Monthly Archives: August 2022

Protons may have more "charm" than we thought, new research suggests.

A proton is one of the subatomic particles that make up the nucleus of an atom. As small as protons are, they are composed of even tinier elementary particles (opens in new tab) known as quarks, which come in a variety of "flavors," or types: up, down, strange, charm, bottom and top. Typically, a proton is thought to be made of two up quarks and one down quark.

But a new study finds it's more complicated than that. Protons can also contain a charm quark, an elementary particle that's 1.5 times the mass of the proton itself. Even weirder, when the proton does contain the charm quark, the heavy particle still only carries about half the proton's mass.

The finding all comes down to the probabilistic world of quantum physics (opens in new tab). Though the charm quark is heavy, the chance of it popping into existence in a proton is fairly small, so the high mass and small chance basically cancel each other out. Put another way, the full mass of the charm quark doesn't get taken up by the proton, even if the charm quark is there, Science News reported (opens in new tab).

Though protons are fundamental to the structure of atoms (opens in new tab) which make up all matter they're also very complicated. Physicists don't actually know protons' fundamental structure. Quantum physics holds that beyond the up and down quarks known to be present, other quarks might pop into protons now and then, Stefano Forte, a physicist at the University of Milan, told the podcast Nature Briefing (opens in new tab). Forte was a co-author of the new paper showing evidence for the charm quark in protons, published in the journal Nature (opens in new tab) Aug. 17.

There are six types of quarks. Three are heavier than protons and three are lighter than protons. The charm quark is the lightest of the heavy batch, so researchers wanted to start with that one to find out whether a proton could contain a quark heavier than itself. They did this by taking a new approach to 35 years of particle-smashing data.

Related: Why physicists are interested in the mysterious quirks of the heftiest quark (opens in new tab)

To learn about the structure of subatomic and elementary particles, researchers fling particles against each other at blistering speeds at particle accelerators such as the Large Hadron Collider, the world's largest atom smasher, located near Geneva. Scientists with the nonprofit NNPDF collaboration gathered this particle-smashing data going back to the 1980s, including examples of experiments in which photons, electrons, muons, neutri (opens in new tab)nos and even other protons were crashed into protons. By looking at the debris from these collisions, researchers can reconstruct the original state of the particles.

In the new study, the scientists handed over all of this collision data to a machine-learning algorithm designed to look for patterns without any preconceived notions of how the structures might look. The algorithm returned possible structures and the likelihood that they might actually exist.

The study found a "small but not negligible" chance of finding a charm quark, Forte told Nature Briefing. The level of evidence wasn't high enough for the researchers to declare the undeniable discovery of the charm quark in protons, but the results are the "first solid evidence" that it can be there, Forte said.

The structure of the proton is important, Forte said, because to discover new elementary particles, physicists will have to uncover minuscule differences in what theories suggest and what's actually observed. This requires extremely precise measurements of subatomic structures.

For now, physicists still need more data on the elusive "charm" within a proton. Future experiments, such as the planned Electron-Ion Collider at Brookhaven National Laboratory in Upton, New York, may help, Tim Hobbs, a theoretical physicist at Fermilab in Batavia, Illinois, told Science News.

Originally published on Live Science.

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Weird quantum experiment shows protons have more 'charm' than we thought - Space.com

Some of the worlds brightest minds are gathering at a hotel conference centre in Vancouver this week to try to solve a question that has baffled physicists for decades.

The two pillars of modern physics the theories of quantum mechanics and general relativity have been used respectively to describe how matter behaves, as well as space, time and gravity.

The problem is that the theories dont appear to be compatible, said Peter Galison, a professor in history of science and physics at Harvard University.

These theories cant just harmoniously live in splendid isolation, one from the other. We know our account of the world is inadequate until we figure out how to make them play nicely together, he said in an interview after giving a talk on how black holes fit into the equation.

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Galison is among several leading thinkers who arrived at the Quantum Gravity Conference for the launch a new global research collaborative known as the Quantum Gravity Institute in Vancouver.

While speakers at the conference are primarily scientists, including Nobel laureates Jim Peebles, Sir Roger Penrose and Kip Thorne, those behind the institute come from less likely fields.

The Quantum Gravity Society represents a group of business, technology and community leaders. Founding members include Frank Giustra of Fiore Group, Terry Hui of Concord Pacific, Paul Lee and Moe Kermani of Vanedge Capital and Markus Frind of Frind Estate Winery. They are joined by physicists Penrose, Abhay Ashtekar, Philip Stamp, Bill Unruh and Birgitta Whaley.

During a panel discussion, Lee said hes been asked several times why Vancouver would host such an event or institute.

Why Vancouver? Because we can, Lee said.

Hui, who studied physics as part of his undergraduate degree, said organizing the conference and launching the institute felt like fulfilling a childhood dream.

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I left the field to pursue other things, you know, he said in an interview.

How do I put this? he said, before likening it to being a guy who never made the high school hockey team getting to hang out in the Canucks locker room.

Hui said he wanted to help and saw his role as philanthropic, adding he believed it would benefit Vancouver economically.

As a non-local and the founder of the Black Hole Initiative at Harvard, Galison said hes happy to see more interdisciplinary support for exploring some of the biggest questions in science. He called the conference an interesting event for bringing together people in technology and venture capitalism with scientists from varied fields. The launch of the institute is also meaningful, he said.

Its also a kickoff event for something much bigger and longer-lasting.

As for the central question of the conference, Galison said its an opportunity to explore where the theories overlap and where they dont from different angles.

One place they intersect is clearly at the beginning of the universe, early cosmology, because when energy is incredibly compressed, when you have enormous energy densities, youre at the limit where the bending of space and time creates so much energy that quantum effects come into play, he said.

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The theory of quantum mechanics, introduced in the 1920s, entered a world already shaken by Albert Einsteins theory of relativity, which inspired responses not just from scientists but from poets and philosophers, he said.

That these things are not compatible is really unnerving, Galison said.

Cracking the code for why isnt something that will happen in a moment, a week or a year, he said.

Theres a tremendous amount of work, he said. Its more like building a cathedral than throwing up a bicycle shed.

2022 The Canadian Press

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Physicists and business figures gather in Vancouver to crack theory of everything - Global News

We know that the universe is expanding, and our understanding of nature based on general relativity and the Standard Model of elementary particles is consistent with this observation. However, these theories of particles and their interactions break down when we try to apply them to the physical phenomena that occurred in the first moments following the Big Bang preventing us from reaching a complete understanding of the evolution of the universe.

Our theories fail because the temperature and density of matter just after the Big Bang were so high that a concept called quantum gravity is required to describe the physical processes that took place. The problem is that this theory requires a unification of general relativity and quantum mechanics. Though this has not yet been fully understood, there are some viable candidates for a theory of quantum gravity, such as string theory.

To address the problem of unknown quantum gravitational effects in the early universe, a team of theoretical physicists from Japan applied a string theory-inspired technique known as holographic duality. This allowed them to perform calculations using familiar methods of elementary particle physics rather than an impossibly complex computation usually required in quantum gravity applications.

The most difficult problem one encounters on the way to finding a correct theory of quantum gravity is a lack of experimental data. Fundamental interactions are usually studied with elementary particle accelerators, which smash together beams of particles moving at velocities close to the speed of light. From the velocities of the particles born in these collisions and the angles at which they leave, scientists can extract valuable information about their fundamental interactions.

The key issue here is that the gravitational effects in most elementary particle interactions are negligible (though not under the extreme conditions in the early universe!), and they cannot be measured using modern accelerators. For example, the gravitational attraction between two electrons is more than 42 orders of magnitude weaker than the electromagnetic repulsion between them. Because of this, studies of quantum gravity have so far been only theoretical.

For decades, the most promising approach to quantum gravity has been string theory, the main postulate of which is that elementary particles are not point-like, but are tiny, oscillating strings. Unique vibrational modes of these strings gives rise to a different elementary particle, such as electrons, quarks, and yet-to-be observed gravitons, which should mediate gravitational interactions similar to how photons mediate electromagnetic interactions.

Unfortunately, our current understanding of string theory is incomplete and doesnt allow us to study many quantum gravitational effects quantitatively.

Although string theory has not yet reached its full potential, research in this area has led to the development of many theoretical tools that can be used outside of it. The most radical and powerful, although not fully proven, is known as holographic duality or correspondence.

The holographic hypothesis claims that events inside a region of space that involve quantum gravity and are described by string theory can also be described by a gravity-free quantum theory defined on the surface of that region. The latter theory is sufficiently easier to deal with, and we have learned much about theories of this type by studying electromagnetic, weak, and strong interactions.

The existence of this duality means that for every measurable quantity in quantum gravitational theory there must be an analogue in the gravity-free alternative. The validity of holographic duality has been verified by hundreds of research papers through direct calculations of various quantities on both sides of the duality.

Since 1997, when the first version of holographic correspondence was proposed by Juan Maldacena, many more pairs of theories connected by this equivalence have been discovered and analyzed, but the rule that a higher-dimensional space includes gravity and a lower-dimensional one does not always remains satisfied.

Some of these theories of quantum gravity are known to be related to string theory, whereas the connection between the rest with strings has not yet been uncovered but is usually believed to exist.

An unfortunate feature of the holographic approach in studying quantum gravity in the real world is that in most known examples of the duality, the higher-dimensional theory mathematically describes quantum gravity in what is called anti-de Sitter space, which doesnt look like our expanding universe, and whose geometry corresponds to what mathematicians call de Sitter space.

The remarkable achievement of the new study is that the authors were able to find a non-gravitational theory equivalent to quantum gravity in a universe that is quite similar to our own. The most important difference is that it has only three dimensions two spatial directions and one time unlike our own universe, which is four-dimensional (three space dimensions and one time dimension).

Gravity in three dimensions is much simpler than in four, said Tadashi Takayanagi, a professor at the Yukawa Institute for Theoretical Physics and one of the authors of the study. However, we believe the basic mechanism of how the holography works in de Sitter space should not depend on the dimension.

The new theory is proposed as an equivalent to quantum gravity in a lower-dimensional expanding universe defined in one spatial and one temporal dimension, known as the Wess-Zumino-Witten model.

Although the three-dimensional universe they deal with is not exactly like ours, the authors think that their work is an important step towards understanding quantum gravity in the real world.

Since we do not know at all the basic mechanisms of how the holography in de Sitter spaces works, it is useful to start with constructing the most simple example, as we did in this work, said Takayanagi. At the same time, this helps us to verify whether a holographic duality exists for de Sitter spaces or not. Moreover, in our simple mode, we can take into account quantum corrections [to general relativity].

As is usual in this branch of theoretical physics, the scientists havent proven the duality because to do so, they would have to compute all possible physical quantities on both sides of the correspondence and compare the results. Instead, they computed some, and found an exact match from which they concluded that their guess was correct.

Most of the authors calculations ignored quantum effects on the gravitational side of duality and taking them into account will be the course of future work. If the scientists are successful in this, they plan to generalize their results and apply them to our four-dimensional universe.

If we can understand this question from our three-dimensional example, we hopewe can generalize the results to higher dimensions and finally challenge theproblem of explaining the emergence of our four-dimensional universe, concluded Takayanagi.

Reference: Yasuaki Hikida, et al., CFT duals of three-dimensional de Sitter gravity, Journal of High Energy Physics, (2022). DOI: 10.1007/JHEP05(2022)129

Image Credit: Johnson Martin Pixabay

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String theory used to describe the expanding universe - Advanced Science News

Of all the pricing games on the iconic television showThe Price Is Right, perhaps the most exciting of all isPlinko. Contestants play an initial pricing game to obtain up to 5 round, flat disksknown as Plinko chipswhich they then press flat against a pegboard wherever they choose, releasing it whenever they like. One-at-a-time, the Plinko chips cascade down the board, bouncing off of the pegs and moving horizontally as well as vertically, until they emerge at the bottom of the board, landing in one of the prize (or no prize) slots.

Quite notably, contestants who drop a chip that happens to land in the maximum prize slot, always found in the direct center of the board, often try to repeat the exact same drop with whatever remaining disks they possess. Despite their best efforts, however, and the fact that the initial positioning of the disks might be virtually identical, the ultimate paths the disks wind up traversing are almost never identical. Surprisingly, this game is a perfect illustration of chaos theory and helps explain the second law of thermodynamics in understandable terms. Heres the science behind it.

Trajectories of a particle in a box (also called an infinite square well) in classical mechanics (A) and quantum mechanics (B-F). In (A), the particle moves at constant velocity, bouncing back and forth. In (B-F), wavefunction solutions to the Time-Dependent Schrodinger Equation are shown for the same geometry and potential. The horizontal axis is position, the vertical axis is the real part (blue) or imaginary part (red) of the wavefunction. These stationary (B, C, D) and non-stationary (E, F) states only yield probabilities for the particle, rather than definitive answers for where it will be at a particular time.

At a fundamental level, the Universe is quantum mechanical in nature, full of an inherent indeterminism and uncertainty. If you take a particle like an electron, you might think to ask questions like:

Theyre all reasonable questions, and wed expect that theyd all have definitive answers.

But what actually transpires is so bizarre that its enormously unsettling, even to physicists whove spent their lifetimes studying it. If you make a measurement to precisely answer Where is this electron? you become more uncertain about its momentum: how fast and in what direction it moves. If you measure the momentum instead, you become more uncertain about its position. And because you need to know both momentum and position to predict where it will arrive with any certainty in the future, you can only predict a probability distribution for its future position. Youll need a measurement at that future time to determine where it actually is.

In Newtonian (or Einsteinian) mechanics, a system will evolve over time according to completely deterministic equations, which should mean that if you can know the initial conditions (like positions and momenta) for everything in your system, you should be able to evolve it, with no errors, arbitrarily forward in time. In practice, due to the inability to know the initial conditions to truly arbitrary precisions, this is not true.

Perhaps for Plinko, however, this quantum mechanical weirdness shouldnt matter. Quantum physics might have a fundamental indeterminism and uncertainty inherent to it, but for large-scale, macroscopic systems, Newtonian physics ought to be perfectly sufficient. Unlike the quantum mechanical equations that govern reality at a fundamental level, Newtonian physics is completely deterministic.

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According to Newtons laws of motionwhich can all be derived fromF= ma(force equals mass times acceleration)if you know the initial conditions, like position and momentum, you should be able to know exactly where your object is and what motion it will possess at any point in the future. The equationF= matells you what happens a moment later, and once that moment has elapsed, that same equation tells you what happens after the next moment has passed.

Any object for which quantum effects can be neglected obeys these rules, and Newtonian physics tells us how that object will continuously evolve over time.

However, even with perfectly deterministic equations,theres a limit to how well we can predict a Newtonian system. If this surprises you, know that youre not alone; most of the leading physicists who worked on Newtonian systems thought that there would be no such limit at all. In 1814, mathematician Pierre Laplace wrote a treatise entitled, A philosophical essay on probabilities, where he predicted that once we gained enough information to determine the state of the Universe at any moment in time, we could successfully use the laws of physics to predict the entire future of everything absolutely: with no uncertainty at all. In Laplaces own words:

An intellect which at a certain moment would know all forces that set nature in motion, and all positions of all items of which nature is composed, if this intellect were also vast enough to submit these data to analysis, it would embrace in a single formula the movements of the greatest bodies of the universe and those of the tiniest atom; for such an intellect nothing would be uncertain and the future just like the past would be present before its eyes.

A chaotic system is one where extraordinarily slight changes in initial conditions (blue and yellow) lead to similar behavior for a while, but that behavior then diverges after a relatively short amount of time.

And yet, the need to invoke probabilities in making predictions about the future doesnt necessarily stem from either ignorance (imperfect knowledge about the Universe) or from quantum phenomena (like Heisenbergs uncertainty principle), but rather arises as a cause of the classical phenomenon: chaos. No matter how well you know the initial conditions of your system, deterministic equationslike Newtons laws of motiondont always lead to a deterministic Universe.

This was first discovered back in the early 1960s, when Edward Lorenz, a meteorology professor at MIT, attempted to use a mainframe computer to help arrive at an accurate weather forecast. By using what he believed was a solid weather model, a complete set of measurable data (temperature, pressure, wind conditions, etc.), and an arbitrarily powerful computer, he attempted to predict weather conditions far into the future. He constructed a set of equations, programmed them into his computer, and waited for the results.

Then he re-entered the data, and ran the program for longer.

Two systems starting from an identical configuration, but with imperceptibly small differences in initial conditions (smaller than a single atom), will keep to the same behavior for a while, but over time, chaos will cause them to diverge. After enough time has gone by, their behavior will appear completely unrelated to one another.

Surprisingly, the second time he ran the program, the results diverged at one point by a very slight amount, and then diverged thereafter very quickly. The two systems, beyond that point, behaved as though they were entirely unrelated to one another, with their conditions evolving chaotically with respect to one another.

Eventually, Lorenz found the culprit: when Lorenz re-entered the data the second time,he used the computers printout from the first runfor the input parameters, which was rounded off after a finite number of decimal places. That tiny difference in initial conditions might have only corresponded to the width of an atom or less, but that was enough to dramatically alter the outcome, particularly if you time-evolved your system far enough into the future.

Small, imperceptible differences in the initial conditions led to dramatically different outcomes, a phenomenon colloquially known as the Butterfly Effect. Even in completely deterministic systems, chaos arises.

A scaled-down, casino-esque version of the game of Plinko, where instead of chips falling down a Plinko board, coins fall, with varying rewards available depending on where the coins land.

All of this brings us back to the Plinko board. Although there are many version of the game available, including at amusement parks and casinos, theyre all based on the idea of a Galton Board, where objects bounce one way or the other down an obstacle-filled ramp. The actual board used on The Price Is Right has somewhere around 1314 different vertical levels of pegs for each Plinko chip to potentially bounce off of. If youre aiming for the central spot, there are a lot of strategies you can employ, including:

Every time your chip hits a peg on the way down, it has the potential to knock you one-or-more spaces to either side, but every interaction is purely classical: governed by Newtons deterministic laws. If you could stumble upon a path that caused your chip to land exactly where you desired, then in theory, if you could recreate the initial conditions precisely enoughdown to the micron, the nanometer, or even the atomperhaps, even with 13 or 14 bounces, you might wind up with an identical-enough outcome, winning the big prize as a result.

But if you were to expand your Plinko board, the effects of chaos would become unavoidable. If the board were longer and had dozens, hundreds, thousands, or even millions of rows, youd quickly run into a situation where even two drops that were identical to within the Planck lengththefundamental quantum limit at which distances make sensein our Universeyoud start to see the behavior of two dropped Plinko chips diverging after a certain point.

In addition, widening the Plinko board allows for a greater number of possible outcomes, causing the distribution of final states to be greatly spread out. Put simply, the longer and wider the Plinko board is, the greater the odds of not only unequal outcomes, but of having unequal outcomes that display an enormous-magnitude difference between two dropped Plinko chips.

Even with down-to-the-atom initial precisions, three dropped Plinko chips with the same initial conditions (red, green, blue) will lead to vastly different outcomes by the end, so long as the variations are large enough, the number of steps to your Plinko board is great enough, and the number of possible outcomes is sufficiently large. With those conditions, chaotic outcomes are inevitable.

This doesnt just apply to Plinko, of course, but to any system with a large number of interactions: either discrete (like collisions) or continuous (such as from multiple gravitational forces acting simultaneously). If you take a system of air molecules where one side of a box is hot and the other side is cold, and you remove a divider between them, collisions between those molecules will spontaneously occur, causing the particles to exchange energy and momenta. Even in a small box, there would be more than 1020 particles; in short order, the entire box will have the same temperature, and will never separate into a hot side and a cold side again.

Even in space, justthree point masses is enough to fundamentally introduce chaos. Three massive black holes, bound within distances the scale of the planets in our Solar System, will evolve chaotically no matter how precisely their initial conditions are replicated. The fact that theres a cutoff in how small distances can get and still make senseagain, the Planck lengthensures that arbitrary accuracies on long-enough timescales can never be ensured.

By considering the evolution and details of a system with as few as three particles, scientists have been able to show that a fundamental time irreversibility arises in these systems under realistic physical conditions that the Universe is very likely to obey. If you cannot calculate distances meaningfully to arbitrary precisions, you cannot avoid chaos.

The key takeaway of chaos is this: even when your equations are perfectly deterministic, you cannot know the initial conditions to arbitrary sensitivities. Even placing a Plinko chip on the board and releasing it with down-to-the-atom precision wont be enough, with a large enough Plinko board, to guarantee that multiple chips would ever take identical paths. In fact, with a sufficiently large board, you can all but guarantee that no matter how many Plinko chips you dropped, youd never arrive at two truly identical paths. Eventually, theyd all diverge.

Minuscule variationsthe presence of air molecules moving from the hosts announcing, temperature variations arising from the contestants breath, vibrations from the studio audience propagating into the pegs, etc.introduce enough uncertainty so that, far enough down the line, these systems are effectively impossible to predict. Along with quantum randomness, this effective classical randomness prevents us from knowing the outcome of a complex system, no matter how much initial information we possess. Asphysicist Paul Halpern so eloquently put it, God plays dice in more ways thanone.

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To understand chaos theory, play a game of Plinko - Big Think

For those who pay attention, it will be noticed that there is a huge inconsistency in the world. Many people are deluded about a lot of things and are acting in opposition to what is logically consistent.

For example, there seems to be a disproportionate number of people who are meeting their demise lately, but no matter who it is, people are confident, based on their condolence comments, that the person is going to heaven. This includes people who would be known as trouble-makers while alive.

People do not stop to think that heaven will not accommodate car-jackers, backbiters, murderers and so many others who have created mayhem on Earth, if, indeed, heaven is a reality.

Another example of illogical behavior is demonstrated by those individuals who are so deluded that they actually believe former president Donald J. Trump was the best president ever, and that those who stormed the capital on January 6, 2021, were mere tourists.

Basically, the problem is that a lot of people are not thinking logically, and have unrealistic expectations that are counter to their actions. One of these is the notion of freedom among people who are not doing anything to ensure that it is achieved.

When considering the foregoing, it becomes evident that there is a great divide; a split between the idea of mind over matter. How we think and what we do lays the foundation for all of our outcomes, and when these are not in sync, chaos results.

Black people, in particular, need to understand this great divide. For example, some resent the use of the word ni**er by white people, but use it constantly among themselves and in public media, making it available for all to hear.

Likewise, those who commit heinous crimes in the Black community are often not blamed for their actions; condolences are publicly sent to families, and teddy bears, flowers and more are deposited at the locations where people lost their lives to violence, but people in the community who know the identities of the perpetrators refuse to reveal that information.

All of this points to the idea that freedom will not be available to us as long as there is a schism between mind and matter. The idea of freedom requires that mind and matter are in sync in order for manifestation to occur.

And just what is freedom? According to the Oxford Languages dictionary, freedom is the power or right to act, speak, or think as one wants without hindrance or restraint. A second definition is an absence of subjection to foreign domination or despotic government.

The problem with acquiring either or both of these forms of freedom is dependent upon how we think and what we do as a result. If people continue to think that they can act in exact opposition to what is mentally required for success, so-called freedom will never be achieved.

The newly deployed James Webb Space Telescope is opening up new vistas and is enabling humanity to see the universe with a clarity that has not been possible before. Mankind is becoming aware of the vastness of existence. This will hopefully result in the realization among the human family that our collective destiny will ultimately depend upon what we do and how we think in the here and now!

New discoveries in quantum physics are revealing a startling truth: that it is really quite possible that our lives are scripted by how effectively we are able to repair our mind/matter rift. In other words, when we focus on what we want to achieve and then act in accordance with our mental assertion, we can achieve our goals.

This idea can be applied to the notion of freedom.

All around us, there are examples of the efficacy of this strategy. For example, although economic success is not the only gauge to measure success, the existence of 15 living Black billionaires does demonstrate that there are Black people who have discovered the secret to making their dreams come true. They have been able to ensure that their actions are in sync with their ideas!

The formula for success, therefore, is for people to identify a goal and make sure their actions are in line with their ideas, with their thoughts, with their minds wishes regarding that goal.

This is how freedom must be attained, and its unrealistic to think that it will be acquired without considering both elements of the process, i.e., the mind and physical activities toward the accomplishment of the goal. A Luta Continua.

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FREEDOM AND THE MIND/MATTER CONNECTION - The Chicago Cusader

You might have noticed, if youve set foot in a cinema this year, that Hollywood has fallen in love with the multiverse. From Marvel to DC to Disney, alternate universes, realities and timelines are being written into scripts to wow audiences and make life a bit easier when A-list celebrities tire of yanking on the latex.

Its not just the big studios that are at it. The sublimely joyful indie film Everything Everywhere All At Once asks and answers, why, if everything is happening everywhere and all at once, should any of it matter?

Likewise, Rick And Morty, Dark and Man In The High Castle use the idea of alternate universes as a kind of funhouse mirror to ponder (sometimes) serious questions about our own Universe. And its fair to point out that the idea is nothing new. Who could forget Spocks evil doppelgnger with his suitably sinister goatee? Clearly, the idea of the multiverse has permeated the fabric of our culture. But what do the scientists think about multiverses? Is there the science to back them up?

Many physicists believe that multiverses could exist, ranging from universes lurking behind the event horizons of black holes, to growing universes expanding like bubbles in soap foam.

A multiverse is something which is really not that strange if you think of it historically, from the point of view of science, says Prof Ulf Danielsson, a theoretical physicist at Uppsala University, Sweden. Our horizons have continuously been expanding. At some time, we thought that Earth was the only planet and that this was the whole world. We now know theres a Universe full of other planets. Its also quite natural to speculate that there is another step and that our Universe is not the only one.

So what are some of the leading multiverse theories, and which of them could harbour an evil, possibly moustachioed, you.

Read more about the multiverse:

This is a theory that has grown out of cosmology, particularly from the discovery that our own Universe is expanding. This concept of a multiverse asks if the initial rapid inflation that our Universe underwent some 13.8 billion years ago, could be happening in distant regions of space-time disconnected from our Universe.

The basic idea is that our Universe is one particular patch of space-time that is evolving as a well-defined entity, explains astrophysicist Prof Fred Adams, from the University of Michigan. This region is homogeneous, isotropic [the same in all directions] and expanding in a well-defined manner. If you trace the evolution backward in time, then you find an age for the Universe of about 13.8 billion years from this initial expansion.

Adams, who wrote the book Our Living Multiverse and authored a Physics Report paper on the topic, also believes that other regions of the multiverse could be experiencing their own Big Bangs, and therefore their own expansions. This means that they are not able to affect our Universe. They are thus other universes and the collection of all such universes is the multiverse, Adams says.

This multiverse idea caught on in fiction because it is an excellent storytelling device. It became popular in cosmology because it could address lingering mysteries, while still fitting with existing physics.

One reason that the concept of the multiverse became popular is that it can naturally arise from the theory of inflation, explains Heling Deng, a postdoctoral researcher in cosmology, particle physics and astrophysics at Arizona University.

It was shown by [physicists] Andrei Linde and Alex Vilenkin, in separate works, that if inflation did occur, it could create infinite disconnected regions.

Although inflation ended 13.8 billion years ago in the Universe we are living in, Deng says that quantum effects can always bring inflation back in another region of space-time. This results in bouts of inflation never ending referred to as eternal inflation and the possibility of an infinite number of different universes.

Stages in the history of the Universe after the Big Bang Science Photo Library

Russian-American theoretical physicist Andrei Linde puts forward one suggestion for the arrangement of this multiverse. He sees the universes as bubbles expanding on something resembling a cosmic canvas, squeezing away from each other in bouts of eternal and chaotic inflation.

How these universes within a multiverse would differ is also currently the topic of speculation, but Adams suggests theres no reason to believe that the laws of physics would be the same in these separate regions.

One reason that these other universes are of interest is that they could have other versions of the laws of physics, he says. That variation could apply across a range of physical parameters, including gravity and the rate at which that universe expands.

That means some of these universes could have laws of physics that arent fit for the formation of large-scale structures like galaxies or stars. They may not even have the same fundamental particles.

Consequently, these universes arent variations of our Universe and thus could not host any life at all, never mind some version of you or I.

String theory is a suggestion put forward by physicists to connect quantum mechanics and General Relativity, which are the best descriptions we have of the infinitesimally small and incomprehensibly large. The underlying idea of string theory is that fundamental particles like quarks and electrons are actually a single point in one-dimensional strings, vibrating at different frequencies.

This string-landscape provides a popular setting for the multiverse, thanks to one of the key elements upon which string theory depends. In order to be mathematically sound, string theory needs extra dimensions to exist.

These arent parallel dimensions like we see in science fiction. Instead, string theorists believe these extra dimensions are curled up within the three traditional dimensions of space. They remain invisible to us, as we evolved only to see in three dimensions. These extra dimensions could offer a way in to the string theory multiverse.

String theory attempts to explain all the fundamental particles in nature by modelling them as tiny strings Science Photo Library

You need to have these extra dimensions, and the number of dimensions needed in total is 10 or 11, Danielsson says. It could also be that you would need to go into some extra dimension in order to get to these other universes.

Even if this was the case and a connection via these dimensions of space to other universes existed, they may still remain permanently out of reach and view, thanks to the fact that the inflation of the Universe means that there is a cosmic horizon beyond which we cant see. If there is no connectivity between universes in a multiverse, it makes the cosmological concept of a multiverse almost impossible to test experimentally.

The evidence to date is theoretical, not experimental. And, unfortunately, we just cannot do any direct experiments to verify or falsify what goes on in other universes, Adams explains.

Our inability to test these ideas is a double-edged sword. While the lack of ways to test a multiverse means we cant prove its existence, it also means we cant disprove it either.

At the end of a massive stars life, when it has run out of fuel for nuclear fusion, itll collapse into a black hole a region of space-time bounded by a surface called an event horizon from which nothing, not even light, can escape.

Einsteins General Theory of Relativity tells us that a large mass can curve space-time. The theory also says that the heart of a black hole has a singularity where the mass is so great that the space-time curvature becomes infinite and, consequently, the laws of physics break down. This is a concept that troubles physicists, but one hypothesis could do away with the singularity and replace it with an entire universe and in turn, a multiverse.

Singularities are unphysical because they cannot be measured. That means their existence indicates that a theory is incomplete, says theoretical physicist Dr Nikodem Poplawski, from the University of New Haven, Connecticut. In my hypothesis, every black hole produces a new, baby universe inside on the other side of the event horizon and becomes an Einstein-Rosen bridge, also known as a wormhole, that connects this infant universe to the parent universe in which the black hole exists.

Could a black hole spawn a new baby universe? This illustration is of a wormhole, a hypothetical shortcut connecting two separate points in space-time Science Photo Library

In this theory, when viewed from the new universe, the parent universe appears as the other side of a white hole, a region of space that cannot be entered from the outside and which can be thought of as the reverse of a black hole.

An analogy of the matter going to a black hole and ending up in a new universe could be blowing a soap bubble through a circular wand, Poplawski says. The wand is the event horizon albeit in one dimension less the soap liquid is the matter crossing the event horizon, and the surface of the bubble is the new universe.

In the hypothesis suggested by Poplawski, a universe may produce billions of black holes and each of them could produce a baby universe. In January of this year, researchers at the International School of Advanced Studies (SISSA) in Italy estimated that there could be as many as 40 trillion thats a four followed by 13 zeros black holes in our Universe alone. Thats a lot of baby universes!

These infant universes would be hidden from the occupants of their parent universe by the light-trapping surface of the event horizon, and once that event horizon is crossed theres no going back. That, and the fact nothing can enter a white hole (which is still purely theoretical but allowed by General Relativity), means no interaction between parent and infant.

According to Einstein's General Theory of Relativity, large objects cause space-time to curve Science Photo Library

However, if two black holes existed in the same universe, and each of these black holes created a new universe, then there is a possibility that these two sibling universes could merge, just as two black holes merge to create one black hole, says Poplawski.

He adds that this would manifest in a baby universe as a large-scale asymmetry in space. This means that if we ever discover some preferred direction in our Universe a direction with increasing matter and energy, for example it could be attributed to our Universe interacting with a sibling.

As for the possibility of an alternate version of you existing beyond the event horizon of a black hole, Poplawski concludes that chances are not good. There would be no alternate you. At any time, an object can only exist in one universe, he says.

But one pop culture mainstay reflects his concept: I think the closest thing could be the TARDIS in Doctor Who. You enter the police box and you realise that you are in something bigger than the box.

In quantum physics, which deals with the physical laws of the subatomic, the term multiverse doesnt exist. Alternate universes are instead referred to as many worlds and are part of a radically different concept, as these arent geographic in nature like the multiverses explored previously.

The many-worlds hypothesis was first suggested by the US physicist Hugh Everett III to explain how a quantum system can exist in seemingly contradictory states at the same time called a superposition and how these paradoxical states seem to vanish.

The effect of many worlds on the existence of a superposition of states can be imagined by considering Erwin Schrdingers infamous thought experiment, Schrdingers cat.

Schrdinger's cat can help explain superposition, but also quantum multiverses Science Photo Library

In the thought experiment, a hapless moggy is placed in a sealed box with a device containing a vial of lethal poison, released only if an atomic nucleus in the box decays. Treating the box, the cat and the device as a single quantum system, each state in this case, dead or alive is described by a wave. As waves can overlap to form a single wave function, the cat can exist in a superposition of states. This means that in quantum mechanics the cat is both simultaneously dead or alive.

This seemingly contradictory state persists only until the box is opened analogous to making a measurement on the system and the wave function collapses meaning the superposition is gone and the state is resolved. The cat is either dead or alive. Yet why measurement causes this collapse of superposition, also known as decoherence, is still a mystery.

The many-worlds hypothesis does away with decoherence altogether. Instead, it suggests that rather than the opening of the box collapsing the wave function, measurement causes it to grow exponentially and swallow the experimenter and eventually the entire Universe.

In the many-worlds formulation of quantum mechanics, each state of a system is a physically distinct world, says Prof Jeffrey Barrett, a philosopher of science at the University of California Irvine.

This means each flick of a light switch would create a near-infinity of worlds. One for each possible path of each photon as the light fills your living room, not just a world in which you didnt flick the switch at all.

That means that in terms of Schrdingers cat thought experiment, the experimenter isnt opening the box to discover if the cat is dead or alive. Rather, they are opening the box to discover if they are in a world in which the cat is dead, or one in which it lives.

At first, the worlds that comprise this quantum multiverse are similar, with infinitesimally small differences. But these changes grow from universe to universe, meaning those that diverged earlier could be strikingly different from each other.

The objects, events and physical records of observers are different in different worlds. There is a world where the Eiffel Tower is in Los Angeles, Barrett says. All of the worlds universes are part of a single global universe. It looks just like this universe from the perceptive of our branch world.

Barrett addresses the question of how likely it is that one of these many worlds would contain an alternate you. He reveals that it isnt just possible, its demanded.

It certainly would contain many alternate copies of me, he says. That is fundamental to how the theory addresses the quantum measurement problem.

All of this makes the quantum version of the multiverse the one that most closely resembles pop culture, at least in principle. This is because it doesnt just probably contain infinite versions of you, it definitely does.

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Evil doppelgngers, alternate timelines and infinite possibilities: the physics of the multiverse explained - BBC Science Focus Magazine