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How Can a Star Be Older Than the Universe?

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Re: How Can a Star Be Older Than the Universe?

#111

Post by Dylan16807 »

wahern wrote: post #90
ecnahc515 wrote: post #47

Earlier quoted context omitted.

> when we say the universe is expanding, we mean that matter is spreading out It's been a while, but I recall reading in a book that's actually the space between everything that's expanding, much like you state in your second paragraph. For example, if you blow up a balloon, two points on it will appear to be moving apart from each other even though they're stationary. I believe this Forbes article is in agreement: h…

It's also been described like a loaf of bread expanding, where stars are like raisins, except the loaf might be infinitely big. See https://en.wikipedia.org/wiki/Inflation_(cosmology) and https://en.wikipedia.org/wiki/Shape_of_the_universe But that's also somewhat misleading as it gives the impression that it's just interstellar space (reinforcing the non-scientific connotation of space) that inflates. At some point…

To be clear, the big rip is only if expansion gets massively faster. At the current rate, the disturbance on matter is ridiculously negligibly small.

Re: How Can a Star Be Older Than the Universe?

#112

Post by calvertdw »

namirez wrote: post #65
ajay-d wrote: post #59

GN-z11 is a galaxy that's 32 billion light years away. Here's the note from wikipedia: At first glance, the distance of 32 billion light-years (9.8 billion parsecs) might seem impossibly far away in a Universe that is only 13.8 billion (short scale) years old, where a light-year is the distance light travels in a year, and where nothing can travel faster than the speed of light. However, because of the expansion of t…

Also, despite the age of the universe (13.8B years), the diameter of the observable universe is 93 billion light years. That's because the universe expanded (and probably still is expanding) faster than light.

As observed, it's only 13.8, though, right?

Re: How Can a Star Be Older Than the Universe?

#113

Post by cgrealy »

ShamelessC wrote: post #109
cpeterso wrote: post #88

Earlier quoted context omitted.

The relevant bit from Excession is the discovery of a mysterious entity that is 50x older than the universe.

What's the explanation?

Without giving too much away, it's not from this universe.

You really should read it, it's one of the best books in the culture series and Banks was a phenomenal writer.

It also contains the Affront, a species that are almost comically awful and coined the term "outside context problem":

"The usual example given to illustrate an Outside Context Problem was imagining you were a tribe on a largish, fertile island; you'd tamed the land, invented the wheel or writing or whatever, the neighbors were cooperative or enslaved but at any rate peaceful and you were busy raising temples to yourself with all the excess productive capacity you had, you were in a position of near-absolute power and control which your hallowed ancestors could hardly have dreamed of and the whole situation was just running along nicely like a canoe on wet grass... when suddenly this bristling lump of iron appears sailless and trailing steam in the bay and these guys carrying long funny-looking sticks come ashore and announce you've just been discovered, you're all subjects of the Emperor now, he's keen on presents called tax and these bright-eyed holy men would like a word with your priests."

Re: How Can a Star Be Older Than the Universe?

#115

Post by laurencei »

namirez wrote: post #65
ajay-d wrote: post #59

GN-z11 is a galaxy that's 32 billion light years away. Here's the note from wikipedia: At first glance, the distance of 32 billion light-years (9.8 billion parsecs) might seem impossibly far away in a Universe that is only 13.8 billion (short scale) years old, where a light-year is the distance light travels in a year, and where nothing can travel faster than the speed of light. However, because of the expansion of t…

Also, despite the age of the universe (13.8B years), the diameter of the observable universe is 93 billion light years. That's because the universe expanded (and probably still is expanding) faster than light.

Can you ELI5 - how can we observe something 93 billion light years away, if the light has only been traveling for 13.8B years? Shouldnt the "observable" distance be the the age of the universe?

Re: How Can a Star Be Older Than the Universe?

#116

Post by devnulloverflow »

laurencei wrote: post #115
namirez wrote: post #65

Earlier quoted context omitted.

Also, despite the age of the universe (13.8B years), the diameter of the observable universe is 93 billion light years. That's because the universe expanded (and probably still is expanding) faster than light.

Can you ELI5 - how can we observe something 93 billion light years away, if the light has only been traveling for 13.8B years? Shouldnt the "observable" distance be the the age of the universe?

Your intuition that there is an limited observable distance because is correct. But because of the expansion, that limit is bigger than "speed_of_light * age of universe" .

I don't know enough General Relativity to give a solid explanation. But here is a rough over-simplification: Imagine you've spent the last 5 seconds blowing up a balloon, but there is an ant walking on that balloon, starting from a marked spot.

In the 1st second, the ant moved 10mm. But in the next four seconds you blew up the balloon, so that 10mm of rubber is now 70mm long. The total distance from the ant's starting mark to her end-point can now be well over than 70mm, even though she only walks at less than 10mm/second.

As the ant, so the photon.

Re: How Can a Star Be Older Than the Universe?

#117

Post by laurencei »

devnulloverflow wrote: post #116
laurencei wrote: post #115

Earlier quoted context omitted.

Can you ELI5 - how can we observe something 93 billion light years away, if the light has only been traveling for 13.8B years? Shouldnt the "observable" distance be the the age of the universe?

Your intuition that there is an limited observable distance because is correct. But because of the expansion, that limit is bigger than "speed_of_light * age of universe" . I don't know enough General Relativity to give a solid explanation. But here is a rough over-simplification: Imagine you've spent the last 5 seconds blowing up a balloon, but there is an ant walking on that balloon, starting from a marked spot. In…

Yep - I kind of understand that. Thanks.

Re: How Can a Star Be Older Than the Universe?

#118

Post by kijin »

calvertdw wrote: post #112
namirez wrote: post #65

Earlier quoted context omitted.

Also, despite the age of the universe (13.8B years), the diameter of the observable universe is 93 billion light years. That's because the universe expanded (and probably still is expanding) faster than light.

As observed, it's only 13.8, though, right?

No, it's observed as 93 billion light years. That's why we call it the "observable" universe.

There is no meaningful spatial boundary at a point that is currently at a distance of 13.8 billion light years from us. We can detect (severely red-shifted) photons from beyond that point perfectly fine! The actual boundary is 46.5 billion light years away in both directions, hence the "observable" diameter of 93 billion.

But of course the meaning of "observed" is kinda strange here, since we're not directly measuring the distance but estimating it based on from other observations.

Re: How Can a Star Be Older Than the Universe?

#120

Post by Udik »

kijin wrote: post #118
calvertdw wrote: post #112

Earlier quoted context omitted.

As observed, it's only 13.8, though, right?

No, it's observed as 93 billion light years. That's why we call it the "observable" universe. There is no meaningful spatial boundary at a point that is currently at a distance of 13.8 billion light years from us. We can detect (severely red-shifted) photons from beyond that point perfectly fine! The actual boundary is 46.5 billion light years away in both directions, hence the "observable" diameter of 93 billion. Bu…

Where I supposed that "observed as " just means how much red-shifted its light is- we don't really have any other way to measure such distances. This in turn only measures how much the space has expanded between us and the original starting point, much closer than 13 billion light years away. So we can say that we're seeing a star that is "now" 46 billion ly from us, but must have been only a few billion ly away when it emitted the light we're receiving. Correct?
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