Categories: Guide to Space

Is the Universe Finite or Infinite?

Two possiblities exist: either the Universe is finite and has a size, or it’s infinite and goes on forever. Both possibilities have mind-bending implications.

In another episode of Guide to Space, we talked: “how big is our Universe”. Then I said it all depends on whether the Universe is finite or infinite. I mumbled, did some hand waving, glossed over the mind-bending implications of both possibilities and moved on to whatever snarky sci-cult reference was next because I’m a bad host. I acted like nothing happened and immediately got off the elevator.

So, in the spirit of he who smelled it, dealt it. I’m back to shed my cone of shame and talk big universe. And if the Universe is finite, well, it’s finite. You could measure its size with a really long ruler. You could also follow up statements like that with all kinds of crass shenanigans. Sure, it might wrap back on itself in a mindbending shape, like a of monster donut or nerdecahedron, but if our Universe is infinite, all bets are off. It just goes on forever and ever and ever in all directions. And my brain has already begun to melt in anticipation of discussing the implications of an infinite Universe.

Haven’t astronomers tried to figure this out? Of course they have, you fragile mortal meat man/woman! They’ve obsessed over it, and ordered up some of the most powerful sensitive space satellites ever built to answer this question.Astronomers have looked deep at the Cosmic Microwave Background Radiation, the afterglow of the Big Bang. So, how would you test this idea just by watching the sky?

Here’s how smart they are. They’ve searched for evidence that features on one side of the sky are connected to features on the other side of the sky, sort of like how the sides of a Risk map connect to each other, or there’s wraparound on the PacMan board. And so far, there’s no evidence they’re connected.

In our hu-man words, this means 13.8 billion light-years in all directions, the Universe doesn’t repeat. Light has been travelling towards us for 13.8 billion years this way, and 13.8 billion years that way, and 13.8 billion years that way; and that’s just when the light left those regions. The expansion of the Universe has carried them from 47.5 billion light years away. Based on this, our Universe is 93 billion light-years across. That’s an “at least” figure. It could be 100 billion light-years, or it could be a trillion light-years. We don’t know. Possibly, we can’t know. And it just might be infinite.

If the Universe is truly infinite, well then we get a very interesting outcome; something that I guarantee will break your brain for the entire day. After moments like this, I prefer to douse it in some XKCD, Oatmeal and maybe some candy crush.

Artist’s conception of Planck, a space observatory operated by the European Space Agency, and the cosmic microwave background. Credit: ESA and the Planck Collaboration – D. Ducros

Consider this. In a cubic meter (or yard) of space. Alright, in a box of space about yay big (show with hands), there’s a finite number of particles that can possibly exist in that region, and those particles can have a finite number of configurations considering their spin, charge, position, velocity and so on.

Tony Padilla from Numberphile has estimated that number to be 10 to the power of 10 to the power of 70. That’s a number so big that you can’t actually write it out with all the pencils in the Universe. Assuming of course, that other lifeforms haven’t discovered infinite pencil technology, or there’s a pocket dimension containing only pencils. Actually, it’s probably still not enough pencils.

There are only 10 ^ 80 particles in the observable Universe, so that’s much less than the possible configurations of matter in a cubic meter. If the Universe is truly infinite, if you travel outwards from Earth, eventually you will reach a place where there’s a duplicate cubic meter of space. The further you go, the more duplicates you’ll find.

Ooh, big deal, you think. One hydrogen pile looks the same as the next to me. Except, you hydromattecist, you’ll pass through places where the configuration of particles will begin to appear familiar, and if you proceed long enough you’ll find larger and larger identical regions of space, and eventually you’ll find an identical you. And finding a copy of yourself is just the start of the bananas crazy things you can do in an infinite Universe.

The Hubble Ultra Deep Field seen in ultraviolet, visible, and infrared light. Image Credit: NASA, ESA, H. Teplitz and M. Rafelski (IPAC/Caltech), A. Koekemoer (STScI), R. Windhorst (Arizona State University), and Z. Levay (STScI)

In fact, hopefully you’ll absorb the powers of an immortal version of you, because if you keep going you’ll find an infinite number of yous. You’ll eventually find entire duplicate observable universes with more yous also collecting other yous. And at least one of them is going to have a beard.

So, what’s out there? Possibly an infinite number of duplicate observable universes. We don’t even need multiverses to find them. These are duplicate universes inside of our own infinite universe. That’s what you can get when you can travel in one direction and never, ever stop.

Whether the Universe is finite or infinite is an important question, and either outcome is mindblenderingly fun. So far, astronomers have no idea what the answer is, but they’re working towards it and maybe someday they’ll be able to tell us.

So what do you think? Do we live in a finite or infinite universe? Tell us in the comments below.

Fraser Cain

Fraser Cain is the publisher of Universe Today. He's also the co-host of Astronomy Cast with Dr. Pamela Gay.

View Comments

  • Good except you can spin out variations - bounded or unbounded for example. A spherical universe is bound but you can go around it forever (a 3d visible universe bent around in 4d space for example.)

    My vote? Infinite. Definitely. And all of me agree.

    :-)

    • Ok, try this one on for size.
      The universe is finite, just like the number of souls in the universe.
      If you think in terms of reincarnation, we are reborn and hopefully advance in our way to becoming saintly.
      When you die, you can be reborn anywhere in the universe, doesn't mean you will, but you can.
      Souls are always moving depending on the population of the planets in the universe.
      On top of that, there is a group of Gods, Jehovah is the one that oversees this part of the universe but the universe is divided into quadrants, there is a God for each with one overseeing all.
      The reason there is newborn deaths is because no being can be born without a soul, and if it is, it dies.
      This Universe is huge, lol a relative term, but it is not infinite, just like there are only so many souls.
      I would be glad to discuss how I came to this conclusion if you would like.
      My email address is rfisherjohn@yahoo.com

  • When I was a schoolboy in the sixties, I wanted the universe to be bounded on the surface volume of of a 4D sphere, with time as the radius vector. That seemed neat as it gave you the Hubble shift, and made time the odd vector out, and didn't waste any of the 4D time-space. It doesn't fit with relativity or the evidence, though.

    10^80 particles in the observable universe sound like the figure from Dirac's LNH paper of 1937...

    http://en.wikipedia.org/wiki/Dirac_large_numbers_hypothesis

    That's another lovely idea, but it would need gravity to vary with time, which is pretty much doesn't. However, I had a search for the number of particles in the observable universe, and I can only find this figure.

  • The universe is infinite, AND getting bigger. Galaxies "appear" to be moving further apart, but not because of a "big bang."

    Where does all the "stuff" come from? That question is answered not by looking up, but looking down. The book "Terra non firma Earth" reveals the geology, and "Big Breach Universe" on the android app store takes it to the next level from where the book leaves off.

    If infinite yous bends your mind, the Big Breach will blow it up!

  • I have conclude the the universe cannot disobey its own laws. the circular motion of visible matter cannot be denied, planets around a central sun, galaxies around a central black hole, multiple galaxies around a seemingly central "great attracter". even electrons around a nucleus. why would the universe want to go on forever without definition when that is not the principle operation of its components ? Yes the universe is finite, disc like and comparatively flat. with leakage of matter from our universe into other multi-universes .

  • The universe is infinite. There are two sources of truth: science and religion. The other comments seem to be from scientists, which as an MD, I only pretend to be. Modern religion, which is as different from traditional religion as modern science is from the 'science' of 500 years ago, now sees 'God' as the infinite (obviously incomprehensible) power behind the infinite universe, represented here by periodic Educators who tell us of closer and closer approximations of true Reality.
    My question is, as I observe all that I can, I see no perfect replication. So is replication a given in an infinite reality, or is the universe infinitely variable so that, wonder of wonders, the 'Creator' (a misnomer fashioned by the finite observers, since there has always been matter/'creation'), has infinite variability in the infinite universe. We think that 'infinity' presupposes replication, but that's human math. Divine math perhaps does not rely on our computations.

  • The universe must be infinite. If we try to define finite bounds for the "universe", the very definition of a bound means there is something outside of the boundary, otherwise there would be no boundary. This would also mean we would need to re-define the universe to include what is outside the boundary. Either way, bounded or boundless, the universe or redefined universe is infinite.

    • If we are going to discuss boundaries, give some thought to including "Universe boundary in Einstein 1931 same as Lemaître 1927" (the issue was brought up by @weasle, but my response was not published. See
      http://www.universetoday.com/119297/how-do-we-know-dark-matter-exists/comment-page-1/ )

      Anyway you make a good point: "What is outside the boundary?"

      If someone hands me a closed cardboard box, I can then define a "size" for the box, and also what I mean by an "inside" and an "outside". But I must have the physical box first; the box is not "made of" an inside, an outside, and a size. It is made of cardboard. . . Modern astronomy has been concerned with the inside, outside, and size of the Universe, but has not defined "the box" itself. Additionally, the thinking now seems to be that the Universe is both centerless and edgeless. Maybe we have been asking the wrong questions.

      This is related to the problem of defining space and time. Time is usually parametric in our equations (even in quantum mechanics), and so physicists are increasingly regarding it as non-fundamental (as Einstein did). The view gaining currency now is that "motion" is more fundamental and would make a better metric. In other words, let "c" (the speed of light) BE the "box" and let space and time be defined by that box. The space and time units are always changing (progressing) but the RATIO remains constant. The progression of space and time ("space/time" instead of "space-time") would become the new Ether--the cardboard of the box, viz., something physical, though immaterial. It is dynamic (unlike the static Aether of old) but non-directional ("non-local") and cannot be detected by a vector dependent experiment like that of Michelson-Morley.

      Finding the right answers is hard enough. But because of what is NOT taught in our schools, we cannot even find the right questions!

  • It truly is a mind boggling question that makes you go bonkers, ..ahem..

    I shared the following over a year ago:

    [
    "Finiteness" or "Infiniteness" of the universe is one of the many mysteries where scientists run around like a chicken with its head cut off trying to figure out!

    Basic science posits that all "physical matter" is finite, the slightest motion in the universe (e.g. expansion, contraction, etc.) is "change," and "change" means that the universe had a "beginning" since it is expanding, hence, it is temporal, hence, it is "finite."

    Now, the problem is science CANNOT figure out if the "spatial size" of the universe is "finite" or "infinite." It is a logical conundrum. It has been one of the most complicated unsolved mysteries all along. Therefore, it became sort of a common practice to refer to the "observable universe," that is made of "physical matter," when speaking of the universe, and that it is "finite."

    If you research this topic, you will find a vast amount of different opinions, and they pretty much revolve around this question: How can the universe have a limit in "spatial size," and what is beyond that limit?!

    Many people think that it does not make sense for the universe to have a limit in "spatial size," some think it is flat, some think it is spherical, and so on and so forth, but no one knows for sure.

    I myself is of the opinion that the universe is "finite" in material (which is already established by science as aforementioned) and in "spatial size," since I believe the "Origin" of it is outside its "beginning," and that "Origin" is "holding it in suspension." I believe that "Origin" is "Metaphysical" (non-physical) and non-temporal (without beginning nor end,) that is Eternal.

    I believe that "Origin," aka "First Cause," is God Almighty, the Father, Son (Lord Jesus Christ) and Holy Spirit.

    Here is a recent historical perspective of the complexity of the subject matter:
    http://www.todayinsci.com/E/Einstein_Albert/EinsteinsUniverse-NYT2Feb1921.htm
    ]

    I was just thinking recently that since the universe is expanding, doesn't that mean new "space" is being "created" all the time?!

    • I believe that the "Universe" as we know it or is defined by us as the extent of our Bounded Big Bang, is finite, whereas the Cosmos is the immense Darkness that is Space. That in my own opinion is infinite.

    • Sometimes I think we stretch out our minds to contemplate that which is beyond our comprehension or ability to prove, because we don't want to dwell on our limitations.

  • I hope the universe is infinite otherwise humans would be limited in possibilities. However, if ,as scientists tell us, we see evidence of the big bang and inflation every direction we look, then this would be the wrap-around. We can't see beyond that because we can't see past where nothing exist. The wrap-around does exist.

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