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

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

#131

Post by Izkata » Sun, Dec 08, 2019, 3:59 PM UTC

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?

My understanding is along the lines of, the surface of a balloon is the "fabric" of the universe: As the balloon is blown up it can expand and push things on it further apart, but the matter itself is always in the same place on the surface/in the universe (or moving slowly along the surface/in the universe). One big difference of course being the surface of a balloon is 2-dimensional, while space is 3-dimensional.

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

#132

Post by ssijak » Sun, Dec 08, 2019, 4:37 PM UTC

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…

The set of positive numbers is infinite but bounded by 0. The same concept could be applied to space.

I don't have trouble with nothingness because of that. Imagining it "visually" yes, but imagining how from something that would be nothing can become something that boggles my mind.

Max Planck would not prevent that. The smallest particle (that we know for know) is much larger than Planck length. But anyway even if it weren't, plack length have different implication.

My understanding is that there is time, just that it is not that simple as Newton imagined.

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

#133

Post by jon_richards » Mon, Dec 09, 2019, 1:30 AM UTC

ctdonath wrote: post #5

It’s not that we can see that far, it’s that what we see has moved away from where it was when it produced the light we see now.

It’s more complicated than that. It hasn’t moved that far because it can’t move faster than the speed of light. If you start 13B light years away and move away at the speed of light, you’d still only be 26B light years away by the time I saw your original light.