The universe may be able to withstand its own annihilation and emerge undamaged. A new "big bounce" model explains how the universe may shrink to a point and then grow again, using only the cosmic elements we now know about. The theory was proposed by George Smoot at the University of California, Berkeley, USA, and is called the cyclic model. It has similarities with other models in which there are multiple periods of expansion and contraction.
In this scenario, our universe goes through periodic collapse events, where all the stars and galaxies that exist today would just disappear. But after each such event, space expands again and the stars and galaxies reappear. This means that over time, all the material that went into making up these objects would be stretched out across the entire universe. In fact, based on current estimates, most of the mass in the form of invisible dark matter plus some of the energy from visible stars and galaxies could have come from material that was once inside dead stars or black holes. Around 5% comes from other universes separated by wall fragments.
The idea of the universe going through cycles of expansion and contraction was first proposed by Alexander Friedman in 1922. However, it was not until the 1990s that researchers began to study it more extensively. Since then, many groups around the world have worked on developing versions of this theory.
However, if there is too much material, the universe's expansion will slow and eventually cease. The cosmos will thereafter begin to contract. A contracting universe will become smaller and smaller as it gets hotter and denser, finally culminating in a fantastically compact inferno known as the Big Crunch, a type of reverse Big Bang. This scenario would also end in extinction for all life.
The most common explanation for this outcome is called "the heat death of the universe". Here the universe becomes evenly distributed again inside itself, so that no more expansion can occur. This happens when the average temperature of the universe reaches 0 degrees Kelvin (or -273 degrees Celsius), the point at which atoms stop moving because they are frozen into place by quantum effects. At this stage, the universe is said to be in thermal equilibrium - any slight deviation from this state would require an external source to restore it, such as another universe or multiverse interacting with ours.
A second possibility is called "the vacuum catastrophe". Here the universe runs out of energy to keep its contents from collapsing back into a dense form. In other words, it collapses under its own weight. This outcome is similar to what would happen if you poured enough liquid nitrogen into a balloon so that it started to float up towards the sky... but then didn't go any higher because it ran out of nitrogen.
A third option is called "the big rip".
Astronomers previously believed that the cosmos will collapse in a "Big Crunch." Most people now believe it will end in a "Big Freeze." If the expanding universe was unable to overcome the collective inward force of gravity, it would expire in a "Big Crunch," similar to the Big Bang played backwards. But if this can be done successfully, then the universe will continue to expand forever or until something stops it.
A few scientists believe we are living in a "Big Freeze" at this moment. The expansion of space is being counteracted by dark energy which is driving the universe further and further away from itself with every passing second! This process will continue indefinitely unless something new comes into play. One possibility is that one day the heat produced by all the stars and galaxies in the universe will become too much for it to handle. When this happens, the cosmic freeze-out will be over and the universe will collapse in on itself.
The answer depends on how you define "everything." If you include black holes in your definition, then yes, everything is going to collapse under its own weight. If you only consider the visible universe plus some fraction of extra dimensions, then no, everything is not going to collapse.
The fate of the universe is an important topic in cosmology. Scientists have different views on this issue but most agree that our universe is going through a phase where expansion is overcoming gravity and will eventually reverse itself and collapse upon itself.
The universe comprises everything in existence, from the tiniest atom to the greatest galaxy; it has been growing and may be limitless in scope since its formation 13.7 billion years ago in the Big Bang. Today, the expansion of the universe is speeding up this growth, with the amount of space between galaxies increasing faster than before due to their distance from each other being stretched by the force of gravity.
However, this expansion is not constant, but rather follows a cyclical pattern of contraction and expansion. This means that the universe will one day collapse under its own weight and then rebound again, only on a larger scale. The exact time when this happens depends on how much energy there is in the universe; if it is too little, then the collapse will happen now, if it is enough, then it can be many billions of years from now.
This scenario was first proposed by Einstein's friend Alexander Friedman (who called it "the world model"): he thought that the universe was shaped like a three-dimensional sphere and was therefore able to explain some observations made at the time about how much light reaches us from different directions. However, modern scientists believe that this model is too simplistic because it fails to take into account the current understanding of physics such as general relativity.
If the cosmos is growing, it must have been much smaller once at a time. This was the original state of the universe after the Planck epoch.
During the Big Bang era, the universe was infinitely small and infinitely dense. It then expanded at an ever-increasing rate until now it is almost exactly the size it needs to be to contain all possible matter and energy. Eventually, it will expand again but this time it will do so in a finite amount of time. This is called "The Eternal Return."
The universe is expanding right now because of something called "Dark Energy". If you pull up any astronomy textbook there are two ways that the universe can be described: it can be thought of as empty space or it can be thought of as full of stuff. Astronomers think that both ideas are correct, but they want to emphasize different aspects of our understanding of how everything fits together. Dark Energy is what is missing out there in order to make sure that the universe continues to expand forever without stopping. Without this mysterious force, the cosmos would eventually collapse under its own weight into a huge explosion known as a "Big Rip".
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