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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)

#21

Post by stan_rogers »

hunter2_ wrote: post #9
leonroy wrote: post #3

Earlier quoted context omitted.

The universe is expanding, at a rate which I believe is heading past the speed of light. This limits our ability to reach galaxies further away from us as they are speeding away faster than we could conceivably travel since our engines would of course be bound by the speed of light. Some more info: https://www.forbes.com/sites/startswithabang/2016/06/10/can-...

Why would some things be bound by the speed of light and not others? I always thought of this limitation as an all-or-nothing law.

It is. Nothing can move through space faster than the speed of light. That's not what's happening with the expansion of the universe. Space itself is expanding.

Silly ananlogy that absolutely should not be taken too far: imagine somehow shimming an extra micron into every metre here on Earth every second. Or an extra nanometre into every millimetre. Locally, nothing much changes at a scale you can observe, but Los Angeles is moving away from New York City at about 4m/s. And getting faster because we're still shimming extra length into "old metres"; the metre itself hasn't changed, but now there are more of them. If there were something a thousand times farther away from New York than LA, it would be moving at 4km/s and accelerating. A million times farther and it's 4000km/s. A hundred million times farther, and you're at 400,000km/s - but light can't go that fast, so you can't see it as the light can never reach you. Nothing is "moving" (other than the light in this case), but the distances between things is getting bigger nonetheless.

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

#22

Post by cobbzilla »

lioeters wrote: post #17
chongli wrote: post #7

Earlier quoted context omitted.

That’s the case for the galaxies furthest away from us. Closer galaxies are receding less quickly and Andromeda is actually coming towards us.

Indeed, and will merge with ours to become..the Milkdromeda (TBD) galaxy. Looking forward to the fireworks. https://en.wikipedia.org/wiki/Andromeda%E2%80%93Milky_Way_co...

Humans (assuming we are still around) will have to watch from another planet: the collision will happen in ~4.5 billion years [1], and Earth will be uninhabitable long before then [2].

[1] https://en.wikipedia.org/wiki/Andromeda%E2%80%93Milky_Way_co...

[2] https://en.wikipedia.org/wiki/Timeline_of_the_far_future#Fut...

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

#23

Post by amelius »

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…

I didn't read the article but I suspect the reason is that space is expanding.

If space wouldn't have expanded sufficiently fast in the beginning of time, all matter would be still clumped together as in a giant black hole. The fact that space expanded "faster" than the speed of light allowed this black hole to become free matter.

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

#24

Post by recursivecaveat »

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…

In essence, it's 'okay' for things to be FTL due to expansion of the medium. Imagine an ant crawling across a balloon as we stretch it. The ant could get some pretty fantastic apparent speeds relative to another ant because the medium is expanding, but step by step its moving at regular ant speed.

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

#25

Post by lmilcin »

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 content and you figured out you will make something difficult so that you can then make it a little bit easier and be a hero.

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

#26

Post by Zenst »

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…

Interesting ratio of 1:3.3141210374639769452449567723343 not exactly Pi.

But then that expansion ratio may of been different over time, but it is a bit like sampling the second hand on a clock in a photo and working out the entire motion and workings of the clock - at least on the scale of the data/measurements we have and the age of the universe. Currently we are still not 100% sure when midnight was, but as always moving in the right direction.

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

#27

Post by deepsun »

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…

I personally prefer to avoid saying "currently" for far away objects, because I don't understand it. Only what's in our light cone.

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

#28

Post by buboard »

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…

your explanation would naturally raise the question why the difference. you can't really explain it without mentioning the expansion of the universe

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

#29

Post by coding123 »

I feel like we are all idiots repeating "space is expanding" if humans could live 14billion years in age, and we were present when it started, but we left good old Bob on the part of the universe that was travelling away from us, he would have traveled FTL from us. Even if you said space expanded, the traveling has been accomplished. So now we know that space expansion is how you travel FTL.

In other words if humans ever invent warp, the space expansion work around we would effectively have FTL travel.

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