Daily Archives: June 5, 2022

Classical physics did not need any disclaimers. The kind of physics that was born with Isaac Newton and ruled until the early 1900s seemed pretty straightforward: Matter was like little billiard balls. It accelerated or decelerated when exposed to forces. None of this needed any special interpretations attached. The details could get messy, but there was nothing weird about it.

Then came quantum mechanics, and everything got weird really fast.

Quantum mechanics is the physics of atomic-scale phenomena, and it is the most successful theory we have ever developed. So why are there a thousand competing interpretations of the theory? Why does quantum mechanics need an interpretation at all?

What, fundamentally, is it trying to tell us?

There are many weirdnesses in quantum physics many ways it differs from the classical worldview of perfectly knowable particles with perfectly describable properties. The weirdness you focus on will tend to be the one that shapes your favorite interpretation.

But the weirdness that has stood out most, the one that has shaped the most interpretations, is the nature of superpositions and of measurement in quantum mechanics.

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Everything in physics comes down to the description of what we call the state. In classical physics, the state of a particle was just its position and momentum. (Momentum is related to velocity.) The position and velocity could be known with as much accuracy as your equipment allowed. Most important, the state was never connected to making a measurement you never had to look at the particle. But quantum mechanics forces us to think about the state in a very different way.

In quantum physics, the state represents the possible outcomes of measurements. Imagine you have a particle in a box, and the box has two accessible chambers. Before a measurement is made, the quantum state is in a superposition, with one term for the particle being in the first chamber and another term for the particle being in the second chamber. Both terms exist at the same time in the quantum state. It is only after a measurement is made that the superposition is said to collapse, and the state has only one term the one that corresponds to seeing the particle in the first or the second chamber.

So, what is going on here? How can a particle be in two places at the same time? This is also akin to asking whether particles have properties in and of themselves. Why should making a measurement change anything? And what exactly is a measurement? Do you need a person to make a measurement, or can you say that any interaction at all with the rest of the world is a measurement?

These kinds of questions have spawned a librarys worth of so-called quantum interpretations. Some of them try to preserve the classical worldview by finding some way to minimize the role of measurement and preserve the reality of the quantum state. Here, reality means that the state describes the world by itself, without any reference to us. At the extreme end of these is the Many Worlds Interpretation, which makes each possibility in the quantum state a parallel Universe that will be realized when a quantum event a measurement happens.

This kind of interpretation is, to me, a mistake. My reasons for saying this are simple.

When the inventors of quantum mechanics broke with classical physics in the first few decades of the 1900s, they were doing what creative physicists do best. They were finding new ways to predict the results of experiments by creatively building off the old physics while extending it in ways that embraced new behaviors seen in the laboratory. That took them in a direction where measurement began to play a central role in the description of physics as a whole.Again and again, quantum mechanics has shown that at the heart of its many weirdnesses is the role played by someone acting on the world to gain information. That to me is the central lesson quantum mechanics has been trying to teach us: That we are involved, in some way, in the description of the science we do.

Now to be clear, I am not arguing that the observer affects the observed, or that physics needs a place for some kind of Cosmic Mind, or that consciousness reaches into the apparatus and changes things. There are much more subtle and interesting ways of hearing what quantum mechanics is trying to say to us. This is one reason I find much to like in the interpretation called QBism.

What matters is trying to see into the heart of the issue. After all, when all is said and done, what is quantum mechanics pointing to? The answer is that it points to us. It is trying to tell us what it means to be a subject embedded in the Universe, doing this amazing thing called science. To me that is just as exciting as a story about a Gods eye view of the Universe.

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What is quantum mechanics trying to tell us? - Big Think

There are some questions that, if you look up the answer, might make you question the reliability of your brain.

Many other examples abound, from the color of different flavor packets of Walkers crisps to the spelling of Looney Tunes (vs. Looney Toons) and Febreze (vs. Febreeze) to whether the Monopoly Man has a monocle or not.

Perhaps the simplest explanation for all of these is simply that human memory is unreliable, and that as much as we trust our brains to remember what happened in our own lives, our own minds are at fault. But theres another possibility based on quantum physics thats worth considering: could these truly have been the outcomes that occurred for us, but in a parallel Universe? Heres what the science has to say.

Visualization of a quantum field theory calculation showing virtual particles in the quantum vacuum. (Specifically, for the strong interactions.) Even in empty space, this vacuum energy is non-zero, and what appears to be the ground state in one region of curved space will look different from the perspective of an observer where the spatial curvature differs. As long as quantum fields are present, this vacuum energy (or a cosmological constant) must be present, too.

One of the biggest differences between the classical world and the quantum world is the notion of determinism. In the classical world which also defined all of physics, including mechanics, gravitation, and electromagnetism prior to the late 19th century the equations that govern the laws of nature are all completely deterministic. If you can give details about all of the particles in the Universe at any given moment in time, including their mass, charge, position, and momentum at that particular moment, then the equations that govern physics can tell you both where they were and where they will be at any moment in the past or future.

But in the quantum Universe, this simply isnt the case. No matter how accurately you measure certain properties of the Universe, theres a fundamental uncertainty that prevents you from knowing those properties arbitrarily well at the same time. In fact, the better you measure some of the properties that a particle or system of particles can have, the greater the inherent uncertainty becomes an uncertainty that you can not get rid of or reduce below a critical value in other properties. This fundamental relation, known as the Heisenberg uncertainty principle, cannot be worked around.

This diagram illustrates the inherent uncertainty relation between position and momentum. When one is known more accurately, the other is inherently less able to be known accurately. Every time you accurately measure one, you ensure a greater uncertainty in the corresponding complementary quantity.

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There are many other examples of uncertainty in quantum physics, and many of those uncertain measurements dont just have two possible outcomes, but a continuous spectrum of possibilities. Its only by measuring the Universe, or by causing an interaction of an inherently uncertain system with another quantum from the environment, that we discover which of the possible outcomes describes our reality.

The Many Worlds Interpretation of quantum mechanics holds that there are an infinite number of parallel Universes that exist, holding all possible outcomes of a quantum mechanical system, and that making an observation simply chooses one path. This interpretation is philosophically interesting, but may add nothing-of-value when it comes to actual physics.

One of the problems with quantum mechanics is the problem of, What does it mean for whats really going on in our Universe? We have this notion that there is some sort of objective reality a really real reality thats independent of any observer or external influence. That, in some way, the Universe exists as it does without regard for whether anyone or anything is watching or interacting with it.

This very notion is not something were certain is valid. Although its pretty much hard-wired into our brains and our intuitions, reality is under no obligation to conform to them.

What does that mean, then, when it comes to the question of whats truly going on when, for example, we perform the double-slit experiment? If you have two slits in a screen that are narrowly spaced, and you shine a light through it, the illuminated pattern that shows up behind the screen is an interference pattern: with multiple bright lines patterned after the shape of the slit, interspersed with dark lines between them. This is not what youd expect if you threw a series of tiny pebbles through that double slit; youd simply expect two piles of rocks, with each one corresponding to the rocks having gone through one slit or the other.

Results of a double-slit-experiment performed by Dr. Tonomura showing the build-up of an interference pattern of single electrons. If the path of which slit each electron passes through is measured, the interference pattern is destroyed, leading to two piles instead. The number of electrons in each panel are 11 (a), 200 (b), 6000 (c), 40000 (d), and 140000 (e).

The thing about this double slit experiment is this: as long as you dont measure which slit the light goes through, you will always get an interference pattern.

This remains true even if you send the light through one photon at a time, so that multiple photons arent interfering with one another. Somehow, its as though each individual photon is interfering with itself.

Its still true even if you replace the photon with an electron, or other massive quantum particles, whether fundamental or composite. Sending electrons through a double slit, even one at a time, gives you this interference pattern.

And it ceases to be true, immediately and completely, if you start measuring which slit each photon (or particle) went through.

But why? Why is this the case?

Thats one of the puzzles of quantum mechanics: it seems as though its open to interpretation. Is there an inherently uncertain distribution of possible outcomes, and does the act of measuring simply pick out which outcome it is that has occurred in this Universe?

Is it the case that everything is wave-like and uncertain, right up until the moment that a measurement is made, and that act of measuring a critical action that causes the quantum mechanical wavefunction to collapse?

When a quantum particle approaches a barrier, it will most frequently interact with it. But there is a finite probability of not only reflecting off of the barrier, but tunneling through it. The actual evolution of the particle is only determined by measurement and observation, and the wavefunction interpretation only applies to the unmeasured system; once its trajectory has been determined, the past is entirely classical in its behavior.

Or is it the case that each and every possible outcome that could occur actually does occur, but simply not in our Universe? Is it possible that there are an infinite number of parallel Universes out there, and that all possible outcomes occur infinitely many times in a variety of them, but it takes the act of measurement to know which one occurred in ours?

Although these might all seem like radically different possibilities, theyre all consistent (and not, by any means, an exhaustive list of) interpretations of quantum mechanics. At this point in time, the only differences between the Universe they describe are philosophical. From a physical point of view, they all predict the same exact results for any experiment we know how to perform at present.

However, if there are an infinite number of parallel Universes out there and not simply in a mathematical sense, but in a physically real one there needs to be a place for them to live. We need enough Universe to hold all of these possibilities, and to allow there to be somewhere within it where every possible outcome can be real. The only way this could work is if:

From a pre-existing state, inflation predicts that a series of universes will be spawned as inflation continues, with each one being completely disconnected from every other one, separated by more inflating space. One of these bubbles, where inflation ended, gave birth to our Universe some 13.8 billion years ago, where our entire visible Universe is just a tiny portion of that bubbles volume. Each individual bubble is disconnected from all of the others.

The Universe needs to be born infinite because the number of possible outcomes that can occur in a Universe that starts off like ours, 13.8 billion years ago, increases more quickly than the number of independent Universes that come to exist in even an eternally inflating Universe. Unless the Universe was born infinite in size a finite amount of time ago, or it was born finite in size an infinite amount of time ago, its simply not possible to have enough Universes to hold all possible outcomes.

But if the Universe was born infinite and cosmic inflation occurred, suddenly the Multiverse includes an infinite number of independent Universes that start with initial conditions identical to our own. In such a case, anything that could occur not only does occur, but occurs an infinite number of times. There would be an infinite number of copies of you, and me, and Earth, and the Milky Way, etc., that exist in an infinite number of independent Universe. And in some of them, reality unfolds identically to how it did here, right up until the moment when one particular quantum measurement takes place. For us in our Universe, it turned out one way; for the version of us in a parallel Universe, perhaps that outcome is the only difference in all of our cosmic histories.

The inherent width, or half the width of the peak in the above image when youre halfway to the crest of the peak, is measured to be 2.5 GeV: an inherent uncertainty of about +/- 3% of the total mass. The mass of the particle in question, the Z boson, is peaked at 91.187 GeV, but that mass is inherently uncertain by a significant amount.

But when we talk about uncertainty in quantum physics, were generally talking about an outcome whose results havent been measured or decided just yet. Whats uncertain in our Universe isnt past events that have already been determined, but only events whose possible outcomes have not yet been constrained by measurables.

If we think about a double slit experiment thats already occurred, once weve seen the interference pattern, its not possible to state whether a particular electron traveled through slit #1 or slit #2 in the past. That was a measurement we could have made but didnt, and the act of not making that measurement resulted in the interference pattern appearing, rather than simply two piles of electrons.

There is no Universe where the electron travels either through slit #1 or slit #2 and still makes an interference pattern by interfering with itself. Either the electron travels through both slits at once, allowing it to interfere with itself, and lands on the screen in such a way that thousands upon thousands of such electrons will expose the interference pattern, or some measurements occurs to force the electron to solely travel through slit #1 or slit #2 and no interference pattern is recovered.

Perhaps the spookiest of all quantum experiments is the double-slit experiment. When a particle passes through the double slit, it will land in a region whose probabilities are defined by an interference pattern. With many such observations plotted together, the interference pattern can be seen if the experiment is performed properly; if you retroactively ask which slit did each particle go through? you will find youre asking an ill-posed question.

What does this mean?

It means as was recognized by Heisenberg himself nearly a century ago that the wavefunction description of the Universe does not apply to the past. Right now, there are a great many things that are uncertain in the Universe, and thats because the critical measurement or interaction to determine what that things quantum state is has not yet been taken.

In other words, there is a boundary between the classical and quantum the definitive and the indeterminate and the boundary between them is when things become real, and when the past becomes fixed. That boundary, according to physicist Lee Smolin, is what defines now in a physical sense: the moment where the things that were observing at this instant fixes certain observables to have definitively occurred in our past.

We can think about infinite parallel Universes as opening up before us as far as future possibilities go, in some sort of infinitely forward-branching tree of options, but this line of reasoning does not apply to the past. As far as the past goes, at least in our Universe, previously determined events have already been metaphorically written in stone.

This 1993 photo by Carol M. Highsmith shows the last president of apartheid-era South Africa, F.W. de Klerk, alongside president-elect Nelson Mandela, as both were about to receive Americas Liberty Medal for effecting the transition of power away from white minority rule and towards universal majority rule. This event definitively occurred in our Universe.

In a quantum mechanical sense, this boils down to two fundamental questions.

The answer seems to be no and no. To achieve a macroscopic difference from quantum mechanical outcomes means weve already crossed into the classical realm, and that means the past history is already determined to be different. There is no way back to a present where Nelson Mandela dies in 2013 if he already died in prison in the 1980s.

Furthermore, the only places where these parallel Universes can exist is beyond the limit of our observable Universe, where theyre completely causally disconnected from anything that happens here. Even if theres a quantum mechanical entanglement between the two, the only way information can be transferred between those Universes is limited by the speed of light. Any information about what occurred over there simply doesnt exist in our Universe.

We can imagine a very large number of possible outcomes that could have resulted from the conditions our Universe was born with, and a very large number of possible outcomes that could have occurred over our cosmic history as particles interact and time passes. If there were enough possible Universes out there, it would also be possible that the same set of outcomes happened in multiple places, leading to the scenario of infinite parallel Universes. Unfortunately, we only have the one Universe we inhabit to observe, and other Universes, even if they exist, are not causally connected to our own.

The truth is that there may well be parallel Universes out there in which all of these things did occur. Maybe there is a Berenstein Bears out there, along with Shazaam the movie and a Nelson Mandela who died in prison in the 1980s. But that has no bearing on our Universe; they never occurred here and no one who remembers otherwise is correct. Although the neuroscience of human memory is not fully understood, the physical science of quantum mechanics is well-enough understood that we know whats possible and what isnt. You do have a faulty memory, and parallel Universes arent the reason why.

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Could quantum mechanics explain the Mandela effect? - Big Think

Today lets take a walk on the wild side and assume, for the sake of argument, that our Universe is not the only one that exists. Lets consider that there are many other universes, possibly infinitely many. The totality of these universes, including our own, is what cosmologists call the Multiverse. It sounds more like a myth than a scientific hypothesis, and this conceptual troublemaker inspires some while it outrages others.

The controversy started in the 1980s. Two physicists, Andrei Linde at Stanford University and Alex Vilenkin at Tufts University, independently proposed that if the Universe underwent a very fast expansion early on in its existence we call this an inflationary expansion then our Universe would not be the only one.

This inflationary phase of growth presumably happened a trillionth of a trillionth of a trillionth of one second after the beginning of time. That is about 10-36 seconds after the bang when the clock that describes the expansion of our universe started ticking. You may ask, How come these scientists feel comfortable talking about times so ridiculously small? Wasnt the Universe also ridiculously dense at those times?

Well, the truth is we do not yet have a theory that describes physics under these conditions. What we do have are extrapolations based on what we know today. This is not ideal, but given our lack of experimental data, it is the only place we can start from. Without data, we need to push our theories as far as we consider reasonable. Of course, what is reasonable for some theorists will not be for others. And this is where things get interesting.

The supposition here is that we can apply essentially the same physics at energies that are about one thousand trillion times higher than the ones we can probe at the Large Hadron Collider, the giant accelerator housed at the European Organization for Nuclear Research in Switzerland. And even if we cannot apply quite the same physics, we can at least apply physics with similar actors.

In high energy physics, all the characters are fields. Fields, here, mean disturbances that fill space and may or may not change in time. A crude picture of a field is that of water filling a pond. The water is everywhere in the pond, with certain properties that take on values at every point: temperature, pressure, and salinity, for example. Fields have excitations that we call particles. The electron field has the electron as an excitation. The Higgs field has the Higgs boson. In this simple picture, we could visualize the particles as ripples of water propagating along the surface of the pond. This is not a perfect image, but it helps the imagination.

The most popular protagonist driving inflationary expansion is a scalar field an entity with properties inspired by the Higgs boson, which was discovered at the Large Hadron Collider in July 2012.

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We do not know if there were scalar fields at the cosmic infancy, but it is reasonable to suppose there were. Without them, we would be horribly stuck trying to picture what happened. As mentioned above, when we do not have data, the best that we can do is to build reasonable hypotheses that future experiments will hopefully test.

To see how we use a scalar field to model inflation, picture a ball rolling downhill. As long as the ball is at a height above the bottom of the hill, it will roll down. It has stored energy. At the bottom, we set its energy to zero. We do the same with the scalar field. As long as it is displaced from its minimum, it will fill the Universe with its energy. In large enough regions, this energy prompts the fast expansion of space that is the signature of inflation.

Linde and Vilenkin added quantum physics to this picture. In the world of the quantum, everything is jittery; everything vibrates endlessly. This is at the root of quantum uncertainty, a notion that defies common sense. So as the field is rolling downhill, it is also experiencing these quantum jumps, which can kick it further down or further up. Its as if the waves in the pond were erratically creating crests and valleys. Choppy waters, these quantum fields.

Here comes the twist: When a sufficiently large region of space is filled with the field of a certain energy, it will expand at a rate related to that energy. Think of the temperature of the water in the pond. Different regions of space will have the field at different heights, just as different regions of the pond could have water at different temperatures. The result for cosmology is a plethora of madly inflating regions of space, each expanding at its own rate. Very quickly, the Universe would consist of myriad inflating regions that grow, unaware of their surroundings. The Universe morphs into a Multiverse.Even within each region, quantum fluctuations may drive a sub-region to inflate. The picture, then, is one of an eternally replicating cosmos, filled with bubbles within bubbles. Ours would be but one of them a single bubble in a frothing Multiverse.

This is wildly inspiring. But is it science? To be scientific, a hypothesis needs to be testable. Can you test the Multiverse? The answer, in a strict sense, is no. Each of these inflating regions or contracting ones, as there could also be failed universes is outside our cosmic horizon, the region that delimits how far light has traveled since the beginning of time. As such, we cannot see these cosmoids, nor receive any signals from them. The best that we can hope for is to find a sign that one of our neighboring universes bruised our own space in the past. If this had happened, we would see some specific patterns in the sky more precisely, in the radiation left over after hydrogen atoms formed some 400,000 years after the Big Bang. So far, no such signal has been found. The chances of finding one are, quite frankly, remote.

We are thus stuck with a plausible scientific idea that seems untestable. Even if we were to find evidence for inflation, that would not necessarily support the inflationary Multiverse. What are we to do?

The Multiverse suggests another ingredient the possibility that physics is different in different universes. Things get pretty nebulous here, because there are two kinds of different to describe. The first is different values for the constants of nature (such as the electron charge or the strength of gravity), while the second raises the possibility that there are different laws of nature altogether.

In order to harbor life as we know it, our Universe has to obey a series of very strict requirements. Small deviations are not tolerated in the values of natures constants. But the Multiverse brings forth the question of naturalness, or of how common our Universe and its laws are among the myriad universes belonging to the Multiverse. Are we the exception, or do we follow the rule?

The problem is that we have no way to tell. To know whether we are common, we need to know something about the other universes and the kinds of physics they have. But we dont. Nor do we know how many universes there are, and this makes it very hard to estimate how common we are. To make things worse, if there are infinitely many cosmoids, we cannot say anything at all. Inductive thinking is useless here. Infinity gets us tangled up in knots. When everything is possible, nothing stands out, and nothing is learned.

That is why some physicists worry about the Multiverse to the point of loathing it. There is nothing more important to science than its ability to prove ideas wrong. If we lose that, we undermine the very structure of the scientific method.

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How the Multiverse could break the scientific method - Big Think

Nothing can prepare you for a conversation with a physicist, certainly not one about abstract art. TIFR physicist Sukant Saran straddles both worlds with mastery

Sukant Saran depicts the notion that any observer in the universe, irrespective of position, would find space expanding in all directions. Pics/Shadab Khan

Sukant Saran would like you to know, right off the bat, that his pieces of art are not diagrams. The clay sculptures do not represent scientific concepts; it is not how he envisions them. They are conceptual melding of art and the laws of physics.

For instance, the story about Isaac Newton discovering gravity after an apple falls on his head, is just that, a story. Newtons great contribution to science, however, says the physicist was the observation that the force that made the apple fall from a tree was also responsible for keeping the moon in its orbit around the Earth. He connected the celestial and the terrestrial in his Theory of Gravitation. Sarans massive clay apple is pock-marked with lunar craters to represent this connection that Newton made. That there are vacuums in the universe is another myth he busted.

With craters on the fruits surface, Newtons Apple posits that the moon and the apple have the same status in Newtons theory of gravitation

The 59-year-old works at TIFR (Tata Institute of Fundamental Research) which is parked at the end of Homi Bhabha Road in Colaba, right next to the entrance of Old Navy Nagar. Too few would go looking for art there, never mind the security clearance. And that is unfair. My colleagues have all seen [the exhibition Sculpting Science: An experiment in art] and supported me, but yes, I dont know how others will find their way here. As it is, there is a bit of mystery about what we do here at TIFR.

Saran is born of a journalist father, and raised in Chandigarh amidst an environment rich with poets, artists and artistes, authors and other cultural elements of the day. I have been drawing and painting since I was a child. Initially, I was engaged in creating abstract pen art and then moved to digital art in 2000, says the scientist. Along the way, he realised that he was thinking in three dimensions and then translating it into two-dimensional art.

In quantum mechanics, particles are waves, and waves are particles. This sculpture shows particles coalescing to make waves, and waves are becoming localised particles

Sculpting seemed a more appropriate form. At first, he would play around with different types of clay, took some basic pottery classes and it became his chosen medium. A few experiments in, he realised that his hand was being informed by science and the sculptures grew into concepts about subatomic particles (particles as waves along the axis of time), physical processes such as evaporation, ductility and malleability (at the sub-atomic particle level), history and symbolism (the apple comes here, as well as an accurate depiction of a tree).

Traditionally, the tree is depicted only by what we see above ground, he says, but the tree as an organism is spread as much below ground as the branches are above it. I have modified the usual traditional symbol to show that this should be the actual drawing of a tree as informed by science. The secondary intent is to emphasise that unseen processes are as important as those seen.

Embryo day 18 shows the division and differentiation of cells as a foetus develops in the womb. The repeated folding, unfolding, stretching and contraction of two interacting layers forms all elements of a developed human body

More sculptures are grouped into Duality: Order/ Disorder, Wave/ Particle, Matter/Antimatter and Interaction; mathematical forms shown through abstract representations of Surfacing, Saddle and Idealisation. For instance, the Earth does not have a smooth surfacethere are mountains and trenches, oceans, overlapping or colliding tectonic plates. But for the sake of calculation, we assume it to be a smooth globe. With this, Saran tries to make the point that science is an abstract representation of nature, just like a poem or painting.

Dualities such as mind-body or good-bad are enmeshed in our daily routine in a way that our lives are governed by them. Wherever you look, whatever you do, some duality is part of our life. Science also has dualities and I have tried to depict some of them. Sometimes they appear as mathematical abstractions, and sometimes as manifestations in the physical environment, he explains. One sculpture shows order merging seamlessly into disorder. Though this is a scientific concept, it can be applied to any situation.

You have heard of the Mbius loop? he asks, walking to the next sculpture. We nod, dishonestly (Its the surface formed by attaching the ends of a strip of paper together with a half-twist, we find out later). I have just used the concept of half turn. If there is a protrusion [on one side], with half turn it becomes a depression. There is no actual theory that uses Mbius strip as a mechanism for pair production.

One of the last two groups is Biological forms that show science-art interaction. Multicellular life-causing mitochondria; the segmentation seen in an earthworm or the bark of a date palm being mimicked by an embryo as it grows; and representations of 18-day and 28-day embryos. The last group is Space and Time, seen in physics as one entity. Twenty four of the 80 pieces he has created are on display until June 10.

No amount of watching Dr Who or Big Bang Theory prepares you for a conversation with a physicist; certainly not one about abstract art. This writer asked him to explain the pieces as if he was addressing a six-year-old, and a round about the room stretches the imagination. Especially if one sat immobile through physics period, eye glazed over. Try understanding this: As per quantum mechanics, waves are particles and particles are waves.

The abstract depiction of space-time or wave-particle duality along the axis of time may need a more specific kind of mind, there is no denying the beauty of each sculpture. Strips of clay meld into each other to depict an expanding universe, with the galaxies going further and further away from each other. Its a complex and chaotic piece, one that draws you in. The biological forms and physical processes (evaporation, ductility, malleability and expansion) are much easier to wrap ones head around.

It was his peculiar position in space and time that guided Sarans education, as well as societal conditioning. I was good at studies and thus considered to be intelligent, and routed to science, he says, If you see this in a wider perspective, it is a very stupid way of thinking. Both disciplines are harmed by this; there is no interplay. It cultivates a very rigid form of thinking.

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The art of physics - Mid Day

Anytime you reach deeper into the unknown than ever before, you should not only wonder about what youre going to find, but also worry about what sort of demons you might unearth. In the realm of particle physics, that double-edged sword arises the farther we probe into the high-energy Universe. The better we can explore the previously inaccessible energy frontier, the better we can reveal the high-energy processes that shaped the Universe in its early stages.

Many of the mysteries of how our Universe began and evolved from the earliest times can be best investigated by this exact method: colliding particles at higher and higher energies. New particles and rare processes can be revealed through accelerator physics at or beyond the current energy frontiers, but this is not without risk. If we can reach energies that:

certain consequences not all of which are desirable could be in store for us all. And yet, just as was the case with the notion that The LHC could create black holes that destroy the Earth, we know that any experiment we perform on Earth wont give rise to any dire consequences at all. The Universe is safe from any current or planned particle accelerators. This is how we know.

The idea of a linear lepton collider has been bandied about in the particle physics community as the ideal machine to explore post-LHC physics for many decades, but only if the LHC makes a beyond-the-Standard-Model discovery. Direct confirmation of what new particles could be causing CDFs observed discrepancy in the W-bosons mass might be a task best suited to a future circular collider, which can reach higher energies than a linear collider ever could.

There are a few different approaches to making particle accelerators on Earth, with the biggest differences arising from the types of particles were choosing to collide and the energies were able to achieve when were colliding them. The options for which particles to collide are:

Travel the Universe with astrophysicist Ethan Siegel. Subscribers will get the newsletter every Saturday. All aboard!

In the future, it may be possible to collide muons with anti-muons, getting the best of both the electron-positron and the proton-antiproton world, but that technology isnt quite there yet.

A candidate Higgs event in the ATLAS detector at the Large Hadron Collider at CERN. Note how even with the clear signatures and transverse tracks, there is a shower of other particles; this is due to the fact that protons are composite particles, and due to the fact that dozens of proton-proton collisions occur with every bunch crossing. Examining how the Higgs decays to very high precision is one of the key goals of the HL-LHC.

Regardless, the thing that poses the most danger to us is whatevers up there at the highest energy-per-particle-collision that we get. On Earth, that record is held by the Large Hadron Collider, where the overwhelming majority of proton-proton collisions actually result in the gluons inside each proton colliding. When they smash together, because the protons total energy is split among its constituent particles, only a fraction of the total energy belongs to each gluon, so it takes a large number of collisions to find one where a large portion of that energy say, 50% or more belongs to the relevant, colliding gluons.

When that occurs, however, thats when the most energy is available to either create new particles (via E = mc2) or to perform other actions that energy can perform. One of the ways we measure energies, in physics, is in terms of electron-volts (eV), or the amount of energy required to raise an electron at rest to an electric potential of one volt in relation to its surrounding. At the Large Hadron Collider, the current record-holder for laboratory energies on Earth, the most energetic particle-particle collision possible is 14 TeV, or 14,000,000,000,000 eV.

Although no light can escape from inside a black holes event horizon, the curved space outside of it results in a difference between the vacuum state at different points near the event horizon, leading to the emission of radiation via quantum processes. This is where Hawking radiation comes from, and for the tiniest-mass black holes, Hawking radiation will lead to their complete decay in under a fraction-of-a-second.

There are things we can worry will happen at these highest-of-energies, each with their own potential consequence for either Earth or even for the Universe as a whole. A non-exhaustive list includes:

If you draw out any potential, it will have a profile where at least one point corresponds to the lowest-energy, or true vacuum, state. If there is a false minimum at any point, that can be considered a false vacuum, and it will always be possible, assuming this is a quantum field, to quantum tunnel from the false vacuum to the true vacuum state. The greater the kick you apply to a false vacuum state, the more likely it is that the state will exit the false vacuum state and wind up in a different, more stable, truer minimum.

Although these scenarios are all bad in some sense, some are worse than others. The creation of a tiny black hole would lead to its immediate decay. If you didnt want it to decay, youd have to impose some sort of new symmetry (for which there is neither evidence nor motivation) to prevent its decay, and even then, youd just have a tiny-mass black hole that behaved similarly to a new, massive, uncharged particle. The worst it could do is begin absorbing the matter particles it collided with, and then sink to the center of whatever gravitational object it was a part of. Even if you made it on Earth, it would take trillions of years to absorb enough matter to rise to a mass of 1 kg; its not threatening at all.

The restoration of whatever symmetry was in place before the Universes matter-antimatter symmetry arose is also interesting, because it could lead to the destruction of matter and the creation of antimatter in its place. As we all know, matter and antimatter annihilate upon contact, which creates bad news for any matter that exists close to this point. Fortunately, however, the absolute energy of any particle-particle collision is tiny, corresponding to tiny fractions of a microgram in terms of mass. Even if we created a net amount antimatter from such a collision, it would only be capable of destroying a small amount of matter, and the Universe would be fine overall.

The simplest model of inflation is that we started off at the top of a proverbial hill, where inflation persisted, and rolled into a valley, where inflation came to an end and resulted in the hot Big Bang. If that valley isnt at a value of zero, but instead at some positive, non-zero value, it may be possible to quantum-tunnel into a lower-energy state, which would have severe consequences for the Universe we know today. Its also possible that a kick of the right energy could restore the inflationary potential, leading to a new state of rapid, relentless, exponential expansion.

But if we instead were able to recreate the conditions under which inflation occurred, things would be far worse. If it happened out in space somewhere, wed create in just a tiny fraction of a second the greatest cosmic void we could imagine. Whereas today, theres only a tiny amount of energy inherent to the fabric of empty space, something on the order of the rest-mass-energy of only a few protons per cubic meter, during inflation, it was more like a googol protons (10100) per cubic meter.

If we could achieve those same energy densities anywhere in space, they could potentially restore the inflationary state, and that would lead to the same Universe-emptying exponential expansion that occurred more than 13.8 billion years ago. It wouldnt destroy anything in our Universe, but it would lead to an exponential, rapid, relentless expansion of space in the region where those conditions occur again.

That expansion would push the space that our Universe occupies outward, in all three dimensions, as it expands, creating a large cosmic bubble of emptiness that would lead to unmistakable signatures that such an event had occurred. It clearly has not, at least, not yet, but in theory, this is possible.

Visualization of a quantum field theory calculation showing virtual particles in the quantum vacuum. (Specifically, for the strong interactions.) Even in empty space, this vacuum energy is non-zero, and what appears to be the ground state in one region of curved space will look different from the perspective of an observer where the spatial curvature differs. As long as quantum fields are present, this vacuum energy (or a cosmological constant) must be present, too.

And finally, the Universe today exists in a state where the quantum vacuum the zero-point energy of empty space is non-zero. This is inextricably, although we dont know how to perform the calculation that underlies it, linked to the fundamental physical fields and couplings and interactions that govern our Universe: the physical laws of nature. At some level, the quantum fluctuations in those fields that cannot be extricated from space itself, including the fields that govern all of the fundamental forces, dictate what the energy of empty space itself is.

But its possible that this isnt the only configuration for the quantum vacuum; its plausible that other energy states exist. Whether theyre higher or lower doesnt matter; whether our vacuum state is the lowest-possible one (i.e., the true vacuum) or whether another is lower doesnt matter either. What matters is whether there are any other minima any other stable configurations that the Universe could possibly exist in. If there are, then reaching high-enough energies could kick the vacuum state in a particular region of space into a different configuration, where wed then have at least one of:

Any of these would, if it was a more-stable configuration than the one that our Universe currently occupies, cause that new vacuum state to expand at the speed of light, destroying all of the bound states in its path, down to atomic nuclei themselves. This catastrophe, over time, would destroy billions of light-years worth of cosmic structure; if it happened within about 18 billion light-years of Earth, that would eventually include us, too.

The size of our visible Universe (yellow), along with the amount we can reach (magenta). The limit of the visible Universe is 46.1 billion light-years, as thats the limit of how far away an object that emitted light that would just be reaching us today would be after expanding away from us for 13.8 billion years. However, beyond about 18 billion light-years, we can never access a galaxy even if we traveled towards it at the speed of light. Any catastrophe that occurred within 18 billion light-years of us would eventually reach us; ones that occur today at distances farther away never will.

There are tremendous uncertainties connected to these events. Quantum black holes could be just out of reach of our current energy frontier. Its possible that the matter-antimatter asymmetry was only generated during electroweak symmetry breaking, potentially putting it within current collider reach. Inflation must have occurred at higher energies than weve ever reached, as do the processes that determine the quantum vacuum, but we dont know how low those energies could have been. We only know, from observations, that such an event hasnt yet happened within our observable Universe.

But, despite all of this, we dont have to worry about any of our particle accelerators past, present, or even into the far future causing any of these catastrophes here on Earth. The reason is simple: the Universe itself is filled with natural particle accelerators that are far, far more powerful than anything weve ever built or even proposed here on Earth. From collapsed stellar objects that spin rapidly, such as white dwarfs, neutron stars, and black holes, very strong electric and magnetic fields can be generated by charged, moving matter under extreme conditions. Its suspected that these are the sources of the highest-energy particles weve ever seen: the ultra-high-energy cosmic rays, which have been observed to achieve energies many millions of times greater than any accelerator on Earth ever has.

The energy spectrum of the highest energy cosmic rays, by the collaborations that detected them. The results are all incredibly highly consistent from experiment to experiment, and reveal a significant drop-off at the GZK threshold of ~5 x 10^19 eV. Still, many such cosmic rays exceed this energy threshold, indicating that either this picture is not complete or that many of the highest-energy particles are heavier nuclei, rather than individual protons.

Whereas weve reached up above the ten TeV threshold for accelerators on Earth, or 1013 eV in scientific notation, the Universe routinely creates cosmic rays that rise up above the 1020 eV threshold, with the record set more than 30 years ago by an event known, appropriately, as the Oh-My-God particle. Even though the highest energy cosmic rays are thought to be heavy atomic nuclei, like iron, rather than individual protons, that still means that when two of them collide with one another a near-certainty within our Universe given the vastness of space, the fact that galaxies were closer together in the past, and the long lifetime of the Universe there are many events producing center-of-mass collision energies in excess of 1018 or even 1019 eV.

This tells us that any catastrophic, cosmic effect that we could worry about is already tightly constrained by the physics of what has happened over the cosmic history of the Universe up until the present day.

When a high-energy particle strikes another one, it can lead to the creation of new particles or new quantum states, constrained only by how much energy is available in the center-of-mass of the collision. Although particle accelerators on Earth can reach very high energies, the natural particle accelerators of the Universe can exceed those energies by a factor of many millions.

None of the cosmic catastrophes that we can imagine have occurred, and that means two things. The first thing is that we can place likely lower limits on where certain various cosmic transitions occurred. The inflationary state hasnt been restored anywhere in our Universe, and that places a lower limit on the energy scale of inflation of no less than ~1019 eV. This is about a factor of 100,000 lower, perhaps, than where we anticipate inflation occurred: a reassuring consistency. It also teaches us that its very hard to kick the zero-point energy of the Universe into a different configuration, giving us confidence in the stability of the quantum vacuum and disfavoring the vacuum decay catastrophe scenario.

But it also means we can continue to explore the Universe with confidence in our safety. Based on how safe the Universe has already shown itself to be, we can confidently conclude that no such catastrophes will arise up to the combined energy-and-collision-total threshold that has already taken place within our observable Universe. Only if we begin to collide particles at energies around 1020 eV or greater a factor of 10 million greater than the present energy frontier will we need to begin to worry about such events. That would require an accelerator significantly larger than the entire planet, and therefore, we can reach the conclusion promised in the articles title: no, particle physics on Earth wont ever destroy the Universe.

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No, particle physics on Earth won't ever destroy the Universe - Big Think