[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 ___________________________________________________________________ (page generated 2023-07-13 23:01 UTC)