The Multiverse E-Book

Brian Clegg

• Herausgeber: Icon Books
• Kategorie: Wissenschaft und neue Technologien
• Sprache: Englisch

Seitenzahl: 203

Veröffentlichungsjahr: 2025

Beschreibung

The universe was supposed to be all there was - the whole of existence. For centuries the size of the universe and whether or not it is finite, fascinated scientists and philosophers. But however big the universe may be, there being only one gave astronomers and cosmologists a headache. Existence as we know it is contingent on so many constants in nature which, if altered only slightly, would make life impossible. This seems so unlikely to happen by chance. What if, instead, there is in fact a vast range of different universes, with many variants of the universal contents, making ours just one of many that happens to be viable for life? In this illuminating exploration, Brian Clegg delves into the endless possibilities of the multiverse. Investigating questions of expanding, parallel and communicating universes, this accessible guide takes the reader into one of the weirdest and most exciting areas of modern physics and cosmology.

Leseprobe

 

 

Published in the UK and USA in 2025 by

Icon Books Ltd, Omnibus Business Centre,

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email: [email protected]

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ISBN: 978-183773-235-7

eBook: 978-183773-236-4

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For Gillian, Chelsea and Rebecca

ACKNOWLEDGEMENTS

Cosmology has always fascinated and frustrated me in equal measures, since well before doing a Natural Sciences degree specialising in physics. As a huge fan of Fred Hoyle in my teens I was disappointed when the evidence moved the prevailing view from his steady state theory to the big bang theory. Once I began to come across ideas of multiverses, as a science-fiction enthusiast I was delighted, but as a science writer I often felt that there was way too much speculation and not enough testable science. Thanks to the many cosmologists, astrophysicists and science writers who have informed and frustrated me in the discovery (you will find details of some in the Further Reading section). Thanks also to the team at Icon Books, including Connor Stait and Steve Burdett for their ever-helpful input.

CONTENTS

1Enter the multiverse

2Universal speculation

3Virtually universal

4Dimensional complexity

5Fine tuning conundrum

6Infinite possibilities

7Inflating everything

8Many worlds

9Colliding universes

10Holographic universes

11Angels on pinheads

Further reading

ENTER THE MULTIVERSE

1

Multiverses turn up so often these days in films that it would be easy to think that the concept behind them was either a perfectly normal part of accepted reality, or a pure fantasy on the same level as superheroes* or magic powers. Marvel’s ‘cinematic universe’ has been riddled with multiverses for years, while other movies such as the 1998 Sliding Doors take a more subtle approach of using a ‘what if?’ decision point to examine how each of two hypothetical parallel worlds would develop.

This is a small-scale version of the sub-genre of science fiction known as alternate history, where writers speculate on how the present would be if, for example, the Reformation never happened, or Germany had won the Second World War. Although in such fiction there is only the ‘counter-factual’ version of reality and any comparison with our world is left to the reader, there are still effectively two instances of the universe in play.

What is a multiverse?

Linguistically, the concept of a multiverse is more than a little baffling, as the universe is supposed to be the word used to describe all that there ever was or will be – the whole of existence. The word ‘multiverse’ seems to have been coined by the American philosopher William James who, in an 1895 contribution to the International Journal of Ethics, wrote, ‘Visible nature is all plasticity and indifference, a multiverse, as one might call it, not a universe.’ As is, perhaps, not atypical with philosophy, this is one of those sentences where it’s possible to understand what all the words mean without having a clue what the writer intended. He certainly had nothing in mind resembling our modern concept.

James may have been suggesting that the universe did not have a single guiding force and meaning but rather was a chaotic environment, something reinforced by the physicist Oliver Lodge who in 1904 was reported as saying, ‘The only possible alternative [to a universe with a purpose] was to regard the universe as a result of random chance and capricious disorder, not a cosmos or universe at all, but rather a “multiverse”.’ This philosophical nicety seems to rather overload the term ‘universe’ with more meaning than most endow it.

It is frequently said that as early as 1848 Edgar Allen Poe wrote about there being a number of universes – a multiverse by any other name. I suspect most who suggest this have not bothered to work their way through Poe’s extremely long and turgid essay based on a lecture, Eureka: A Prose Poem. This is probably better known for presenting the correct solution to Olbers’ paradox, which we explore further in the next chapter.

What Poe actually says is this: ‘Have we, or have we not, an analogical right to the inference that this perceptible Universe – that this cluster of clusters – is but one of a series of clusters of clusters, the rest of which are invisible through distance …’ He is making the distinction between what we now call the visible universe and the rest of it, containing plenty more galaxies (his clusters) – but he was not suggesting there was more than one universe.

In the modern physical sense, the word ‘multiverse’ seems to have entered the lexicon in a story by the English science-fiction and fantasy writer Michael Moorcock in 1963. His novella The Blood Red Game, published in the SF magazine Science Fiction Adventures, introduced the kind of multiverse familiar from comics and their movie spinoffs. (The comics had featured the concept earlier, but it was Moorcock who named it.)

As American physicist Brian Greene has pointed out, our definition of what a universe and a multiverse is can be decidedly vague. He recommends adopting ‘the approach famously adopted by [US] Justice Potter Stewart to define pornography. While the U.S. Supreme Court struggled to delineate a standard, Stewart declared “I know it when I see it.”’

Extra dimensions

For centuries, the size of the universe and whether or not it was finite fascinated scientists and philosophers. And that’s part of the story. But however big it may be, once mathematicians and scientists began to think outside of the apparent natural limits of three spatial dimensions, it seemed possible that the universe we experience might not be all there is to reality.

An early addition to those familiar three dimensions was when time began to be considered as a fourth, if rather different, dimension. In his 1895 novel The Time Machine, H. G. Wells has his time traveller explain that: ‘Clearly any real body must have extension in four directions: it must have length, breadth, thickness, and – duration.’ This concept would become truly scientific with the development of Einstein’s theories of relativity, which pull time and space into a single integrated body of spacetime.

At the same time, mathematicians were escaping from the familiar geometry that had reigned supreme since the work of Ancient Greek mathematician Euclid (and is still the most widely taught). Basic geometry is limited to two-dimensional, flat planes. Clearly this isn’t enough to deal with the three-dimensional world around us. As a trivial example, we are taught that the angles of a triangle add up to 180 degrees. But you can happily draw a triangle featuring three right angles (270 degrees) on a sphere like the Earth.*

That is only the start. We might experience three spatial dimensions, but mathematics is not limited to describing the physical world that we inhabit. In a mathematical universe there could be as many dimensions as were needed for the most extravagant flights of fancy. We might not be able to envisage, say, the true appearance of the four-dimensional hypercube known as a tesseract – but maths can easily describe it.*

Although the mathematical universe only partially intersects with reality, it can be an effective starting point for what-if speculation. That term ‘what-if?’ is arguably the basis of all storytelling, reaching its heights in science fiction and fantasy. As human beings we are not limited to what we have directly experienced – we can speculate and fantasise about possibilities that might never be susceptible to scientific probing.

Fiction writers picked up on the potential for adding dimensions early on. Arguably, though, the first text to play with dimensions involved removing a dimension rather than adding new ones. The 1884 book Flatland by the entertainingly named Edwin Abbott Abbott described experiences of creatures living in a two-dimensional universe and how they would experience three-dimensional objects passing through their plane. This gives us insights into how we might experience higher dimensions – but the far more common approach in fiction would be to extend the dimensional structure available to the writer. In a fantastical sense, this had been done for centuries, with magic employed to connect our world to a parallel location – be it a fairy realm or an astral plane.

Such imaginings were often described as featuring ‘another dimension’ or a ‘parallel dimension’ in a hand-waving sense, without really explaining what this meant. In reality ‘another dimension’ probably refers to the potential existence of another three spatial dimensions that don’t intersect with our own at all, while a parallel dimension had the feel of three new dimensions parallel to our own but slightly shifted in yet another orthogonal direction. To make stories interesting, there usually had to be some kind of portal to bridge between the multidimensional spaces, though if considering science rather than magic as the mechanism, it was hard to see how such a connection could ever be made.

A good example of such an extra-dimensional approach is in Algernon Blackwood’s 1917 story ‘A Victim of Higher Space’. Likely inspired by Abbott, Blackwood imagined that physical objects we experience do have more than three spatial dimensions. So, for example, a box in our world would actually be (at least) four dimensional, we just can’t experience the fourth. Except (by magical means, though wrapped up in ‘psychic’ waffle) one individual starts to experience this and can even move in the fourth dimension, which he can handle, but is terrified of slipping into even more dimensions and never returning.

One of the first stories to attempt a more scientific approach made use of the fourth physical dimension, time, rather than space as the dividing feature between two sets of universes. Murray Leinster’s 1934 story ‘Sideways in Time’ effectively imagined a second time dimension running at right angles to the time we experience – so identical physical dimensions could be experienced with no intersection in time with our own world. More commonly, though, the new ‘dimensions’ would be in the same time stream but spatially separated, even if time was able to flow at different rates in the locations. This happens in everything from C. S. Lewis’ Narnia to the ‘demon dimension’ of Buffy the Vampire Slayer.

Most of these examples, including the comic-book concept of ‘parallel dimensions’, have been based on pure fantasy with little more than magic to enable the transition between the two, but one of the most common ‘cheat conventions’ of science fiction also makes use of what amounts to extra dimensions. To make it possible to explore space in a timescale accessible to humans, writers often make use of some kind of faster-than-light drive. A common mechanism for this to work is to invoke a ‘hyperspace’ which is (somehow) dimensionally separate from everyday space. Movement in hyperspace works on a different scale to normal space, enabling rapid travel between two points that are far apart in the real universe. Not surprisingly, there is no known physical equivalent in reality.

Philosophical multiverses

But leaving aside speculation about invisible parallel dimensions, just having a single universe would eventually give astronomers and cosmologists a headache. This is because of something known as fine tuning: there are many constants of nature that would only have to be slightly different for life never to be possible. This seems so unlikely to happen by chance that many cosmologists, striving to avoid the need to invoke a creator, believe that there are a vast range of different universes, forming a multiverse with many variants of the universal contents, making ours just one of many that happens to be viable for life.

Then there is the argument from similars. Some astronomers (who perhaps should know better) have pointed out that a number of astronomical features we have historically thought unique – the Earth, the solar system, the galaxy – have turned out to be just one of many. So, they argue, this should apply to the universe too. This is, unfortunately, magical thinking, which is why I used the expression ‘argument from similars’, the pseudoscientific justification used for homeopathy. The idea in that unscientific discipline is that a treatment will be effective in homeopathic form if it has a similar effect to the disease or ailment it is treating.*

Using such an argument to justify multiple universes seems an odd one to deploy with any scientific rigour: just because some things in science have turned out to be more numerous than was first thought does not mean all will. After all, early atomic theory assumed each type of substance had a different atom – so, for example, cheese atoms were different from bread atoms. In reality, our picture of fundamental particles has not multiplied as we discovered more but has greatly reduced – a frequently occurring situation that provides entirely the opposite reasoning.

Another challenge that cosmologists face is the mystery of inflation, the sudden vast expansion that the early universe may have gone through. Some theories predict this has to happen all the time, producing a whole range of unconnected universes. And then there are the vast numbers of parallel universes suggested by the ‘many worlds’ interpretation of quantum theory. To make it even more fun, some suggest that the cosmologists expecting a multiverse have got their understanding of probability all wrong.

This is all entertaining speculation, but while most agree there can be no communication between universes, some scientists have devised ways this might happen – or even expect universes to collide in extra dimensions, creating big bangs like the one we consider to be the start-point of our own universe. Welcome to one of the weirdest and most exciting aspects of modern physics and cosmology, attempting to explore the mysteries of what we can know of the outer limits.

Before we start to dig into the potential reality of the different forms of multiverse, let’s take a brief visit to one way that, even in conventional space and time, the picture of a simple universe with three spatial dimensions at right angles to each other ceases to make sense. This is when we encounter the space-mangling form of a black hole.

Into the black hole

‘Black hole’ is a term that now appears regularly in common usage. However, the physical phenomenon described as a black hole is anything but something we come across in everyday life. In reality, because of the immense distances of interstellar space, humanity may never directly be able to experience a black hole, as happens all too often in SF movies such as Interstellar (and probably this is just as well). The concept of a black hole emerges from two aspects of physics – Einstein’s general theory of relativity and the life cycle of stars.

To get his masterpiece to work, Einstein had to move away from the rigid three-dimensional geometry that dates in part back to Ancient Greece. He realised that massive bodies distort the space and time around them. For example, the Earth is moving in a straight line through space. But the space around the Sun is warped by the star’s powerful gravitational pull sufficiently to turn that straight line into a curve, locking the Earth into an orbit. The planet’s path through space doesn’t twist – it is space itself that is distorted to produce the near-circular path.

When Einstein first published his theory, although he was able to specify the equations that described the actions of gravity, they proved too complex to solve. But another German physicist, Karl Schwarzschild, in hospital after being injured in the First World War, simplified the equations by imagining a very simple body that was entirely spherical, uniform and did not rotate. He discovered that if such a body were dense enough, its gravitational pull would distort spacetime sufficiently nearby it that light (or anything else moving) would have its path bent back into the body and could never escape – it was a theoretical description of a black hole. (The term itself was only dreamed up in the 1960s.*)

At the time Schwarzschild wrote his paper, in 1915, no one thought of this as anything other than a model which made it possible to explore one small aspect of Einstein’s equations. But as more became known about the mechanisms driving stars it was realised that at the end of their lives, some very specific types of star would suffer a catastrophic collapse. As they ran out of fuel, resulting in no nuclear reactions to push against gravity, the most massive stars would collapse – and with sufficient mass involved, no force of nature could prevent that collapse from occurring. The star should effectively disappear to a dimensionless point known as a singularity.

Such a black hole would not appear as a point when seen from outside – from Scharzschild’s solution it was clear that, for any particular mass, there would be a sphere known as an event horizon from inside which nothing, not even light, could escape. But the horizon is just that – not a membrane or barrier, but simply a distance from the centre of the sphere. An object passing through it would not be aware of doing so. Instead, it would head towards oblivion in the centre of the black hole, where the gravitational force should become infinite.

An important word there is ‘should’ – in practice, when anything physical becomes infinite (with the possible exception of the universe) the theory supporting it breaks down. We know that there are many bodies out there in the depths of space that we call black holes, and which have every appearance of being just that. But exactly what happens at the heart of the black hole is unknown – it seems likely that something would prevent singularities forming, but we don’t know for certain.

What we do know, though, is that space and time distort more and more as something heads towards the centre of such a body. As a result, the familiar dimensions of time and space become so distorted that, in effect, a body falling to the centre of a black hole is heading for a point in time, not a point in space. The part of the universe inside the black hole is so different from the rest of existence that it could be argued it exists in a different universe in its own right – as we will see later, some have even speculated that our own universe is contained in the event horizon of a black hole.

But we are heading too quickly down one of the many conceptual rabbit holes that litter our view of reality. Let’s take a step back and look at what we mean by the universe in the first place, and how ideas about it have evolved over time.

* Superhero stories are often presented as being science fiction – and this is occasionally feasible with a character like Batman or Iron Man, where there are no superpowers involved. But as soon as powers crop up there tends to be little more than a veneer of pseudoscientific explanation, pasted over what is simply magic.

* The easiest way to envisage a three-right-angle triangle is to take two lines at right angles to each other down from the North or South pole to the equator, which they will meet at right angles.

* The simplest three-dimensional projection of a tesseract can be envisaged as a pair of cubes, one within the other, with lines linking equivalent vertices, though all of the three-dimensional ‘sides’ formed this way are actually identical cubes. American science-fiction writer Robert Heinlein wrote a very impressive 1941 short story, And He Built a Crooked House, in which an architect creates a house in the form of an unfolded tesseract which, as a result of an earthquake, collapses into its true four-dimensional form.

* The idea that homeopathy deploys poisons with similar effects to diseases and ailments would be disconcerting were it not for the way that the active substance is diluted so much that it is likely there is not a single molecule of it left in the final remedy.

* The term ‘black hole’ is often attributed to American physicist John Wheeler, who certainly popularised it in the 1960s. The first recorded use of the term, though, was at a January 1964 American Association for the Advancement of Science meeting. Unfortunately, it was not recorded who used the term, but the article mentioning it in Science News-Letter was written by Ann Ewing.

UNIVERSAL SPECULATION

2

Our modern vision of the whole of existence operates on several levels. With the exception of a few space flights, human life has been limited to the surface of planet Earth. This planet forms part of our solar system, based on our mid-sized star, the Sun. Our star is just one of over 100 billion in our reasonably chunky galaxy, the Milky Way. Although there are various nominal structures of which the galaxy forms a part, it is itself a small component in the observable universe, which is estimated to contain hundreds of billions of galaxies (we’ll come back to the concept of ‘observable’ in a moment). And if there is such a thing as a multiverse it’s possible that our universe is just one of many, but let’s start with the assumption that the word means what it was historically understood to describe – all of space and time.

What is our universe?

The word ‘universe’ itself is something of an oddity. It means in the original Latin form universum ‘one turn’, though from the start it was taken to refer to everything that exists. It came to English via the French word univers in the late-sixteenth century. Some think that the ‘turn’ part implies that all the separate parts of existence are ‘turned into’ one thing by this word, though it seems a weak way to derive the meaning. Whatever, we are stuck with it. But the key part is that opening ‘uni’ – there should only be one universe in the way that the term was originally envisaged. If there is indeed a multiverse, then that strictly should be the universe, where what we can experience is just a small subset of the whole.

How small a subset our direct experience applies to becomes clear when we look at the limits of human exploration. At the time of writing, the human beings who are furthest from the surface of the Earth are the temporary inhabitants of the International Space Station. Although this is often described as being in space, which makes it sound extremely far away, the space station orbits at a ridiculously short distance from the rest of us – a little over 400 kilometres (250 miles) up. That is, for example, closer than Paris is to London or about the same distance as Washington DC to Pittsburgh.

The furthest that humans have ever travelled out into space is to the Moon. This means covering a more respectable distance of 384,000 kilometres (239,000 miles). But that’s around 160 million times closer than the nearest star other than the Sun, a red dwarf called Proxima Centauri, itself more than 10 billion times closer than the furthest distance potentially visible in the universe. The word ‘universe’ simply doesn’t give a clear picture of just how enormous our environment is.

Even if there genuinely is only one universe, there is likely to be plenty of it that we can’t ever know about – and this is where the word ‘observable’ comes in. Our ability to explore the universe beyond the near vicinity of Earth makes use of light, or strictly electromagnetic radiation in all its forms, including radio, microwaves, infrared, ultraviolet, X-rays and gamma rays*