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

Infinite Regress | Why is everyone telling me I am wrong?

  1. Sep 10, 2014 #1
    I love having discussions with my friends about cosmology, physics and just the universe is general but can someone explain to me why ALL my friends tell me this way of thinking is just plain wrong.

    We were talking about whether or not we think the universe is infinite or not and I told them that if the universe is everything that exists, then by its own definition it must be infinite, otherwise it clearly isn't everything that exists.

    Secondly I said to them that if the universe isn't everything then the universe must be inside of something else which in turn is infinite, and likewise if that isn't infinite then that something must be inside of something etc.

    So even if that is true that must mean that a is inside b, b is inside c, c is inside d ... to infinity so whichever way you look at you always arrive at infinite.

    They told me that infinite regression like this is a paradox and basically it stems from the inability to ask or even think about different possibilities, we simply don't have the mental capacity to think of other possibilities.

    They said that if everything needs to be inside something else then nothing can exist as there can never be the first "thing" but I told them that this is ok with infinity because just as +infinity doesn't have a finish point, -infinity doesn't have a starting point so it just means that it has been happening forever.

    To be honest none of us really have a clue what we are talking about but as friends sometimes they frustrate me when they say I am wrong lol so I come here for some advice.

    It just seems that no matter how many layers you peel back, no matter what when if or how the final answer just seems to be infinite.
  2. jcsd
  3. Sep 10, 2014 #2


    User Avatar
    Science Advisor
    Gold Member

    The universe can be everthing there is, and be finite. It could be curved like the hypersurface of a 4-dimensional hypersphere, or one of many other closed shapes, of finite size.

    The usual analogy is the one dimension-lower case of the universe being the 2-dimensional surface of a 3-dimensional sphere. The surface is finite(you can calculate the area easily). It is all there is. It's got no boundaries.

    Note that the existence of the higher dimension to embed the surface(or our universe) in is not required for the curvature to be present. All you need to have is certain rules about parallel lines and angles in a triangle being satisfied.
  4. Sep 10, 2014 #3
    I remember an analogy which said that you can't teach a dog physics, it can't comprehend physics. Likewise we might not be able to comprehend physics to an extent.
  5. Sep 10, 2014 #4
    So it's possible to travel in any given direction at the speed of light for eternity and I will never come back to where I started and I will never "escape" the universe?

    Because with the Earth analogy I can see me eventually coming back to where I started not to mention being able to travel outwards and eventually leave Earth which means it isn't 3dimensionally unbounded.

    Are you saying that no matter where we are located in space we are always on the 2 dimensional plane and we can never enter the 3 dimensional plane?
  6. Sep 10, 2014 #5


    User Avatar
    Science Advisor
    Gold Member

    If the universe is a closed hypersphere, then just as on Earth, you could conceivably travel in one direction for so long so as to come back to where you started. That is, if not for the expansion of space.

    You can never "escape" the universe, whether it's finite or not.

    And yes, in the Earth-surface analogy, no entering higher dimension. In that analogy, there are two-dimensional beings, to whom the third dimension is as abstract as the fourth spatial dimension is to us. Furthermore, the 3rd dimension might or might not exist. That is, it is not required.
  7. Sep 10, 2014 #6
    I think the issue here is your assertion that "something must be inside something else." One of the first misconceptions big bang cosmologists try to dispel to their listeners is that, after the big bang, space expanded into something. The standard big bang view (save multiverse theories) is that the expanding space is all there was or is, and to talk about it expanding into something else is a confounding way to look at the expansion.

    Once you start talking about" a" expanding into "b," and b expanding into c, etc., your friends are right, you can't avoid an infinite regress. The assumption when you do this is that you must implicitly give this b, c, d, etc. "space" some sort of physical properties, or else it makes no sense to talk of their existence. What are those physical properties? See where this is going?
  8. Sep 10, 2014 #7
    Yes and I know that our universe doesn't expand into something, unless our universe is finite? Even if we live in a bubble universe that must mean these bubble universe are contained in something, even if that something has 0 properties. Basically just an empty void volume.

    But my main argument was that if the universe is everything then it has to be infinite and if the universe isn't everything then it must be finite.
  9. Sep 10, 2014 #8


    User Avatar
    Science Advisor
    Gold Member

    Infinities give rise to paradoxes, which is why scientists attempt to remove mathematical infinities from calculation that express the laws of nature [e.g., renormalization]. In, for example, an infinite universe everything that can possibly happen has happened somewhere at sometime in the universe. That would imply the universe is not infinite because we have not observed all possible events in the universe [like black dwarfs], and we have compelling reasons to believe the universe has a finite age. That raises the question how can an infinite universe have a finite age? This question has haunted philosophers and physicists alike for millennia. We are forced to admit the obvious - that the OBSERVABLE universe is temporally and spatially finite. There may be distant recesses beyond our observational grasp [where all this unobserved stuff resides] that will forever be inaccessible. We do not know and probably never will. Every test ever imagined, many of which are quite ingenious, has failed to answer this fundamental question.
  10. Sep 10, 2014 #9
    The problem is an empty void volume has properties. The point has been made by a previous poster, a universe can be closed and not imbedded in anything.
  11. Sep 13, 2014 #10
    Traveling at the speed of light

    According to the Lorentz Transformation formula, space and time disappear when you travel at the speed of light. To an outside observer you'd be perceived as a photon, while your own observation would be that you are not going anywhere, because "where" doesn't exist.
  12. Sep 14, 2014 #11


    Staff: Mentor

    No, this is not correct. The Lorentz transformation is mathematically undefined for ##v = c##. That means it doesn't correspond to anything physical: if you're traveling slower than light, you can't change your state of motion to travel at the speed of light.
  13. Sep 17, 2014 #12
    You are in fact wrong and so are your friends. Your argument is actually pretty good, though. Your assumptions are certainly plausible and your reasoning is sound. But here's the problem:
    The key concept here is the 'boundedness' of the universe. All bounded spaces have an edge and all finite spaces are bounded. So if the universe is finite then it has an edge, which means there has to be something beyond it and then that leads to all that infinite regression stuff up there. Now for the interesting part:
    Slap the next person that gives you that "beyond our comprehension/mental capacity" crap and erase that phrase from your mind forever. There's no reason that the universe has to be limited to just 3 dimensions like we are. It could be 4 dimensional space where there can exist finite spaces that are not bounded. If it's not bounded then it doesn't have any edges and without edges there's no "beyond" for anything else to be.
  14. Sep 18, 2014 #13


    User Avatar
    Science Advisor

    That's simply not true. "Bounded" is not the same as "having a boundary". Bandersnatch gave counter examples.
    If there is no boundary, it is not necessary to introduce an "outside world", so iDimension's line of reasoning is invalid.
  15. Sep 18, 2014 #14


    Staff: Mentor

    That's not limited to 4 dimensional spaces. A circle is a 1-dimensional space that is finite but not bounded. A 2-sphere (like the surface of the Earth, or at least of an idealized Earth)is a 2-dimensional space that is finite but not bounded. And so on.
  16. Sep 18, 2014 #15
    I meant to say "in 4 dimensional space there can exist finite spaces that have no boundary." Wish I could go back and fix that.
  17. Sep 18, 2014 #16
    Are you saying that the universe could be 2 dimensional?
  18. Sep 18, 2014 #17


    Staff: Mentor

    No. But you seemed to be saying that, in order for it to be even possible to have a finite space that is not bounded, you have to have a 4-dimensional space (i.e., 4 spatial dimensions, not just 3). That's not correct. You can have a 3-dimensional space that is finite but not bounded (as well as the 1- and 2-dimensional ones that I gave examples of).
  19. Sep 19, 2014 #18
    I didn't mean to say a finite space that isn't bounded I meant to say a finite space without boundaries. And how is a circle not bounded? All finite spaces are bounded.

    Honestly I was way too tired at the time and that post is really poorly written so I don't blame anyone for being confused. I read it the next morning and even I had a hard time following what I was trying to say.
  20. Sep 19, 2014 #19


    User Avatar
    Staff Emeritus
    Science Advisor

    Not true. The surface of a finite sized sphere is unbounded. You can continue to move around the surface of the sphere forever without ever reaching a boundary. Note that we are talking only about the surface of the sphere, nothing else.
  21. Sep 19, 2014 #20
    Sorry if I am repeating myself but I hope you can explain it a little better. If the universe is finite then it has a shape and like all shapes, they have boundaries in the 3rd dimension. So it would seem that if I travel in the 3rd dimension long enough, I will escape the "surface" and after some time, I can look down and see the object which means that I must be in some other space or volume.

    I don't think we have anyway to tell which direction in space is the 3rd dimension, in fact I don't think it makes any sense to ask that question as the universe is hollow so any direction is the 3rd dimension so eventually, moving at the speed of light or even 1million times the speed of light, it would theoretically be possible to leave this universe and again after some time, look down and see the universe.

    I believe that to understand cosmology correctly one must train their mind to think abstractly and it takes time to understand this stuff but I am having real difficulties.

    I can just imagine travel at 20billion times the speed of light (impossible I know but to make a point) and then just crashing into an untraversable wall that stops us going further, but even then that wall must have some thickness which itself should extend to infinity?

    Either that or physics will troll us once again by just teleporting you back to where you started from once you cross a certain boundary. Why is this stuff so hard to understand :(
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Similar Threads - Infinite Regress everyone Date
A How can the universe keep on expanding if it's infinite? Jan 14, 2018
I If the universe is truly infinite in size... Jan 3, 2018
I Infinite versus finite space Sep 1, 2017
I A copy of me in an infinite universe Jul 29, 2017
I Infinite regress Jun 29, 2017