Early cosmic inflation and the expansion of the universe.

In summary, inflation gave the 'push' so to speak that set the everything moving apart. The Hubble parameter gives the relative expansion rate of the universe, i.e., the rate of expansion divided by size. Assuming the scale of the universe has increased by a factor of 10^30 since inflation ended, I calculate that Hubble parameter was about 10^58 times larger at the end of inflation than it is now.
  • #1
Herbascious J
165
7
My question is regarding the early inflationary phase of the Big Bang. As I understand it, inflation is what gave rise to the expansion energy of the universe. Meaning, inflation gave the 'push' so to speak that set the everything moving apart. This makes sense because obviously the universe has a tremendous amount of energy behind it's expansion. However, I am confused about a certain point...

If inflation is the mechanism behind the momentum of the expansion of the universe, then shouldn't the universe be expanding WAY more quickly. As I understand it, inflation was extremely rapid. So, when inflation 'shut off' what slowed down the expansion to what we observe with the Hubble flow? I realize without inflation the universe will stop doubling exponentially, but it seems something had to 'put on the brakes'. What am I missing? Thanks.
 
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  • #2
Be careful with the scale of expansion. Inflation was very quick, but only relative to the size of the universe at that time. Afterwards, gravity slowed it a bit, and some billion years ago the expansion accelerated again (but that effect is small compared to the other scales). I'm not sure how fast exactly expansion was, but it does not have to be much quicker than today.
 
  • #3
The Hubble parameter gives the relative expansion rate of the universe, i.e., the rate of expansion divided by size. Assuming the scale of the universe has increased by a factor of 10^30 since inflation ended, I calculate that Hubble parameter was about 10^58 times larger at the end of inflation than it is now.
 
  • #4
Oh, I see, that is the source of my misunderstanding then. I had assumed that the universe had achieved a fairly comparable size during inflation. But it makes sense that it shut off at a much smaller scale (many orders of magnitude) this of course allows the relative velocities of different regions to all spread out, and appear slower locally, as we see today. Thanks so much.
 
  • #5
George Jones said:
The Hubble parameter gives the relative expansion rate of the universe, i.e., the rate of expansion divided by size. Assuming the scale of the universe has increased by a factor of 10^30 since inflation ended, I calculate that Hubble parameter was about 10^58 times larger at the end of inflation than it is now.
Hmm, I think your estimate is a bit off, because that would fit the entire observable universe within a single Planck length at the end of inflation.
 
  • #6
Chalnoth said:
Hmm, I think your estimate is a bit off, because that would fit the entire observable universe within a single Planck length at the end of inflation.
I get 400µm. 40 billion light years / 10^30

Give or take a factor of 2 for radius vs. diameter, definition of size and so on, but that is far away from the Planck scale.
 
  • #7
mfb said:
I get 400µm. 40 billion light years / 10^30

Give or take a factor of 2 for radius vs. diameter, definition of size and so on, but that is far away from the Planck scale.
Ugh, sorry. My mistake. I was taking the change in expansion rate rather than the change in scale factor.

That sounds much more reasonable.
 

1. What is cosmic inflation and how does it relate to the expansion of the universe?

Cosmic inflation is a theory that suggests the universe underwent a rapid period of expansion in the first fraction of a second after the Big Bang. This expansion is thought to have been incredibly fast, causing the universe to grow exponentially in size. This theory helps explain the large-scale structure of the universe and provides a potential explanation for the uniformity of the cosmic microwave background radiation. Inflation is closely related to the expansion of the universe because it is believed to have set the initial conditions for the expansion that we observe today.

2. How was cosmic inflation first proposed and what evidence supports it?

The concept of cosmic inflation was first proposed in the late 1970s by physicist Alan Guth. It was later refined by other scientists such as Andrei Linde and Paul Steinhardt. One of the main pieces of evidence that supports cosmic inflation is the uniformity of the cosmic microwave background radiation. This radiation is thought to be leftover from the Big Bang and should have a uniform temperature across the entire observable universe. Inflation helps explain how this uniformity was achieved.

3. What is the role of the inflaton field in cosmic inflation?

The inflaton field is a hypothetical field that is thought to have caused the rapid expansion of the universe during inflation. It is a scalar field, meaning it has a single value at each point in space, and is characterized by its potential energy. As the inflaton field rolled down its potential energy hill, it is believed to have released a tremendous amount of energy, driving the rapid expansion of the universe.

4. Can cosmic inflation be tested or observed?

There are several ways in which scientists are currently testing and observing the effects of cosmic inflation. One way is through observations of the cosmic microwave background radiation, which can provide evidence of the universe's early expansion. Another way is through experiments that measure the amount of gravitational waves in the universe, as inflation is predicted to have produced a specific pattern of these waves. Additionally, scientists are using particle accelerators and other experiments to try and recreate the conditions of the early universe to further test the theory of inflation.

5. How does cosmic inflation fit into the current understanding of the universe's evolution?

Cosmic inflation is currently the most widely accepted explanation for the large-scale structure and uniformity of the universe. It is believed to have set the initial conditions for the expansion and development of the universe, including the formation of galaxies and other structures. However, it is important to note that inflation is still a theory and there are ongoing debates and research about its exact role in the universe's evolution. As our understanding of the universe continues to evolve, the role of cosmic inflation may also be refined or revised.

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