Trying to find out how exactly we find out how big the visible universe is.

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In summary, the distance that light has traveled since the big bang can be calculated by dividing the speed of light by Hubble's constant and converting to parsecs, which results in a distance of approximately 13.2 billion light years. However, this calculation only gives the proper distance to galaxies with a recession velocity in proper distance coordinates, and is not strictly the distance that light has traveled. This number is a coincidence due to similar orders of magnitude for matter and dark energy density in the current epoch.
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zeromodz
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Okay, can someone please tell me how you find how far light has traveled since the big bang. I know the answer is 13.2 billion year, and I know you can get it by using

c / H = answer in parsecs

Then I convert parsecs to light years and I can get the time and distance from there. But, how do you get the speed of light divided by Hubbles constant. It doesn't make sense to me.
 
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What do you mean, "how do you get"? Do you mean you want a derivation?
 
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zeromodz said:
Okay, can someone please tell me how you find how far light has traveled since the big bang. I know the answer is 13.2 billion year, and I know you can get it by using

c / H = answer in parsecs

Then I convert parsecs to light years and I can get the time and distance from there. But, how do you get the speed of light divided by Hubbles constant. It doesn't make sense to me.

You can do the division okay, as long as units are consistent; but what you get is not strictly how far light has traveled.

It gives you the proper distance now to galaxies with a recession velocity in proper distance co-ordinates of c, which is a different thing.

c is 300,000 km/s and H is about 74 km/s/Mparsec. The division will give you a distance in MegaParsecs of 4051, which is indeed about 13.2 billion light years.

That this number is so close to the age of the universe is something of a co-incidence, associated with the fact that in the current epoch we have similar order of magnitudes for matter density and dark energy density (following the ΛCDM model).

Cheers -- sylas
 

Related to Trying to find out how exactly we find out how big the visible universe is.

1. How do scientists measure the size of the visible universe?

Scientists use various methods to measure the size of the visible universe, including triangulation, redshift analysis, and cosmic microwave background radiation. Triangulation involves measuring the distance between two points in space and using mathematical equations to calculate the distance to other objects. Redshift analysis looks at the light emitted by objects in the universe and measures how much the wavelength of the light has stretched due to the expansion of the universe. Cosmic microwave background radiation is the leftover radiation from the Big Bang and can be used to estimate the size and age of the universe.

2. How accurate are the measurements of the visible universe?

The measurements of the visible universe are constantly improving with advancements in technology. Currently, scientists estimate the visible universe to be around 93 billion light-years in diameter. However, due to the expanding nature of the universe and limitations in our ability to observe distant objects, there is a margin of error in these measurements. As technology continues to advance, scientists hope to refine these measurements and get a more accurate understanding of the size of the visible universe.

3. Can we ever know the exact size of the visible universe?

As the visible universe is constantly expanding, it is impossible to know the exact size at any given moment. However, scientists can continue to gather data and refine their measurements to get a better understanding of the size and shape of the universe. With advancements in technology and further exploration of space, our understanding of the visible universe will continue to improve.

4. Are there any theories about the end or edge of the visible universe?

Currently, there are several theories about the end or edge of the visible universe, including the Big Crunch theory, the Big Rip theory, and the Heat Death theory. The Big Crunch theory suggests that the universe will eventually stop expanding and start to collapse in on itself. The Big Rip theory proposes that the expansion of the universe will continue to accelerate until everything is torn apart. The Heat Death theory suggests that the universe will continue to expand until all energy is evenly distributed and the universe reaches a state of maximum entropy.

5. How does the size of the visible universe compare to the entire universe?

The visible universe is just a small fraction of the entire universe. The visible universe only includes the objects and regions of space that we can observe with our current technology. It is estimated that the entire universe is much larger than the visible universe, possibly infinite in size. However, since we cannot observe beyond the visible universe, we may never know the exact size of the entire universe.

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