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I've always been puzzled by the estimated age of the universe at being 13 billion years. That's just the size of the observable universe, correct? Isn't there a

I've always been puzzled by the estimated age of the universe at being 13 billion years. That's just the size of the observable universe, correct? Isn't there a future horizon beyond which light will not currently reach us?

vkou 6y ago
No, 13 billion years is the age of the universe. The observable universe is a sphere with a diameter of ~93 billion light years (And is likely to only be a subset of the entire universe).
- skykooler 6y ago
  How can we observe things over 40 billion light years away if they've only been around to emit light for 13 billion years?
  - wffurr 6y ago
    https://en.m.wikipedia.org/wiki/Observable_universe#Misconceptions_about_its_size https://en.m.wikipedia.org/wiki/Observable_universe#Misconce...
  - function_seven 6y ago
    The universe has been expanding ever since the Big Bang. Things that are very far away are moving away from us at speeds "faster" than light. No, they're not violating the cosmic speed limit. The fabric of spacetime itself is expanding everywhere, and that makes objects at very large distances apart get even further apart faster than a lightspeed traveler could move them. https://www.space.com/33306-how-does-the-universe-expand-faster-than-light.html https://www.space.com/33306-how-does-the-universe-expand-fas...
  - vkou 6y ago
    They were closer to us when they emitted that light. They've since moved further away.
- wffurr 6y ago
  "Measurements made by NASA's WMAP spacecraft have shown that the universe is 13.7 billion years old, plus or minus about 130,000 years." https://starchild.gsfc.nasa.gov/docs/StarChild/questions/question28.html#:~:text=Although%20the%20numbers%20are%20still,or%20minus%20about%20130%2C000%20years https://starchild.gsfc.nasa.gov/docs/StarChild/questions/que....
  - lkbm 6y ago
    Whoa, that's crazy precise. They got it down to the tens of thousands? If so, seems like they should write "13.700 billion" for the first part. I'm a little suspicious of this number as-is. Looking for a source for those numbers, I found this[0]: > While previous estimates were 13.7 billion years old, give or take 130,000 years, new predictions hone in with more precision- at around 13.77 billion years, plus or minus 40 million years. Which is much less precise and feels a lot more believable. [0] https://www.labroots.com/trending/space/18295/light-bang-reveals-age-universe https://www.labroots.com/trending/space/18295/light-bang-rev...
    - bhk 6y ago
      So NASA said "plus or minus 130,000 years" when they were actually off by about 70 million years?
      - johncolanduoni 6y ago
        That’s a misprint, the WMAP measurement was plus or minus 130 million years.
- joombaga 6y ago
  Sorry to bikeshed, but I was struck by the word "likely" in your parenthetical. Are there models of the universe that predict our observable universe is _not_ a subset of the entire universe? How would one describe cosmological expansion in such a model?
  - enkid 6y ago
    Some weird geometry where space is curved into a four dimensional sphere. The sphere gets bigger, adding space between all the points. If the sphere is exactly the size of the observable universe, then the observable universe and universe would be the same thing.
  - dumbfoundded 6y ago
    The Cosmic Microwave Background Radiation is a pretty uniform field that exists over the entirety of the observable universe. It was created in the earliest days in our universe. The fact that it exists everywhere we look with high regularity lets us guess that we're only a subset of a larger universe. There are many theories about the unobservable parts of the universe but these are impossible to test with any foreseeable technology that doesn't fundamentally break our understanding of physics.
    - djsumdog 6y ago
      One analogy I've heard: Imagine the big bang split into 4 spheres and they accelerated away from each other. Because they'll all be expanding and accelerating, there could be 4 equally sized spheres of stuff just like our own, but it would be impossible for us to observe them. Change the number 4 to 2 or 1000 or n. We really would have no idea.
      - dumbfoundded 6y ago
        A testable hypothesis is a strong standard in science. Most scientists don't worry about things that cannot or more importantly, will probably never be testable. They can be fun to think about but that's pretty much it.
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- dumpsterdiver 6y ago
  I have a question: Just over 20 years ago when the accepted view was that the expansion of the universe was slowing down, would you have backed that position with as much certainty as you are backing this one? That the universe is a mere 13.7 billion years old? We cannot prove the absence of light in a place that is already so far away that it's light will never reach us. Do you agree? We can prove what we can observe, and from that proof we can make inferences about what we cannot observe. The entire premise of dating our universe is based on its observed rate of expansion. This was accomplished by extrapolating data from observable light and tracing it back to the so called Big Bang. I see a lot of problems with this one dimensional assumption, which to me seem really obvious. First of all, let's assume that we actually got it right this time and accurately traced light back to the Big Bang - how can anyone be sure that it was the first and only Big Bang? Pangea, the super continent, for instance - many may think of as a single place and time in history, but in fact it's more likely that many Pangea's have come and gone in various states as the planet roils on. There will likely be another in the far future. Perhaps the Big Bang was merely a "localized" event and there are Big Bangs occuring in distant places whose light will never reach us. Perhaps we have gone through many Big Bang / Big Crunch cycles. We simply cannot prove it one way or the other, and so to take a strong position on this would be unscientific. More food for thought - imagine that the universe has already been through a near infinite number of Big Bang / Big Crunch cycles, it begs the question, do we reset the clock every time or do we let it run? In my opinion, currently accepted theory is akin to believing that the Earth is the center of the universe and the sun revolves around us. We were wrong about that too.
  - morganvachon 6y ago
    > Perhaps the Big Bang was merely a "localized" event and there are Big Bangs occuring in distant places whose light will never reach us. Perhaps we have gone through many Big Bang / Big Crunch cycles. This was always my view of the state of the universe from childhood onward. The Void of space is infinite, and within that Void our universe could be one of an infinite number of other universes that we will never know about because they are so far outside our ability to observe them. Perhaps there is as as much relative distance between universes in the Void as there is between galaxies in our own universe. This concept is the only way I've ever been able to accept that our own universe has a measurable size.
- f154hfds 6y ago
  Naive question here - is the 13bn years relative to the surface of the Earth? I assume this matters right? If we're in a bit of a gravity well wouldn't the vacuum of space experience this time a bit longer? According to [1], the ratio is about 5.56E-10, so I guess this would contribute about a year to the age of the universe, so.. not that much. I guess I answered my own question. However, this does pose an interesting question about the age of the universe in extreme gravity wells doesn't it? Or am I misunderstanding something? [1] https://www.quora.com/How-much-time-on-earth-is-1-hour-in-space https://www.quora.com/How-much-time-on-earth-is-1-hour-in-sp...
  - weswpg 6y ago
    Well, given that there is no universal clock and time is defined locally for each observer, including each particle, it would be more strictly accurate to say that "the matter which later formed our solar system has experienced 13 billion years of time" since the Big Bang or maybe 13 billion years is from the frame of reference of the Cosmic Microwave Background? that would make more sense. I'm going to check again then edit this comment. (i am not a physicist, not an authoritative source on this) edit: so it turns out that the age of the universe is given from the frame of reference of the CMB rather than from Earth's frame of reference.: > Measurements of the cosmic background radiation give the cooling time of the universe since the Big Bang > Cosmic time, or cosmological time, is the time coordinate commonly used in the Big Bang models of physical cosmology.[1][2][3] Such time coordinate may be defined for a homogeneous, expanding universe so that the universe has the same density everywhere at each moment in time (the fact that this is possible means that the universe is, by definition, homogeneous). The clocks measuring cosmic time should move along the Hubble flow. https://en.wikipedia.org/wiki/Cosmic_time https://en.wikipedia.org/wiki/Cosmic_time

vkou 6y ago

No, 13 billion years is the age of the universe. The observable universe is a sphere with a diameter of ~93 billion light years (And is likely to only be a subset of the entire universe).

skykooler 6y ago
How can we observe things over 40 billion light years away if they've only been around to emit light for 13 billion years?
- wffurr 6y ago
  https://en.m.wikipedia.org/wiki/Observable_universe#Misconceptions_about_its_size https://en.m.wikipedia.org/wiki/Observable_universe#Misconce...
- function_seven 6y ago
  The universe has been expanding ever since the Big Bang. Things that are very far away are moving away from us at speeds "faster" than light. No, they're not violating the cosmic speed limit. The fabric of spacetime itself is expanding everywhere, and that makes objects at very large distances apart get even further apart faster than a lightspeed traveler could move them. https://www.space.com/33306-how-does-the-universe-expand-faster-than-light.html https://www.space.com/33306-how-does-the-universe-expand-fas...
- vkou 6y ago
  They were closer to us when they emitted that light. They've since moved further away.
wffurr 6y ago
"Measurements made by NASA's WMAP spacecraft have shown that the universe is 13.7 billion years old, plus or minus about 130,000 years." https://starchild.gsfc.nasa.gov/docs/StarChild/questions/question28.html#:~:text=Although%20the%20numbers%20are%20still,or%20minus%20about%20130%2C000%20years https://starchild.gsfc.nasa.gov/docs/StarChild/questions/que....
- lkbm 6y ago
  Whoa, that's crazy precise. They got it down to the tens of thousands? If so, seems like they should write "13.700 billion" for the first part. I'm a little suspicious of this number as-is. Looking for a source for those numbers, I found this[0]: > While previous estimates were 13.7 billion years old, give or take 130,000 years, new predictions hone in with more precision- at around 13.77 billion years, plus or minus 40 million years. Which is much less precise and feels a lot more believable. [0] https://www.labroots.com/trending/space/18295/light-bang-reveals-age-universe https://www.labroots.com/trending/space/18295/light-bang-rev...
  - bhk 6y ago
    So NASA said "plus or minus 130,000 years" when they were actually off by about 70 million years?
    - johncolanduoni 6y ago
      That’s a misprint, the WMAP measurement was plus or minus 130 million years.
joombaga 6y ago
Sorry to bikeshed, but I was struck by the word "likely" in your parenthetical. Are there models of the universe that predict our observable universe is _not_ a subset of the entire universe? How would one describe cosmological expansion in such a model?
- enkid 6y ago
  Some weird geometry where space is curved into a four dimensional sphere. The sphere gets bigger, adding space between all the points. If the sphere is exactly the size of the observable universe, then the observable universe and universe would be the same thing.
- dumbfoundded 6y ago
  The Cosmic Microwave Background Radiation is a pretty uniform field that exists over the entirety of the observable universe. It was created in the earliest days in our universe. The fact that it exists everywhere we look with high regularity lets us guess that we're only a subset of a larger universe. There are many theories about the unobservable parts of the universe but these are impossible to test with any foreseeable technology that doesn't fundamentally break our understanding of physics.
  - djsumdog 6y ago
    One analogy I've heard: Imagine the big bang split into 4 spheres and they accelerated away from each other. Because they'll all be expanding and accelerating, there could be 4 equally sized spheres of stuff just like our own, but it would be impossible for us to observe them. Change the number 4 to 2 or 1000 or n. We really would have no idea.
    - dumbfoundded 6y ago
      A testable hypothesis is a strong standard in science. Most scientists don't worry about things that cannot or more importantly, will probably never be testable. They can be fun to think about but that's pretty much it.
- 6y ago
deleted 6y ago
[deleted]
dumpsterdiver 6y ago
I have a question: Just over 20 years ago when the accepted view was that the expansion of the universe was slowing down, would you have backed that position with as much certainty as you are backing this one? That the universe is a mere 13.7 billion years old? We cannot prove the absence of light in a place that is already so far away that it's light will never reach us. Do you agree? We can prove what we can observe, and from that proof we can make inferences about what we cannot observe. The entire premise of dating our universe is based on its observed rate of expansion. This was accomplished by extrapolating data from observable light and tracing it back to the so called Big Bang. I see a lot of problems with this one dimensional assumption, which to me seem really obvious. First of all, let's assume that we actually got it right this time and accurately traced light back to the Big Bang - how can anyone be sure that it was the first and only Big Bang? Pangea, the super continent, for instance - many may think of as a single place and time in history, but in fact it's more likely that many Pangea's have come and gone in various states as the planet roils on. There will likely be another in the far future. Perhaps the Big Bang was merely a "localized" event and there are Big Bangs occuring in distant places whose light will never reach us. Perhaps we have gone through many Big Bang / Big Crunch cycles. We simply cannot prove it one way or the other, and so to take a strong position on this would be unscientific. More food for thought - imagine that the universe has already been through a near infinite number of Big Bang / Big Crunch cycles, it begs the question, do we reset the clock every time or do we let it run? In my opinion, currently accepted theory is akin to believing that the Earth is the center of the universe and the sun revolves around us. We were wrong about that too.
- morganvachon 6y ago
  > Perhaps the Big Bang was merely a "localized" event and there are Big Bangs occuring in distant places whose light will never reach us. Perhaps we have gone through many Big Bang / Big Crunch cycles. This was always my view of the state of the universe from childhood onward. The Void of space is infinite, and within that Void our universe could be one of an infinite number of other universes that we will never know about because they are so far outside our ability to observe them. Perhaps there is as as much relative distance between universes in the Void as there is between galaxies in our own universe. This concept is the only way I've ever been able to accept that our own universe has a measurable size.
f154hfds 6y ago
Naive question here - is the 13bn years relative to the surface of the Earth? I assume this matters right? If we're in a bit of a gravity well wouldn't the vacuum of space experience this time a bit longer? According to [1], the ratio is about 5.56E-10, so I guess this would contribute about a year to the age of the universe, so.. not that much. I guess I answered my own question. However, this does pose an interesting question about the age of the universe in extreme gravity wells doesn't it? Or am I misunderstanding something? [1] https://www.quora.com/How-much-time-on-earth-is-1-hour-in-space https://www.quora.com/How-much-time-on-earth-is-1-hour-in-sp...
- weswpg 6y ago
  Well, given that there is no universal clock and time is defined locally for each observer, including each particle, it would be more strictly accurate to say that "the matter which later formed our solar system has experienced 13 billion years of time" since the Big Bang or maybe 13 billion years is from the frame of reference of the Cosmic Microwave Background? that would make more sense. I'm going to check again then edit this comment. (i am not a physicist, not an authoritative source on this) edit: so it turns out that the age of the universe is given from the frame of reference of the CMB rather than from Earth's frame of reference.: > Measurements of the cosmic background radiation give the cooling time of the universe since the Big Bang > Cosmic time, or cosmological time, is the time coordinate commonly used in the Big Bang models of physical cosmology.[1][2][3] Such time coordinate may be defined for a homogeneous, expanding universe so that the universe has the same density everywhere at each moment in time (the fact that this is possible means that the universe is, by definition, homogeneous). The clocks measuring cosmic time should move along the Hubble flow. https://en.wikipedia.org/wiki/Cosmic_time https://en.wikipedia.org/wiki/Cosmic_time