[HN Gopher] The Expansion of the Universe
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The Expansion of the Universe
Author : nabla9
Score : 51 points
Date : 2021-04-09 19:33 UTC (3 hours ago)
(HTM) web link (johncarlosbaez.wordpress.com)
(TXT) w3m dump (johncarlosbaez.wordpress.com)
| WindyLakeReturn wrote:
| One 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
|
| 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.
| strange_things wrote:
| The 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 wrote:
| It 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 wrote:
| Sorry my friend, I think I do not follow you!
| andrewstuart wrote:
| It makes me sad that the universe will eventually become
| completely invisible in all directions.
| lmilcin wrote:
| Most of the universe already became invisible.
|
| And most of what is still visible is also completely
| unreachable.
| dogma1138 wrote:
| We don't know how much there is beyond the observable
| universe really.
| mensetmanusman wrote:
| The funny thing is that it will really look like earth is the
| center of the universe for those people...
| andrewstuart wrote:
| My understanding is our galaxy will still be here.
| dogma1138 wrote:
| We might actually be close to it
| https://en.m.wikipedia.org/wiki/Axis_of_evil_(cosmology)
| transfire wrote:
| Even 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 wrote:
| Don't worry, Andromeda has got you covered. It is predicted to
| collide with The Milky Way in 4.5 billion years.
| macintux wrote:
| Related recent discussion:
|
| https://news.ycombinator.com/item?id=26732996
| gattr wrote:
| If 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
| markus_zhang wrote:
| Meantime, some programmer is frantically adjusting his cosmic
| expansion variable to get the best pic to his boaed of directors
| (Gods)
| mike_ivanov wrote:
| * Given that the current measurement of expansion acceleration is
| accurate and, most importantly, non-local.
| trhway wrote:
| so 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 wrote:
| That 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 wrote:
| Aren'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 wrote:
| A lot of thought has gone into this topic [1].
|
| Enjoy!
|
| [1]: https://www.youtube.com/playlist?list=PLIIOUpOge0LvHsTP5
| fm8o...
| waynesonfire wrote:
| related 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
| distribot wrote:
| It'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 wrote:
| The visible light era of the Universe is relatively short
| compared to what comes after. People think of this as a
| long dark night. To some extent that's true.
|
| Another perspective is that this will be the Golden Age
| of the Universe [1].
|
| [1]: https://www.youtube.com/watch?v=Qam5BkXIEhQ
| cletus wrote:
| I believe that spacefaring life is relatively rare in our
| neighbourhood to the point where it's entirely possible we're
| the only one.
|
| As for signs of alien civilization being everywhere, here I
| have to respectfully disagree. I'll summarize why.
|
| I firmly believe the likely future of humanity is not on
| planets but in orbitals. Planets are a great way of storing
| mass. They're a poor way of creating living area. I think the
| estimate is that 1% of the mass of Mercury could fully
| encompass the Sun in a Dyson Swarm of orbitals with no material
| stronger than stainless steel. I believe humanity will be
| capable of this within 1,000 years and that's super-
| conservative.
|
| Objects in space that absorb Solar radiation heat up. The only
| way of releasing that is by radiating it away. That radiation
| is of a wavelength solely determined by the temperature of the
| object. For any reasonable temperatures, that's in the infrared
| spectrum.
|
| So a Dyson Swarm will have a very particular spectrum. They'll
| be IR lanterns. Sure one star we may not see out of a whole
| galaxy but the barrier between doing this to one star to the
| whole galaxy is only a matter of a relatively short amount of
| time (cosmologically speaking). One million years for the Milky
| Way (out of 10B+ years).
|
| There are a bunch of assumptions in this and each would be
| their own topic. But as a solution to the Fermi Paradox, it
| only takes one.
|
| Recycling waste heat is a common objection but that just
| reduces your emissions, it doesn't eliminate them. If it did,
| that would break thermodynamics.
|
| This argument is strengthened by this article: over time more
| mass is becoming unreachable. For truly long-lived
| civilizations it makes the most sense to grab as much mass as
| you can and sequester it. Again, it only takes one.
| gibybo wrote:
| Can't they reflect that radiation away from other galaxies,
| or even in to their host star?
| cletus wrote:
| Materials absorb some quantity of IR radiation. This will
| heat them up. What you're talking about is essentially a
| variation of recycling heat. It's imperfect so there'll be
| some IR signature.
| simonh wrote:
| Also for most of those 14 bn years heavy elements weren't
| abundant enough for many rocky planets to form. It took several
| generations of stars and cycles of supernovas to end up with
| the heavy element rich environment we find ourselves in. Our
| star's siblings might be the first generation with a rich
| enough planetary environment and abundance of heavy elements to
| support life and technological civilizations.
| twhb wrote:
| I 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 wrote:
| We'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 wrote:
| Evidence 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_o
| f_cosmological_theor...
| hankchinaski wrote:
| relevant to the expansion of the universe is "Do You Expand With
| The Universe" from Veritassium
| https://www.youtube.com/watch?v=9DrBQg_n2Uo
| mseepgood wrote:
| It's not clear if humankind survives the next couple hundred
| years.
| simonh wrote:
| It'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.
| fairity wrote:
| Indefinitely? The sun will eventually blow up.
| simonh wrote:
| And it might be possible to escape or survive that, at
| least for a while, I don't know for sure.
| mshumi wrote:
| One 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 wrote:
| > 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?
| __blockcipher__ wrote:
| This 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.
| simonh wrote:
| Distant 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!
| tobmlt wrote:
| Parsing 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 wrote:
| > 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 wrote:
| The speed of light ought to remain constant (for inertial
| observers). So nothing would be different locally as far as
| I'm aware.
| krapp wrote:
| At 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.
| agumonkey wrote:
| essentially it's similar to a black hole.. nothingness
| rendall wrote:
| No. The expansion of the universe does not mean that atoms
| themselves will fly apart
| anbende wrote:
| Actually it might. If expansion accelerates indefinitely,
| which is one of the theories, then eventually expansion
| will be stronger than the binding force of atoms and then
| sub-atomic particles. This is called the "Big Rip".
|
| https://en.wikipedia.org/wiki/Big_Rip
| amelius wrote:
| I'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 wrote:
| I'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.
| nahuel0x wrote:
| Fear 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.
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