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

What is the evidence for the multiverse?

  1. Aug 30, 2014 #1
    The multiverse is a theory that the are countless universes.

    What is the evidence for the existence of the multiverse?
  2. jcsd
  3. Aug 30, 2014 #2
    To my limited understanding, there is no 'Multiverse Theory' as a theory makes testable predictions and as far as I know, there are no testable parts to a belief in a multiverse. Mathematics and quantum theory suggest that it is possible for multiple universes to exist, but at the moment there is no way to even test any of it regarding 'other' universes. There are many whom are far more enlightened on this topic that will probably give you a better explanation.

    Last edited: Aug 30, 2014
  4. Aug 30, 2014 #3
    There is no evidence that I'm aware of but, I believe that it's very likely that a multiverse exists because if it's possible for this universe to create itself than it's surely possible for countless others...that's just my personal opinion.
  5. Aug 31, 2014 #4
    There are a couple of flaws to your logic. Just because there is one doesn't mean there are any others at all, it depends on exactly how it came about, which we have no evidence of. Also, there is no evidence that the universe created itself, all we know that its creation was in a place and time that our current physics won't go.
    Personal opinions are not allowed on the forum as they do not require any science to back the claims that that opinion suggests.

  6. Aug 31, 2014 #5
    The observation that we exist provides some evidence for the existence of the multiverse, but is circumstantial evidence and open to doubt:


    As the main alternative to the anthropic principle is God, then you can (i) choose your favourite (ii) flip a coin (iii) decide to keep the question open.
  7. Aug 31, 2014 #6


    User Avatar
    Gold Member

    I think "circumstantial" is WAY overstating the case. There really isn't any evidence for a multiverse, it's just wishful thinking that solves at least one problem ("fine tuning") that we don't have a testable solution for YET.
  8. Aug 31, 2014 #7


    Staff: Mentor

    As long as it remains true that we can never observe anything outside our own universe, then speculation on what might be out there is pointless. There can be no evidence without observation.
  9. Aug 31, 2014 #8
    There was a time when we couldn't observe atoms, but atomic theory produced good results before atoms were actually observed.
  10. Aug 31, 2014 #9


    User Avatar
    Science Advisor

    There is no reason to think that a unique universe should be the ontological default.
  11. Aug 31, 2014 #10


    Staff: Mentor

    That's not true. We couldn't resolve individual atoms but we could observe that something was there.

    Making an observation is quite a bit less than having knowledge and understanding of what the observation means. For things outside our universe, we can't even meet that minimal standard.

    Now some people suggest that our universe could collide with another universe. If thst happened, we could make observations, and the two universes would become one.
  12. Aug 31, 2014 #11
    There is a flaw in your logic because creation didn't happen in a place it happened everywhere at the same time and btw why even comment at all if there isn't any science to back up any claims related to a multiverse in the first place.
  13. Aug 31, 2014 #12


    User Avatar
    Science Advisor
    Gold Member
    Dearly Missed

    Occam's Razor says "don't make up unnecessary stuff". If it's irrelevant to our universe, don't bother with it. If something is causally connected and interacts with us then it is part of our universe. This is one reason why the traditional idea of a single universe is the default.

    In answer to your question, there is no evidence for the existence of "other universes". IMHO the idea is speculation on the part of a certain group, and strikes me as a bit funny. It gets more play in the media than it does in the scientific research literature. :biggrin:
  14. Aug 31, 2014 #13


    User Avatar
    Science Advisor
    Gold Member

    To an extent, the multiverse concept originated with quantum physics. It's a back door way to impose causality on the indeterminacy of quantum processes. The basic idea is every indeterminate process results in every possible outcome 'somewhere' in the multiverse. It's main appeal is in the ability to render fine tuning 'problems' irrelevant. IMO, it's the 'scientific' version of creationism. Instead of having just one universe with unique fine tuning issues imposed by the hand of a creator, you can take comfort in the belief this is just one of an infinite ensemble of uniquely fine tuned universes. Aside from rendering a creator irrelevant, this version of reality offers no real advantages. It also invokes other annoyances, like the Fermi question - where are they? [visitors from other 'universes']. I share marcus' inference it deserves rejection on the grounds of Occam's Razor, and inhibits motivation to seek explanation for fine tuning 'problems' in this universe.
  15. Sep 1, 2014 #14
    We could observe 'a lump of wood', but why deduce 'atoms' from that? Maybe you can keep dividing the wood forever? Still, by assuming, on little evidence, that atoms were there, fruitful progress was made. So just making one observation: "Look there's some stuff!" can lead to useful deductions, "I think the stuff is composed of atoms!"

    In deducing the existence of the multiverse two key observations were made: (i) we see one universe (ii) we see us in it! There are other key supporting theories and observations, of course: the laws of physics and measurements giving us the values of universal constants.

    If there's only one universe then why is it so complex that life should form? Change the constants of nature, just slightly, and you'd expect no stars to form, no complex chemistry, and no life. The constants need to be fine tuned to give the conditions where life could form.

    "There is now broad agreement among physicists and cosmologists that the Universe is ... ‘fine-tuned' for life". - Paul Davies

    "The laws of science, as we know them at present, contain many fundamental numbers, like the size of the electric charge of the electron and the ratio of the masses of the proton and the electron. ... The remarkable fact is that the values of these numbers seem to have been very finely adjusted to make possible the development of life." - Stephen Hawking

    The ratio of the strengths of gravity to that of electromagnetism is 1,000,000,000,000,000,000,000,000,000,000,000,000. According to Martin Rees, if it were smaller, only a small and short-lived universe could exist. It is difficult to imagine life developing in such short lived universes - where everything quickly collapses under gravity. So why did did this universe develop rather than one of the incredibly large number of dead universes? The, at first sight, very unusual is more acceptable then the incredibly unlikely. So it looks like the multiverse is the hypothesis to run with at the moment. Have you any better ideas? (Please don't say, "God"!)

  16. Sep 1, 2014 #15
    At the very least, the multiverse idea is fascinating. Isn't it? Fascinating ideas may not be necessary to "build bridges" and other practical stuff that physics leads to, but do you really want to dump fascinating ideas because they have no conceivable impact on GDP? In any case, they may have practical impact in the future - like all that unnecessary reasoning Democritus indulged himself with about atoms.

    Who says it's the default? Is Paul Davies just making it up about the multiverse idea being the standard with cosmologists?

    A lot of people found Einstein's ideas funny, 'finding something funny' is not an argument for or against anything. It does get significant play in the research literature.

    It does get a lot of play in the media, probably because it's a 'big idea' with instant fascination. Maybe it *does* get too much air time, compared to other areas of physics.

    I'm not sure how you would measure the 'play in the media: play in the scientific literature' ratio, or how useful it might be. 'Newspaper articles: scientific papers' perhaps? This could be useful! A low ratio for solid state physicists could allow them to complain to newspaper editor & politicians about their raw deal.
  17. Sep 1, 2014 #16
    Isn't "rendering a creator irrelevant" a really bid deal, perhaps the biggest deal there is? If it did that alone that would be enough for me!

    Doesn't the Fermi question relate to visitors from other stars in our universe? The lack of visitors from other stars is a much bigger annoyance, because as Marcus points out the universes in the multiverse may not be connected. Of course that leaves me in the position of believing in the universe but never being able to go to another universe to prove it definitely - that's an annoyance. (less annoying then trying to believe in Gawd almightay, though...:))

    Occam's Razor is a rather blunt instrument; it would have done for atoms. The Greek anti-atomists thought it was "wood all the way down" - this did away with having to invent things like carbon atoms, and suggesting insane things like diamonds are really the same stuff! Wood is wood, diamonds are diamonds, what could be simpler...

    I'm not sure it inhibits motivations to seek other explanations - quite the opposite in fact. Humans like a good argument, it's very motivating. "Those darn multiversists, I'll show them..."

    Go on then, show me :)
  18. Sep 1, 2014 #17


    User Avatar
    Science Advisor
    Gold Member

    Let's leave the philosophising to philosophy forums, and focus on science.

    What's the status of eternal inflation? Does anyone know? Because if one could establish its validity from observation within our observable universe, then all the implications it brings about would follow. The existence of other universes would be necessary, the inability to observe them notwithstanding.
  19. Sep 1, 2014 #18
    That surely can't be all that you took from the above comments!

    Yes, you are correct (ironically, that point should have come from a believer in the single universe idea rather than a multiverse crowd). But as your belief would have had a time and a place for our current universes creation when viewed from outside of it (according to the grand GPS for the multiverse).

    I commented because there is no evidence for the multiverse at all, yet all evidence of all science points to a common past in the one we are in.

    Mal4mac, I think what Chronos was getting at with the Fermi paradox is, if you believe in infinite universes where all the possible things do indeed happen, where there are an infinite number of universes where we are having this same discussion, there also must be an infinite number of universes where inter universe travel is allowed, even to universes that don't have the physics which allow it. This would imply that there would be an infinite number of visitors to this place at this time to make all the non believers of the multiverse change their minds!:smile:

  20. Sep 1, 2014 #19


    User Avatar
    Gold Member

    This whole discussion is devolving into "how many angels can dance on the head of a pin?"
  21. Sep 1, 2014 #20
    You are correct in the case of atoms that we followed evidence that "something was there". However that isn't always the case. Mathematics all by itself makes predictions and most often leads to later discovery and some level of verification.

    Black Holes should be a case in point. The math predicted such beasts long before the wildest dreamer could imagine how to observe one, or the effects of one. We still have yet to "see one" and likely never will by definition (no light escapes) but we at least now do have observations of effects that are easiest explained by Black Holes and they seem to be all over, instead of exceedingly rare as was once thought.

    Mathematics is not just a measurement tool or descriptive of patterns. Math has become predictive more all the time and will likely increase as computer modeling advances.

    Specific to this thread if there is some 4D ejecta measurable in the CMB, perhaps in gravity waves, we would then have some physical evidence that would bear a great deal of further investigation to nail down from where or whence it came and a 4D Parent Universe is one candidate. Our latest CMB efforts wiped out many Quantum Gravity theories in one fell swoop, leaving a few relatively intact, struggling with new data. With ever deeper probes already planned, it seems way too late to just dismiss this idea offhand. We may not be all that far away from an important step.

    It may not be impossible to "see" before the Big Bang. It may be still highly speculative but it does have some backing, perhaps as much as predicting Black Holes circa 1920.
  22. Sep 1, 2014 #21
    Fair enough, but what if there aren't an infinite number? Or couldn't you have infinite universes where not all possible things happen? Either case would be enough to satisfy the anthropic principle.
  23. Sep 1, 2014 #22


    User Avatar
    Science Advisor

    Eternal inflation is as yet unknown. However, the many worlds interpretation of quantum mechanics has been demonstrated, and that alone guarantees a multiverse of sorts.
  24. Sep 2, 2014 #23
    First, you need to define what you mean by multiverse. The term has been used to describe a number of different things. Both Brian Greene and Max Tegmark have attempted to classify the different types of multiverse.

    Arguably, the least controversial, is the multiverse that is described by Everett's Many Worlds Interpretation of Quantum Mechanics. What is the evidence for this? Nothing more than Quantum Mechanics itself. It's simply a way of thinking about QM. Nevertheless, there are physicists who find this interpretation fantastical.

    Another example, that I think many cosmologists would agree with, is that there is strong reason to believe that there exists (I use the term loosely to avoid argument, here), space and time beyond our comsic horizon, though, not causally linked to us, here and now.

    More controversially, a multiverse has been hypothesised to explain the apparent fine tuning of the constants of nature. When we apply Occam's Razor then physicists differ on whether some form of multiverse offers the simplest explanation. Though, I have heard of no other plausible explanation, nevermind a simpler one! Presumably for many, an as yet unknown explantion is the simplest explanation available to us. The evidence for this type of multiverse comes from Weinberg's prediction of the Cosmological constant.

    There have been many more types of multiverse proposed over the years, most notably, Penrose's Cylical Universe and Smolin's Cosmic Natural Selection, who ironically objects to the term multiverse and in its place just uses the word universe. Both these come with some form of predictions, though I'm unaware of their current status.

    Perhaps the most interesting form of multiverse comes from Tegmark's suggestion of a Theory of Everything, where he proposes that the Everettian multiverse is actually the same thing as an infinite universe beyond our cosmlogical horizon. That is, that the Schrodinger equation applies to many, perhaps infinite number of, regions of spacetime which are not causally linked. The evidence for this is really just our current understanding of the shape of the whole universe. Tegmark is really just noting that the maths is the same for an observer who can't self-locate in spacetime, in a very large or infiinite universe, as that which arises from QM.
    Last edited: Sep 2, 2014
  25. Sep 2, 2014 #24
    I remember reading an idea about universe bruising as a way in which we could proof multiverse. I believe the basic idea is that if another universe would collide with our own we should see some kind of effect or 'bruising' according to the source i was reading it from. I'll try and find it and post it along side my blabbering of nonsense.
    Sorry if someone had already pointed this out, didn't see it.
  26. Sep 2, 2014 #25
    I think what you're refering to is Dark Flow. There are conflicting analyses of the latest data and differing suggestions, as to its origin, should it turn out to be a proven phenomenon.
    Last edited: Sep 2, 2014
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook