The End Of The Universe

Physics ERT The End of Our Universe

This essay attempts to explain how the universe is going to end. Astronomers have varied ideas on how the universe will end. Some say the universe will fly apart forever until the cosmos is cold and dark. Others say that it will stop expanding, and will implode in on itself in a final Big Crunch. However, discoveries being made have proven one thing: the universe is expanding faster and faster all the time. Many factors, mostly dark energy, affect the expansion of the universe. Dark energy causes an acceleration of the expansion of the universe, and since dark energy increases as a function of space, its effects grow, and with it so does the speed at which the universe expands.

Madhavi Madala Explanation of Physics

The Milky Way is a massive, twirling pinwheel of 100s of billions of stars but is only one of the 10s of billions other galaxies in the universe rushing pell-mell away from each other in the aftermath of the Big Bang. Astronomers have diverse ideas on how the universe will end. The galaxies may fly apart forever with their glow fading until the cosmos is dark and cold. Maybe the expansion will slow to a halt, reverse direction and send the stars and galaxies flying back together in a final Big Crunch. With a series of discoveries being made, the answer may have been provided once and for all. There is no Big Crunch, just the expansion of space for essentially eternity. Astronomers have known since the 1920s that the galaxies were flying apart. But recently theorists have discovered that the whole cosmos must have been at one point, hotter and smaller. About 300,000 years after the Big Bang the universe would have been a cloud of hot, dense gas glowing white hot. Because this cosmic glow had nowhere to go, it must still be there, although so diminished that it took the form of feeble microwaves. The discovery of the cosmic-microwave background radiation convinced scientists that the universe really had initiated from the Big Bang 15 billion years ago. As the universe expands, the combined gravity from all the matter within it tends to slow down the expansion of the universe. If the pull by the gravity is strong enough, the expansion would stop and reverse direction. If it was not, the universe would go on expanding forever. A way to determine whether or not the gravity is slowing down the expansion of the universe is to weigh the cosmos by calculating the gravity of all the stars and galaxies in the universe and comparing it to the expansion rate of the universe. If the universe is expanding faster than the pull of gravity is slowing it down, then the universe will not end in a Big Crunch; it will go on expanding forever. However, to calculate the total amount of gravity if very hard as it is unknown exactly how much matter is present in the universe. Scientists have known since the 1930s that there existed matter other than the visible stars and gases. The only possible explanation was that an invisible dark matter held together individual galaxies and also those in clusters and stopped them from flying off into space. While inferring the mass of dark matter in and around galaxies is easy, it is unknown whether dark matter fills up other parts of the universe where its effects are imperceptible. Another way to determine whether the expansion of the universe is slowing down and by how much, known formally as the deceleration parameter, is to compare the speed at which the nearby and distant universe is expanding. To do this, the brightness of Type 1a Supernovas, which are so bright that they can be seen all the way across the universe, are measured. Since the entire universe expands at the same rate at any given time, more distant galaxies fly away from the centre of the universe and also the Earth, faster than closer galaxies. To get the rate of the expansion of the universe, both now and in the past, the distance to these supernovas inferred from their brightness and their speed of recession inferred by the reddening of their light, a phenomenon known as the Doppler shift, are measured. However, the results obtained are not expected. The cosmic expansion should be slowing down depending on how much matter it contains. But the results obtained state that the expansion is speeding up. Distant supernovas should be brighter than closer ones, but they appear fainter. This acceleration of the expansion of the universe suggests that a powerful antigravity forces the galaxies to fly away from each other although normal gravity tries to pull them together. Einstein also discussed antigravity in his General Theory of Relativity. This theory suggested that the universe must either be expanding or shrinking. The cosmological constant is a force that counters gravity and inflates the universe. The strange properties of the cosmological constant propose that the universe slowed down

during the early stages of expansion then started to accelerate because dark energy grows as a function of space. Since there was not much space in the early universe, the effects of gravity would have suppressed that of dark energy. Now, as the universe has grown to immense proportions, the growing distance between galaxies has proven the effects of gravity less influential than that of dark energy. With the discovery of a distant supernova which was 50% closer to the centre of the universe than any other supernova observed before, scientists can determine its speed of recession from Earth and also infer that this supernova was shining when the expansion of the universe was slowing down. What makes this discovery more convincing is that the incessant search for lumpiness in the cosmic background radiation has proven that dark energy is real. Since the discovery of cosmic-microwave background radiation, scientists have explored the cosmic afterglow for variations in intensity. Matter is not distributed evenly in the modern universe. Galaxies tend to group together fairly close to each other in clumps known as clusters and superclusters. Scientists have rationalized that this lumpiness must have evolved from original lumpiness in the primitive cloud of matter that gave rise to the background radiation. After numerous observations and measurements from several satellites and telescopes, scientists have confirmed that the lumps are real and that this primitive lumpiness has continued into modern times. It is clear now that galaxies cluster together into enormous lumps that manifest the state of the universe shortly after the Big Bang. Lumps in the young universe were areas of warm or cool radiation which usually came in fixed sizes. Information about the premature cosmos can be obtained by observing the typical sizes and temperatures of these warm and cool regions. From the equations of nuclear physics and measurements of the amounts of H2, He and Li in the universe, we can infer that the subatomic particles (electrons, protons and neutrons) amount to around only 4% of the critical density. A further 23% of the matter is dark matter. Dark matter is composed of objects that are difficult to detect, such as black holes, brown dwarfs, and intergalactic dust. It also includes particles such as neutrinos, neutralinos and axions. Dark energy makes up the remaining 73% of the matter in the universe. Critical density is the average density of matter in the universe that would be needed to eventually stop the expansion of the universe. A universe at exactly the critical density is said to be flat or Euclidean. When the density of the universe is greater than the critical density, then the expansion will stop and the universe will eventually implode under its own gravitational pull, the Big Crunch. This is a closed universe scenario. However, when the density of the universe is less than critical density, the cosmic expansion will continue for eternity in an open universe scenario. The average density inferred from all the visible matter in the universe is about one hundredth of the critical density. However, when the inferred existence of dark matter and dark energy are taken into account, the universe seems almost at critical density and has an overall flattish shape. The flatness of the universe suggests that the theory of inflation is true. The theory says that the entire visible universe grew in a bout of turbo-expansion from almost nowhere in almost no time at all. The consequence of this inflation is that the universe is flat. If this is

true, scientists can safely assume the fate of the universe. All the matter in the universe together does not have enough gravity to stop its expansion and the antigravity effect of dark energy speeds up this expansion. And because the amount of dark energy grows as a function of space, its effects will only increase over time. This means that the universe will continuously grow forever until finally, all that is left is black holes which would disintegrate into vagrant particles which will also decay to leave an empty, infinitely large void. Astronomers have varied ideas on how the universe will end. Some say the universe will fly apart forever until the cosmos is cold and dark. Others say that it will stop expanding, and will implode in on itself in a final Big Crunch. However, discoveries being made have proven one thing: the universe is expanding faster and faster all the time. Many factors affect the expansion of the universe. Dark energy causes an acceleration of the expansion of the universe, and since dark energy increases as a function of space, its effects grow, and with it so does the speed at which the universe expands. The universe will continue to expand for eternity until it is nothing but an empty, cold and desolate void

Glossary Big Bang: the explosion of a single extremely dense mass of matter that started the universe. Big Crunch: a hypothetical end of the universe in which all of the mass would contract back together if its expansion were to slow down sufficiently which would occur if there is enough mass in the universe for gravity to slow, halt, and eventually reverse the current expansion Cosmological constant: a term added by Einstein to his equations of relativity, amounting to a force that opposed gravity and inflates the universe. Dark energy: it is a hypothetical force that opposes the attraction of gravity throughout the universe and causes the expansion of the universe to accelerate Type 1a Supernovas: these are special supernovas which are so bright that they can be seen all the way across the universe, and uniform enough to have their distance from Earth accurately calculated.

Questions Q1. *

What are the components of the universe?

Ans.

The universe is made of 4% ordinary matter like subatomic particles, etc.

Q2. **

Explain how the ‘Big Crunch’ would occur.

Ans. The Big Crunch is a hypothetical situation where the combined gravity of all of the mass in the universe would act as a reverse to the expansion of the universe. The gravity would slow down the expansion of the universe until it stopped, and then reverse direction to pull the universe back on itself. However there is not enough mass in the universe for this to happen. And the effect of dark energy acts to enhance the expansion of the universe and acts as an antigravitational force, accelerating this expansion. Q3. ***

If the Big Crunch did happen, what would be the ultimate fate of the universe?

Ans. If the Big Crunch happened, which would only happen if there was enough matter in the universe to oppose the expansion of the universe, the universe could collapse and everything in it will end in one infinitely tiny point of mass and energy called a singularity. The galaxies would rush towards each other and after adequate time they will come into contact. Their gases will mix and their atoms will be heated under the immense pressure exerted on the shrinking universe and eventually the universe will return to the heat and chaos from which it emerged, another Big Bang. In this way the universe will continue to exist in a never-ending cycle of birth, death and rebirth.