[HN Gopher] The Universe Is Expanding Faster Than It Should Be
___________________________________________________________________
The Universe Is Expanding Faster Than It Should Be
Author : samspenc
Score : 159 points
Date : 2021-12-18 06:28 UTC (16 hours ago)
(HTM) web link (www.nationalgeographic.com)
(TXT) w3m dump (www.nationalgeographic.com)
| ngcc_hk wrote:
| The key is just not observation. Theory has a lot of issues. For
| that problem mentioned in the article see this
| https://en.wikipedia.org/wiki/Cosmological_constant_problem . As
| a joke, whilst I agreed hard to deal with matters and energy, but
| even nothing you can model that is tough.
|
| I love cosmology and reading about it. Always exciting. But not
| because of the human part. More positively as said in the article
| ... a lot to be learnt, just do not use the word should you are
| ok I am ok.
| vermilingua wrote:
| Reading articles like this one always give me spooky vibes. Last
| Contact by Stephen Baxter [1] is a great way to get those vibes.
|
| [1]
| https://web.archive.org/web/20080725045740/http://www.solari...
| NateEag wrote:
| That's a lovely, heartbreaking story.
|
| Thank you for sharing it.
| guerrilla wrote:
| Well that was sad. A good metaphor for meditating on the fact
| that everyone will die too.
| ahyes123 wrote:
| humans and their ignorance never ceases to amaze me
| devenvdev wrote:
| We are having an impostor syndrome as humanity, which is a good
| thing.
|
| There was an obvious security hole sitting for years in the
| most common library in the most common programming language,
| and no one noticed... We fly to space and begin to do some mega
| projects, yet some of the most intelligent people in the world
| are facepalming themselves on a daily basis... We are not smart
| enough yet.
| NoMAD76 wrote:
| I have a tiny theory but since I'm not anywhere near this domain
| it could just look dumb. It implies the existence of a multiverse
| system, billions of universes like ours, like soap bubbles, all
| floating around each other. Well, if the gravity (and other
| forces, matter, energy, etc) works as intended then
| "objects/forces" closer to the universe edge gets pulled away by
| "objects/forces" from the other universe.
| marcyb5st wrote:
| Possible, but we would to be more or less in the center of the
| host universe since we see the same expansion rate in every
| direction. Statistically, that is unlikely.
|
| Also, we see far away clusters or galaxies receding faster than
| light away from us. This is impossible in a non expanding
| universe since faster than light travel _through_ spacetime is
| impossible but spacetime between two objects expanding faster
| than light is.
| me_me_mu_mu wrote:
| Same I feel like that is the only way. I can't wrap my head
| around the concept of infinity. There has to be a beginning and
| end. What the heck caused the Big Bang? Why?
| bencollier49 wrote:
| Well we can use this to execute a reductio ad absurdam on
| scientific materialism. Let us assume that the logic of cause
| and effect is all there is to the universe. Then the big bang
| must have had a cause, and that cause a cause in turn, and so
| on. That's obviously absurd, even if we point at time
| beginning with the big bang. Within any human reasoning,
| things do not appear _ex nihilo_.
|
| The alternative is that the thing on which our universe
| depends (being careful not to say 'caused' here) is beyond
| our ideas of cause and effect, and certainly passes human
| understanding.
| goldenkey wrote:
| What's far more reasonable is that the universe is a loop.
| The big bang is simply equivalent to the death of the
| universe: see conformal cyclic cosmology. Cause and effect
| cease to have priority over eachother. We are equally
| coupled to both faces of the boundary, the past and the
| future, which are actually two sides to the same coin, our
| origin and our destination.
| bencollier49 wrote:
| Is it? That's still wedded to cause and effect, it just
| moves the frame of reference outside the looped universe
| to ask what sustains it or why it exists.
| goldenkey wrote:
| It is no longer unidirectional wedding, it's
| bidirectional as QM would predict, which is commonly
| known as coupling. Once a circle is drawn, the starting
| point is no longer visible. All you have is the
| symmetries of the circle itself :-)
| mensetmanusman wrote:
| Maybe it's not possible since our minds exist in space-time.
| Before the big bang space-time didn't exist, so it's not sure
| what that means...
| podgaj wrote:
| >There has to be a beginning and end.
|
| Ha! No, there does not. Humans use create a hallucinated
| duality as a means of navigating a non-dual reality.
|
| Let me ask you; How long was the time before you were alive,
| and how long will the time be after you are dead?
|
| As Julian Barbour puts it: "We see from this that time has no
| role to play as an independent element of reality."
|
| http://www.platonia.com/nature_of_time_essay.pdf
|
| You should read his whole book, it's time to wake up!
| lloeki wrote:
| (caveat: IANA astrophysicist/cosmologist/whatever, I just
| like to wrap my head around things with some bits of logic)
|
| > Let me ask you; How long was the time before you were
| alive, and how long will the time be after you are dead?
|
| This is misleading as it posits that since there's a
| "before you" and an "after you", "you" are standing within
| some time continuum.
|
| > There has to be a beginning and end.
|
| Wrap your head around this: if there is a "beginning" and
| an "end" to our universe, both would define discrete stop
| points, thus there would be some way to say "before" or
| "after" these discrete points, and thus the universe sits
| inside something that has time.
|
| But then either this something of a container either has
| infinite time (which goes back to square one of things not
| having beginning and end) or has a beginning and end
| itself.
|
| But again, if this container has a discrete beginning and
| end then you can apply the same logic that you applied to
| our universe in the first place. So there's another
| container of the container, to which you can recursively
| apply the same logic (assuming logic itself somehow applies
| to this container). So if you want all these container
| things to have beginnings and ends, it implies there's an
| infinite set of nested containers.
|
| The alternative is that time exists _within_ our universe,
| but our universe doesn 't _sit_ within time. Thus
| "beginning" and "end" are not discrete points but concepts
| that only exist as limits (in the mathematical sense of
| "limit"): by travelling the arrow of time forward or
| backward you can only move closer and closer to either but
| never actually reach these because these points don't
| actually exist.
|
| Such a universe could be freestanding (as in: it's all
| there is), or it could have a container of sorts, and maybe
| even neighbour universes. But since time only exists within
| our universe, there could very well be no concept of time
| in the container (or other universes), or similar concepts
| but behaving entirely differently. In any case these (the
| container, the other universes) would be unbelievably
| incomprehensible to us.
|
| These concepts of unreachable zero, unreachable infinite,
| or unreachable value do exist in other areas: absolute zero
| is basically unreachable, reaching c velocity requires
| infinite energy+...
|
| + which creates other interesting conundrums such as a pair
| of photons travel at the same delta speed whether they go
| away or towards each other, or there's no "velocity = 0"
| either, or tachyonic vs baryonic realms.
| podgaj wrote:
| > This is misleading as it posits that since there's a
| "before you" and an "after you", "you" are standing
| within some time continuum.
|
| It was not misleading, it was a question. What person
| does not think they were born or that someone died?
|
| In my experience, time does not exist. It is an illusion.
| Have you read Barbour's book?
| gpderetta wrote:
| You think that there has to be a beginning, yet are looking
| for something that has caused the big bang. Isn't that
| inconsistent? Why cant the Big bang be the beginning?
| Otherwise you might next be looking for what caused whatever
| caused the big bang
| ErikVandeWater wrote:
| The God's Daddy effect: Keep asking for progressively
| deeper causes until you find one you like.
| podgaj wrote:
| And this is why I feel science is a religion, both ask
| questions which can never be finally resolved by
| humanity's finite brains.
| pixl97 wrote:
| Why does that make science a religion? Part of science is
| defining what is definable and what is not.
| NoMAD76 wrote:
| There are things (trivial or not) that we can't know or
| explain with our limited knowledge. But reality is always
| beyond our wildest dreams.
| Twisol wrote:
| Not an uncommon lay theory, actually. Unfortunately, I recall
| reading somewhere [0] that, experimentally, the effects of
| gravity are consistent with it propagating in only three
| spatial dimensions. If it could leak out of (or into) "our"
| universe along an auxiliary dimension, gravity's effects would
| be weaker than we observe.
|
| Not to say it couldn't work some other way -- I'm not a
| physicist either! But (as these things always seem to end up)
| it would have to be a little more complicated. (Part of the
| "rolled-up dimensions" side of string theory is that the extra
| dimensions can't meaningfully attenuate the effects of
| gravity.)
|
| [0] I don't think this is the one I read, but it rings the
| right bells: https://www.sciencealert.com/gravitational-waves-
| have-ruled-...
| ALittleLight wrote:
| If our gravity is restricted to three dimensions does that
| imply anything about gravity in other universes?
| Twisol wrote:
| By the nature of the question, no.
| NoMAD76 wrote:
| I'm not thinking of other dimensions, a multiverse could be
| something like our body with millions and millions of cells
| that are interacting. Somehow I just cannot stand with this
| "universe is infinite" when for sure it has a border but we
| will never be able to go past that border to know what's
| beyond.
| newsbinator wrote:
| > for sure it has a border
|
| There's no reason to believe our "common sense" or
| "intuitive understanding" has any relevance to how the
| universe is or isn't.
|
| According to an ant's common sense humans for sure have
| antennas somewhere on their bodies, even if not visible to
| an ant.
| danparsonson wrote:
| Further to @Twisol's answer, consider the surface of a
| sphere - it is two-dimensional (if you're confined to the
| surface, you can only move in two directions) and bounded
| in size, but it has no boundary as such; if you started
| walking around on a sphere, you could keep walking forever
| without hitting a wall.
|
| Now imagine there are two such spheres near to each other.
| Two beings whose physical laws and interactions were
| entirely confined to their respective surfaces would be
| unaware of each other and unable to influence each other in
| any way - gravity for example is only able to travel around
| the surface of the sphere, not into whatever 'space' lies
| in between. The surface of each sphere is its own universe.
| Twisol wrote:
| Sorry, when I say "dimension" I mean another continuous
| spatial direction that you could move along, not the
| "another place" understanding of the word. Flatland [0] is
| a classic for trying to get in the right headspace.
|
| [0] http://www.geom.uiuc.edu/~banchoff/Flatland/
|
| Also, not having a border is not the same as being
| infinite. Zogg from Betelgeuse started a great series on
| the topic [1], but disappeared after two episodes. I highly
| recommend it! But, long story short, it's entirely possible
| to have a finite universe that, nonetheless, has no edge.
| Go far enough in one direction and you might end up back
| where you started.
|
| [1] https://www.youtube.com/watch?v=_k3_B9Eq7eM
|
| Assuming there's a physical edge to our universe, there's
| still the problem of the "observable universe" -- there's a
| lot more of the universe that we will simply never be able
| to see or reach, because it's moving away from us too
| quickly. That defines another kind of edge, one that's much
| "closer". Entities beyond our observable universe can't
| affect us gravitationally; it takes time for the effects of
| gravity to propagate from one point to another, as
| "gravitational waves", and the universe is inflating too
| quickly for those to reach us.
|
| You might say that things further away from us, but within
| the observable universe, might be affected by things
| beyond, because they're "closer" to it than we are. I think
| that's correct, but by the same token, I think the
| information about those effects would never reach us in
| finite time.
|
| That's why I was thinking in terms of extra spatial
| dimensions. You might have a bunch of matter "nearby" but
| totally inaccessible to you, because we're incapable of
| moving along the extra axis. But that gets back to the
| research I linked.
| tempodox wrote:
| > It implies the existence of a multiverse system
|
| _entia non sunt multiplicanda praeter necessitatem._
|
| Thou shalt not multiply entities beyond necessity.
| siddboots wrote:
| While we are airing our pet dumb theories, is there any way
| that a universe with a cyclic geometry, like the geometry of a
| sphere, could explain the accelerating universe with just
| gravitation? Could the attraction of the matter in our universe
| from "the other side of the world" be made to explain the
| observed acceleration?
| xwolfi wrote:
| Waho impressive. This theory you invented sounds so much like
| all the popsci articles you see in ads like "Scientists dont
| want you to know it, but this guy think we live in a
| multiverse" kind of things.
|
| Are you the one who started this whole movement ? Or in fact
| you just rehash the same bullcrap ? Closer to the universe edge
| he says, not defining the universe or an edge...
| IAmGraydon wrote:
| And you've acted like a petulant child while adding nothing.
| Well done. This is not the place to air your emotional
| shortcomings.
| TekMol wrote:
| Could we say that we simply don't know what is going on in the
| universe?
|
| We (well, Einstein & Co. I was not involved.) made models about
| how the universe works. Then when looking at the broader scope,
| we noticed that the models differ from reality. So instead of
| saying the models are wrong, we invented "dark matter". Some
| unmeasurable type of matter that is responsible for the
| difference of how reality behaves in contrast to our models. And
| then we invented dark energy.
|
| Now to make our models "work" we have to assume 85% of the matter
| in the universe is made of dark matter. And 68% of energy in the
| universe is made from dark energy.
|
| How about just saying that our models do not work on large
| scales?
|
| I have a lot more arguments that prove dark matter is a hoax. Let
| me write them down in dark text (an unmeasurable form of text).
| Here we go:
| Frenchgeek wrote:
| The models are correct: We're just living in the wrong
| universe.
| ErikVandeWater wrote:
| Is this a quote? It's a good one!
| mkl wrote:
| Dark matter and dark energy _are_ models, "made up" to try and
| model reality's differences from general relativity. General
| relativity was "made up" when the Newtonian model was found to
| differ from reality. The Newtonian model was "made up" to
| explain the Copernican model, which was "made up" when the
| Ptolemaic model was found to differ from reality.
|
| _All_ models are wrong. Some models are useful. Everyone knows
| that the models aren 't perfectly accurate; that's what models
| do: model. We literally say "this model is wrong" all the time.
| naveen99 wrote:
| There is a difference between models like Newton and
| Einstein, and models like dark energy and dark matter. Do
| dark matter and dark energy make any falsifiable predictions
| ?
| shusaku wrote:
| Sabine Hossenfelder explains: https://youtu.be/GatiekRziok
| devenvdev wrote:
| I liked her videos a lot, until this one:
| https://youtu.be/zpU_e3jh_FY
|
| She should stick to physics, not philosophy. Proving free
| will with physics is ignorant and arrogant. The hard problem
| of consciousness is much deeper than "in our models, we see
| that there is no randomness anywhere, ergo no free will."
| theduder99 wrote:
| no, they can't. the dark matter debacle is the tip of the
| iceberg. they feel compelled to produce theories that do not
| involve supernatural or divine concepts.
| h2odragon wrote:
| One of the early patch sets had a much higher speed of light; but
| it was eventually fixed.
|
| There's debate about further revising it in a future release; but
| no consensus on if it needs to be faster or slower. People kept
| hard coding it as a constant so the legacy issues would make the
| tachyon situation look simple.
|
| More seriously: when the Universe was smaller and denser could
| the speed of light been higher, analogous to speed of sound in
| higher pressure and density materials?
| sp332 wrote:
| It's still an exotic model, but if there's an extra dimension
| that light can fit into - even a tiny loop that it just spirals
| around as it propagates - then it's possible that at higher
| energy densities, it spirals at a shallower angle. That would
| make it appear to propagate through the three normal spatial
| dimensions faster even if it has the same speed across all four
| dimensions.
|
| Joao Magueijo wrote an approachable book on this called "Faster
| than the Speed of Light: The Story of a Scientific
| Speculation".
| jfengel wrote:
| Density doesn't figure into it. It's about space itself, rather
| than the rate at which light travels. Light in a vacuum moves
| at that rate, which is a straightforward constant that figures
| into several other things.
|
| The space itself does change and you could try to redefine the
| formulas in terms of a changing speed of light, but it just
| makes it harder. The space metric fits very neatly into the
| Einstein field equations, and the expanding universe pops out
| of that directly. The acceleration doesn't, but it's a very
| simple tweak to make it do so. (Einstein had originally added
| that tweak to make the universe not expand, but then expansion
| was discovered.)
|
| If you change the speed of light you throw off chemistry, and
| all of the observations of distant galaxies show that chemistry
| still works. So a changing speed of light is unlikely.
| uh_uh wrote:
| > The space metric fits very neatly into the Einstein field
| equations, and the expanding universe pops out of that
| directly.
|
| Is there a simple way to understand why? I don't have an
| understanding of the relevant math. It's a bit hard for me to
| imagine how we get from the axiom of "speed of light is
| constant in every reference frame" to an expanding universe.
| Unless there are other axioms used for this.
| adgjlsfhk1 wrote:
| the other axiom you need is that gravity and acceleration
| are the same. the speed of light being constant only gets
| you special relativity.
| raattgift wrote:
| The equivalence is between _uniform_ acceleration and a
| _uniform_ gravitational field. Breaking the uniformity,
| which the universe does for us whether we like it or not,
| has consequences.
|
| Real gravitational sources aren't uniform (they tend
| towards spherical) and come equipped with a tidal field
| with a potential and gradient. This is intrinsically
| gravitational, not accelerational.
|
| The non-uniform distribution of matter (including
| radiation) in the universe also matters.
|
| You can rest an accelerometer on the surface of the Earth
| and it will report ~ 1 g (upwards) for many -- even
| billions of -- years, with no ill effect.
|
| How long can you accelerate a rocket containing an
| identical accelerometer? Consider fuel, and crashing into
| matter (up to distant starlight and the cosmic microwave
| radiation) after a few months (of ship time) of the
| accelerometer indicating ~ 1 g (forwards).
|
| You don't get strong twin-paradox effects involving the
| Moon-walking astronauts, or long-mission robot probes on
| the Moon or Mars, even though the local equivalent of "g"
| is considerably lower than that here on Earth. By
| comparison, if you and and two roughly identical
| astronauts were to undergo hundreds of days (or Martian
| sols, or a few lunar days) ship's time in spacecraft
| doing a round-trip under constant accelerations of ~ 1g,
| 0.6g, and 0.17g respectively, the lesser-accelerated
| "twins" would be visibly older than you at the end of
| your respective round-trip journeys.
| jfengel wrote:
| It comes out of extending that to an accelerating reference
| frame, which gives you a curved spacetime. That doesn't
| stay stable by itself. It has to either expand or contract,
| depending on how much energy is in it. (Mass is a form of
| energy, and so you get gravity.)
|
| It's a bit like noticing that objects can't float. They can
| either fly away or fall but they can't just sit there. It's
| not exactly the same thing, since we're talking about the
| spacetime itself rather than gravity as separate from the
| objects, but the analogy mostly works.
| contravariant wrote:
| The speed of light is just a constant for converting units of
| time into distances, even if the speed of light were to change
| we'd probably choose to just change the units of distance to
| forcibly keep it constant.
| wavefunction wrote:
| The speed of light differs depending on the medium it's
| transiting already though. I've wondered in the past if in
| the primordial universe time or space were different than
| what we've observed "now." It seems like they could both
| compress or expand like other physical characteristics of
| reality.
| contravariant wrote:
| There's two different meanings for the phrase 'the speed of
| light'. One is the conversion constant I mentioned (which
| is currently used to define the metre in terms of time and
| is therefore constant by definition).
|
| The other is the speed at which light travels (through a
| medium).
| IsThisYou wrote:
| As far as I understand current physics, the solution seems
| simple: Just through some more "dark" matter in there, and the
| standard model is save again.
| Khaine wrote:
| PBS Space Time has an excellent set of videos on this, including
| this one https://www.youtube.com/watch?v=72cM_E6bsOs
| known wrote:
| https://en.wikipedia.org/wiki/Timeline_of_the_formation_of_t...
| looks strange and twisted turns
| MrYellowP wrote:
| "Than it should be."
|
| Am I the only one who thinks that the wording roots in Hubris?
|
| And then, at the same time, I read "are flying apart" as if
| that's how it actually works. It doesn't. Wording it that way is
| misleading.
|
| I never read National Geographic, but I thought it's better than
| this.
| bumby wrote:
| From the article:
|
| "faster than our best models of the cosmos predict it should."
|
| It's more an implied statement about the current models than
| the limits of human of human knowledge.
| marcyb5st wrote:
| The target audience of National Geographic are people with some
| science background but not researchers/experts. It a
| publication for the masses and so they have to tone down the
| technical lingo. For physics I read Nature, but for every other
| topic that might interest me but is above my knowledge level
| National Geographic works.
| throwaway984393 wrote:
| Strange title. The universe is expanding exactly as fast as it
| should be... It's the universe. We just misunderstood the
| expansion rate.
| notfed wrote:
| It's also only an 8% difference...
| tdfirth wrote:
| This is probably really dumb but I'm interested to hear people's
| reactions to yet another amateur dark energy theory.
|
| Could the observation that the universe is expanding actually be
| the result of a sort of gravitational lensing and not the result
| of space expanding or bodies moving through space?
|
| My rough line of thinking is: - We believe that
| gravity has a warping effect on spacetime. - We believe
| that this warping can distort light. - When we observe
| light from distant galaxies, it must first exit the gravity well
| of the source, traverse the universe and then make its way down
| into our gravity well. - Therefore, the light must have
| been subject to some distortion. It traversed two regions of
| 'stretched' space time and so became 'stretched' itself. -
| This 'stretching' is interpreted as redshift and is
| indistinguishable from if the light source had just been moving
| away quickly.
|
| Naively, I would have thought this interpretation explains a
| couple of things quite well: - Light would be
| redshifted in every direction as every bright and distant source
| (i.e. galaxies) resides in a large gravity well. - It would
| explain a lack of redshift in nearby objects as we sit in a
| broadly similar part of the Milky Way's gravity well. As such the
| relative lensing effect would not be apparent.
|
| Anyway, I obviously have no idea what I'm talking about and
| someone will have thought of this before - however I'm interested
| to know why the theory doesn't work.
|
| Most likely I don't really understand gravitational lensing and
| it wouldn't distort the wavelength of light as I suggested.
| Alternatively, perhaps someone has done the maths and the impact
| of any such effect does not align with observations.
|
| edit: formatting
| sigmoid10 wrote:
| Light is indeed redshifted as it climbs through a gravitational
| well, but it is also blueshifted again when it travels down the
| gravitational well of our own galaxy. For distant galaxies, the
| total effect is negligible compared to the doppler redshift due
| to their velocity. Also, when you look in any direction in the
| sky, the redshift increases with distance, irrespective of
| galaxy or cluster masses. So the further they are away, the
| faster they are receding from us. This is also exactly what the
| Hubble constant measures.
| arcastroe wrote:
| > the further [galaxies] are away, the faster they are
| receding from us
|
| I've heard this repeated many times as a surprising
| discovery. Why is this surprising? Let's say you have some
| number of objects moving at different speeds (relative to
| Earth). After enough time, the objects that move fastest
| should be farthest away, by the simple definition of speed!
|
| What am I missing?
| kadoban wrote:
| That seems like it would itself need an explanation. Why
| would the initial conditions be objects starting at the
| ~same place but moving with random velocity?
|
| The CMB would also need explanation and I'm thinking the
| curves of galaxy speeds wouldn't match unless you tweak the
| initial speeds way too much, but I'm not sure how to
| formulate that right.
| luma wrote:
| Substitute "speed" (really, "velocity") with "acceleration"
| and your statement is true. So, you're pretty close in your
| reasoning - if everything is accelerating at the same rate,
| then things further away from us should be moving away from
| us faster.
|
| So here's the problem: maintaining a constant velocity
| requires no outside force, but acceleration does. So, we're
| seeing everything accelerate away from us.... but why?
| Where does that force come from?
| vlovich123 wrote:
| Amateur so I'm sure this is a stupid idea. What if
| they're not accelerating away from us but space time
| itself is growing (because of the original Big Bang) and
| taking everything else along for the ride on top of the
| original exploding outward, resulting in acceleration of
| acceleration? Probably it's growth rate would be
| decreasing which might be observable in the derivative of
| the derivative of acceleration? If that were happening, I
| wonder if virtual particles have some link to that
| process.
|
| My reasoning here is that everything is accelerating from
| everything else since our position in the galaxy isn't
| particularly special right? Then the only way for that
| really to be true would be for space time itself to be
| growing.
| sigmoid10 wrote:
| That's sort of what's happening. If you imagine space as
| a rubber sheet with the galaxies pinned to certain
| places, something is pulling the sheet apart, making it
| seem like the galaxies are accelerating away from each
| other. We know the math behind this mechanism thanks to
| general relativity (it only needs a certain energy
| density for empty space), but we don't know what causes
| it. So we just call it "dark energy." Without it, the
| original expansion of the universe caused by the big bang
| should be slowing down due to gravity. Dark energy causes
| it to accelerate instead.
| arcastroe wrote:
| Ah thank you :).
|
| One more question: How do we know that each galaxy is
| actually accelerating and not moving at a constant speed?
|
| I'm seeing some circular logic. As I understand it, we
| think they are accelerating _because_ we see that
| galaxies that are farther away are moving faster away
| from us.
|
| But we just agreed that we expect to see this same
| observation even if each individual galaxy maintains
| constant velocity. Apologies. It's a bit late. I'm sorry
| if I'm missing something incredibly obvious.
| adgjlsfhk1 wrote:
| between 1970 and now, if you look at the same far away
| galaxies, they are receding faster now than they were in
| 1970.
| arcastroe wrote:
| ^_^ thank you
| koheripbal wrote:
| Wait... Is this correct? Do you have a source? This is
| the first that I've heard of this being directly
| measurable.
| donohoe wrote:
| Dumb question: is it actually accelerating or are we
| slowing down?
| ByteJockey wrote:
| Possibly dumb answer: If everything else was moving at a
| constant velocity and we were slowing down, wouldn't the
| things on the other side of us appear to be accelerating
| towards us?
|
| My understanding is that basically everything is moving
| away from us (presumably our reputation precedes us).
| cecilpl2 wrote:
| They are all accelerating away from us, in every
| direction.
| albert_e wrote:
| do you mean slowing down in how we experience time?
| tdfirth wrote:
| Cool, thanks for the reply! I hadn't considered the
| blueshifting part, that makes a lot of sense though.
|
| I also hadn't heard of Hubble's constant, which I am now
| learning about :). Very mysterious indeed.
| instakill wrote:
| In line with your (possibly misguided) thinking, I too have
| some amateur thoughts that are probably equally wrong:
| https://pawel.fyi/post/red-shift
| d--b wrote:
| So our gravitation models weren't working very well, so we
| thought maybe dark matter. Then that wasn't working very well
| either, so we thought maybe dark energy? And now this is showing
| a lot of shortcomings too? I know nothing of astro physics, but I
| find it odd that a majority of astro physicians think of dark
| energy as a near certainty when all mainstream articles are about
| contradicting its implications.
| wereHamster wrote:
| Which mainstream articles are you referring to?
| dilyevsky wrote:
| Expansion of the universe (dark energy) has nothing to do with
| the dark mater. At least not according to any models known
| today. We know galaxies are racing away faster because we can
| see it (from red shift) so that part is certain. Why they are
| moving away is not certain hence "dark" energy
| ErikVandeWater wrote:
| Peripheral question: Without dark matter, would there be more
| red shift?
| raattgift wrote:
| This is an excellent question.
|
| Light exiting from stars deep in a galaxy (which is in turn
| deep in a galaxy cluster) is subject to gravitational
| redshift. The greater the mass of the galaxy and cluster,
| the greater the redshift.
|
| If we add transparent, non-radiating mass to a galaxy and
| its cluster, the mean redshift of starlight from the galaxy
| will redshift, and we'll see the result on various
| absorption and emission lines in the spectrum.
|
| Note, we do not need _dark matter_ for this; increasing the
| central mass of a galaxy cluster will do the trick too. We
| can do this by adding more stars, or by adding black holes,
| or by making a central black hole more massive. All of this
| will cause an increase in gravitational redshift.
|
| However, adding more central mass to galaxies will be
| reflected in the trajectories of clouds of gas and
| collections of stars within the galaxies; likewise, adding
| more concentrated mass to a galaxy cluster will alter the
| trajectory of galaxies within it. In general, these objects
| will have faster orbits -- fast enough that a non-
| gravitational redshift will be apparent in the arrangement
| of spectral lines. (We would also need to figure out how to
| keep any central masses from being extremely bright
| anywhere in the electromagnetic spectrum, and how to keep
| them from eclipsing parts of their home galaxies and
| clusters that are behind them from our perspective.)
|
| If we instead redistribute our increase in galactic mass
| into a gaseous halo-like structure that extends well beyond
| the outer stars, we get the increased gravitational
| redshift without requiring stars and gas to travel faster
| to avoid falling inwards. The halo still has to be
| electromagnetically quiet, and non-eclipsing, or we would
| see it. (This all applies to clusters, too).
|
| Stepping away from the "dark matter puzzle" of the spectral
| lines of molecular and atomic gas clouds in galaxies and
| clusters of them, we can then look at another aspect of
| your question.
|
| Galaxy clusters, from their point of view, are just
| floating passively in space.
|
| The expansion of the universe follows a model wherein if we
| treat the astrophysical content of galaxies and clusters as
| sensitive accelerometers that in aggregate show off the
| peculiar accelerations experienced by these large scale
| objects, there is no evidence that these accelerometers
| should report a non-zero magnitude or point in any
| particular direction. That is, galaxies and galaxy clusters
| are themselves _in free fall_ , and we can see this because
| of lines of evidence including expansion-direction-and-
| magnitude squashings of
| https://en.wikipedia.org/wiki/Light_echo lines turn out to
| be null, likewise there are no radio-loud edge shocks for
| galaxies that appear to be accelerating away from us, there
| are no shape distortions of the most highly "accelerated"
| distant galaxies, and so forth. There is simply a spectral
| redshift.
|
| So, for an isolated galaxy the spectrum it emits depends on
| a combination of its starshine, any noise from close to its
| central black hole(s), the noise from any thick gas clouds
| undergoing gravitational collapse, and the absorption and
| reemission of diffuse gas clouds heated by these types of
| emission and absorption-and-reemission sources _and_ the
| distribution of dark matter within and around the galaxy.
| The more dark matter, the more redshifted the galaxy 's
| spectral lines will be.
|
| Preserving the Copernican Principle, immersing a set of
| such isolated galaxies into an expanding cosmos leads to
| the inhabitants of each galaxy observing a cosmological
| redshift on the gravitatonally-redshifted spectrum emitted
| by other sufficiently distant galaxies. The gravitational-
| redshift depends on the mass of the galaxies including
| their dark matter. The cosmological redshift only depends
| on a light-travel distance from the galaxy, no matter how
| light or how massive that galaxy (or its parent cluster)
| is.
|
| Next, if we have an arrangement b-->F-->U, where b is a
| background galaxy, F is a foreground galaxy, and U is an
| observer, we will that the light from b is _cosmologically
| redshifted_ before it interacts with the molecular and
| atomic gas clouds in F, causing a spreading of absorption
| and reemission lines rather than a thickening. For the very
| obvious lines from neutral atomic hydrogen, we see this as
| the https://en.wikipedia.org/wiki/Lyman-alpha_forest which
| is an important tool in astrophysics and in checking the
| soundness of our theory of gravitation.
|
| We would get a Lya-forest structure even in the absence of
| dark matter in b or F or anywhere else; only the fine
| strucutre would differ. Indeed, we could substitute a
| diffuse static cloud of atomic hydrogen for F and still see
| a "forest" structure minus small contributions from the
| starshine in F and the orbital motions of the gas in F
| around some central mass. The deep infrared noise from F in
| that case, however, would not be gravitationally
| redshifted.
|
| Finally the answer to your question: the cosmological
| redshift does not in general depend on the "late"
| distribution of dark matter. (Late as in at least millions
| of years after the hot big bang). But the gravitational
| redshift on light emitted by stars and galaxies _does_
| depend on dark matter and in general the starshine is
| reddened by it. The reddening is because of the additional
| mass of the dark-matter-containing structures, and also
| because the distribution of the dark matter into halos
| allows for slower orbits of stars and gas clouds, thus
| suppressing their non-gravitational non-cosmological
| redshifts. (In an edge-on spiral galaxy without dark matter
| we would see a greater difference in the blueshift of one
| extreme tip of the thin disk and the redshift of the
| opposite extreme tip of the thin disk, compared to the same
| spiral galaxy with dark matter; the light-and-radio from
| the central bulge would be less redshifted in the absence
| of dark matter).
|
| So, no, the cosmological redshift does not depend on dark
| matter. The gravitational redshift on light from galaxies,
| however, does. So does the non-gravitational, non-
| cosmological redshift on gas clouds whirling around the
| edges of rotating (e.g. spiral) galaxies, or rising and
| sinking on radial orbits within elliptical galaxies.
| Keysh wrote:
| One important caveat to all this is that the
| gravitational redshift for a galaxy or galaxy cluster is
| an _incredibly tiny_ effect. For example, the mean
| gravitational redshift for massive galaxy clusters has
| been measured (e.g., link below), and has a value of ~ 10
| or 15 km /s. This can be compared with the typical
| motions of galaxies within a cluster (dispersions of ~
| 1000 km/s) and the cosmological redshift of the clusters
| (for the sample in the paper I linked to, it's equivalent
| to an average Doppler shift of ~ 50,000 km/s).
|
| In order to make that measurement, the authors had to
| combine redshift measurements for ~ 20,000 galaxies from
| ~ 2,500 different clusters; as they note, it's impossible
| to detect the effect for just a single cluster: "... even
| assuming that every galaxy in a cluster could be
| spectroscopically measured, there are simply too few
| galaxies to allow the statistical detection of a non-zero
| gravitational redshift."
|
| So while it's technically true that adding dark matter to
| a galaxy would increase its gravitational redshift and
| thus its total observed redshift, this effect is
| immeasurably small.
|
| Mpetha et al. (2021), "Gravitational redshifting of
| galaxies in the SPIDERS cluster catalogue"
| https://arxiv.org/abs/2102.11156
| raattgift wrote:
| I can only reply to your "impossible to detect" with
| respect to _clusters_ with the "technically challenging
| but apparently real and prospects for better measurements
| and extension to larger scales is promising" at the end
| of Kaiser's 2018 slide deck https://chalonge-
| devega.fr/Kaiser_29mars2018.pdf which I do not think is
| contradicted by the (interesting, thank you!) Mpetha et
| al (2021) paper, which cites at least three of Kaiser's
| earlier publications.
|
| Broadhurst & Scannapieco (2000)
| https://iopscience.iop.org/article/10.1086/312630 is also
| relevant here, as it distinguishes between X-Ray studies
| and optical ones (SPIDERS being an example of the latter)
| pointedly at SS4.2.
|
| I do not disagree that ~ 10-20 km/s is small, but it's
| the little things that cause "tension" headaches, isn't
| it?
| Keysh wrote:
| Kaiser's presentation doesn't suggest you can do the
| measurement for individual clusters; the example analysis
| is from Wojtak et al. (2011), which is similar to Mpetha
| et al. in using thousands of galaxies and thousands of
| clusters.
|
| The Broadhurst & Scannapieco discussion about X-ray
| studies is interesting and potentially promising, but no
| one seems to have tried doing for real.
| Keysh wrote:
| _The reddening is because of the additional mass of the
| dark-matter-containing structures, and also because the
| distribution of the dark matter into halos allows for
| slower orbits of stars and gas clouds, thus suppressing
| their non-gravitational non-cosmological redshifts. (In
| an edge-on spiral galaxy without dark matter we would see
| a greater difference in the blueshift of one extreme tip
| of the thin disk and the redshift of the opposite extreme
| tip of the thin disk, compared to the same spiral galaxy
| with dark matter; the light-and-radio from the central
| bulge would be less redshifted in the absence of dark
| matter)._
|
| This is the exact opposite of the truth. An edge-on
| spiral galaxy without dark matter would have _less
| extreme_ observed rotation velocities (comparing the
| blueshifted and redshifted sides of the disk), because
| only the visible mass (stars and gas) is relevant. But in
| practice we see higher rotation velocities (greater
| difference between blueshifted and redshifted sides) than
| can be explained by just the visible mass, and so we have
| to postulate extra mass in the form of "dark matter" in
| the galaxy.
|
| (Dark matter halos are not just dark matter outside the
| visible galaxy, they extend all the way to the centers of
| galaxies, and in fact become _denser_ the closer to the
| galaxy center you get. Of course, the visible matter also
| becomes denser the closer to the center you get, and
| usually faster than the dark matter does, so the central
| regions of massive galaxies are dominated by the visible
| matter. But there 's still dark matter there, and in some
| dwarf galaxies, the dark matter even in the central
| regions.)
| raattgift wrote:
| You're quite right about the non-parenthetical, I failed
| to re-read what I wrote in an editing pass. It should of
| course be "with" instead of "without", or alternatively
| change the "greater" to "lesser". I am grateful for the
| correction.
|
| As to your parenthetical, cuspiness is not really
| relevant to the scale of the points raised in the bulk of
| my comment, and it is not clear to me why you raise the
| DM density profile here.
| Keysh wrote:
| It wasn't clear to my why you said what you did. (Good to
| know it was just an editing failure.) Sometimes people
| get confused and think "dark matter halo" means all the
| dark matter is outside the main body of the galaxy, so I
| was pointing out that this isn't the case.
| mensetmanusman wrote:
| Does thermodynamics apply at cosmological length-scales
| when/where spacetime is being created (with its
| accompanying non-zero energy)?
| tsimionescu wrote:
| Note that the red shift data has been coming into question
| lately, as it relies on some assumptions of the uniformity of
| the universe beyond the scale of galaxy super clusters, which
| doesn't seem like a safe assumption anymore as far as I
| understand.
| Twisol wrote:
| Yes; the "dark" in these terms reflects our lack of
| understanding about both topics, not that they share some
| "dark" aspect in common. They're names for holes in our
| models, not for entities predicted by them.
| denton-scratch wrote:
| They're both "dark" because neither interacts with
| electromagnetic radiation.
|
| I share the opinion that they're names for holes, not
| entities; but I'm not qualified to defend that opinion.
| 6nf wrote:
| That's true but even more than that, we're not really
| sure dark matter is actual particles at all. Modified
| gravity for example is one alternative explanation that
| don't require a new particle or field.
| jquery wrote:
| I don't know about dark energy, but dark matter isn't
| called such because it's a "hole in our models". The theory
| is it doesn't react electromagnetically with other matter.
| So it's quite literally, "dark" matter.
| Twisol wrote:
| Is that theory or observation? My understanding is that
| we know it doesn't react electromagnetically with other
| matter because we (failed to) observe that behavior, not
| because we expected it to behave that way _a priori_.
|
| If modified Newtonian (MOND) theories won out, the theory
| would explain this observation by saying that there was
| no matter there to begin with. If neutrino theories won
| out, the theory would explain this observation by saying
| that dark matter is electromagnetically neutral. But
| those are two entirely different theories, trying to
| explain the same observations, and trying to fill the
| hole in our currently accepted models in different ways.
|
| EDIT: Per a child comment, you might mean "theory" as
| "idea", as in "the [idea] is that it doesn't react
| electromagnetically with other matter." In which case,
| yes!
| kzrdude wrote:
| There seems to be a lot of evidence for dark matter,
| that's how I understand it as an outsider. What it means
| is that there is a lot of consistency in observations,
| things add up, to the dark matter theory.
|
| I usually agree with your understanding of dark
| matter/dark energy as placeholders for missing knowledge.
| Twisol wrote:
| Ah; I think we might only be disagreeing on terminology
| at this point, then. A physical "theory" is a coherent
| model that makes testable predictions in its own right,
| as in the "theory of gravitation". A hypothesis is an
| explanatory idea, like dark matter.
|
| There's definitely lots of evidence for dark matter,
| yes~!
| usgroup wrote:
| a priori is the wrong term because our physical theories
| are not a priori.
|
| Dark matter has lots of reasons to be assumed but a
| common one is that when we try to explain the
| gravitational effects of galaxies based on a
| quantification of observable matter, there is a huge
| shortfall. That creates a space for something with a
| gravitational effect that is unobservable otherwise.
|
| That many of the objects of our physics are theory laden
| is true, but that they are therefore "unreal" or merely
| an artefact of theory does not necessarily follow.
| chrisdinn wrote:
| Just to be pedantic, I'll point out that's literally
| "transparent" matter and we use the term "dark" which is
| really more appropriate for something that absorbs EM
| radiation because it also implies the mystery of the
| holes in our knowledge. English is great.
| spaetzleesser wrote:
| "I know nothing of astro physics,l
|
| Before criticizing physicists you should keep this in mind.
| notfed wrote:
| No...
|
| We observe with telescopes that the universe is expanding. We
| don't know why, so we call the mysterious force dark energy.
| It's just a name for something that we are objectively
| observing.
|
| (Also this has nothing to do with dark matter, that unrelated
| to this discussion and you're just getting the names
| conflated.)
| arbitrage wrote:
| dark matter is pretty solid of an idea. it's been around for
| over a hundred years at this point. it isn't a band-aide fix
| for wonky math in an inaccurate theory. the foundations of the
| concept of dark matter are fairly reasonable.
| Maursault wrote:
| > dark matter is pretty solid of an idea
|
| Not really. It is a hypothesized form of matter. There are
| competing hypotheses. Dark matter came to popularity in order
| to explain observations of galaxy rotation curves in the late
| 1930s. But these galaxies were observed in isolation, giving
| the illusion of gravitational isolation, which doesn't exist.
| Once accounting for the tidal effects of nearby galaxies, [1]
| dark matter becomes unnecessary to explain galaxy rotation
| curves, all that is needed is Newtonian physics. But in the
| period since dark matter was hypothesized, other observations
| that could not be readily explained were lumped into dark
| matter. Dark matter is nothing if not an amalgamation of
| unexplainable observations. So while dark matter is
| unnecessary to explain galaxy rotation curves, it is still
| somehow useful to explain unrelated observations.
|
| > it isn't a band-aide fix
|
| It really sort of seems like that: can't explain an
| observation, so invent something out of thin air to explain
| it. Honestly, an hypothesis that elves are causing the
| observations has just as much validity (or lack thereof).
| Now, elves have not been proven to be the cause of these
| unexplained observations, but neither has dark matter.
|
| > the foundations of the concept of dark matter are fairly
| reasonable.
|
| See above concerning galaxy rotation curves and endnote.
| Please understand it is quite possible that dark matter does
| not exist. The reason why it seems like accepted science has
| to do with scientific paradigms. Once a notion becomes an
| accepted part of the science paradigm, it takes years if not
| decades after disproving it beyond all doubt to dislodge it
| from the paradigm. If science has a problem, it is paradigms.
|
| [1] https://www.youtube.com/watch?v=PL0ewiwqoTw&t=6m11s
| Keysh wrote:
| The observations in the 1930s you allude to were of the
| motions of galaxies in _galaxy clusters_. The rotation-
| curve measurements for individual galaxies started in the
| 1970s and really took off in the 1980s.
|
| "Tidal effects" are a non-starter, and do nothing to
| explain galaxy rotation curves. Nor do they explain the
| excess motions of individual galaxies in galaxy groups and
| clusters, or the excess pressure of hot, X-ray emitting gas
| in groups and clusters -- all of which requires either some
| kind of dark matter, or some kind of alternate theory of
| gravity, or both.
|
| (I notice that I pointed out the ignorant nonsense of that
| video when you posted a link to it 7 months ago --
| https://news.ycombinator.com/item?id=27085979#27090683)
| mrtri wrote:
| so earth is moving with the expanding universe? why I'm not
| feeling any motion? while earth is spinnging wobbling, tilting,
| going around the sun at 66600mph.following the sun at 450000mph,
| following the milkyway at 1.3million mph, following the expanding
| universe at millions of mph.
| bmitc wrote:
| > than it should be
|
| This may be pedantic on my part, but I don't like this framing.
| It has the implication that our models dictate what happens in
| the universe and not the other way around. The universe is
| expanding faster than our models predict or there's something up
| with our observations or both. Maybe this is what people have in
| mind, but I think it's a subtle communication difference and can
| miscommunicate that science is truth, whereas science is the
| collection and evolution of models and observations describing
| the reality we experience.
| paulmooreparks wrote:
| I had the same thought when I read that, so it's not just you.
| "Faster than predicted by current theories" would have been a
| better way of stating it.
| [deleted]
| zigzag312 wrote:
| Agree. Models are only our attempts of describing how something
| behaves.
|
| That's why I'm also not a fan of using the word "law" for names
| of the models, because it implies as if the universe is
| obligated to follow this "law", but a law of physics is still
| essentially only our description (even if it uses math
| equations instead of words to describe).
| kybernetyk wrote:
| yes, but then the title wouldn't be as click-baity
| nathias wrote:
| The title is fine, you have a problem with your own
| implications.
| ncmncm wrote:
| Not pedantry. This is a common failing in cosmology.
| imoverclocked wrote:
| This is a common failing everywhere.
|
| A friend once told me, "stop shoulding yourself." Turns out,
| I should've listened.
| simonh wrote:
| It is pedantry. This is just idiomatic human communication
| and not specific to any single domain. People say thing like
| this all the time. Saying 'than it should be' instead of
| 'than we expect' is everyday English language usage that
| confuses nobody and complaining about it is entirely
| performative. You're technically correct, here have a round
| of applause, but it contributes nothing. Dealing with smug
| nitpicking like this that's completely beside the point is
| one of the tedious chores or reading HN.
| a9h74j wrote:
| > idiomatic
|
| Absolutely. If one person does their best work and is still
| frustrated after trying dozens of options, it is fair for
| them to be scratching their head and saying, "This
| shouldn't be happening."
|
| The article itself provides exceptionally precise reporting
| (though IANAA) of mutual work toward a grand challenge in
| astronomy --- which is still leaving people scratching
| their heads at discrepancies after trying dozens of model
| or analysis variations. The word 'should' in the title (I
| believe it only appears there) to me conveys well-enough
| (it is _only_ a title) that there are human elements
| /expectations and legitimate after-the-best-of-care puzzles
| remaining.
|
| I don't know if it is a good comparison, but if the time
| for the g-2 result reveal came, and the result was a
| 20-sigma discrepency, I would expect every experimentalist
| _and_ every theorist involved to immediately scowl and say,
| "F***, this should never have happened."
|
| Also perfectly ordinary and ideomatic: To say, This _should
| be_ compiling without errors.
|
| Great science reporting in the article, hence my rant to
| defend it.
| caf wrote:
| Right, when you say, deep in a debugging session, _" hmm,
| this variable shouldn't have this value"_, this is
| shorthand for _" according to my assumptions about the
| way this code operates and the initial conditions, it
| shouldn't be possible to observe the variable with this
| value"_. As far as I can see, it's similar here.
| simonh wrote:
| To be fair, in the programming case you change the code
| or data to make the variable correct, while in science
| unless there's a mistake somewhere you follow the data,
| you don't change things to 'fix' it. However we all know
| this, we know scientists aren't going to try and
| 'correct' reality or the data to fit our assumptions.
| Well, excepting the tin foil hat brigade, but we
| shouldn't pander to them or let them dictate our use of
| language.
| bmitc wrote:
| It's a problem because it miscommunicates to non-scientists
| about what science actually is and it causes scientists
| themselves to be misinformed about what they're really
| doing. I greatly enjoy science, but you have to admit that
| there's a problem of scientists being viewed as "elites who
| think they know everything" that is fueled by journalism
| and the miscommunication of science.
|
| It's alright to critique something to try and improve it,
| you know?
|
| Lastly, it's not really besides the point, as our models
| and possibly our observations being wrong is entirely the
| crux of this "problem".
| eecc wrote:
| Oh please, it's a headline. The pedantically correct
| phrasing is right below in the second heading, not buried
| in a footnote.
|
| Have you even glanced at the article?
| bmitc wrote:
| I read it.
|
| I admitted it was possibly pedantic, and then I got "smug
| nitpicking". And this happens all the time, so there's
| some pre-existing bias on my part in terms of being
| bothered by these communication mishaps. I struggle to
| watch many science documentaries these days due to
| communication issues such as these.
| spaetzleesser wrote:
| It's just wording. When you talk to a scientist they would
| tell you " The Universe Is Expanding Faster Than It Should Be
| according to our models". That's how fundamental research is
| done. You collect data, develop a model that fits the data,
| collect more data and check if the model still works. If not,
| go back to the drawing board and develop a model that fits
| the new data. And most scientists will be excited if they
| find such a gap because now the interesting work starts.
| agumonkey wrote:
| I bet 10$ they do it on purpose two fold. They know it's absurd
| to say reality is not behaving well and they know it sounds
| better to say it anyway.
| sslayer wrote:
| I've always maintained that we are slowly falling toward the
| center of a black hole that is larger than our current known
| universe. The rate of expansion is just the speed the universe is
| "falling, yet due to the absolutely fantastic size of the black
| hole it will take billions of years to collapse in on ourselves.
| prox wrote:
| I think a theory winning when it comes to "end of the universe
| - scary version" is what is known as vacuum decay :
| https://bigthink.com/hard-science/vacuum-decay-end-of-the-un...
| thehappypm wrote:
| At the speed of light we'd all be gone. Even if the Mars
| colony was snuffed out first, we wouldn't even know, since
| the information about the change wouldn't be able to reach us
| before the decay did!
| Zigurd wrote:
| Is it not a bit odd to consider things that will happen long
| after the sun is a cinder "scary." There are enough genuinely
| scary things that could flash-sterilize the planet, or smash
| a big enough hole in it to end all complex life forms.
| Nearer-term scary things are likely to come from how poorly
| humans can adapt to long term life in space or on planets
| with different gravity.
|
| Time stretches beyond the ability of life to survive in both
| directions. Nobody will be around to be scared.
| prox wrote:
| I agree my comment is way too antropomorphic centric. As
| you say, in terms of the timescales involved it might not
| be a time humans are around.
| mrtnmcc wrote:
| Expansion wouldn't be isotropic in that model, so no?
| exo-pla-net wrote:
| Fun idea. However, acceleration would be different in different
| directions, were this the case. In our universe, the
| acceleration is the same in every direction.
| marcyb5st wrote:
| That would add a directionality component as some objects
| closer to said black hole would accelerate faster.
|
| A more plausible but unprovable option is that we are close to
| the center of a big void (the density of the matter in our
| neighborhood is much lower than outside the observable
| universe). So the higher mass concentration attracts objects in
| our neighborhood giving the impression of an accelerating
| expansion. The problem with this theory are that we would have
| to be almost at the center of this bubble of almost nothing (so
| the notion that earth is not in a special position is lost) and
| that if spacetime is not expanding we cannot explain why very
| distant galaxies recede from us faster than light. FTL travel
| though spacetime should be impossible but spacetime expanding
| faster than light is.
| gizmo686 wrote:
| If we are within the event horizon, then the direction
| towards the center of the black hole is not a spatial
| direction, but a temporal one. The cental singularity is in
| the future. As it turns out, the temporal direction is the
| only direction of spacetime which is not symetric. Objects in
| the future are accelerating faster, which is presisly the
| prediction you made.
| AnimalMuppet wrote:
| If I understand correctly, if you add up the mass in the
| universe, the Schwarzchild radius of that mass is 13
| billion light years, which is a really interesting number.
|
| If we were inside a universe-sized black hole, would we be
| able to tell? Can we experimentally distinguish a black
| hole universe from a not-black-hole universe?
| DeRock wrote:
| Here's a website that explores that idea:
| http://www.flatuniversesociety.com/
| ncmncm wrote:
| Issue it a speeding citation, hope it learns from its mistake.
|
| This is probably just youthful exuberance. If it's still at it
| after another 13 billion years, take away its license.
| [deleted]
| choeger wrote:
| Do you have the universe's home address? Maybe it's still
| living with its creator?
| ncmncm wrote:
| The amazing thing about the universe's home address is that
| it is always _right here_ , no matter where here is. The Big
| Bang happened exactly at the tip of your nose. And mine.
| BurningFrog wrote:
| Why _is_ the entire universe speeding away from us?
|
| What do they know??
| ngcc_hk wrote:
| Failure is so common in this area that using "should" is a bit
| odd. The problem today is not like the Mercury minor difference
| (which in one stage some tried to invent a planet inside Mercury
| orbit called Vulcan).
|
| But we are not of that scale. 90+% things we do not know, we just
| label them as dark ... matters or energy. It looks like we know.
| The key is the dark part.
|
| If you do not know 90+% things out there, there is no way you can
| think of should.
|
| Just say the universe once again serve us a curve ball ...
| magicalhippo wrote:
| > If you do not know 90+% things out there, there is no way you
| can think of should.
|
| They're just leaving off the implied "according to our models"
| at the end of the sentence. This is mostly fine, because it's
| obvious we don't know the true model of the universe, so our
| expectations are based on our current understanding.
| PicassoCTs wrote:
| The anti-matter mirror universe is contracting ever faster.. /s
| cainxinth wrote:
| Do you ever marvel at the fact that we have learned and continue
| to learn so much and yet still really understand basically
| nothing about why this universe exists, what its limits are,
| what's driving its changes, and what its ultimate fate will be?
|
| We don't know what we don't know, and we're trying to figure out
| how a black box works from inside an infinitesimally small corner
| of it. Frankly, I find it amazing we've worked as much as we
| have.
| Aperocky wrote:
| Which is really nice, because nothing on Earth really matters
| when you consider the scale of the universe that we live in.
|
| Very blessed to be an observer though.
| wait_a_minute wrote:
| It is not the scale of the universe that would determine if
| Earth matters or not, but whether or not there is
| significance to the universe and to Earth. Significance
| conferred by observers or parties interested in these things.
|
| Example: $100 isn't less or more just because of increasing
| or decreasing the physical footprint of the bill. We still
| confer a purchasing power of $100 to a $100 bill regardless
| of the bill's physical dimensions.
|
| So the takeaway here is that it's a non-sequitur to say that
| because of Earth's small scale relative to the rest of space,
| nothing on Earth matters.
| Aperocky wrote:
| You're right, we still matter as people, but only for our
| own feelings and circumstances.
|
| It's humbling because it puts all that hubris away, which
| most people tend to have an excessive amount of - and begin
| to focus on living and achieving simple happiness instead
| of some illusion of grandeur.
| wait_a_minute wrote:
| How do you know that people matter only for our own
| feelings and circumstances?
| papito wrote:
| A couple of years ago, Netflix added a science series about the
| Universe, and I could not understand why they referred to the
| process behind planet and star formation as a mystery. We know
| that dust, left to just float in space, will create clumps,
| rocks, boulders, and so on - due to microgravity.
|
| The series was from the mid 2000s.
|
| No one suggested this very obvious process until an astronaut
| on the ISS had a fine-grain substance in a small plastic bag
| (no, not THAT one), and they noticed the grains stuck together.
| cgriswald wrote:
| You're sort of conflating what scientists are pretty sure
| about in a general sense and what they actually know about
| how it works in the specifics.
|
| Take a look at the wikipedia page for this topic:
| https://en.wikipedia.org/wiki/Nebular_hypothesis
|
| Just as an example:
|
| > The formation of planetesimals is the biggest unsolved
| problem in the nebular disk model. How 1 cm sized particles
| coalesce into 1 km planetesimals is a mystery. This mechanism
| appears to be the key to the question as to why some stars
| have planets, while others have nothing around them, not even
| dust belts.
| pleb_nz wrote:
| Interesting as I thought that the theory was quite old.
| Certainly sure I believed that well before the mid 2000s. And
| a quick search on DDG says that theory was first proposed in
| 1941 referring to plant formation?
| albert_e wrote:
| One less discussed aspect of how small and insignificant a
| place we occupy in the grand scheme of things is the time
| scale.
|
| Our entire civilization past and future may be just a momentary
| bubble in a cosmic ocean frothing with countless happenings for
| aeons.
| officialjunk wrote:
| say an advanced civilization learns how to time travel and
| walk the multiverse. trying to find us would be hard. the
| time scale is very small, yes, we occupy a small area, true,
| but also the scale of life itself may not be discussed much.
|
| there's dozens upon dozens of orders of magnitude of space
| that a being could occupy. scanning for life through the
| multiverse and time, it would also be easy to miss us. too
| small and you see cells and organelles, larger we see organs
| mixed with bacterial cultures, etc, and at just the right
| scale we are visible.
|
| there are arguments that earth is a living entity, and there
| may be larger forms of life going many orders of magnitude
| larger than planet-sized.
|
| with such a large range of time, location and scale to scan
| for life, it could be argued we basically don't even exist.
| lisper wrote:
| > it would also be easy to miss us
|
| Or maybe they found us but they just don't care because on
| cosmic scales we aren't as special as we appear to be from
| our own limited perspective.
| devmunchies wrote:
| That's not less discussed. That concept is pervasive in
| media, literature, and philosophy. Nihilism 101.
| thom wrote:
| It does sometimes feel like we wake up, stretch, and open our
| eyes every morning to realise we're at the edge of a cliff, the
| ground plummeting away into fog beneath us. But then we roll
| over and there's green grass on the other side, so off we go to
| work.
|
| That said, whatever breakthroughs we make from one generation
| to the next, what a stroke of luck it is that some things
| remain constant: we can fall in love, enjoy a good story,
| drink, eat, be merry, and argue about the meaning of life in
| whatever fora present themselves.
| onion2k wrote:
| _Do you ever marvel at the fact that we have learned and
| continue to learn so much and yet still really understand
| basically nothing about why this universe exists, what its
| limits are, what's driving its changes, and what its ultimate
| fate will be?_
|
| Not really. Modern science has been looking at the origin of
| the universe for less than a single human lifespan. It's not
| surprising how little we know. It's pretty amazing that we know
| anything really. If you'd been studying physics 70 years ago
| you'd be wondering if the Big Bang or the Steady State theory
| is right.
| gibolt wrote:
| Most humans ever born, are still alive today. Our population
| growth over the past centuries dwarf populations of the prior
| centuries.
|
| That means, more people than ever working on more problems,
| with more tools, background knowledge, resources, distinct
| goals, and collaboration.
| vo2maxer wrote:
| That's not the case given the estimate of 107 billion
| people who have ever lived:
| https://www.prb.org/articles/how-many-people-have-ever-
| lived...
| BurningFrog wrote:
| From memory, the actual number is 6%.
| sicromoft wrote:
| > Most humans ever born, are still alive today
|
| This is not even close to being true
| smhenderson wrote:
| It's not, but I can see how it seems that way - I found
| this with a two second search:
|
| _The world population increased from 1 billion in 1800
| to 7.7 billion today._
|
| I'm not going to do the math but there's something to be
| said about how many we are today vs. even 200 years ago.
| But, no, the majority of humans ever born are not, in
| fact, still alive today...
|
| https://ourworldindata.org/world-population-growth
| sophacles wrote:
| Most humans ever born, are still alive today. Our
| population growth over the past centuries dwarf populations
| of the prior centuries.
|
| Please explain how you get to this conclusion. It makes no
| sense.
| mensetmanusman wrote:
| I think OP is saying that if you add up all the humans
| that have died in the past 10,000 years or so (modern
| humans), then that number is smaller than today's global
| population.
| fellowniusmonk wrote:
| Honestly our rate of increased knowledge is unreal, basically
| humanity had very little tech/science improvements for most
| of our history and then just world changing improvements in
| the last 2 generations/lifetimes.
|
| Crazy.
|
| Who knows what things will look like in 1 more lifetime. I'm
| still blown away by the memory of getting constantly lost
| growing up, my dad hand drawing maps for people, comedians
| stopped telling jokes about men not asking for directions and
| it still feels like nobody stopped to notice.
|
| It's partly that impulse to never stop and appreciate what we
| have, that dissatisfaction, that keeps people pushing into
| the unknown.
| pyrrhotech wrote:
| > Honestly our rate of increased knowledge is unreal,
| basically humanity had very little tech/science
| improvements for most of our history and then just world
| changing improvements in the last 2 generations/lifetimes.
|
| I feel like this is more a modern misconception than
| reality. Play a game of Civilization and you'll start to
| appreciate just how deep human technology really is. In
| Roman times, they probably said similar things thinking
| about how advanced they were compared to the Macedonians a
| couple hundred years back.
|
| Yea we lost some progress or at least the rate of change
| greatly slowed from 400 - 1600, but other than that blip I
| think the progress has actually been fairly linear from
| 4000 BC to 2021 CE. It just seems like it's not because of
| the cognitive bias to take for granted all the things that
| seem so basic compared to computers or nuclear reactors,
| but in reality, those things actually were very difficult
| to develop with the knowledge and production techniques
| available at the time.
| fellowniusmonk wrote:
| We'll have to disagree on the shape of the curve I guess,
| it's just my personal take.
|
| For what it's worth...
|
| I've been to Ephesus (which is amazing, I'd like to check
| out Pompeii as well) the armory in Venice is one of my
| favorite repos of old cutting edge tech and having spent
| time in Rome, truly their achievements are amazing and
| the Pantheon absolutely blows my mind, it's no wonder the
| village dwellers believed the God's lived in Rome, I
| would have.
|
| But harnessing the power of the atom, understanding
| fundamental physics, biology and sound/light speed global
| communication... and the technology that these things
| have enabled (including my own living past 3 years of age
| due to modern medicine) is truly a leap, in my opinion
| the Roman's and those brilliant technologists and
| logistics civilizations of the past were still closer to
| living in caves by modern comparison.
|
| I would not have wanted to live back then and I literally
| couldn't have. Our recent exponential explosion certainly
| depends on their hard fought knowledge, but in my
| reckoning even their best tech and logistics are deep in
| the early part of the curve.
| simonh wrote:
| >Who knows what things will look like in 1 more lifetime.
|
| The usual prediction I see is that the rate of discovery
| will continue and in another 2 lifetimes everything we
| think we know now will seem just as silly and naive as what
| people believed 2 lifetimes before us.
|
| I don't think that's the case. It's a question of whether
| we're on a (near) infinite exponential curve of discovery,
| or on the rapid upward stretch of an S curve. I'm in the S
| curve camp, and I suspect we're at least half way up it on
| most topics.
|
| Just look at relativity, quantum mechanics and cosmology.
| Most of the great discoveries in these fields were actually
| quite a while ago. Relativity and Quantum mechanics are
| over 100 years old and most of the advances were made in
| the early decades. Progress has not stopped but massively
| slowed down.
|
| In cosmology it's been slower progress, but we've charted
| time back to milliseconds after T=0 of the big bang,
| detected thousands of exoplanets, analysed the
| gravitational waves from black hole collisions and mapped
| the cosmic microwave background. There's more to learn
| about dark matter and dark energy for sure, some serious
| mysteries there, but how much difference will those answers
| actually make? The Higgs boson discovery was cool, but
| really just a cherry on top of the standard model rather
| than a revolutionary discovery that upended science. I'm
| not sure there are any of those still to come.
|
| The closing chapter on the big questions in science still
| has to be written, but I think the chances it will force us
| to completely rewrite, rather than simply revise and update
| the previous chapters, seems slight IMHO. I'm expecting the
| GUT to simply update or reframe relativity and quantum
| mechanics to make them compatible, not throw them out
| completely.
|
| It truly is astonishing to be alive at this nexus in human
| development, whatever our individual take on it might be.
| manigandham wrote:
| Progress has slowed down because we solved all the easier
| problems that we could with the human mind.
|
| Now technology is catching up to give us the computing
| power, massive collective memory, digital records, and AI
| to start gaining again. We basically have to build a
| better mind to get to the next level.
| fellowniusmonk wrote:
| Agree. I think people really underestimate how many
| intractable "needle in a haystack" problems are now
| tractable due to RNNs, CNNs and other ML/ai stuff.
|
| We are still in the early days of applying that tech to
| the fields it's going to effect most.
|
| We're in the "get a home page for your local business"
| phase not yet the "faang has changed the face of
| civilization" (for the better or worse) phase.
|
| This is going to continue to ramp knowledge in
| bioinformatics and other areas, the technology is still
| in the infancy of being harnessed for biology and
| medicine.
|
| That combined with cheaper robotic arms and cheaper
| sequencing machines which is just now coming dropping
| below certain cost thresholds.
|
| (I know a group/lab that's automating discovery of
| drug/compound targets doing purely NDA'd work for merck
| and other pharmaceuticals, the tech is wild and still in
| it's infancy.)
|
| Cutting edge voice and image style transfer, realistic
| computer speech, computer vision.. the list goes on,
| that's just the highly visible stuff and there is still
| only a small pool of people versed in those areas of
| tech.
| brobdingnagians wrote:
| I think it is likely that some things will be revised and
| tweaked, but other things will have to be majorly
| rewritten. We may not know what those are yet, but from
| looking at history, it is wise to believe that in some
| things we are hammering away at a faulty path. When we
| rewrite that, there will probably be major rapid
| improvements very quickly, then slow over time. Perhaps a
| lot is slowing recently because we've had less major
| breakthroughs which usually open up fertile fields. Maybe
| that's because we have the low hanging fruit of major
| breakthroughs or our society isnt as good at getting
| them, either way, it will be interesting to see what the
| future holds.
| manigandham wrote:
| Yes, always reminds me of Louis CK's "Everything's amazing
| and nobody's happy" clip:
| https://www.youtube.com/watch?v=PdFB7q89_3U
| spacemadness wrote:
| Everything is not amazing. We're still social creatures
| and there is arguably a lot of stress and angst in the
| social world we find ourselves in. If "everything" is so
| amazing why are people working over 40/50/60+ hours a
| week to make ends meet? Why are people made destitute
| over hospital bills in America? This is something the
| more privileged among us seem to forget over and over
| again. Humanity has a ways to go yet before everything is
| amazing. We can't just look at our incredible advances in
| science and technology and call that enough. Yes I'm fun
| at parties.
| chrononaut wrote:
| This. It's amazing when you also take into account that the
| beings evaluating it originated from the very arbitrary matter
| that we strive to understand.
|
| I always express that the greatest science "fiction" story is
| actually the reality above us, and the multitude of unanswered
| questions.
| papito wrote:
| I actually find that the process of formation of everything
| around us is pretty straight forward. After all, none of it
| is explained by magic.
|
| Now, how all this shocking amount of matter came to exist
| from energy, which also had to come from somewhere... That's
| a head scratcher alright. The path to God is hidden behind
| rock solid plausible deniability.
| gtsop wrote:
| The world is infinate, so the knowledge we have of it will
| always be a subset.
| podgaj wrote:
| The arrogance!
|
| The universe is not expanding faster than it "should" be! Your
| math is wrong!
| Quekid5 wrote:
| It's a figure of speech. "Should" here is short for "should
| according to our best theories. Therefore those theories are
| inaccurate".
| podgaj wrote:
| I know it is a figure of speech, but it is quite a convenient
| one! It implies their math is right and the universe is
| wrong!
|
| Let me fix it:
|
| "Scientists models of the expanding universe fail again."
| guerrilla wrote:
| That's what the title already says for people who
| understand the figure of speech.
| podgaj wrote:
| When did scientists get so afraid of a failed experiment?
| guerrilla wrote:
| I don't know why this is a response to my comment or this
| article at all...
| stareatgoats wrote:
| Cosmology is not a done science. There are a great number of
| advances that have answered specific problems regarding the
| behavior of light and energy, mass and gravity and so forth, but
| our knowledge is not complete (and will likely never be).
|
| Articles like this get traction because the lay person may have
| believed that the science was more mature than it is. (Some)
| scientists are also notoriously famous for exaggerating how much
| science "knows" - Stephen Hawkings claim to the mind of God comes
| to mind.
|
| We need to relieve such scientists of the burden of needing to
| know it all, and be grateful for all the things still left to
| discover.
| dgb23 wrote:
| Something not being a done science is one of the core
| assumptions of science to begin with. Any statement where
| further progress is excluded is not scientific in a strict
| sense.
|
| In my opinion scientists (and everyone else) should be allowed,
| maybe even encouraged to fantasize. Fantasizing, play, shifting
| around assumptions can help progress. But the problem arises if
| we accept anything a scientists says as scientific truth.
|
| Understanding that science is always evolving and that
| scientists often need play and fantasize, increases trust and
| accelerates progress. We need both to face the challenges of
| nature.
| blueprint wrote:
| > Any statement where further progress is excluded is not
| scientific in a strict sense.
|
| Then that is not a scientific statement.
| jhardy54 wrote:
| Correct, the definition of words is not a science.
| vo2maxer wrote:
| The study of the definition of words is Linguistics which
| is a science:
| https://en.wikipedia.org/wiki/Linguistics?wprov=sfti1
| NineStarPoint wrote:
| Any statement about how science should work is indeed
| philosophy and not science, science is for obvious reasons
| incapable of defining itself.
| podgaj wrote:
| > Cosmology is not a done science.
|
| Cosmology will never be a done science. The universe is
| infinite but the human mind is finite.
| auntienomen wrote:
| Cosmology is not the study of the universe but only its large
| scale structure.
| cgriswald wrote:
| > The universe is infinite ...
|
| Yet we can describe most of what we observe with a tiny set
| of equations. What's more meaningful to science is that the
| universe is not bound to our models and assumptions. Even the
| assumption that the universe is ordered and so will remain
| ordered is not guaranteed. It's just a convenient and
| historically effective assumption that appears to be
| justified as far back as we can look. No science, therefore,
| is a done science.
|
| > ...the human mind is finite.
|
| A whiteboard is finite. It is bound in spacetime and no
| matter how small the writing, there is an upper limit to the
| amount of information that can be displayed on it at any one
| time. No matter how quick the erasing, there is an upper
| limit amount of information that can be displayed within the
| lifetime of the board.
|
| Despite this, it can have an uncountably infinite variety of
| information impressed upon it.
| Trasmatta wrote:
| > The universe is infinite
|
| Well, an open question in cosmology is whether the universe
| is actually infinite or not...
| ajross wrote:
| Strictly that's a question about philosophy, not cosmology.
| Cosmology just says the universe is _unbounded_ and leaves
| it at that. In fact "The Universe", meaning all the matter
| or energy which we will ever even theoretically be able to
| obvserve, is definitely finite. The distance to the point
| of infinite redshift (where we're looking at the big bang,
| essentially) is finite. It doesn't make sense to talk about
| anything "farther" out.
| DougN7 wrote:
| Is that true? (Honest question) Whatever the "thing" was
| that exploded at the big bang (which I read once was the
| size of a grapefruit for what it's worth) - could there
| not have been other similar "things"? And what about
| where that "thing" came from? I've read theories of the
| universe expanding, but then eventually falling back onto
| itself to recreate another "thing" that will explode
| again. Anyway, it feels like there might indeed be more.
| datavirtue wrote:
| I picture the big bang as a bunch of heavy "black holes"
| approaching eachother discharging something that looks
| like lightening between them that grows more intense as
| they all pulled closer together. Eventually fusing into a
| persistent electromagnetic "explosion." Like a really bad
| welding accident.
| arbitrage wrote:
| A way that I heard this described, is that what we
| recognize as the observable universe right now was the
| size of a grapefruit at the beginning of the big bang.
| The stuff that expanded due to whatever the big bang
| actually did, that stuff could have been just the size of
| a grapefruit and nothing more, or itself infinite. But
| the part we can access given speed of light restrictions
| was the part that was the size of a grapefruit. There
| might actually be a lot more stuff out there ... we can
| just never get to it.
| Trasmatta wrote:
| > Cosmology just says the universe is unbounded and
| leaves it at that
|
| I don't think that's right. The shape and topology of the
| universe is an open question in cosmology, and
| cosmologists haven't just "left it at that".
| ajross wrote:
| Let me be stricter: models consistent with general
| relativity don't discuss the idea of a universe being
| "infinite", and just in general theories in science don't
| predict the unobservable. Open universe topologies are
| unbounded. They aren't "infinite".
| rgrieselhuber wrote:
| Is there such thing as any kind of done science? Sounds like
| an oxymoron to me.
| ewindal wrote:
| So is the set of all positive integers, but there is no
| unknown number in there, even though we haven't seen them
| all.
| mensetmanusman wrote:
| There is though, what's the prime number after 314159265378
| 979323846264338327950288419716939937510582090494459?
| Blammar wrote:
| It's ....58209_7_494459... I checked against my memorized
| pi expansion. Oddly enough yours and mine stop at the
| same place!
| mensetmanusman wrote:
| You only need a hundred digits to know the circumference
| of the universe within the accuracy of the diameter of
| hydrogen!
| Jweb_Guru wrote:
| There are plenty of unknown numbers :) For example, the
| number that is 1 if the Goldbach Conjecture is true, and 0
| if it is false.
|
| (BTW, if you want to know the difference between
| constructive and nonconstructive mathematics, it's that
| constructive mathematics doesn't let you say "well, it's
| definitely 0 or 1" because it leaves open the possibility
| that there's no proof of either termination or
| nontermination in the current theory... which is basically
| the philosophical distinction under discussion).
| aszantu wrote:
| I thought that if more stuff collapses into singularity there
| might be something pushing outwards... Maybe like turning a
| balloon inside-out - which leads to the space-time expansion...
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