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What was it like when the universe first generated atoms?




<div _ngcontent-c16 = "" innerhtml = "[196591] When free electrons combine with hydrogen nuclei, the electrons cascade down the energy levels and emit photons as they go, forming stable, neutral atoms early universe, they must reach the ground state without producing a potentially ionizing, ultraviolet photon. Brighterorange & Enoch Lau / Wikimdia Commons

When it comes to our world, our solar system and everything we can see in ours The Universe exists from the same constituents: Atoms, electrons, and atomic nuclei interact and unite to form not just single atoms, but simple and complex molecules, some of which have produced macroscopic structures and even life, the most impressive facts about the universe: that it exists that we allow the complex structure that we find in it today.

But for Hundertta Years from the moment of the hot big bang, it was impossible to make the eve of a single atom. It took a huge amount of cosmic evolution and a series of important steps to create it. Here is the story of how we came here.

The density fluctuations in the cosmic microwave background (CMB) provide the seeds for the emergence of modern cosmic structures, including stars, galaxies, clusters of galaxies, filaments and large-scale cosmic cavities. But the CMB itself can not be seen until the universe makes its atoms and electrons neutral atoms, which takes hundreds of thousands of years. Chris Blake and Sam Moorfield

When the universe is four minutes old, it is ready to merge all the atomic nuclei that merge in this hot, dense, early state. There are no more free neutrons; They were all built into heavier cores. These include:

  • helium-4 (two protons and two neutrons),
  • deuterium (a proton and neutron),
  • helium-3 (two protons and one neutron) and tritium (one proton and two neutrons)
  • and lithium-7 (three protons and four neutrons) and beryllium-7 (four protons and three neutrons).

That's pretty much everything. There are exactly enough free electrons to keep the universe electrically neutral and to exactly balance the number of protons. While photons that continuously scatter the particles that are the quantum of light from the electrons and atomic nuclei, it is far too hot or energetic to form something else.

The predicted abundances of helium-4, deuterium, helium-3, and lithium-7 as predicted by Big Bang's nucleosynthesis, with observations shown in the red circles. The universe consists of 75-76% hydrogen, 24-25% helium, a bit of deuterium and helium-3 and a trace amount of lithium. The first stars in the universe will consist of this combination of elements; nothing more. NASA / WMAP Science Team

The reason for this is simple: there is not enough energy to fuse these nuclei into heavier combinations, but there is too much energy for electrons to bind to them and form atoms. In fact, there is too much energy way to form neutral atoms. Over time, the universe is a few minutes old, the temperature is still hundreds of millions of degrees, but to form a stable, neutral atom, the temperature must fall below a few thousand degrees.

Sure, the Universe expands, which means that it cools when the wavelength of light in it expands. But to stretch that much – by a factor of about 100,000 – will take a lot of time.

Radiation is redshifted as the Universe expands, which means that in the universe's past it was more energetic with more energy per photon. Whether the universe is dominated by matter or radiation is irrelevant; the red shift is real. E. Siegel / Beyond The Galaxy

So the universe is waiting. And with time it expands and cools. When the minutes change to hours and then days, beryllium-7 begins to decay radioactively. By trapping electrons, it slowly turns into lithium-7, and after a year or two it almost completely disappears. Over the years, tritium will radioactively decay (by electron emission) into helium-3. The transformation is completed after about a century.

And yet it is still too hot to form a stable atom. So the universe expands, cools and becomes less dense.

With the expansion of the structure of the universe, the wavelengths of any existing radiation are also stretched. As a result, the universe becomes less energetic and many high-energy processes that spontaneously occur in early times become impossible in later, cooler epochs. It takes hundreds of thousands of years for the universe to cool down enough to form neutral atoms. E. Siegel / Beyond The Galaxy

As the centuries reach millennia, the redshift of these photons – superior to other particles by about a billion to one – becomes so strong that they have lost almost all of their energy , After a few tens of thousands of years, the radiation density falls below the density of matter, which means that the universe is now dominated by slowly moving matter rather than by radiation moving at the speed of light.

Gravitation can pull dark matter into lumps that grow and grow and attract more matter. With no radiation to wash these lumps, the universe begins to form structure. The seeds of our cosmic web have been planted.

The fluctuations in CMB are due to primitive fluctuations caused by inflation. In particular, the "flat part" on large scales (left) has no explanation without inflation. The flat line represents the germs that will emerge from the peak and valley pattern in the first 380,000 years of the universe. NASA / WMAP Science Team

But it is still too hot to form neutral atoms. Each time an electron successfully binds to an atomic nucleus, it does two things:

  1. It emits an ultraviolet photon because atomic transitions are always predictably cascaded into energy levels.
  2. It is bombarded by other particles that contain about one thousand photons that exist for every electron in the universe.

And during these early stages, even when the universe is tens of thousands of years old, there are enough photons with enough energy to make it as fast as possible. An electron binds to a nucleus – be it a free proton or a heavy nucleus – it is blasted again immediately.

In early times (left), photons scatter electrons and are high enough to repel atoms into an ionized state. Once the universe has cooled down enough and no longer has such high-energy photons (right), they can not interact with the neutral atoms and instead simply flow freely because they have the wrong wavelength to excite these atoms to a higher energy level. E. Siegel / Beyond the Galaxy

But something is beginning to change when the universe is about 300,000 years old. The background photons, which are part of the leftover Big Bang, become too cool to immediately eject electrons from their cores. There are still some of these very high energies, but there are fewer photons than electrons in the universe now; less than 1 billion photons can ionize a neutral atom.

This means that neutral atoms can begin to form, but there is a problem for them to stay. When you form a stable, neutral atom, they emit ultraviolet photons. These photons then continue in a straight line until they encounter another neutral atom, which they then ionize. Although we can form a small number of neutral atoms, they do not stay that way.

As the universe cools, atomic nuclei form, followed by neutral atoms as it continues to cool. All these atoms are (practically) hydrogen or helium, and the process that allows them to form stable neutral atoms takes hundreds of thousands of years. E. Siegel

One might think that these ultraviolet photons eventually travel through space, redshifting and no longer interacting with the neutral atoms (because they are not on the right wavelength). That they will not arouse them and make them non-ionizable.

It is true that this is an effect that happens, but it accounts for only a few percent of the neutral atoms that are first formed in the Universe. There is another effect that prevails instead. It's extremely rare, but with all the atoms in the Universe and the more than 100,000 years of atoms needed to finally and stably become neutral, it's an incredible and complicated part of the story.

When you switch from an "orbital" to a low-energy "orbital," you can rarely do so by emitting two photons of equal energy. "This two-photon transition even occurs between the 2s state ( first excited state) and 1s state (ground state), about once per 100 million transitions. R. Roy et al., Optics Express 25 (7): 7960 * April 2017

When an electron is in the first excited state, it usually falls into the lowest energy state in a hydrogen atom and emits an ultraviolet photon of a specific energy: a Lyman alpha photon, but about once in 100 million transitions, the drop-down process will take place in a different way and instead emit two low-energy photons, referred to as a two-photon decay or transition, and is primarily responsible for making the Universe neutral.

Photon emits, it almost always collides with another hydrogen atom, excites it and finally leads to its reionization. But if you emit two photons, it is extremely unlikely that they will hit an atom at the same time, which means you will reach an additional neutral atom.

A universe in which electrons and protons are free and collide with photons, transforms into a neutral atom. This is transparent to photons as the universe expands and cools. Here is the ionized plasma (L) before the CMB is emitted, followed by the transition to a neutral universe (R) that is transparent to photons. It is the spectacular two-photon transition in a hydrogen atom that allows the universe to become just as neutral as we observe it. Amanda Yoho

The rest is history. Sure, it takes more than 100,000 years for the process to complete, but that's the universe. This two-photon transition, rare though it is, is the process by which neutral atoms first form. It takes us from a hot, plasma-filled universe to an almost equal universe with 100% neutral atoms. Although we say that the universe formed these atoms 380,000 years after the Big Bang, this was actually a slow, gradual process that took about 100,000 years on either side of this figure to complete. Once the atoms are neutral, there is nothing left to scatter the light of the Big Bang. This is the origin of the CMB: the cosmic microwave background

Arno Penzias and Bob Wilson at the location of the antenna in Holmdel, New Jersey, where the cosmic microwave background was first identified. Physics Today Collection / AIP / SPL

We first discovered this light in 1964, confirming the Big Bang and ushering in the era of modern cosmology. From our best observations, we were able to confirm this spectacular image and even measure the depth and thickness of the last scattered area from that time. Two-photon transitions have been verified here in laboratories on Earth, and what we have observed is a spectacular match between our theoretical predictions and what actually happened in the distant past of the universe. It took about half a million years until the universe finally formed completely neutral atoms, while gravitation began to contract the universe into lumps. The cosmic story that was to come to us was ready to move on to the next phase.


For more information on how the universe was, see:

  • What was it like when the universe flew open?
  • What was it like when the big bang started?
  • What was? it was when the universe was hottest?
  • What was it like when the universe first created more matter than antimatter?
  • What was it like when Higgs existed? Mass to the universe?
  • What was it like when we first made protons and neutrons?
  • How was it when we lost the last of our antimatter?
  • What was it like when the universe created its first elements?

"

When free electrons combine with hydrogen nuclei, the electrons cascade down the energy levels and emit photons as they go. For stable, neutral atoms to form in the early universe, they must reach the ground state without a potentially ionizing one Ultraviolen et photon. Brighterorange & Enoch Lau / Wikimdia Commons

When it comes to our world, our solar system, and everything we can see in our universe, everything is made up of the same components: atoms, electrons, and Atomic nuclei interact and combine not just individual atoms, but simple and complex molecules, some of which have led to macroscopic structures and even to life, one of the most impressive facts about the universe: that it exists in such a way that it is the most complex Structure that we find in it today.

But for hundreds of thousands of years, Starting from the moment of the hot big bang, it was impossible to form even a single atom. It took a huge amount of cosmic evolution and a series of important steps to create it. Here is the story of how we came here.

The density fluctuations in the cosmic microwave background (CMB) provide the seeds for the emergence of modern cosmic structures, including stars, galaxies, clusters of galaxies, filaments and large-scale cosmic cavities. But the CMB itself can not be seen until the universe forms neutral atoms from its ions and electrons, which takes hundreds of thousands of years. Chris Blake and Sam Moorfield

With time, the universe is already four minutes old, that's it! By fusion of all atomic nuclei, it can merge in this hot, dense early state. There are no more free neutrons; They were all built into heavier cores. These include:

  • helium-4 (two protons and two neutrons),
  • deuterium (a proton and neutron),
  • helium-3 (two protons and one neutron) and tritium (one proton and two neutrons)
  • and lithium-7 (three protons and four neutrons) and beryllium-7 (four protons and three neutrons).

That's pretty much everything. There are exactly enough free electrons to keep the universe electrically neutral and to exactly balance the number of protons. While photons that continuously scatter the particles that are the quantum of light from the electrons and atomic nuclei, it is far too hot or energetic to form something else.

The predicted abundances of helium-4, deuterium, helium-3, and lithium-7 as predicted by Big Bang's nucleosynthesis, with observations shown in the red circles. The universe consists of 75-76% hydrogen, 24-25% helium, a bit of deuterium and helium-3 and a trace amount of lithium. The first stars in the universe will consist of this combination of elements; nothing more. NASA / WMAP Science Team

The reason for this is simple: there is not enough energy to fuse these nuclei into heavier combinations, but there is too much energy for electrons to bind to them and form atoms. In fact, there is too much energy way to form neutral atoms. Over time, the universe is a few minutes old, the temperature is still hundreds of millions of degrees, but to form a stable, neutral atom, the temperature must fall below a few thousand degrees.

Sure, the Universe expands, which means that it cools when the wavelength of light in it expands. But to stretch that much – by a factor of about 100,000 – will take a lot of time.

The radiation is redshifted as the universe expands, meaning that in the universe's past it was more energetic with more energy per photon. Whether the universe is dominated by matter or radiation is irrelevant; the red shift is real. E. Siegel / Beyond The Galaxy

So the universe is waiting. And with time it expands and cools. When the minutes change to hours and then days, beryllium-7 begins to decay radioactively. By trapping electrons, it slowly turns into lithium-7, and after a year or two it almost completely disappears. Over the years, tritium will radioactively decay (by electron emission) into helium-3. The transformation is completed after about a century.

And yet it is still too hot to form a stable atom. The universe is expanding, cooling and becoming less dense.

With the expansion of the structure of the universe, the wavelengths of the existing radiation are also stretched. As a result, the universe becomes less energetic and many high-energy processes that spontaneously occur in early times become impossible in later, cooler epochs. It takes hundreds of thousands of years for the universe to cool down enough to form neutral atoms. E. Siegel / Beyond The Galaxy

As the centuries reach millennia, the redshift of these photons – superior to other particles by about a billion to one – becomes so strong that they have lost almost all of their energy , After a few tens of thousands of years, the radiation density falls below the density of matter, which means that the universe is now dominated by slowly moving matter rather than by radiation moving at the speed of light.

Gravitation can pull dark matter into lumps that grow and grow and attract more matter. With no radiation to wash these lumps, the universe begins to form structure. The seeds of our cosmic web have been planted.

The fluctuations in CMB are due to primitive fluctuations caused by inflation. In particular, the "flat part" on large scales (left) has no explanation without inflation. The flat line represents the germs that will emerge from the peak and valley pattern in the first 380,000 years of the universe. NASA / WMAP Science Team

But it is still too hot to form neutral atoms. Each time an electron successfully binds to an atomic nucleus, it does two things:

  1. It emits an ultraviolet photon because atomic transitions are always predictably cascaded into energy levels.
  2. It is bombarded by other particles that contain about one thousand photons that exist for every electron in the universe.

And during these early stages, even when the universe is tens of thousands of years old, there are enough photons with enough energy to make it as fast as possible. An electron binds to a nucleus – whether a free proton or a heavy nucleus – it is blasted again immediately.

In early times (left), photons scatter electrons and are high enough to knock atoms back into an ionized state. Once the universe has cooled down enough and no longer has such high-energy photons (right), they can not interact with the neutral atoms and instead simply flow freely because they have the wrong wavelength to excite these atoms to a higher energy level. E. Siegel / Beyond the Galaxy

But something is beginning to change when the universe is about 300,000 years old. The background photons, which are part of the leftover Big Bang, become too cool to immediately eject electrons from their cores. There are still some of these very high energies, but there are fewer photons than electrons in the universe now; less than 1 billion photons can ionize a neutral atom.

This means that neutral atoms can begin to form, but there is a problem for them to stay. When you form a stable, neutral atom, they emit ultraviolet photons. These photons then continue in a straight line until they encounter another neutral atom, which they then ionize. Although we can form a small number of neutral atoms, they do not stay that way.

As the universe cools, atomic nuclei form, followed by neutral atoms as it continues to cool. All these atoms are (practically) hydrogen or helium, and the process that allows them to form stable neutral atoms takes hundreds of thousands of years. E. Siegel

One might think that these ultraviolet photons eventually travel through space, redshifting and no longer interacting with the neutral atoms (because they are not on the right wavelength). That they will not arouse them and make them non-ionizable.

It is true that this is an effect that happens, but it accounts for only a few percent of the neutral atoms that are first formed in the Universe. There is another effect that prevails instead. It is extremely rare, but with all the atoms in the Universe and the more than 100,000 years of atoms needed to finally and stably become neutral, this is an incredible and complicated part of the story.

If you move from an "orbital" to a low-energy "orbital," you can rarely do so by emitting two photons of equal energy. "This two-photon transition even occurs between the 2s state ( first excited state) and 1s state (ground state), about once per 100 million transitions. R. Roy et al., Optics Express 25 (7): 7960 * April 2017

When an electron is in the first excited state, it usually falls into the lowest energy state in a hydrogen atom and emits an ultraviolet photon of a specific energy: a Lyman alpha photon, but about once in 100 million transitions, the drop-down process will take place in a different way and instead emit two low-energy photons, referred to as a two-photon decay or transition, and is primarily responsible for making the Universe neutral.

Photon emits, it almost always collides with another hydrogen atom, excites it and finally leads to its reionization. But if you emit two photons, it is extremely unlikely that they both hit an atom at the same time, which means you are creating an additional neutral atom.

A universe in which electrons and protons are free and collide with photons, transforms into a neutral atom. This is transparent to photons as the universe expands and cools. Here is the ionized plasma (L) before the CMB is emitted, followed by the transition to a neutral universe (R) that is transparent to photons. It is the spectacular two-photon transition in a hydrogen atom that allows the universe to become just as neutral as we observe it. Amanda Yoho

The rest is history. Sure, it takes more than 100,000 years for the process to complete, but that's the universe. This two-photon transition, rare though it is, is the process by which neutral atoms first form. It takes us from a hot, plasma-filled universe to an almost equal universe with 100% neutral atoms. Although we say that the universe formed these atoms 380,000 years after the Big Bang, this was actually a slow, gradual process that took about 100,000 years on either side of this figure to complete. Once the atoms are neutral, there is nothing left to scatter the light of the Big Bang. This is the origin of the CMB: the cosmic microwave background

Arno Penzias and Bob Wilson at the location of the antenna in Holmdel, New Jersey, where the cosmic microwave background was first identified. Physics Today Collection / AIP / SPL

We first discovered this light in 1964, confirming the Big Bang and ushering in the era of modern cosmology. From our best observations, we were able to confirm this spectacular image and even measure the depth and thickness of the last scattered area from that time. Two-photon transitions have been verified here in laboratories on Earth, and what we have observed is a spectacular match between our theoretical predictions and what actually happened in the distant past of the universe. It took about half a million years until the universe finally formed completely neutral atoms, while gravitation began to contract the universe into lumps. The cosmic story that would lead to us was ready to move on to the next phase.


For more information on how the universe was, see:


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