# how big is the universe?

## Recommended Posts

just a question. If, and Ill use the hubble space telescope for my question, if the hubble can "see" objects out about 14 billion light years in a particular direction, and you spun the hubble around to the opposite direction and it can "see" objects about 14 billion light years wouldnt that make the universe 38 billion years old? If your point of reference was the object viewed by the hubble 14 billion light years away and you were viewing the earth from there and that was as far as you could see, the object in the opposite direction would still be another 14 billion light years away right? im just asking. Just a reference to the fact that if you drew a circle with hubble as the center, wouldn't 14billion light years be the radius and not the diameter?

##### Share on other sites

Well, first of all, we don't know how big the Universe is or how big it started out, we can only view a spherical volume around Earth which we call the observable universe. We don't know if the whole Universe is smaller or greater than the observable universe but most likely the whole Universe is much much bigger than the tiny part we can currently see.

Secondly, the Universe is and has always, so far back in time we can view, been expanding so when we see something very distant, we don't really see how it looks today or where it is, we see light emitted sometime very far in the past and as such these objects emitting this light has probably changed a lot since then and further on they are no longer located anywhere close to where the light we see was emitted from.

Lastly, the expansion of the Universe is not caused by objects moving outward through space, according to modern cosmology based on Einsteins theory of Relativity it is caused by space itself between objects expanding, and as such space is able to expand faster than the speed of light, making the observable universe grow faster than it is aging.

The age of the Universe, ~14 billion years, is close to how long it took for the most distant light to reach us, but the Cosmic Microwave Background Radiation was emitted from a distance of only ~4o million lightyears and the matter that emitted it is now ~46 billion lightyears distant. When the CMBR we observe today was emitted, its source was receding from us with ~57 times lightspeed due to expansion of space and it is currently receding with ~3 times lightspeed.

##### Share on other sites

just a question. If, and Ill use the hubble space telescope for my question, if the hubble can "see" objects out about 14 billion light years in a particular direction, and you spun the hubble around to the opposite direction and it can "see" objects about 14 billion light years wouldnt that make the universe 38 billion years old? If your point of reference was the object viewed by the hubble 14 billion light years away and you were viewing the earth from there and that was as far as you could see, the object in the opposite direction would still be another 14 billion light years away right? im just asking. Just a reference to the fact that if you drew a circle with hubble as the center, wouldn't 14billion light years be the radius and not the diameter?

How do you get "38 Billion years old" for the age of the universe?

Hubble cannot "see" objects 14 Billion LY away. It can see light from ancient galaxies and quasars about 13 Billion years OLD. Those objects are much further now than when their light, which we see now, left them. The furthest galaxies seen are now about 30 Billion LY away, and the Cosmic Microwave Background is about 50% further away than the furthest galaxies, or as Spyman told us is now about 46 Billion LY away. This gives us an observable universe of about 92 Billion LY across, with us at the center, but that only makes us the center of our observable, or visible, universe.

If you drew a circle with hubble as the center, and the CMB as the radius, the radius is NOW 46 Billion light years.

Edited by Airbrush
##### Share on other sites

How do you get "38 Billion years old" for the age of the universe?

Hubble cannot "see" objects 14 Billion LY away. It can see light from ancient galaxies and quasars about 13 Billion years OLD. Those objects are much further now than when their light, which we see now, left them. The furthest galaxies seen are now about 30 Billion LY away, and the Cosmic Microwave Background is about 50% further away than the furthest galaxies, or as Spyman told us is now about 46 Billion LY away. This gives us an observable universe of about 92 Billion LY across, with us at the center, but that only makes us the center of our observable, or visible, universe.

If you drew a circle with hubble as the center, and the CMB as the radius, the radius is NOW 46 Billion light years.

Can you expand (excuse the pun) on this part? Isn't the CMB everywhere?

##### Share on other sites

Can you expand (excuse the pun) on this part? Isn't the CMB everywhere?

The CMB is everywhere at a distance of now approx 46 Billion light years. That is how far you have to go to find regions of the universe that have cooled that much, and that is the furthest anything can be detected. There is plenty more beyond that which will always remain invisible to all our detection techniques. The limits to our observable universe is the CMB.

Here is my question for anyone: If the universe began from a region smaller than a proton, or down about the Planck length in size (which is 1/(10 to the 20th power) the diameter of a proton, how can it be infinite in size? It had a finite amount of time to expand (13.7 Billion years) and expanding at a finite rate, even many times the speed of light, it should have a finite size.

##### Share on other sites

The CMB is everywhere at a distance of now approx 46 Billion light years. That is how far you have to go to find regions of the universe that have cooled that much, and that is the furthest anything can be detected. There is plenty more beyond that which will always remain invisible to all our detection techniques. The limits to our observable universe is the CMB.

Here is my question for anyone: If the universe began from a region smaller than a proton, or down about the Planck length in size (which is 1/(10 to the 20th power) the diameter of a proton, how can it be infinite in size? It had a finite amount of time to expand (13.7 Billion years) and expanding at a finite rate, even many times the speed of light, it should have a finite size.

This "CMB at a distance"; how is it different from the CMB here and now? It is here as well, correct?

For your question, I think you are mixing old BB theory for the start, with the present BB theory for "now". Given those assumptions I think you are correct that there is a contradiction, but I think the new assumption is that if it is infinite now it was infinite then also, only denser.

The old theory assumed a very small finite compact dense hot start, leading to an expanded finite current cooler state.

The new theory assumes it was a possibly infinite and possibly finite, hot dense start leading to the expanded and cooler current state that is still infinite or finite (though expanded)

##### Share on other sites

I think J.C. MacSwell's reply covers it very well.

The popular notion the the early universe "...began from a region smaller than a proton..." places a restriction on initial conditions that the big bang theory itself doesn't. This notion evokes a very specific image in the mind of the reader.

As far as I know, the only conditions that the big bang theory requires is that the universe was very hot and dense and that all parts of it that are in our observable universe were in causal contact when the inflationary epoch began (about 10-36 sec. after the initial event). After the inflationary epoch (about 10-32 sec. after the initial event) the universe was many orders of magnitude larger (at least 1026), hot and dense (but less so) and there were parts of it that were no longer in causal contact.

One might reason that the volume of our observable universe "...began from a region smaller than a proton..." by "running the clock backward" so-to-speak, but our observable universe doesn't necessarily encompass the entire universe.

Our observations indicate that our observable universe is "very nearly flat":

The value of Ω at the present time is denoted Ω0. This value can be deduced by measuring the curvature of spacetime (since Ω=1, or ρ = ρc, is defined as the density for which the curvature k=0). The curvature can be inferred from a number of observations....

...Data from the Wilkinson Microwave Anisotropy Probe (measuring CMB anisotropies) combined with that from the Sloan Digital Sky Survey and observations of type-Ia supernovae constrain Ω0 to be 1 within 1%.[7] In other words the term |Ω − 1| is currently less than 0.01, and therefore must have been less than 10−62 at the Planck era.

As far as I know, this observered flatness implies that the entire universe is either very much larger than our observable universe or, perhaps, infinite. (NOTE: I'm not sure about the relationship between flatness and size, though)

Chris

Edited by csmyth3025
##### Share on other sites

I guess we interpret the OP differently, if you want to discuss some part more thoroughly you need to express your concern more precisely.

Here is my question for anyone: If the universe began from a region smaller than a proton, or down about the Planck length in size (which is 1/(10 to the 20th power) the diameter of a proton, how can it be infinite in size? It had a finite amount of time to expand (13.7 Billion years) and expanding at a finite rate, even many times the speed of light, it should have a finite size.

While I agree with both J.C.MacSwell and csmyth3025, I would also like to point out that popular science articles almost always translates and mention the "observable universe" as simply the "Universe", which can cause some confusion in this matter.

Both popular and professional research articles in cosmology often use the term "universe" to mean "observable universe". This can be justified on the grounds that we can never know anything by direct experimentation about any part of the universe that is causally disconnected from us, although many credible theories require a total universe much larger than the observable universe.

http://en.wikipedia.org/wiki/Observable_universe#The_universe_versus_the_observable_universe

We don't know in what size or from what conditions the Universe we observe today emerged, it could have been infinite already at the initial event of the Bang.

Without any evidence associated with the earliest instant of the expansion, the Big Bang theory cannot and does not provide any explanation for such an initial condition; rather, it describes and explains the general evolution of the universe since that instant.

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

##### Share on other sites

This "CMB at a distance"; how is it different from the CMB here and now? It is here as well, correct?

For your question, I think you are mixing old BB theory for the start, with the present BB theory for "now". Given those assumptions I think you are correct that there is a contradiction, but I think the new assumption is that if it is infinite now it was infinite then also, only denser.

The old theory assumed a very small finite compact dense hot start, leading to an expanded finite current cooler state.

The new theory assumes it was a possibly infinite and possibly finite, hot dense start leading to the expanded and cooler current state that is still infinite or finite (though expanded)

The CMB is here and now, if you were now 46 Billion light years away looking back at our Earth, our Earth, along with our entire galaxy, would appear only as a CMB radiation 13 Billion years ago, before our sun or any nearby stars and galaxies have formed.

The new theory makes sense to me, that the entire universe originated from a very dense, hot condition, but of undeterminable size, not necessarily smaller than a proton.

Edited by Airbrush
##### Share on other sites

• 2 weeks later...

just a question. If, and Ill use the hubble space telescope for my question, if the hubble can "see" objects out about 14 billion light years in a particular direction, and you spun the hubble around to the opposite direction and it can "see" objects about 14 billion light years wouldnt that make the universe 38 billion years old? If your point of reference was the object viewed by the hubble 14 billion light years away and you were viewing the earth from there and that was as far as you could see, the object in the opposite direction would still be another 14 billion light years away right? im just asking. Just a reference to the fact that if you drew a circle with hubble as the center, wouldn't 14billion light years be the radius and not the diameter?

"How big is the universe?" is a matter of conjecture. According to the BB model and a Hubble constant concerning a constant rate of expansion, you would be able to follow the expansion of the entire universe, regardless of its size, back to a single point -- accordingly about 13.7 billion years ago. Nowadays with the Dark Energy hypothesis concerning differing expansion rates over time, the Hubble constant (H0) is now used as the average rate of expansion (instead of a constant rate of expansion) resulting in the same calculation. The Inflation hypothesis asserts that the universe may have expanded originally at a superluminal rate/ velocity resulting in a universe of conceivably unknown extension. In a closed universe model the extent of the extension of the universe relates to General Relativity and Riemann geometry concerning the extent of the "warping of space."

Different versions of the standard model have different ideas on this subject as do different cosmologies.

##### Share on other sites

• 1 month later...

The big question is are we living in an illusion? If everything we see through our telescopes are billions of years in the past,Could it be that we are now living in a universe that has expanded so much that if we looked up at the present night sky we would see a starless sky? How can we make definitive statements and calculations about objects that might not even exist anymore,even though their light is just arriving at our telescopes after billions of year traveling through space.

##### Share on other sites

The big question is are we living in an illusion? If everything we see through our telescopes are billions of years in the past,Could it be that we are now living in a universe that has expanded so much that if we looked up at the present night sky we would see a starless sky? How can we make definitive statements and calculations about objects that might not even exist anymore,even though their light is just arriving at our telescopes after billions of year traveling through space.

The answer to your question is yes, the sky is an illusion. Everything we see is older than it looks because the light from it took time to reach us.

##### Share on other sites

• 2 weeks later...

It's like if someone 100s years ago, made a letter in a bottle into the sea, resides in a shore nowadays discovered by someone who don't know when it was sent !

But, studying the materials, one can knows its age, and explain many things ...

##### Share on other sites

This is not just an academic issue. In order to make the universe appear to be "flat" in measurements of the anisotropy in the CMB, the estimated amount of matter and energy in our inventory of "stuff" in the universe is only about 4.5% of the total necessary to achieve this "flatness". To make up for the rest, Dark Energy and Dark Matter have been invented. But the discussion here highlights a problem. We can make up for the "missing mass" simply by postulating a larger universe than has been estimated. So, 100/4.5 = 22.2, that is, the universe needs to be 22.2 times larger than estimates have concluded to make the CMB appear "flat". If the universe is, in fact, this much larger, then Dark Energy and Dark Matter are unnecessary. Also, the gravitational lensing effects and the Sunyaev-Zeldovich effect and other consequences of a more massive universe would be accounted for. Since the actual size of the universe is so speculative, how can we discount this? How can we be so sure that acceleration of the universe expansion rate, Dark Energy and Dark Matter are real? It is far more parsimonious to postulate a bigger universe than to hypothesize Dark Energy and Dark Matter, with their unintended implications. Actually, these are complications that raise more questions than they answer.

##### Share on other sites

It would seem that Inflation was devised in order to plug a somewhat unresolved difference into the equation in order to make ends meet. However, without being able to see that far for verification, not to mention the mythical nature of it, it always seems like that is the first place to look for errors.

##### Share on other sites

...If the universe is, in fact, this much larger, then Dark Energy and Dark Matter are unnecessary. Also, the gravitational lensing effects and the Sunyaev-Zeldovich effect and other consequences of a more massive universe would be accounted for. Since the actual size of the universe is so speculative, how can we discount this? How can we be so sure that acceleration of the universe expansion rate, Dark Energy and Dark Matter are real? It is far more parsimonious to postulate a bigger universe than to hypothesize Dark Energy and Dark Matter, with their unintended implications. Actually, these are complications that raise more questions than they answer.

Dark matter and dark energy are two separate subjects currently being investigated. Dark matter ("some non-visible form of matter") was proposed originally by Fritz Zwicky in 1934 to explain his observations of the greater than expected velocities of galaxies orbiting each other in the Coma cluster of galaxies. His work was largely ignored. In 1975 Vera Rubin and Kent Ford announced results of their study of galactic rotation curves indicating that there must be a lot of "missing mass" in order for the stars in the galaxies studied to orbit at the velocities they observed. They published a paper based on their work in 1980. It wasn't well recieved by the scientific community at the time. This gradually changed when other researchers confirmed their observations. Since then there has been a considerable amount of evidence compiled based on galactic rotation curves as well as the gravitational lensing effect of this "non-visible" matter.

The notion of dark energy was spawned separately around 1998-1999 when two teams of researchers independently conlcluded that the expansion of the universe has been accelerating since the universe was about half its present size (z=~0.5) based on observations of Type I-A supernovae. Since then similar independent observations and other evidence has confirmed their conclusions.

In both cases the size of the universe is not relevant to the observations obtained.

Chris

Edited to correct spelling errors

Edited by csmyth3025
##### Share on other sites

Without knowing the exact specifications of inflation, a very questionable theory in itself, it is impossible to know.

##### Share on other sites

Without knowing the exact specifications of inflation, a very questionable theory in itself, it is impossible to know.

What, exactly, is it impossible to know?

Chris

## Create an account

Register a new account