[HN Gopher] Why is there a normal galaxy sitting at the edge of ...
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Why is there a normal galaxy sitting at the edge of the Universe?
Author : Santosh83
Score : 227 points
Date : 2020-09-09 15:12 UTC (7 hours ago)
(HTM) web link (www.syfy.com)
(TXT) w3m dump (www.syfy.com)
| rinze wrote:
| They're looking at us, wondering exactly the same thing.
| pier25 wrote:
| Isn't it possible that the galaxy is much younger and it actually
| moved faster than light?
|
| I seem to remember reading that "islands" of spacetime could do
| that.
| dylan604 wrote:
| Which sci-fi author wrote that? That might make for interesting
| reading if you find it and share with the rest of the class.
| pier25 wrote:
| https://phys.org/news/2015-10-galaxies-faster.html
| SahAssar wrote:
| That article explains that the galaxies are only moving
| faster than light from our perspective since every part of
| space between us and it is expanding.
|
| So, no it's not moving faster than light. The space between
| it and everything else is expanding.
| brian_herman__ wrote:
| syfy really good science information for being a entertainment
| channel I wish more places would do this like the history
| channel.
| BurningFrog wrote:
| First thought is that it can be a small blob galaxy in front of a
| bigger one.
| giantrobot wrote:
| But the odds of that happening are _astronomical_!
| macawfish wrote:
| The only reasonable explanation is aliens
| [deleted]
| Randor wrote:
| I found an interesting paper on the subject over on the European
| southern observatory website:
|
| https://www.eso.org/public/archives/releases/sciencepapers/e...
| rcarmo wrote:
| It's likely to be the parking lot for The Restaurant At The End
| Of The Universe, no?
|
| (I can't help but wonder what Douglas Adams would make of this
| sort of thing - or the present time, for that matter.)
| SloopJon wrote:
| I find it funny when scientific articles (esp. pop astronomy)
| describe something as weird, bizarre, or extremely unlikely.
| We're reversing the effects of gravitational lensing on a galaxy
| at a distance that's a significant fraction of the radius of the
| observable universe.
|
| Are astronomers that confident in their models that the inferred
| shape of this galaxy is bizarre? I'd love to have that level
| confidence in software.
| slg wrote:
| That is the premise of the article. It is bizarre in relation
| to our models of the universe. We don't know if it is unusual
| in relation to the universe itself. As the article states:
|
| >Clearly, the theoretical models are wrong, or at least (and
| more likely) incomplete. Obviously, there's more to learn about
| galaxies that exist at the edge of the observable Universe.
|
| I am reminded of that tale about how "Eureka!" is not
| exclamation of good science but instead "That's odd.". This
| article is saying "That's odd." in a way that signals we are on
| the verge of new scientific discovery.
| freeqaz wrote:
| We can more readily validate gravitational lensing than any
| early universe physics. So my guess would be that modeling the
| lensing is the easy part to validate :)
| iwonderwhy wrote:
| All right hackernews. Genuine question, not sure where else to
| ask.
|
| If galaxies and stars at the other "end" formed out of matter
| resulting from the big bang, just as the matter we are made of,
| how did we get here at the same time that that matter got there?
|
| Is it because speeds faster than light are possible, and around
| the big bang all matter was spread near instantly at that speed?
| I don't understand how matter of the same "kind" was spread
| throughout the universe all at the same time without traveling at
| speeds greater than the speed of light. Because if we watch the
| "opposite" direction from where the big bang occurred we don't
| really observe matter in a state closer to its original state, or
| parts of the universe in radically different states - which
| should result from that matter traveling further than the matter
| we are made of, as for us to now catchup with light that is
| "younger" than that towards the core of the universe. Am i
| missing something?
| gmadsen wrote:
| there is no direction of the big bang. You sitting in your
| chair is the exact center of the universe for your frame of
| reference.
|
| all we have is the sphere of light that can reach us. That
| doesn't imply anything about a global universe frame
| at_a_remove wrote:
| To give you specific terms to research on, in cosmology this is
| called the "horizon problem" or the "homogeneity problem,"
| basically put as "Why is the stuff _over there_ so similar to
| the stuff _right here_ when they 're so far away? They ought to
| be causally disconnected by distance!"
|
| The answer to this in the early universe is called _inflation_
| , which you can tag onto Alan Guth around 1981 or so. It
| involves spacetime itself stretching. Originally, everything
| was nearby and so it was all evened out -- about the same
| temperature, density, and so on, then it just gets pulled apart
| and "writ large" in a twinkling.
| iwonderwhy wrote:
| Thanks for this - will read more in the two terms.
| zemnmez wrote:
| this is because things aren't 'moving apart'-- space itself is
| expanding (into what? nobody knows). it's not that the galaxies
| are being propelled apart from a force in a particular place
| either; _everything_ is expanding away from _everything else_.
|
| On the traditional balloon model, the surface of the balloon
| represents space itself. Those dots on the surface of an
| expanding balloon are not moving relative to space (the surface
| of the balloon), and so despite the distance increasing between
| us, the rate of increase of that distance is not bound by the
| speed of light, which only limits passage _through_ spacetime.
|
| The wikipedia page on redshift describes well how redshift
| applies to objects which are in space that is expanding:
| https://en.wikipedia.org/wiki/Redshift#Expansion_of_space
| ddevault wrote:
| In case anyone is confused, I prefer to explain the expansion
| of space without metaphors.
|
| Space itself is getting larger, everywhere, all at once. The
| _scale factor_ of the universe is getting larger. New space
| is constantly being "made". Every second, every kilometer in
| the universe grows by 2.2x10^-18 centimeters. If no other
| forces were in play, it'd carry everything along with it and
| pull everything a bit further apart. However, local forces
| like gravity and the strong and even the weak nuclear force
| are more than sufficient to hold everything together despite
| this, so the expansion cannot be locally observed.
|
| That's a small number, but the universe is very big. The
| hubble constant is usually represented in km/s/Mpsc
| (kilometers per second per megaparsec), and in those units it
| comes out to 68. So, every second, every Megaparsec in the
| universe grows by 68 kilometers. The more parsecs between us
| and some distant thing, the more space is growing between us
| and them every second.
|
| For reference, our nearest galactic neighbor is Andromeda,
| which is 67 kpc away, so about 100 meters of new space is
| created between our galaxies every second. That being said,
| Andromeda is heading towards the Milky Way at 110 km/s, so it
| easily overcomes this and will crash into us any day
| now^W^W^Win 4.5 billion years.
| iwonderwhy wrote:
| Very interesting.
|
| So the I wonder if everything expands along with the
| universe, does it mean that from outside, things moving at
| the speed of light in our universe, are potentially moving
| at speeds greater than the speed of light within our
| universe? If i was watching from outside, a rectangle
| moving at the speed of light in our universe, would one of
| its edges be moving away from me at the speed of light +
| the speed of expansion? If it makes sense.
| ddevault wrote:
| That question is too abstract for me to reason about. A
| "rectangle" couldn't move at the speed of light; light is
| point-like (oh dear, saying that could get me in
| trouble). Anything with mass cannot move at the speed of
| light, and anything without mass must move at the speed
| of light, and all known objects without mass are point-
| like. And then there's the question of observation in the
| first place - observation itself is governed by
| fundamental particles, and observing a fundamental
| particle at its scale is theoretically impossible.
|
| I know you want me to cheat and set aside all of these
| complications and just imagine a rectangle moving at the
| speed of light, but such an answer would be nonsensical.
|
| But the answer to the more specific question, "does the
| expansion of space make something move faster than the
| speed of light?", is "no", but it does cause the distance
| between objects to increase faster than the speed of
| light. To an external observer (which is inherently
| difficult to reason about, for the record), these objects
| would appear to "move" away from one another faster than
| lightspeed. However, the very idea of "movement" is
| rooted in the context of spacetime, and is bounded by the
| speed of light, so it's a confusing/nonsensical question.
| saagarjha wrote:
| See also the observable universe:
| https://en.wikipedia.org/wiki/Observable_universe. As the
| universe's expansion speeds up, we will never receive
| further information from some parts of the universe as it
| "moves away from us" faster than the speed of light.
| mensetmanusman wrote:
| Do particles in this model re-adjust their spacing to the
| new space being created?
|
| e.g. after 10^18 seconds, would the diameter of a hydrogen
| atom still be the same? or is it scaled to be huge
| (relative to now) ?
| ddevault wrote:
| Space is growing, not the matter within it. The diameter
| of a hydrogen atom is dominated by the fundamental
| forces, and the expansion of space is insufficient to
| overcome this force.
| joshspankit wrote:
| It would be interesting to hear your answer to mekkkkkk's
| question
| maxekman wrote:
| It was answered, as far as I can tell:
|
| > However, local forces like gravity and the strong and
| even the weak nuclear force are more than sufficient to
| hold everything together despite this, so the expansion
| cannot be locally observed.
| thaumasiotes wrote:
| OK, we have a meter stick. It's made of pure iron and,
| for whatever physical reasons, it is 1 meter long
| exactly.
|
| After some time, the scale factor of the universe grows,
| so that 1 new meter is 1.05 old meters. But, by
| hypothesis, _as this happens_ , our meter stick
| _contracts_ , so that it ends up being just 0.952 new
| meters (= 1 old meter) long. Why? Did the physical laws
| governing iron atoms change so that they pack more
| densely than before?
|
| And if so, why do _all particles_ pack at _exactly the
| same_ new density? Shouldn 't it differ from molecule to
| molecule?
| ddevault wrote:
| >And if so, why do all particles pack at exactly the same
| new density? Shouldn't it differ from molecule to
| molecule?
|
| The dominant factor on this scale is the strong nuclear
| force, which governs interactions at the scale of quarks
| - much smaller than molecules.
| thaumasiotes wrote:
| But the scale of quarks increases just as much as every
| other scale, doesn't it? Why did the iron rod shrink
| while space grew? Why are the iron atoms closer together
| now than they were before? Why are the protons in each
| iron atom closer together now than they were before?
| phaemon wrote:
| > But the scale of quarks increases just as much as every
| other scale
|
| No, there is no scaling of matter or light. It just has a
| bigger space to play in.
| ddevault wrote:
| The iron rod didn't shrink, it's more like it just held
| together. If I have a rubber sheet with a ball on it, and
| I pull at the ends of the rubber sheet, it's not going to
| pull the ball apart. The binding force of the ball's
| constituent atoms is sufficient to overcome the pulling
| force. And in the case of dark energy, the pulling force
| is absoultely _miniscule_ at those scales.
| thaumasiotes wrote:
| The iron rod started out being 1 meter long, and now it's
| 0.952 meters long. In what sense did it not shrink?
| ddevault wrote:
| >The iron rod started out being 1 meter long, and now
| it's 0.952 meters long. In what sense did it not shrink?
|
| In the sense that it did not become 0.952 meters long. It
| didn't "become" anything - it did not change at all. The
| universe grew around it, or perhaps "underneath" it. More
| space appeared for it to exist in. It's like putting an
| iron rod in a 10 meter square house, then moving the
| walls out another meter.
|
| Edit: let me phrase this another way. Let's imagine that
| you and I were pulling on the bar at either end. We could
| pull it forever and ever and it would never come apart
| (unless it rusted and became brittle or something, but
| let's imagine it doesn't). That's because we aren't
| putting in enough force to overcome the forces which are
| holding it together. Well, the expansion of the universe
| is putting like 10^-20 times less force into it than our
| arms would be.
| thaumasiotes wrote:
| > More space appeared for it to exist in.
|
| This is a very different idea from "it's the same amount
| of space, but bigger", which is what I understand by the
| claim that a scale factor is increasing.
| ddevault wrote:
| Well, space isn't a tangible (and finite) thing. It's the
| manifold in which the universe exists. Increasing the
| scale factor doesn't "stretch" space, it just makes...
| more of it.
| ddevault wrote:
| I didn't really understand mekkkkkk's question, but I
| wrote up a longer reply here at your prompting:
|
| https://news.ycombinator.com/item?id=24424626
| joshspankit wrote:
| Thank you.
|
| If I understand what you've written already, the essence
| of the answer in terms of mekkkkkk's question (for
| reference: " Sorry for also asking a space 101 question,
| but since the fabric of space is expanding, does that
| mean that things are getting bigger as well? Naively, it
| would seem that way. In your balloon example, the dots
| would get bigger."), I _think_ the answer would be:
|
| Anything held together (for example by gravity, or the
| force that keeps out atoms together) is not growing along
| with the universe simply because those forces are (for
| now) stronger than the expansion.
|
| This does produce an interesting side question though:
| aren't we (humans) _shrinking_ in relation to the
| universe? Or, without the click-baity phrasing: isn't the
| universe growing without us?
| ddevault wrote:
| >This does produce an interesting side question though:
| aren't we (humans) shrinking in relation to the universe?
| Or, without the click-baity phrasing: isn't the universe
| growing without us?
|
| Yep.
| noizejoy wrote:
| I thought it was explained. Local gravity is moving
| things together much faster than general expansion is
| moving them apart. At super super long distances, gravity
| is weaker than expansion, so something very far is
| disappearing while something nearby may be collapsing.
|
| However, that questions a different future I've seen in
| popular science talks: That the future becomes dark
| because of expansion. That makes less sense to me now,
| since it would seem that a merged set of galaxies would
| keep plenty of local stars in the skies. Assuming that
| stars are born as fast as they die (but I don't recall
| seeing an answer to the ratio of star births vs star
| deaths at a local level).
| ddevault wrote:
| The rate of expansion is speeding up. If it continues to
| increase, eventually it'll have observable effects at
| interstellar scales, and even interplanetary scales, and
| ultimately tear everything apart in the "big rip". Note
| that I'm omitting a lot of context here, there's a lot of
| other factors which make the big rip scenario much less
| likely.
|
| Also, the age of star formation will eventually end.
| Stars will stop forming somewhere between 1 trillion and
| 100 trillion years in the future.
| [deleted]
| mekkkkkk wrote:
| Sorry for also asking a space 101 question, but since the
| fabric of space is expanding, does that mean that things are
| getting bigger as well? Naively, it would seem that way. In
| your balloon example, the dots would get bigger.
| ben_w wrote:
| Just to add to your question:
|
| The usual response of "it only affects space between
| galaxies not inside galaxies" is _deeply_ unsatisfying, and
| feels like it must be an oversimplification.
|
| What I think is meant, _but I absolutely want someone wiser
| to confirm or refute_ , is that the rate of expansion is
| proportional to distance, and therefore so small inside a
| single galaxy it can be ignored.
|
| What I don't know is: can _any_ orbits still be stable in
| an expanding universe?
|
| (In theory I could simulate the orbits question easily; in
| practice, last time I tried to do astrophysics maths I made
| an elementary mistake).
| reubenswartz wrote:
| Yes, because the "Hubble Constant" is expressed as
| km/s/Mpc (that's Megaparsec), and the value is thought to
| be around 70. 70km/s seems crazy fast, until you divide
| by the 3,300,000ish light years (each light year being
| about 6,000,000,000,000 miles).
|
| Of course, if you calculate out far enough time, you
| would eventually end up with the observable universe
| getting smaller (because the stretching of spacetime
| would take away more space than was added by light
| reaching us from further away), down to our galaxy, and
| eventually everything getting torn to shreds, even down
| to protons...
|
| In the "near" term, the effect is so small that we have
| much more to worry about from the sun expanding in a few
| billion years than the Big Rip.
| wruza wrote:
| _it only affects space between galaxies not inside
| galaxies_
|
| It obviously affects all space, inside galaxy or outside
| of it. Let's just check the rough math, not even
| bothering about the fact that expansion was not linear.
| The universe expanded to around 100BLY in about 10BY,
| i.e. got ten times bigger than its potential light cone.
| So, for every "initial" 1km, there is additional 9km in
| 10BY timespan, or 0.0009mm per year, or 0.00003nm per
| second. The general ratio is around 1e-17 per second per
| length unit.
|
| Proton size is around 1e-15m, Planck size is around
| 1e-35m. A thousand Planck units per second is not that
| much, really. And on sub-milliseconds it just loses its
| effect completely, due to that Heisenberg guy. (If we
| take my bullshit math seriously, I mean.)
| thaumasiotes wrote:
| > What I think is meant, _but I absolutely want someone
| wiser to confirm or refute_ , is that the rate of
| expansion is proportional to distance, and therefore so
| small inside a single galaxy it can be ignored.
|
| I am not that person. But I feel like this can't work --
| if all space is expanding equally, in proportion to its
| own extent, then we would perceive no expansion at all.
| If two points start out 1 light year apart, and over time
| 1 light year expands to be 10% longer than it was
| before... and also, everything in the universe expands to
| be 10% larger in all spatial dimensions... then the
| distance _in meters_ between the two points hasn 't
| changed, because meters grew too.
| saagarjha wrote:
| You'd notice a slower speed of light, wouldn't you?
| johncolanduoni wrote:
| The problem with that model is that as was previously
| said, the electromagnetic, nuclear, and gravitational
| forces easily countermand the expansion on non-inter-
| galactic scales, to the point of not being measurable on
| the scale of a meter. Ultimately the molecular structure
| of your meter-stick is determined by various structure
| constants that aren't changing, so the expansion can't
| affect it unless it starts ripping bonds apart.
| thaumasiotes wrote:
| > Ultimately the molecular structure of your meter-stick
| is determined by various structure constants that aren't
| changing
|
| Really? These structure constants never involve any units
| of distance? Isn't distance changing at all levels?
|
| If I have a meter stick, and then space expands by 10%,
| you're saying that my meter stick will end up being 0.91
| new-meters long, yes? Wouldn't that require the structure
| constants to change, to allow for the same molecules to
| take up less space?
| xenophonf wrote:
| It's not the idea of a meter that's expanding. It's the
| physical space that starts out a meter long/deep/wide
| that's expanding.
|
| The meter-long stick you put into that space to measure
| it is still one meter long at some time in the future
| because the force that pulls the space apart (dark
| energy) doesn't pull on the matter that makes up the
| meter stick strong enough to overcome the forces that
| hold the stick together. But even if it did, the idea of
| one meter hasn't changed its definition. It's just the
| tool you used to measure one meter has broken.
| johncolanduoni wrote:
| Structure constants are unitless by design. But obviously
| constants like the speed of light that do involve
| distance are unchanged too so that's not a satisfying end
| to the story.
|
| Let's come at this from the other direction: if
| everything including the space between atoms and galaxies
| expands by 10%, how do you tell the difference between an
| old-meter and new-meter? For this to be observable,
| something has to still scale by the old-meter, or you
| wouldn't be able to observe a difference at all. That
| something would be the physical constants with units,
| like the speed of light. This means the electrical force
| governing the chemical bonds in your meter stick will
| still try to restore the distance between them to their
| original old-meter distance, but in new-meter units.
|
| Then if you define the actual meter by the length of your
| meter stick, or the physical constants, you end up
| getting the same meter that everything not macro-scale
| "snaps back" to.
| ddevault wrote:
| Local factors (gravity, strong & weak nuclear force) easily
| overcome the expansion of space. So things stick together.
| chowells wrote:
| Not in practice. In practice, this provides a very tiny
| force pulling subatomic particles apart in an atom's
| nucleus, or pulling atoms away from each other in a
| molecule, or pulling a celestial body's molecules away from
| each other. It makes no difference at all, because that
| force is absolutely dwarfed by the strong nuclear force,
| electromagnetism, or gravity, respectively. Systems that
| are coupled together by those forces, up to and including
| galaxies, are impacted only very minutely by this
| expansion.
|
| For the expansion to have a significant impact on relative
| distances, the distances involved have to be so extreme
| that there's no real other interaction between the objects
| you're measuring from.
| hashmymustache wrote:
| Does that expansion provide potential energy by creating
| space between attractive bodies? If so how do you account
| for conservation of energy?
| chowells wrote:
| Yes, it will create some additional potential energy.
|
| That doesn't contradict strict conservation of energy -
| it just adds another energy source that has to be
| accounted for when balancing everything.
|
| It might contradict the aphorism "energy is never created
| or destroyed", but I'm not sure that was ever science.
|
| It's more fun to think about it in terms of
| thermodynamics. Can that extra energy be used to reverse
| the second law of thermodynamics? I'm guessing not - it's
| so diffuse that it's probably impossible to use it to
| reduce entropy. The math for actually doing those
| calculations is well beyond what I know, though, so I'll
| just say that one's no more than a guess.
| alec_kendall wrote:
| When I was reading your comment, I envisioned the universe
| colliding with a boundary at the edge of an expansion zone,
| like a bug hitting a windshield.
| iwonderwhy wrote:
| Interesting analogy. So in effect to someone "watching" from
| outside our universe anything moving at the speed of light in
| our context, is moving either faster or slower than the speed
| of light in their context. Since the ballon and everything
| inside is expanding it means that either things are moving at
| the speed of light + speed of expansion, or speed of light -
| speed of expansion, when watched from outside. Assuming that
| everything expands along with the balloon. If I understand
| this correctly, and according to:
|
| "Due to the expansion increasing as distances increase, the
| distance between two remote galaxies can increase at more
| than 3x108 m/s, but this does not imply that the galaxies
| move faster than the speed of light at their present location
| (which is forbidden by Lorentz covariance)."
|
| But from outside we can move faster than the speed of light?
| Sorry having trouble getting my head around this.
| timcederman wrote:
| Since there's no frame of reference outside the universe,
| you can't make that analogy.
|
| I think you're getting tripped up on a variation of this
| idea, e.g. moving a laser pointer across the moon's surface
| faster than light.
| https://www.universetoday.com/109147/how-a-laser-appears-
| to-...
| Supermancho wrote:
| > Since there's no frame of reference outside the
| universe
|
| That's unknown. The observable universe is all we know
| for sure and there's evidence that there is both
| something beyond what we can observe, which conforms to
| what we know as space and matter, and something beyond
| that (whatever existed around the big bang locality).
| krapp wrote:
| >there's evidence that there is something beyond what we
| can observe
|
| By definition, there can't be. Evidence implies something
| we can observe, which would mean it isn't beyond the
| observable universe.
| vermilingua wrote:
| Then explain the Hubble volume: unless you believe the
| Earth is at the center of the universe, basic reasoning
| tells you that there is a sphere beyond which is outside
| our light cone, and yet outside which the universe still
| exists.
|
| Are you saying the observable universe is bounded to our
| Hubble volume?
| krapp wrote:
| >basic reasoning tells you that there is a sphere beyond
| which is outside our light cone, and yet outside which
| the universe still exists.
|
| Of course, but basic reasoning isn't evidence. Again...
| "evidence" implies something that can be observed, and
| something that can be _observed,_ by definition, lies
| _within_ the observable universe.
|
| >Are you saying the observable universe is bounded to our
| Hubble volume?
|
| I'm saying the observable universe is bounded to what we
| can observe, and evidence of something beyond the
| observable universe is a contradiction in terms.
|
| I don't know how I can _possibly_ make it simpler.
| mensetmanusman wrote:
| Wouldn't that be interesting...
|
| great sci fi plot, the earth is the center of the
| universe because anything out side of our sphere can't be
| observed by our consciousness and 'collapse' into
| existence :)
| pas wrote:
| kind of yes, relatively from an "outside observer" that
| would be the case.
|
| but if the usual laws of physics apply to that outside
| "observer" then it will not be able to observe photons from
| those objects.
|
| the usual assumption is that space is basically infinite
| but we can only observe our own "observable universe"
| sphere of it. every point in space has its own universe
| basically.
|
| see also cosmic light horizon:
| https://www.thedallasgeek.com/single-post/2018/06/11/Our-
| Cos... (the difference between regions we can communicate
| with and regions from where a photon coming toward us will
| eventually reach us)
| dumpsterdiver wrote:
| >"space itself is expanding (into what? nobody knows)"
|
| I have a terrifying theory on this (granted, the Earth will
| be long gone). What if the universe is not actually expanding
| in the sense that it is being propelled by an initial
| explosion, but instead falling towards a much greater mass -
| the end of time so to speak, where all mass ends. Considering
| that gravity is a "weak force", the scale of such a mass
| makes me uncomfortable to think about.
|
| Perhaps what we observe as the fabric of space-time itself
| "stretching" is actually a similar process to what happens to
| matter as it enters a black hole?
| meowface wrote:
| From my layman's perspective, I think this is plausible,
| and many physicists seem to agree it's plausible. Maybe
| another plausible explanation could be the reverse: maybe
| before the Big Bang, our/the universe was in the state you
| describe, and the Big Bang is our perception of it
| "snapping back" and exploding violently outward (aka a
| white hole).
|
| Carlo Rovelli and others propose that black holes actually
| only appear as they do to us due to the extreme time
| dilation, and similar to how a photon's "perspective" is
| that it's experiencing all of time at once, a black hole's
| perspective is that it's basically a massive explosion that
| occurs at essentially the same moment it forms. So under
| this hypothesis, a black hole never reaches a true
| singularity, but as close to a singularity as physically
| possible, and then it almost instantaneously bounces back
| like a taut rubber band that's stretched back as far as
| it'll go. From our perspective on the outside, it's an
| intense explosion occurring in very slow motion, and from
| the perspective on the inside, it's an intense explosion
| happening all at once.
|
| Rovelli posits a Planck star, not a singularity, exists
| past the black hole's event horizon, and the Planck star is
| the state of maximal compression between the black hole and
| white hole phases. And somewhat related to this, if I
| understand the theories correctly, our universe might be a
| supermassive white hole, and we might hold the perspective
| of being inside of a super(super)massive black hole that's
| turned into a white hole and is exploding and jettisoning
| everything inside of it. Or some stage after that. The
| ultra-compressed energy before the Big Bang would be an
| (extremely massive and dense) Planck star.
|
| I have no idea how likely the Planck star theory or white
| hole universe theory might be, but my blind speculation is
| that if it's true, maybe dark energy is whatever's
| fundamentally responsible for gravity/curvature causing our
| white hole explosion to bend some outer medium - the
| hypothetical potential medium which our black hole/universe
| originally formed in - and interact with other extreme
| contractions and explosions also happening in that medium,
| in complex and multivariate ways. Maybe a white hole being
| pushed into or prodded or yanked by many other black holes
| and white holes from different directions and angles could
| be perceived from the inside as accelerating expansion of
| space at certain scales.
|
| Maybe this is happening recursively, even; maybe that outer
| medium is itself within another even greater medium, which
| also is within another greater medium, etc. Maybe the
| nesting depth is small, or near-infinite, or infinite. Or
| maybe there is no outer medium to our universe, in which
| case that whole idea's shot.
|
| And I'm not sure if this could be related, but Rovelli
| suggests the hypothetical Planck star cycle of black hole
| to white hole applied to primordial black holes that formed
| in our early universe could explain dark matter, so even
| without the outer medium idea there could be something here
| that helps us understand our large-scale observations.
| Maybe there could be some relation to the "dark fluid" and
| negative energy idea, too:
| https://en.m.wikipedia.org/wiki/Dark_fluid
|
| I have absolutely no clue if your or my speculation is
| reasonable or not (there's currently zero evidence of any
| sort of outer medium, as far as I know), but the general
| concept of our universe being the result of a black and/or
| white hole does definitely seem to interest a lot of
| physicists.
| Aerroon wrote:
| > _So under this hypothesis, a black hole never reaches a
| true singularity, but as close to a singularity as
| physically possible, and then it almost instantaneously
| bounces back like a taut rubber band that 's stretched
| back as far as it'll go._
|
| Kind of like a graph of 1/x, where everything behaves
| predictably, but there's that one point that doesn't fit?
| meowface wrote:
| I'm absolutely terrible and uneducated when it comes to
| math, so I'm not sure exactly what you mean. But if you
| mean 1/x where x = infinity, then yes, the classical idea
| of a singularity (such as what's been theorized to exist
| within a black hole, curving to an infinitely small
| point) is basically like 1/infinity or dividing by zero.
|
| Rovelli hypothesizes this never actually happens and is
| not physically possible, and rather, when the most
| physically extreme possible level of curvature does
| occur, it "snaps back". If true, this ensures black holes
| do actually behave predictably, and physics doesn't
| actually break down; it just gets as extreme as it can
| possibly get.
|
| So under this hypothesis, x gets really high, but the
| universe prevents it from ever reaching infinity. This
| would also potentially resolve some paradoxes related to
| black holes.
| codeulike wrote:
| See also Magnetospheric Eternally Collapsing Object for
| another no-singularity theory of Black Holes
|
| https://en.wikipedia.org/wiki/Magnetospheric_eternally_co
| lla...
| jquery wrote:
| > Carlo Rovelli and others propose that black holes
| actually only appear as they do to us due to the extreme
| time dilation, and similar to how a photon's
| "perspective" is that it's experiencing all of time at
| once, a black hole's perspective is that it's basically a
| massive explosion that occurs at essentially the same
| moment it forms. So under this hypothesis, a black hole
| never reaches a true singularity, but as close to a
| singularity as physically possible, and then it almost
| instantaneously bounces back like a taut rubber band
| that's stretched back as far as it'll go. From our
| perspective on the outside, it's an intense explosion
| occurring in very slow motion, and from the perspective
| on the inside, it's an intense explosion happening all at
| once.
|
| I've been yelling like a crank for a while that a black
| hole is actually a massive explosion we see in (ultra)
| slow motion, so it's really cool to hear I'm not alone,
| and that other people call it a "planck star". I haven't
| heard anyone connect that to the big bang being a white
| hole, but it does make a __lot __of sense, even if we
| currently have no direct observable evidence or even any
| theoretical predictions.
|
| Thanks for sharing, now I can follow along the research.
| meowface wrote:
| Don't know why you're being downvoted. It's definitely
| not too crazy of an idea, given what's been known since
| general relativity was confirmed and the discovery that
| black holes do indeed exist. I haven't looked into it,
| but I wouldn't be surprised if many other people have
| proposed it in the past. I haven't heard or thought of it
| before, but when I first read it it definitely made a lot
| of sense, intuitively.
|
| Maybe the downvotes (which seem to no longer outweigh the
| upvotes?) are because you said "is actually" rather than
| "might actually be". Humility and uncertainty is crucial
| in science. Even for a field that's much more testable,
| and even for a leading scientist in a field, let alone
| some random speculator on the internet. It's fun to think
| and talk about these things, but especially as total
| amateurs, we should never claim anything with even a
| little bit of confidence.
|
| My own speculative stuff I posted above is probably all
| dead wrong and hopelessly confused; I'm just throwing it
| out there as stuff that's popped into my head. And
| Rovelli may be wrong, too, though he's a highly-respected
| theoretical physicist and has published several papers
| about it. And even if the Planck star and black
| hole/white hole theory is true, it may not necessarily
| mean it has anything to do with how our universe started;
| that's just additional unsubstantiated speculation by me
| and some other people, and not anything Rovelli has
| claimed, though his theory seems to have increased
| discussion about that topic.
|
| Here're some resources:
|
| https://phys.org/news/2014-02-astrophysicists-duo-planck-
| sta...
|
| https://en.wikipedia.org/wiki/Planck_star
|
| https://en.wikipedia.org/wiki/White_hole#Big_Bang/Superma
| ssi...
| throwaway568 wrote:
| Interesting, this adds to a thought I had a couple of weeks
| ago.
|
| We can see the past, but we can't go there, like an
| observer inside event horizon looking out, they can see
| light coming in, but can't leave.
|
| We can't see the future, but when we are going there, like
| an observer falling into the event horizon. They can't see
| what's inside, but they can fall inside.
|
| As we experience time, it's like we are falling into a
| black hole made of time.
| Swizec wrote:
| My high school physics professor had a great take on this:
| The universe is defined as "everything". If we ever find
| anything outside the universe, we'll call that the universe
| too.
| whatshisface wrote:
| That doesn't really answer the question, what the parent
| is really asking about is whether we are living on the
| surface of a manifold that's due for some kind of a
| collision with something else.
| YorickPeterse wrote:
| Isn't this basically what the Big Rip hypothesis is about?
| bena wrote:
| It's possible. The issue is that the we really don't have
| any information beyond what we have. We have an idea of the
| big bang and the expansion of the universe. We have
| knowledge of certain factors etc. But really, we're not
| really equipped to handle the scale of the cosmos.
| DeRock wrote:
| If you want to delve further into this idea, check out
| http://www.flatuniversesociety.com
| cgriswald wrote:
| > On the traditional balloon model, the surface of the
| balloon represents space itself...
|
| For any still confused, there is also a 'raisin bread' model
| (which I prefer because it's 3D, unlike the surface of a
| balloon). The raisins are galaxies, and the bread is the
| space between them. As it bakes, the raisins get further
| apart, even though the raisins aren't moving through the
| dough.
|
| (Although galaxies also have movement through space, this
| isn't what is causing them to get further apart.)
| nelsonenzo wrote:
| Omg, thank you for this! The balloon model always confused
| me because I could never understand what was in the middle
| of the balloon, and why we were on top of it. It's an odd
| 2d example using an object that is 3d, the balloon.
|
| Raisin bread, oh I love thee even more today.
| jecel wrote:
| The raisin bread is a 3D expansion in 3D space. So from
| the viewpoint of a specific raisin the others are moving
| differently depending on what direction you look and you
| can use that to determine where the center of the bread
| is.
|
| The balloon is a 2D expansion in 3D space, which is a
| better analogy for our 3D universe expanding in 4D space.
| From the viewpoint of a particular dot you see the exact
| same thing no matter what 2D direction you look. There is
| no center.
|
| I agree that the balloon is more confusing, but it is
| more correct in that it doesn't lead to ideas like "the
| point where the big bang happened".
| rosstex wrote:
| Why not chocolate chip bread? I suppose raisins more
| closely represent galaxies.
| ddevault wrote:
| I don't fully understand your question to give a direct answer,
| but I think that's mostly due to a number of misconceptions you
| hold about the universe. So I'll just try to clear those up
| instead.
|
| First of all, the big bang didn't happen _somewhere_ , it
| happened _everywhere_. There 's no "center" of the universe
| that everything is moving away from. The universe did not start
| from a point, it started from a small _scale factor_ and the
| _scale factor_ rapidly increased.
|
| Assuming the universe is infinite (we're not sure), you could
| think of it as expontentially more infinities being created all
| the time. Say you take a 1-dimensional line and put tick marks
| 1cm apart, to positive and negative infinity. Then you multiply
| every tick mark position by 2. Two times infinity is still
| infinity, but the nature of the infinity has changed: it's
| _scaled up_ by a factor of two. You could then subdivide it
| again, adding markings in between, 1 cm apart. You can think of
| these new markings as representing _new centimeters_ which have
| appeared on your 1D line. This is happening to the universe in
| three dimensions.
|
| Now, instead of doing this by discrete intervals, just do it
| constantly, so the scale factor is always expanding. Any two
| points are always moving apart from each other at the rate of
| this expansion, let's say 1cm/cm/sec. Now, introduce an
| attractive force between objects (e.g. gravity) which obeys the
| inverse square law. If the objects are sufficiently close to
| one another, they'll move towards each other at a rate faster
| than 1cm/sec, which would overcome the expansion force and
| allow them to remain together. In the real universe, the
| fundamental forces have this effect, and this is why we don't
| observe everything flying apart on local scales.
|
| Now let's say that the maximum speed limit is 10cm/sec, and
| light travels at this speed across our 1D line. If we have two
| objects 2cm apart, then the distance between them will grow by
| 2cm in one second. In that time, light from each will have
| travelled the same distance and met one another. Now, they're
| 4cm apart, and in the next second will travel 4cm apart, twice
| as fast. Light can still make this journey. At the next tick,
| they're 8cm apart, and light still makes it. 2/16th of a second
| later and they'll be 10cm apart and moving away from each other
| at the speed of light.
|
| At this point, no future emissions will reach them. However, we
| haven't been emitting discrete light pulses - galaxies
| continuously emit staggering amounts of light. So, the space
| between them is full of light which is constantly making the
| journey towards the other end. If no other factors were at
| play, they'd still be receiving _old_ light from each other
| forever. But there are other factors at play: the inverse
| square law, combined with the increasing redshift, will
| eventually reduce the light to effectively nothing.
|
| These factors are sufficient to extend the effective
| observation duration of distant objects well after they've
| crossed the lightspeed event horizon. To recontextualize this
| into our real universe, we can look at extremely distant
| objects like GN-z11, which is 32 billion light years away. If
| light were to re-tread this distance, it would require twice
| the current age of the universe to complete the journey.
| However, this light only took 13.4 billion years to reach us,
| because it was emitted when the universe was much closer
| together, and carried towards us on the "flow" of expanding
| space time, while the object was carried away from us on that
| same "flow" - faster than the speed of light.
|
| Oh, and it's also worth noting that the rate of expansion
| wasn't always consistent. Check out this wiki:
| https://en.wikipedia.org/wiki/Inflation_(cosmology)
| noizejoy wrote:
| So will expansion accelerate enough to eventually be a
| stronger "force" than local gravity?
| ddevault wrote:
| We don't understand why expansion is occuring, so we can't
| say for certain. It would be a very long time in the future
| if that were to come to pass, and that's a whole lot of
| time for poorly-understood physics to happen in.
|
| But yes, it is accellerating, and if it continues to do so,
| eventually it will overcome gravity. But like I said, this
| depends on an incomplete understanding of physics, and the
| current evidence suggests (inconclusively) that this
| outcome is unlikely. Check out dark energy if you want to
| learn more.
| [deleted]
| iwonderwhy wrote:
| Ok, thanks for clarifying - indeed i seem to have had quite a
| few misconceptions. But from outside the universe, are things
| inside of our universe moving faster than the speed of light
| due to our universe expanding, and as such, things traveling
| at the speed of light when seen from the outside are
| traveling at the speed of light + speed of expansion?
| ddevault wrote:
| The answer is similar to the one I gave for your other
| question:
|
| https://news.ycombinator.com/item?id=24424912
|
| But I'll give you another analogy anyway. Say you put two
| rocks into a mass of water in an environment without
| gravity (e.g. the ISS), then freeze the water, causing it
| to expand. The expanding ice will cause the rocks to become
| more distant from each other, but they're not "moving" in
| local terms - the manifold in which they exist is itself
| expanding. That said, the frozen water and the rocks both
| exist in space, and the expanding ice moved the rocks
| _through space_. But, in this metaphor, there is no second,
| external "space" - the water itself represents space.
|
| And so to for our universe. Space itself isn't a part some
| other, second "space" that it's expanding into (at least
| not so far as we're aware). The existence of somewhere for
| space to expand "into" is not necessary for the expansion
| to take place. Remember, it's the scale factor which is
| changing, not a discrete object (i.e. the universe)
| physically expanding.
| db48x wrote:
| The big bang didn't fling matter out into the universe, it
| created more distance to go between all the matter that was in
| the universe.
| peter303 wrote:
| The universe may have alway been infinitely large. Its just
| that 14.8 billion years it started expanding, first at
| inflationary rates, then a slower strain of 10E-18 / second.
|
| Its a lot like looking at a number line. That is infinitely
| long in both directions. And if consider all real numbers, it
| is infinitely expandable.
| hacknat wrote:
| No part of the Universe is older than another.
| mhh__ wrote:
| > Genuine question, not sure where else to ask.
|
| Physics stack exchange
| adventured wrote:
| > The thing is, where they found it is not normal: The light we
| see from it left the galaxy 12.4 billion years ago, meaning we're
| seeing it as it was when the Universe itself was only 1.4 billion
| years old!
|
| It's not confusing at all. It's because the long-worshipped,
| conventional big bang theory is wrong. The universe doesn't have
| a beginning or end. It's eternal. The original sin of that theory
| is that it's tainted with forced space for a deity belief at the
| center and always has been. The universe cycles unevenly through
| phases of motion, it doesn't magically start from nothing and
| then 'die.' The conventional big bang theory is as bad as any
| other children's tale going, it's up there with Santa Claus.
|
| We're going to find a lot more supposed abnormalities like this
| over time. They're not abnormalities, it's the entrenched
| incorrect theories that are the problem.
|
| The universe (everything that exists) is drastically larger than
| we already think it is. Humans are arrogant, we didn't realize
| the extent of the micro world, and the same exact mistake is
| being made at the macro scale. What they think is a singular
| ~14-15 billion year old universe, is nothing more than one
| collection of galaxies, there are many more like it nearby (many
| as in trillions and trillions). The micro world was far smaller
| than we imagined; the macro world is far larger than we're
| imagining. It's the same mental mistake playing out, caused by
| the same arrogance. What's beyond the 'universe' that we can see
| so far? More massive collections of galaxies, similar to the one
| we inhabit that we mistakenly call the universe.
| depressedpanda wrote:
| Strong claims, but can you back them up?
|
| How do you explain the apparent accelerating expansion of the
| universe, i.e. that the farther away something is, the more
| redshifted it gets?
|
| How do you explain the cosmic microwave background radiation
| enveloping us in all directions?
| outworlder wrote:
| Of course they can't back this up.
|
| What the universe really is, is a simulation. We are trapped
| in it.
|
| "Lightspeed limit": this is because the simulation has a
| finite computing power. You can either move in time normally,
| or you can move in space. If you go to the max allowed speed,
| there's no processing left over to simulate time, therefore
| time stops for that entity. At intermediate speeds, slow down
| time accordingly.
|
| "Planck length": resolution of the simulation. It's discrete,
| and you can't go any smaller.
|
| "Heisenberg uncertainty principle": another simulation
| optimization. Instead of simulating all particles, just use a
| probabilistic function. You actually don't have to simulate
| it, just the macroscopic effects, _unless there 's an
| observation_. In which case you can compute either the
| position or speed of the particle. See also: atom orbitals
|
| "Superluminal" expansion: it's just so we don't try to get to
| other galaxies, which are only being simulated in a macro
| scale. This was left by the developer to turn the 'lightspeed
| bug' into a feature. Also closes bug UNIVERSE-001 where the
| background radiation was still visible, but other galaxies
| visibility was off due to performance concerns. Now they can
| be enabled.
|
| "Dark matter": other civilization experiments that we don't
| have permissions to see. Still there and interacting with
| matter. Bug is still in the backlog.
|
| See, anyone can come up with whacky stuff.
| xwdv wrote:
| Wouldn't a universe with no beginning or end begin to exist
| only when the first sentient being is able to observe it?
| djsumdog wrote:
| I've always been puzzled by the estimated age of the universe at
| being 13 billion years. That's just the size of the observable
| universe, correct? Isn't there a future horizon beyond which
| light will not currently reach us?
| vkou wrote:
| No, 13 billion years is the age of the universe. The observable
| universe is a sphere with a diameter of ~93 billion light years
| (And is likely to only be a subset of the entire universe).
| dumpsterdiver wrote:
| I have a question: Just over 20 years ago when the accepted
| view was that the expansion of the universe was slowing down,
| would you have backed that position with as much certainty as
| you are backing this one? That the universe is a mere 13.7
| billion years old?
|
| We cannot prove the absence of light in a place that is
| already so far away that it's light will never reach us. Do
| you agree? We can prove what we can observe, and from that
| proof we can make inferences about what we cannot observe.
|
| The entire premise of dating our universe is based on its
| observed rate of expansion. This was accomplished by
| extrapolating data from observable light and tracing it back
| to the so called Big Bang.
|
| I see a lot of problems with this one dimensional assumption,
| which to me seem really obvious.
|
| First of all, let's assume that we actually got it right this
| time and accurately traced light back to the Big Bang - how
| can anyone be sure that it was the first and only Big Bang?
|
| Pangea, the super continent, for instance - many may think of
| as a single place and time in history, but in fact it's more
| likely that many Pangea's have come and gone in various
| states as the planet roils on. There will likely be another
| in the far future.
|
| Perhaps the Big Bang was merely a "localized" event and there
| are Big Bangs occuring in distant places whose light will
| never reach us. Perhaps we have gone through many Big Bang /
| Big Crunch cycles. We simply cannot prove it one way or the
| other, and so to take a strong position on this would be
| unscientific.
|
| More food for thought - imagine that the universe has already
| been through a near infinite number of Big Bang / Big Crunch
| cycles, it begs the question, do we reset the clock every
| time or do we let it run?
|
| In my opinion, currently accepted theory is akin to believing
| that the Earth is the center of the universe and the sun
| revolves around us. We were wrong about that too.
| s1artibartfast wrote:
| I think you are generally critiquing assumptions that most
| astrophysicists are not making. Most Theorists would not
| claim with confidence that _the_ big bang was the first or
| only one, or that future big bangs are not possible. I
| think your criticism is more valid for the way the history
| of the universe is portrayed in news articles and high
| school text books.
|
| The term "multiverse" is used to describe the collection of
| multiple universes.Some have speculated that time has no
| direction in the multiverse and that time in each universe
| may be different. If our universe is cyclic, it makes sense
| to reset the clock because it may have run in a different
| direction last time or next time.
| outworlder wrote:
| > Just over 20 years ago when the accepted view was that
| the expansion of the universe was slowing down
|
| Was it ever a mainstream view? I thought it was just a
| conjecture, leading to the 'big crush', and was disproven
| long ago, way more than 2 decades ago.
|
| > The entire premise of dating our universe is based on its
| observed rate of expansion
|
| Also there's the cosmic microwave background radiation. We
| have mapped it, and this has also allowed us to corroborate
| when the universe has formed, what temperature it had, and
| when large scale structures appeared.
|
| There's probably other sources that allows us to estimate
| the age of the universe.
|
| > how can anyone be sure that it was the first and only Big
| Bang?
|
| We can't. But it is an irrelevant conjecture outside of
| philosophy, we can't observe anything _before_ the big
| bang.
|
| > but in fact it's more likely that many Pangea's have come
| and gone in various states as the planet roils on
|
| Sure, but that's a planet. We can't extrapolate much from
| that and apply to the universe at large.
|
| > Perhaps the Big Bang was merely a "localized" event and
| there are Big Bangs occuring in distant places whose light
| will never reach us
|
| Unobservable, therefore unfalsifiable, therefore
| unscientific. Philosophy again.
|
| > imagine that the universe has already been through a near
| infinite number of Big Bang / Big Crunch cycles
|
| Unless the rate of expansion starts to slow down or we have
| indication that it will ever reverse, there's no big
| crunch. The rate of expansion is _increasing_
|
| > currently accepted theory is akin to believing that the
| Earth is the center of the universe and the sun revolves
| around us
|
| Not really. You are dismissing generations of people
| dedicated to the study of these things. We have a _pretty
| good idea_ of what 's going on based on the scientific
| method, not conjectures from single individuals.
|
| There are things that we don't know yet. On a macroscopic
| scale, dark matter. Things don't really behave as they
| should based on observations, so this is why we have dark
| matter as a hypothesis. There could be another mechanism,
| research is ongoing. But as far as the macro universe goes,
| that's the major thing we don't understand yet.
|
| Most discoveries will likely come from a better
| understanding of the 'building blocks', of which quantum
| physics is at the forefront.
|
| There's probably much more we don't know yet. But the _age_
| of the universe, as we observe it, is not among them.
| HideousKojima wrote:
| >Unless the rate of expansion starts to slow down or we
| have indication that it will ever reverse, there's no big
| crunch. The rate of expansion is increasing
|
| Unless space wraps around like a globe and we'll all meet
| at the "south pole" (with the big bang being the "north
| pole") or something to that effect. Which is itself wild,
| unfalsifiable conjecture, but there are other ways for a
| Big Crunch to happen other than the expansion of space
| slowing down or reversing
| dumpsterdiver wrote:
| > Unobservable, therefore unfalsifiable, therefore
| unscientific. Philosophy again.
|
| I completely agree. Apologies if my comment above rubbed
| anyone the wrong way. The point you just made was my
| overall point. Our concept of time is confined to our
| current existence / cycle - that's what I meant by the
| sun revolving around the Earth comment, but others were
| correct when they responded that as a current metric
| that's not really useful.
| morganvachon wrote:
| > _Perhaps the Big Bang was merely a "localized" event and
| there are Big Bangs occuring in distant places whose light
| will never reach us. Perhaps we have gone through many Big
| Bang / Big Crunch cycles._
|
| This was always my view of the state of the universe from
| childhood onward. The Void of space is infinite, and within
| that Void our universe could be one of an infinite number
| of other universes that we will never know about because
| they are so far outside our ability to observe them.
| Perhaps there is as as much relative distance between
| universes in the Void as there is between galaxies in our
| own universe.
|
| This concept is the only way I've ever been able to accept
| that our own universe has a measurable size.
| s1artibartfast wrote:
| I don't think your childhood view holds up with
| contemporary views. My understanding is that 3
| dimensional space, as well as time are properties of our
| local universe. There is no space outside the big bang
| and between universes if multiple exist
| memetomancer wrote:
| The problem here is that you are taking a simplified
| layman's description, making naive assumptions about it and
| then brazenly dismissing the whole of contemporary
| cosmology as if you have profound insights that went
| completely over the heads of some seriously smart
| physicists.
|
| You then make an analogy about "Pangaea" as if you alone
| are the brilliant shining light of reason, but if you took
| just a small amount of time to read even Wikipedia you
| would find, for example, that several super-continents have
| formed and broken apart over the history of the Earth. The
| very first section of the Wikipedia article on
| Supercontinents lists eleven of them! [https://en.wikipedia
| .org/wiki/Supercontinent#Supercontinents...]
|
| I for one see a lot of problems with your one dimensional
| analysis and obvious lack of awareness on these topics. In
| my opinion, your currently insufficient knowledge is akin
| to believing that the Earth is flat because you can't
| personally see curvature on the horizon.
|
| Seriously though, I recommend you take the time to read
| about 'the entire premise of dating our universe', all the
| many decades of development, criticisms, refinements and
| confirmations of the current best theory. You'll find that
| it's an amazing subject, that all of your concerns have
| been poured over for the past century in great detail, that
| many brilliant people have worked out fantastically
| brilliant methods for figuring this out... and then
| finally, maybe, you'll be ready to read about the various
| cyclic cosmological models.
| luhn wrote:
| This is just pedantry. Don't get me wrong, these are
| interesting questions, questions that should be asked and
| should be thought about, even if the answers are likely
| unknowable. But taking issue with the age of the universe
| because we don't know what existed before isn't useful.
|
| Age is a relative thing. I say I'm xx years old based on
| the date of my birth. But I existed as a fetus before then.
| I existed as an ovum before that. I existed as stardust for
| billions of years before that. Perhaps I can mull over what
| it means to exist, and when "me" came to be, but when I
| have to enter my age while filling out some form I'm not
| going to write a philosophy essay. For practical purposes I
| am xx years old, and for practical purposes the universe is
| 13.7 billion years old.
| [deleted]
| skykooler wrote:
| How can we observe things over 40 billion light years away if
| they've only been around to emit light for 13 billion years?
| vkou wrote:
| They were closer to us when they emitted that light.
| They've since moved further away.
| wffurr wrote:
| https://en.m.wikipedia.org/wiki/Observable_universe#Misconc
| e...
| function_seven wrote:
| The universe has been expanding ever since the Big Bang.
| Things that are very far away are moving away from us at
| speeds "faster" than light. No, they're not violating the
| cosmic speed limit. The fabric of spacetime itself is
| expanding everywhere, and that makes objects at very large
| distances apart get even further apart faster than a
| lightspeed traveler could move them.
|
| https://www.space.com/33306-how-does-the-universe-expand-
| fas...
| wffurr wrote:
| "Measurements made by NASA's WMAP spacecraft have shown that
| the universe is 13.7 billion years old, plus or minus about
| 130,000 years."
|
| https://starchild.gsfc.nasa.gov/docs/StarChild/questions/que.
| ...
| lkbm wrote:
| Whoa, that's _crazy_ precise. They got it down to the tens
| of thousands?
|
| If so, seems like they should write "13.700 billion" for
| the first part. I'm a little suspicious of this number as-
| is.
|
| Looking for a source for those numbers, I found this[0]:
|
| > While previous estimates were 13.7 billion years old,
| give or take 130,000 years, new predictions hone in with
| more precision- at around 13.77 billion years, plus or
| minus 40 million years.
|
| Which is much less precise and feels a lot more believable.
|
| [0] https://www.labroots.com/trending/space/18295/light-
| bang-rev...
| bhk wrote:
| So NASA said "plus or minus 130,000 years" when they were
| actually off by about 70 _million_ years?
| johncolanduoni wrote:
| That's a misprint, the WMAP measurement was plus or minus
| 130 million years.
| f154hfds wrote:
| Naive question here - is the 13bn years relative to the
| surface of the Earth? I assume this matters right? If we're
| in a bit of a gravity well wouldn't the vacuum of space
| experience this time a bit longer?
|
| According to [1], the ratio is about 5.56E-10, so I guess
| this would contribute about a year to the age of the
| universe, so.. not that much. I guess I answered my own
| question.
|
| However, this does pose an interesting question about the age
| of the universe in extreme gravity wells doesn't it? Or am I
| misunderstanding something?
|
| [1] https://www.quora.com/How-much-time-on-earth-is-1-hour-
| in-sp...
| weswpg wrote:
| Well, given that there is no universal clock and time is
| defined locally for each observer, including each particle,
| it would be more strictly accurate to say that "the matter
| which later formed our solar system has experienced 13
| billion years of time" since the Big Bang
|
| or maybe 13 billion years is from the frame of reference of
| the Cosmic Microwave Background? that would make more
| sense. I'm going to check again then edit this comment.
|
| (i am not a physicist, not an authoritative source on this)
|
| edit: so it turns out that the age of the universe is given
| from the frame of reference of the CMB rather than from
| Earth's frame of reference.:
|
| > Measurements of the cosmic background radiation give the
| cooling time of the universe since the Big Bang
|
| > Cosmic time, or cosmological time, is the time coordinate
| commonly used in the Big Bang models of physical
| cosmology.[1][2][3] Such time coordinate may be defined for
| a homogeneous, expanding universe so that the universe has
| the same density everywhere at each moment in time (the
| fact that this is possible means that the universe is, by
| definition, homogeneous). The clocks measuring cosmic time
| should move along the Hubble flow.
|
| https://en.wikipedia.org/wiki/Cosmic_time
| joombaga wrote:
| Sorry to bikeshed, but I was struck by the word "likely" in
| your parenthetical. Are there models of the universe that
| predict our observable universe is _not_ a subset of the
| entire universe? How would one describe cosmological
| expansion in such a model?
| sdflhasjd wrote:
| It depends on the size and topology of the entire universe.
| It's possible the universe is smaller and sort of wraps
| around: literally, objects that appear far away are just
| past images of the back of objects that are closer to us.
|
| More boringly, measurements of the curvature of the
| universe mean this is probably not the case.
| enkid wrote:
| Some weird geometry where space is curved into a four
| dimensional sphere. The sphere gets bigger, adding space
| between all the points. If the sphere is exactly the size
| of the observable universe, then the observable universe
| and universe would be the same thing.
| dumbfoundded wrote:
| The Cosmic Microwave Background Radiation is a pretty
| uniform field that exists over the entirety of the
| observable universe. It was created in the earliest days in
| our universe. The fact that it exists everywhere we look
| with high regularity lets us guess that we're only a subset
| of a larger universe. There are many theories about the
| unobservable parts of the universe but these are impossible
| to test with any foreseeable technology that doesn't
| fundamentally break our understanding of physics.
| djsumdog wrote:
| One analogy I've heard: Imagine the big bang split into 4
| spheres and they accelerated away from each other.
| Because they'll all be expanding and accelerating, there
| could be 4 equally sized spheres of stuff just like our
| own, but it would be impossible for us to observe them.
| Change the number 4 to 2 or 1000 or n. We really would
| have no idea.
| dumbfoundded wrote:
| A testable hypothesis is a strong standard in science.
| Most scientists don't worry about things that cannot or
| more importantly, will probably never be testable. They
| can be fun to think about but that's pretty much it.
| tectonic wrote:
| Nice gravitational lens observation! We're hoping to use the same
| technique with the Sun to observe exoplanets by launching a fleet
| of small satellites to 547 AU (80 billion km / ~3 light days).
| The craft would sample the distorted Einstein ring around our Sun
| from that vantage point, then combine and reconstruct an image of
| the disk of an Earth-like exoplanet up to 100 light-years beyond,
| at a resolution of 25 kilometers / pixel.
|
| https://orbitalindex.com/archive/2020-07-08-Issue-72/#more-o...
| mensetmanusman wrote:
| Wow.
| sandworm101 wrote:
| Not the same technique, but there are similar architectures
| that could be implemented far sooner.
|
| Earth's atmosphere as a refractive telescope:
| https://www.scientificamerican.com/article/earth-could-be-a-...
| tectonic wrote:
| Not nearly as powerful, though.
| sandworm101 wrote:
| That depends on the planet used. If it works for earth, the
| next step might be Jupiter or Saturn, something that might
| be possible by only repositioning the spacecraft. It may
| even be possible to use the sun's atmosphere, the
| transparent part, as a lens.
| trimbo wrote:
| > it'd still take 25 to 30 years for them to reach a vantage
| point .... > mission designers would have to pick carefully
| because they could observe only a single target
|
| It will take 30 years to get in position but then we can only
| look at one target? While it sounds very neat, I'd rather fund
| something we can use more than once, and sooner.
| mrfusion wrote:
| We should build one for each target we want to observe.
|
| Starship is going to open so many opportunities.
| freeqaz wrote:
| Still valuable as a way to observe a potentially habitable
| planet in more detail. If we wanted to launch a probe there,
| it would take a lot more time!
| augusto-moura wrote:
| You CAN use for more than 1 target, you just need to
| reposition the telescope a bit. See [1], is a great great
| video on the subject. I can't recommend enough
|
| [1]: https://www.youtube.com/watch?v=NQFqDKRAROI
| pas wrote:
| The whole concept is that we should launch a fleet of them
| every few months. Very lightweight semi-autonomous smart
| lightsails with some optics.
|
| The first fleet helps targeting the second, and all those who
| come after them.
|
| https://www.youtube.com/watch?v=NQFqDKRAROI (already linked
| by a sibling comment, but yes, can't recommend this enough!)
| networkimprov wrote:
| It's not a new idea... I first heard of it in the intro segment
| of this Cool Worlds Lab vid
|
| https://www.youtube.com/watch?v=jgOTZe07eHA
| plasticchris wrote:
| Your link suggests the satellites word need to be around 2000
| AU to avoid the corona, though I suppose the delta v
| requirements would be pretty small for such a large change so
| far from the sun (but my only source for the intuition is
| kerbal so take it with a grain of salt).
| lordnacho wrote:
| How does the lensing work? Why doesn't the galaxy in the middle
| between us and the faraway galaxy pollute the image with its
| own light? It it separated by frequency or some trick?
| z92 wrote:
| > 547 AU
|
| For comparison Voyager-1 is now at a distance of 40 AU only.
| onlyrealcuzzo wrote:
| Is Voyager-1 still accelerating?
| saagarjha wrote:
| Nope, both are slowly decelerating as they leave the solar
| system: https://upload.wikimedia.org/wikipedia/commons/0/0c
| /Voyager_...
| hashtagmarkup wrote:
| That is not correct... it is 150 AU away from earth.
|
| https://voyager.jpl.nasa.gov/mission/status/
| dmead wrote:
| Is that number correct? Why not just launch at those starts
| at that point?
| lpghatguy wrote:
| For comparison, the nearest star to us is 268,770 AU away,
| or around 491 times further away. It would take quite a bit
| longer to get there!
| cgriswald wrote:
| That is incorrect. It's approximately at 150 AU[0]. For
| reference, that's about three times the distance of Pluto at
| aphelion. 547 AU is about 11 times the distance of Pluto at
| perihelion.
|
| [0] - https://voyager.jpl.nasa.gov/mission/status/
| skykooler wrote:
| 25 kilometers per pixel is incredible resolution for something
| that far away!
| biotinker wrote:
| That would be tremendous.
|
| Earth is 12700 km in diameter, so such an image would be a
| bit more than 500px across.
|
| Here is a picture of the Earth that is about 500px in
| diameter:
| https://cdn.mos.cms.futurecdn.net/3upZx2gxxLpW7MBbnKYQLH.jpg
| ckosidows wrote:
| 20 AU per year is a tremendous distance. Pluto is apparently
| right around 25 AU. Is this speed actually feasible even with
| solar sails?
|
| Big layman here. I only skimmed this link but this stood out to
| me.
| s1dev wrote:
| How do you propose to power a fleet of spacecraft at 550AU?
| Would you be able to acquire enough RTGs? What about DSN time
| for the downlink?
| pvarangot wrote:
| That webpage says a tech demo is due 2024, with launch in
| 2034 and the constellation would reach 550AU by 2064, so
| probably a lot of how this will work is still WIP.
| skissane wrote:
| The problem with dates like that is they are pure best
| wishes. They might have funding for a demo in 2024 -
| although it isn't even clear they've got that yet, it
| sounds like they may just have funding to develop their
| proposal further. Even assuming the tech demo is
| successful, it sounds like they don't even yet have a
| detailed costed proposal for a 2034 launch, and no idea how
| likely that it will actually get funded.
|
| Politicians and bureaucrats want immediate results, so a
| "launch now and see results in 30 years" mission - by which
| time many of the senior decision-makers will likely be dead
| - is going to be less attractive than competing missions
| offering results much sooner.
|
| If you go back through the history of space exploration, it
| is full of proposals that "by year X we will be doing Y!"
| which never came to pass, because the money never turned
| up.
| withinboredom wrote:
| > Politicians and bureaucrats want immediate results
|
| This makes me sad. The entire point of Government is to
| be an enterprise spanning multiple generations.
| PopeDotNinja wrote:
| And how would you get them out to, and stop at, 550 AU?
| Voyager 1 and 2 are nuclear powered with RTGs and they are
| respectively about 150 AU and 125 AU from the sun, and they
| are going really fast. The Voyager RTGs are also fairly
| depleted at this point. I'm guessing these spacecraft would
| need a faster, more efficient mode of propulsion, like a
| nuclear thruster or ion drive (or Epstein drive?!). One could
| also get a lot more fuel for the journey if the the probes
| didn't have to launch fully fueled from the Earth's surface.
| rini17 wrote:
| No need to stop at 550AU, the gravitational lens keeps
| working beyond that(theoretically all the way to infinity).
|
| As for how to get there, yes, innovative propulsion is
| required. My idea is that the probe would dive close to Sun
| and use solar energy (sail? electric propulsion?) to
| accelerate itself out to hundreds of km/s.
| 205guy wrote:
| I was wondering how fast myself and found this:
|
| https://voyager.jpl.nasa.gov/mission/status/
|
| Voyager-1 is the fastest at 38,000 mph (61000 km/h) with
| respect to the Sun, but currently about 90,000 mph (144000
| km/h) relative to earth (I guess this fluctuates annually).
| pas wrote:
| Sun slingshot, solar sail
|
| https://www.youtube.com/watch?v=NQFqDKRAROI
| pas wrote:
| the recommendation is RTG + rad-hardened battery, naturally
| the question of will there be enough RTGs is a perfectly
| valid one.
|
| https://arxiv.org/ftp/arxiv/papers/2002/2002.11871.pdf
|
| for downlink can't they launch a few extra sats that just sit
| around the Sun and form a big virtual dish (via baseline
| interferometry or what's that occult DSP magic called these
| days)?
| sandworm101 wrote:
| >>> Like this one, it's not understood how it can exist.
|
| I don't like that phrase. It suggests the possibility that this
| galaxy might not exist, that this could be observational error. I
| think it does exist. We understand exactly how it exists because
| we can observe it existing. The more accurate phrasing might be
| "it's not understood how it could have evolved so quickly".
| Avamander wrote:
| You can never sum up an entire paper in one sentence with all
| the nuance.
| newacct583 wrote:
| > that this could be observational error
|
| This could _absolutely_ be observation error. Messups in
| science happen all the time. You never take a single data point
| at face value without question, in any field. The spectrum
| might be polluted by another more distant object, the line
| matching might have been faked by some other intervening
| medium, the modelling for the lensing galaxy could be wrong. I
| agree, it looks good.
|
| But it could totally be a mistake.
| crusso wrote:
| Observational error is always a good speculation. It seems to
| be at the heart of most of these "impossible physics" stories.
|
| Remember not long ago when neutrinos were thought to have been
| observed moving faster than the speed of light? Cold fusion?
|
| Before people jump on the idea of re-evaluating Einstein's
| theories, it's always good to get more people looking at the
| data, independently verifying it, thinking about it. In a few
| months, it's likely that this blip will disappear like most
| others.
| CDSlice wrote:
| I think the phrase is fine since according to our best models
| of galaxy formation these galaxies should not be able to exist
| and yet they do. As such we don't understand how these galaxies
| can exist and need to do more research to come up with better
| models that can explain the existence of these galaxies.
| undersuit wrote:
| The article also states that a galaxy making stars at the rate
| of this new one shouldn't be a disc galaxy.
|
| >the theoretical models are wrong, or at least (and more
| likely) incomplete.
| natch wrote:
| I never understand why articles like this use present tense to
| talk about past events. It _was_ churning out a lot of new
| stars.. not is.
|
| I guess the "as seen from our current vantage point" is
| understood, but to me the needless emphasis of that perspective
| just muddies things, no?
|
| Anyone of you downvoters care to enlighten me?
| erulabs wrote:
| Strictly speaking our observations are not continuous. We
| pointed a large array at it and then the array probably went on
| to other work and looked elsewhere - so technically "was" is
| more correct, since we do not know what it "is" doing, rather
| only what it appeared to be doing.
|
| Either way it's a pretty uninteresting difference in tense.
| excalibur wrote:
| > Why is there a normal galaxy sitting at the edge of the
| universe?
|
| To facilitate the restaurant?
| cheschire wrote:
| One must ponder which came first, the universe or the
| restaurant.
| djsumdog wrote:
| We'd know if we only listened to the dolphins.
| KarimDaghari wrote:
| Don't forget about the ants!
| logotype wrote:
| Sounds like Vogon poetry.
| dddw wrote:
| Don't forget your towel!
| sidcool wrote:
| Terminus?
| disown wrote:
| Not that anyone cares what I say, but the Restaurant is on the
| other end of the universe.
| jahnu wrote:
| Give it a rest, Marvin
| AnimalMuppet wrote:
| Right! _This_ galaxy is there for the Big Bang Burger Bar.
| komali2 wrote:
| This is a reference to Douglas Adams' absurdist Sci Fi series,
| "Hitchhiker's Guide to the Galaxy," which is amazing and I
| recommend everyone read!
|
| https://www.goodreads.com/book/show/13.The_Ultimate_Hitchhik...
|
| (The first book is "Hitchhiker's Guide to the Galaxy," there
| are 5 books, one of which is titled "The Restaurant at the End
| of the Universe")
| jahnu wrote:
| Many people don't know that a radio series preceded the
| books. I find that the funniest version, personally.
| pmachinery wrote:
| > Many people don't know that a radio series preceded the
| books.
|
| Which, as you will already know but others may not, the
| brilliant TV series was adapted from (not the books):
|
| https://vimeo.com/338525482
|
| (Iconic music: _Journey of the Sorcerer_ by The Eagles.)
| webkike wrote:
| It bugs me that no one realizes that the "end" refers not to
| the "edge" but at the closing of the universe - the
| restaurant is in a frozen time bubble that can watch the
| universe end.
| outworlder wrote:
| Yes. The Restaurant is at the "end" in the time dimension,
| not the spatial dimension.
| dxdm wrote:
| People may realize but still decide to have some fun with
| this opportunity. :)
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