<p>No, the oldest light we can see is as old as the Universe<span class="math-container">$^\dagger$$^\ddagger$</span>. This is simply because light started traveling at that time, so after one year you'd se light that had been traveling for one light-year, after 1 million years you'd see light that had been traveling for a million light-years, and so on. There  is (most likely) more Universe beyond the horizon, but light from those regions just haven't had the time to reach us yet.</p>
<p>You might think that the <em>distance</em> to the cosmic horizon today is 13.7 billion light-years, but because the Universe is expanding, the distance is much larger (in fact 43.6 billion light-years).</p>
<hr />
<p><span class="math-container">$^\dagger$</span><sub>Because the Universe was opaque the first 380,000 years, we can't see <em>all</em> the way, but that's a technical detail.</sub></p>
<p><span class="math-container">$^\dagger$</span><sub>In some theories, notably those with <a href="https://en.wikipedia.org/wiki/Eternal_inflation" rel="nofollow noreferrer">eternal inflation</a>, the Universe has existed for indefinite time before the Big Bang. In this answer, I take &quot;the age of the Universe&quot; to mean the time since the Big Bang.</sub></p>

CC BY-SA 4.0
2019-06-22T08:02:39.860Z
So the age of the universe is still 13.7 Billion years, except that it is expanding so the horizon is increasing? Am i getting it right?
raptorAcrylyc
CC BY-SA 4.0
2019-06-22T08:28:14.963Z
@quantumbiker You're right that the age is 13.7 billion years, and you're right that the Universe is expanding, and you're right that the (distance to the) horizon is increasing. I just wouldn't use the word "except" to join those clauses, because the Universe get older regardless of whether it's expanding or contracting. Moreover, even in a hypothetical, static universe, the distance to the horizon increases as time goes, because light from more and more distant regions reaches you (in this hypothetical case, the distance in light-years would be equal to the age in years).
pela
CC BY-SA 4.0
2019-06-22T10:42:16.223Z
FWIW, Google says the radius of the observable universe is 46.508 billion light years, but I don't know where it gets that number, I just pasted `radius of observable universe` into the search bar.
PM 2Ring
CC BY-SA 4.0
2019-06-22T11:08:26.603Z
@PM 2Ring that must depend on the scale factor and is susceptible of modification as it depends on the model.
Alchimista
CC BY-SA 4.0
2019-06-22T18:31:40.267Z
@Pela Your answer does not seem to take account of temporary or permanent separations of causality, such as the separations preventing us from seeing the interior of astronomical black holes (which are nevertheless evident by their gravitational effects on stars accompanying them), or of the resemblance between the cosmological horizon and the black holes' "event" or "apparent" horizons.
Edouard
CC BY-SA 4.0
2019-06-22T21:08:13.090Z
@Edouard No, my answer doesn't take that into account, but those horizons don't really have anything to do with each other. If you're referring to the fact that an observer near an astrophysical event horizon will experience another age of the Universe, that's true, but the term "age of the Universe" is defined for _comoving_ observers, so that doesn't change the conclusion.
pela
CC BY-SA 4.0
2019-06-22T21:11:51.877Z
@PM2Ring The distance to the horizon is calculated by integrating the expansion of the Universe through time, i.e. d = c∫dt/a(t) (see [here](https://en.wikipedia.org/wiki/Cosmological_horizon#Event_horizon)).
pela
CC BY-SA 4.0
2019-06-22T23:48:16.493Z
On p. 8 in arxiv.org/pdf/astro-ph/0402278.pdf. by Davis, the OP will find diagrams that, if he googles the names of the horizons and other surfaces that are depicted on them as complete phrases (within quotation marks), will give him the reasons for the different considerations we've brought to his attention. Someone asking the age of the universe is sort of asking something that can show what its age is, so I think that the accurate response is the comoving one. If he's asking about the size of the currently observable region, that would appear to be what Pela's talking about.
Edouard
CC BY-SA 4.0
2019-06-22T23:50:12.290Z
One thing that might be essential for the OP's understanding is that cosmological theories need to explain a similarity between regions that were once in causal contact with each other, but no longer are: The current standard explanation is cosmic inflation (a nearly-exponential expansion of space), which blew the oldest massive and energetic material outside the observable region. Inflationary theories posit a return of some of that material, resulting in slight changes seen in the CMB.
Edouard
CC BY-SA 4.0
2019-06-22T23:51:18.543Z
An example of such changes is seen at NASA's site at  imagine.gsfc.nasa.gov/educators/programs/cosmictimes/educators/…
Edouard
CC BY-SA 4.0
2019-06-23T08:14:36.220Z
@Edouard I don't quite follow where you're getting at, but you don't need inflation to have regions that "fall out of" causal contact, you just need accelerated expansion. If expansion continues as we think it will (i.e. if governed by a cosmological constant that doesn't evolve in time), then _every_ point (there aren't gravitationally dominated) will fall out of causal contact.
pela
CC BY-SA 4.0
2019-06-23T08:15:28.760Z
But all of this has nothing to do with what the OP is asking.
pela
CC BY-SA 4.0
2019-06-23T16:05:54.190Z
Let us [continue this discussion in chat](https://chat.stackexchange.com/rooms/95299/discussion-between-edouard-and-pela).
Edouard
CC BY-SA 4.0
2019-06-23T16:11:03.720Z
Because of unusual technology in my computer, my replies are not easily accomodated thru chat, but I'll make a comment on my own answer.
Edouard
CC BY-SA 4.0
2022-09-17T03:55:50.837Z
One detail that might clarify some things is the fact that the capitalization of universe (as "Universe") does, because the names of particular localities are capitalized in English (ASE's language), refer either to a single universe encompassing everything, or to a "local universe" (a region causally separated from any and all others) in a "multiverse" of local universes.  As Pela's answer capitalizes "universe" as "Universe", he is, in effect, using the first of these definitions, whereas the OP appears to be using the 2nd.
Edouard
CC BY-SA 4.0
2022-09-17T04:10:01.913Z
The NASA style manual, which the OP may possibly be using, recommends leaving "universe" uncapitalized, but NASA (an American research & transportation agency) is not currently planning or conducting any intergalactic travel.  "Universe" is larger than "universe", and, in languages of a region (China) that's close to the origin of our species, ideogrammatic languages retain traces of a noun's physical model, but that's not the case in regions using alphabetic languages.  The confusion is, consequently, a very natural one.
Edouard
CC BY-SA 4.0
2022-09-17T08:29:45.807Z
I'm pretty sure the OP refers to our Universe but, like many others, just doesn't capitalize it.
pela
CC BY-SA 4.0
2019-06-22T07:52:09.887Z
2022-09-17T08:39:30.780Z
2022-09-17T08:39:30.780Z
pela
<p>The universe might be eternal to the past, as well as to the future.  The simplest theory for that is described in "Steady state eternal inflation", formulated by Anthony Aguirre and Steve Gratton, and available free online:  It is compatible with observations of the Cosmic Microwave Background, and is centered on a Cauchy surface from which time extends in opposite spatial directions.  A similar but somewhat more elaborate cosmology, by Carroll and Chen, is analyzed, together with the Aguirre-Gratton one, by Vilenkin, in his online paper "Arrows of time and the beginning of the universe".  </p>

<p>The Borde-Guth-Vilenkin Theorem is usually construed as preventing the "past eternality" of inflation by requiring a balancing of universal expansion by universal contraction, but the references in the last (2003) formulation of that theorem by its three authors include a footnote exempting the Aguirre &amp; Gratton theory from its strictures.  Also, the BGV Theorem does not rule out a start of the universe at arbitrarily long times before the start of inflation (quasi-exponential expansion), as hypothesized in Martin Bojowald's 2010 book titled "Once Before Time:  A Whole Story of the Universe", which utilizes Loop Quantum Cosmology. Some of the "bouncing" cosmologies, of which the Wiki "Big Bounce" provides an overview, also imply past eternality, and substitute a repetition of "bounces" for the "Big Bang".</p>

<p>What these cosmologists, as well as the three mentioned in the last of my comments below, are trying to do is resolve that contradiction of infinite density in the zero volume of the singularity at which General Relativity has been considered to break down:  Because densities in "negative time" might cancel densities in"positive time", the densities of the objects duplicated in either version of the temporal dimension might  cancel each other, thereby replacing that contradiction with zero density in zero volume, which makes sense.</p>

<p>I believe that a widespread misconception leading to the belief that the universe, or its massive and energetic contents, are finite is the fact that their limitation to some finite amount would provide the simplest explanation for the fact that the sky is dark at night:  However, because of the fact that expansion is different from speed or velocity, and is (consequently) NOT limited to a rate no higher than the speed of light, such accelerations as were witnessed by the Supernova 1A observations in the late 1990's are entirely permissible in General Relativity. The simplest explanations do not necessarily provide the best explanation of scientific phenomena.</p>

CC BY-SA 4.0
2019-06-23T16:36:50.987Z
Re my exchange of comments with Pela, I haven't followed my own advice to the OP carefully enough, and have confounded conformal time with comoving time. Technical difficulties with my computer are preventing me from replying in chat, and time constraints prevent elaboration now, but the differences in our views stem from different definitions of "universe":  I'm using BGV's, and Pela's using Davis's.  I've upvoted his answer, but mine stands:  Other participants can upvote either, both, or neither.
Edouard
CC BY-SA 4.0
2019-06-24T17:48:31.683Z
At https://www.youtube.com/watch?v=gfYYkC-TO4k, Guth gives a 2018 lecture supporting a past- and future-infinite multiverse based on the possibility of entropy being infinite, with details being worked out in collaboration with Sean Carroll.  As in BGV's exemption of Aguirre's past- and future-infinite proposal, the BGV Theorem would apply separately. in each of the two directions outward from a Cauchy surface.  Both of these theories resemble the mathematician Barbour's "Janus universe".  The astronomical facts detailed by Pela would apply in whichever of the two halves we find ourselves.
Edouard
CC BY-SA 4.0
2019-06-22T18:11:53.343Z
2019-06-25T15:13:50.873Z
2019-06-25T15:13:50.873Z
Edouard
<p>We didn't determine the age of the universe by looking at what the farthest object is we can see. </p>

<p>Instead, we looked at closer objects and <a href="https://en.wikipedia.org/wiki/Age_of_the_universe" rel="nofollow noreferrer">determined their distance, speed and rate of acceleration</a>. When you know those, you can work backwards and find a time when all those galaxies would have been in the same place, which is 13.7 billion years ago. </p>

CC BY-SA 4.0
2019-06-24T18:13:58.733Z
That's true, but the OP's 1st two tags were "cosmology" and "cosmological-horizon",  so I think an answer should take account of them, which is why mine still stands.
Edouard
CC BY-SA 4.0
2019-06-24T07:47:54.263Z
2019-06-24T07:47:54.263Z
Hobbes
<p>When we look at objects really far away we determine the distance using the so called &quot;redshift&quot;. One of the furthest known galaxies &quot;<a href="https://en.wikipedia.org/wiki/GLASS-z13" rel="nofollow noreferrer">GLASS-z13</a>&quot; sits at a redshift of 13.1. According to our models this corresponds to light sent out 13.46 billion years ago.</p>
<p>Note that the model used to connect redshift to distance is constructed in such away that no matter how redshifted an object is that we observe, it can never be estimated to reside at a larger distance than 13.72 billion years. You can check this out using <a href="https://www.astro.ucla.edu/%7Ewright/CosmoCalc.html" rel="nofollow noreferrer">this calculator</a>.</p>
<p>For instance if we were to find an object with a redshift of 20, this would be interpreted as the objected sending out its light 13.54 billion years ago.</p>
<p>A hypothetical object of redshift z=100 would be interpreted as sending out its light 13.7 billion years ago and an object of redshift z=1000 would be interpreted as having sent out its light 13.72 billion years ago.</p>
<p><strong>Answer:</strong> Nobody knows if the universe is more than 13.72 billion years old but no light that reaches us can be interpreted as being older than that because of the model we use to interpret the age of the incoming light.</p>

CC BY-SA 4.0
2022-09-17T10:59:57.580Z
I always ask the following question (and I've never received an answer): How can emptiness, AKA space, have a beginning? Literal infinite space *must* have always been there. As for matter, that's another matter entirely (pun intended), but still.
White Prime
CC BY-SA 4.0
2022-09-17T11:09:12.193Z
@WhitePrime I can see that you received a technically wrong answer to a now closed question on finding objects further away than 14 billions light year because of the modelling I just mentioned.
Agerhell
CC BY-SA 4.0
2022-09-17T21:20:30.880Z
@WhitePrime Especially at a quantum level, space is never really empty. Quantum fields exist everywhere, and particles come in and out of existence all the time, with effects that are measurable. Photons fill what would otherwise be considered ‘empty’ space as well, with at the very least the CMB being (almost) isotropically found. In essence, emptiness is far from being space. I think one could comfortably say there has never been a truly empty part of the universe, ever.
Justin T
CC BY-SA 4.0
2022-09-17T10:51:57.817Z
2022-09-17T10:51:57.817Z
Agerhell
<p>I came to know that the cosmic horizon is the part of universe beyond which we cannot see. So if the light from 13.7 billion years ago is what we can observe, does that mean the universe is older than that and we can't see it?</p>

<cosmology><cosmological-horizon><cosmic-microwave-background>
Is the universe older than 13.7 Billion years?
raptorAcrylyc
# Is the universe older than 13.7 Billion years?

(Asked by: username_0 on 2019-06-22)

I came to know that the cosmic horizon is the part of universe beyond which we cannot see. So if the light from 13.7 billion years ago is what we can observe, does that mean the universe is older than that and we can't see it?

**Tags:** cosmology, cosmological-horizon, cosmic-microwave-background


---

## 4 answers

### Answer by username_1 on 2019-06-22. Score: 7

No, the oldest light we can see is as old as the Universe$^\dagger$$^\ddagger$. This is simply because light started traveling at that time, so after one year you'd se light that had been traveling for one light-year, after 1 million years you'd see light that had been traveling for a million light-years, and so on. There is (most likely) more Universe beyond the horizon, but light from those regions just haven't had the time to reach us yet.

You might think that the *distance* to the cosmic horizon today is 13.7 billion light-years, but because the Universe is expanding, the distance is much larger (in fact 43.6 billion light-years).

---

$^\dagger$Because the Universe was opaque the first 380,000 years, we can't see *all* the way, but that's a technical detail.

$^\dagger$In some theories, notably those with [eternal inflation](https://en.wikipedia.org/wiki/Eternal_inflation), the Universe has existed for indefinite time before the Big Bang. In this answer, I take "the age of the Universe" to mean the time since the Big Bang.

> **Comments:**
> **username_0**: So the age of the universe is still 13.7 Billion years, except that it is expanding so the horizon is increasing? Am i getting it right?  
> **username_1**: @quantumbiker You're right that the age is 13.7 billion years, and you're right that the Universe is expanding, and you're right that the (distance to the) horizon is increasing. I just wouldn't use the word "except" to join those clauses, because the Universe get older regardless of whether it's expanding or contracting. Moreover, even in a hypothetical, static universe, the distance to the horizon increases as time goes, because light from more and more distant regions reaches you (in this hypothetical case, the distance in light-years would be equal to the age in years).  
> **username_2**: FWIW, Google says the radius of the observable universe is 46.508 billion light years, but I don't know where it gets that number, I just pasted `radius of observable universe` into the search bar.  
> **username_3**: @username_2 that must depend on the scale factor and is susceptible of modification as it depends on the model.  
> **username_4**: @username_1 Your answer does not seem to take account of temporary or permanent separations of causality, such as the separations preventing us from seeing the interior of astronomical black holes (which are nevertheless evident by their gravitational effects on stars accompanying them), or of the resemblance between the cosmological horizon and the black holes' "event" or "apparent" horizons.  
> **username_1**: @username_4 No, my answer doesn't take that into account, but those horizons don't really have anything to do with each other. If you're referring to the fact that an observer near an astrophysical event horizon will experience another age of the Universe, that's true, but the term "age of the Universe" is defined for _comoving_ observers, so that doesn't change the conclusion.  
> **username_1**: @username_2 The distance to the horizon is calculated by integrating the expansion of the Universe through time, i.e. d = c∫dt/a(t) (see [here](https://en.wikipedia.org/wiki/Cosmological_horizon#Event_horizon)).  
> **username_4**: On p. 8 in arxiv.org/pdf/astro-ph/0402278.pdf. by Davis, the OP will find diagrams that, if he googles the names of the horizons and other surfaces that are depicted on them as complete phrases (within quotation marks), will give him the reasons for the different considerations we've brought to his attention. Someone asking the age of the universe is sort of asking something that can show what its age is, so I think that the accurate response is the comoving one. If he's asking about the size of the currently observable region, that would appear to be what username_1's talking about.  
> **username_4**: One thing that might be essential for the OP's understanding is that cosmological theories need to explain a similarity between regions that were once in causal contact with each other, but no longer are: The current standard explanation is cosmic inflation (a nearly-exponential expansion of space), which blew the oldest massive and energetic material outside the observable region. Inflationary theories posit a return of some of that material, resulting in slight changes seen in the CMB.  
> **username_4**: An example of such changes is seen at NASA's site at  imagine.gsfc.nasa.gov/educators/programs/cosmictimes/educators/…  
> **username_1**: @username_4 I don't quite follow where you're getting at, but you don't need inflation to have regions that "fall out of" causal contact, you just need accelerated expansion. If expansion continues as we think it will (i.e. if governed by a cosmological constant that doesn't evolve in time), then _every_ point (there aren't gravitationally dominated) will fall out of causal contact.  
> **username_1**: But all of this has nothing to do with what the OP is asking.  
> **username_4**: Let us [continue this discussion in chat](https://chat.stackexchange.com/rooms/95299/discussion-between-username_4-and-username_1).  
> **username_4**: Because of unusual technology in my computer, my replies are not easily accomodated thru chat, but I'll make a comment on my own answer.  
> **username_4**: One detail that might clarify some things is the fact that the capitalization of universe (as "Universe") does, because the names of particular localities are capitalized in English (ASE's language), refer either to a single universe encompassing everything, or to a "local universe" (a region causally separated from any and all others) in a "multiverse" of local universes.  As username_1's answer capitalizes "universe" as "Universe", he is, in effect, using the first of these definitions, whereas the OP appears to be using the 2nd.  
> **username_4**: The NASA style manual, which the OP may possibly be using, recommends leaving "universe" uncapitalized, but NASA (an American research & transportation agency) is not currently planning or conducting any intergalactic travel.  "Universe" is larger than "universe", and, in languages of a region (China) that's close to the origin of our species, ideogrammatic languages retain traces of a noun's physical model, but that's not the case in regions using alphabetic languages.  The confusion is, consequently, a very natural one.  
> **username_1**: I'm pretty sure the OP refers to our Universe but, like many others, just doesn't capitalize it.  

---

### Answer by username_4 on 2019-06-22. Score: 2

The universe might be eternal to the past, as well as to the future. The simplest theory for that is described in "Steady state eternal inflation", formulated by Anthony Aguirre and Steve Gratton, and available free online: It is compatible with observations of the Cosmic Microwave Background, and is centered on a Cauchy surface from which time extends in opposite spatial directions. A similar but somewhat more elaborate cosmology, by Carroll and Chen, is analyzed, together with the Aguirre-Gratton one, by Vilenkin, in his online paper "Arrows of time and the beginning of the universe".

The Borde-Guth-Vilenkin Theorem is usually construed as preventing the "past eternality" of inflation by requiring a balancing of universal expansion by universal contraction, but the references in the last (2003) formulation of that theorem by its three authors include a footnote exempting the Aguirre & Gratton theory from its strictures. Also, the BGV Theorem does not rule out a start of the universe at arbitrarily long times before the start of inflation (quasi-exponential expansion), as hypothesized in Martin Bojowald's 2010 book titled "Once Before Time: A Whole Story of the Universe", which utilizes Loop Quantum Cosmology. Some of the "bouncing" cosmologies, of which the Wiki "Big Bounce" provides an overview, also imply past eternality, and substitute a repetition of "bounces" for the "Big Bang".

What these cosmologists, as well as the three mentioned in the last of my comments below, are trying to do is resolve that contradiction of infinite density in the zero volume of the singularity at which General Relativity has been considered to break down: Because densities in "negative time" might cancel densities in"positive time", the densities of the objects duplicated in either version of the temporal dimension might cancel each other, thereby replacing that contradiction with zero density in zero volume, which makes sense.

I believe that a widespread misconception leading to the belief that the universe, or its massive and energetic contents, are finite is the fact that their limitation to some finite amount would provide the simplest explanation for the fact that the sky is dark at night: However, because of the fact that expansion is different from speed or velocity, and is (consequently) NOT limited to a rate no higher than the speed of light, such accelerations as were witnessed by the Supernova 1A observations in the late 1990's are entirely permissible in General Relativity. The simplest explanations do not necessarily provide the best explanation of scientific phenomena.

> **Comments:**
> **username_4**: Re my exchange of comments with username_1, I haven't followed my own advice to the OP carefully enough, and have confounded conformal time with comoving time. Technical difficulties with my computer are preventing me from replying in chat, and time constraints prevent elaboration now, but the differences in our views stem from different definitions of "universe":  I'm using BGV's, and username_1's using Davis's.  I've upvoted his answer, but mine stands:  Other participants can upvote either, both, or neither.  
> **username_4**: At https://www.youtube.com/watch?v=gfYYkC-TO4k, Guth gives a 2018 lecture supporting a past- and future-infinite multiverse based on the possibility of entropy being infinite, with details being worked out in collaboration with Sean Carroll.  As in BGV's exemption of Aguirre's past- and future-infinite proposal, the BGV Theorem would apply separately. in each of the two directions outward from a Cauchy surface.  Both of these theories resemble the mathematician Barbour's "Janus universe".  The astronomical facts detailed by username_1 would apply in whichever of the two halves we find ourselves.  

---

### Answer by username_5 on 2019-06-24. Score: 1

We didn't determine the age of the universe by looking at what the farthest object is we can see.

Instead, we looked at closer objects and [determined their distance, speed and rate of acceleration](https://en.wikipedia.org/wiki/Age_of_the_universe). When you know those, you can work backwards and find a time when all those galaxies would have been in the same place, which is 13.7 billion years ago.

> **Comments:**
> **username_4**: That's true, but the OP's 1st two tags were "cosmology" and "cosmological-horizon",  so I think an answer should take account of them, which is why mine still stands.  

---

### Answer by username_6 on 2022-09-17. Score: 1

When we look at objects really far away we determine the distance using the so called "redshift". One of the furthest known galaxies "[GLASS-z13](https://en.wikipedia.org/wiki/GLASS-z13)" sits at a redshift of 13.1. According to our models this corresponds to light sent out 13.46 billion years ago.

Note that the model used to connect redshift to distance is constructed in such away that no matter how redshifted an object is that we observe, it can never be estimated to reside at a larger distance than 13.72 billion years. You can check this out using [this calculator](https://www.astro.ucla.edu/%7Ewright/CosmoCalc.html).

For instance if we were to find an object with a redshift of 20, this would be interpreted as the objected sending out its light 13.54 billion years ago.

A hypothetical object of redshift z=100 would be interpreted as sending out its light 13.7 billion years ago and an object of redshift z=1000 would be interpreted as having sent out its light 13.72 billion years ago.

**Answer:** Nobody knows if the universe is more than 13.72 billion years old but no light that reaches us can be interpreted as being older than that because of the model we use to interpret the age of the incoming light.

> **Comments:**
> **username_7**: I always ask the following question (and I've never received an answer): How can emptiness, AKA space, have a beginning? Literal infinite space *must* have always been there. As for matter, that's another matter entirely (pun intended), but still.  
> **username_6**: @username_7 I can see that you received a technically wrong answer to a now closed question on finding objects further away than 14 billions light year because of the modelling I just mentioned.  
> **username_8**: @username_7 Especially at a quantum level, space is never really empty. Quantum fields exist everywhere, and particles come in and out of existence all the time, with effects that are measurable. Photons fill what would otherwise be considered ‘empty’ space as well, with at the very least the CMB being (almost) isotropically found. In essence, emptiness is far from being space. I think one could comfortably say there has never been a truly empty part of the universe, ever.  

---

