The story of creating the Universe in six days-(5)-What’s next
03-11-2024, 09:47 AM
Speculating about the potential endpoint of the Universe is inevitable when we hypothesize that it had a beginning. If the Universe originated from a tiny point of infinite density and began to expand, does it logically follow that it will expand indefinitely
Since the debate over the correct model of the Universe began, cosmologists have concentrated their efforts on answering this crucial question. Prior to the discovery of Dark Energy in the 1990s, which came after the widespread acceptance of the Big Bang Theory, cosmologists primarily considered two scenarios as the most plausible explanations for the evolution of our Universe
In the first scenario, known as the "Big Crunch," the Universe will reach its maximum size before collapsing in on itself. This will only be possible if the Universe's mass density exceeds the critical density. In other words, the Universe will eventually contract if the density of matter remains at or above a certain value (1-3x10^-26 kg of matter per m3)
If the density of the Universe were equal to or less than the critical density, the expansion would slow but never stop. In this scenario, known as the "Big Freeze," the Universe would continue to expand until star formation ceased due to the consumption of all interstellar gas in each galaxy. Meanwhile, all existing stars would die and turn into white dwarfs, neutron stars, or black holes
Collisions between these black holes would result in mass accumulating into larger and larger black holes over time. The average temperature of the Universe would approach absolute zero, and black holes would vanish after emitting their final Hawking radiation. Finally, the Universe's entropy would grow to the point where no organized form of energy could be extracted from it -a scenario known as "heat death"
More and more of the Universe will pass beyond our event horizon (the CMB, the outer limit of what we can see), becoming invisible to us, according to contemporary observations, which include the existence of Dark Energy and its impact on cosmic expansion. Although the end result is not yet known, "heat death" is also thought to be a likely outcome in this scenario
Other explanations for dark energy, known as phantom energy theories, predict that the ever-expanding universe will eventually rip apart galaxy clusters, stars, planets, atoms, and even matter itself. The "Big Rip" scenario holds that the universe will ultimately perish due to its own expansion
Finally: The Universe expansion continues, while the time to leave Earth has arrived: "Humans must leave Earth within the next few centuries if they are to survive," declared the eminent theoretical physicist Stephen William Hawking in the months preceding his death in 2018. Hawking, regarded as one of the most famous theoretical physicists of his generation, believed that life on Earth could end in a disaster, such as when the Earth collides with a massive meteor, or when robots (or artificial intelligence) control humans, or when aliens from other planets invade the Earth. He also warned that overpopulation, anti-human hostility, and climate change could wreak havoc on Earth's life, and that if our species was to survive, it needed to create new life in space. One of Hawking's greatest fears for the Earth was global warming, which he warned, "Our natural resources are being depleted at an alarming rate" and that we are "giving our planet the catastrophic gift of climate change". He predicted(1) that if we do not reduce greenhouse gas emissions, the Earth will one day resemble Venus, which has a surface temperature of 460 degrees Celsius (mainly because of Carbon Dioxide accumulation in its atmosphere). He pointed out that this is not science fiction, but rather a matter governed by physical laws
------------------------------Since the debate over the correct model of the Universe began, cosmologists have concentrated their efforts on answering this crucial question. Prior to the discovery of Dark Energy in the 1990s, which came after the widespread acceptance of the Big Bang Theory, cosmologists primarily considered two scenarios as the most plausible explanations for the evolution of our Universe
In the first scenario, known as the "Big Crunch," the Universe will reach its maximum size before collapsing in on itself. This will only be possible if the Universe's mass density exceeds the critical density. In other words, the Universe will eventually contract if the density of matter remains at or above a certain value (1-3x10^-26 kg of matter per m3)
If the density of the Universe were equal to or less than the critical density, the expansion would slow but never stop. In this scenario, known as the "Big Freeze," the Universe would continue to expand until star formation ceased due to the consumption of all interstellar gas in each galaxy. Meanwhile, all existing stars would die and turn into white dwarfs, neutron stars, or black holes
Collisions between these black holes would result in mass accumulating into larger and larger black holes over time. The average temperature of the Universe would approach absolute zero, and black holes would vanish after emitting their final Hawking radiation. Finally, the Universe's entropy would grow to the point where no organized form of energy could be extracted from it -a scenario known as "heat death"
More and more of the Universe will pass beyond our event horizon (the CMB, the outer limit of what we can see), becoming invisible to us, according to contemporary observations, which include the existence of Dark Energy and its impact on cosmic expansion. Although the end result is not yet known, "heat death" is also thought to be a likely outcome in this scenario
Other explanations for dark energy, known as phantom energy theories, predict that the ever-expanding universe will eventually rip apart galaxy clusters, stars, planets, atoms, and even matter itself. The "Big Rip" scenario holds that the universe will ultimately perish due to its own expansion
Finally: The Universe expansion continues, while the time to leave Earth has arrived: "Humans must leave Earth within the next few centuries if they are to survive," declared the eminent theoretical physicist Stephen William Hawking in the months preceding his death in 2018. Hawking, regarded as one of the most famous theoretical physicists of his generation, believed that life on Earth could end in a disaster, such as when the Earth collides with a massive meteor, or when robots (or artificial intelligence) control humans, or when aliens from other planets invade the Earth. He also warned that overpopulation, anti-human hostility, and climate change could wreak havoc on Earth's life, and that if our species was to survive, it needed to create new life in space. One of Hawking's greatest fears for the Earth was global warming, which he warned, "Our natural resources are being depleted at an alarming rate" and that we are "giving our planet the catastrophic gift of climate change". He predicted(1) that if we do not reduce greenhouse gas emissions, the Earth will one day resemble Venus, which has a surface temperature of 460 degrees Celsius (mainly because of Carbon Dioxide accumulation in its atmosphere). He pointed out that this is not science fiction, but rather a matter governed by physical laws
1. Mike Wall, Stephen Hawking Warns: Humanity May Have Less Than 600 Years to Leave Earth; LIVE SCIENCE, November 13, 2017 10:21 am ET
