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A new Einstein cross is discovered

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Re: A new Einstein cross is discovered

#91

Post by gregdunn »

vanderZwan wrote: post #79
btilly wrote: post #76

Earlier quoted context omitted.

I haven't heard the cupcake version. It does have something to recommend it, though raisins don't crawl. So that may make it harder to visualize the difference between how fast you're expanding versus how fast you're moving versus local space. Which is the whole point.

What I find confusing is that the space inside the ants/raisins should expand as well. Why do we not experience this expansion locally?

It's not strong enough to overcome the forces keeping us together.

But that might not be the case for forever: https://en.wikipedia.org/wiki/Big_Rip

Re: A new Einstein cross is discovered

#92

Post by whatshisface »

plazmaphyujin wrote: post #58
teekert wrote: post #35

Earlier quoted context omitted.

There is not really a center, galaxies are more like raisins in a rising bread. They all move away from each other with the same relative speeds. At least... Any physicists here to tell me whether or not space-time density get less closer to the edge? I mean... Is there an Edge?

There is no edge. It defies the normal way of thinking but every point in the universe is also the center of the universe. The Big Bang happened at every point and space-time is expanding at every point.

There could be an edge, but it's definitely not within the distance we can see out. The main mind-bender is that there's no need for an edge.

Re: A new Einstein cross is discovered

#93

Post by plazmaphyujin »

whatshisface wrote: post #92
plazmaphyujin wrote: post #58

Earlier quoted context omitted.

There is no edge. It defies the normal way of thinking but every point in the universe is also the center of the universe. The Big Bang happened at every point and space-time is expanding at every point.

There could be an edge, but it's definitely not within the distance we can see out. The main mind-bender is that there's no need for an edge.

Well, not really. The distance we can see out is measured in time and we can very nearly see the Big Bang. We can observe the Universe's Recombination event and it is in every direction we look as the Cosmic Microwave Background. This happened everywhere in existence.

If there is an edge to the Universe it is in the fourth dimension when the Universe was a singularity.

Re: A new Einstein cross is discovered

#94

Post by monkeydreams »

mirimir wrote: post #64
mirimir wrote: post #34

Earlier quoted context omitted.

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 e…

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

I have no grounding in physics on which to place this hunch but... doesn't this sound like a wee fudge factor to make the Big Bang theory fit evidence?

I am reminded of the concept of "aether" and "land bridge theory" where people had a workable hypothesis except for the niggly little problem that the hypothesis was contraindicated by some of the evidence.

Re: A new Einstein cross is discovered

#95

Post by 6nf »

rough-sea wrote: post #55
saagarjha wrote: post #53

Earlier quoted context omitted.

Isn’t the natural extension of things being “closer together” that they were at a singularity at some point (the Big Bang)?

Nope. The universe is infinite, according to the model. We see observe galaxies speeding away from us in every direction - and it seems unlikely that the earth was the exact center of the Big Bang.

We see stuff in all directions because the stuff extends much further than what we can observe. There may well be a 'middle' of the universe but there's no way to tell how close we are to it (or if it even exists at all.)

Re: A new Einstein cross is discovered

#96

Post by 6nf »

gmm1990 wrote: post #11

How can the further Galaxy be 20 billion light years away?

The universe began 13.8 billion years ago. However the universe is not expanding at the speed of light. It's expanding faster than that, such that the observable universe from earth's perspective is about 47 billion light years in radius.

Re: A new Einstein cross is discovered

#97

Post by 6nf »

UlisesAC4 wrote: post #40
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...

Space still expands lower than light speed, the moment expansions goes faster night skies will be completely dark because other objects' light won't be able to reach our field of vision. I do not remember how that phenomenon is called.

You might be referring to the Big Rip?

Re: A new Einstein cross is discovered

#98

Post by oska »

bhaak wrote: post #8
jbf1001 wrote: post #6

Earlier quoted context omitted.

I had to look it up too, it's the German word for Quasar. https://en.wikipedia.org/wiki/Quasar .

That's wrong, Quasar is also the German word for Quasar. But it looks like that the Scandinavian and the Slavic languages use the form "kvasar".

Wiktionary is good for finding what languages a particular sequence of characters appears in.

https://en.wiktionary.org/wiki/kvasar

According to that entry, it appears in both Swedish and Czech (as an alternate spelling).

Given the commenter's username is krokku and the fact that "krok ku" means "(a) step forward/towards" in Czech, I think we can assume that the commenter is Czech.

Re: A new Einstein cross is discovered

#100

Post by cthalupa »

Qwertystop wrote: post #56
rough-sea wrote: post #55

Earlier quoted context omitted.

Nope. The universe is infinite, according to the model. We see observe galaxies speeding away from us in every direction - and it seems unlikely that the earth was the exact center of the Big Bang.

Wouldn't that also be consistent with a finite universe as long as the distribution of galaxies is not biased towards or away from the edge, as long as the edge itself is beyond the observable part of the universe? We wouldn't have to be in the exact center, just not too close to the boundary.

>Wouldn't that also be consistent with a finite universe

It would. It is not an unanimous conclusion that "stuff" is found everywhere in the universe and that the universe is infinitely big. However, that doesn't necessarily imply a center or an edge.

The universe might be infinite and unbounded.

The universe might be finite and bounded.

The universe might be finite and unbounded.

If the universe is finite and unbounded, we can go back to the ants on a balloon analogy. As expansion continues (and indeed speeds up) the balloon will continue to inflate, for forever. It is not possible to ever make the trip around the balloon to get back to your starting destination due to the expansion of the universe. The universe and spacetime are the 'surface' of the balloon - there is nothing inside of it, the center is not the middle of the balloon, and you cannot tunnel from one side of the balloon through to another. That isn't to say the observable universe is likely to be the extent or even close to the extent of the actual universe - it is likely still just the tiniest of fractions of the actual universe.

We're probably finite and unbounded, and expanding into nothing. As the universe expands, it creates space where it did not exist.

There's other theories that are reasonable, however. Some posit that our universe is a bubble in a true vacuum, and that there could be other bubbles containing other universes. Those theories are largely driven by the theory of inflation, which is the most accepted explanation as to how the universe expanded so far and so quickly in its early stages. (That's not to imply that the bubble multiverse theory is the most accepted explanation, though - just that most theories relating to bubble multiverses stem from looking at vacuum energy)

We probably won't know for certain in our lifetimes. Intelligent lifeforms might never know for certain.

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