- #1
Jupiter60
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- TL;DR Summary
- Expansion
Will the universe keep expanding faster and faster for all eternity or is there a limit to how fast the expansion will get?
Accelerating expansion of the Universe
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- Thread starter Jupiter60
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In summary: This is because the scale factor (a) increases without limit, and the Hubble parameter (H) stays constant.
- #2
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In the current model, the expansion is driven by the dark (vacuum) energy. As the universe expands, the vacuum energy becomes ever more dominant and the expansion rate increases without limit.
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- #3
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The expansion rate approaches the one corresponding to the vacuum energy. It is decreasing towards that value as total energy density decreases.PeroK said:
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- #5
Bandersnatch
Science Advisor
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To clarify the above exchange for the OP: there's a difference between expansion and expansion rate.
In the current model the former continues growing without limit, with distances growing ever faster, and approaching exponential expansion (meaning: any two sufficiently distant galaxies will recede faster and faster).
The latter decreases towards a constant value (meaning: every distance will eventually grow by the same percentage after the same amount of time).
Constant expansion rate equates exponential expansion.
In technical parlance expansion is the growth of the scale factor ##a##, i.e. ##\dot a>0##. While expansion rate is the value of the Hubble parameter ##H##.
Expansion:
Expansion rate vs time:
In the current model the former continues growing without limit, with distances growing ever faster, and approaching exponential expansion (meaning: any two sufficiently distant galaxies will recede faster and faster).
The latter decreases towards a constant value (meaning: every distance will eventually grow by the same percentage after the same amount of time).
Constant expansion rate equates exponential expansion.
In technical parlance expansion is the growth of the scale factor ##a##, i.e. ##\dot a>0##. While expansion rate is the value of the Hubble parameter ##H##.
Expansion:
Expansion rate vs time:
- #6
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What @Bandersnatch said.phinds said:
- #7
JimJCW
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Jupiter60 said:
For models that assume a non-expanding universe, the scale factor, a, remains constant and the expansion rate, da/dt = 0.
In the Big Bang model, a(t) continues to increase and da/dt > 0.
Using Jorrie’s calculator, we can calculate a(t) and the Hubble parameter, H(t) (see Post #5). The expansion rate can be calculated with the equation,
da/dt = a(t) H(t) (see, for example, Hubble's law)
The results are plotted below:
The above figure suggests that, according to the ΛCDM model, the universe will keep expanding faster and faster forever (see Post #2).
FAQ: Accelerating expansion of the Universe
What is the accelerating expansion of the Universe?
The accelerating expansion of the Universe is the observed phenomenon that the rate at which the Universe is expanding is increasing over time. This means that galaxies and other objects in the Universe are moving away from each other at an ever-increasing rate.
What is causing the accelerating expansion of the Universe?
The exact cause of the accelerating expansion of the Universe is still unknown, but it is believed to be due to a mysterious force called dark energy. This force is thought to make up about 70% of the total energy in the Universe.
How is the accelerating expansion of the Universe measured?
The accelerating expansion of the Universe is measured through various methods, including using the brightness of supernovae (exploding stars) and the distribution of galaxies in the Universe. These measurements are then compared to theoretical models to determine the rate of expansion.
Is the accelerating expansion of the Universe a recent discovery?
No, the idea of an accelerating expansion of the Universe has been around since the 1990s, but it was not confirmed until 1998 when two independent teams of scientists observed distant supernovae and found evidence of an accelerating expansion. This discovery was awarded the Nobel Prize in Physics in 2011.
What implications does the accelerating expansion of the Universe have for the future of the Universe?
The accelerating expansion of the Universe suggests that the Universe will continue to expand at an increasing rate, eventually leading to a "Big Freeze" scenario where all matter is spread out and the Universe becomes cold and dark. However, this is just one of many possible outcomes and much is still unknown about the future of the Universe.