“This universe, perhaps, is yet incomplete, For I hear repeated sounds of “Be, And It Is.”
The Universe is all existing matter and space considered as a whole, the cosmos. It is a huge wide-open space that holds everything from the smallest particle to the biggest galaxy. It is believed to be at least 10 billion light years in diameter and contains a vast number of galaxies. Astronomers use a special instrument called a spectroscope to tell whether an object is moving away from Earth or toward Earth. Based on the information from this instrument, scientists have learned that the universe has been expanding since its creation in the Big Bang about 13.7 billion years ago.
The most popular theory of our universe’s origin centres on a cosmic cataclysm unmatched in all of history — the Big Bang. This theory was born of the observation that other galaxies are moving away from our own at great speed, in all directions, as if they had all been propelled by an ancient explosive force.
What is Big Bang Theory?
Scientists have gathered a lot of evidence and information about the universe. They have used their observations to develop a theory called the Big Bang. Scientists believe that before the Big Bang, the entire vastness of the observable universe, including all of its matter and radiation, was compressed into a hot, dense mass just a few millimetres across. This began to enlarge rapidly in a hot explosion, and it is still expanding today.
According to NASA, after inflation — a brief exponential expansion of the universe (faster than the speed of light) postulated to have occurred shortly after the big bang — the growth of the universe continued, but at a slower rate. As space expanded, the universe cooled and matter formed. One second after the Big Bang, the universe was filled with neutrons, protons, electrons, anti-electrons, photons and neutrinos.
A Belgian priest named Georges Lemaître first suggested the Big Bang theory in the 1920s when he theorized that the universe began from a single primordial atom. The idea subsequently received major boosts by Edwin Hubble’s observations that galaxies are speeding away from us in all directions, and from the discovery of cosmic microwave radiation by Arno Penzias and Robert Wilson.
The glow of cosmic microwave background radiation, which is found throughout the universe, is thought to be a tangible remnant of leftover light from the Big Bang. The radiation is akin to that used to transmit TV signals via antennas. But it is the oldest radiation known and may hold many secrets about the universe’s earliest moments.
Evidence for the Big Bang includes:
1. All other galaxies are moving away from us
2. The further away a galaxy is, the faster it is moving away
3. These two features are found in explosions — the fastest moving objects end up furthest away from the explosion.
The large-scale structure of the universe is made up of voids and filaments that can be broken down into superclusters, clusters, galaxy groups, and subsequently into galaxies. At a relatively smaller scale, we know that galaxies are made up of stars and their constituents, our own Solar System being one of them.
Until about 30 years ago, astronomers thought that the universe was composed almost entirely of ordinary atoms, or “baryonic matter”. 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 4.6 percent of the universe. 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. The strength of the pull in question depends in part on the density of the matter in the universe.
If the density of the universe exceeds a specific critical value, then the universe is “closed” and “positive curved” like the surface of a sphere. This means light beams that are initially parallel will converge slowly, eventually cross and return back to their starting point, if the universe lasts long enough. If so, according to NASA, the universe is not infinite but has no end, just as the area on the surface of a sphere is not infinite but has no beginning or end to speak of. The universe will eventually stop expanding and start collapsing in on itself, the so-called “Big Crunch”.
If the density of the universe is less than this critical density, then the geometry of space is “open” and “negatively curved” like the surface of a saddle. If so, the universe has no bounds, and will expand forever.
If the density of the universe exactly equals the critical density, then the geometry of the universe is “flat” with zero curvature like a sheet of paper, according to NASA. If so, the universe has no bounds and will expand forever, but the rate of expansion will gradually approach zero after an infinite amount of time. Recent measurements suggest that the universe is flat with only a 2 percent margin of error.
It is possible that the universe has a more complicated shape overall while seeming to possess a different curvature. For instance, the universe could have the shape of a torus, or doughnut.