[HN Gopher] Shouldn't distant objects appear magnified?
___________________________________________________________________
Shouldn't distant objects appear magnified?
Author : frabert
Score : 429 points
Date : 2023-08-20 13:29 UTC (9 hours ago)
(HTM) web link (astronomy.stackexchange.com)
(TXT) w3m dump (astronomy.stackexchange.com)
| psychphysic wrote:
| Love this, there are a few topics you hear about in class and you
| don't realise how mind boggling they are until someone less says
| hold up...
|
| The interpretation of the Poynting vector is another.
| NHQ wrote:
| "Give us one free miracle and we can explain anything!" -
| Terrance McKenna on modern science.
| ww520 wrote:
| And based on the size of the magnification of the galaxies
| throughout time, we can tell whether the universe is expanding at
| a constant rate or accelerated or decelerated at certain point.
| cvoss wrote:
| Take this a further step. Assuming we had telescopes big enough
| and sensors sensitive enough, what does the structure of the
| deepest parts of space look like? Are there pre-galaxy-formation
| structures which are smaller than galaxies and yet take up huge
| swaths of sky? Are there structures from some point in the past
| that take up so much space on the sky that not very many of them
| can "fit", and, if so, do the calculations work out so that an
| equivalent explanation for having not very many of them is that
| the [region of the] universe [which is observable to us] was just
| that much smaller back then?
| MaxikCZ wrote:
| The furthest we can see is the physical limit of universe: we
| can literaly see thefirst photons after universe became
| transparent. That is the CMB (cosmic microwave background, and
| you can easily google a real picture). The problem is, while
| these are the oldest photons we will ever be able to see, they
| still are from when universe was cca 400 000 years old, and by
| that time it was 100 million lightyears wide. That picture
| tells us that the universe was extremely homogenous (altho not
| perfectly), and basically no such structures you talk about.
|
| If we would like to see even further, we must give up on
| photons completely, and probably probe the ultra deep space
| gravitation waves. Those should give us picture even of
| completely opaque universe, as it was before then. So far we
| can only "see/hear" the brightest/loudest events in the
| universe with our gravitational waves observatories, but the
| fact we can even do that is astounding nontheless: we built a
| new sense for humanity, that no other known creature in the
| universe posses. LISA project should hear more.
| skykooler wrote:
| Neutrinos should also allow seeing back before the CMB,
| though they're nearly as hard to detect as gravitational
| waves.
| waynecochran wrote:
| Fascinating. A related question: When we look at Andromeda, which
| has a diameter of 220,000 light years, we are looking at it
| slightly edge on. Shouldn't the stars on the back edge be in a
| relatively different place in the sky than the stars on the front
| edge since the galaxy has moved relative to us over that 220K
| light years?
| Filligree wrote:
| Yes. And, of course, they are.
| waynecochran wrote:
| They appear as if I am looking at the front and back edge at
| the same point in time -- i.e. not 220K years apart.
| hughes wrote:
| How would you expect it to look that is different from its
| current appearance?
| tekla wrote:
| /gif head exploding meme
| waynecochran wrote:
| I would expect something kind of stretched out and warped
| like taffy. i.e. the front edge of the galaxy would be
| stretch out ahead of the back edge of the galaxy since
| the back edge is running behind time-wise.
| ahazred8ta wrote:
| > stretched out ahead
|
| You have apparently not figured out (1) by how much? and
| (2) in which direction? - Andromeda rotates so slowly
| that after 220K years the far side has made only 1/1000th
| of a rotation. Please draw on a picture of Andromeda how
| far the far side moves after 1/1000th of a rotation.
| That's how small the image warping is.
| waynecochran wrote:
| Thank you. The "how much" is too small to stretch it out
| visually. Need a much larger spiral galaxy to see the
| effect I am thinking of.
| dmbche wrote:
| Makes me think of this :
| https://en.m.wikipedia.org/wiki/Terrell_rotation
|
| How when going at relativistic speeds, you start to appear to
| rotate to obervers even if you are going straight - you can even
| see behind the object!
| vikingerik wrote:
| Took me a minute to wrap my head around it, that explanation
| isn't worded that clearly, but then I got it.
|
| That happens because time is a factor in how light from
| different parts of the object will reach the observer. Light
| from its far side takes longer and in that time the object
| continues to move. You can see behind the object, because its
| rear end moves out of the way of the light coming from itself
| during the travel time of that light.
| someplaceguy wrote:
| Man, the universe is weird... Whoever created it was not a fan
| of the KISS principle.
| fallingknife wrote:
| I have to disagree. The fundamental laws are quite simple.
| All the complexity arises from their interaction like in
| Conway's game of life.
| nickpeterson wrote:
| I think our senses are just imprecise and it undermines all
| our thoughts and perceptions of the universe when things
| approach limits.
| dredmorbius wrote:
| Our senses are evolved to maximise our fitness function
| within our immediate reality. There's a view that our
| senses don't reflect _truth_ so much as _evolutionary
| fitness_ , which involves both compromises and biases.[1]
|
| Our evolutionary environment for the most part has excluded
| relativistic effects.
|
| Though that raises the interesting question of what sense
| perceptions of an organism evolving under such
| circumstances might be.
|
| ________________________________
|
| Notes:
|
| 1. Donald Hoffman is the principle proponent of this that
| I'm aware of: <https://www.quantamagazine.org/the-
| evolutionary-argument-aga...>. I'm not _entirely_ sold on
| the hard-line version of his argument; it seems to me that
| there 's a _general_ tendency for adherence to truth to be
| more parsimonious than outright fabulation, in which the
| _nonessential_ inaccuracies of the sensing system incur
| additional costs.
| he0001 wrote:
| Frankly, it may very well be KISS because the other options
| were so much more complex. Or they said that if we put speed
| of light to constant to make it simple, there were so many
| unforeseen edge cases because of it. The devil is in the
| details, perhaps?
| potamic wrote:
| You haven't seen this other post today
|
| https://news.ycombinator.com/item?id=37197977
| lamontcg wrote:
| That should be "all of physics in 6 lines, two flawed
| overly simplistic arguments and one crackpot theory (and 18
| particles and 27 constants buried in the last two items)".
|
| https://news.ycombinator.com/item?id=30733666
| lamontcg wrote:
| Nah, its real simple. SR just comes about because you want to
| keep chemistry working the same on a rocket doing 99% of the
| speed of light as it is at rest.
|
| Working out all the implications becomes very complex.
|
| But then you probably wouldn't have life to observe it if the
| simple rules didn't have complex emergent behaviors.
| ilyt wrote:
| Just look at near any 30+ years long programming project and
| then extrapolate the growth of complexity and weirdness into
| billions of years
| wheelerof4te wrote:
| Spaghetti code? Try "The Big Bang code".
| hn_throwaway_99 wrote:
| I actually think the opposite is true. The way I've heard it
| phrased and explained that makes the most sense to me is
| "everything moves through spacetime at the same rate" - it's
| basically the clock speed of the universe. It's just that if
| you move faster in a space dimension that your relative
| movement in the time dimension slows down.
|
| It only seems weird to us because our senses and minds
| evolved in an environment where things we can perceive never
| differ by relativistic speeds.
| someplaceguy wrote:
| While I do like that intuitive explanation, it's lacking in
| describing all other aspects of the universe.
|
| Like, how the energy required for an object with mass to
| approximate the speed of light in spacial dimensions goes
| to infinity, even though it's already traveling at that
| speed through spacetime.
|
| Or quantum mechanics.
| hn_throwaway_99 wrote:
| Sure, one simple sentence is not going to explain the
| universe. But, at least from the simple relativity side
| of things, essentially _everything_ falls out of (that
| is, it 's a consequence of) that simple sentence. I.e.
| starting from that you can derive other consequences.
| E.g. "how the energy required for an object with mass to
| approximate the speed of light in spacial dimensions goes
| to infinity" is actually a direct consequence of that
| statement: every amount of energy you push into an object
| with mass causes it to accelerate, but due to the
| essential "clock speed of the universe", that
| acceleration is less and less as you approach the speed
| of light, and thus it takes an infinite amount of energy
| to reach the speed of light. Another way to think of it
| is that if it took anything less than an infinite amount
| of energy to reach the speed of light, then the speed of
| light couldn't be the universal speed limit, because you
| could add more energy that would accelerate it further.
|
| On the other hand, my understanding is that quantum
| mechanics is another beast entirely, and one of the
| biggest problems in physics, and to developing a "theory
| of everything", is to unify quantum mechanics with
| general relativity.
| DougMerritt wrote:
| Although nothing will explain everything, still it's fine
| with the first point: increasing the rotation vector of
| momentum in spacetime increases mass. The rest follows,
| since you know that the more mass, the more energy
| required to accelerate still more.
|
| But if you are interested, a significant amount of the
| basics of quantum mechanics follow directly from Fourier
| transforms -- which unfortunately are harder to self-
| study than spacetime rotations.
| rakoo wrote:
| Or, they just set the speed of light as a #define and left
| the rest as undefined behaviour
| hn_throwaway_99 wrote:
| Perhaps nit picky, and I know you were joking, but I think
| this is the wrong way to think about it. It's not that the
| other behavior is undefined, it's you essentially have all
| of these functions that use "C" in their definitions, and
| then you have "#define C ..." in a header file somewhere.
| combat-banana wrote:
| It's very simple depending upon your context. (God's object)
| russdill wrote:
| A limit to the speed of causality makes physics _so_ much
| simpler. Without it you 'd need to factor in the interaction
| of every particle with every other particle in the universe.
| someplaceguy wrote:
| Don't you need to do that anyway, because of gravity?
|
| Wouldn't the causality speed limit just cause those gravity
| interactions to arrive with a time delay rather than being
| instantaneous?
|
| Which means that to simulate the universe you essentially
| have to keep a history of how gravity is propagating, which
| requires keeping more information than if interactions were
| instantaneous?
|
| In a sense perhaps this applies to light too, because since
| it has a finite velocity now you have to keep track of how
| all the photons individually propagate through spacetime,
| whereas if light traveled instantly this would not be
| necessary?
|
| EDIT: The advantage I see in a speed limit is that you
| should be able to compute what happens in a point of
| spacetime based only on the information that is around that
| point (which still might have come from any or all other
| particles in the universe, mind you). For me, this
| emphasizes how important locality must be and it basically
| converts the popular "spooky action at a distance" claims
| into nonsense to me.
|
| I guess that's why I'm a fan of the Many Worlds
| Interpretation.
| BiteCode_dev wrote:
| Gravity is not instantaneous.
| knome wrote:
| https://spaceplace.nasa.gov/gravitational-waves/en/
|
| Gravity waves also travel at the speed of light.
| someplaceguy wrote:
| Isn't that what I was saying?
|
| Since they have a speed limit you have to keep track of
| all gravity waves associated with all particles of the
| universe throughout all time and space.
|
| So all particles still interact with all other particles,
| all the time, it's just that they do it with a time
| delay.
|
| If there wasn't a speed limit it would be much simpler
| because all gravity interactions would be instantaneous
| and you wouldn't have to keep track of gravity waves.
| depressedpanda wrote:
| If light acted instantaneously you would have to
| calculate the effect of it's rays everywhere all at once,
| which I think is quite expensive given how _vast_ space
| is.
|
| However, since the speed of light is miniscule compared
| to the size of the universe you can ignore all but the
| most local interactions, and just schedule a computation
| sometime in the future when you know that the light
| vector will interact with something.
|
| While instant calculations would perhaps make for a
| simpler system conceptually, the speed limit and locality
| principle ensures that less processing power is needed
| (at the cost of a lot of memory).
| tshaddox wrote:
| What's unique about gravity with what you're talking
| about? The Coloumb force also applies between every pair
| of electrically charged particles, right? And with the
| same inverse-square function of distance?
| someplaceguy wrote:
| > What's unique about gravity with what you're talking
| about?
|
| Nothing, it was just the most obvious example (to me).
| wheelerof4te wrote:
| As someone already mentioned, you would have to account
| for all the interactions with light -> everywhere at
| once.
|
| With a effective speed limit to space-time, you can
| "localize" the computation to the spaces where light has
| reached. And who knows, maybe light can't travel forever,
| it might just disappear after crossing some distance we
| still haven't measured (how we'd do that, who knows).
|
| Giving yet another evidence to the "grand simulation"
| theory. "The universe" is just a group of simulated
| worlds connected by interacting photon particles (light).
| someplaceguy wrote:
| Right, that's what I meant when I said that the advantage
| of a speed limit is locality. It allows you to compute
| the next state of a point in spacetime based only on the
| points around it.
|
| But my point was that this also makes the universe more
| complex than an alternative fictional universe where
| information can be accessed instantaneously across any
| distance (which still allows for distributed computation,
| if synchronization or lazy computation is possible).
| wheelerof4te wrote:
| Possible alternative, but what would be a factor of
| locality in such an universe? And how would the universe
| store the infinite "light matter" in it's "memory", since
| light particle beam being instant means that it has no
| limits to where it can reach, and will grow depending on
| distance traveled (which is infinite)?
|
| Some processes that are outside of scope we can sense
| seems like a too cheap explanation.
| cmpalmer52 wrote:
| A universe is a computer that simulates a universe.
| wheelerof4te wrote:
| We actually don't know and can't really know what
| simulates the universe.
|
| But we can deduce from various cues that it is being
| "simulated".
|
| The Double slit experiment is one, experience of deja-vu
| another, dreams that partly manifest in reality after
| some time, the apparent speed limit of light, out of body
| experiences, the fact we are the only local top
| intelligent lifeform in this part of galaxy, etc...
|
| All signs of processes and memory "bugging out". Except
| the last one, that one seems to be by design.
| LadyCailin wrote:
| Tangential question: is the speed of causality
| coincidentally the same as the speed of light? Or are
| they the same because of some underlying principal that
| inherently links them?
| squeaky-clean wrote:
| Not an expert, but can't resist chiming in anyways... One
| thing to think about it what exactly is causality?
| There'll be tons of different definitions, but they'll
| all have one thing in common, events that cause "later"
| events, and/or events that depend on "earlier" events.
|
| And in a physics sense what is an event? An interaction
| between two things, right? And since there doesn't exist
| any force that can interact instantaneously across
| distance, the speed limit of causality is equal to the
| speed of our fastest forces.
|
| If we discovered some scifi-esque Tachyon particle that
| traveled at 2C, we could no longer say the speed of light
| is the speed of causality.
| mr_mitm wrote:
| I'm an expert, and an event is just a point in spacetime.
| someplaceguy wrote:
| I'm not an expert either, but I like to think that the
| speed of causality is the speed at which a piece of
| information (e.g. a particle, a gravity wave, etc) is
| traveling through space.
|
| So the speed of light / gravity is essentially the
| maximum speed of causality, because nothing can travel
| faster than that.
|
| EDIT: Or you can think in terms of how information
| propagates through _spacetime_. In this point of view,
| the speed of causality is always the speed of light, for
| everything, including particles with mass.
| squeaky-clean wrote:
| Yeah that's what I was trying to work towards. Basically
| that causality is an abstraction, or at least a "higher
| level" idea. And if we look at the components of it, we
| can see that interaction between two things is a central
| part of it. And an interaction between two things in our
| universe has a maximum bound of the speed of light (and
| gravity and so on). The speed of causality is just the
| speed of the fastest thing.
| satvikpendem wrote:
| Correct, the speed of light is actually the speed of
| causality, we just so named it after light because that
| was what we first discovered as going at _c_ , but many
| other things in the universe also due because it's the
| same underlying principle. That is why gravitational
| waves also travel at _c_ , ie if you removed the sun
| instantaneously from the solar system, the Earth will
| continue to orbit for 8 minutes, as that is how long
| light (and the gravitational force) takes to get from the
| sun to the Earth.
| someplaceguy wrote:
| I'm not a physicist, but AFAIU the speed of
| travel/causality for light is only the maximum speed of
| causality because photons have a mass of literally zero.
|
| If photons had non-zero mass they could only travel
| slower than the maximum speed of causality (which would
| probably be called speed of gravity rather than speed of
| light, in this alternative universe).
| d1sxeyes wrote:
| They are the same, because there's no such thing as the
| "speed of light".
|
| Theoretically as I understand it, everything moves at
| exactly the same speed through space-time, whether it is
| light, the Earth, etc.
|
| At non-relativistic speeds, this means moving along the
| time axis at approximately one second per second, with
| the rest of the movement in space. At relativistic
| speeds, higher proportions of the "speed" of an object
| are along the time axis.
|
| As the energy requirements for moving massive objects
| through space at relativistic speeds are huge, we can
| only really observe this phenomenon with light, which has
| no mass, and therefore does not need huge amounts of
| energy to move through space.
|
| As a result, we call 186k miles per second the "speed of
| light" when actually it is just the maximum speed
| anything can travel through space, and due to light being
| massless, it happens to be the speed that light travels
| through space too.
| brabel wrote:
| That's amazing. I've watched lots of videos about length
| contraction and I don't think any of them ever mentioned this
| (the shape of an object moving a near light speed won't change
| to an observer, it will just appear as if it had rotated
| instead of being "squeezed" as every video about this seems to
| imply)!
| rand0mx1 wrote:
| This video might change your perceptive.
|
| https://youtu.be/watch?v=uTyAI1LbdgA
| MayeulC wrote:
| You rather showed the opposite. While interesting, this
| video only explains length contraction, not the Terrell-
| Penrose effect. In this video, the passing spaceship would
| appear to be rotated to the observer, not just contracted,
| as, to quote Penrose via Wikipedia, _the light from the
| trailing part reaches the observer from behind the
| [spaceship], which it can do since the [spaceship] is
| continuously moving out of its way "_
| ricksunny wrote:
| This nascent series on YouTube , Hypercubist Math, sets
| out to make four dimensions intuitive to our three-
| dimensions-accustomed brains. Baseline is just basic
| calculus, which the inaugural video provides in context:
|
| https://youtu.be/XfWgfZ5V2qI
| h1fra wrote:
| Reminds me of this video
| https://www.youtube.com/watch?v=ge_j31Yx_yk explaining the
| Terrel rotation (and other effects) in a video game engine.
| yokem55 wrote:
| This is kind of mind blowing to me. The linked xkcd is a
| fantastic (if exaggerated?) illustration of this effect.
|
| Objects in mirror may be further then they appear.
| [deleted]
| Etrnl_President wrote:
| https://xkcd.com/2622
|
| Turn up brightness, and zoom in...
| SquareWheel wrote:
| Larger version for others who are visually challenged.
|
| https://imgs.xkcd.com/comics/angular_diameter_turnaround_2x..
| ..
| kortex wrote:
| I love that the battery depletes slowly over time. Though
| it's a bit ominous that the most recent one shows battery
| in the red...
| xnx wrote:
| This would be a fantastic little toy/demo in VR.
| soligern wrote:
| What am I looking for?
| baq wrote:
| spoiler alert:
|
| The oldest phone doesn't fit the comic strip...
| usrusr wrote:
| Clearly because Munroe hasn't adjusted for screen size
| inflation. If we extrapolate based on whatever Samsung or
| Apple are selling these days and the 8210, will we even
| see meaningful redshift before the Planck constant chimes
| in?
| miquong wrote:
| The dimmest phones are larger than any others
| accrual wrote:
| The included explanation is mind boggling to me:
|
| > Things that are far away look smaller, but things that
| are REALLY far away look bigger, because when their light
| was emitted, the universe was small and they were close
| to us.
| dav_Oz wrote:
| This educational paper [0] titled "Expanding Confusion" (2003) is
| a classic on the general topic and well worth the read.
|
| Holding the two concepts of an accelerated (!) (in terms of
| objects [1]) expanding universe and the fixed finite speed of
| light simultaneously in one's Euclidean head can be dizzying, so
| be prepare to draw and enjoy the hard earned manual labor of
| counterintuitive conclusions.
|
| [0]https://arxiv.org/pdf/astro-ph/0310808.pdf
|
| [1]https://bigthink.com/starts-with-a-bang/universe-
| expansion-n...
| misio wrote:
| You write like an LLM designed to provide references, enjoyable
| as that may be.
| baq wrote:
| [flagged]
| xen0 wrote:
| Is it reasonable to view the Cosmic Microwave Background
| Radiation as being the limit of this? The remains of the big
| bang, maximally scaled up and red shifted as far as things can be
| today?
| __MatrixMan__ wrote:
| I think there's a coherent explanation of the cmb be had there,
| but it's not the conventional explanation.
|
| Under this alternative, the universe cooled to light
| transparency some time before the moment depicted by the cmb,
| and anything "further away" than that hugely magnified scene
| just happened outside of our light cone. That is to say, it's
| "elsewhere" (a technical term
| (https://web.phys.ksu.edu/fascination/Interlude1.pdf)).
|
| Seems to me that in this alternative, cosmic expansion could be
| explained as gravitational attraction between elsewhere-matter
| and matter in our light cone.
|
| Imagine there's some argument to be made for why this is not
| the case, but I don't know it. It would require a bit of
| explaining re: why that point in history and not some other?
|
| - Is it that the maximal distance is constant and that the cmb
| is subtly changing in ways we havent noticed (as the point of
| most-distant-past moves forward in time)
|
| - Or maybe something caused the speed of light to change at
| that time, pruning the rest of the universe from our view.
| drorco wrote:
| So essentially one giant blob of cosmic background radiation
| was at the time its light was emitted, the size of an atom or
| so?
| ben_w wrote:
| Kinda but different scale, the CMB era universe was about
| 1100 times smaller than that now, so still huge.
|
| There may be a neutrino background behind the CMB, where the
| universe was even smaller, and the gravitational wave
| background behind that with even more of a size difference.
| bloopernova wrote:
| Would the universe in those other 2 older events have been
| 2 orders of magnitude smaller still? Have there been any
| estimates made for the sizes in each "event"?
|
| Are there even more events further back, or is the next one
| after gravity the big bang?
|
| What a fascinating subject, thank you for expanding my own
| little universe!
| bozhark wrote:
| Plays right into the white hole theory, interesting
| bloopernova wrote:
| As in a white hole is the big bang? That has a kind of
| poetic symmetry to it, with black holes (big crunches?)
| being the end, and white holes being the beginning of our
| particular universe.
|
| But our universe has black holes in it. Forgive the
| layman thinking, but does that mean we're just one of an
| infinite series of "nested" universes?
| pelorat wrote:
| The energy in our universe is not unlimited, so perhaps
| each black hole spawns a new universe, and each has less
| and less energy in it. Think about, WHY is there a
| certain amount of energy in the universe? Why not more or
| less. Maybe it's just universes all the way down.
| devoutsalsa wrote:
| The cosmic microwave background radiation didn't appear until
| the universe was about 380,000 years old.
|
| https://en.m.wikipedia.org/wiki/Cosmic_microwave_background
| oneshtein wrote:
| So CMB is just 14B years old? Then why we see objects older
| than CMB? Moreover, why these older than CMB objects
| appearing in front of CMB?
| jvanderbot wrote:
| We dont see galaxies older than CMB.
| oneshtein wrote:
| Yep. This is the problem. Why CMB is emitted at the edge
| of our Universe only? Where are atoms, which produced the
| CMB?
| wolfendin wrote:
| Because the "edge" of our universe where we see the CMB
| is not a point in space we are viewing in real time that
| is currently emitting the CMB.
|
| That edge is a sphere in space that was far enough away
| when the CMB was emitted in the past that we only see the
| light from it now.
| [deleted]
| bigbillheck wrote:
| > Why CMB is emitted at the edge of our Universe only?
|
| I thought CMB was emitted everywhere.
| oneshtein wrote:
| CMB is produced by atoms, right? We see darker/lighter
| regions in CMB, so we should see a transition somewhere.
| 300M years is very short period of time, unless
| everything cooled very very uniformly, which is not the
| case. Sometimes, somewhere there must be a galaxy past
| CMB.
| bigbillheck wrote:
| > a transition somewhere
|
| A transition from what to what?
|
| > which is not the case.
|
| Why not?
|
| > Sometimes, somewhere there must be a galaxy past CMB.
|
| If there is we'd have to wait for the light from it to
| get to us, by which time the CMB will have receded
| further and it would then be in front of the CMB.
| oneshtein wrote:
| > A transition from what to what?
|
| A transition from plasma to the cold mater in the form of
| galaxies we see.
|
| > Why not?
|
| As you see, there are big clusters everywhere. It means
| that some regions were cooler from the start, to form
| these cluster in so short period of time. It means that
| regions around them were hotter, thus they should emit
| light longer.
|
| > If there is we'd have to wait for the light from it to
| get to us, by which time the CMB will have receded
| further and it would then be in front of the CMB.
|
| 300My is a short period of time. Why they cannot
| sometimes overlap?
| ben_w wrote:
| > 300M years is very short period of time, unless
| everything cooled very very uniformly, which is not the
| case
|
| ~300M years is the time between the Big Bang singularity
| and the CMB, but not really relevant. The entire universe
| was _everywhere as hot as the surface of a star_ at the
| time of the CMB, so any evidence of galaxies forming
| before that is surprising.
|
| The surprisingly high uniformity of the temperature of
| the CMB -- isotropic to roughly one part in 100,000 -- is
| one of the reasons the Big Bang model replaced one of the
| older competing hypotheses (continuous creation IIRC).
|
| So it is in fact the case that everything cooled very
| very uniformly and I'm not sure why you think otherwise?
|
| I'm also not clear what you're saying with
|
| > so we should see a transition somewhere
|
| Given the CMB is itself the transition that we see.
|
| > Sometimes, somewhere there must be a galaxy past CMB.
|
| I think here you're mixing up space and time.
|
| It's reasonable (please permit my use of conventional
| language rather than 4-vectors) to assume that a galaxy
| exists on the other side _in space_ of the CMB _as we see
| it now_ , but that happens at a point in _time_ after the
| recombination epoch began and space became transparent,
| and light from that event hasn 't reached us yet; when it
| does, the apparent distance of the CMB will be large
| enough for the galaxy to appear on this side.
|
| Are you familiar with light cones and the convention of
| one space axis and one time axis? It might help you
| visualise it if you draw what's going on.
| devoutsalsa wrote:
| There were no objects before the CMBR. The universe was
| so hot that atoms couldn't even form. Once it cooled to
| the point where hydrogen atoms came into existence, the
| CMBR became possible. I'm talking at the limits of my
| knowledge, so allow me to refer you to this video by
| Fermilab that's pretty good.
|
| _What is the Cosmic Microwave Background?_ --
| https://youtu.be/AYFDN2DSVgc
| TheCapeGreek wrote:
| I think OP's question related to the _observable_
| universe vs what is beyond. We see the CMB (and thus our
| limit of light) only to a point, but that doesn 't mean
| there's nothing beyond that - otherwise we'd be the
| literal center of the universe (I recall an old
| minutephysics video[0] on this).
|
| [0] https://www.youtube.com/watch?v=W4c-gX9MT1Q
| thayne wrote:
| Huh. That would make such objects even harder to detect, since
| the light is spread out over a larger area, so the amount of
| light hitting each pixel of the detector is less than if it
| wasn't magnified.
|
| On the other hand, it means you can see details you might not be
| able to otherwise.
| _dain_ wrote:
| man that's fucked up. i dont want to look at the sky anymore.
| sulam wrote:
| Is there an xkcd for _everything_?!?
| oneshtein wrote:
| > xkcd for _everything_
|
| https://xkcd.com/968/
| dentemple wrote:
| Better question: If there's no XKCD of it, does it really
| exist?
| tomjakubowski wrote:
| I've heard of "adjusting for inflation" but this is ridiculous!
| beltsazar wrote:
| Speaking of the expansion of the universe, in a very distant
| future when the expansion speed is so high that most of the
| galaxies won't be visible from earth, their astronomers will be
| thinking the whole universe contains only a few galaxies. But
| wait, what if the universe we observe today also misses some
| parts that can't be observed anymore?
|
| Neil deGrasse Tyson explained it more clearly:
| https://www.youtube.com/watch?t=436&v=TgA2y-Bgi3c
|
| That's probably why it's called the _observable_ universe.
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