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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)

#101

Post by troubler »

michelpp wrote: post #11
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.

Everything that moves through space is bound by the speed of light. But space itself is expanding at a rate such that two distant points can move away from each other faster than the speed of light. Think of it like two ants on opposite sides of a balloon, one ant starts moving toward the other as fast as it can go, but then you start to inflate the balloon. The distance between the two ants expands faster than an an…

So, we can calculate speed of Earth relatively to our segment of space, right? Can you do the calculation and tell us speed of Ether Wind, please?

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

#102

Post by cygx »

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…

Still not quite right: 13.8 Gly is the light travel distance, whereas proper distance at time of emission was less than that.

For example, for redshift z=9, light travel time is 13.17 Gy, proper distance at time of absorption (aka comoving distance) is 30.72 Gly and proper distance at time of emission (which, in a spatially flat universe, corresponds to angular diameter distance) is 3.07 Gly. The factor of 10 between these two distances is no coincidence as the ratio of the scale factor is given by 1+z.

( The values have been calculated via http://www.astro.ucla.edu/~wright/CosmoCalc.html )

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

#103

Post by chongli »

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...

If we can figure out how to solve our political issues and become a eusocial species, we may be able to build some generational starships. In 4.5 billion years we could potentially colonize many of the planets in the habitable zone of stars in the Milky Way.

Sure, it could take millions of years to cross the galaxy, but we could grow exponentially (like lily pads crossing a pond), at least until other limiting factors kick in.

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

#104

Post by meteor333 »

Sorry, can some explain the ‘universe is expanding’ concept? So far I thought it only meant that the space universe occupies is expanding, meaning the matter keeps going farther from its origin point, but I didn’t know the ‘fabric’ of the universe is expanding. I’m not able wrap my head around this concept. Can some please point me a resource that dumbs it down?

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

#105

Post by fghtr »

meteor333 wrote: post #104

Sorry, can some explain the ‘universe is expanding’ concept? So far I thought it only meant that the space universe occupies is expanding, meaning the matter keeps going farther from its origin point, but I didn’t know the ‘fabric’ of the universe is expanding. I’m not able wrap my head around this concept. Can some please point me a resource that dumbs it down?

"The universe does not expand "into" anything and does not require space to exist "outside" it. Technically, neither space nor objects in space move. Instead it is the metric governing the size and geometry of spacetime itself that changes in scale."

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

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

#106

Post by fghtr »

csomar wrote: post #96
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 boun…

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

>Max Planck.

For those who did not understand: https://en.wikipedia.org/wiki/Planck_length

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

#107

Post by hcarvalhoalves »

meteor333 wrote: post #104

Sorry, can some explain the ‘universe is expanding’ concept? So far I thought it only meant that the space universe occupies is expanding, meaning the matter keeps going farther from its origin point, but I didn’t know the ‘fabric’ of the universe is expanding. I’m not able wrap my head around this concept. Can some please point me a resource that dumbs it down?

This was confusing for me too. As time passes, the less the universe is made up of "something" (observable matter), so maybe a more accurate analogy would be saying the universe is "diluting" rather than "expanding"?

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

#108

Post by salutis »

kr4 wrote: post #38
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…

I can give one thing for you to ponder: what's the true difference of the world you experience in the waking state and the world you experience during dreaming state and the cause behind both of these? The puzzle of the universe, infinity and multiverse can become apparent if you ponder over the above question.

The world we experience in the waking state is persistent and objective. The world we experience during the dreaming state is subjective and temporary. There, I pondered, and it did not make “the puzzle of the universe, infinity and multiverse apparent”.

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

#109

Post by manigandham »

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…

Things moving in space/time are limited to the speed of light. Space itself isn't.

It's like a blowing up a balloon. There's no limit to how big it gets or how fast it grows, so objects on opposing sides can move apart at greater than the speed of light even if they're not moving themselves.

This rate of expansion is accelerating too, driven by something called "dark" (as in unknown) energy which is overpowering all the gravity that should be pulling things together. It's fascinating to think that in 100s of billions of years, our local galaxy will be the only thing we can see in space. Any civilizations then would believe that there's nothing else out there.

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

#110

Post by nvrspyx »

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…

I'm sorry, but that's exactly what I said unless I'm misunderstanding your point.

I said what we're seeing was 13.8B light years away 13.8B years ago, since it took 13.8B years for the light to reach us from the point it was emitted. I never said we could see now where they currently are. What I failed to account for was the space expansion during the time that the light was traveling meaning that the light had to travel further to reach us than the point of emission actually was when it emitted.

So really, it wasn't 13.8B years ago; it was emitted later. I don't know by how much, but it seems like maybe the other commenter does.

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