A new Einstein cross is discovered • Hacker News Board

Re: A new Einstein cross is discovered

#61

Post by plazmaphyujin » Mon, Mar 25, 2019, 7:31 PM UTC

TaylorAlexander wrote: post #46

samstave wrote: post #41

ELI5: How can the universe be "infinitely big" yet have a measurable "finite age" and the velocity arc of the 'expanding' universe not be some known rate? Such that we can estimate the actual farthest distance. And WHAT THE HECK is the universe 'expanding into'? The answers to these questions make me dubious on tiny-human understanding of the nature of reality. Mechanical Elves, anyone?

Normally the term I hear is “finite, but unbounded”, but I suppose it’s hard to grok that either. I also really wonder what is the universe “inside of”? Like why is spacetime here in the first place? I agree that our explanation must be impoverished compared to the true nature of nature. It really boggles my mind. I enjoy the public physics lectures scattered around YouTube, but it all still leaves me realizing how l…

There isn't really an "inside of". There is no other universe that our universe is expanding into. The universe itself just "is", it is made of space-time and that metric is expanding and accelerating. Why it exists is philosophy. Maybe it was made just for us to exist in. Maybe it doesn't give a shit about us and we're simply hydrogen left to own devices long enough to futilely question its own existence.

When we talk about the universe we're rarely talking about what do not know yet, but rather what is possible to know.

Whether there is another universe "outside" of ours is not just something we don't know. It's something we cannot know but it's also something that cannot matter. The observable universe is, by definition, the total encompassment of everything that can possibly ever matter to us in even the strictest mathematical sense.

Re: A new Einstein cross is discovered

#62

Post by mordero » Mon, Mar 25, 2019, 7:33 PM UTC

mirimir wrote: post #34

jhoechtl wrote: post #28

Earlier quoted context omitted.

Which makes it then effectivelly infinite?

IANAP, but I think so. I vaguely recall that early inflationary expansion was very fast. Like several times the speed of light.

Space itself is expanding. At small scales, it isn't really that "fast" (gravity can/does overcome the effects within our galaxy and the Local Group). However, at large scales, it can exceed the speed of light (google "Hubble volume") so at some point, light emitted from sources outside this range will not longer reach us because the space between here and there expanded faster than light travels.

Re: A new Einstein cross is discovered

#63

Post by PopeDotNinja » Mon, Mar 25, 2019, 7:34 PM UTC

teekert wrote: post #27

McKayDavis wrote: post #20

WMAP measurements put the age of the universe at ~13.77 billion years, so I was initially perplexed by this part of the article: > The object acting as a lens turns out to be an elliptical galaxy located at a distance of approximately 7 billion light years (z = 0.556), while the source is at least 20 billion light years away (z = 3.03). ...but I found this explanation in the Wikipedia article on the most distant know…

Thank you, went to the comments to learn this. So the universe actually expands pretty fast then! Faster than the speed of light? Strangely...

Yup! There is light moving towards us from the other side of the universe, but we'll never see it because the space between that light is stretching faster than thr light can travel (or something like that). Check out this page on the Observable Universe... https://en.wikipedia.org/wiki/Observable_universe.

Re: A new Einstein cross is discovered

#64

Post by mirimir » Mon, Mar 25, 2019, 7:35 PM UTC

mirimir wrote: post #34

jhoechtl wrote: post #28

Earlier quoted context omitted.

Which makes it then effectivelly infinite?

IANAP, but I think so. I vaguely recall that early inflationary expansion was very fast. Like several times the speed of light.

Belated edit: More like ~10^81 times the speed of light.

> According to the theory of inflation, the Universe grew by a factor of 10 to the sixtieth power in less than 10 to the negative thirty seconds, so the "edges" of the Universe were expanding away from each other faster than the speed of light [0]

It seems that the universe was on the order of ~1 meter in diameter then.[1] So the "'edges' of the Universe were expanding away from each other" at ~10^90 meters per second.

0) http://curious.astro.cornell.edu/physics/109-the-universe/co...

1) https://www.forbes.com/sites/startswithabang/2017/03/24/how-...

Edit: Upon reflection, I get that "~1 meter in diameter" makes no sense. Maybe just say that the "edges" were ~1 meter apart.

Re: A new Einstein cross is discovered

#65

Post by Causality1 » Mon, Mar 25, 2019, 7:38 PM UTC

Why does the lense effect produce four separate images instead of a single image in the middle or a smeared ring all the way around the outside?

Re: A new Einstein cross is discovered

#66

Post by sizzzzlerz » Mon, Mar 25, 2019, 8:11 PM UTC

Space is big. You just won't believe how vastly, hugely, mind-bogglingly big it is. I mean, you may think it's a long way down the road to the chemist's, but that's just peanuts to space.

20 billion light-years! Truly mind-boggling.

Re: A new Einstein cross is discovered

#67

Post by roywiggins » Mon, Mar 25, 2019, 8:11 PM UTC

sandworm101 wrote: post #57

earenndil wrote: post #52

Earlier quoted context omitted.

I'm no expert (so correct me if I'm wrong), but from what I'm read, flat, concave, and convex universes are all possibilities and they would all look flat to us because our measurements take place on such a small scale.

Our measurements occur across billions of light-years. By comparing redshift agaist the standard candles we measure relative speeds of vastly distant objects. And given the speed of light, we are also measuring what those speeds were billions of years ago. It is a very big ruler.

We've measured the flatness of the universe on the scale of the cosmic microwave background, which is essentially as big a ruler as could possibly exist.

https://map.gsfc.nasa.gov/mission/sgoals_parameters_geom.htm...

https://wmap.gsfc.nasa.gov/universe/uni_shape.html

Re: A new Einstein cross is discovered

#68

Post by mehrdadn » Mon, Mar 25, 2019, 8:16 PM UTC

btilly wrote: post #30

teekert wrote: post #27

Earlier quoted context omitted.

Thank you, went to the comments to learn this. So the universe actually expands pretty fast then! Faster than the speed of light? Strangely...

This is a well-known phenomena. The usual image is to consider ants traveling on an expanding balloon. The speed of light is the limit of how fast the ants can walk. The expansion of the universe is the expansion of the balloon. And now you see how two distant ants can be carried away from each other faster than they can walk towards each other. If you understand manifolds and general relativity, this analogy is surp…

I've heard of raisins on a cupcake instead (I hate raisins on cupcakes btw), I assume since it's a 3D example. It's meant to show how it's possible for everything to be getting farther away from each other without anything being at the center.

Re: A new Einstein cross is discovered

#69

Post by waterhouse » Mon, Mar 25, 2019, 8:20 PM UTC

teekert wrote: post #27

McKayDavis wrote: post #20

WMAP measurements put the age of the universe at ~13.77 billion years, so I was initially perplexed by this part of the article: > The object acting as a lens turns out to be an elliptical galaxy located at a distance of approximately 7 billion light years (z = 0.556), while the source is at least 20 billion light years away (z = 3.03). ...but I found this explanation in the Wikipedia article on the most distant know…

Thank you, went to the comments to learn this. So the universe actually expands pretty fast then! Faster than the speed of light? Strangely...

I think it expands uniformly, so that, after time t, a distance of x becomes a distance of x * k, with k being very slightly greater than 1. Then there will always exist large enough x to outstrip the speed of light.

To illustrate, imagine the expansion factor is, say, 10^-20 per second. Then a distance of 10^30 meters will increase to a distance of 10^30 + 10^10 meters in one second, while light travels at 3 * 10^8 meters per second, so expansion would outstrip lightspeed at that distance. If the expansion factor were 10^-40 per second, then a distance of 10^50 meters would be increasing faster than lightspeed.

Re: A new Einstein cross is discovered

#70

Post by balabaster » Mon, Mar 25, 2019, 8:21 PM UTC

TaylorAlexander wrote: post #46

samstave wrote: post #41

ELI5: How can the universe be "infinitely big" yet have a measurable "finite age" and the velocity arc of the 'expanding' universe not be some known rate? Such that we can estimate the actual farthest distance. And WHAT THE HECK is the universe 'expanding into'? The answers to these questions make me dubious on tiny-human understanding of the nature of reality. Mechanical Elves, anyone?

Normally the term I hear is “finite, but unbounded”, but I suppose it’s hard to grok that either. I also really wonder what is the universe “inside of”? Like why is spacetime here in the first place? I agree that our explanation must be impoverished compared to the true nature of nature. It really boggles my mind. I enjoy the public physics lectures scattered around YouTube, but it all still leaves me realizing how l…

> there’s likely a trillion inhabited worlds full of beings we will never know.

And by the time our radio signal gets to them, the ones there now will all be long dead, interpreted by some future generation. By the time we get the response, humanity may be long extinct. So for all intents and purposes, we may as well be alone in the universe.