Calculating universe age vs. size of universe

In summary, The age of the universe is 13.73 billion years, and has remained unchanged by the assumptions made about it.
  • #1
BrianConlee
65
0
Hello,

I was pondering the age of the universe and reading about how it was calculated, but then I began questioning something.

Two scenarios, BIG IF. (I know, it's a big IF. I'm sure I'll get a lot of comments about how it's not possible, or improbable. I get it. but...) IF:

-We determine the exact size of the universe in both of these scenarios-

1. The universe is "almost exactly" the size of the observable universe. (yes I know that's qualitative not quantitative, but you know what I mean)

2. The universe is "approximately" 100 times the size of the observable universe. (see scenario 1 comment)


Ok, so this begs the question: How do these two scenarios differ in the universe's age FROM 13.73 billion years?

Would this alter the Hubble constant possibly?

Thanks.
 
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  • #2
Ok, so this begs the question: How do these two scenarios differ in the universe's age FROM 13.73 billion years?
They don't.
Would this alter the Hubble constant possibly?
No. There's a theorem (Birkhoff) that sperical shells of matter (the universe outside the observable part) have no gravitational influence whatsoever on what's inside.
So the evolution is the same whether the universe is as big as a cherry stone or infinite.
 
  • #3
Thanks for the response. It was really bothering me how they could determine the age without knowing the at least approximate true size.

Can I ask while we're on the topic, what assumptions are being made in order to determine the age?
 
  • #4
There has been some recent observations which suggest that there may be a large source of gravitational attraction outside the observable universe. It appears that a large group of galactic clusters are traveling in some particular direction, over and above the expected expansion.
 
  • #5
Can I ask while we're on the topic, what assumptions are being made in order to determine the age?
The assumptions are:
- General Relativity is an accurate enough description of gravity, space and time
- The (observable) universe is homogeneous
- The universe as we see it is isotropic

The last assumption is more or less experimental fact (the alleged dark flow would be a perturbation, if it exists).
The second assumption has a reasonable basis in observations, and is quite natural given the observed isotropy.
The first assumption seems also safe, given the succes of GR in all tests done so far.

All of these assumptions are being questioned all the time. However, as of now, there is no unambiguous evidence against them, and there have been no really viable alternatives proposed.

With the assumption, you're constrained to the Friedman models of the universe. The current LCDM model is the one best fitting the observations.
 

1. How do scientists determine the age of the universe?

Scientists calculate the age of the universe by using a variety of methods, including observing the cosmic microwave background radiation, measuring the expansion rate of the universe, and studying the ages of the oldest stars and galaxies.

2. What is the current estimated age of the universe?

The most recent estimate of the age of the universe is about 13.8 billion years. This number is constantly being refined as new data and research becomes available.

3. Does the size of the universe affect its age?

No, the size of the universe does not affect its age. The age of the universe is determined by the rate at which it has been expanding since the Big Bang. However, the size of the observable universe, which is the portion of the universe that we can see, does impact our understanding of its age.

4. How does the expansion rate of the universe relate to its age?

The expansion rate of the universe, also known as the Hubble constant, is a key factor in calculating the age of the universe. By measuring the current expansion rate and working backwards, scientists can estimate the age of the universe.

5. Can we accurately determine the exact age of the universe?

While scientists have made significant progress in determining the age of the universe, it is still an ongoing area of research and there is no definitive answer yet. As technology and scientific understanding continue to advance, we may be able to get closer to an exact age for the universe.

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