Giant clouds of these primordial elements later coalesced through gravity to form stars and galaxies. This all began roughly Through the testing of theoretical principles, experiments involving particle accelerators and high-energy states, and astronomical studies that have observed the deep universe, scientists have constructed a timeline of events that began with the Big Bang and has led to the current state of cosmic evolution.
Given that the laws of physics as we know them could not have existed at this time, it is difficult to fathom how the Universe could have been governed. Still, many theories prevail as to what took place in this initial instant in time, many of which are compatible. At this time, all matter was condensed on a single point of infinite density and extreme heat. During this period, it is believed that the quantum effects of gravity dominated physical interactions and that no other physical forces were of equal strength to gravitation.
This Planck period of time extends from point 0 to approximately 10 seconds, and is so named because it can only be measured in Planck time. Due to the extreme heat and density of matter, the state of the universe was highly unstable. It thus began to expand and cool, leading to the manifestation of the fundamental forces of physics.
From approximately 10 second and 10 , the universe began to cross transition temperatures. It is here that the fundamental forces that govern the Universe are believed to have began separating from each other. The first step in this was the force of gravitation separating from gauge forces, which account for strong and weak nuclear forces and electromagnetism. Then, from 10 to 10 seconds after the Big Bang, the temperature of the universe was low enough 10 28 K that the forces of electromagnetism strong force and weak nuclear forces weak interaction were able to separate as well, forming two distinct forces.
With the creation of the first fundamental forces of the universe, the Inflation Epoch began, lasting from 10 seconds in Planck time to an unknown point. Most cosmological models suggest that the Universe at this point was filled homogeneously with a high-energy density, and that the incredibly high temperatures and pressure gave rise to rapid expansion and cooling. This began at 10 seconds, where the phase transition that caused for the separation of forces also led to a period where the universe grew exponentially. It was also at this point in time that baryogenesis occurred, which refers to a hypothetical event where temperatures were so high that the random motions of particles occurred at relativistic speeds.
As a result of this, particle—antiparticle pairs of all kinds were being continuously created and destroyed in collisions, which is believed to have led to the predominance of matter over antimatter in the present universe. After inflation stopped, the universe consisted of a quark—gluon plasma, as well as all other elementary particles. From this point onward, the Universe began to cool and matter coalesced and formed.
As the universe continued to decrease in density and temperature, the energy of each particle began to decrease and phase transitions continued until the fundamental forces of physics and elementary particles changed into their present form. Since particle energies would have dropped to values that can be obtained by particle physics experiments, this period onward is subject to less speculation. For example, scientists believe that about 10 seconds after the Big Bang, particle energies dropped considerably.
At about 10 -6 seconds, quarks and gluons combined to form baryons such as protons and neutrons, and a small excess of quarks over antiquarks led to a small excess of baryons over antibaryons. Since temperatures were not high enough to create new proton-antiproton pairs or neutron-anitneutron pairs , mass annihilation immediately followed, leaving just one in 10 10 of the original protons and neutrons and none of their antiparticles. A similar process happened at about 1 second after the Big Bang for electrons and positrons. After these annihilations, the remaining protons, neutrons and electrons were no longer moving relativistically and the energy density of the universe was dominated by photons — and to a lesser extent, neutrinos.
A few minutes into the expansion, the period known as Big Bang nucleosynthesis also began. After about , years, electrons combined with these nuclei to form atoms again, mostly hydrogen , while the radiation decoupled from matter and continued to expand through space, largely unimpeded.
This radiation is now known to be what constitutes the Cosmic Microwave Background CMB , which today is the oldest light in the Universe. As the CMB expanded, it gradually lost density and energy, and is currently estimated to have a temperature of 2. The CMB can be seen in all directions at a distance of roughly Over the course of the several billion years that followed, the slightly denser regions of the almost uniformly distributed matter of the Universe began to become gravitationally attracted to each other.
They therefore grew even denser, forming gas clouds, stars, galaxies, and the other astronomical structures that we regularly observe today. This is what is known as the Structure Epoch, since it was during this time that the modern Universe began to take shape. This consists of visible matter distributed in structures of various sizes, ranging from stars and planets to galaxies, galaxy clusters, and super clusters — where matter is concentrated — that are separated by enormous gulfs containing few galaxies.
The details of this process depend on the amount and type of matter in the universe, with cold dark matter, warm dark matter, hot dark matter, and baryonic matter being the four suggested types. However, the Lambda-Cold Dark Matter model Lambda-CDM , in which the dark matter particles moved slowly compared to the speed of light, is the considered to be the standard model of Big Bang cosmology, as it best fits the available data.
The Lambda refers to the Cosmological Constant , a theory originally proposed by Albert Einstein that attempted to show that the balance of mass-energy in the universe was static. In this case, it is associated with Dark Energy , which served to accelerate the expansion of the universe and keep its large-scale structure largely uniform.
Hypothesizing that the Universe had a starting point naturally gives rise to questions about a possible end point. If the Universe began as a tiny point of infinite density that started to expand, does that mean it will continue to expand indefinitely? Or will it one day run out of expansive force, and begin retreating inward until all matter crunches back into a tiny ball? Answering this question has been a major focus of cosmologists ever since the debate about which model of the Universe was the correct one began.
With the acceptance of the Big Bang Theory, but prior to the observation of Dark Energy in the s, cosmologists had come to agree on two scenarios as being the most likely outcomes for our Universe. This will only be possible if the mass density of the Universe is greater than the critical density. Alternatively, if the density in the universe were equal to or below the critical density, the expansion would slow down but never stop. Meanwhile, all existing stars would burn out and become white dwarfs, neutron stars, and black holes.
Very gradually, collisions between these black holes would result in mass accumulating into larger and larger black holes. The average temperature of the universe would approach absolute zero, and black holes would evaporate after emitting the last of their Hawking radiation.
Modern observations, which include the existence of Dark Energy and its influence on cosmic expansion, have led to the conclusion that more and more of the currently visible universe will pass beyond our event horizon i. Other explanations of dark energy, called phantom energy theories, suggest that ultimately galaxy clusters, stars, planets, atoms, nuclei, and matter itself will be torn apart by the ever-increasing expansion.
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The earliest indications of the Big Bang occurred as a result of deep-space observations conducted in the early 20th century. In , American astronomer Vesto Slipher conducted a series of observations of spiral galaxies which were believed to be nebulae and measured their Doppler Redshift. In almost all cases, the spiral galaxies were observed to be moving away from our own.
Big Bang - Wikipedia
At the same time, Hubble began developing a series of distance indicators using the inch 2. In , he took this further, suggesting that the current expansion of the Universe meant that the father back in time one went, the smaller the Universe would be. At some point in the past, he argued, the entire mass of the universe would have been concentrated into a single point from which the very fabric of space and time originated.
These discoveries triggered a debate between physicists throughout the s and 30s, with the majority advocating that the universe was in a steady state.
In this model, new matter is continuously created as the universe expands, thus preserving the uniformity and density of matter over time. Among these scientists, the idea of a Big Bang seemed more theological than scientific, and accusations of bias were made against Lemaitre based on his religious background. Other theories were advocated during this time as well, such as the Milne Model and the Oscillary Universe model. After World War II, the debate came to a head between proponents of the Steady State Model which had come to be formalized by astronomer Fred Hoyle and proponents of the Big Bang Theory — which was growing in popularity.
Eventually, the observational evidence began to favor Big Bang over Steady State. The discovery and confirmation of the cosmic microwave background radiation in secured the Big Bang as the best theory of the origin and evolution of the universe. From the late 60s to the s, astronomers and cosmologist made an even better case for the Big Bang by resolving theoretical problems it raised. These included papers submitted by Stephen Hawking and other physicists that showed that singularities were an inevitable initial condition of general relativity and a Big Bang model of cosmology.
In , physicist Alan Guth theorized of a period of rapid cosmic expansion aka. The s also saw the rise of Dark Energy as an attempt to resolve outstanding issues in cosmology. Significant progress was made thanks to advances in telescopes, satellites, and computer simulations, which have allowed astronomers and cosmologists to see more of the universe and gain a better understanding of its true age.
Today, cosmologists have fairly precise and accurate measurements of many of the parameters of the Big Bang Theory model, not to mention the age of the Universe itself. And it all began with the noted observation that massive stellar objects, many light years distant, were slowly moving away from us. We have many interesting articles about the Big Bang here at Universe Today. For instance, here is What is the Evidence of the Big Bang?
Astronomy Cast has also has several relevant episodes on the subject.
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Globular clusters are spherical blobs of, say, 10, stars. They are abundant in numbers, do not collapse under their own gravitation, nor do they expand without limit. They are manifestly very stable structures, and current theory says they are very old. Galaxies are likewise, and even they can cluster like stars in a globular cluster. And what of Quasars and radio galaxies? What of the CMB?
Big Bang Theory
What of the fact that these stable structures are part of an expanding universe, and the expansion is accelerating? Quasars, pulsars, radio galaxies, exploding galaxies, etc. I have already commented on the CMB below. These are observationally superimposed.
Was the Big Bang Actually an Explosion?
Non-local radiation will be spatially diffuse, and local radiation will ultimately have spatially localized, specific sources. And that is why the search for a diffuse infrared component is so difficult. There are answers to these other questions, but we will never find them if astronomers are focused on these off-in-the-weeds, way-out theories.
You are correct, but a theory, BB or otherwise, cannot be thought of as a fact, can it? The BBT is the best we have to date because it is based on confirmed facts. So long as any part of the theory is consistent with the known facts, it is only a possible idea, concept that has a possibility of being true.
Nothing wrong with such theories so long as they are based on the facts! It is up to us to learn the facts so that we can compare them against the endless ideas we can think up.