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Why the Universe Didn't Become a Black Hole

Posted by Soulskill on from the would-have-been-a-bit-dull dept.

StartsWithABang writes: With some 10^90 particles in the observable Universe, even stretched across 92 billion light-years today, the Universe is precariously close to recollapsing. How, then, is it possible that back in the early stages after the Big Bang, when all this matter-and-energy was concentrated within a region of space no bigger than our current Solar System, the Universe didn't collapse down to a black hole? Not only do we have the explanation, but we learn that even if the Universe did recollapse, we wouldn't get a black hole at all!

68 of 109 comments (clear)

  1. Because of the expansion by penguinoid · · Score: 4, Interesting

    You can't use the Schwarzschild radius calculation for expanding space. The only kind of new part was the bit about not becoming a black hole if it should re-collapse.

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    1. Re:Because of the expansion by Rockoon · · Score: 4, Insightful

      Even if we use the Schwarzschild radius, the radius is so large that we cannot rule out actually being in a black hole anyways.

      --
      "His name was James Damore."
    2. Re:Because of the expansion by Black+Parrot · · Score: 1

      The only kind of new part was the bit about not becoming a black hole if it should re-collapse.

      Which he stated, but did not attempt to explain.

      I always wondered why collapsing matter would drag space with it. After reading the link, I still do.

      --
      Sheesh, evil *and* a jerk. -- Jade
    3. Re:Because of the expansion by Tablizer · · Score: 1

      A survey of what's on TV will confirm that.

      --
      Table-ized A.I.
    4. Re:Because of the expansion by St.Creed · · Score: 1

      As far as I understood the physics, it was because "space" doesn't have a set of well-defined borders with customs etc. but is a curved area, where the curve is defined by the energy available inside the universe (energy == mass). Once the whole thing collapses it should curve the area much steeper, "contracting" the universe.

      But I may be totally off base here, I'm not a physicist.

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    5. Re:Because of the expansion by TiggertheMad · · Score: 1

      Which is really interesting, as being within a SR could be equated to being within the 'universe' as there is no know way to escape either via simple acceleration...

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    6. Re:Because of the expansion by penguinoid · · Score: 1

      Yes you can use the Schwarzschild argument. Expanding space is only a handwaving rationalization, a coordinate-dependent way of thinking that is not compatible with the principle of general covariance.

      I've never heard anything about that, care to explain? It also seems contrary to what I know, see below.

      A less-known fact about black holes is that the bigger they are, the lower the density. If you use the Schwarzschild radius, for an arbitrarily large mass, the radius gets arbitrarily large, and the density gets arbitrarily close to zero. If this applied to expanding space, then it wouldn't be an open question as to whether the universe was infinite or not, as if it were we would be guaranteed to be in a black hole. Then again, maybe we are in a black hole and don't know how to tell the difference.

      If the gravitational source density was ever more than zero, then it follows that the contents of the universe were less massive in the past. In an inertial set of coordinates, not the screwy Freidmann coordinates, it can be understood that the shards of the Big Bang, flying apart at next to lightspeed, still add mass to the universe today, but at a diluted density.

      If you use inertial coordinates, then you don't have gravity because gravity is equivalent to acceleration (this was the insight Einstein used to think up General Relativity). In particular I'd like to see how you deal with expanding spacetime in an inertial reference frame.

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    7. Re:Because of the expansion by Rockoon · · Score: 1

      I find it more interesting that if you graph the density of black holes of varying mass/radius, that you see that the required mass density to form a black hole drops as the mass/radius increases. The radius of the event horizon of a mass equal to the estimated mass of the visible universe (just the ordinary matter) is about 15 billion light years and has a density of only 8.703E-27 kg per cubic meter (about 29 orders of magnitude less than the density of ordinary water at sea level.)

      --
      "His name was James Damore."
    8. Re:Because of the expansion by mburns · · Score: 1

      Actually, because of the principle of general covariance, it is necessary for academics to show that their cosmological calculations work in different coordinates. Thinking that is bound to special coordinates such as the Freidmann coordinates will only be confused by the fictitious forces exhibited therein. The standard mathematical precautions taken against this sort of problem have failed in this case.

      Relativity itself disallows the necessity of thinking that space inherently expands or contracts. The principle of relativity instead allows anyone to think that space is stationary, and that matter and radiation are flying apart in it.

      --
      Michael J. Burns
  2. Business relationship by demachina · · Score: 4, Interesting

    So does ./ have some kind of promotional relationship with startswithabang? If so you should disclose it.

    The blog does have interesting material, and its appropriate for /., so its not like its bad that every article on there is making the /. front page. But its kind of odd that every article on there is making the ./ front page.

    --
    @de_machina
  3. Early universe by rossdee · · Score: 1

    Hadn't they proved (mathematically) that just after the big bang there was a time (inflation) when it was expanding faster than light. If you are going faster than light then you can escape from a black hole.

    1. Re:Early universe by BitZtream · · Score: 3, Interesting

      If you are going faster than light then you can escape from a black hole.

      There is no part of physics that says speed has anything to do with escaping a black hole. If you could produce enough thrust to travel at just one meter per billion years, you could escape a black hole ... assuming you could keep that speed while inside the event horizon of the black hole. Unfortunately, from a mathematical perspective this appears to be impossible.

      After a certain point (the event horizon) light simply bends two quickly back on itself to escape a black hole and stays inside the radius of the event horizon. It doesn't slow down, it changes directions, because space is all sorts of fubar inside the event horizon of a black hole.

      What they've proved mathematically as that at the event horizon of a black hole the math fails. It falls apart and no longer makes any sense because the numbers get too large on one side of the equation.

      In reality, this doesn't mean 'nothing can escape a black hole'. It means 'nothing we've observed can escape a black hole'. Well, except it can. Hawking radiation escapes a black hole as it evaporates, but all the explanations for why are just silly as they are pretty arbitrary compared to 'light' not escaping.

      Another obvious but often overlooked theory is that our universe IS a black hole inside a larger universe. It explains a great many aspects that don't make sense ... but then it also introduces a whole bunch of aspects that don't make sense without making a bunch of assumptions about what is outside our universe, and these assumptions are so absurd from our view point that we just assume they are false.

      The truth of the matter is ... science knows a lot less than they claim to about black holes, the big bang, and the nature of the universe. Many scientist treat theories with holes the size of the planet in them as obvious fact when they are no such thing. They have no fucking clue why the universe exists in the state it exists today, but many of them refuse to acknowledge that FACT to anyone. The good ones do. Einstein as an example, had no problem admitting his theories were nothing more than theories and that they were often wrong because they were simply based on the little bits of the universe we can observe.

      --
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    2. Re:Early universe by boristhespider · · Score: 5, Interesting

      "What they've proved mathematically as that at the event horizon of a black hole the math fails. It falls apart and no longer makes any sense because the numbers get too large on one side of the equation."

      Not so. The maths dies at the singularity at the centre of the hole, but it doesn't at the event horizon except in a badly-chosen coordinate system. Alas, the usual coordinate system we'd present the Schwarzschild solution in is indeed badly-chosen and has an apparent singularity at the horizon, but this is not an actual singularity, as can be seen quickly by calculating a scalar curvature invariant - the Ricci scalar is the immediate choice, it's basically a 4d generalisation of the more-familiar Gaussian curvature - and seeing that it's entirely well-behaved except at the centre of the hole. So we look for a coordinate system well-behaved at the horizon and quickly come across Painleve-Gullstrand coordinates, in which spacetime is locally flat and perfectly behaved at the horizon. The implication is the poor sod wouldn't be able to tell that he'd got to the horizon, except through tidal forces (which depend on the size of the hole), and then he'd struggle to navigate before slamming into a singularity.

      Even more confusingly, for a *realistic* hole, the insides are rather different. A Schwarzschild hole has a singularity inevitably in the future - all future-directed paths one can travel on, or light can travel on, end at the singularity. That's a bit of a bummer if you happen to be in a Schwarzschild hole. But a Schwarzschild hole is not physical; it is a non-rotating, uncharged hole, and that's not a realistic setup. In a charged (Reisser-Noerdstrom) or a rotating (Kerr) or, come to that, a charged rotating (Kerr-Newman) hole the singularity is "spacelike" -- there exist paths on which we could, in principle, travel, that avoid the singularity. In the case of a Kerr(-Newman) hole it's even smeared out into the edge of a disc. In reality, good luck navigating in there, but the singularity is not inevitably in the future in there.

      A bit closer to the point, you're right that speed doesn't really have anything to do with it. Instead it's the type of path you can travel on, and where *they* go. An event horizon can be defined as the surface on which "null" geodesics, on which light travels, remain equidistant from the hole. If you travel, as massive particles do, on a "timelike" geodesic then you're fucked; you're never going to be able to accelerate enough that you even travel on a null geodesic, let alone a "spacelike" geodesic along which you can basically access anywhere. On a spacelike geodesic you could get out of a hole no problem. You could also travel in time, and you could break causality fifteen times before breakfast. I'd like to travel on a spacelike geodesic - it would be fun. Though managing to get back to a timelike geodesic might be significantly less so.

      "Another obvious but often overlooked theory is that our universe IS a black hole inside a larger universe."

      That's an extraordinarily strong statement. Our universe might be indistinguishable from a black hole from the outside, yes, but there's a big "might" in there, and an "outside" that doesn't necessarily make much sense either. It all depends on the setup you're assuming. Sure, we could end up finding that the universe is "inside" a black hole for a given definition of "universe", "inside" and "black hole", or we might find that that statement does not make any extent. I wouldn't want to say anything stronger than that, frankly, not least as I'm aware of models of cosmology that are observationally indistinguishable from a standard, infinitely-extended, flat universe, which are also flat, but which have finite extent. One way to do so is to simply put the universe into a toroidal topology. Since GR is a local theory it says nothing about topology, and it would be hard to argue that a universe extended on a torus would look like a black hole from the "outside", since that would be the entire extent of spacetime.

    3. Re:Early universe by HiThere · · Score: 1

      But do note that you're talking about the velocity at which space is expanding. (Yeah, I know you know that, but I still find it confusing.) This doesn't imply anything about how objects located within space can accelerate. And since in order to get that 5x c velocity you need to be an immense number of light-years away, even contemplating talking about their relative velocities gives me a headache. I mean, if it currently looks to us as if they are moving apart at 5x c, how fast would they be moving apart in a simultaneous framework? We're only talking about three objects, so it should be possible to calculate such a framework, if we presume that no gross disaster has happened while we couldn't observe them because of time lag. IIUC that 5x c relative velocity was calculated based on current observations, but since they are so far away, and space has continued expanding during the time that light was on it's way here, they're probably moving apart much faster than that in "current" time (which, admittely, cannot be observed).

      --

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  4. Re:Big Bang is RELIGION by PPH · · Score: 3, Funny

    In related news, ants develop a religion around the question of why they have not been stepped on by an elephant.

    --
    Have gnu, will travel.
  5. Re:Thats a no brainer! by ArcadeMan · · Score: 1

    The Hitchhiker's Guide to the Galaxy, "Universe":

    1. Area: Infinite. Bigger than the biggest thing ever and then some. Much bigger than that in fact, really amazingly immense, a totally stunning size, real "wow, that's big," time. Infinity is just so big that, by comparison, bigness itself looks really titchy. Gigantic multiplied by colossal multiplied by staggeringly huge is the sort of concept we're trying to get across here.

    2. Imports: None. It is impossible to import things into an infinite area, there being no outside to import things in from.

    3. Exports: None. See Imports.

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  6. Short version by Livius · · Score: 4, Informative

    If at some point in the past the mass of the universe was in a volume wholly contained within its own Schwarzschild radius, why did the universe not become (or, more accurately, remain) a black hole?

    "...Schwarzschild’s solution is a static one, meaning that the metric of space does not evolve as time progresses. But there are plenty of other solutions—de Sitter space, for one, and the Friedmann-Lemaître-Robertson-Walker metric, for another—that describe spacetimes that either expand or contract."

    Literally everything else in the article was off-topic, and I can't help but feel this highly evasive 'answer' might have been "Ask Ethan" admitting he just didn't know.

    Which is a pity because it is a fascinating question.

  7. Re:Big Bang is RELIGION by pikine · · Score: 1

    Sure, in an imaginary world where the graceful and faithful elephant works freakishly hard to make the ants live happy lives even though the ants are so tiny to imagine what this great elephant looks like or means to them. The ants who hate the elephant drown themselves in puddles of water, and we the outsider look at these drowning ants in this imaginary world and think "these ungratefully stupid ants deserve to be eliminated by natural selection." And the elephant looks at us and say "if we can save one more ant from drowning, then why don't we?"

    --
    I once had a signature.
  8. Re:Thats a no brainer! by dimeglio · · Score: 1

    Is it a case of "Honey, I Blew Up the Universe"? The total mass/energy would remain constant but space between particles would just grow larger. The energy which created, and is now expanding the universe, would likely be external to the universe itself.

    --
    Views expressed do not necessarily reflect those of the author.
  9. entropy by StripedCow · · Score: 2

    Wasn't there some conjecture some time ago that entropy decreased inside a black hole, and that our universe corresponded to a time-reversed version of a star collapsing into a black hole? Which of course would be interesting because the "arrow of time" would point two opposite ways in the "meta-universe".

    --
    If Pandora's box is destined to be opened, *I* want to be the one to open it.
    1. Re:entropy by PolygamousRanchKid+ · · Score: 1

      because the "arrow of time" would point two opposite ways in the "meta-universe".

      This is a seriously silly question, but has any serious physicist conjectured that the "arrow of time" could have more than two directions? I mean, like going sideways or something? And what would be the bizarre implications of that?

      --
      Schroedinger's Brexit: The UK is both in and out of the EU at the same time!
  10. terrible article by Charliemopps · · Score: 3, Informative

    Stop posting links to medium.com... the worst Science site I've ever seen short of timecube... wait, actually timecubes at least entertaining.
    All of their articles boil down to:
    Subject "Could *insert some inane scifi topic* really be??"
    10 pages of images scraped from geocities homepages, font type and spacing worthy of a freshman English paper and then...
    No, not really, but thanks for reading!

    You want real science news? Here you go: http://phys.org/physics-news/

  11. Re:Big Bang is RELIGION by Black+Parrot · · Score: 2

    Can't you folks see it is just religion disguised as science, how it implies a divine hand?

    No, you're thinking about the Divine Monkeyspank hypothesis, which is indeed religion, but not disguised as science.

    p.s. - Your troll score is: 0

    --
    Sheesh, evil *and* a jerk. -- Jade
  12. If we're poking holes in the accepted dogma... by emil · · Score: 1

    ...then how about this one?

    One mystery which has not been solved as of 2009 is the absence of red dwarfs with no metals. (In astronomy, a metal is any element heavier than hydrogen or helium.) The Big Bang model predicts the first generation of stars should have only hydrogen, helium, and trace amounts of lithium. If such stars included red dwarfs, they should still be observable today, but none have yet been identified. The preferred explanation is that without heavy elements only large and not yet observed population III stars can form, and these rapidly burn out, leaving heavy elements which then allow for the formation of red dwarfs. Alternative explanations, such as the idea that zero-metal red dwarfs are dim and could be few in number, are considered much less likely as they seem to conflict with stellar evolution models.

  13. Re:because... GOD! by Black+Parrot · · Score: 3, Funny

    God is the fundamental reason for why the universe didn't became a black hole in the early stages after the Big Bang

    I can stated with equal evidence and authority that the stray cat I almost ran over yesterday is the fundamental reason for why the universe didn't become a black hole in the early stages after the Big Bang.

    Be glad I missed him.

    --
    Sheesh, evil *and* a jerk. -- Jade
  14. Re:Thats a no brainer! by blue+trane · · Score: 1

    The universe seems to be expanding faster and faster. Dark Energy is coming from nowhere to do that work.

  15. Re:Big Bang is RELIGION by angel'o'sphere · · Score: 1

    I just learned on Facebook that cats have a religion, and it is 'catolisch' ... to understand this you need to be german or have a similar language like dutch or perhaps a scandinavian one ... but its funny!

    --
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  16. Re:Summary by Black+Parrot · · Score: 3, Interesting

    So to extrapolate from the TFA: The laws of physics do not exist in a vacuum...

    There's a difference between 'a vacuum' and 'nothing'.

    --
    Sheesh, evil *and* a jerk. -- Jade
  17. Re:because... GOD! by Black+Parrot · · Score: 1

    God is the fundamental reason for why the universe didn't became a black hole in the early stages after the Big Bang

    I can stated with equal evidence and authority that the stray cat I almost ran over yesterday is the fundamental reason for why the universe didn't become a black hole in the early stages after the Big Bang.

    Be glad I missed him.

    Ok, let's hear it.

    [clears throat] "the stray cat I almost ran over yesterday is the fundamental reason for why the universe didn't become a black hole in the early stages after the Big Bang."

    --
    Sheesh, evil *and* a jerk. -- Jade
  18. Re:Black Magic is the reason! by Black+Parrot · · Score: 1

    This is all hogwash.

    At least that much of your theory is correct.

    --
    Sheesh, evil *and* a jerk. -- Jade
  19. Re:LOL by Black+Parrot · · Score: 1

    It has a psychological effect because ignorant economists use limited knowledge about the universe to justify austerity policies. Friedman using TANSTAAFL, for example. Except now Dark Energy violates TANSTAAFL, and it didn't hold in General Relativity anyway. So we suffer from an artificially imposed scarcity of money because economists suffer from a lack of knowledge about the universe.

    That's not rigorous enough for physics, but I do believe it meets the standards for good economics.

    --
    Sheesh, evil *and* a jerk. -- Jade
  20. Re:When did the universe get so big? by Black+Parrot · · Score: 2

    The speed of light is a limit on how fast you can accelerate something *in* space, but it's not a limit on how fast space can expand.

    In fact you can't even state the rate of expansion of space as a velocity, because the velocity apparent as the speed of recession depends on how far away you're looking.

    --
    Sheesh, evil *and* a jerk. -- Jade
  21. Re:When did the universe get so big? by wonkey_monkey · · Score: 1

    I don't buy 92 billion light years.

    You don't get (understand) 92 billion light years.

    The observable universe is that big because, in the 13-14 billion years that light has been travelling from "out there" to here, space has been expanding. That means that the most distant objects we can see are now 90+ billion light years away. They weren't that far away when the light left.

    --
    systemd is Roko's Basilisk.
  22. Re:because... GOD! by Black+Parrot · · Score: 1

    No, my life would have been changed (i.e., ended in the cosmic collapse) if I *had* hit him.

    --
    Sheesh, evil *and* a jerk. -- Jade
  23. Re:Big Bang is RELIGION by lgw · · Score: 2

    No point splitting hairs over what qualifies as "religion," but if this is the case, then there's more evidence for the Big Bang than for any other religion ever devised in the history of humanity, and that's saying something.

    The evidence (which is nothing new, BTW) is amazing though. If the density of the universe were too low, or too high, we wouldn't have a universe to live in today. OK, that's not too odd - big crunch one way, big rip the other. What's astonishing is that the required density in the 1 ns universe to allow our universe to reach its current age must be correct to 24 significant digits.

    Talk about fine tuning! One part in 10^24 higher or lower, and no universe today. That's about as anti-Copernican as you can get. Either we accept the "hand of god" in tuning the universe so precisely, or (far stupider IMO), we believe some silly anthropomorphic principle, or we simply accept that the physics is incomplete.

    The last choice is of course where most working cosmologists are. There must be something we don't understand that explains why the early universe was necessarily so fine tuned - that it wasn't a happy accident, but could only be that way, or was very likely to be that way. Work on "inflationary" theories is a big part of the field these days, and this question is central to them.

    There are a bunch of hypotheses that say, effectively, "the effect driving the early, very rapid inflation of the universe stopped, by it's very nature, at the point where the universe was exactly 'flat'". The dark energy seen driving expansion today is then explained as a different effect, incredibly weak by comparison.

    --
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  24. Re:because... GOD! by Tablizer · · Score: 1

    Where do I mail my Thank You gift to?

    --
    Table-ized A.I.
  25. Re:Big Bang is RELIGION by St.Creed · · Score: 1

    I think we can use the English equivalent: Cat-holic :)

    --
    Therefore, by the (faulty) logic you're using, you're just a cow with a keyboard - osu-neko (2604)
  26. Re:Big Bang is RELIGION by St.Creed · · Score: 2

    Either we accept the "hand of god" in tuning the universe so precisely, or (far stupider IMO), we believe some silly anthropomorphic principle, or we simply accept that the physics is incomplete.

    While I agree the last explanation is probably the most likely one (a dampening effect that occurs at a certain point could be a plausible explanation), don't discount nr. 2: we just don't know (and we cannot know) how many universes are generated at any given point in time. Perhaps quantum fluctuations generate 1 billion "universe seeds" per cubic centimeter at any given second, and since they are random, most don't lead to another universe. Some do, and the ones that are "exactly right" give rise to universes like ours. Should we ever find a way to measure these things (not in the next decades, I think), we might find that option 2 is actually the real one. But I agree that option 3 is the most likely one.

    --
    Therefore, by the (faulty) logic you're using, you're just a cow with a keyboard - osu-neko (2604)
  27. Re:Big Bang is RELIGION by NotSanguine · · Score: 1

    From TFA, "As it turns out, we live almost in the Goldilocks case, with just a tiny bit of dark energy thrown in the mix ...

    Umm...70+% of the universe is "just a tiny bit"?

    --
    No, no, you're not thinking; you're just being logical. --Niels Bohr
  28. Cat addiction by tepples · · Score: 1

    "Cat-holic" sounds like it'd mean someone addicted to cats the way an alcoholic is addicted to alcohol, possibly as a side effect of toxoplasmosis.

  29. Re:Big Bang is RELIGION by pikine · · Score: 1

    In case you're feeling a bit dense today, I believe the author meant tiny bit by volume, not mass, since the expansion of the Universe concerns volume.

    You are very welcome.

    --
    I once had a signature.
  30. Re:Thats a no brainer! by tnk1 · · Score: 1

    Dark "energy" is probably a false description, or a misleading one. Dark energy is thought by many to simply be a property of space-time itself. It isn't being added, it is just what happens to space-time in this configuration or density.

    Much like a rubber band will be elastic up to a certain point, and then full stop, the universe could also hit such a point with no warning (because that point has never been reached before) and then change its acceleration again, or even suddenly boomerang back. Until we know the properties of space-time itself, there is potential for a lot of surprises that science may be entirely unable to predict based on a complete lack of data.

  31. Re:Big Bang is RELIGION by tnk1 · · Score: 2

    There's nothing wrong with the anthropic principle, it just can't be used as the explanation of what is happening. It is not a physical theory.

    It simply states that, "the existence of the human inhabitable universe proves only that the existence of such a universe must be possible, because we are here to observe it." It's almost tautological.

    It doesn't prove nor disprove deities, or the scientific method, or any theories derived therein. It is only useful for logically refuting the unproven assumption that our existence ipso facto assumes that the universe was designed specifically for us.

    That said, it does not disprove the intelligent design theory either, it just points out that there do exist other explanations for the facts. So yeah, it's a valid point to make, but we still might be living in a big terrarium.

  32. Re:because... GOD! by tnk1 · · Score: 1

    A change to the density of the universe is likely what triggered a phase change in space-time to bring us to a now-accelerating expansion of the universe. Movement of the mass of that cat away from a storage facility with a number of tons of heavy metals could well have prevented the density figure in this part of the universe from reaching a critical point which causes another phase change.

    Of course, the problem with that is that the change would then have happened about an hour later when came over to inspect a recent shipment, but hey, even the standard model has currently stated limits, right?

    Seriously, let's get over the religion vs. science twaddle. The existence of a universe with an omniscient, omnipotent Creator who doesn't want to be seen by us is identical to a universe that has no Creator. For whatever reason, that Creator, should they exist, wants you to take it on faith. So let's stop trying to disprove the deities, when we can't do so, and let's stop trying to prove the deities, when they clearly don't want you to be able to. Thanks.

  33. Re:Black Magic is the reason! by tnk1 · · Score: 1

    Any material from an Earth-Theia collision would settle into predictable orbits shortly (in geologic time) after the collision. Presumably, this is well understood by scientists and they would pick material that is not from that predictable band.

    Understand that space, despite the gigatons and gigatons of material out there, is not an unpredictable or chaotic place. It isn't just ping-ponging all over the place, messing people up. If you obtain material from a comet, asteroid, or even a particular type of meteor, you can model where it came from pretty well by determining its orbit, as well as materials analysis of its components. There are just some rocks out there that could not have formed on Earth or on the planetoid that may have produced the Moon.

    As for the evidence, the Big Bang is still the current mainstream theory as far as I know, and I do watch carefully for any significant changes to major cosmological theories. I'd like for one of them to succeed, because then things would get interesting, but while there have always been contenders, they're nowhere near as accepted. Don't grab on to the fact that there exist alternatives... there's always people who are working on them in good faith, but good faith does not mean that they are any more correct or accepted than the crank theories out there.

    Don't get me wrong, there's more to find out there, but as time marches on, the discrepancies are getting smaller and smaller in well studied fields. The belief in a 6,000 year old universe was the product of Biblical interpretation, not scientific investigation and everyone knew it. It wasn't science making a mistake, it was simply NOT science at all. And Christians didn't necessarily believe it either, it had been posited by ancient and medieval scholars that the Earth was old and that the Bible timeline was not going to be precise. Arguing that there must be a bigger universe because we've found certain things is the same sort of argument as saying that the Speed of Light is not real because we broke the sound barrier, so we just need a faster spaceship. That's not how it works.

    We know that the Webb telescope will let us see more, but the we have already have calculated the extent of the non observable universe from principles. If space-time meets certain properties and has certain values, we can extrapolate the size of the universe from existing data in the same way that I can give you a reasonably accurate circumference of the Earth by measuring shadows at noon on two relatively close places on the planet and applying certain calculations. I don't need to circumnavigate the Earth to do so, I only need to go far enough away to make up for the imprecision of my instruments. This was done accurately even in Ancient times by only having to measure in Greece and Egypt, a trivial distance. It can be done for the whole universe in the same manner through theories and observation of stellar bodies.

  34. Re:Big Bang is RELIGION by lgw · · Score: 1

    There's a quite important principle in science, generalized from the Copernican principle, that theories that require a lot of "fine tuning" of constants in order to work are bad. The big problem with the anthropic principle is that it's too often used as an excuse to ignore the glaring weaknesses in some areas of science. We shouldn't be comfortable with such things (and for the most part, of course, scientists aren't). It's not that the anthropic principle is some overt fallacy, but it really makes me cringe to see once-respected figures like Tipler taking it seriously. It bothers me a lot less to see a religious figure suggest similar ideas - at least that guy is sticking to his principles.

    --
    Socialism: a lie told by totalitarians and believed by fools.
  35. Re:Big Bang is RELIGION by thunderclap · · Score: 1

    Sure, in an imaginary world where the graceful and faithful elephant works freakishly hard to make the ants live happy lives even though the ants are so tiny to imagine what this great elephant looks like or means to them. The ants who hate the elephant drown themselves in puddles of water, and we the outsider look at these drowning ants in this imaginary world and think "these ungratefully stupid ants deserve to be eliminated by natural selection." And the elephant looks at us and say "if we can save one more ant from drowning, then why don't we?"

    Well, that is a good question. What can't we? Also another good question is: How do we know we aren't already inside a black hole? No one has ever been to one or seen its inside so all we have is good guesses.

  36. Explain it like I'm not an astrophysicist by EmagGeek · · Score: 1

    Because I'm not. But, where does the 92 billion light year thing come from? I would think what, 28 billion across if it's 14 billion years old?

  37. Re:Big Bang is RELIGION by NotSanguine · · Score: 1

    In case you're feeling a bit dense today, I believe the author meant tiny bit by volume, not mass, since the expansion of the Universe concerns volume.

    You are very welcome.

    Not feeling particularly dense at the moment, but thanks for asking! Your point did get to me read TFA, though.

    Since IANAP, perhaps I'm a bit confused, but as I understand it, dark energy "can have such a profound effect on the universe, making up 68% of universal density, only because it uniformly fills otherwise empty space."

    What is more, volume "is the quantity of three-dimensional space enclosed by some closed boundary, for example, the space that a substance (solid, liquid, gas, or plasma) or shape occupies or contains."

    So I'm left with something of a quandary. If the two statements above are correct, that dark energy is 68% (more by other estimates) of the universe by density, and "uniformly fills otherwise empty space," and volume "is the quantity of three-dimensional space enclosed by some closed boundary, for example, the space that a ... shape occupies" that brings us to the question, how much "otherwise empty space" there is in the universe? Quite a bit as I understand it. Much, much more than non-empty space, AFAIK.

    Since I am (apparently) much denser than dark energy, perhaps you could explain how it is that, by mass, dark energy is ~68% of the universe and is uniformly spread across otherwise empty space (the vast majority of the *volume* of the universe), anyone could consider that to be a "tiny bit?"

    It's entirely possible that I'm missing something obvious. If so, there's definitely a "whoosh!" going on over here. I suppose it's possible that there was much less dark energy (if it's an inherent property of space-time, that could explain it) at and shortly after the big bang than there is now, which I guess could, for some values of "much less" be "a tiny bit."

    However, (and again, I am not a cosmologist) we don't really understand "dark energy" except for its effect increasing the speed of the expansion of the universe, so I'm not sure how anyone could make such a statement with a high confidence.

    Please, feel free to school me.

    --
    No, no, you're not thinking; you're just being logical. --Niels Bohr
  38. Because of the expansion by mburns · · Score: 1

    Yes you can use the Schwarzschild argument. Expanding space is only a handwaving rationalization, a coordinate-dependent way of thinking that is not compatible with the principle of general covariance.

    If the gravitational source density was ever more than zero, then it follows that the contents of the universe were less massive in the past. In an inertial set of coordinates, not the screwy Freidmann coordinates, it can be understood that the shards of the Big Bang, flying apart at next to lightspeed, still add mass to the universe today, but at a diluted density.

    --
    Michael J. Burns
  39. Marty, you're not thinking 4th-dimensionally! by ulatekh · · Score: 1

    Perhaps the answer doesn't lie in the 3rd dimension.

    One of the possible consequences of the curvature of 4th-dimensional space-time is that our universe may be a 3-dimensional surface of a 4th-dimensional hypersphere. And if the 4-dimensional universe is expanding, the 3-dimensional universe would expand too.

    This model of the universe was also used in a famous sci-fi novel.

    --
    "Once we've identified and embraced our sickness, we'll have strength...and that's when we get dangerous." - John Waters
  40. Stable universe? by ChrisMaple · · Score: 1

    TFA proposes a kinda-stable universe if it contains an exact amount of stuff, not one neutrino more or less. My question is: "If the universe has net angular momentum, can't it be stable for a large range of stuff?" much like a solar system?

    --
    Contribute to civilization: ari.aynrand.org/donate
    1. Re:Stable universe? by boristhespider · · Score: 1

      It would certainly change the stability analysis, yes, but the universe does not have a significant angular momentum. That would leave a characteristic signature on the CMB, a preferred direction, and it's been hunted, with each new and improved dataset, and we still don't have it. The hunt has turned up other interesting anomalies such as the appallingly-named "axis of evil", but those signatures are also (probably) not due to an intrinsic net angular momentum. That doesn't say there isn't one, just that it's not particularly significant and is, as yet, unobservable. (In case you're interested, a universe with a net angular momentum could be described by one of the Bianchi models rather than a (Frieman-Lemaitre-)Robertson-Walker. A simpler case that might interest people is the Goedel universe, notorious because it contains closed timelike loops, which allow for the possibility of time travel. The Goedel universe wouldn't form a realistic model of the universe but it's an interesting spacetime.)

  41. Re:Big Bang is RELIGION by pikine · · Score: 1

    It's kind of useless arguing with me since I shouldn't be putting words in the mouth of Ethan Siegel, and arguing on whether it is appropriate to call dark matter tiny really has no bearing on what I'm telling you about God and the Universe. But just in case you find it a pleasure to discuss these fine points with me, the very notion of mass distributed over volume involves statistics, and as you know, you can make statistics tell any story.

    Consider this figure that I just randomly found so I don't have to draw one myself. You can see that the two clouds of green dots span about the same space. But the cloud on the right is more concentrated than the cloud on the left. You can imagine a third figure where there are several clumps of dots and still has the same overall space and density. Do you count the space between the dots as occupancy? Do you impose some form of density threshold to eliminate spaces that are simply too sparse? Not to mention that an atom consisting of a dense nucleus and a cloud of electrons is really more than 99.999% of space.

    I'm not saying your Wikipedia references are wrong; they want to paint a picture illustrating the pervasiveness of dark matter, but Ethan Siegel is also entitled to say the amount is tiny. Tininess is really in the eyes of the beholder.

    --
    I once had a signature.
  42. beware! by dpedu · · Score: 1

    > the Universe is precariously close to recollapsing. Hah what?

  43. I was under the impression that it *IS* one... by mark-t · · Score: 1

    And we are inside of its event horizon. Anything that might exist beyond it, if the laws of physics are the same as they are here (which they may not be), would not be able to see anything that happens inside. Similarly, we cannot see outside of it because every straight line (how light travels) in our space does not go beyond its event horizon, just like in a black hole.

    --
    File under 'M' for 'Manic ranting'
    1. Re:I was under the impression that it *IS* one... by countach · · Score: 1

      Hmm, in a black hole a theoretical photon trying to escape is sucked back in because of gravity. But what will happen when a photon hits the hypothetical edge of the universe? Bounce back? I haven't heard of anyone theorising that.

    2. Re:I was under the impression that it *IS* one... by mark-t · · Score: 1

      Photons trying to escape are don't actually escape not because they are sucked back in by gravity, but because space is so curved by gravity that straight lines which are inside of the event horizon never leave it.

      --
      File under 'M' for 'Manic ranting'
  44. Re:Big Bang is RELIGION by mgf64 · · Score: 1

    In Italian: Gattolico

  45. Re:Thats a no brainer! by boristhespider · · Score: 1

    Well, it violates the weak energy condition, although it does satisfy (just) the strong energy condition. The weak energy condition says that density + three times pressure is greater than zero, and that's pretty easy to violate if you've got a scalar field. The strong energy condition says that density + pressure is greater than zero, which is far harder to violate; dark energy is right on the border of it, and a cosmological constant *is* the border (pressure = - density).

    Of course, you're totally right - none of this means that they violate conservation of energy. That's built in to the theory...

  46. Re:Big Bang is RELIGION by gzuckier · · Score: 1

    Judy Tenuta, of course, has her own religion, Judyism.

    --
    Star Trek transporters are just 3d printers.
  47. Re:Big Bang is RELIGION by gzuckier · · Score: 1

    Reminds me of the old saying "Existence is pain. It is better not to exist at all. But how many people are that lucky? Maybe one in a hundred."

    --
    Star Trek transporters are just 3d printers.
  48. Re:Summary by gzuckier · · Score: 1

    So to extrapolate from the TFA: The laws of physics do not exist in a vacuum...

    There's a difference between 'a vacuum' and 'nothing'.

    \ Nothing is emptier than a vacuum!

    --
    Star Trek transporters are just 3d printers.
  49. Re:When did the universe get so big? by mburns · · Score: 1

    Actually, the claimed superluminal expansion is a coordinate artifact. Convert to a different set of coordinates and the expansion is understood as lightspeed at a maximum.

    --
    Michael J. Burns
  50. Re:Big Bang is RELIGION by angel'o'sphere · · Score: 1

    Hehe, funny :D

    --
    Cost free eBook I read (by iBook/Kobo/Amazon/ObookO/Gutenberg etc.): "The Green Odyssey" by Philip Jose Farmer.
  51. Re:because... GOD! by glitch23 · · Score: 1

    You don't have equal evidence nor is that equal logic since your cat exists in the universe after the Big Bang. But you already knew that.

    --
    this nation, under God, shall have a new birth of freedom. -- Lincoln, Gettysburg Address
  52. Creator vs accident by glitch23 · · Score: 1

    One part in 10^24 is why having a Creator makes a difference. One part in 10^24 is no accident. And some people still don't what to admit what created the Big Bang but there is no other answer. How much faith does it take to believe all this was an accident?

    What about the "some 92 billion light-years worth of space contained in a volume of space no bigger than our own Solar System"? That was a miracle. Accidents don't "give rise to all the wondrous diversity of nuclear, atomic, molecular, cellular, geologic, planetary, stellar, galactic and clustering phenomena we have today."

    --
    this nation, under God, shall have a new birth of freedom. -- Lincoln, Gettysburg Address
  53. Or are we inside this black hole? by Barryke · · Score: 1

    I wonder why nobody pointed out the real possibility of our 3D universe being inside a black hole.
    I could even imagine temporal displacement causing us to see the bigbang as a instant event, while on the outside its just near ethernity.

    I've often wondered about this, only to end up with the question how many black holes deep we are..

    --
    Hivemind harvest in progress..