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The Expansion of the Universe
- __blockcipher__ 6y agoThis might be obvious to most, but at first it wasn't clear to me why in 150 billion years the vast majority of the known universe will be unreachable. The answer is in the acceleration of expansion (which the blogpost mentioned but I didn't connect the dots on at first); eventually the rate of expansion ("velocity") will greater than the speed of light.
- tobmlt 6y agoParsing this, I’d like to match it up with the Hubble horizon, at least for your stated condition that the velocity of expansion is greater than the speed of light: That already holds for us relative to points across the Hubble horizon. Their “past-emitted” light is still reaching us, meanwhile their “presently emitted” light never will. I need to check the proper definitions but that’s the gist. Kinda erie!
- amelius 6y ago> eventually the rate of expansion ("velocity") will greater than the speed of light. What will that do to the speed of light as measured on Earth? And will this affect, say, the correct operation of computers?
- WillySchu 6y agoThe speed of light ought to remain constant (for inertial observers). So nothing would be different locally as far as I'm aware.
- raattgift 6y agoThe speed of light (in vacuum) is constant for accelerated observers too. :-) The dipole anisotropy of the Cosmic Microwave Background will continue to be a good tool to see the constancy of the speed of light for all observers into the practically infinite future, assuming the infinite future looks a lot like de Sitter space (which is essentially what the standard cosmology predicts). http://www.astro.ucla.edu/~wright/CMB-dipole-history.html http://www.astro.ucla.edu/~wright/CMB-dipole-history.html The far future of the universe will still have generally covariant physics, as does its far past, sharpening up your second sentence.
- krapp 6y agoAt that point in time (assuming time has any meaning in that reference frame,) everything will be moving away from everything else faster than any force, even information, could possibly travel between them. There won't be computers. There won't even be atoms to make matter to make computers with.
- amelius 6y agoI'm still wondering if the change would be instantaneous or gradual. Will the speed of light be constant and then suddenly impossible to measure?
- WillySchu 6y agoI'm not precisely sure what you're referring to as "the change" here. The rate of expansion is increasing continuously though, if that's what you're asking. As far as the measurability of the speed of light, I don't think anything changes in principle. It should remain measurable and constant. However, it gets a lot more complicated in practice, since it's pretty unclear who or what would actually be doing the measuring and how they might go about it.
- agumonkey 6y agoessentially it's similar to a black hole.. nothingness
- rendall 6y agoNo. The expansion of the universe does not mean that atoms themselves will fly apart
- simonh 6y agoDistant regions of the universe already are receding from us faster than light. Due to the accelerating rate of expansion, that horizon beyond which this is true is shrinking inwards towards us, so that in 150 bn years even galaxies outside our local group will be beyond that horizon. Hurry up Elon, we're running out of time!
- andrewstuart 6y agoIt makes me sad that the universe will eventually become completely invisible in all directions.
- lmilcin 6y agoMost of the universe already became invisible. And most of what is still visible is also completely unreachable.
- dogma1138 6y agoWe don’t know how much there is beyond the observable universe really.
- mensetmanusman 6y agoThe funny thing is that it will really look like earth is the center of the universe for those people...
- dogma1138 6y agoWe might actually be close to it https://en.m.wikipedia.org/wiki/Axis_of_evil_(cosmology) https://en.m.wikipedia.org/wiki/Axis_of_evil_(cosmology)
- mensetmanusman 6y agoWow, this is great. Thanks
- andrewstuart 6y agoMy understanding is our galaxy will still be here.
- macintux 6y agoRelated recent discussion: https://news.ycombinator.com/item?id=26732996 https://news.ycombinator.com/item?id=26732996
- hankchinaski 6y agorelevant to the expansion of the universe is "Do You Expand With The Universe" from Veritassium https://www.youtube.com/watch?v=9DrBQg_n2Uo https://www.youtube.com/watch?v=9DrBQg_n2Uo
- mseepgood 6y agoIt's not clear if humankind survives the next couple hundred years.
- simonh 6y agoIt's a reasonable concern. I think we'll probably survive indefinitely, after all if Mars can be colonised it's hard to imagine we could screw up Earth so badly it's less habitable than that. However, the planetary environment could become so hostile that it takes so much effort to maintain civilization that our capabilities become severely limited. So my concern isn't so much us dying out, as we become doomed to a fairly marginal existence, incapable of interesting achievements such as interstellar exploration.
- nahuel0x 6y agoFear of individual/personal death is somewhat mitigated because we know other beings will survive us. Now imagine if all the life forms and stars destiny is an eternal and permanent death, all of them, just like forever. Feels as staring at an abyss.
- gattr 6y agoIf anyone begins to feel trapped in a cage, please don't just yet. For instance, astronomers currently estimate on the order of 10¹² planets in Milky Way alone, of which up to 11 billion could be Earth-sized and orbiting Sun-like stars [1]. So there's still plenty to explore/colonize, especially if you include the few tens of neighboring galaxies. [1] https://en.wikipedia.org/wiki/Milky_Way#Contents https://en.wikipedia.org/wiki/Milky_Way#Contents
- mike_ivanov 6y ago* Given that the current measurement of expansion acceleration is accurate and, most importantly, non-local.
- transfire 6y agoEven the closest galaxies are so far away, its unlikely we can reach them even with a warp drive. However, it's possible that the accelerated expansion might prove an aberration that only makes the galaxies seem as if they are "quickly" moving beyond our reach. In which case, what a relief! LOL
- btilly 6y agoDon't worry, Andromeda has got you covered. It is predicted to collide with The Milky Way in 4.5 billion years.
- trhway 6y agoso a star A at the distance 13.7B ly from us is running away with "c". Until you believe that today is an unique moment in time, we can expect that in 100M years a star B at the distance 13.8B ly will be also moving with "c" away from us. If we allow for accelerated expansion of the Universe, then it means that the star B is closer to us then the star A (with the star A moving away faster than "c" in 100M years from today - i.e. accelerated expansion) - i.e. today the star B is closer to us than 13.7B ly and runs away slower then "c", and thus in the next 100M years the star B would be expected to make a journey longer than 100M ly - from some point today closer to us than 13.7B ly to the point at 13.8B ly in 100M years - i.e. it would need to run away faster then "c" during those 100M years which is clearly a contradiction. That leads to conclusion that whatever speed a star runs away with today, it will be running away with the same speed tomorrow - that means decreasing Hubble constant - which is normal giving the same energy being spread in a bigger and bigger space. And when it comes to observing the observable Universe - the star A will always run away with "c", and whatever stars B are closer to us then the star A ( and thus running away slower than "c" today), those stars B will never run away faster than "c" - thus the light from them will always come to us. Note: the stars which are farther away moving faster isn't acceleration of expansion. Acceleration of expansion would be if the same stars were running away faster tomorrow than today - which would clearly lead to the contradiction pointed above. Hubble constant decreasing with time is the only way to avoid that contradiction. That also probably explains different Hubble constant values we currently have - as they are obtained using signals from different points in the Universe history.
- rendall 6y agoThat humans exist a mere 14 billion years into a universe that will exist for many quintillions of years is so exceedingly improbable that we may very well be the first sentient life. This is one of my favorite explanations for the Fermi Paradox. My other favorite is that there is no Paradox. The signs of alien civilizations are everywhere, but humans cannot perceive or understand it
- taberiand 6y agoAren't most of those quintillions spent during the heat death when there no real available energy and everything is nothing more than a barely held together soup of matter?
- cletus 6y agoA lot of thought has gone into this topic [1]. Enjoy! [1]: https://www.youtube.com/playlist?list=PLIIOUpOge0LvHsTP5fm8oxB1qPS54sTMk https://www.youtube.com/playlist?list=PLIIOUpOge0LvHsTP5fm8o...
- waynesonfire 6y agorelated to this, i love this video: TIMELAPSE OF THE FUTURE: A Journey to the End of Time (4K) https://www.youtube.com/watch?v=uD4izuDMUQA https://www.youtube.com/watch?v=uD4izuDMUQA
- distribot 6y agoIt's definitely interesting, but I don't get how this kind of thing doesn't make other people feel a kind of intense sadness. It's like the intersection of the insignifigance and smallness of my own individual existence + the immense scale of time to underscore that fact + the fact that even all the things that are spectacular and powerful also meet the same kinda end as me. Something about the 58 billion trillion trillion trillion trillion years last black hole thing just bums me out.
- cletus 6y ago
- twhb 6y agoI don’t think human science is remotely advanced enough to make one million year predictions, let alone 150 billion. We still have the giant dark matter fudge factor that eludes experimental verification, we’re still inventing new particles to make quantum math work, we still can’t come up with any theory that explains all our observations. Extreme predictions require extreme precision of data and model, and it seems that our models have already hit their limits on much more pedestrian problems. Like Newton’s physics, they are a function that fits reality well only within a certain range of values. This is not an anti-science sentiment, by the way, just maintaining scope and margins of error.
- cletus 6y agoWe're talking about the expansion of the Universe here. This expansion has 14 billion years of evidence in the observable Universe to support it. Experimental evidence has shown this expansion is increasing not decreasing. This isn't to say that the expansion won't slow, stop or even reverse but that claim requires a testable theory. The Universe is expanding based on all our understanding and all the experimental evidence we have to date is not an equivalent position to "well, we really don't know what will happen in a billion years".
- twhb 6y agoEvidence doesn’t show anything, it supports things. Theories are replaced all the time by new theories that are supported by all the same evidence, and even more. Since this has been happening to theories on the fate of the universe on average once per generation for the past 100 years, and each successive theory has also had experimental support and scientific consensus, I’d say evidence supports a prediction of at least one more change, wouldn’t you? Amid other information, this page lists major changes to cosmological theory: https://en.wikipedia.org/wiki/Timeline_of_cosmological_theories https://en.wikipedia.org/wiki/Timeline_of_cosmological_theor...
- markus_zhang 6y agoMeantime, some programmer is frantically adjusting his cosmic expansion variable to get the best pic to his boaed of directors (Gods)
- mshumi 6y agoOne wonders if it is some fundamental assumption that limits further understanding of the Universe. Is it our intuitive relationship with numbers, time, and physical space that is limiting? We all grow up with societally imposed relationships between numbers, time, and physical space, but are these learned or do they actually reflect objective reality. The frameworks derived from these fundamental assumptions are excellent for making predictions and are testable within those frameworks.
- tralarpa 6y ago> One wonders if it is some fundamental assumption One could even go further... Russell once compared the movement of the planets around the sun with people carrying torchs and walking around a mountain during the night. Because it is dark, we don't see that people are carrying those torchs and we are wondering why those lights move in such strange ways. Then then sun rises (Einstein presents his relativity theory) and we understand. We hope such an explanation also exists for the entire universe and its physical laws. But could it be that the explanation is beyond the capabilities of the human brains? I am not talking about complexity or problem size. That could be solved with computers. Maybe there is an elegant, obvious and compact explanation why the universe behaves like it does, but it so much beyond what we consider as logical that if an alien had written it down in a book, we would not even realize what the book is about. Like trying to explain to a dog the concepts of "yesterday" and "tomorrow". Is there a reason to assume that our ape brains are able to understand everything?
- WindyLakeReturn 6y agoOne interesting question of this is if science changes once the other galaxy groups disappear. By that I mean if a human was to redo all previous experiments have we lost any data that would result in us building a different model of the universe than what we've built with the other galaxy groups present. Sure, we will have records of evidence from the past, but records of evidence from experiments that can no longer be repeated is no longer reliable data. This is ignoring the whole development of humanity and science in the intervening 150 billion years which may change what options are available to use then. I'm also not sure if this is the most up to date model of the universe. I've recently dived deep into quantum field theory and theoretical physics (well as deep as one can without understanding a field of spinors) and I've watched a number of lectures given over the last decade that include alternate takes on expansion. I could be completely misunderstanding what was being spoken about, but it appears one possible model of reality is a sort of bubble in hyperexpanding space that gives rise to a big bang event that eventually leads to the bubble becoming hyper expanding space itself that can give rise to further bubbles. Here is one talk. https://www.youtube.com/watch?v=jhnKBKZvb_U https://www.youtube.com/watch?v=jhnKBKZvb_U I recommend the whole thing if you aren't familiar with Boltzmann brains and boxes, but if you want to see the issue with the current model presented in this article go to 41 minute mark and to see a possible alternate model go to about 44:50.
- raattgift 6y agoThe galaxies of the local group won't recede from us. Telescopes as recently as the early 20th century could not resolve the sky well enough to determine which nebulae are in the Milky Way, are satellites of the Milky Way, are in the local group, or are outside it. This lack of observation allowed the Shapeley-Curtis https://en.wikipedia.org/wiki/Great_Debate_(astronomy) https://en.wikipedia.org/wiki/Great_Debate_(astronomy) to last as long as it did -- it ended with clear observations of light curves within M31 and other galaxies in the local group. Those observations will remain available for a lonnnnnnnnnnng time after there are no other galaxy groups in the view of anything in the local group. Moreover, the relic fields (cosmic microwave background and cosmic neutrino background) will be detectable (at least in principle) as they grow ever colder in the far future, so at least the radiation and dark energy sectors can be rediscovered in the distant future when there are no highly redshifted galaxies left to see. We are lucky to have clear views of redshifted, dimmed, smaller-on-the-sky spiral galaxies at all sorts of orientations to us (including face on). Those certainly help us to understand galactic evolution, and also provide us lots of interesting objects (gas and dust clouds, active nuclei, stars, supernovae) "in the past". In the far future, the local group will have fewer spirals, fewer stars, almost no low-metallicity stars, and so on, and recovering those from observation of what's left in the distant future will be more difficult. But around the garganguan black holes left in the local group in the very far future there will still be plenty of dust and gas and cooling stellar remnants; the occasional star will probably form, but not often. Still, the volume will be large enough far into the future that "not often" simply invites wider searches of the sky. Supernovae don't happen often, but thanks to all-sky surveys like http://www.astronomy.ohio-state.edu/~assassin/index.shtml http://www.astronomy.ohio-state.edu/~assassin/index.shtml we see A LOT more of them than could have been hoped for a hundred years ago. Far future astronomers might have a super-hyper-ultra ASAS-SN type programme to look for the earliest signs of star formation in what's left of the local group. Of course as you note, even better would be if the far future astronomers can recover the records of earlier astronomers, rather than having to rediscover everything from scratch using the "records" provided by nature at astronomical scales. The far far future where one cannot see distant galaxies from the local group is very very very very very much earlier than the epoch of fluctuations into Boltzmann brains, vacuum decay, etc. etc., none of which is a really reliable prediction of well-tested theory. (In fact, they are diagnostic of theoretical deficiencies: how do we prevent objects that can happen according to a theory from happening according to that theory, given that we do not see those objects? This recurs a lot at the edges of theoretical physics: in General Relativity it's the basis for developing the https://en.wikipedia.org/wiki/Energy_condition https://en.wikipedia.org/wiki/Energy_condition (s) for instance).
- strange_things 6y agoThe following seems to be missed by many anons: * spacetime itself literally “creates itself out of nothingness”. We say it “stretches”, but don't picture a string of cheese “thinning out” but rather something of constant density being continuously expanded. * local groups (of galaxies) are gravitationally bound i.e they won’t scatter around and they attract each other with gravity so they will stay together even though more spacetime is created inside of them. * in the empty “space” between local groups something (dark matter? Dark energy? ) causes this steady continuous creation of new spacetime * this creation of spacetime is itself accelerating, but this is not speed, so distant local groups are not “moving away from us” but are being “displaced away from us”. Hence the displacement rate is allowed to be faster than the speed of light (since it’s not a speed) * every single object in the universe moves at exactly and precisely the speed of light c through spacetime. Objects at rest (a completely stationary astronaut stranded in the empty space between local groups) is also moving at the speed of light in spacetime: he is moving only through time. * A photon is moving only through space and has no time Sources: The Elegant Universe, Brian Greene, ScienceClic YouTube, and my memory of these
- pyinstallwoes 6y agoIt makes sense if one pictures the aether as a finite substance over an infinite surface area of and in of itself. Like a limited amount of paint that gets smooshed and pushed around. Intuitively I'd postulate that the aether is an incompressible fluid at 'neutral' - a fundamental formless form with directionality. Then when the aether interacts with itself in opposing currents it creates an inertia against itself causing it to evaporate into matter all the way into planet cores, rock, water, air, then outer space. It basically becomes a pressure gradient at different critical boundaries. Makes sense to me. Can simply a lot of Science most likely, just import the electron as a monopole that builds up into hydrogen and so on. Aether splits into E- and E+ and clumps until 1836 (proton/2 918 aether e+ e-). Can be radically simplified with Torus, Aether, and Hyperboloid fluidic models around Vortices.
- strange_things 6y agoSorry my friend, I think I do not follow you!