Sinister Security: Multiverse Theory

Yes, The Multiverse Is Real, But It Won't Fix Physics

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“We are all agreed that your theory is crazy. The question that divides us is whether it is crazy enough to have a chance of being correct.” Niels Bohr spoke these words to Wolfgang Pauli about the latter's theory of elementary particles, but it could just as easily apply to many of today's most controversial modern physics ideas.

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One that's gotten a lot of attention recently is that of a Multiverse. In short, it's the idea that our Universe, and all that's contained within it, is just one small region of a larger existence that includes many similar, and possibly many different, Universes like our own. On the one hand, if our current theories of physics are true, the Multiverse absolutely must exist. But on the other hand, as Sabine Hossenfelder rightly points out, it's unlikely to teach us anything useful.

The observable Universe might be 46 billion light years in all directions from our point of view, but there's certainly more, unobservable Universe, perhaps even an infinite amount, just like ours beyond that.

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Why must the Multiverse exist? Quite simply: there must be more Universe than the part that is observable to us. If you look just at the portion of the Universe we can see, you can measure its spatial curvature, and find that it's incredibly close to flat. No regions repeat; no locations connect or loop back on one another; no large-curvature regions show themselves on a scale approaching that of the Universe we can observe.

If the Universe were a hypersphere, the four-dimensional analogue of a sphere, it must have a radius of curvature hundreds of times the size of what we can observe. There must be more Universe out there than what we can access.

Inflation causes space to expand exponentially, which can very quickly result in any pre-existing curved space appearing flat. If the Universe is curved, it has a radius of curvature hundreds of times larger than what we can observe.

But this isn't just a conclusion from observations; it's the same conclusion that we'd draw from our leading theory of the Universe's origin: cosmological inflation. Prior to the hot Big Bang, the fabric of the Universe was expanding at an exponential rate, where every 10-35 seconds or so, it would double in scale in all dimensions. Inflation went on for at least as long as 10-33seconds or so, but could have lasted far longer: seconds, years, millennia, trillions of years or an arbitrarily long length of time. When inflation ends, the Universe we're left with is stretched flat, the same temperature everywhere, and far, far vaster than anything we can ever hope to observe. Considering the finite nature of all we can see, inflation is the natural way to create a Multiverse of possibilities.

Inflation set up the hot Big Bang and gave rise to the observable Universe we have access to, but we can only measure the last tiny fraction of a second of inflation's impact on our Universe.

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Without a solid knowledge of how inflation began, or if it ever had a beginning, we cannot know how much "Multiverse" there is out there beyond our actual Universe. But based on the properties of inflation that imprint themselves on the Universe we inhabit, we can draw a few conclusions about it. In particular:

The lack of spatial curvature,
The adiabatic nature and spectrum of fluctuations imprinted on the cosmic microwave background,
The magnitude of imperfections that gave rise to the large-scale structure we see,
The constraints on the gravitational waves inflation could have created,
And the superhorizon fluctuations that we observe (on scales larger than the visible Universe),

All give us some important constraints on the type of inflation that occurred, and teach us two very important lessons, if the implications of these verified and validated theories are correct, about our Multiverse.

The fluctuations in the CMB are based on primordial fluctuations produced by inflation. In particular, the 'flat part' on large scales (at left) have no explanation without inflation, and yet the magnitude of the fluctuations constrains the maximum energy scales the Universe reached at the end of inflation. It's far lower than the Planck scale.

1.) Inflation did not occur at arbitrarily high energies. There's an energy scale at which the laws of physics no longer make sense: the Planck scale, or about 1019 GeV. This is about 100 trillion times larger than the maximum energies the LHC achieves, and a factor of about 100 million higher than the highest energy cosmic particles we've ever detected in the Universe. From the imprints of inflation, we can conclude that the temperature at the start of the hot Big Bang never got higher than about 1015 or 1016 GeV, safely below the Planck scale. This implies that inflation likely occurred below that scale as well. If true, this would mean that the inflationary epoch obeyed the current laws of physics, as well as every region of the Multiverse that inflation created.

Artist’s logarithmic scale conception of the observable universe. Note that we're limited in how far we can see back by the amount of time that's occurred since the hot Big Bang: 13.8 billion years, or (including the expansion of the Universe) 46 billion light years. Anyone living in our Universe, at any location, would see almost exactly the same thing from their vantage point.

2.) There are countless regions where inflation did not end, and still continues today. The idea that the Big Bang happened everywhere at once may apply to our Universe, but certainly ought not to apply to the vast majority of Universes existing in the Multiverse. Assuming that inflation is a quantum field, like all fields we know of, it must spread out over time, meaning that in any region of space, it has a probability of ending at a certain time, but also a probability of continuing on for a while longer.

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.

In the region that became our Universe, which may encompass a large region that goes far beyond what we can observe, inflation ended all-at-once. But beyond that region, there are even more regions where it didn't end. Those regions grow and inflate as time goes on, and even though many of those new regions will see inflation end, the ones where it doesn't will continue to inflate. Inflation, therefore, should be eternal to the future, at least in some regions of space. This is irrespective of whether it was eternal to the past or not.

Wherever inflation occurs (blue cubes), it gives rise to exponentially more regions of space with each step forward in time. Even if there are many cubes where inflation ends (red Xs), there are far more regions where inflation will continue on into the future. The fact that this never comes to an end is what makes inflation 'eternal' once it begins.

Accepting all of this leads to an inescapable conclusion: we live in a Multiverse, and our Universe is just one of countlessly many that exist within it. However, the standard predictions that come out of this are difficult to do science with. They include:

That different regions where inflation ends should never collide or interact.
That the fundamental constants and laws in different regions should be the same as they are here.
And that unless inflation was truly eternal to the past, there isn't enough "space" to contain all the parallel Universes that the many-worlds interpretation of quantum physics would require.

The idea of parallel Universes, as applied to Schrödinger's cat. As fun and compelling as this idea is, without an infinitely large region of space to hold these possibilities in, even inflation won't create enough Universes to contain all the possibilities that 13.8 billion years of cosmic evolution have brought us.

It's always possible to construct a contrived model that defies these generic predictions, and some scientists make a career of doing so. Writing in NPR, Sabine Hossenfelder is right to criticize that approach, stating, "Just because a theory is falsifiable doesn't mean it's scientific." But just because variants of the Multiverse are falsifiable, and just because the consequences of its existence are unobservable, doesn't mean that the Multiverse isn't real. If cosmic inflation, General Relativity, and quantum field theory are all correct, the Multiverse likely is real, and we're living in it.

An illustration of multiple, independent Universes, causally disconnected from one another in an ever-expanding cosmic ocean, is one depiction of the Multiverse idea.

Just don't expect it to solve your most burning questions about the Universe. For that, you need physics you can put to an experimental or observable test. Until that day arrives, the consequences of a Multiverse will likely remain in the realm of science fiction: where they presently belong. It's okay to speculate, but if you insist on attributing a physics problem's solution to an untestable feature of the Universe, you're essentially giving up on physics. We all know that the mysteries of the Universe are hard, but that's no reason to not even try to find a solution. The Multiverse is real, but provides the answer to absolutely nothing.

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The Multiverse Is Inevitable, And We’re Living In It

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“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

Imagine that the Universe we observe, from end-to-end, is just a drop in the cosmic ocean. That beyond what we can see, there’s more space, more stars, more galaxies, and more everything, for perhaps countless billions of light years farther than we’ll ever be able to access.

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And that as large as the unobservable Universe is, that there are again innumerably more Universes just like it — some larger and older, some smaller and younger — dotted throughout an even larger spacetime. As rapidly and inevitably as these Universes expand, the spacetime containing them expands even more quickly, driving them apart from one another, and ensuring that no two Universes will ever meet. It sounds like a fantasy picture: the scientific idea of a Multiverse. But if the science we accept today is correct, it’s not only a valid idea, it’s an unavoidable consequence of our fundamental laws.

Artist’s logarithmic scale conception of the observable universe. Note that we’re limited in how far we can see back by the amount of time that’s occurred since the hot Big Bang: 13.8 billion years, or (including the expansion of the Universe) 46 billion light years.

Image credit: Wikipedia user Pablo Carlos Budassi.

The idea of the Multiverse has its roots in the physics required to describe the Universe that we see and inhabit today. Everywhere we look in the sky, we see stars and galaxies, clustered together in a great cosmic web. But the farther away in space we look, the farther back in time we look as well. The more distant galaxies are younger, and hence less evolved. Their stars have fewer heavy elements in them, they appear smaller as fewer mergers have happened, there are more spirals and fewer ellipticals (which take time to form from mergers), and so on. If we go all the way to the limits of what we can see, we find the very earliest stars in the Universe, and then a region of darkness beyond that, where the only light is the leftover glow from the Big Bang.

Looking out at more and more distant objects in the Universe reveals them to us as they were farther back in time, going all the way back to before there were atoms, all the way to the Big Bang.

Image credit: NASA, ESA, and A. Feild (STScI).

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But the Big Bang itself — occurring everywhere at once some 13.8 billion years ago — wasn’t the start of space and time, but rather the start of our observable Universe. Before that, there was an epoch known as cosmic inflation, where space itself expanded exponentially, full of energy inherent to the fabric of spacetime. Cosmic inflation is itself an example of a theory that came along and superseded the one that came before it, in that it:

1. Was consistent with all the successes of the Big Bang and encompassed all of modern cosmology.

2. Explained a number of problems that the Big Bang couldn’t address, including why the Universe was the same temperature everywhere, why it was so spatially flat, and why there were no leftover high-energy relics like magnetic monopoles.

3. And it made many distinct new predictions that could be tested observationally, most of which have been confirmed.

There’s also, however, one consequence that inflation predicts that we do not know whether we can confirm or not: the Multiverse.

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).

The way inflation works is by causing space to expand at an exponential rate. This takes whatever existed before the hot Big Bang and made it much, much, much larger than it was previously. So far, so good: this explains how we get such a uniform, large Universe. When inflation ends, that Universe gets filled with matter and radiation, which is what we see as the hot Big Bang. But here’s where it gets weird. In order for inflation to end, whatever quantum field is responsible for it has to roll from the high-energy, unstable state that drives inflation down into a low-energy, equilibrium state. That transition, and “rolling” down into the valley, is what causes inflation to come to an end, and create the hot Big Bang.

If inflation were a classical field, you’d get inflation for as long as the field value remained large, but as it got smaller by, say, rolling into the valley below, inflation would come to an end and reheat the Universe. Image credit: E. Siegel / Beyond the Galaxy.

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But whatever field is responsible for inflation, like all other fields that obey the laws of physics, must be an inherently quantum field in nature. Like all quantum fields, it’s described by a wavefunction, with the probability of that wave spreading out over time. If the value of the field is rolling slowly-enough down the hill, then the quantum spreading of the wavefunction will be faster than the roll, meaning that it’s possible — even probable — for inflation to wind up farther away from ending and giving rise to a Big Bang as time goes on.

Because space is expanding at an exponential rate during inflation, this means that exponentially more regions of space are being created as time goes on. In a few regions, inflation will come to an end: where the field rolls down into the valley. But in others, inflation will continue on, giving rise to more and more space surrounding each and every region where inflation ends. The rate of inflation is far more rapid than even the maximum rate of expansion of a matter-and-energy-filled Universe, so in very short order, the inflating parts take over everything. According to the viable mechanisms that give us enough inflation to produce the Universe we see, there are many more regions of space surrounding our own — where inflation did end — where inflation doesn’t end right away.

Image credit: E. Siegel / Beyond the Galaxy.

This is where the phenomenon known as eternal inflation comes from. Where inflation ends, we get a hot Big Bang and a Universe — of which we can observe part of the one we’re in — very much like our own. (Denoted by the red “X” above.) But where inflation doesn’t end, that produces more inflating space, which gives rise to some regions that will have hot Big Bangs causally disconnected from our own, and other regions that will continue to inflate. And so on.

As vast as our observable Universe is and as much as we can see, it’s

only a tiny fraction of what must be out there.

Image credit: NASA, ESA, R. Windhorst, S. Cohen, and M. Mechtley (ASU), R. O’Connell (UVa),

P. McCarthy (Carnegie Obs), N. Hathi (UC Riverside), R. Ryan (UC Davis), & H. Yan (tOSU).

This picture, of huge Universes, far bigger than the meager part that’s observable to us, constantly being created across this exponentially inflating space, is what the Multiverse is all about. It’s important to recognize that the Multiverse is not a scientific theory on its own. It makes no predictions for any observable phenomena that we can access from within our own pocket of existence. Rather, the Multiverse is a theoretical prediction that comes out of the laws of physics as they’re best understood today. It’s perhaps even an inevitable consequence of those laws: if you have an inflationary Universe governed by quantum physics, this is something you’re pretty much destined to wind up with.

While many independent Universes are predicted to be created in an inflating spacetime, inflation never ends everywhere at once, but rather only in distinct, independent areas separated by space that continues to inflate. This is where the scientific motivation for a Multiverse comes from.

Image credit: Karen46 / FreeImages.

It’s possible that our understanding of the state before the hot Big Bang is incorrect, and that our ideas 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.

What is the Multiverse, then? It may go well beyond physics, and be the first physically motivated “metaphysics” we’ve ever encountered. For the first time, we’re understanding the limits of what our Universe can teach us. There is information we need, but that we’ll never obtain, in order to elevate this into the realm of testable science. Until then, we can predict, but neither verify nor refute, the fact that our Universe is just one small part of a far grander realm: the Multiverse.

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Alleged 'Proof of a Multiverse' to Become a 'Game Changer in Astronomy'

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Astronomers believe they may have found a proof of a parallel universe. A group of researchers at Durham University found evidence suggesting that a parallel universe could have crashed into ours creating a so-called ‘cold spot’.

The spot was first discovered thirteen years ago and astonished the scientific community as it contained less matter than it should. However, the experts from Durham University believe that the spot might be a remnant of a collision between our universe and innumerable other universes.

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The impact created by such a collision might have displaced the energy from a huge region of space causing the phenomenon. The cold spot in question is said to have occurred at the formation of the universe more than thirteen billion years ago.

Radio Sputnik spoke with Professor Tom Shanks, an astronomer at Durham University and a co-author of the study.

“It is very speculative and some people say that it is not very testable but with the observations that we make and others make, I think it is quite possible to test these ideas whether they are correct or not,” Shanks said.

Talking about how he and his team conducted these tests, the professor said, “The way we have done it is we looked to the microwave background, which is the glow from the big bang, and that looks pretty uniform over the sky but in one patch about twenty times the diameter of the full moon, you see lower temperatures even more than the —270 Centigrade temperature of the rest of the microwave background radiation. And that is a puzzle, as to how that spot in the microwave background had formed,” the professor said.

He further said that he and his team had been testing this observation and trying to decipher if it is a super void or an under dense area in the foreground of the cold spot, in order to explain this away, but now it has been observed that the “void explanation cannot clarify the cold spot, so that means we are looking for other explanations,” Shanks said.

The professor shed some light on the standard model of cosmology and discussed the theories behind them which were proposed by various scientists including Russian and British scientists many years ago.

Coming back to the idea of the multiverse, Shanks said that despite the fact that some people are saying that the theory of the multiverse is not testable the observations that are being made of the microwave background and the technical detail or polarization as it is called, should provide a final proof.

“The proof of a multiverse will be a game changer in astronomy,” he said.

Furthermore, Shanks spoke about string theory and how there is a connection between that theory and the recent observations made by his team about the multiverse possibility.

“This idea that if you believe in the inflation of the universe, and that predicts the multiverse, it ties in very nicely to physics, and string theory can provide range of models which is almost infinite. And the almost infinite models can fit in those infinite universes and people like to draw these conclusions as it is a popular thought in the physics community,” the professor said.

The interview also discusses what the next step in researching the multiverse theory is and the actions that he and his team plan to take in order to find out more answers to this phenomenon.

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Five Unsolved Mysteries That Keep Scientists up at Night

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Across all disciplines of science there exists an abundance of unanswered questions and mysteries that have endured for as long as humans have attempted to solve them.

Perhaps one of the most query-filled fields is physics, which continues to confound even the most brilliant minds. While it’s unlikely that all these quandaries will be answered in our lifetime, some of them may well could be.

Why is there More Matter than Antimatter?

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In theory, the Big Bang should have created as much matter as antimatter in the universe. But it didn’t — at least not as far as physicists can see. Matter is everywhere, all around us — it makes up everything. But so far, we’ve only found small amounts of antimatter.

Why is that? Shouldn’t a particle of matter have an antimatter counterpart? It must be that the laws of the universe and nature just don’t apply to antimatter the same way they do to matter. Scientists have to figure out why that is and what it means for the universe.

What is Dark Energy/Dark Matter/All this Dark Stuff?

For all we can see of our universe, there’s much more that we have yet to see — in part because it’s made up of invisible stuff called dark energy and dark matter. The thing is, we haven’t even actually visualized dark matter — only the effect it has on what we can see.

Physicists are trying to gain a deeper understanding of the invisible force by studying the behavior of stars and galaxies which appear to react to the presence of it. It is, however, a challenge to study something we can’t see. We need technology to catch up and let us come face-to-face with these “dark” substances.

The Universe’s Unsolved Mysteries

One of the simplest questions to ask may be one of the hardest to answer:

How Big is the Universe?

Asking how big, or how old, the universe is depends on what part of the universe you’re talking about: the observable universe, or the entirety of it. We know through studying light that the observable universe is around 13.8 billion years old — that’s 46 billion light years. Determining how big even the observable universe is presents challenges because it isn’t a static entity: the universe is still expanding.

Are there Parallel Universes?

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Even though we don’t quite have a handle on our own universe, it hasn’t stopped us from wondering if there are others out there — particularly so-called parallel universes. The idea is part of the multiverse theory, for which there are at least five accepted theories.

Those who don’t think it’s possible point out that after the Big Bang, with all that matter taking up space in space, inflation would have slowed down. Because it slowed down, if there were multiverses they wouldn’t be expanding at the same rate as our universe is. That would throw a wrench in the idea of a truly parallel universe.

This is merely a fraction of the questions physicists are asking, and it all kind of comes down to answering one final question: what’s the ultimate fate of the universe? How will it end? Some theories posit that it will be a lot like how it began: a big bang. More specifically, a big crunch. One of the most prominent theories about the inevitable death of the universe is that eventually, as the universe expands, it will eventually reach a density that exceeds critical density — at which point it would collapse in on itself in an event referred to as the Big Crunch.

Of course, that’s just one theory. Another posits that the end will be more of an endless void — but in either case, it won’t happen for billions, if not trillions, of years. As far as we know, anyway.

References: Livescience, CERN, National Georgraphic, Phys.org

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Ripples in Space-Time Might Indicate That We Live in a Multiverse

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As important as gravity is to us here on Earth, it is actually surprisingly weak in comparison to other fundamental forces in our universe, such as electromagnetism. In fact, as researchers struggle to unite quantum effects and gravity in single theories that make sense, they find that extra dimensions, usually with gravity, are implied.

However, theorizing the existence of these extra dimensions is much easier than actually proving that they exist. Scientists were hopeful that the Large Hadron Collider (LHC) might reveal evidence of their existence. After all, the device gives them the ability to run specialized experiments searching for massive particle traces, microscopic black holes, and missing energy caused by the migration of gravitons to higher dimensions. So far, however, definitive proof has not been discovered with the LHC.

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In their search for answers, researchers Gustavo Lucena Gómez and David Andriot at the Max Planck Institute for Gravitational Physics in Potsdam, Germany, have honed in on two strange effects: high frequency gravitational waves and the “breathing mode,” a modification of how gravitational waves stretch space.

The researchers calculated that extra dimensions should result in the creation of extra, high frequency gravitational waves. Unfortunately, we don’t currently have observatories that can detect frequencies in the range they predict, nor are any in development.

However, we do have the tech needed to observe the breathing mode. Space changes shape as it reacts to gravity passing through it. The breathing mode is seen when, in addition to stretching and squishing, space expands and contracts in reaction to additional gravitational waves.

“With more detectors we will be able to see whether this breathing mode is happening,” Lucena Gómez told New Scientist.

Based on the researchers’ calculations, the additional waves at high frequencies would point decisively to extra dimensions. However, the breathing mode could have explanations beyond those theoretical dimensions, but its detection would be a significant clue pointing toward their existence.

Explaining Our Universe

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Even without definitive proof, we’re making progress in our hunt for other dimensions. Since 2015, scientists have been able to observe gravitational waves, and because gravity probably exists in other dimensions, observing and analyzing the behavior of these waves under different conditions might provide clues about those extra dimensions. The existence of another dimension makes weak gravitational force more understandable — if gravity exists throughout all of these extra dimensions as well, it should be weaker.

Put another way, the existence of extra dimensions would allow for a coherent, comprehensive theory of the universe. It would also explain uncertainties about the nature of gravity. It would even put us on the road to explaining why the universe is expanding faster and faster.

“If extra dimensions are in our universe, this would stretch or shrink space-time in a different way that standard gravitational waves would never do,” explained Lucena Gómez.

Proof of an extra dimension would be extraordinarily exciting for physicists working to explain the laws of the universe with a single, coherent theory. If we were able to reconcile the conflicts between quantum field theory and general principles of relativity, for example, things like antigravity, instantaneous communication and transport, transmutation of matter, and faster-than-light travel might all be possible. For now, we don’t have a definitive answer, but understanding the behaviors of gravitational waves would be a remarkable step in the right direction.

References: New Scientist, LIGO, Forbes, Atlas CERN

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