“It’s hard to build models of inflation that don’t lead to a multiverse. It’s not impossible, so I think there’s still certainly research that needs to be done. But most models of inflation do lead to a multiverse, and evidence for inflation will be pushing us in the direction of taking [it] seriously.” -Alan Guth

It sounds like an unprovable fantasy: the idea that our Universe is just one of countless others, dotted across an eternally expanding empty space separating them. That’s generally how we picture the Multiverse, with each Universe having its own hot Big Bang distinct from every other Universe. But this isn’t simply pure speculation, but the result of a few simple facts combined: our Universe is quantum in nature, inflation gave rise to the Big Bang, and quantum fields spread out in value over time.

Inflation causes space to expand exponentially, which can very quickly result in any pre-existing curved space appearing flat. Image credit: E. Siegel (L); Ned Wright’s cosmology tutorial (R).

Put those pieces together, and you’ll find that no matter how small of a region inflation starts off in, so long as you demand you get enough inflation to stretch our Universe flat, it will continue on for an eternity into the future. In some locations, inevitably, it will come to an end, giving rise to a hot Big Bang, but in many others, it will continue forever, separating the regions where inflation ends from one another for all time.

If inflation is a quantum field, then the field value spreads out over time, with different regions of space taking different realizations of the field value. In many regions, the field value will wind up in the bottom of the valley, ending inflation, but in many more, inflation will continue, arbitrarily far into the future. Image credit: E. Siegel / Beyond The Galaxy.

The Multiverse itself may not give rise to any observable, testable predictions, but arises as a direct consequences of other physical theories that have already been validated. Find out today why it’s inevitable.

Comments

  1. #1 CFT
    October 12, 2017

    Ok, this is going off the rails completely. Ethan admits “The Multiverse itself may not give rise to any observable, testable predictions, but…” Ok, stop right there. There are no ‘buts’. the moment you put a ‘but’ in that sentence, you walked away from several of the main tenants of science: prediction, observation, and experiment. What you are talking about isn’t science at all anymore at all, its desperate metaphysics seeking validation for untestable theory.

    Examine the language of multiverse talk, words like: “arises”, and “direct consequences of other physical THEORIES” (my emphasis added), etc. This is a lot of assumption and interpretation intent on propping up other theories which will be in trouble otherwise. Once again, this is not good science, it’s just bad ‘to big to fail’ theory life support.

  2. #2 Michael Mooney
    October 12, 2017

    “The Multiverse Is Inevitable…”

    “It’s important to recognize that the Multiverse is not a scientific theory on its own.”

    The contradiction speaks for itself without further comment.

  3. #3 CFT
    October 12, 2017

    His previous blog was about ‘learning how to be wrong’. And in the very next blog he jettisons most of the methodology of the scientific method in favor of a theory which will not get traction otherwise… and gets it ass backwards. If you have a speculative theory on the one side, and the scientific method on the other…ditch the theory and go back to the drawing board. All good theory has to pass muster with the scientific method, not the other way around.

  4. #4 mehrdad
    October 12, 2017

    I thing that string theory is completely wrong,because we don’t see any similar symptons in our universe,for example we have about or more than 100millions of black holes just in milky way galaxy and we can guess that The bigger ones are The result of merging of smaller ones,but we don’t see any of them to have a string shape ,in fact all visible matter contaings,,planets,stars,galaxies,quasars,even big bang ..are seperated matters.so how can we assume The possibility of string theory as a mother universe.

  5. #5 mehrdad
    October 12, 2017

    I have typed a comment about string theory and it disappeared when i submitted

  6. #6 Pino
    Magna Graecia
    October 12, 2017

    … “It’s possible that our understanding of the state before the hot Big Bang is incorrect, and that our idea about inflation are completely wrong for this application. If that’s the case, then the existence of a Multiverse isn’t a foregone conclusion. But the prediction of an eternally inflating state, where an uncountably large number of pocket Universes are continuously born and driven inextricably apart from one another, is a direct consequence of our best current theories, if they’re correct.” …
    ???
    by far too many “ifs” …
    pino.

  7. #7 Anonymous Coward
    October 12, 2017

    It’s not a scientific theory because it can’t be tested as the other known laws of physics seem to preclude any possibility of testing it. But it does fall out as an intriguing consequence of the other bits of theory that do have observational consequences that can and have been successfully tested. However, unless there is some way to move substantially faster than c or somehow obtain information from these fabulously distant pieces of spacetime, both of which are precluded by other known physical laws, there is no way to test it.

    There’s no contradiction there.

  8. #8 Ragtag Media
    October 12, 2017

    Miguel, your taking this to seriously. Dude you need to get laid..LOL
    For FRICK Sake Ethan Provided SO Many Caveats for example:

    “Rather, the Multiverse is a THEORETICAL prediction that comes out of the laws of physics as they’re BEST UNDERSTOOD TODAY!!!!!!!!!!!!!!.

    It’s A STORY with CAVEATS what do you not get about that?

    When Ethan or any others publishes a (racist LOL) White paper, Then critique that, but to cherry pick silly sentences from a story that is not being published to the world and science community as fact makes you look like you have a chip on your shoulder causing you to punch at well… nothing.

  9. #9 CFT
    October 12, 2017

    @Ragtag Media,
    The problem with calling the Multiverse a theoretical ‘prediction’ is that it can not be falsified, like inflation and superstrings, the multiverse predicts literally everything. It isn’t science at all, it’s actually not even good metaphysics.
    .
    This is why HEP physics is in trouble, nonsense like the multiverse sucks up limited resources and talent and produces nothing but untestable fantasy. A good deal of the community knows it, isn’t very happy about it, and folks like Ethan are NOT helping when he sings the praises of un-falsifiable, untestable theory. Perhaps if Ethan had taken a philosophy class and learned about reductio ad absurdum, he wouldn’t be cheerleading a descent into absurdity.
    .
    As theories like the multiverse and super string theory continue to produce nothing testable (for over thirty years now), funding will shift to other projects with expectations of actual measureable and testable results.
    .
    .
    “I don’t like that they’re not calculating anything. I don’t like that they don’t check their ideas. I don’t like that for anything that disagrees with an experiment, they cook up an explanation — a fix-up to say, ‘Well, it still might be true’.”
    — Richard Feynman
    .
    .
    “Scientific ideas should be simple, explanatory, predictive. The inflationary multiverse as currently understood appears to have none of those properties.

    These concerns and more, and the fact that we have made no progress in 30 years in addressing them, are what have made me skeptical about the inflationary picture.”
    __Paul Steinhardt <–the guy who helped invent inflation thinks it's a bad idea.

  10. #10 CFT
    October 12, 2017

    “To me, the accidental universe idea is scientifically meaningless because it explains nothing and predicts nothing. Also, it misses the most salient fact we have learned about large-scale structure of the universe: its extraordinary simplicity when averaged over large scales…

    Scientific ideas should be simple, explanatory, predictive. The inflationary multiverse as currently understood appears to have none of those properties.

    These concerns and more, and the fact that we have made no progress in 30 years in addressing them, are what have made me skeptical about the inflationary picture. ”
    –Physicist Paul Steinhardt (one of the originators of the inflation concept)

  11. #11 mehrdad
    October 13, 2017

    For checking The submit comment

  12. #12 mehrdad
    October 13, 2017

    I think that the string theory is completey wrong and it can be understood by almost infitite signs in our universe .

  13. #13 Another Commenter
    October 13, 2017

    As Aristotle derived “God” from the experience of motion, the Multiverse, if it exists, may not be the first metaphysical entity derived from the study of Nature.

  14. #14 Sean T
    October 13, 2017

    RM,

    Thank you. I 100% agree. What people like MM don’t get is that this blog is NOT a scientific journal. It is an attempt to communicate the current scientific consensus, along with other speculative ideas that may prove fruitful, to an audience that is composed of non-experts in the relevant scientific fields. The audience includes fellow physicists, other scientists who are not physicists (I fall into this category), and non-scientists. This type of communication can be very difficult due to the variety of the audience, and I personally think it’s well done, which is why I continue to read Ethan’s blog.

    However, much like all science, the topics covered here ALL come with the same caveats — that this is our current best understanding of things and that this understanding might well change as new observations come to light. I am not sure why people like MM insist that these topics are treated as gospel truths by the author. It is fundamental to any science topic that the conclusions reached are subject to future modification as new evidence is produced. This should go without saying, so MM’s objections are completely unfounded. Science NEVER insists that its theories are correct 100% now and forever; that is the type of thing that religion does, not science. It would get a bit tedious, though, to have to write “this is our best understanding of the universe based on currently available evidence. This understanding could change as new evidence is produced” before EVERY article. Such a disclaimer is of course unnecessary to anyone who actually understands what science is and what it does. MM, even if not explicitly written, you can certainly assume that this disclaimer applies to any article Ethan writes on a scientific topic.

  15. #15 Alan G.
    Good Grief, ID
    October 13, 2017

    RM & Sean T: Agreed

    I’ve struggled mightily over the last 30 years on the best, most constructive ways to handle the infinite and conflicting ways people interact with each other online, when nothing is known of their background except for the very narrow portion we see online, and the ability the communicate clearly is already severely impaired for all in the best of circumstances.

    I’ve tried hard to tone down my own visceral reactions over time, with only partial success.

  16. #16 Michael Mooney
    October 13, 2017

    Mathematicians are so proud of the precision and specificity of their math, but don’t apply the same criteria to the language they use describing their concepts. Ethan constantly contradicts himself and often speaks pure nonsense as if it were factual. I have pointed out these instances countless times. This blog is dishonest “science.”

  17. #17 CFT
    October 13, 2017

    @Sean T #4,
    Some caveat. Jettison the major tenets of the scientific method so you can…prop up interpretation of theory that can’t carry it’s own weight? No. That is worse than bad science, as it isn’t science at all. When the going gets tough you do not excuse yourself from observation, testing, and prediction so you can keep your pet theory and claim it works marvelously, quite the reverse actually.
    .
    If you wish to contend with my ‘science denier’ view, perhaps the man who helped invent the very theory of inflation might carry a little more weight…and a hell of a lot more than Ethan’s screed to metaphysics by consensus.

    “To me, the accidental universe idea is scientifically meaningless because it explains nothing and predicts nothing. Also, it misses the most salient fact we have learned about large-scale structure of the universe: its extraordinary simplicity when averaged over large scales. In order to explain the one simple universe we can see, the inflationary multiverse and accidental universe hypotheses posit an infinite variety of universes with arbitrary amounts of complexity that we cannot see. Variations on the accidental universe, such as those employing the anthropic principle, do nothing to help the situation.

    Scientific ideas should be simple, explanatory, predictive. The inflationary multiverse as currently understood appears to have none of those properties.”
    —Paul Steinhardt (one of the originators of inflation theory)
    .
    And if you wish to read the whole article:
    .
    https://blogs.scientificamerican.com/cross-check/physicist-slams-cosmic-theory-he-helped-conceive/
    .
    That is called refutation of a bad idea by the highest source possible, the person who thought it up. Think on that a little before you go marching off a cliff with Ethan.

  18. #18 CFT
    October 13, 2017

    The guy who helped invent the inflation theory, Paul Steinhardt, thinks it’s a really bad idea.
    You might want to take it from the horses mouth before you believe what Ethan is selling.
    .
    https://blogs.scientificamerican.com/cross-check/physicist-slams-cosmic-theory-he-helped-conceive/

  19. #19 CFT
    October 13, 2017

    @Sean T. #4,
    Before you go down the primrose path with Ethan’s political science of consensus, and discard prediction, experiment, and observation, you should know the guy who helped invent the idea thinks it isn’t science and that it doesn’t do anything to explain anything without making the problem of fine tuning worse.
    .
    “To me, the accidental universe idea is scientifically meaningless because it explains nothing and predicts nothing. Also, it misses the most salient fact we have learned about large-scale structure of the universe: its extraordinary simplicity when averaged over large scales. In order to explain the one simple universe we can see, the inflationary multiverse and accidental universe hypotheses posit an infinite variety of universes with arbitrary amounts of complexity that we cannot see. Variations on the accidental universe, such as those employing the anthropic principle, do nothing to help the situation.

    Scientific ideas should be simple, explanatory, predictive. The inflationary multiverse as currently understood appears to have none of those properties.”
    —Peter Steinhardt (one of the originators of inflation)
    .
    You can read the entire interview here:
    .
    https://blogs.scientificamerican.com/cross-check/physicist-slams-cosmic-theory-he-helped-conceive/
    .
    Straight from the horses mouth to your ears. Real physicists don’t abandon the scientific method to get the results they want.

  20. #20 CFT
    October 13, 2017

    Good grief. I thought the posts had not gone through, not into a holding bin. Didn’t mean to keep posting the same thing, just thought the blog server was down.

  21. #21 Michael Mooney
    October 13, 2017

    CFT, It came through clearly.
    ” Real physicists don’t abandon the scientific method to get the results they want.”
    Thanks.

  22. #22 Ragtag Media
    October 13, 2017

    @CFT

    “This is why HEP physics is in trouble, nonsense like the multiverse sucks up limited resources and talent and produces nothing but untestable fantasy”

    That there is a very succinct comment that I can totally understand with regard to the money/research issue in the science research field.
    Thanks for pointing that out,

    I would be happy to vote for a removal of funds from climate scientist and give them to theoretical scientist for the next few years.. LOL..

  23. #23 Quentin Rowe
    New Zealand
    October 16, 2017

    Welcome aboard, Ethan 🙂