Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

? The universe is doughnut shaped ? tell me it ain't so

  1. Jul 22, 2003 #1
    Got into a conversation with someone today, suggested that the universe might be doughnut shaped? Although I could possibly consider this idea valid in some aspects, I've always assumed the universe was a spherical object, Matter pushing away from the center, in all directions, what's the general opinion for the doughnut idea then ?, or was his suggestion just sugar coated ?
     
  2. jcsd
  3. Jul 22, 2003 #2

    marcus

    User Avatar
    Science Advisor
    Gold Member
    2015 Award
    Dearly Missed

    People dont know what the shape of the universe is. I personally don't think it is shaped at all like a donut, but how can I confidently tell you it isn't when we Earthlings simply do not know!

    Personally I don't think it is spherical either. Neither do the experts, for whatever that's worth. Do you care what the expert opinion is? because a consensus based on improved observations has emerged in the past 5 years or so.

    Expert consensus doesnt automatically mean they're right, but for what its worth, here goes:

    Space is ordinary 3D Euclidean space---extending without limit in all directions----just the usual highschool x,y,z coordinate flat space (little local dimples can result from concentrations of mass like stars and galaxies, etc, but on a large scale its flat).
    And space has a metric with a scale factor which keeps increasing so the the distance between any two points keeps increasing.
    The scale factor is governed by a couple of differential equations which Friedmann derived from Einstein's original equation.

    Thats all. There is no sphere, there is no doughnut, there is no balloon, there is no explosion. Boring maybe, but that is the model universe the cosmologists have come to agree on and
    what they do their work with for the most part.
     
  4. Jul 22, 2003 #3

    marcus

    User Avatar
    Science Advisor
    Gold Member
    2015 Award
    Dearly Missed

    why we keep hearing about donuts

    It is always possible that ordinary Euclidean x,y,z flat space is an enormous cube with its top and bottom identified, and opposite faces identified

    Like videogames where the little guy goes off the top of the screen and comes in at the bottom----as if there were identical screens above and below and on each side----and if he runs off to the right he reappears coming in from the left.

    That screen was like a flat square that had its pairs of opposite edges glued by topologist-glue. So even if it was flat it was nevertheless TOPOLOGICALLY the same as the surface of a donut.

    But it was not SHAPED like a donut. Donuts are curved and the square game-screen was flat.

    Now cosmologist's idea of space is that it is flat in a 3D sense and this would ordinarily suggest infinite in all directions. But you can think of it as maybe finite if it is a huge cube with opposite faces identified. It would have a toroidal topology but its SHAPE would still be flat. Zero curvature. Indistinguishable from Euclidean 3D space for billions and billions of lightyears. It is still very boring and basically no different except that if you went far enough you would come round again. But practically you cant because it is too far---too far even for light to have made it around yet, or someone would have noticed the same quasar on opposite sides of the sky.

    So the donut business does not amount to anything very exciting, for practical purposes just the same old flat 3D space which for practical purposes extends out to infinity.

    What seems more remarkable to me is the expansion of it, distances to things increasing, and also an earlier possible contracting phase. The expansion gives a kind of curvature to space-time. So spacetime can be curved even if space (in the large) is flat.
     
  5. Jul 22, 2003 #4
    Actually, it is theorized that the shape of the universe is like a number of CD-ROMS stacked one on top of the other.

    The first CD-ROM is followed ontop by one that is twice the size(exept for the hole in the middle), then by another slightly larger again and so on..so on..

    The middle remains a constant size, but the CD-ROMS differ, when the equator is reached(the equilibrium of expansion)the CD-ROMS are now decreasing in size, the reverse of what is above. You end up with a torus/doughnut shape who's centre is uniform.

    To get a real-time image of this shape without melting som precious CDs, take a look at your eye in the mirror close up, as you look into the center of your eye, this in the doughnut/torus CD-ROM shape, would be from above looking down through the hole in the middle of CDs.

    Of course there are other models, one where there is a doughnut, balenced on the back of a giant turtle! who happens to have swam off the island shore he called home?
     
  6. Jul 22, 2003 #5

    marcus

    User Avatar
    Science Advisor
    Gold Member
    2015 Award
    Dearly Missed

    LOL

    I like the giant turtle

    For whimsical cosmology I dont know of anything that beats
    the Hindu creation myth.
    too long and fantastical to recount at the moment
    but your turtle with the donut would feel right at home
     
  7. Jul 22, 2003 #6

    marcus

    User Avatar
    Science Advisor
    Gold Member
    2015 Award
    Dearly Missed

    Devilin, sorry if we are digressing from topic. I tried to answer your shape of universe question as best I could, but whimsicality of ranyarts nonsense cosmos reminds me of the ancient Hindu creation story.

    Vishnu is asleep on a giant cobra floating in a boundless ocean when a lotus grows up out of his navel. The lotus bud opens and a person pokes his head up out of the flower and looks around---it is the god Brahma. Brahma comes out of the flower and creates the universe for their amusement. Vishnu is delighted by the universe and rules over it for 4.3 billion years (a period of time known as the Kalpa, or "the Day of Brahma").
    At the end of the Day of Brahma the universe is uncreated back into nothing and there is another 4.3 billion year period called "the Night of Brahma". More to the story, but that gives an idea.
     
  8. Jul 22, 2003 #7
    Re: Re: ? The universe is doughnut shaped ? tell me it ain't so

    Marcus you seem to be missing the point here?, it may be you did not detect the humour at the end of devlins post, so here it is again: or was his suggestion just sugar coated ?

    It is quite obvious that the Question of the shape of the universe cannot be defined from the inside? in your Vishnu model: Devilin, sorry if we are digressing from topic. I tried to answer your shape of universe question as best I could, but whimsicality of ranyarts nonsense cosmos reminds me of the ancient Hindu creation story.

    Are you not seeing that: The lotus bud opens and a person pokes his head up out of the flower and looks around---it is the god Brahma. Brahma comes out of the flower and creates the universe for their amusement. Vishnu is delighted by the universe and rules over it for 4.3 billion years (a period of time known as the Kalpa, or "the Day of Brahma").
    is no different, except for our Universe, someone has to stick their head out side, just to check and confirm the Universe's shape?

    You can certainly volonteer, you seem to be gullable enougth!

    Just kidding :)..it is obvious that being internal we can never assert the Universe in its entirety, the best we can do is to estimate an age, but this gives no account of its shape, and like my post above, everything that enters your eye in the form of light, takes on the shape of the eye itself, thats why I suggested the suttle 'beauty is in the eye of the beholder! the universe will be the shape of your eye, because that collects the information that allows us to observe.

    Trying to answer the question is asking someone to step outside the Universe it cannot be answered from the inside at least until there is a defined boundery, so please lighten up, you cannot possibly think you know everything..can you?
     
  9. Jul 22, 2003 #8
    We must also show a repect to the ancient philosophers, from every corner of our Globe who tried to answer many deep and quite problematic questions.

    These peoples from all over the world share one common trait, every civilization seemed to asked the same typical questions, almost as if the question was inherent to existence.

    In its simplistic reasoning the Vishnu take on 'why' things are the way they are, would have sufficed in its ancient context, in fact the author may have been the equivilent of our current Ed Witten, exept for the maths, both are saying the same abstract thing ;)
     
  10. Jul 22, 2003 #9

    LOL! your friend might be taking the Simpsons a little to seriously!
     
  11. Jul 24, 2003 #10

    jcsd

    User Avatar
    Science Advisor
    Gold Member

    The reason why some physicits have theorized that the universe is a torus, is that observations seem to show that the universe is globally flat. In order for it to be flat and finite it would most probably be donut-shaped.
     
  12. Jul 25, 2003 #11
    Re: Re: Re: ? The universe is doughnut shaped ? tell me it ain't so

    Thanks everybody,
    from what I understand so far the doughnut is simply a working model, until they find a better model,


    Of course I expect to know everything, and I've already done the philosophy stuff, and solved all of the problems, answered all of the question, in that particular field, I'm working on a web site where I'll publish my findings , and the reason for asking the question about the universe was, I wanted to know what shape would eventually contain my ego, of course once my ego exceeds the boundaries of the universe itself, I should have a better understanding of it,
     
  13. Aug 3, 2003 #12
    I think the current scientific consensus is that the universe is flat (this is supported by the cosmic microwave backround measurements) and we can't yet determine the size. the sphere point of view some people hold is a result of a misconception from heaing about the big bang. As I understand it, even though they show an exploding sphere on tv, it not that way at all. The big bang is a 4d event and so though it happened in a point in 4d space, it occured in all three normal dimensions at once. That is why one can't point to the center of the universe, because technickally it was everywhere. (An ant on a expanding ballon can't point down to the center because it's world is 2d and a third perpendicular axis is not expressible.)
     
  14. Aug 9, 2003 #13


    You mean like an upside down volcano with a constant sized hole all the way through?
     
  15. Aug 9, 2003 #14

    Eh

    User Avatar

    Stack a bunch of CD's and you basically get a torus, ie. a doughnut. It won't taste as good though.
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?



Similar Discussions: ? The universe is doughnut shaped ? tell me it ain't so
  1. Shape of the universe (Replies: 4)

  2. Shape of universe (Replies: 21)

  3. Tell me why (Replies: 8)

  4. Try telling me this (Replies: 10)

Loading...