The universe started very small but then started to expand. In 1998 two teams of scientists discovered that the universe was speeding up. This discovery revealed that what astronomers can directly detect only makes up five percent of the total mass and energy in the universe. Invisible dark matter makes up another 24, while the arrest is a mysterious phenomenon known as dark energy.
If the kinetic energy of expansion and the potential energy of collapse are perfectly balanced, the universe will expand to a huge size and grind to a near halt. Essentially, that’s if the expansion is equal to the escape velocity. Some expansion energy remains after gravity is diluted to nothing, and the universe will expand forever, never stopping. The universe will eventually fall back inwards, and many of those distant galaxies up very close and personal as the universe undergoes the Big Crunch.
The expansion rate now is called the “Hubble constant.” It’s around 70 kilometers per second per megaparsec. Astronomers worked for decades to weigh up the galaxies across vast swaths of the universe, including their dark matter. But the universe’s density turns out to be too low, only about a quarter of what is needed to reverse the expansion. The density term, the recollapsing term, falls short of the expansion term.
Is the universe expanding?
The space-time between all 100 billion galaxies in the universe is increasing. New empty space-time is created as the universe ages like a roiling seething froth. The distances between the galaxies are growing and pushing them apart. There is no evidence that a boundary exists. Space may extend to infinity, or it may not.
In the universe, things can be curved. If things can be curved, they can be curved in on themselves. They are twisting, bending the shape of the universe and to virtually anything imaginable. – Albert Einstein
General relativity makes it possible to live in an infinite universe with no boundary at all. Because of general relativity, space-time is not a static entity. It is a dynamic and ever-changing fabric within which the locations of all galaxies are woven. Galaxies are not moving very much, but they appear to move because of new cosmic real-estate continually injected and increased distance. This creation of new space-time and the rate at which it is being created determines how fast a galaxy appears to be moving away from us.
So what is the universe expanding into? When is new space-time created, into what do the edges go? The answer depends on whether or not there are edges.
- If there is an infinite universe, then the answer has to be nothing. Adding more fabric to infinity doesn’t make more infinity. An infinite universe would have no edges that expand, and the question is meaningless. In such a universe, there would be no outside.
- If the universe is finite with a boundary, then the answer may be that the universe is expanding into something.
Waves have two basic properties:
- Wavelength: It is the length of a complete cycle measured with a ruler.
- Frequency: It is how often peaks pass one spot.
These two properties combine to give a speed, but how quickly a wave moves depends on the stuff doing the waving. For light, that’s the electromagnetic field. Anyway, since the fundamental properties of the electromagnetic field never change, neither does the speed of light. The color of light can vary.
- If it shifts toward the blue end of the spectrum, it blue-shifted.
- If it shifts toward the red end, it red-shifted.
Since light is emitted with a specific wavelength, we expect it to be received or observed with the same wavelength. In other words, this ratio to be equal to one. But sometimes it’s not. If not, then a “red-shift” has been added.
The “Doppler Effect” is one way that light can change color. But cosmological red-shift is not caused by the Doppler Effect. Besides the Doppler effect, there are 2 other sources of red-shift.
- The expansion of space.
Light redshifts as it escapes from a source of gravity. This is more apparent when the gravity is strong, like the light emitted by the accretion disk of a black hole. The expansion of space can also cause a redshift. But that expansion is slow, so the light needs to be traveling a long time for noticeable. With the light coming from stuff close by, it mixed up with the other two sources of red-shift.
Other forces like gravity are strong enough to things together despite the expansion. The fact is cosmological red-shift is not the result of a galaxy’s speed away from us. It is not the Doppler Effect! It’s the result of the space stretching along the trip. When light travels between galaxy super-clusters, that light gets stretched
as space, it’s traveling through stretches.
The more time that light travels, the more expansion it experiences. The cosmic microwave background is the oldest light in the universe. It was emitted so long ago that it isn’t even visible light anymore. It’s a microwave light. That’s a red-shift of over 1000!
Given that the universe is expanding, we cannot see the boundary now. It will forever get further and further away. There’s no to the universe will expand forever. Over billions of years, they will slip beyond the cosmic horizon, leaving only darkness beyond the local region of the Milky Way. According to the first Friedmann equation, the universe’s fate determined by its expansion and density should be intrinsically tied to its shape. After all, matter tells spacetime how to curve.
How universe is expanding?
Expanding the universe topic now becomes one of the greatest quests in modern science. The universe is getting bigger every day, and the universe’s expansion is accelerating. Ironically, it means that the universe is getting bigger as time goes on. A few years ago, scientists tried to measure how much the universe slowed down over time. It makes sense, right? An explosion happened a long time ago with the Big Bang. They assumed the Big Bang would slow down and gravity would pull things back together.
Astronomers think that the universe appears to be expanding at an accelerating rate. But they have no idea what’s causing this. They tend to say about dark energy. They know this dark energy makes up seventy percent of what’s out there in the cosmos. It’s stronger than gravity and may eventually be stronger than the forces that hold atoms together.
The human body is held together by electromagnetism in atoms. But does the expansion of space increase and accelerate, and does it even overcome those forces? Astronomers call that the big rip, and it’s a possibility that eventually, the expansion will get strong enough to rip apart atoms.
Example: Suppose many tennis balls are connected by elastic rope. Each tennis ball represents a galaxy. It could be the Milky Way galaxy, and the elastic is space itself. Since the universe is spreading, it’s like taking this elastic and stretching it. As the elastic expands, the galaxies start to spread out and become more remote from one another. So the simple model of the universe with tennis balls and elastic breaks down if we try to apply it to one ruled by dark energy.
It shows a universe where the rate of expansion between the galaxies is accelerating over time. Elastic would have to stretch infinitely far, and we would have to run away from each other instantly fast. But it is not possible with a simple model, and that, in a way, is an example of how bizarre a dark energy-dominated universe could be.
What is the universe expanding into?
The universe is expanding faster than light! Whenever someone starts talking about an expanding universe, there’s always at least one person asking this: What is it expanding into? Let’s say you have a balloon with some bit of thingies attached.
These represent galactic super-clusters, which contain 10s of 1000s of galaxies. People don’t see the universe’s expansion on scales because other forces like gravity are strong enough to hold things together despite the expansion. If anyone blows air into the balloon, it expands, carrying the superclusters with it. They got farther apart without having to do any actual moving in space.
The problem is the expanding balloon has curvature, positive curvature. None of that applies to the universe. Remember, the entire universe is everything. Even if the universe were finite like that balloon, the balloon is all there is. If the universe is infinite, it solves the nothingness issue because the universe can expand into itself. If space is infinite, that’s more and more infinity. In an infinite universe, there is no edge, there is no center, and the big bang happens everywhere.
Experiments of universe expansion
The year after the big bang was hypothesized, Edwin Hubble found evidence of the expanding universe. He showed the galaxies were moving away from earth, and the further away moving faster. These objects not only blasted away from each other through space, but space itself was growing in size and moving the matter with it. The galaxies are not only moving away from earth. They are expanding away from everywhere all at once. Subsequent observations have helped astronomers to tell the history of the enlarging universe.
In 1964 the discovery was made of the cosmic microwave background. It is a cold glow left over from the big bang. It was shown redshift that the universe had been expanding for approximately 13.8 billion years. Surveys of large-scale structures of the universe have since revealed billions of galaxies are clustered together around vast empty voids. The large-scale structures in the universe, such as filaments of galaxies, correspond to minute ripples in the cosmic microwave background.
However, the future of the universe is somewhat uncertain. It was unknown whether it would expand forever or one day collapses under its gravity. The expansion of the universe is assumed to be slowing down. Due to the force of gravity, measuring the deceleration should reveal the ultimate fate of the universe. However, when measured, the cosmic expansion is found to be accelerating. This acceleration is due to a previously unknown force that works against gravity. It is now known to be dark energy.
Throughout the 20th century, cosmologists assumed that the expansion rate was slowing down following a rapid initial expansion. Gravity would start decelerating the universe. It seemed like there were two main possibilities for the universe’s fate.
- If the universe were heavy enough, gravity would eventually slow the expansion to a stop and then begin to pull back together in a big cataclysmic crunch. This is a big bang in reverse.
- The second possibility was that the universe was too light to stop the expansion, which would continue forever but gradually slow down. This process would result in a heat death where the universe’s material had broken up and became infinitely dispersed.
A measurement of the deceleration of the universe’s expansion would tell cosmologists which future possibility the universe was heading for it. By the mid-1990s, two programs were underway to measure the universe’s expansion rate. These two projects considered merging, but they had rather different ideas about proceeding. So they opted instead for a healthy rivalry.
Both projects used a discovery made by the supernova survey. This was carried out in chile between 1989 and 1995. The survey found that type 1A supernovae could be used as standard candles. It means that a certain type of supernova can be used to measure distances across space. A standard candle is an object of known brightness, its apparent magnitude.
The brightness of the earth shows how far away it is. A type 1A supernova is a little different than a standard supernova. It forms when a large star runs out of fuel and explodes. One of these stars is a giant star, and the other is a white dwarf. The white dwarf’s gravitational pole whole stellar material over from the giant because it is denser and has a larger gravitational pull.
The material then accretes on the surface of the white dwarf until it has grown to 1.38 solar masses. At this point, the temperature and pressure are so much that the star ignites and explodes. It creates an object that is billions of times brighter than the sun.
Both surveys used the observatory in Chile to find these type 1A supernovae. The plan was not simply to find the positions of the supernovae. They wanted to find their distance. So they used the keck telescope in Hawaii to take the spectra of each explosion. This gave its redshift. So therefore, the brightness or magnitude of each star can give its distance, which could be billions of light-years.
While its redshift indicated its relative speed to earth, this is caused by the universe’s expansion. The teams aimed to measure the rate at which the universe was changing. As indicated by distant objects, the expansion rate was expected to be tailing off. Exactly how fast it would show if the universe were heavy or light.
However, when the teams looked beyond 5 billion light-years, the universe’s expansion was not slowing down. It was speeding up. This result was first thought to be an error, but successive checks showed it wasn’t. Both teams discovered the very same thing. In 1998 the teams went public with their findings, which shook the scientific world.
Using Einstein’s general relativity equations, they found that these results appeared to give the universe a sort of negative mass. In other words, it appeared an anti-gravitational force was pushing apart. This source of energy was named dark energy. They theorized that if dark energy continues to grow in the future, it may push the universe apart and disperse all galaxies.
So that eventually they would be too far away to be seen from earth. Finally, the particles in atoms would also be scattered, resulting in heat death. It is dubbed the big rip. The universe relies on a critical value and an average density. It can give us a good clue to the future of the universe.
The critical value is estimated to be the equivalent of 5 protons per cubic meter. So if the average density of the universe is below a certain critical value, it should be closed and end in a big crunch. If the density is equal to the critical density, the universe’s geometry will be flat, and the universe ought to carry on into the future, neither expanding nor contracting.
If the density is below a critical value, the universe should be open and expand forever to end a heat death eventually. Observations suggest that the universe’s expansion accelerates due to this mysterious dark energy. Dark energy may also indicate the apparent acceleration because we are inside a region with less matter than anywhere else in the universe.
Dark energy may also be explained by a mathematical device einstein created in 1917 called the cosmological constant. Einstein used this as a value that would counteract the pull of gravity and would make the universe a static and very unchanging place.
However, Einstein’s equations show that the universe can only be dynamic, meaning it can only expand or contract. Once the universe became big and empty, the effects of dark energy appeared to have become the most dominant force in the universe. It may be that a different force takes over in the future, or it might be that dark energy’s effects continue to grow.
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Overbye, Dennis (20 February 2017). “Cosmos Controversy: The Universe Is Expanding, but How Fast?”. The New York Times. Retrieved 21 February 2017.
Radford, Tim (3 June 2016). “Universe is expanding up to 9% faster than we thought, say scientists”. The Guardian. Retrieved 3 June 2016.
Slipher, V. M. (1913). “The Radial Velocity of the Andromeda Nebula.”
Vesto Slipher – American astronomer.
“On the Curvature of Space.” General Relativity and Gravitation: 1991–2000.