Big Bang and you could keep track of two different places, one would correspond to the place where the Milky Way is today and the first one. other to a distant and disconnected galaxy, what would happen? you see?

The answer would change over time. When the light arrived for the first time, you could see the Universe as it was at 380,000 years ago: when cosmic microwave background radiation came to you. Over time, molecular clouds formed and contracted, followed by star formation in a group of ancient nebulae, then fusion of star groups to form proto-galaxies. Over time, these proto-galaxies merged, gravitated and grew. They would eventually evolve to the galaxies we know best, while they were going through quiet periods punctuated with starburst shrapnel.

Galaxies comparable to the current Milky Way are numerous, but younger galaxies resembling the Milky Way are inherently smaller, bluer, more chaotic, and richer in gas than the galaxies we see today. For the first galaxies, this effect reaches its extreme, although the true "first galaxies" have yet to be discovered. This image also shows, from right to left, the evolution of galaxies in the universe.NASA and ESA

One of the things we do not usually talk about is what we would see with the redshift. One of the great properties of the Universe is that the laws of physics seem to be immutable and immutable over time. This means that the atoms absorb and emit light at very specific frequencies: identical frequencies everywhere and determined by the energy levels occupied by the electrons of the atom.

By identifying series of atomic absorption or emission lines corresponding to the same element at the same red shift, we can identify the downward shift observed by an object. By determining its distance from us, we can use the distance / redshift combination to reconstruct the history of the expanding Universe.

First seen by Vesto Slipher, the longer a galaxy is, on average, the faster it gets away from us. For years, this explanation has been belied out until Hubble's observations allow us to gather the elements: the universe was expanding.Vesto Slipher, (1917): Proc. Bitter. Phil Soc., 56, 403

In reality, we can only make observations at a given moment: today or when the light of all the distant objects of the Universe reaches us at last. But we can just as well imagine our hypothetical scenario.

What would we see if we could follow a single galaxy – including both its distance and its redshift, as we see from our point of view & nbsp; – throughout the history of the Universe?

The answer is perhaps a little counter-intuitive, but it is extremely illustrative and educational to illuminate not only what is dark energy, but also its impact on the expansion of the world. ;Universe.

Far-off galaxies, like those found in the cluster of Hercules galaxies, not only move towards the red and move away from us, but their apparent recession speed accelerates. Eventually, they reach a distance at which we can no longer send signals they will receive, and they can no longer send signals that will be received by us.ESO / INAF-VST / OmegaCAM. Acknowledgment: OmegaCen / Astro-WISE / Kapteyn Institute

In the early stages, the light that came first allowed you to combine two parameters: a relatively small distance from the distances we see today and a significant redshift from what we see today . The redshift is a speed of apparent recession, or the speed with which the object in question seems to move away from us.

In reality, it is not that the movement of the object causes the redshift, although the movement towards (blues shift) or away from (redshift) an observer can certainly cause this effect. Instead, it is the fact that the light passes through the structure of the space – and that the structure expands as the light moves – causing what appears to be a red shift.

As the fabric of the Universe expands, the wavelengths of any radiation present are also stretched. As a result, the Universe loses less energy and makes many high-energy processes that occur spontaneously in early life impossible at cooler times. It takes hundreds of thousands of years for the universe to cool enough for neutral atoms to form, and billions of years before the density of matter goes down. under the dark energy density.E. Siegel / Beyond the galaxy

Initially, the distances would be small and the red offsets would be large: we would deduce that this galaxy far away very quickly away from us.

But then, time goes on, and the distance and the speed seem to change in opposite directions.

Distances become bigger with time, as the Universe continues to grow. This removes all objects that are not gravitationally bound to each other, increasing the distance measured between them.
The rate of expansion of the Universe changes, and it varies according to the total density of matter and energy present in the Universe. Since a growing volume means a decreasing energy density, the rate of expansion decreases and the galaxy seems to move away from us at a slower and slower speed.

The light can be emitted at a particular wavelength, but the expansion of the universe will stretch as it moves. The light emitted in the ultraviolet will be fully transferred into the infrared if we consider a galaxy whose light arrives 13.4 billion years ago; the Lyman-alpha transition at 121.5 nanometers becomes infrared radiation at Hubble's instrumental boundaries.Larry McNish of RASC Calgary Center

This makes sense when one thinks of the expanding universe in the context of the Big Bang. There is a great cosmic race going on: between gravity, working to put everything back together, and the initial expansion rate, working to put everything in pieces. The race has been going on for 13.8 billion years and the Big Bang was the starting point.

Everything begins to move away from everything else, extremely quickly at first, while gravity works as hard as possible to put everything back in place. If there was too much matter in the universe, everything would only grow until one time, when the universe would reach a maximum size then the expansion would reverse. Eventually, the Universe would re-establish itself. On the other hand, if there was too little material, the expansion would continue forever, with the rate of expansion decreasing and apparent recession rates asymptoting to zero.

A graph of the apparent expansion rate (y-axis) versus distance (x-axis) corresponds to a universe that has developed more rapidly in the past, but where distant galaxies are accelerating today. In their recession. It is a modern version of Hubble's original work, which extends thousands of times farther than this one. Note the fact that the dots do not form a straight line, indicating the evolution of the rate of expansion over time. The fact that the Universe follows the curve that it does is indicative of the presence and late dominance of black energy.Ned Wright, based on the latest data from Betoule et al. (2014)

This last case corresponds exactly to what we would have seen for a long time: billions of years, in the case of our universe. An individual galaxy seems to be moving away from us at an incredibly fast rate, but its rate of recession then decreases with falling density of matter and radiation. Since it is the total energy density that determines the rate of expansion, and the rate of expansion that determines what we infer from the speed of recession, all this has a intuitive sense.

And then, 7.8 billion years after the Big Bang, things start to get weird. It turns out that the universe is not just filled with matter and radiation. Even adding neutrinos, black holes, dark matter and more is not everything. In addition to all this, we have dark energy: a form of energy inherent to the space itself. As the universe develops, black energy does not dilute; it remains at a constant density.

While matter (both normal and dark) and radiation become less dense as the Universe grows due to its increasing volume, dark energy is an inherent form of energy. to the space itself. When a new space is created in the expanding universe, the dark energy density remains constant.E. Siegel / Beyond the galaxy

After 7.8 billion years, the density of matter decreases enough for the effects of dark energy to begin to become significant. 7.8 billion years after the Big Bang, the black energy density will have reached half the density of matter, which is the critical value to be achieved to prevent a distant galaxy from slowing down from our point of view.

At this moment of cosmic history, 7.8 billion years after the Big Bang, every distant object of the Universe will seem to be moving away from us: it will continue to accelerate to the speed that he had previously. It will not accelerate or slow down, but will maintain a consistent apparent movement in its recession. This is a critical moment: the repulsive effects of black energy on the expansion of the Universe counteract exactly the attractive effects of the material.

The relative importance of different components of energy in the universe at different times of the past. Note that when dark energy reaches nearly 100% in the future, the Universe's energy density (and hence the rate of expansion) will remain arbitrarily constant and far apart over time. Due to dark energy, distant galaxies are already accelerating from us, their apparent speed of recession, since the dark energy density was half the total matter density, there are 6 billion d & rsquo; # 39; years.E. Siegel

But time does not stop there. Instead, it continues toward the front and the density of matter continues to decrease. Once the cosmic clock reaches 7.8 billion years, dark energy becomes more important than matter and radiation with respect to the rate of expansion. The distant galaxies may have reached their minimum recession speed at that time, but will then appear as accelerated again.

As time progresses, distant objects that are not linked to each other move further and further away from their point of view. At the time the universe reached 9.2 billion years ago, just as our solar system is being formed, the density of matter will have dropped below the dark energy density. At present, 13.8 billion years after the Big Bang, dark energy represents about 70% of the total energy of the Universe. All the while, distant galaxies will continue to accelerate, from our point of view, into their apparent recession.

The observable (yellow) and reachable (magenta) parts of the universe, which are what they are thanks to the expansion of space and energetic components of the universe . 97% of the galaxies in our observable universe are contained outside the magenta circle; they are inaccessible to us today, even in principle, although we can still see them in their past because of the properties of light and space-time.E. Siegel, based on the work of users of Wikimedia Commons Azcolvin 429 and Frédéric MICHEL

For 6 billion years, the expansion of the Universe is accelerating, which means that any distant galaxy we are watching seems to be moving away from us at an ever increasing speed . Once a galaxy has reached a distance of about 15 to 16 billion light years from us, it will seem to move away faster than the speed of light, which means that we will never be able to do anything to reach or contact her again. Since the Universe already has 46 billion light years of radius, it means that 97% of the galaxies in the universe are already out of reach forever.

For billions of years, the density of black energy would have been insignificant compared to the density of matter, which means that its effects would have been undetectable if we had found ourselves too early. In tens of billions of years, it will have pushed everything beyond our local group away from us; & nbsp; the merged remains of the local group will be the only remaining galaxy. It's only because we came at that time, in this golden cosmic time, that we can perceive what the universe is actually made of. Dark energy is real and dominates our universe since its 7.8 billion years. It will determine the fate of our universe from now on.

To learn more about the nature of the universe when:

These are the first signals, and the way in which this light extends over longer wavelengths – that is to say, shifted towards the red – as a function of distance, allows us to deduce how the Universe has developed throughout its history. That's how we discovered that the Universe was not just expanding, but accelerating. This is how we discovered black energy and measured its properties. Our image of the universe will never be the same again. This is what the first dark energy looked like.

If you were somehow alive at the time of the Big Bang and you could keep track of two different places – one of them would correspond to where the Milky Way today is located. ### 39; hui and the other to a distant and disconnected galaxy – what would you see? ?

Galaxies comparable to the current Milky Way are numerous, but younger galaxies resembling the Milky Way are inherently smaller, bluer, more chaotic, and richer in gas than the galaxies we see today. For the first galaxies, this effect is extreme, although the real "first galaxies" remain to be discovered. This image also shows, from right to left, the evolution of galaxies in the universe.NASA and ESA

By identifying series of atomic absorption or emission lines corresponding to the same element at the same red shift, we can identify the observed redshift of an object. By determining its distance from us, we can use the distance / redshift combination to reconstruct the history of the expanding Universe.

What would we see if we could follow a single galaxy – including both its distance and its redshift, as we see from our point of view – throughout the history of the galaxy? 39; universe?

In reality, it is not that the movement of the object causes the redshift, although the movement towards (blues shift) or away from (redshift) an observer can certainly cause this effect. Instead, it's the fact that light travels through the structure of the space – and that the structure expands as the light moves – which causes what appears to be a redshift.

Initially, the distances would be small and the red offsets would be large: we would deduce that this galaxy far away very quickly away from us.

But then, time goes on, and the distance and the speed seem to change in opposite directions.

Distances become bigger with time, as the Universe continues to grow. This removes all objects that are not gravitationally bound to each other, increasing the distance measured between them.
The rate of expansion of the Universe changes, and it varies according to the total density of matter and energy present in the Universe. Since a growing volume means a decreasing energy density, the rate of expansion decreases and the galaxy seems to move away from us at a slower and slower speed.

While matter (both normal and dark) and radiation become less dense as the Universe grows due to its increasing volume, dark energy is an inherent form of energy. to the space itself. Lorsqu'un nouvel espace est créé dans l'univers en expansion, la densité d'énergie sombre reste constante.E. Siegel / Au-delà de la galaxie

Après 7,8 milliards d'années, la densité de matière diminue suffisamment pour que les effets de l'énergie noire commencent à devenir importants. 7,8 milliards d'années après le Big Bang, la densité d'énergie noire aura atteint la moitié de la densité de matière, ce qui est la valeur critique à atteindre pour empêcher une galaxie lointaine de ralentir de notre point de vue.

En ce moment de l'histoire cosmique, 7,8 milliards d'années après le Big Bang, chaque objet lointain de l'Univers paraîtra s'éloigner de nous: il continuera à accélérer à la vitesse qu'il avait précédemment. Il n'accélérera ni ne ralentira, mais maintiendra un mouvement apparent constant dans sa récession. C'est un moment critique: les effets répulsifs de l'énergie noire sur l'expansion de l'Univers contrecarrent exactement les effets attractifs de la matière.

L'importance relative des différentes composantes de l'énergie dans l'univers à différentes époques du passé. Notez que lorsque l’énergie sombre atteindra près de 100% dans l’avenir, la densité énergétique de l’Univers (et, par conséquent, le taux d’expansion) demeurera constante de façon arbitraire et très éloignée dans le temps. En raison de l'énergie sombre, les galaxies lointaines accélèrent déjà de nous, leur vitesse apparente de récession, depuis que la densité d'énergie sombre était la moitié de la densité de matière totale, il y a 6 milliards d'années.E. Siegel

Mais le temps ne s'arrête pas là. Au lieu de cela, elle continue vers l'avant et la densité de matière continue à diminuer. Une fois que l’horloge cosmique a atteint 7,8 milliards d’années, l’énergie sombre devient plus importante que la matière et le rayonnement en ce qui concerne le taux de dilatation. Les galaxies lointaines ont peut-être atteint leur vitesse de récession minimale à ce moment-là, mais apparaîtront alors comme accélérées à nouveau.

À mesure que le temps avance, les objets distants non liés les uns aux autres s'éloignent de plus en plus rapidement de leur point de vue. À l’époque où l’Univers aura atteint 9,2 milliards d’années, au moment même où notre système solaire se formera, la densité de matière aura chuté sous la densité d’énergie noire. À l’heure actuelle, 13,8 milliards d’années après le Big Bang, l’énergie noire représente environ 70% de l’énergie totale de l’Univers. Pendant tout ce temps, les galaxies lointaines continueront à accélérer, de notre point de vue, dans leur récession apparente.

Les parties observables (jaune) et atteignables (magenta) de l'univers, qui sont ce qu'elles sont grâce à l'expansion de l'espace et des composantes énergétiques de l'univers. 97% des galaxies de notre univers observable sont contenues à l'extérieur du cercle magenta; ils sont inaccessibles par nous aujourd'hui, même en principe, bien que nous puissions toujours les voir dans leur passé en raison des propriétés de la lumière et de l'espace-temps.E. Siegel, basé sur les travaux des utilisateurs de Wikimedia Commons Azcolvin 429 et Frédéric MICHEL

Depuis 6 milliards d'années, l'expansion de l'Univers s'accélère, ce qui signifie que toute galaxie lointaine que nous surveillons semble s'éloigner de nous à une vitesse sans cesse croissante. Une fois qu'une galaxie aura atteint une distance d'environ 15 à 16 milliards d'années-lumière, elle semblera s'éloigner plus rapidement que la vitesse de la lumière, ce qui signifie que nous ne pourrons jamais rien faire pour l'atteindre ou la contacter à nouveau. Etant donné que l'Univers a déjà 46 milliards d'années-lumière de rayon, cela signifie que 97% des galaxies de l'Univers sont déjà hors de notre portée.

Pendant des milliards d'années, la densité de l'énergie noire aurait été infime comparée à la densité de la matière, ce qui signifie que ses effets auraient été indétectables si nous nous étions trouvés trop tôt. Des dizaines de milliards d’années à partir de maintenant, cela aura tout poussé au-delà de notre groupe local, loin de nous; les restes fusionnés du groupe local seront la seule galaxie restante. C'est seulement parce que nous sommes venus à ce moment-là, à cette époque cosmique dorée, que nous pouvons percevoir de quoi l'univers est réellement fait. L’énergie noire est réelle et domine notre univers depuis ses 7,8 milliards d’années. Elle déterminera le destin de notre univers à partir de maintenant.

Pour en savoir plus sur la nature de l'univers quand: