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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)

#91

Post by wahern »

lmilcin wrote: post #81
wahern wrote: post #66

Earlier quoted context omitted.

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.

Ah, fair enough. I glossed right over that qualification, which is not a smart thing to do on HN--a credit to the quality of discourse here :)

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

#92

Post by saagarjha »

csomar wrote: post #86
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.

https://en.wikipedia.org/wiki/Hubble_volume

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

#93

Post by saagarjha »

lisper wrote: post #82
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…

Just because we can’t see them now doesn’t mean they didn’t move…

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

#94

Post by saagarjha »

coding123 wrote: post #29

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…

https://en.wikipedia.org/wiki/Alcubierre_drive

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

#95

Post by saagarjha »

cobbzilla wrote: post #22
lioeters wrote: post #17

Earlier quoted context omitted.

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...

Plus it’ll take quite a while to complete.

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

#96

Post by csomar »

ssijak wrote: post #32

If you are turning in bed and can't sleep I'll give you some questions to think about. Even though some are non-sensical in a way, they are a good starting point to ponder about: - Is space really flat (infinite) or curved (finite)? - If it is flat and the universe had the beginning (big bang) then does it just have "potential infinity", by ever-expanding? - If it is curved is it implied that it is encompassed by som…

> - What would happen if you would happen to stand at the edge of space/universe and push a hand through the edge?

That doesn't make sense if you say the universe is curved or infinite. There will be no edge.

> - Space could be infinite but at the same time with a boundary. Can you imagine that boundary without trying to imagine what it is bounded from?

No. That's what the definition of infinite is. There are no bounds.

> - What is space fabric actually made from? Is it discrete or not.

Probably numbers. But then I like Math, so...

> - Are there other universes outside ours?

I don't think we are any special. But I'd be happy to be proven otherwise!

> - Try to imagine nothing.

> - Try to imagine infinite.

You are having trouble with nothingness because you are linking it to your consciousness. Infinity is easy though. You keep pushing infinitely and there is no edge!

> - Is there free will?

No. But don't go and do stupid stuff because of that.

> - Can you even imagine a proper mechanism that would allow for free will to exist?

There isn't. You are the product of your environment and your parents.

> - What would prevent you from "cutting" the smallest possible particle in 2 parts?

Max Planck.

> - Are there several dimensions of time?

> - Is there a beginning of time?

There is no time. Try understanding the theory of general relativity.

> - Is math invented or discovered?

Math is very basic. It starts with set theory and then builds on top of that. It is invented since set theory is invented.

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

#97

Post by gls2ro »

simonh wrote: post #53
coding123 wrote: post #29

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…

Ok, but you can’t use it to go to anywhere FTL. You can only use it to get further away from somewhere FTL.

I think we can use it to go back to a place. It is the same as going further just that now we “just” need to shrink the space. Of course all is so far just an exercise of our imagination.

You can take a look at the curvature or more concrete to the density of the Universe. It is possible to be positive and in this case at one point in the future the Universe will collapse back on itself. Nothing will stop it to do this apparently FTL.

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

#98

Post by troubler »

saagarjha wrote: post #90
corrund wrote: post #61

Earlier quoted context omitted.

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

Not really.

FTL speed requires infinite amount of energy in this iteration of physics, except for case when vacuum is not empty, but even in this case medium cannot move at supersonic speed of medium, while still in one piece. If far away vacuum moves at FTL speed, then there must be "sonic" barrier somewhere.

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

#99

Post by troubler »

saagarjha wrote: post #88
corrund wrote: post #64

Earlier quoted context omitted.

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

What’s the difference, observationally?

Shrinking releases energy. Expanding consumes energy.

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

#100

Post by troubler »

drekembe wrote: post #13
hunter2_ wrote: post #9

Earlier quoted context omitted.

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.

Things can't move faster than light through space. The space itself has no such limitation. You can imagine an expanding balloon and ants walking on it that have a limit to how fast they can move relative to the surface of the balloon.

Then space itself is a thing, not a nothing, thus Theory of Relativity is wrong, because we can attach point to space itself. Chose your poison.
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