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GN-z11 is a galaxy that's 32 billion light years away. Here's the note from wikipedia: At first glance, the distance of 32 billion light-years (9.8 billion pa
by ajay-d 7y ago
GN-z11 is a galaxy that's 32 billion light years away. Here's the note from wikipedia:
At first glance, the distance of 32 billion light-years (9.8 billion parsecs) might seem impossibly far away in a Universe that is only 13.8 billion (short scale) years old, where a light-year is the distance light travels in a year, and where nothing can travel faster than the speed of light. However, because of the expansion of the universe, the distance of 2.66 billion light-years between GN-z11 and the Milky Way at the time when the light was emitted increased by a factor of (z+1)=12.1 to a distance of 32.2 billion light-years during the 13.4 billion years it has taken the light to reach us.
[1] https://en.wikipedia.org/wiki/GN-z11#Notes https://en.wikipedia.org/wiki/GN-z11#Notes
- namirez 7y agoAlso, despite the age of the universe (13.8B years), the diameter of the observable universe is 93 billion light years. That's because the universe expanded (and probably still is expanding) faster than light.
- NetOpWibby 7y agoThat’s fascinating to think about.
- calvertdw 7y agoAs observed, it's only 13.8, though, right?
- kijin 7y agoNo, it's observed as 93 billion light years. That's why we call it the "observable" universe. There is no meaningful spatial boundary at a point that is currently at a distance of 13.8 billion light years from us. We can detect (severely red-shifted) photons from beyond that point perfectly fine! The actual boundary is 46.5 billion light years away in both directions, hence the "observable" diameter of 93 billion. But of course the meaning of "observed" is kinda strange here, since we're not directly measuring the distance but estimating it based on from other observations.
- Udik 7y agoWhere I supposed that "observed as <distance>" just means how much red-shifted its light is- we don't really have any other way to measure such distances. This in turn only measures how much the space has expanded between us and the original starting point, much closer than 13 billion light years away. So we can say that we're seeing a star that is "now" 46 billion ly from us, but must have been only a few billion ly away when it emitted the light we're receiving. Correct?
- kijin 7y agoYou're right. The star could not have been more than a few billion light years away when it emitted the photons that we're seeing. Otherwise, not only would the photons have not reached us yet, they will probably never reach us because the universe is expanding faster than the speed of light.
- pkofod 7y agoI feel so stupid when talking and hearing about physics... but we are not in any meaningful way "at the center" of the universe are we? Or is every point in some sense at the center (a point of reference thing)? I'm asking because why would it be 46.5 "each way"?
- spc476 7y agoImagine we exist in a 2D universe, but one that happens to be the surface of a sphere. Any point you pick on that surface is "at the center of the universe."
- laurencei 7y agoCan you ELI5 - how can we observe something 93 billion light years away, if the light has only been traveling for 13.8B years? Shouldnt the "observable" distance be the the age of the universe?
- devnulloverflow 7y agoYour intuition that there is an limited observable distance because is correct. But because of the expansion, that limit is bigger than "speed_of_light * age of universe" . I don't know enough General Relativity to give a solid explanation. But here is a rough over-simplification: Imagine you've spent the last 5 seconds blowing up a balloon, but there is an ant walking on that balloon, starting from a marked spot. In the 1st second, the ant moved 10mm. But in the next four seconds you blew up the balloon, so that 10mm of rubber is now 70mm long. The total distance from the ant's starting mark to her end-point can now be well over than 70mm, even though she only walks at less than 10mm/second. As the ant, so the photon.
- laurencei 7y agoYep - I kind of understand that. Thanks.
- sytelus 7y agoI'm bit confused. Regardless of expansion, these objects are right now > 13.8B ly away. So the light from them still needs that much time to get here. If light from them has arrived sooner, we would see less redshift and perceive them as a closer. No?
- rokalakt1337 7y agoSo does this mean speed faster than light is possible?
- zaarn 7y agoTwo objects can move away from eachother faster than the speed of light as seen by a third observer. The space between objects can also expand faster than light, the object itself can still not move faster than light. If the space between two objects is expanding faster than light then for all intents and purposes, the other objects no longer exists to another. There is no way to contact or observe that object other than the light that was send your way before space went FTL.
- eru 7y agoTo give another example: If you have a laser pointer and flick your wrist fast enough, the spot on the ground that your cat chases can move faster than light without violating any laws of physics. That's perhaps easier to see, if you think of a giant laserpointer aimed at the moon. Similarly, a shadow on the wall can move faster than the speed of light.
- Aenyn 7y agoWouldn't there be a delay between the time you flicked your wrist and the time the spot actually aligns, due to the limited speed of light?
- doliveira 7y agoYeah, and observing this is a good way to see that information isn't actually being transferred faster than light.
- eru 7y agoYep, definitely. An outside observer that just sees the spot on the moon (but has no clue that it's produced by you flicking your wrists), just sees a spot that moves insanely fast. No information, energy nor matter travels faster than light here, of course.
- eecc 7y agoAah of course... somehow we should believe that at some stage something accelerated to an impossible - according to all current observation - speed and then decelerated, somehow dissipating this energy somewhere. Just to fit a bunch of observations that wouldn't otherwise make sense for the current model. I remember the story of a chap from Pisa having a hard time trying to budge a bunch of clerics to consider his observations proof that their model was broken. ;)
- marzell 7y agoSeriously... what's the difference between 'universe expansion' and 'travel'? A particle can't travel faster than c but it can effectively if the universe expands in addition to its travel speed? Are there any established sci-fi concepts that replace the concepts of wormholes with 'universe compression'?
- namirez 7y agoYes, it's called Alcubierre Drive, where spacetime is compressed in front and expanded behind a ship to drive it through the spacetime like a gravitational wave. https://en.wikipedia.org/wiki/Alcubierre_drive https://en.wikipedia.org/wiki/Alcubierre_drive
- Filligree 7y agoOr the Krasnikov tube, where time is tilted such that travel through it (in one direction) takes you back in time (from a stationary perspective). That's very similar to a wormhole, but without the topological flaw.
- haecceity 7y agoThe first one means the space time metric changes
- semiotagonal 7y agoIs it possible that the universe stays the same size and everything within it shrinks?
- BurningFrog 7y agoI think those are just two equivalent ways of thinking of the same thing. The standard way is probably much easier to reason about.
- tux1968 7y agoDon't think there is a way to tell the difference without stepping outside the universe to look back on the system relative to another frame. But AFAIU, there is no edge to the universe with an unknown something beyond the barrier. Space is not an expanding balloon inside a bigger balloon. Ie, there is no space beyond space. Not that i'm truly able to wrap my head around it, but at the moment of the big bang, time and space themselves exploded into existence.
- leggomylibro 7y agoSo, is it possible for an event in the Milky Way to ever affect GN-z11 (or vice-versa)? Or are the galaxies permanently 'read-only' to each other?
- lacker 7y agoThere is no such thing as “read-only” in physics. If we can observe the other galaxy, that means it is affecting the particles in this galaxy. Even if it’s just a single molecule in a telescope responding to a photon that hit it from the other universe.
- leggomylibro 7y agoI guess that makes sense, thanks. I was wondering if it might have been something like the theories of what might happen much later in the universe's life, where things eventually get so far apart while still accelerating that light can't travel between them. But it couldn't be something like that if we can see the other galaxy, right?
- thisBrian 7y agoThat still holds true, eventually nearby clusters will go beyond our "observable" view.
- gpderetta 7y agoAt some point in the far distant future the night sky will be black, with everything being beyond our visible edge of the universe.
- Filligree 7y agoWe can see light that was emitted from it billions of years ago, before we split apart. Similarly, they can see light that ours emitted billions of years ago. They can never be affected by anything we do now, or vice versa. This doesn't make it "read-only", though -- we can't read it either. All we're seeing is their distant past, back when we were mutually able to reach each other.
- hinkley 7y agoThis still doesn’t add up. For one, now it’s saying that when the universe was .4 billion years old we were already 2.6 billion light years apart, so now you have to explain that first.