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If the universe is 13.8B years old, how can we see 46B light years away? (2018)

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Re: If the universe is 13.8B years old, how can we see 46B light years away? (2018)

#81

Post by lmilcin »

wahern wrote: post #66
lmilcin wrote: post #54

Earlier quoted context omitted.

Except the galaxies do not travel. Galaxies are more or less stationary, it's the space inbetween that expands. Think in terms of raisins in a dough or points on expanding baloon. Neither of them could be said to travel, yet they can be seen to become more and more far away.

Technically, galaxies do travel: > In physical cosmology, peculiar velocity refers to the components of a galaxy's velocity that deviate from the Hubble flow. .... > Galaxies are not distributed evenly throughout observable space, but are typically found in groups or clusters, where they have a significant gravitational effect on each other. Velocity dispersions of galaxies arising from this gravitational attraction…

That's why I wrote "more or less stationary", which is describing 1000km/s compared to double the speed of light that would come from naive calculation.

Re: If the universe is 13.8B years old, how can we see 46B light years away? (2018)

#82

Post by lisper »

nvrspyx wrote: post #20

If what we’re seeing was 13.8B light years away 13.8B years ago and are now 46B light years away, wouldn’t that mean that those things traveled ~32.2B light years in 13.8B years. Wouldn’t that thus mean they travelled faster than the speed of light? Maybe I’m misunderstanding though. EDIT: I guess you also have to take into account the expansion of the fabric of space as well and not just the movement of the galaxies…

[EDIT] Everyone please ignore this comment. It is totally wrong.

> If what we’re seeing was 13.8B light years away 13.8B years ago and are now 46B light years away, wouldn’t that mean that those things traveled ~32.2B light years in 13.8B years.

No. What we're seeing was 13.8BLY away (in our reference frame) when the light was emitted. Those things are 46BLY away now (again, in our reference frame) but we can't see them now, we can only see them as they were 138B years ago.

Re: If the universe is 13.8B years old, how can we see 46B light years away? (2018)

#83

Post by lmilcin »

NeedMoreTea wrote: post #59
lmilcin wrote: post #25

And... another author that doesn't get it or looks for a controversial, clickbaity title. The correct way to state it would be to say: "We are seing things that are currently 46B light years away but since they are so far away we see them as they were 13.8B years ago when they were much closer than they are now." I see absolutely nothing difficult about that statement unless you really need to create some piece of co…

Yet you can't account for them now being 46B light years away without breaching C, or encompassing the expansion of the universe, within which things are moving. I think he manages a clear explanation of that without scaring away too many. Your "correct" version on the other hand, leaves more questions than answers, not least of which being how do we ever get 46B ly distance in something 13.8B years old. Then you hav…

This was described almost hundred years ago.

https://en.wikipedia.org/wiki/Hubble%27s_law

"(...) the notion of the universe expanding at a calculable rate was first derived from the general relativity equations in 1922 by Alexander Friedmann"

The space expands. It's been known for a long time.

We might not know why exactly this happens and there is still some discussion about ultimate fate of the universe although prevalent theory is that it will expand at an ever faster rate until every molecule will be torn from each other and matter will no longer be able to form.

Re: If the universe is 13.8B years old, how can we see 46B light years away? (2018)

#86

Post by csomar »

nvrspyx wrote: post #20

If what we’re seeing was 13.8B light years away 13.8B years ago and are now 46B light years away, wouldn’t that mean that those things traveled ~32.2B light years in 13.8B years. Wouldn’t that thus mean they travelled faster than the speed of light? Maybe I’m misunderstanding though. EDIT: I guess you also have to take into account the expansion of the fabric of space as well and not just the movement of the galaxies…

My understanding is that space is expanding faster than the speed of light. I don't recall where I read it, though.

Re: If the universe is 13.8B years old, how can we see 46B light years away? (2018)

#87

Post by saagarjha »

lmilcin wrote: post #83
NeedMoreTea wrote: post #59

Earlier quoted context omitted.

Yet you can't account for them now being 46B light years away without breaching C, or encompassing the expansion of the universe, within which things are moving. I think he manages a clear explanation of that without scaring away too many. Your "correct" version on the other hand, leaves more questions than answers, not least of which being how do we ever get 46B ly distance in something 13.8B years old. Then you hav…

This was described almost hundred years ago. https://en.wikipedia.org/wiki/Hubble%27s_law "(...) the notion of the universe expanding at a calculable rate was first derived from the general relativity equations in 1922 by Alexander Friedmann" The space expands. It's been known for a long time. We might not know why exactly this happens and there is still some discussion about ultimate fate of the universe although pr…

Great, now you’ve started to touch on the points mentioned in the article.

Re: If the universe is 13.8B years old, how can we see 46B light years away? (2018)

#88

Post by saagarjha »

corrund wrote: post #64
lmilcin wrote: post #54

Earlier quoted context omitted.

Except the galaxies do not travel. Galaxies are more or less stationary, it's the space inbetween that expands. Think in terms of raisins in a dough or points on expanding baloon. Neither of them could be said to travel, yet they can be seen to become more and more far away.

No, space inbetween is stationary. It's galaxies that shrinks. Think of ice in water.

What’s the difference, observationally?

Re: If the universe is 13.8B years old, how can we see 46B light years away? (2018)

#89

Post by csomar »

brianberns wrote: post #69
donpark wrote: post #30

My two cents worth: One is a measure of time. The other is a measure of distance. The two are unrelated.

Um, no. Distance and time are related by the speed of light, which travels 1 light year (distance) in 1 year (time). If space wasn’t expanding, the distance to a stationary object (in light years) would be exactly equal to the travel time of light from it (in years).

They are related (in fact there is no "time") but I think what the OP wanted to say is that you can have a universe that it is "that" big from the get go and so objects will be very far from the beginning.

Re: If the universe is 13.8B years old, how can we see 46B light years away? (2018)

#90

Post by saagarjha »

corrund wrote: post #61
ggggtez wrote: post #42

Earlier quoted context omitted.

No, the universe is expanding. No magic required.

Infinite amount of dark mathemagic is required for faster than light expansion of nothing.

Not really.
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