[HN Gopher] Age of universe at 26.7B years, nearly twice as old ...
___________________________________________________________________
Age of universe at 26.7B years, nearly twice as old as previously
believed
Author : hsnewman
Score : 159 points
Date : 2023-07-13 18:51 UTC (4 hours ago)
(HTM) web link (phys.org)
(TXT) w3m dump (phys.org)
| labster wrote:
| Spacetime is expanding to meet the needs of expanding spacetime.
| Certhas wrote:
| From the articles' description, it sounds like a hodgepodge of
| discredited ideas. Maybe unsurprisingly: If you add _all_ of
| them, you get enough wiggle room to evade observational
| constraints...
| intrasight wrote:
| It's always seemed wrong to me that the age of the Milky Way and
| the age of the universe where about the same. Older universe
| seems intuitively correct.
| wodenokoto wrote:
| I remember in middle school I had a very passionate physics
| teacher who held extra astronomy classes for kids who wanted to
| join.
|
| Particularly I remember when he presented the age of the
| universe.
|
| The age was estimated with something like plus minus 10 billion
| years. The teacher made a big deal about how incredible this was.
| When I first heard that number it sounded beyond imprecise. But
| he explained: Now we actual had a ballpark figure. Before we
| didn't know if it was thousands or quintillions of years, so plus
| minus 10 billions was really good and ground breaking.
|
| With that in mind, this kinda seems like a minor adjustment.
| mydriasis wrote:
| > Zwicky's tired light theory proposes that the redshift of light
| from distant galaxies is due to the gradual loss of energy by
| photons over vast cosmic distances. However, it was seen to
| conflict with observations. Yet Gupta found that "by allowing
| this theory to coexist with the expanding universe, it becomes
| possible to reinterpret the redshift as a hybrid phenomenon,
| rather than purely due to expansion."
|
| Aww, the light needs a little nap. No wonder we ( potentially )
| got it wrong...!
| bamfly wrote:
| Where's the energy _going_ , supposedly? I'd assumed "the
| light's losing energy" had been firmly ruled out long ago--it
| was a potential explanation that occurred to me the very first
| time I heard about the observed red shift of distant galaxies,
| so I figured it must be _very_ and _obviously_ wrong if I 'd
| never heard an actual physicist even mention the possibility of
| that as a notable factor.
|
| [EDIT] Wikipedia "Tired Light" article:
|
| > The concept was first proposed in 1929 by Fritz Zwicky, who
| suggested that if photons lost energy over time through
| collisions with other particles in a regular way, the more
| distant objects would appear redder than more nearby ones.
|
| Oh, so, what I might have guessed, "it hits stuff sometimes".
|
| Article goes on to make it seem like there's a lot working
| against the notion, including that distant images ought to be a
| lot fuzzier if light's interacting with other stuff along the
| way.
| signalToNose wrote:
| Light is affected by gravity. But since astrophysics consider
| the universe to be equal all over it's often not calculated
| olddustytrail wrote:
| Apart from gravitational lensing of course. How does that
| affect the wavelength?
| andrewstuart wrote:
| This should not be the headline.
| RcouF1uZ4gsC wrote:
| I would almost be willing to bet that in 5 years, the consensus
| will be much closer to the tradition 13.7 billion years, rather
| than than 26.7 Billion years.
|
| I am not a physicist, but my understanding was that multiple
| different ways of calculating age converge toward the traditional
| number. For his new estimate seems to be using theories that are
| still at the fringes of mainstream physics. Based on this, my bet
| would be on the traditional number.
| incogitor wrote:
| The convergence is only valid if the distance ladder is
| accurate. There are a variety of deductive bottlenecks in the
| distance ladder which could implicate the whole current
| distance model. Standard candles and redshift measurements are
| calibrated together, for example. If either is off then the
| whole current ladder could be invalid.
| olddustytrail wrote:
| If absorption lines could magically match that shift, you
| mean?
| Nesco wrote:
| Title doesn't reflect it's the result of a newly hypothesised
| model
| dandanua wrote:
| by a single author
| shagie wrote:
| ... based on an... "interesting" model for the red shifting
| of light.
|
| > Zwicky's tired light theory proposes that the redshift of
| light from distant galaxies is due to the gradual loss of
| energy by photons over vast cosmic distances. However, it was
| seen to conflict with observations. Yet Gupta found that "by
| allowing this theory to coexist with the expanding universe,
| it becomes possible to reinterpret the redshift as a hybrid
| phenomenon, rather than purely due to expansion."
|
| (context for that theory...)
|
| https://en.wikipedia.org/wiki/Tired_light
|
| > The concept was first proposed in 1929 by Fritz Zwicky, who
| suggested that if photons lost energy over time through
| collisions with other particles in a regular way, the more
| distant objects would appear redder than more nearby ones.
| ... Despite periodic re-examination of the concept, tired
| light has not been supported by observational tests and
| remains a fringe topic in astrophysics.
|
| https://en.wikipedia.org/wiki/Non-
| standard_cosmology#Tired_l...
|
| > Tired light theories challenge the common interpretation of
| Hubble's Law as a sign the universe is expanding. It was
| proposed by Fritz Zwicky in 1929. The basic proposal amounted
| to light losing energy ("getting tired") due to the distance
| it traveled rather than any metric expansion or physical
| recession of sources from observers. A traditional
| explanation of this effect was to attribute a dynamical
| friction to photons; the photons' gravitational interactions
| with stars and other material will progressively reduce their
| momentum, thus producing a redshift. Other proposals for
| explaining how photons could lose energy included the
| scattering of light by intervening material in a process
| similar to observed interstellar reddening. However, all
| these processes would also tend to blur images of distant
| objects, and no such blurring has been detected.
|
| > Traditional tired light has been found incompatible with
| the observed time dilation that is associated with the
| cosmological redshift. This idea is mostly remembered as a
| falsified alternative explanation for Hubble's law in most
| astronomy or cosmology discussions.
| gigs wrote:
| The article really should not have even mentioned tired
| light. It's not really what Gupta is proposing. He is
| instead proposing that Dirac was correct about some things
| we view as constants not actually being constant.
| shagie wrote:
| That tickled a tangent to a different theory that is also
| fairly recent...
|
| https://www.newscientist.com/article/2380881-time-
| appears-to... (paywalled)
|
| https://www.sciencealert.com/time-appears-to-have-
| run-5-time...
|
| https://www.advancedsciencenews.com/time-ran-slowly-in-
| the-e...
|
| > Scientists have confirmed that just 1.5 billion years
| after the Big Bang, time ran five times slower than it
| does today, 13.8 billion years later. Though scientists
| have long been aware that conditions just after Big Bang
| were radically different than those in the cosmos we see
| around us today, the discovery shows that time is
| relative in regards to the age of the Universe, too, just
| like Einstein predicted.
|
| The referenced paper:
| https://www.nature.com/articles/s41550-023-02029-2
| doctoboggan wrote:
| Yes, there would need to be much, much more study and evidence
| to change the accepted age of the universe. JWST has shown some
| "problematic" galaxies as the article notes, so it may indeed
| be true the universe is older than originally thought, but we
| aren't there yet.
| elashri wrote:
| It is hardly a new model [1]
|
| [1]
| https://en.wikipedia.org/wiki/Conformal_cyclic_cosmology?use...
| cygx wrote:
| That's a totally different model.
| singularity2001 wrote:
| and the known diameter is 43B lightyears, which is still
| mindbending
| hasmanean wrote:
| Isn't that a dead giveaway? The universe expanded outwards at
| the speed of light from a central point...the radius is 21.5
| billion lightyears and the diameter is 43B.
| ianburrell wrote:
| I'm pretty sure the 43B is the radius. The diameter that we
| can see is 93B ly according to Wikipedia.
|
| The universe is expanding which means we can see more than
| the age of the universe. The light from far away was carried
| long as the universe expanded which makes it look like
| traveled faster than light.
| akira2501 wrote:
| Isn't that a radius, or more specifically, the distance from
| the earth to the edge of the observable universe?
| smaddox wrote:
| When the model doesn't fit, add an extra free parameter!
|
| Seriously though, I wonder what the ramifications to other parts
| of astrophysics would be if this is true.
| redroyal wrote:
| [flagged]
| areoform wrote:
| > no productive utility to us tiny human beings whatsoever.
| It's a racket
|
| Do you use GPS?
|
| https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5253894/
|
| Have you ever used a MRI or undergone a CAT scan?
|
| https://en.wikipedia.org/wiki/IDL_(programming_language)#His.
| ..
|
| https://en.wikipedia.org/wiki/IRAF
|
| Used anything that involves interferometry - contact lenses,
| anything with a lens or a laser, optical coherence tomography
| (OCT) etc?
|
| https://nexsci.caltech.edu/workshop/2003/2003_MSS/07_Monday/.
| ..
|
| I can go on, but I think I've made my point.
|
| But even if these fruits didn't come of it, something doesn't
| have to be "productive" or useful according to your
| definition to justify its existence. Just like art or music
| doesn't have to be "productive," useful or even beautiful by
| your definitions to exist.
|
| There is more to human existence than breathing, eating and
| leaving bad comments on websites.
| redroyal wrote:
| I think you made my point actually
| helsontaveras18 wrote:
| Love the idea that it's a racket, that astrophysicists are
| making millions of dollars watching stars, and we're paying
| for the fancy cars they drive.
| FredPret wrote:
| Yeah, down with Big Telescope. This thing goes all the way to
| the top.
|
| In all seriousness, no portion of my tax payer dollars make
| me happier than the money that goes to the ISS and JWT and
| other expensive sciency things in space
| Euphorbium wrote:
| [flagged]
| psychphysic wrote:
| Can't tell if you're being tongue in cheek here.
| kgwxd wrote:
| History would imply not.
| photonerd wrote:
| Please tell me this is sarcasm
| 7373737373 wrote:
| Tell that to the dinosaurs
| dandanua wrote:
| And what is a productive utility for you, exactly?
| notaustinpowers wrote:
| It's okay to admit you don't understand what astrophysicists
| do.
| coding123 wrote:
| I'm certain there was time and space before that.
| mynameisash wrote:
| How can you be certain of that?
| josh_today wrote:
| [dead]
| Takennickname wrote:
| Wow. Science sucks.
| enduser wrote:
| No wonder I feel tired
| readthenotes1 wrote:
| Huh. I would guess someone named End User would have come from
| the termination not the origin!
| local_crmdgeon wrote:
| Cosmological constant change proposals are always spicy. I don't
| know shit about any of this but I learn a ton from these
| comments.
| idlewords wrote:
| "if a whole bunch of fundamental physical constants change over
| time in a specific, coordinated way"
| Pxtl wrote:
| This reads like wishful thinking -- "The universe can't be
| expanding _that_ rapidly, then galaxies outside of the Local
| Group will leave the cosmological horizon in 100 billion years!
| Surely redshift must be a lie! "
| tehologist wrote:
| The universe is aging at an alarming rate.
| jmyeet wrote:
| IANAP but I'm skeptical at any theory that revises the age of the
| Universe by a factor of 2. It could be the case but the bar is
| pretty high for such a massive revision.
|
| One thing about a lot of this from the Big Bang to black holes is
| that a lot of it makes sense as mathematical concepts but doesn't
| necessarily translate to something intuitive.
|
| Example: the Big Bang is often described as the Universe starting
| from a single point. That's an attempt an intuitive explanation
| but here's another based on the maths. In maths you have the
| concept of a space that has certain properties. A metric space is
| a type of space that has, well, a metric. What is a metric? It's
| a function that defines the distance between two points. So at
| the start of the Universe, it's more accurate to say the metric
| between all points was 0. Does that mean it started from a single
| point? No one really knows. But the metaphor arguably confuses
| the issue.
|
| One issue is the question of whether or not the Universe is
| infinite. This is an open question in cosomology. Many suspect it
| is based on spacetime being incredibly flat based on all our
| observations. But if you assume the Universe is infinite, how do
| you reconcile that with the Universe starting from a single
| point? How does something intuititvely finite become infinite? It
| sort of breaks down. Simply saying the metric was 0 is less
| problematic (but also less satisfying, in a way).
|
| There's an awful lot of evidence for the current age estimate.
| Expanding that by another 13B years should yield a bunch more
| stellar objects in the expanded age range. There is AFAIK only
| one such object we've detected, which the article mentions, the
| so-called Methusalah star [1], which was originally dated at ~16B
| years [2].
|
| What's more likely: one object is incorrectly dated or the
| Universe is twice as old as all observations to this point have
| suggested? I know where my money is.
|
| [1]: https://en.wikipedia.org/wiki/HD_140283
|
| [2]: https://www.space.com/how-can-a-star-be-older-than-the-
| unive...
| javajosh wrote:
| Read phys.org with a grain of salt. Or better, don't read it.
| vitehozonage wrote:
| Yes it seems like 100% of the articles are misleading
| clickbait. I don't think it's a suitable source for HN ever
| nubinetwork wrote:
| https://news.ycombinator.com/item?id=36696295
| https://news.ycombinator.com/item?id=36700919
| acumenical wrote:
| From what I know about academia and the people who occupy
| positions within it, who function solely to gatekeep progress and
| then ship the bare minimum to keep their privileged positions, I
| look at articles like this one and roll my eyes.
| jjoonathan wrote:
| Gatekeep progress? Dude, it's cosmology research. What kind of
| progress are they keeping from whom?
|
| As for shipping the bare minimum, academia has too many smart
| people competing with each other over too little money. I'd
| hazard a guess that the "bare minimum" as represented by this
| paper is considerably higher per dollar than the bar set by
| someone who uses the word "shipping" to describe publishing.
| pfdietz wrote:
| > tired light
|
| Not credible. Tired light doesn't preserve the density of photons
| in blackbody radiation; the CMBR has density precisely that of
| blackbody radiation.
| gigs wrote:
| He isn't proposing steady state. He's basically saying that
| Dirac might have been right in proposing things like the
| gravitational constant or fine-structure constant are time
| variant over long enough times. If what we think are constants,
| aren't, anything is possible.
| pfdietz wrote:
| I don't care. If he's tossing in tired light anywhere, the
| CMBR won't look like it does. Once you lose the match of
| density to temperature, you don't get it back.
| gigs wrote:
| He isn't. That's the pop science article author's attempt
| to relate to his work, I think.
|
| https://arxiv.org/pdf/2201.11667.pdf
|
| Here's one of Gupta's papers.
| ineedasername wrote:
| The tone of the headline makes it sound like 26.7B is now
| accepted, but the article indicates it's mostly just a theory
| that has a little additional evidence. Is the later a correct
| reading of the situation?
| golergka wrote:
| Pop science in general doesn't pay enough attention to which
| theories are solid and believed to be 99,99% true, and which
| are just accepted as best guess in lieu of good data. Although
| history (not science, pop version) is a much worse offender
| than physics in that regard.
| frfl wrote:
| Had to check Wikipedia[1] just to be sure this was actually an
| accepted number. That still says ~13B years right now. The
| headline is edited to be more sensational than the actual
| linked article.
|
| [1]: https://en.wikipedia.org/wiki/Age_of_the_universe
| U2EF1 wrote:
| It's all just theories. But yes the article is basically
| summarizing a new paper/model. Most likely: the model is
| incorrect in some ways. But maybe useful in others.
| mistermann wrote:
| Try to convince a member of science's fan base (which
| includes many actual scientists) of this _during an object
| level discussion about a particular point of contention_ and
| see how well it goes over.
| myko wrote:
| > just a theory
|
| A theory is the highest possible idea here, "just" a theory
| makes no sense
|
| That said, this theory may or may not be better than the other
| theories regarding the age of the universe.
| dheera wrote:
| Yes, you are correct that it is not the widely accepted number
| as of now, and that it is just one theory. It's just that
| without this tone the headline would have never made it to the
| front page.
|
| Our upvote tendencies incentivize drastic tones, so it's
| effectively what we ask for, and what we get as a result.
| lamontcg wrote:
| > it's effectively what we ask for, and what we get as a
| result.
|
| "It's me, hi, I'm the problem, it's me"
| surfsvammel wrote:
| Ok. I'm a novice in this. But isn't time relative, and also
| affected by gravity and velocities? When we talk about the age of
| the universe, from which perspective are we considering it?
| flumpcakes wrote:
| From my poor understanding of a Physics degree: the "age" is
| just counted from when everything existed in the same space,
| before it's rapid expansion. Although, can you say it expanded?
| It didn't expand into anything because space does not exist
| outside of the universe. Or do we say it 'expanded' because the
| distance between the constituent parts inside of the universe
| grew? It's not good to think about really.
| superposeur wrote:
| Indeed time is relative. But, the observed distribution of
| matter in the universe turns out to single out one particular
| frame of reference (= large scale spacetime coordinate system).
| Namely the one in which the CMB radiation is isotropic (same in
| all directions, neither red shifted nor blue shifted). It is
| with respect to this particular reference frame that the "age
| of the universe" is defined.
| zehaeva wrote:
| That is an awful lot of "mights" and "maybes" stacked on top of
| an extension hypothesis of an hypothesis
| causality0 wrote:
| _Zwicky 's tired light theory proposes that the redshift of light
| from distant galaxies is due to the gradual loss of energy by
| photons over vast cosmic distances._
|
| Wouldn't this being true require upending half of what we know
| about the nature of photons?
| mentos wrote:
| Anyone feel like beginning and ends are just an illusion of the
| third dimension and at some higher dimension things just 'exist'?
| booleandilemma wrote:
| It doesn't look a day over 10 billion!
| kleene_op wrote:
| IANAP, but as a mathematician it seems extremely inelegant that
| there would be a start to the time dimension of the space-time
| object we live in, when we don't even know if the spatial
| dimensions are finite themselves.
|
| It is my understanding that the density of the universe billions
| of years ago was radically different from the one we now observe,
| and since density is intrinsically tied to our perception of
| space and time, wouldn't it make more sense that time actually
| stretches infinitely the further back we go, thus nullifying the
| concept of a beginning?
|
| I guess I'm having a hard time with the idea that space-time
| could be discontinuous.
| lioeters wrote:
| Similarly, I find the idea of the end of time to be weirdly
| unreal and impossible. It feels like time is not a thing that
| has a beginning or an end, and that it would just stretch and
| dissipate infinitely into the future.
| empyrrhicist wrote:
| If electrons decay, there will be a time when there's nothing
| in the universe which can function as a clock.
| eis wrote:
| Which does not mean that time stops. If no one hears a tree
| fall that does not mean the tree isn't falling.
| 8note wrote:
| You can still imagine that as an end, and define an end based
| on that infinite stretch. At some point, you can't tell the
| difference between before and after more stretching, and
| you'll never be able to stretch in a way that can be noticed.
|
| There's no more events to happen, and more so, no ability for
| more events to happen.
|
| Thats still likely an artifact of our models though, and that
| when you do to something like that, that new events start
| happening again
| akira2501 wrote:
| > that space-time could be discontinuous.
|
| Why not? Tons of things are, for example, entropy. I have a
| crackpot idea that the Big Bang itself was just an "entropy
| population inversion." The big bang is literally just the
| moment where the discontinuity occurs.
| misnome wrote:
| Are you sure that you never read Asimov's "The last
| Question"?
| akira2501 wrote:
| I have not. Judging from the plot summary, it is a very
| similar idea... albeit from a highly metaphysical
| perspective.
| speak_plainly wrote:
| I think that by definition if the universe was at one point a
| singularity then there is a start to time and space.
|
| This idea goes all the way back to Plato and his Parmenidean-
| inspired rejection of the Pythagorean notion of the Monad as
| being at the centre of the universe as the Number One implies
| certain properties like perfection, unity, etc., and we see
| none of those properties in our existence. This led Plato to
| argue that the One existed separately from our reality, which
| was just an imperfect copy associated with the idea of an
| indefinite Dyad.
|
| So it wasn't just that the universe was a densely packed packed
| ball of all the stuff we see today and it somehow spilled out
| or burst forward, what existed before was a monad, and all the
| stuff we see including space-time, the elements, and more were
| created at the time of the Big Bang.
| justrealist wrote:
| s/"universe"/"Observable universe"/
|
| that's the context in which physicists are talking
| [deleted]
| kevinventullo wrote:
| As a fellow mathematician, I think maybe the right way to think
| about physics is that the claims are never even supposed to be
| "true" in some absolute mathematical sense. It's more like true
| to some first approximation.
|
| So maybe we can interpret this claim as saying that 25 billion
| years ago, the universe was kinda similar to what we have now,
| but 27 billion years ago everything was ultra compressed and
| gravity didn't have a significant effect on anything. Or maybe
| time is like a left-open interval. Finite, but didn't have a
| start. I dunno, I'm making stuff up.
| Certhas wrote:
| Left open interval is the right way to view it. There is no
| contradiction or paradox here. Merely unfamiliarity. But
| maybe you should not expect the rules of the early universe
| to be very familiar...
| WallyFunk wrote:
| > wouldn't it make more sense that time actually stretches
| infinitely the further back we go, thus nullifying the concept
| of a beginning?
|
| I believe it could be 'turtles all the way down' as the phrase
| goes. Maybe our Universe started by a collision of two or more
| _other_ Universes and we got this mess called the Big Bang.
| This doesn 't explain how those other Universes started though.
|
| But then as mere humans, we can't conceptually grasp Infinity
| itself. This is not some failing of ours, it's actually
| convenient to not imagine infinity, as it would drive us mad.
| The minute you include the Infinity Symbol ([?]) in a math
| equation, all logic starts to cease and get very wobbly.
| belfalas wrote:
| _> Maybe our Universe started by a collision of two or more
| other Universes and we got this mess called the Big Bang._
|
| Once upon a time I watched PBS Nova program about string
| theory. I remember they talked about something along these
| lines. It's been almost two decades since I saw it so memory
| is rusty. But it was something along the lines of universes
| existing in these big "planes" (they visualized them like
| these big floating membranes) that would vibrate and
| occasionally smack into each other. When one of these
| collisions would occur, there was the potential for a new
| plane to be formed from that collision.
|
| Like you said, that could potentially explain where new
| universes come from, but not how the other "turtles" got
| there in the first place.
| award_ wrote:
| That's brane or membrane theory. I think Ed Witten was a
| big proponent of it? I saw the same documentary btw ;-)
| [deleted]
| gmmeyer wrote:
| The question is "how long has it been since the big bang." It's
| an important and relevant question for cosmology and physics.
| It isn't really a stance on the "beginning of time," which may
| have started long before this moment, but it is the start of
| the universe as far as physics is concerned.
| malux85 wrote:
| One thing I have always wondered, since gravity is
| proportional to the mass of the two objects and inversely
| proportional to the square of the distance between them, if
| the universe was smaller with the same mass, wouldn't gravity
| have been more "dense" in an earlier universe?
|
| And since we know that gravity affects the rate of flow of
| time, wouldn't the rate of time be enormously distorted
| earlier universe?
|
| I'm not trained in any of this, so hopefully there are
| greater minds here who can help me understand
| ben_w wrote:
| > inversely proportional to the square of the distance
| between them
|
| As I understand it, that's an approximation for Euclidean
| space because the area of a sphere is also proportional to
| the square of the radius in such a space, but it's not true
| of non-Euclidean spaces like in GR because the area-radius
| relation is different.
|
| IIRC, the cosmic microwave background has a gamma factor of
| about 1100, so the area of that shell is the same as one
| 1100 times closer or 1/1100^2 times the area as a Euclidean
| sphere with that radius.
|
| > And since we know that gravity affects the rate of flow
| of time, wouldn't the rate of time be enormously distorted
| earlier universe?
|
| Time did indeed slow down then compared to now, although
| it's not entirely obvious to me that this has any physical
| interpretation when it happens "everywhere":
| https://youtu.be/66V4RSmDqYM
| candiodari wrote:
| We know that the force carrying particles of all forces
| have a frequency, just like any other particle. That means
| that if particles on average move faster than, say, double
| that frequency, they can't exist.
|
| So there must have been a time when electromagnetism, the
| weak and even the strong force just didn't exist. They
| couldn't. So particles would just have totally ignored
| those forces.
|
| We don't know if gravity is the same, but ... why wouldn't
| it. Though of course according to relativity gravity just
| wouldn't care, but that just raises a lot more questions
| than it answers.
| addaon wrote:
| > particles on average move faster than, say, double that
| frequency
|
| What does it mean to compare ("faster") a velocity and a
| frequency (inverse time)?
| ajross wrote:
| > It isn't really a stance on the "beginning of time," which
| may have started long before
|
| Well... yes it is, in the rigorous sense of "time" defined by
| general relativity. There's no "before" for a singularity. It
| may not be the whole story, but whatever metaphysical notion
| defines the "before/beyond/outside/why" that drives the big
| bang, it's not a place on the "time" axis of spacetime.
| Natsu wrote:
| > There's no "before" for a singularity.
|
| How does that work for black holes? It seems like there
| would be a 'before' they formed in the time dimension of
| our universe, if not within the singularity itself.
| [deleted]
| mathematicaster wrote:
| IMHO this conflates model with reality. GR is a model.
| lvncelot wrote:
| Specifically, GR is a model that breaks down at
| singularities. That time "begins" at the Big Bang is a
| prediction of GR, but until we have a model of quantum
| gravity there's no telling whether that's actually true
| or whether the conditions at the big bang are something
| GR can't fully describe.
|
| Similar to the singularities in black holes - everything
| up to a stone's throw of the event horizon is pretty well
| explained by GR, but as far as the horizon itself or the
| region beyond are concerned, there might be dragons as
| far as we know.
| davorak wrote:
| > but it is the start of the universe as far as physics is
| concerned
|
| At least what we currently spend most of time
| studying/researching in physics right now. We can hope to
| expand beyond that given enough time.
| philipov wrote:
| > _...given enough time._
|
| There might literally not be enough time to expand beyond
| that, given how cosmological horizons work. Being part of
| the system we're trying to observe puts some nasty limits
| on what we can know, even in principle.
| outworlder wrote:
| There are even (ever shrinking) limits on how much of the
| universe we can observe.
| [deleted]
| fnordpiglet wrote:
| Maybe I guess. Many models stipulate that time began with the
| Big Bang. Many propose the Big Bang was a local event that
| obliterated our ability to observe time before it. We have
| models where the universe rips apart, collapses, or just
| evolves forever and always has and always will. I think
| what's crucial to understand is we have a lot of different
| possible explanations for what we see, some of them discuss
| beginnings and ends, some do not. Perhaps as a mathematician
| with a relatively closed set of possibilities for
| explanations that's unsettling. But, I've always found the
| various paradoxes in math to illustrate similar problems in
| formulating a closed and coherent anything, including the
| universe.
| tomp wrote:
| As a mathematician, I don't think about _Big Bang_ as the
| "start of time" (or any other dimension), but simply as "fixed
| point" (of the "physical evolution of all particles in the
| universe" function).
| Certhas wrote:
| It's not a fixed point of the equations, though. That is
| technically incorrect and also not the right intuition. It's
| the exact opposite. It's a point at which the acceleration of
| (the density of) all particles diverges, and thus the
| equations can not be continued past that point.
| [deleted]
| marcyb5st wrote:
| While I agree with you on this "hack", I also believe that if
| we accept that geodesic incompleteness idea is right then time
| for all intense and purposes has a start. At least as observers
| within the bubble of space-time that is causally connected.
|
| If time/space-time existed before the BigBang is probably an
| unanswerable question (unless we are within a 4d black hole and
| we can listen to waves that perturbed the matter before the
| formation of our universe).
| rightbyte wrote:
| > If time/space-time existed before the BigBang is probably
| an unanswerable question
|
| Why? Any sign of another Big Bang going from some other point
| somewhere else would indicate that "our" Big Bang might not
| have been the first one. It is harder to prove absence
| though.
| marcyb5st wrote:
| Several (possible) reasons:
|
| Because if inflation is also correct we lost every causal
| connection with whatever was there before, or is so diluted
| that we might not be able to detect.
|
| Another possibility could be that at the time of the
| BigBang the energy density was so high that everything was
| unified, and so when forces actually separated they "tabula
| rasa" anything that occupied the bubble of space-time we
| expanded into.
|
| However, it could also be that the fluctuations we see in
| the CMB are due to perturbations of what happened before.
| But that possible clue is better explained by comic
| inflation expanding quantum fluctuations at an incredible
| speed that disconnected them.
|
| That's why I said it's (probably) unanswerable. I also hope
| I am wrong though.
| goodbyesf wrote:
| As I understand it, 'the beginning' is when 'the universe' had
| a 'once-in-a-gazillion' moment where the probabilistically
| unlikely event of entropy shrinking to a very small value
| happened ( aka 'the beginning' ) and from whence entropy
| started to increase again as it is wont to do.
|
| It all goes back to thermodynamics and the probabilistic
| understanding that entropy 'always' increases. But if entropy
| always increases then by reason, it must have started off at
| small minuscule point sometime in the past. But if energy/mass
| are constant, how could it have gotten to the low entropy in
| the first place? Given enough time, a 'once-in-a-gazillion'
| event actually happened. At a fundamental level, it's all
| mathematical guesswork.
| fnordpiglet wrote:
| My understanding is that in models where time began at the Big
| Bang space typically also began concurrently. Before this time
| (harhar) there was nothing, but that's meaningless because time
| also didn't exist. It's immeasurable before a certain point.
| Likewise space began at that time and expanded to fill all
| space rapidly, which I'm often a little unclear here, but my
| understanding is in a similar way to how space expands today
| outside of galaxies by space simply expanding from within
| itself (I.e., without force or movement). This
| conceptualization might help quiet that discontinuity
| discomfort.
|
| I'll search for it but PBS Space time has some wonderful
| intuition building visualizations and explanations in some of
| their parts on models for the beginning of the universe. If I
| can find the ones I'm thinking of I'll edit later, but
| regardless I find their background material on "wtf" re:
| physics can be helpful.
| Certhas wrote:
| It's unclear what exactly you have in mind, but the equations
| of GR simply predict that the topology of space-time is not
| that of R^4, but includes boundaries at finite (temporal)
| distance, so-called space-like singularities [1]. This is not
| unusual. For example, the solutions to the ODE dx/dt = -1/x
| topologically live on the half line.
|
| [1]
| https://en.wikipedia.org/wiki/Penrose%E2%80%93Hawking_singul...
| nonameiguess wrote:
| This isn't really what "start" is usually intended to mean.
| They're just identifying the time of the Big Bang, beyond which
| any possible causal connection is lost and we can't possibly
| look back further. More time, more space, more something else
| may have existed and been causally prior, but we can't
| meaningfully talk about it except speculatively. It isn't part
| of _our_ spacetime.
|
| Of course, people do speculate. I seem to recall some level of
| anisotropy in the cosmic microwave background that was a bit
| more than expected purely from quantum vacuum fluctuations in
| the pre-inflationary early universe and at least one physicist
| musing that it might be a perturbation from some other universe
| that has since lost causal connection. This, of course, makes
| no testable predictions, can't be falsified, isn't really
| science, but human intellectual curiosity goes beyond science.
| soligern wrote:
| It's all irrelevant until we can answer what does the universe
| exist _in_ , which we never will.
| uwagar wrote:
| could be 'on' too. like on a gigantic tortoise.
| n_sweep wrote:
| it's tortoises all the way down
| VincentEvans wrote:
| I propose the universe exists in itself. That the
| interstellar space - is the same as subatomic space. Its both
| at the same time, like a mobius strip. Space between stars is
| space between atoms, etc.
| ouid wrote:
| [dead]
| boeingUH60 wrote:
| I can't even comprehend 26.7 billion years. That's like the
| average American living 342 million lives over.
|
| The current world superpower is barely 300 years. Imagine what
| could change in a thousand, then a million, then billion...mind-
| boggling!
| Sharlin wrote:
| Food for thought:
| https://en.wikipedia.org/wiki/Timeline_of_the_far_future
| shagie wrote:
| Video version: https://youtu.be/uD4izuDMUQA
| The_Colonel wrote:
| Compare that to the size of the observable universe which is a
| sphere with a diameter of 5 x 10^23 kilometers.
|
| Or to the number of stars in the observable universe - 200 x
| 10^21. One star / (roughly corresponding) solar system is
| unimaginably huge and then there's so many of them.
|
| In comparison to some of these other measures, the age on the
| order of 10s of billion years seems actually surprisingly
| modest.
| Koshkin wrote:
| A few minutes in, this video talks about billions of _trillions
| of trillions_ years into the future.
|
| https://www.youtube.com/watch?v=uD4izuDMUQA
| tristanc wrote:
| Woah, is this suggesting that the cumulative human-years
| experienced by current living US population will add up to the
| age of the entire universe?
|
| Mind-boggled again!
| eindiran wrote:
| >>> 27600000000 / 332000000
|
| 83.13253012048193
|
| According to google the current life expectancy (in 2020) is:
|
| 77.28 years
|
| So a touch shy, but almost.
| [deleted]
| [deleted]
| esun wrote:
| and this <waves hands around> is all we have to show for it?
| konfusinomicon wrote:
| if it wasn't for those pesky extinction level events that come
| about every now and then
| 7373737373 wrote:
| There are these two nice videos with the (apparently now
| outdated?) 13 billion years:
|
| To Scale: TIME: https://www.youtube.com/watch?v=nOVvEbH2GC0
|
| Timelapse of the entire Universe:
| https://www.youtube.com/watch?v=TBikbn5XJhg
| largbae wrote:
| Wouldn't this have profound implications for Drake's Equation? If
| the universe is that much older, then heavy elements have likely
| been around much longer. If that's true, then the Solar system is
| much younger than it was yesterday, relatively speaking...
| jfengel wrote:
| Not really. Many of the Drake equation numbers have enormous
| error bars.
|
| Which means that the result goes from "We don't really have any
| idea" to "We don't really have any idea, times two". I suppose
| you could think of that as a big update to your prior, but it's
| no change at all to your confidence, which still runs from (0,
| 1).
| consumer451 wrote:
| Obligatory relevant xkcd: https://xkcd.com/384/
| Pxtl wrote:
| At this point it's reasonable to assume the great filter is
| ahead of us. Even in the "13-billion-year-old universe"
| scenario, even a 1% head-start gives another alien species time
| to colonize every habitable planet in the galaxy thanks to the
| miracle of geometric growth... if interstellar colonization is
| at all possible.
|
| Which it almost certainly isn't.
| cogman10 wrote:
| That assumes that they want to colonize and that our
| definition of "habitable" matches is close to their own.
| Perhaps the most common form of intelligent life likes to
| live without oxygen. Requires very light gravity. Or has a
| temperature range widely different from our own.
|
| I'd assume that if they wanted to spread out, they'd probably
| have the ability (like we do) to scout out a solar system
| before sending a ship. Maybe our 8 planets don't have
| anything of value for the species looking.
| Pxtl wrote:
| We can ignore all those cases. Because the fact is that
| carbon-based oxygen-breathing mostly-liquid-water lifeforms
| must exist out there since they're the only kind we're
| aware of. And if exotic life does not interact with
| carbon/oxygen/water life, then those other aliens can still
| expand freely. And so they should be here already.
| AgentME wrote:
| Why assume it's ahead of us? That would be assuming there are
| many intelligent civilizations in the local observable
| universe, facing challenges that are much more insurmountable
| than the tiny chances of abiogenesis and development of
| intelligent life. Interstellar colonization sounds hard, but
| when you include possibilities like self-replicating probes
| and AI, it doesn't sound so impossible to expect no
| intelligent life to have managed it yet in a well-populated
| universe. The possibility of the great filter being behind us
| (life, complex life, or intelligent life is exceedingly rare)
| still makes a lot of sense.
| ben_w wrote:
| An industrial and expansionary civilisation which came into
| existence anywhere in the Milky Way 10 Mya, and whose
| interstellar travel was limited to 0.01c, would've
| colonised Earth while we were still in the process of
| losing our body fur and interbreeding with Neanderthals.
|
| This is fairly recent compared to the age of the universe,
| and the speeds can be achieved with know (albeit expensive)
| human technology.
|
| If the aliens had self replicating probes (of the robotic
| kind, not the organics-in-factories kind), the known rules
| of physics _suggest_ that a Dyson swarm can be built in
| less than a century, at which point (0) now you have to ask
| why there are stars to see, and (1) 0.9c is easy, as is
| going intergalactic, so such a civilisation can't have been
| that recent in half the Council of Giants either.
|
| That we can see stars and that we exist, says that
| expanding industrial intelligences like us, either never
| got to this stage, or are filtered in what currently looks
| like a small gap between here and there.
|
| Misaligned AGI that doesn't want to expand could be one, so
| could in-fighting necessarily becoming too easy at the same
| time as any tech for interstellar expansion.
|
| Personally, I think there's dozens to hundreds of small-ish
| (think factors of 0.95-0.10) filters, some ahead, some
| behind.
| m3kw9 wrote:
| I think the ideas about needing our seeds spreading across
| the universe made us very narrow minded. My theory is that
| the desire to do that is eliminated with advanced enough
| tech. Say they can create their own universe, dimensions/
| virtual worlds/ transfer consciousness/ live forever/etc
| witch would go against us expecting alien species populating
| every corner
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