Do we live in a multiverse? | The Economist

when the actions looked into the night sky they thought the heavens revolved around the earth and mankind over the centuries this view has changed radically we discovered we lived on a planet orbiting a star within the solar system and the solar system was found to be part of the Milky Way galaxy later we learned that our universe was filled with billions of other such galaxies but could it be that we're committing the same error as our ancestors by thinking the universe contains everything there is could it be that we live in a multiverse the word multiverse refers to the general idea that our universe might not be unique there might be many many universes and there are a number of different ways of thinking about multiverses now this idea of a multiverse is not gratuitous speculation no it really comes out of both experiment or observational physics about the universe and the current theories as best we understand them there are a number of different theories about what the multiverse could be one proponent of the idea of the multiverse is max tegmark of the Massachusetts Institute of Technology dr. tegmark suggests a four fold classification of possible types of multiverse the first type of multiverse is just an extension of what we already know our universe expanding into infinity rather than ending at the limits of our vision when we astrophysicists talk about our universe we don't mean everything that exists we mean this we mean the spherical region of space from which life has had time to reach us so far because no matter how good telescopes we build if there's a galaxy out here light from it just hasn't reached us yet we have no access to it we can look back almost to the beginning of time shortly after the Big Bang some 13.8 billion years ago to the edge of the observable universe but we can see no further so the space beyond that distance known as the Hubble radius is literally out of sight but that doesn't mean there isn't anything there you've got every reason to think that our universe goes on far beyond what we can see that there are many galaxies which are unobservable because they're so far away and indeed many people think that the universe extends far far beyond what we can see maybe billions of times further because the expansion of the universe has stretched space astronomers are able to see out to a distance of about 42 billion light years how far things extend beyond this is unknown but may not be unknowable and if they stretch to infinity as some theory suggests there could be numerous isolated universes cut off from one another by their own Hubble radius depending on the observers vantage point I don't have a single colleague in science who thinks that space actually ends here at the edge of our universe the way it starts getting more controversial is when you ask how much more space is there to understand the second type of multiverse in dr. tegmark system it is first necessary to understand how the universe was formed and the theory of inflation it was first conceived of by Alan Guth in 1979 and then later refined and expanded upon by Andrei Linde who had some key insights so inflation is a twist on the classic Big Bang Theory it's really an answer to the question of what is it that held the Big Bang but initially the universe was in kind of energetic vacuum lake state the universe expanded so nearly exponentially fast during one trillionth of a trillionth of a trillionth of a second it have grown up to this size much larger than the size of the part of the universe which we are capable seeing right now the thinking is that inflation may not have stopped at the same time everywhere so we live in a universe that was spawned by one area of inflation but bubble universes or pocket universes could have continued to form elsewhere we don't know much about how inflation started and we don't know if it started only once or many times perhaps it started many times but even if it only started once that's enough to create an infinite number of these pocket universes because once the inflation goes the pocket universe ones here a pocket universe forms there and just goes on forever and as a result the universe becomes a self-reproducing it definitely growing fractal what these universes could be like is a mystery but it is conceivable that the laws of physics within them would be totally different from our own they may not allow gravity to exist they may not allow a periodic table of elements they may not allow stars to be stable for long enough etc this is one of the ideas of string theory which attempts to unify general relativity with quantum mechanics the thinking is that all of the solutions produced by string theory that don't match up with what we can see in our own universe may actually represent reality in other universes so the basic idea of a multiverse is that the different solutions of string theory control the environment in these different regions very far away so if we are in a multiverse where the different constituents are governed by different physical laws then we have to introduce a concept called anthropic selection the idea we are not in a typical universe because most of them will be sterile or stillborn because the laws governing them won't allow complexity to emerge the anthropic principle is the idea that our universe is fine-tuned to allow humans to live a small fiddle with the strength of gravity for example and life as we know it would not exist a coincidence that does not sit easily with scientists the concept of a multiverse neatly addresses this problem within the infinite number of universes that could exist we are simply living in the one we are able to in the third type of tech mark multiverse as in the first the laws of physics are the same from one to another in this type though the component universes are separated not by distance but by time at every moment within such a multiverse all of the possible futures allowed by the uncertainties of quantum mechanics actually happen cryogenics is not a predictive theory it's a probabilistic theory so it says for example of a photon goes through a polarizer at 45 degrees to the angle polarization it just has a 50/50 chance of going through or not and there's no way of knowing one interpretation of quantum mechanics which I think makes a lot of sense says that when the photon hits the polarizer at 45 degrees there's actually two futures that happen one where that goes through the polarizer and one where it doesn't and each feature continues as if the other future were not there in the many worlds theory of the multiverse the entirety of the universe acts like the quantum photon but instead of having to potential future States every possible outcome would be manifested so our entire universe and everything within it including you would be constantly undergoing multiple visions into daughter universes each with its own reality and future Andy give an observer though would only see one outcome in the final classification the level 4 multiverse doctor tegmark proposes that all coherent mathematical systems describe a physical reality of some sort those different systems are of necessity different universes what this last idea translates to in practice is hard to conceive of it is more the province of metaphysics than physics but the other three types of multiverse though they push the bounds of physical theory do not overstep them observational data supporting the theory of inflation have convinced some scientists that a multiverse is possible but the idea is still controversial I I think the jury is still out on whether the multiverse it's odd that some people get very emotional some people are very hostile to the idea because they don't view we should talk about entities we can't directly observe I think we've got to be open-minded because we have good theories which predict that a multiverse must exist and I hope that we can settle this I think it's a empirical question although the idea that there are other universes I regard is a very reasonable speculation of modern cosmology taking a step back I mean it's proven very difficult surprisingly hard to come up with a theory of physics that predicts only what we see and predict that there's nothing else it may be impossible to ever directly observe the multiverse but some scientists hope to eventually gather enough data supporting the theories that predict it - one day confirm its existence if that were to happen like the ancients before us we would be given a whole new perspective on how the cosmos works and on our place in it [Music]

Channel: The Economist

Views: 1,818,335

Rating: 4.865591 out of 5

Keywords: The Economist, Economist, Economist Films, Economist Videos, Politics, News, short-documentary, multiverse, multiverse theory, do we live in a multiverse, multi verse, multiuniverse, multi universe, is there a multiverse, multi universe theory, what is multiverse, what is a multiverse, parellel universe, max tegmark, universe, theory of inflation, cosmology, many worlds interpretation, our mathematical universe, pocket universe, bubble universe

Id: Rx7erWZ8TjA

Length: 8min 58sec (538 seconds)

Published: Fri Aug 14 2015

Reddit Comments

[u/TheeImmortal]

As a Scientist that works in R&D in a top 10 Scientific company, this is the most Scientifically inaccurate description of our Universe and a very deceiving picture of Physics in general for the general public.

Firstly before I criticise this here is a proper discussion of a Multiverse done by Sixty Symbols: https://www.reddit.com/r/mealtimevideos/comments/68gt7l/can_a_multiverse_ever_be_real_sixty_symbols_608/

Timestamp and Responses to video:

0:24: Are we making the same error as our ancestors by thinking the Universe is all there is. Well by definition the word Universe means that which contains everything or as Merriam Webster states: "the whole body of things and phenomena observed or postulated : cosmos: ".

So if you find something outside the universe, that's technically within the universe once you find it.

It's a small technicality but it's important to understand to LEAVE our universe is something scientists cannot do. We are bound by it, so to talk of other universes outside our own that are not observable is very unscientific and is more philosophy and theology than science.**

0:45: So Leonard Susskind's appearances in the video always lead to crazy and wacky claims. Here he claims a Multiverse isn't speculation it "... comes out of both experimental or observational physics about the universe and the current theories as best we understand them."

This is by far the most dishonest scientific statement and disproved by the video itself at the 7:40 mark: "It's odd that some people get very emotional, some people are very hostile to the idea, because they don't view we should talk about entities we can't directly observe. I think we have to mind it because we have good theories that predict a Multiverse exist and I hope we can settle this."

It's not just that you can't directly observe, there is no possible way to ever gather or measure anything outside our own Universe; thus it is not falsifiable which is very convenient but which also makes the theory unscientific.

Karl Popper in his book the Logic of Scientific discovery, supported by millions of scientists throughout time has observed about science that: "In so far as a scientific statement speaks about reality, it must be falsifiable; and in so far as it is not falsifiable, it does not speak about reality."

There is no experiment that we can run that will allow us to go outside our Universe and find other Universe's, and as such any theory of their existence is similar to a Spaghetti monster which you can't disprove and is simply believed as a tenet of faith, lacking the attribute of falsifiability that all Scientific theories must have in order to be considered such.

Less than a minute in, the video already claims observation and evidence that is both untrue and misleading for non-science viewers watching it.

1:10: Type one of 4 types of Multiverse is scientifically laughable. It claims a theory that has long been debunked which is an infinitely large universe that could hold other universes with different properties. Or it proposes a similar strange idea that the laws of the universe do not hold everywhere which is asked and answered on reddit more times than should ever be as it's a fundamental assumption of all Physics. Physics would literally fall apart if every time we looked at a distant star our laws would change.

1:20: "When we astrophysicists talk about our universe we don't mean everything that exists, we mean this, we mean the spherical region of space from which light has had time to reach us so far."

That is a blatant lie, not only in that it goes against the definition of the word Universe but scientists do not speak in that way. When Neil Degrasse Tyson or Einstein or anyone else says Universe, they mean the whole universe, they do not mean the Observable universe. There is a term for that, we use that term in science all the time, it is Observable universe. People do not limit the laws of physics or the discussion of the universe to only what is the observable sphere.

The very fundamental assumption of physic is that the laws of our Universe hold everywhere, not just in the observable region of space.

2:25 "...and if they stretch to infinity as some theories suggest there could be numerous isolated universes cut off from one another by their own Hubble radius"

This is such a controversial claim even the follow up discussion of this statement mentions the controversy: "I don't have a single colleague in science who thinks that space actually ends at the edge of our universe(observable universe). Where it starts to getting more controversial is when you ask where how much more space is there."

This is a very subtle way of trying to get the viewer to believe our universe is potentially infinitely big. That theory has LONG been disproven both by observation and measurement. There are no hidden pocket universes in our finite universe.

That theory was the Steady State Theory, it was thoroughly disproven about 100 years ago by the Big Bang theory and cosmological expansion.

Even a 10 year old knows that the universe can't both be infinitely large and expanding at the same time. If the universe had a beginning and it expanded, by definition it is finite in size which means there IS an edge of the universe, it is expanding, and our universe was once nothing and now is a gigantic, but not infinite.

By nothing Einstein tells us that means there was no Space, no Matter, and no Time. People that claim the universe is infinitely big go against the vast majority of astrophysicists and cosmologists.

One simple proof that works to destroy the principle is our own sun. If our universe is infinitely big and old our sun would have burned out by now, not just our sun, all suns.

The 1st law of thermodynamics tells us the amount of energy and matter in the universe is constant; after an infinite amount of years all the Hydrogen in the universe would have merged together with gravity, created suns, and become helium, in the fusion cores of all stars. As it Helium fused together it would continue fusing until the sun finally ran out of energy and burned out into a black hole or a white dwarf. This process is discussed by Neil Degrasse here: https://www.youtube.com/watch?v=rJ5kkT6YCTM

Imagine that before the point of your birth an infinite amount of time had passed, all the hydrogen in the universe would have all run out, like fuel in a car, there would be no sun, and you would never have been born.

That's why we estimate the age of the universe at about 13.82 billion years. Our universe came from nothing(no space, time, or matter) and then came into existence. Since then suns have been created and burning out. This will continue for billions of years until ALL suns burn out in our universe, which is called the Big freeze.

Here is a video discussing the main possible endings of our universe by Michio Kaku: https://www.youtube.com/watch?v=R5orcCuprG4

The core takeaway of all this is thus: the Steady State theory of the Universe has been disproven thoroughly. The expansion of our universe by the red shift and the cosmological background radiation and other observed and measured evidence has shown us that our universe is finite in age and finite in size, it is not infinitely big and no serious Physicists really think it is, and it will never be infinitely big since it started out as a finite size which by definition in mathematics is an impossibility.

So once you know there is a limited size/age to the universe this whole pocket universe nonsense quickly evaporates as there is nowhere to hide as there is no infinitely large universe.

End of Part 1

Edit: Typos

[u/sheeshwhataretrees]

Do we live in a giant condom?

[u/sobrohog]

just take a second to think about how fucking big a multiverse would be if it was a fractal of universes

[u/BestRedditAccount2]

Couldn't stop thinking about Rick & Morty watching this video

[u/Mentioned_Videos]

Other videos in this thread: Watch Playlist ▶

VIDEO	COMMENT
(1) Neil deGrasse Tyson on the Big Bang and Heavy Elements (2) Michio Kaku: What's the Fate of the Universe? It's in the Dark Matter	+15 - As a Scientist that works in R&D in a top 10 Scientific company, this is the most Scientifically inaccurate description of our Universe and a very deceiving picture of Physics in general for the general public. Firstly before I criticise this here i...
Can a Multiverse ever be "real"? - Sixty Symbols	+7 - Part 2 below 4:40 Type 2 multiverses use string theory and conveniently create universes outside our own that we can never travel to, observe, or experiment on. Thus as I mentioned earlier these non-falsifiable claims are unscientific. This is just ...

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[u/[deleted]]

Our universe is a giant condom.

[u/Uncle_Charnia]

The Fermi paradox is evidence for a multiverse if it is possible to travel back in time. Any nearby extrasolar civilisation that can detect us is ahead of us, because we are new. If it's ahead of us, and time travel is easy, then it will go back in time and kill our ancestors when it realises how dangerous we are. We can only exist in a universe in which we are either isolated or alone. The ubiquity of extrasolar planets suggests that our being alone is improbable if there is no multiverse, but probable if there is. The problem of falsifiability remains, so it's just a bit of fun.