[HN Gopher] Stars in distant galaxies are typically more massive
___________________________________________________________________
Stars in distant galaxies are typically more massive
Author : DeusExMachina
Score : 100 points
Date : 2022-05-28 14:22 UTC (8 hours ago)
(HTM) web link (nbi.ku.dk)
(TXT) w3m dump (nbi.ku.dk)
| antisthenes wrote:
| Could this just be a luminosity effect?
|
| Larger [More massive] stars are typically more luminous. Could be
| that there is a selection bias towards them. since they are the
| only ones that can be detected from that far away.
| naveen99 wrote:
| the earth has elements that were formed in previous generation of
| stars. I wonder if the sun is also not a first generation star.
| eloff wrote:
| It definitely is not a first generation star. It's only about 5
| billion years old, while the universe is almost 14 billion
| years old.
|
| Not only does earth have elements formed in older stars, so do
| all the planets in the solar system and our own sun.
| pohl wrote:
| The sun is estimated to have formed less than 5B years ago. The
| universe is roughly 13B and change years old, and the first
| stars started forming only 100M years after the beginning.
| There's absolutely no way it could be a first generation star.
| ncmncm wrote:
| The first-generation stars are imagined to have lasted only a
| few million years before going supernova and (because of
| their size) becoming black holes.
|
| We can never be certain, of course, because they are all long
| gone. Like, 13 billion years gone. The James Webb telescope
| is hoped to see back nearly that far back, but not likely
| near enough to catch any of them.
| sulam wrote:
| The sun is absolutely not a first generation star. It is
| approximately one third the current best estimated age of the
| universe (4.6B vs 13.8B years).
| Zigurd wrote:
| The entire solar system precipitated out of the same
| interstellar dust, which has to contain the remnants of
| previous generations of stars, including collided neutron
| stars, in order for there to be heavy elements beyond iron.
| AceyMan wrote:
| We get heavier elements from supernovas, ergo, I don't see
| how neutron star collisions are a requirement to explain our
| composition. Citation?
| shagie wrote:
| Not all heavier elements are from supernovae. This is known
| as nucleosynthesis (
| https://en.wikipedia.org/wiki/Nucleosynthesis ) and there
| are a number of different origins of elements. Exploding
| massive stars really only get you up to Rb (atomic number
| 37).
| Zigurd wrote:
| I guess my habit of listening to PBS SpaceTime is paying
| off.
| https://iopscience.iop.org/article/10.3847/2041-8213/ac26c6
| gameswithgo wrote:
| maxnoe wrote:
| It very surely isn't. It formed 4.5e9 years ago, while there
| are stars that formed only hundreds of millions years after the
| big bang in the milkyway.
| DelightOne wrote:
| Implications for the lifetime of suns?
| kabdib wrote:
| It's a power law. Increased mass more than proportionally
| decreases the lifetime of a star. (A star with 100 X the mass
| of our sun would last about a million years).
| ianai wrote:
| That sort of sounds like a "sorting" process or something
| like survivor bias. The conditions were more likely to
| produce pockets of material dense and large enough to produce
| the larger, shorter living stars the earlier back in the
| universe. i.e. as Time progresses forward the stars which
| remain are those with more burn time and thus less mass.
| Otherwise would require some forces to exist which pull mass
| back together to counter the overall expansion of the
| universe.
| zionic wrote:
| Does this have implications for dark matter? The whole angle
| there is explaining "missing mass" right?
| hoyd wrote:
| My first thought too
| sgt101 wrote:
| I don't think so because many of the observations of the
| galaxys that make folks think that dark matter must be present
| (because the visible matter is not sufficient to make the
| galaxy stick together) are in the local group.
| pvg wrote:
| The research is about the distribution of stars in a galaxy,
| not mass that is missing or extra. Distant galaxies apparently
| have more massive stars than whatever widely used model says.
| From the article:
|
| _Stars in distant galaxies are typically more massive than
| those in our "local neighborhood"_
| phkahler wrote:
| Funny thing about the missing mass. Papers will say "this could
| be explained by a dark matter Halo with this distibution". They
| assume it gravitationally affects regular matter the same way
| regular matter does. What is usually missing is 1) how dark
| matter interacts with dark matter 2) why it should have this
| particular distribution - dynamic model. Without those things,
| the explanation is IMHO worse than MOND because it doesnt make
| sense that some matter would end up with a completely different
| distribution. Oh and we cant actually detect it directly
| either, but trust us it must be there.
| gliptic wrote:
| This is not actually missing from the models. See for
| instance https://www.nature.com/articles/s41550-021-01598-4
| ncmncm wrote:
| There is no reason for matter with very different interaction
| properties from the familiar stuff to have the same
| distribution.
|
| In particular, familiar stuff has ways to dispose of kinetic
| energy, allowing it to clump into our stars and planets, that
| might be unavailable to putative dark matter, making any dark
| matter more diffuse.
|
| Generally, you can start with the assumption that people
| working on dark matter hypotheses are not idiots. They might
| still be wrong, but if they are, they will be wrong in
| interesting and subtle ways, not obvious ones.
| phkahler wrote:
| >> There is no reason for matter with very different
| interaction properties from the familiar stuff to have the
| same distribution.
|
| Sure there is. It has similar interaction with regular
| matter. Any other properties need to be defined and shown
| to produce this claimed distribution as a result of a
| dynamic process. Anything less and we can just say dark
| matter is fairy dust.
| ncmncm wrote:
| "different interaction" != "similar interaction".
|
| Apparent effort to understand what you criticize may make
| your criticism seem worth more.
| phkahler wrote:
| >> Generally, you can start with the assumption that people
| working on dark matter hypotheses are not idiots.
|
| Actually no I cant. When someone looks at galaxy rotation
| curves and is surprised they dont follow keplers laws, it
| activates the bozo bit in my mind.
| ncmncm wrote:
| Are there others?
| Ralfp wrote:
| It doesn't. Galaxies studied were very far from Milky Way and
| hence much older. This discovery shows that era of massive
| stars ended later in evolution of universe than we've assumed,
| not that we got mass of stars wrong.
|
| We still see younger galaxies with less massive stars not
| rotating as expected.
| [deleted]
| hexomancer wrote:
| > Galaxies studied were very far from Milky Way and hence
| much older
|
| You mean younger, right?
| forgotusername6 wrote:
| Like looking at an old photograph of a child. Both older
| and younger at the same time.
| rsstack wrote:
| Weird English quirk when you have relativistic distances:
| They are older in a sense that they aren't recent. They
| aren't older in a sense that they've existed for a longer
| time. (At least in the radiation we're seeing.)
| hoyd wrote:
| http://archive.today/poJee
| [deleted]
| codingbeer wrote:
| Albert, the graduate student behind this work, was also in the
| news just a week ago with another cool discovery, see
| https://nbi.ku.dk/english/news/news22/danish-astrophysics-st...
|
| Edit: and this from last year
| https://nbi.ku.dk/english/news/news21/danish-student-solves-...
| ffhhj wrote:
| >> This "total" temperature can also be described as a sum of
| temperatures on coarse (large) scales, temperatures on finer
| scales, even finer scales, etc. On large scales we see the
| well-known climate changes. Albert Sneppen's study documents
| that the temperature differences become stronger on small
| scales (credit: Albert Sneppen).
|
| >> In other words, climate change makes the differences in
| temperature grow locally -- and with large temperature
| differences come even more extreme weather patterns.
|
| Makes a lot of sense.
| joebob42 wrote:
| He "discovered" this? This has been my understanding of how
| this all worked for years, unless there's some subtlety I'm
| missing here.
| akeck wrote:
| I don't think he discovered the conclusion per se. I think
| he discovered an analytical path to an already
| known/suspected conclusion via a novel application of
| cosmology math to planetary climate.
| labster wrote:
| It's been common knowledge in atmospheric science for the
| past 20 years (based on personal knowledge, it's probably
| decades longer). Not only does it shake out of climate
| models, but it's intuitive that more heat to redistribute
| will increase the amplitude of all the wave-like
| properties of the atmosphere.
| samstave wrote:
| Why does "heavier" mean something when talking about a mass
| suspended in the vacuum of space?
|
| Does the mass and resultant gravitational force attenuate the
| same ratio for small vs big stars?
|
| Also, how do super dense neutron stars work - in the sense that
| atoms (and neutrons) are "mostly empty space" -- are the
| particles in the atoms compressed closer together? Or does an
| atom of one substance at the center of a star have the same
| mass/volume as an atom of the same, either floating by itself or
| say, on earths surface?
| colechristensen wrote:
| "Weight" words and "mass" words get used interchangeably
| because it usually becomes obvious which one is meant based on
| context.
|
| Here, obviously we're talking about stellar mass.
|
| You can't really talk about the "volume" of an atom because the
| distance between one atom and the next closest atom really
| depends on the bulk material and isn't just atoms sorted into
| their one fixed size but is a balance of various forces.
|
| A neutron star isn't made of atoms, but is, in a sense, one
| enormous atom or just a nucleus (but it's more complex than
| that). Mostly neutrons with some electrons and protons mixed in
| not separated into atoms which repel each other but in a super
| dense fluid of particles packed about as closely as particles
| in the nucleus of a normal atom.
|
| http://astro.vaporia.com/start/neutronmatter.html
| Aardwolf wrote:
| Assuming the universe is mainly uniform, why would distant
| galaxies have different starts than nearby ones? Is it related to
| time (the light from those farther away that reaches us being
| from the distant past)?
| SemanticStrengh wrote:
| The universe is not uniform/isotropic at large scales
| gizmo686 wrote:
| The universe is not isotropic in the time dimension. However,
| across space the prevailing thinking is that the universe is
| isotropic on a large scale in the spatial dimensions.
| SemanticStrengh wrote:
| It's not in space, see the theoretical limit being bypassed
| "List of the largest cosmic structure" https://en.wikipedia
| .org/wiki/List_of_largest_cosmic_structu...
| spookthesunset wrote:
| If it wasn't isotopic across space, that would be a huge
| deal.
| SemanticStrengh wrote:
| As you can see, it clearly isn't homogenous https://en.wi
| kipedia.org/wiki/List_of_largest_cosmic_structu...
| enriquepablo wrote:
| As far as I understand (I'm not a physicist), to be able
| to say that the universe is isotropic across space, you
| need a point of view that just doesn't exist. You cannot
| speak about an absolute synchronicity among events
| happening in locations scattered among an arbitrary
| subset of the set of all visible galaxies, and without
| that, you cannot abstract time out of the picture, which
| you'd need to do to speak about isotropicity across
| space.
|
| I don't think that, in this regard, you can say much more
| than "the universe is not isotropic across space-time".
| cygx wrote:
| _You cannot speak about an absolute synchronicity among
| events happening in locations scattered among an
| arbitrary subset of the set of all visible galaxies_
|
| The cosmic microwave background gives you a physical
| realization of just that (but of course only
| approximately so), at least as far as cosmologists are
| concerned. The rules of relativity of course still apply,
| making this particular synchronicity convention just one
| of many others...
| enriquepablo wrote:
| But the cosmic microwave background refers to one single
| event, that has echoes everywhere, right? If I understand
| correctly, you don't need to synchronize anything to have
| echoes everywhere.
| cygx wrote:
| _But the cosmic microwave background refers to one single
| event, that has echoes everywhere, right?_
|
| An event is a single point in spacetime, whereas photon
| decoupling happens everywhere, defining a spacelike
| hypersurface we use for synchronization (in the idealized
| scenario).
|
| Subsequently, the CMB allows us to single out a
| particular reference frame (the one where it looks
| isotropic) and provides a measure of expansion via its
| redshift/temperature which we can then translate to
| cosmological time (ie time since the big bang as measured
| by an observer following the Hubble flow) via our
| cosmological models.
| JumpCrisscross wrote:
| > _why would distant galaxies have different starts than nearby
| ones?_
|
| I know one reason: metallicity.
|
| The very early universe didn't have clumps of heavy elements to
| create nucleation points of sort for fusion. So big clouds of
| hydrogen had to very slowly draw together via
| "molecular...cooling in the gas phase," which meant more
| massive stars that burned furiously for a short while [1].
|
| [1]
| https://iopscience.iop.org/article/10.1088/0004-637X/745/1/5...
| disconcision wrote:
| distant means younger means different composition (less heavy
| elements), dunno if that's the deal here though
| mrits wrote:
| Unless we are the center of the universe I don't see how
| distant could mean younger
| Archelaos wrote:
| You are the oldest thing in the universe you can observe.
| Even the person next to you, as you observe her or him, is
| younger, because the speed of light is finite.
|
| In this respect, you are the centre of your universe. But
| objectively speaking, there is no centre.
| mrits wrote:
| So I'm older than my grandparents?
| thatwasunusual wrote:
| From your perspective, you're the oldest in the whole
| universe, AND you're the center of the universe.
| Congratulations! :)
| varajelle wrote:
| No.
|
| Not according to the classical definition of age which is
| the time since birth. I was born a few decade ago. My
| grandparents are decades older then me. The earth in
| millions of year older than me. And the galaxies billions
| of lightyears away are still billions of year older than
| me.
|
| Maybe the Milkyway is older than the other galaxies we
| observe, assuming they were all born at the same time.
| Taniwha wrote:
| oldest since the big bang, not oldest since you were
| created
| p1esk wrote:
| This doesn't make any sense
| brianpan wrote:
| It's similar to how every sound you hear is of an event
| in the near past. Every thunderclap is caused by a past
| and distant lightning event. As a child, we'd see
| lightning and then count seconds waiting to hear the
| thunder (sound travels slower and takes longer to arrive
| than the light- about 2 seconds per mile).
|
| If you're hearing thunder now, in a way, you're hearing
| an event in the past. The farther the thunder traveled,
| the farther into the past you are experiencing.
|
| Across the expanse of space, you are not just hearing,
| but seeing into the past. The farther the light traveled,
| the farther into the past you are experiencing now.
| p1esk wrote:
| Yeah, so I'm older than the lightning. Am I also older
| than the sun?
|
| By this logic, I'm the newest thing in the universe,
| because it takes the shortest time for me to observe
| myself.
| [deleted]
| [deleted]
| [deleted]
| [deleted]
| tromp wrote:
| When you see someone standing 3m away from you, the light
| took 10 nanoseconds to reach your eye, so you see them as
| they were a _very_ short time ago. Of course, they 're
| only younger when measuring their age not from their
| birth but from the big bang.
| jpollock wrote:
| I find it useful to think of photons as vector clocks:
|
| https://en.wikipedia.org/wiki/Vector_clock
|
| Take a photon starting from your chest and give it t1.
|
| * Assume that the speed of light is symmetrical. *
|
| When the photon hits the next person's eyes, it is t1 +
| distance/speed of light.
|
| Meaning, the photon is "from the past".
|
| Since all photons arriving are from the past, the photons
| travelling the shortest distance are the newest
| (representing the largest timestamp).
|
| So, the thing with the largest observable timestamp is
| yourself.
| p1esk wrote:
| We are not talking about the age of photons. We are
| talking about the age of the thing that emits/reflects
| photons.
|
| The confusion arose because the OP said "you are the
| oldest thing in the universe you can observe". They
| should have said "you are the most recent thing in the
| universe you can observe".
| ncmncm wrote:
| Strangely enough, everything that emitted a photon is at
| least as old as that photon.
| nwallin wrote:
| > You are the oldest thing in the universe you can
| observe.
|
| The moon is older than we are, due to gravitational time
| dilation. So is Mars. Even if you account for the time it
| takes for light to travel to here from there.
| BurningFrog wrote:
| The universe has no center.
|
| All places are equally old.
|
| So a galaxy a billion light years away is as old as ours.
| But we see it as it was 1 billion years ago.
| akomtu wrote:
| Some heretical thoughts. How do we measure distance to
| galaxies? By measuring redshift of the light from those
| galaxies and making an assumption that the only cause of
| redshift is spacetime expansion? What if photons slowly
| lose energy, and those very far galaxies are in fact much
| closer?
| cygx wrote:
| Errors in Tired Light Cosmology:
| https://www.astro.ucla.edu/~wright/tiredlit.htm
| ncmncm wrote:
| That is the "tired light" hypothesis. It is not favored
| lately because if it were the principal cause of
| redshift, certain observed details would differ.
|
| I don't think it is entirely ruled out, but two causes of
| redshift are considered less likely than one.
| samstave wrote:
| I've always had trouble understanding this; if everything
| is the same age, how did they get billions of light years
| away from the Big Bang?
|
| How do we know where the Big Bang occurred?
|
| Unles it means that our galaxy is on the spherical
| plane(?) directly projected out in all directions from
| the bang, and it's the diameter of this sphere that is
| billions across?
| BurningFrog wrote:
| This doesn't help with understanding, but I think it's
| true:
|
| Our intuitions about physical reality come from evolving
| as primates on Earth. We're pretty great at intuitively
| understanding the world at that scale.
|
| But at vastly different scales of size and time, those
| intuitions just don't apply much. So quantum physics
| events on nano -meter and -second scale seems completely
| bizarre, as do cosmological event on giga -lightyear and
| -year scale.
| yodsanklai wrote:
| Here's how I understand it (but I may be totally wrong so
| please correct me if this is wrong).
|
| Common knowledge is that there was an initial event
| called the Big Bang but there's no observational or
| theoretic evidence that there was such an initial event
| or explosion. Observations are limited by cosmological
| horizon, and our theories are unable to describe the
| state of the universe in its "early on" stage.
|
| What we do know however is that the universe is expanding
| and getting less dense and colder as a result. By going
| backward, we interpolate the state of the universe far in
| the past up to a stage where it was very dense and very
| hot "soon after" an hypothetical instant zero that we
| don't know happened.
|
| Also at that stage, the universe may have been infinite
| already (provided it's infinite now). Maybe it's better
| to think of the Big Bang has a past state of the universe
| rather than an "explosion" that happened at given time
| and place.
| beeforpork wrote:
| Nothing stayed where the big bang was, but everything
| flew away at the same speed. There is a flaw in your
| imagination, because as a being in 3D you probably cannot
| imagine how a 3D thing explodes (I certainly can't).
| Don't think of the universe as sphere-shaped -- it is not
| a 3D sphere. Think of it as the 3D surface of a 4D
| sphere.
|
| Why? Let's reduce by one dimension to be able to imagine
| this: imagine a small thing (a grain of sand) explodes in
| our 3D world and all the tiny pieces are flying away at
| equal speed, then the structure that is created by the
| explosion is not a 3D sphere, but the surface of a
| sphere, a 2D structure, because where the explosion
| started, there is nothing left of the original thing, as
| every particle of it has moved away from that point, so
| at any point in time after the start of the explosion,
| the particles are on the surface of a sphere. That
| surface is a 2D structure embedded into our 3D world,
| much like the surface of an expanding balloon. In the
| same way, our universe is a 3D structure, so looked at
| from the outside (which we obviously cannot do), it is
| not a 3D sphere, but probably more like the surface of a
| 4D sphere.
|
| Now imagine us as a dot on a balloon that is expanding,
| and other stars are also dots on the surface of the
| balloon. In whichever direction you look, all the stars
| are moving away from you (the balloon is expanding). You
| do not need a center of this structure to observe this
| moving away -- nothing is in the center -- there is no
| center.
| dr_dshiv wrote:
| Your argument and examples actually don't imply that
| there is no center. The Big Bang wasnt an explosion per
| se, but in so far as there is a 3D spatial distribution
| that is not infinite, there will be parts with empty
| skies---that is, edges, last stars, ends of the universe.
| fsckboy wrote:
| _Your argument and examples actually don't imply that
| there is no center_
|
| if the 4th dimension is time, the argument implies that
| the center is "a long time ago"
| dr_dshiv wrote:
| Yeah, but the heat death end of the universe is _way_
| further in the future than the Big Bang is in the past.
| nlitened wrote:
| As far as I understand, if the "empty skies" regions even
| exist, we physically will _never_ be able to observe
| them, because due to cosmic expansion they are moving
| away from us faster than speed of light.
|
| So from our point of view, we can never know if universe
| is actually infinitely distributed or not.
| dr_dshiv wrote:
| Well, just because we can't reach the emptiness doesn't
| mean we wouldn't be able to observe the trend -- of less
| and less stars towards the edge.
| x3n0ph3n3 wrote:
| The big bang occurred _everywhere_.
| JumpCrisscross wrote:
| To add to this: we are used to seeing explosions
| propagating across space and time. The Big Bang was an
| explosion _of_ spacetime.
| hdjjhhvvhga wrote:
| Why did it happen?
| burnished wrote:
| eeuugh, marketing thought it would make a splash and
| fucking sales wanted more people to talk at
| beeforpork wrote:
| Nice try, I'd also like to know. But I am afraid no-one
| here will be able to answer you. But maybe we're lucky --
| I'll monitor this thread.
|
| We can never know the answer, because any possible cause
| was outside of our observable universe. Inside of our
| universe, time started at the big bang, so there was no
| 'before' and thus there was no cause, because the cause
| needs the time to be before the effect.
| hdjjhhvvhga wrote:
| Well, if it's true the universe will start contracting at
| some point (which, some speculate, could happen sooner
| than we had thought[0]), and if a big crunch leads to a
| big bang, it is not impossible that this very moment - in
| the sense of these actual circumstances we're in -
| already happened an infinite number of times. (Still
| doesn't really answer the 'why?')
|
| [0] https://www.independent.co.uk/space/universe-
| expanding-colla...
| jquery wrote:
| Someone outside the universe hit "build" on their
| "universe sandbox generator". The sandbox is still
| loading from our perspective, although from their
| perspective perhaps it loads instantaneously.
|
| I mean, obviously this is nonsense, but... I can't
| exactly disprove it.
| hdjjhhvvhga wrote:
| It looks each epoch speaks about the universe in its own
| terms: as gods' creation, as a machine, as a computer,
| AI... So while there is no way to disprove the sandbox
| theory you presented, we can be 100% sure that at some
| point in time people will see it in a different way, and
| then it will change again and again. Sometimes I feel sad
| that there are so many mysteries of the universe and so
| few of them will be discovered during my lifetime.
| sdmike1 wrote:
| Good question, my understanding is that we frankly just
| don't know, it may be one of those things that we can't
| know, but that is getting awfully close to the realm of
| philosophy
| JumpCrisscross wrote:
| > _it may be one of those things that we can 't know_
|
| This is true for anything we don't know.
|
| For the Big Bang, we know the intermediate problem: black
| holes. Gravity and quantum mechanics interacting at the
| same scale. The singularities there are accessible in a
| way the singularity of the Big Bang is not.
| zokula wrote:
| ianai wrote:
| This kind of brings up another point that is interesting
| about our universe. We're under the impression that every
| point in the universe is experiencing the same amount of
| distance from the beginning of the universe from that
| individual point's frame of reference. But this kind of
| makes time so fundamentally weird compared to the spacial
| dimensions. We assume no point in the universe is the
| center, for instance. And the topology of the universe
| would look fundamentally different if there were some
| spacial coordinate (of the three) upon which every point
| was "pinned." But isn't saying from every individual
| point's frame of reference the universe is the same age
| equivalent to making a central point within time at the
| beginning? aka the big bang, of course, but that also
| seems to imply something about the topology of the
| universe for eternity after the big bang, as well. It's
| got one complicated topology for sure.
| BurningFrog wrote:
| Yeah, the time dimension _is_ different from the space
| dimensions.
|
| To mention the obvious: everything is constantly moving
| through the time dimension together, for unknown reasons.
| Nothing like that happens with space.
| cmehdy wrote:
| But how would we know if all spatial dimensions were
| moving along a constant vector? We can't rely on
| redshit/blueshift if the medium of transmission itself is
| moving like everything else. The next question might be
| "moving in what, then?" but then why not abstractly ask
| the same about time.
| smolder wrote:
| This is a bit of a tangent, but the idea of "moving
| through time" always struck me as a little weird, because
| the concept of motion is dependent on time already. I
| like to think of things having a shape that exists along
| the time axis in addition to the spacial ones. The 4D
| shape of a thing is fixed, but captures within itself
| what we perceive as motion in 3D space.
| ianai wrote:
| There was some ancient religion where their god or satan
| figure was responsible for time - literally the god/satan
| beings way of destroying the universe.
|
| Wish we could figure out some better ways to experiment
| with time. Seems like it's very telling of what's really
| going on that it's so different.
| tsimionescu wrote:
| The theory of the Big Bang is based on the observation of
| inflation: spacetime itself is constantly expanding -
| that is, the distance between galaxies that are at rest
| relative to each other is increasing (more precisely, the
| galaxies are not at rest, but the distance between them
| is increasing faster than their relative speed).
|
| So, extrapolating this in the past, at some point the
| universe must have been really tiny, and then grew much
| larger. But this growth happened essentially everywhere:
| spacetime itself expanded and pushed things apart at
| speeds greater than the speed of light (which is allowed
| if the coordinate system itself is what's changing),
| leading to objects which were once microns apart now
| being tens of billions of lightyears away in just a few
| billion years.
| yodsanklai wrote:
| > So, extrapolating this in the past, at some point the
| universe must have been really tiny, and then grew much
| larger.
|
| Isn't it our _observable universe_ which must have been
| really tiny? the universe itself could have been infinite
| in its early stage as well right?
| simonh wrote:
| Sure, in fact if Roger Penrose is right about conformal
| cyclic cosmology scale itself in those conditions doesn't
| really matter.
| michaelmrose wrote:
| The big bang happened everywhere. Space is not a fixed
| size nor infinite emptiness into which the big bang
| poured matter. Space itself expanded from near nothing to
| the universe we have today. The big bang wasn't a matter
| grenade it was the expansion of everything including
| space itself from nearly infinitely small to current
| state.
|
| This means that the tip of your nose, a distant
| mountaintop, Olympus Mons on Mars and indeed a distant
| galaxy were all the same space.
|
| Imagine a balloon blowing up with an ant on it. The ant
| can only walk so fast but the balloon can blow up
| expanding the space between ants in a way that is in no
| way limited by ant walking speed.
|
| Now that we are so separated it takes so long for light
| to get to us that we can only see the light that left
| billions of years ago from our frame of reference
| Cthulhu_ wrote:
| That's an interesting one to think about; every galaxy
| moves away from every one, so (if I got this right) from
| every other galaxy's point of view, all the other galaxies
| are younger... or older, either / or I don't know anymore.
| cmehdy wrote:
| It's more like every point of view looks at the past.
| Which is also true if you look at your screen right now,
| it's just that you're looking at your screen some
| nanoseconds ago.
| ianai wrote:
| Light and thus causality and information travel at a
| constant speed of "c." As far as we know, nothing can
| travel faster than "c" - other than the universe itself
| as in during the inflationary epoch. So the further out
| any observer would look the longer that light would have
| had to travel relative to that observer. Seeing something
| 3 billion light years away would mean the light took 3
| billion years to arrive at the observer.
| ncallaway wrote:
| The further away it is, the more time light has spent
| traveling to us.
|
| So, more distant means we are viewing events that happened
| further in the past.
|
| We are (almost certainly) not at the center of the
| universe, but we are, by definition, at the center of our
| observable universe.
| Jenk wrote:
| The light took far longer to reach us, thus what we are
| _observing_ is from a much younger (than it really,
| currently, is) star.
| yk wrote:
| They are older, so they had less time to produce heavier
| elements. Additionally lighter stars live longer, so it may be
| that the heavy stars just burned out in nearby galaxies.
| jeremyjh wrote:
| Why wouldn't that have already been the assumption? When we
| look at distant galaxies we are looking billions of years in
| the past; so it would seem natural to find more heavy stars
| there that haven't burned out like they have more locally.
| superjan wrote:
| I expect this effect is not ignored. But please note that
| heavy stars do not burn in billions of years but in
| millions. Not seeing them locally suggests that we have
| slower starformation, not that we had more of them (heavy
| stars) billions of years ago.
|
| https://en.wikipedia.org/wiki/Stellar_evolution
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