What was the universe like before stars formed

In two teams of astronomers working independently at Berkeley, California observed that supernovae — exploding stars — were moving away from Earth at an accelerating rate. This earned them the Nobel prize in physics in Physicists had assumed that matter in the universe would slow its rate of expansion; gravity would eventually cause the universe to fall back on its centre. Though the Big Bang theory cannot describe what the conditions were at the very beginning of the universe, it can help physicists describe the earliest moments after the start of the expansion.

In the first moments after the Big Bang, the universe was extremely hot and dense. As the universe cooled, conditions became just right to give rise to the building blocks of matter — the quarks and electrons of which we are all made.

A few millionths of a second later, quarks aggregated to produce protons and neutrons. Within minutes, these protons and neutrons combined into nuclei. It is so small that we cannot relate it to anything in our everyday experience. When the universe was that young, its density was so high that the theory of general relativity is not adequate to describe it, and even the concept of time breaks down.

Scientists, by the way, have been somewhat more successful in describing the universe when it was older than 10 —43 second but still less than about 0.

We will take a look at some of these ideas later in this chapter, but for now, we want to start with somewhat more familiar situations. By the time the universe was 0. Each particle collided rapidly with other particles. The temperature was no longer high enough to allow colliding photons to produce neutrons or protons, but it was sufficient for the production of electrons and positrons Figure 4.

There was probably also a sea of exotic subatomic particles that would later play a role as dark matter. All the particles jiggled about on their own; it was still much too hot for protons and neutrons to combine to form the nuclei of atoms.

Figure 4. Particle Interactions in the Early Universe: a In the first fractions of a second, when the universe was very hot, energy was converted into particles and antiparticles. The reverse reaction also happened: a particle and antiparticle could collide and produce energy.

Instead, existing particles fused to create such nuclei as deuterium and helium. Most of the universe was still hydrogen. Think of the universe at this time as a seething cauldron, with photons colliding and interchanging energy, and sometimes being destroyed to create a pair of particles. The particles also collided with one another. Frequently, a matter particle and an antimatter particle met and turned each other into a burst of gamma-ray radiation.

Among the particles created in the early phases of the universe was the ghostly neutrino see The Sun: A Nuclear Powerhouse , which today interacts only very rarely with ordinary matter. By the time the universe was a little more than 1 second old, the density had dropped to the point where neutrinos no longer interacted with matter but simply traveled freely through space. In fact, these neutrinos should now be all around us. Since they have been traveling through space unimpeded and hence unchanged since the universe was 1 second old, measurements of their properties would offer one of the best tests of the Big Bang model.

Unfortunately, the very characteristic that makes them so useful—the fact that they interact so weakly with matter that they have survived unaltered for all but the first second of time—also renders them unable to be measured, at least with present techniques. Perhaps someday someone will devise a way to capture these elusive messengers from the past. When the universe was about 3 minutes old and its temperature was down to about million K, protons and neutrons could combine.

At higher temperatures, these atomic nuclei had immediately been blasted apart by interactions with high-energy photons and thus could not survive. But at the temperatures and densities reached between 3 and 4 minutes after the beginning, deuterium a proton and neutron lasted long enough that collisions could convert some of it into helium Figure 4. In essence, the entire universe was acting the way centers of stars do today—fusing new elements from simpler components.

In addition, a little bit of element 3, lithium, could also form. This burst of cosmic fusion was only a brief interlude, however. By 4 minutes after the Big Bang, more helium was having trouble forming. The universe was still expanding and cooling down. After the formation of helium and some lithium, the temperature had dropped so low that the fusion of helium nuclei into still-heavier elements could not occur.

No elements beyond lithium could form in the first few minutes. That 4-minute period was the end of the time when the entire universe was a fusion factory.

In the cool universe we know today, the fusion of new elements is limited to the centers of stars and the explosions of supernovae. Still, the fact that the Big Bang model allows the creation of a good deal of helium is the answer to a long-standing mystery in astronomy.

Put simply, there is just too much helium in the universe to be explained by what happens inside stars. All the generations of stars that have produced helium since the Big Bang cannot account for the quantity of helium we observe. Because light from these objects is shifted to the red. Redshift means that light that is emitted by these first stars and galaxies as visible or ultraviolet light, actually gets shifted to redder wavelengths by the time we see it here and now.

For very high redshifts i. For that reason, to see the first stars and galaxies, we need a powerful near- and mid-infrared telescope, which is exactly what Webb is! Webb will address several key questions to help us unravel the story of the formation of structures in the Universe such as: When and how did reionization occur?

What sources caused reionization? What are the first galaxies? To find the first galaxies, Webb will make ultra-deep near-infrared surveys of the Universe, and follow up with low-resolution spectroscopy and mid-infrared photometry the measurement of the intensity of an astronomical object's electromagnetic radiation.

To study reionization, high resolution near-infrared spectroscopy will be needed. Until around a few hundred million years or so after the Big Bang, the universe was a very dark place. There were no stars, and there were no galaxies. When the universe started cooling, the protons and neutrons began combining into ionized atoms of hydrogen and deuterium. Deuterium further fused into helium These ionized atoms of hydrogen and helium attracted electrons turning them into neutral atoms.

Ultimately the composition of the universe at this point was 3 times more hydrogen than helium with just trace amounts of other light elements. This process of particles pairing up is called "Recombination" and it occurred approximately , to , years after the Big Bang.

The Universe went from being opaque to transparent at this point. Light had formerly been stopped from traveling freely because it would frequently scatter off the free electrons. Now that the free electrons were bound to protons, light was no longer being impeded. Following this are the cosmic dark ages - a period of time after the Universe became transparent but before the first stars formed.