How to work out the radius and diameter of the universe?

[ShaneJ]

Hey, How would you work out the radius and diameter of the universe?

[EdEarl]

Astronomers have been working on measuring distances for quite a while. It has been a challenge.

 

Distance to some of the nearest stars is calculated by triangulation, as surveyors do to measure distances on earth. This method uses trigonometry.

 

 

Type 1a supernova always explode with the same brightness; thus, they are used as a standard candle to measure distances to galaxies that contain them. See video.

 

Using the distances to various galaxies, the amount of redshift in light from these galaxies is calibrated. Now redshift can be used to measure the distance to galaxies.

 

Next, the redshift to the most distant galaxies is recorded and used to determine their distance from us.

 

http://i3.ytimg.com/vi/rpXBAFJ2KUI/mqdefault.jpg

http://newscenter.lbl.gov/news-releases/2011/12/14/sn-2011fe/

 

I am not an expert, but believe this to be fairly accurate. Someone may teach me a bit more if I am wrong. If you want more detail, please ask questions.

Edited June 4, 2013 by EdEarl

[SamBridge]

If you know how long ago the universe started expanding, it's initial size as well as it's growth rate you could model the radius. However we don't concretely have any of these things, supposedly space was expanding even faster than light, all we can see is the radius of the sphere we observe.

[Airbrush]

If the entire universe was really smaller than a proton when it began, and it has been expanding at a finite rate since the Big Bang, even if inflation happened many times since the Bang (faster than light speed expansion is not an infinite rate), the universe would have to now be FINITE in size.

 

The only way this cannot be true is if only the OBSERVABLE portion of the universe was smaller than a proton at the moment of the Big Bang. That would suggest that the entire universe began infinite in size for it to now be infinite in size.

 

"...The size of the Universe is unknown; it may be infinite. The region visible from Earth (the observable universe) is a sphere with a radius of about 46 billion light years,[33] based on where the expansion of space has taken the most distant objects observed...."

 

http://en.wikipedia.org/wiki/Universe

 

This means the CMBR (Cosmic Microwave Background) is about 46 Billion LY away, which is about 50% further in distance from us than the most distant observable galaxies and quasars, which are about 30 Billion LY away from us at this moment.

Edited June 20, 2013 by Airbrush

[EdEarl]

I understand some of the reason for 96*10⁹ LY size. However, I am confused.

 

What is meant by

The farthest distance that it is theoretically possible for humans to see is described as the observable Universe.

(my emphasis) And, why does that differ from what we have been actually able to see.

 

 

The following two quotes, indicate inflation occurred before the CMB.

The CMB is a snapshot of the oldest light in our Universe, imprinted on the sky when the Universe was just 380,000 years old. It shows tiny temperature fluctuations that correspond to regions of slightly different densities, representing the seeds of all future structure: the stars and galaxies of today.

From: http://en.wikipedia.org/wiki/Cosmic_Background_Radiation

 

In physical cosmology, cosmic inflation, cosmological inflation, or just inflation is the theorized extremely rapid exponential expansion of the early universe by a factor of at least 1078 in volume, driven by a negative-pressure vacuum energy density.[1] The inflationary epoch comprises the first part of the electroweak epoch following the grand unification epoch. It lasted from 10−36 seconds after the Big Bang to sometime between 10−33 and 10−32 seconds. Following the inflationary period, the universe continued to expand, but at a slower rate.

From: http://en.wikipedia.org/wiki/Cosmic_inflation

 

Does inflation account for the 96*10⁹ LY size? If so, why do they refer to it as observable? If not, then at some later point the universe must have expanded faster than the speed of light, which AFAIK would make the additional size unobservable.

[Delta1212]

I understand some of the reason for 96*10⁹ LY size. However, I am confused.

 

What is meant by

(my emphasis) And, why does that differ from what we have been actually able to see.

 

 

The following two quotes, indicate inflation occurred before the CMB.

From: http://en.wikipedia.org/wiki/Cosmic_Background_Radiation

 

From: http://en.wikipedia.org/wiki/Cosmic_inflation

 

Does inflation account for the 96*10⁹ LY size? If so, why do they refer to it as observable? If not, then at some later point the universe must have expanded faster than the speed of light, which AFAIK would make the additional size unobservable.

It's not saying that we can't see as far as we theoretically could. It's saying that we could not, even in theory, see any farther than we do.

 

It's like saying that the fastest we can theoretically communicate over any distance is the speed of light. We frequently do communicate at that speed, but the importance of noting it as a theoretical limit is conveying that it's impossible to do any better, not that it's a limit we think we can reach but haven't.

[EdEarl]

Scientific observation of the Universe, the observable part of which is about 93 billion light years in diameter,[7] has led to inferences of its earlier stages. These observations suggest that the Universe has been governed by the same physical laws and constants throughout most of its extent and history. The Big Bang theory is the prevailing cosmological model that describes the early development of the Universe, which in physical cosmology is calculated to have occurred 13.798 ± 0.037 billion years ago.

From: http://en.wikipedia.org/wiki/Universe#Observational_history

 

Does this mean the light we see is 13.798 ± 0.037 billion years old, but we see out to about 46 billion light years distance? The CMB comes to us further than the oldest galaxies, but according to the figure titled "Big Bang Explosion, 13.7 billion years" it is 13.7 billion years old. See figure above: http://en.wikipedia.org/wiki/Universe#Big_Bang_model

 

I am still confused.

[Delta1212]

From: http://en.wikipedia.org/wiki/Universe#Observational_history

 

Does this mean the light we see is 13.798 ± 0.037 billion years old, but we see out to about 46 billion light years distance? The CMB comes to us further than the oldest galaxies, but according to the figure titled "Big Bang Explosion, 13.7 billion years" it is 13.7 billion years old. See figure above: http://en.wikipedia.org/wiki/Universe#Big_Bang_model

 

I am still confused.

Universal expansion means that everything is moving away from us. So light emitted 13 billion years ago from an object 13 billion ly away reaches us after 13 billion years, during which time the distance has increased to 46 billion ly.

[EdEarl]

Universal expansion means that everything is moving away from us. So light emitted 13 billion years ago from an object 13 billion ly away reaches us after 13 billion years, during which time the distance has increased to 46 billion ly.

tyvm That is a good way to say it.

[Delbert]

Hey, How would you work out the radius and diameter of the universe?

Not forgetting that when we look out X billion light years we are looking back in time that amount. So all we see is the past universe all around us which, according to big bang theory, was much smaller! It seems that asking how big it is is somewhat difficult if we can't see parts of the universe billions of light years way as it is now!