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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)

#41

Post by corrund »

jeffdavis wrote: post #39
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…

It's at lesst a little confusing how something went from 14B light years away to 46B light years away (seems to be a distance of 32B light years total travel) in 14B years.

It's called "mathemagick".

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

#42

Post by ggggtez »

corrund wrote: post #41
jeffdavis wrote: post #39

Earlier quoted context omitted.

It's at lesst a little confusing how something went from 14B light years away to 46B light years away (seems to be a distance of 32B light years total travel) in 14B years.

It's called "mathemagick".

No, the universe is expanding. No magic required.

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

#43

Post by bravoetch »

gesman wrote: post #35

All this assumes that time is a single thing (sort of gigantic X-axis with "t") that works for everyone in universe equally. What if we have multiple (billions) of realities with their own t-axis and with us being only one of these with our own timeline?

It's not an assumption, it's the observed model. Feel free to propose and test other models.

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

#44

Post by michaelmrose »

jeffdavis wrote: post #39
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…

It's at lesst a little confusing how something went from 14B light years away to 46B light years away (seems to be a distance of 32B light years total travel) in 14B years.

You aren't stationary and space itself is expanding.

The metaphor I normally see is a balloon being blown up.

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

#46

Post by ianai »

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…

There’s a huge difference between click bait and this. Click bait makes a crazy claim anyone would want to click on, “click here to learn the secret of immortality”, and delivers something mundane with little connection like “antioxidants are good.” This is choosing a compelling title for a topic or concept that otherwise might be a little boring or otherwise get viewer clicks - aka, marketing.

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

#47

Post by ianai »

michaelmrose wrote: post #44
jeffdavis wrote: post #39

Earlier quoted context omitted.

It's at lesst a little confusing how something went from 14B light years away to 46B light years away (seems to be a distance of 32B light years total travel) in 14B years.

You aren't stationary and space itself is expanding. The metaphor I normally see is a balloon being blown up.

Importantly, the expansion of the universe is necessary. Under special relativity two things could be moving at .9c toward one another and their velocities won’t somehow add to 1.8c in relative velocity. Light will still travel at c from one to the other.

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

#48

Post by harshreality »

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…

FTL travel of anything (matter, photons, EM fields, gravitational fields) would result in potential causality issues. I don't know if there are models of universes where GR doesn't apply; that would be interesting, but the causality problems might make such a universe uninteresting even if it were possible. I suppose that's using the anthropic principle as justification for GR?

Metric expansion does not result in causality issues because it's an isolating phenomenon (one that slows down interactions between things) rather than an interconnecting phenomenon (one that would speed up interactions between things). Therefore it's at least possible, and observations (which you can read a brief summary of in TFA) back it up.

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

#50

Post by goodluckchuck »

finchisko wrote: post #49

how can universe be expanding faster than speed of light? general relativity doesn't apply here?

Idk, but if we travel 13B light years one way, it moves 13B the other then were at 26, and space itself has to have expanded 20 billion light years within the time it takes light to travel 13... So yeah, sounds like something is moving faster than light.
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