After only a few seconds, protons, neutrons, and electrons could form. After a few minutes, those subatomic particles came together to create hydrogen. Energy in the universe was great enough to initiate nuclear fusion and hydrogen nuclei were fused into helium nuclei.
The first neutral atoms that included electrons did not form until about , years later. The matter in the early universe was not smoothly distributed across space. Dense clumps of matter held close together by gravity were spread around.
Eventually, these clumps formed countless trillions of stars, billions of galaxies, and other structures that now form most of the visible mass of the universe. Dark matter makes up another 27 percent. In essence, all the matter you've ever seen—from your first love to the stars overhead—makes up less than five percent of the universe. All rights reserved. Origins of the Universe Aftermath of cosmic inflation As time passed and matter cooled, more diverse kinds of particles began to form, and they eventually condensed into the stars and galaxies of our present universe.
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This estimate came from measuring the composition of matter and energy density in the universe. This allowed researchers to compute how fast the universe expanded in the past. With that knowledge, they could turn the clock back and extrapolate when the Big Bang happened.
The time between then and now is the age of the universe. Scientists think that in the earliest moments of the universe, there was no structure to it to speak of, with matter and energy distributed nearly uniformly throughout. According to NASA, the gravitational pull of small fluctuations in the density of matter back then gave rise to the vast web-like structure of stars and emptiness seen today.
Dense regions pulled in more and more matter through gravity, and the more massive they became, the more matter they could pull in through gravity, forming stars , galaxies and larger structures known as clusters, superclusters, filaments and walls , with "great walls" of thousands of galaxies reaching more than a billion light years in length. Less dense regions did not grow, evolving into area of seemingly empty space called voids.
Until about 30 years ago, astronomers thought that the universe was composed almost entirely of ordinary atoms , or "baryonic matter," According to NASA. However, recently there has been ever more evidence that suggests most of the ingredients making up the universe come in forms that we cannot see. It turns out that atoms only make up 4. Of the remainder, 23 percent is made up of dark matter , which is likely composed of one or more species of subatomic particles that interact very weakly with ordinary matter, and 72 percent is made of dark energy, which apparently is driving the accelerating expansion of the universe.
When it comes to the atoms we are familiar with, hydrogen makes up about 75 percent , while helium makes up about 25 percent, with heavier elements making up only a tiny fraction of the universe's atoms, according to NASA.
The shape of the universe and whether or not it is finite or infinite in extent depends on the struggle between the rate of its expansion and the pull of gravity. We can imagine, after all, a location outside of space; a moment beyond the confines of time; a set of conditions that have no physical reality to constrain them.
And those imaginings — if we define these physical realities as things we need to eliminate to obtain true nothingness — are certainly valid, at least philosophically.
Without a physical theory to describe what happens outside of the Universe and beyond the realm physical laws, the concept of true nothingness is physically ill-defined. Fluctuations in spacetime itself at the quantum scale get stretched across the Universe during While inflating space can rightfully be called 'nothing' in many regards, not everyone agrees. What does it mean to be outside of space and time, and how can space and time sensibly, predictably emerge from a state of non-existence?
Where do the rules governing quanta — the fields and particles both — arise from? But if you leave physical constraints behind, then all certainly about our ultimate cosmic origins disappears. Unfortunately for us all, inflation, by its very nature, erases any information that might be imprinted from a pre-existing state on our observable Universe. Despite the limitless nature of our imaginations, we can only draw conclusions about matters for which tests involving our physical reality can be constructed.
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