Daily Archives: February 27, 2021

February 25, 2021• Physics 14, 27

A new analysis of heavy-ion collision experiments uncovers evidence that two colliding nuclei behave like a Josephson junctiona device in which Cooper pairs tunnel through a barrier between two superfluids.

The Josephson effect is a remarkable example of a macroscopic quantum phenomenon, in which, without an applied voltage, current flows between two superconductors separated by a thin film of normal material. In this structure, called a Josephson junction, the current is due to the quantum tunneling of paired, superconducting electrons (so-called Cooper pairs) [1]. For decades, nuclear physicists have hypothesized that similar effects can occur on much smaller scales, since atomic nuclei could be regarded as superfluids consisting of paired nucleons. Recent experiments have supported this hypothesis, delivering hints that two colliding nuclei could be described as a Josephson junction in which entangled neutron pairs play the role of Cooper pairs (Fig. 1) [2, 3]. Now, Gregory Potel from Lawrence Livermore National Laboratory in California and colleagues have put these ideas on firmer ground [4]. Analyzing tin-nickel collisions from previous experiments, they found that experimental observables offer compelling signatures that two nuclei indeed form, for a split second, a Josephson junction.

The orderly motion of gigantic ensembles of correlated electron pairs makes superconductors behave as a single objecta macroscopic quantum state called a condensate. The condensate is characterized by its density and phase, and the latter plays the same role as the orientation of magnetic moments in a ferromagnet: an isolated ferromagnet can be rotated at no energy cost, but two ferromagnets with different orientations affect each other. Similarly, according to quantum mechanics, the phase doesnt have implications for a single condensate. But if two condensates are sufficiently close, a Cooper-pair current, whose magnitude depends on the phase difference, may flow from one condensate to the other. A striking feature of this effect is that electric current may flow without a driving voltage.

There may be other systems in Nature where this effect occurs, and atomic nuclei, which can be regarded as superfluid ensembles of nucleons, are good candidates. This idea appeared among nuclear physicists as early as the 1970s [5]. In the 1980s and 1990s, several experiments indicated an enhanced probability of neutron-pair transfer between colliding nucleia possible manifestation of the Josephson effect. But the evidence for this interpretation wasnt compelling. There were doubts, in particular, about whether ensembles of nucleons are sufficiently large to be treated as a pair condensate. Superconductivity is an emergent phenomenon: It appears when dealing with a huge number of particles but vanishes when the system is broken down into smaller constituents. But can we consider a nucleus made of about 100 nucleons a huge ensemble of particles? Can we expect that two nuclei in close proximity exhibit a Josephson effect?

The study by Potel and his colleagues provides strong arguments for affirmative answers to these questions. The researchers analyzed data from previous experiments in which tin-116 ( 116Sn) nuclei were collided with nickel-60 ( 60Ni) [2]. With energies between 140.60 and 167.95 MeV, these collisions are gentle: they allow the nuclei to overcome just enough of the Coulomb repulsion to get sufficiently close to exchange a few neutrons at most. Under such conditions, two reactions are possible: the transfer of one neutron and the transfer of two neutrons, producing 115Sn+61Ni and 114Sn+62Ni, respectively. The case of two-neutron transfer is particularly interesting, as it may carry signatures of the correlated pairing of neutrons in the nuclei.

The team devised a way to uncover the experimental evidence of Josephson flow. Their idea is that there can be a nuclear equivalent of the alternating current (ac) Josephson effect (Fig. 1). In this variant of the Josephson effect, a constant, or dc, voltage applied to a Josephson junction produces an ac current. This striking behavior arises because the voltage causes the phase difference between the two condensates to increase over time. Since phases that differ by multiples of 2 are equivalent, a linear phase growth produces an oscillating current. The researchers argue that for the nuclear case, a similar effect can occur because neutron pairs inside two colliding nuclei possess different energies. This energy difference plays the role of the dc voltage in the ac Josephson effect.

Therefore, similar oscillatory behavior is expected to occur during a nuclear collision: the back-and-forth tunneling of neutron pairs means that 116Sn+60Ni transforms into 114Sn+62Ni and then again into 116Sn+60Nia cyclical process whose frequency is determined by the energy difference of neutron pairs in initial and final nuclei. Because the collision lasts for only a short time, the team estimates that only about three such back-and-forth transfer cycles may occur in an experiment. However, even these few oscillations can lead to observable consequences. Since neutrons and protons interact strongly, oscillating neutron pairs cause protons to oscillate at the same frequency. Because of their charge, oscillating protons should emit electromagnetic radiation at this frequency. While electrons oscillating in a standard Josephson junction emit microwave photons [6], nuclei are expected to emit gamma-ray photons because of the much larger nuclear energy differences involved. The researchers calculate the expected radiation energy to be slightly less than 4 MeV, which matches the gamma-ray spectrum seen in previous experiments.

The results are thrilling for two reasons. First, they indicate that the principles of superconductivity valid for macroscopic phenomena in solids may be applicable to the much smaller (femtometer) nuclear scalesa truly spectacular conclusion. Second, the analysis shows that the pairing description is appropriate for a small number of particlesthe hundreds of nucleons making up the nuclei. It is worth pointing out, however, that this description contains a puzzling inconsistency. According to quantum mechanics, the phase and the number of particles in the condensate are related by the uncertainty principlemuch like the position and momentum of a quantum particle: if either quantity is well defined, the other isnt. But for the nuclear case, the number of nucleons is always exactly defined. Further theoretical work will need to resolve this inconsistency.

These findings whet our appetite for more work aimed at validating superfluid nuclear models by confronting theory with experiments. In particular, it would be crucial to show that such models can deliver accurate, quantitative predictions for analogous effects in nuclear collisions beyond those involving tin and nickel.

Piotr Magierski is Professor of Physics and Head of the Nuclear Physics Division at Warsaw University of Technology, Poland, and an Affiliate Professor at the University of Washington. He is a theoretical physicist whose research interests include superfluidity and superconductivity in systems far from equilibrium, such as nuclear fission and fusion reactions, nuclear matter in neutron stars, and ultracold atomic gases.

Two mirror nuclei, in which the numbers of neutrons and protons are interchanged, have markedly different shapesa finding that defies current nuclear theories. Read More

Particle physicists have detected a short-lived nucleus containing two strange quarks, whose properties could provide new insights into the behavior of other nuclear particles. Read More

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Physics - The Tiniest Superfluid Circuit in Nature - Physics

I still believed in god (I am now an atheist) when I heard the following question at a seminar, first posed by Einstein, and was stunned by its elegance and depth: If there is a god who created the entire universe and all of its laws of physics, does god follow gods own laws? Or can god supersede his own laws, such as travelling faster than the speed of light and thus being able to be in two different places at the same time? Could the answer help us prove whether or not god exists or is this where scientific empiricism and religious faith intersect, with no true answer?

I was in lockdown when I received this question and was instantly intrigued. It is no wonder about the timing tragic events, such as pandemics, often cause us to question the existence of god: if there is a merciful god, why is a catastrophe like this happening?

So the idea that god might be bound by the laws of physics which also govern chemistry and biology and thus the limits of medical science was an interesting one to explore.

If god was not able to break the laws of physics, she arguably would not be as powerful as you had expected a supreme being to be. But if she could, why have not we seen any evidence of the laws of physics ever being broken in the universe?

To tackle the question, let us break it down a bit. First, can god travel faster than light? Let us just take the question at face value. Light travels at an approximate speed of 300,000 kilometres every second. We learn at school that nothing can travel faster than the speed of light not even the USS Enterprise in Star Trek when its dilithium crystals are set to max.

But is it true? A few years ago, a group of physicists posited that particles called tachyons travelled above light speed. Fortunately, their existence as real particles is deemed highly unlikely. If they did exist, they would have an imaginary mass and the fabric of space and time would become distorted leading to violations of causality (and possibly a headache for god).

It seems, so far, that no object has been observed that can travel faster than the speed of light. This in itself does not say anything at all about god. It merely reinforces the knowledge that light travels very fast indeed.

Things get a bit more interesting when you consider how far light has travelled since the beginning. Assuming a traditional big bang cosmology and a light speed of 300,000 km/s, then we can calculate that light has travelled roughly 10 to the 24th power kilometres in the 13.8 billion years of the universes existence. Or rather, the observable universes existence.

The universe is expanding at a rate of approximately 70km/s per Mpc (1 Mpc = 1 Megaparsec ~ 30 million km), so current estimates suggest that the distance to the edge of the universe is 46 billion light years. As time goes on, the volume of space increases and light has to travel for longer to reach us.

There is a lot more universe out there than we can view, but the most distant object that we have seen is a galaxy, GN-z11, observed by the Hubble Space Telescope. This is approximately 13.4 billion light years away, meaning that it has taken 13.4 billion years for light from the galaxy to reach us. But when the light set off, the galaxy was only about 3 billion light years away from our galaxy, the Milky Way.

We cannot observe or see across the entirety of the universe that has grown since the big bang because insufficient time has passed for light from the first fractions of a second to reach us.

Some argue that we therefore cannot be sure whether the laws of physics could be broken in other cosmic regions perhaps they are just local, accidental laws. And that leads us on to something even bigger than the universe.

Many cosmologists believe that the universe may be part of a more extended cosmos, a multiverse, where many different universes co-exist but do not interact. The idea of the multiverse is backed by the theory of inflation the idea that the universe expanded hugely before it was 10 to the minus 32nd power seconds old. Inflation is an important theory because it can explain why the universe has the shape and structure that we see around us.

But if inflation could happen once, why not many times? We know from experiments that quantum fluctuations can give rise to pairs of particles suddenly coming into existence, only to disappear moments later.

And if such fluctuations can produce particles, why not entire atoms or universes? It is been suggested that, during the period of chaotic inflation, not everything was happening at the same rate quantum fluctuations in the expansion could have produced bubbles that blew up to become universes in their own right.

But how does god fit into the multiverse? One headache for cosmologists has been the fact that our universe seems fine-tuned for life to exist. The fundamental particles created in the big bang had the correct properties to enable the formation of hydrogen and deuterium substances which produced the first stars.

The physical laws governing nuclear reactions in these stars then produced the stuff that lifes made of carbon, nitrogen and oxygen. So how come all the physical laws and parameters in the universe happen to have the values that allowed stars, planets and ultimately life to develop?

Some argue it is just a lucky coincidence. Others say we should not be surprised to see biofriendly physical laws they after all produced us, so what else would we see? Some theists, however, argue it points to the existence of a god creating favourable conditions.

But god is not a valid scientific explanation. The theory of the multiverse, instead, solves the mystery because it allows different universes to have different physical laws. So it is not surprising that we should happen to see ourselves in one of the few universes that could support life. Of course, you cannot disprove the idea that a god may have created the multiverse.

This is all very hypothetical, and one of the biggest criticisms of theories of the multiverse is that because there seem to have been no interactions between our universe and other universes, then the notion of the multiverse cannot be directly tested.

Now let us consider whether god can be in more than one place at the same time. Much of the science and technology we use in space science is based on the counter-intuitive theory of the tiny world of atoms and particles known as quantum mechanics.

The theory enables something called quantum entanglement: spookily connected particles. If two particles are entangled, you automatically manipulate its partner when you manipulate it, even if they are very far apart and without the two interacting. There are better descriptions of entanglement than the one I give here but this is simple enough that I can follow it.

Imagine a particle that decays into two sub-particles, A and B. The properties of the sub-particles must add up to the properties of the original particle this is the principle of conservation. For example, all particles have a quantum property called spin roughly, they move as if they were tiny compass needles.

If the original particle has a spin of zero, one of the two sub-particles must have a positive spin and the other a negative spin, which means that each of A and B has a 50% chance of having a positive or a negative spin. (According to quantum mechanics, particles are by definition in a mix of different states until you actually measure them.)

The properties of A and B are not independent of each other they are entangled even if located in separate laboratories on separate planets. So if you measure the spin of A and you find it to be positive. Imagine a friend measured the spin of B at exactly the same time that you measured A. In order for the principle of conservation to work, she must find the spin of B to be negative.

But and this is where things become murky like sub-particle A, B had a 50:50 chance of being positive, so its spin state became negative at the time that the spin state of A was measured as positive.

In other words, information about spin state was transferred between the two sub-particles instantly. Such transfer of quantum information apparently happens faster than the speed of light. Given that Einstein himself described quantum entanglement as spooky action at a distance, I think all of us can be forgiven for finding this a rather bizarre effect.

So there is something faster than the speed of light after all: quantum information. This does not prove or disprove god, but it can help us think of god in physical terms maybe as a shower of entangled particles, transferring quantum information back and forth, and so occupying many places at the same time? Even many universes at the same time?

I have this image of god keeping galaxy-sized plates spinning while juggling planet-sized balls tossing bits of information from one teetering universe to another, to keep everything in motion. Fortunately, God can multitask keeping the fabric of space and time in operation. All that is required is a little faith.

Has this essay come close to answering the questions posed? I suspect not: if you believe in god (as I do), then the idea of god being bound by the laws of physics is nonsense because God can do everything, even travel faster than light. If you do not believe in god, then the question is equally nonsensical, because there is not a god and nothing can travel faster than light. Perhaps the question is really one for agnostics, who do not know whether there is a god.

This is indeed where science and religion differ. Science requires proof, religious belief requires faith. Scientists do not try to prove or disprove gods existence because they know there is not an experiment that can ever detect god. And if you believe in god, it does not matter what scientists discover about the universe any cosmos can be thought of as being consistent with god.

Our views of god, physics or anything else ultimately depends on perspective. But let us end with a quotation from a truly authoritative source. No, it is not the bible. Nor is it a cosmology textbook. It is from Reaper Man by Terry Pratchett: Light thinks it travels faster than anything but it is wrong. No matter how fast light travels, it finds the darkness has always got there first, and is waiting for it.

Monica Grady is a Professor of Planetary and Space Sciences at The Open University.

This article first appeared on The Conversation.

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Can god be disproved using the laws of physics? An expert explains how it depends on perspective - Scroll.in

Indian author Ashwin Sanghi's book Keepers Of The Kalachakra is being adapted into a series. The bestseller is a mythological-science fiction thriller that tells the story of men who guard the Kalachakra' or Wheel of Time.

In an exclusive chat with ETimes, Ashwin Sanghi spoke candidly about this upcoming venture, his dream cast and Bollywoods new trend of turning book adaptations into blockbusters.

Sharing his thoughts about the ideal person to take this franchise forward, he said, The person I wanted, alas, is no more - Sushant Singh Rajput. He was like an excited child when it came to quantum physics, which is what this thriller is about.

While the nation continues to feel the void left by late Bollywood actor Sushant Singh Rajput, one of the country's most eminent awards in entertainment, Dadasaheb Phalke Award, has honoured the star with the 'Critic's Best Actor' accolade in the prestigious award ceremony held on Saturday.

When quizzed about his favoured movie adapted from a book, pat came his reply, The Godfather wins hands down.

As far as 'Keepers Of The Kalachakra' is concerned, the Vikram Malhotra-headed Abundantia Entertainment has acquired the rights to the book and plans to convert it into a multi-season series. The author will work closely with the screenwriters' team to bring the book to life.

Sharing his excitement on his new venture, Ashwin said, Vikram Malhotra, Shikhas Sharma and Abundantia are outstanding partners to collaborate with. Their vision for this book is exhilarating. I am sure that we will deliver a series that will pack a punch.

The book follows scientist Vijay Sundaram, who races against time to save humanity from impending doom. Zigzagging from the Ramayana to the birth of Buddhism; from the origin of Wahhabism to the Einsteinian gravitational wave-detectors of LIGO; from tantric practitioners to the Oval Office; and from the rites of Minerva, shrouded in frankincense, to the smoke-darkened ruins of Nalanda, Keepers Of The Kalachakra has it all.

The virtual world can be as fake as you want your story to be

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Most people with a scientific worldview agree with the idea of causal determinism, the notion that everything is subject to the laws of physics, and anything that happens is the result of these laws acting on how things exist in the world or existed in a prior moment. However, it can be challenging to figure out how this idea meshes with the notion of free will.

After all, if everything else is subject to causal determinism, how can we not be? How can our decisions be somehow exempt? Many people argue that we obviously are also part of a clockwork universe and that physics kills off free will.

But is this saying too much? Can we really treat free will as the subject of physics alone? Today, we'll consider some stances on free will and how they relate to physics alongside some philosophers' ideas on if we can outsource our views on the human experience to science.

Some philosophers have taken the argument of casual determinism mentioned above and used it to say that there is no room for free will at all. This stance, called "hard determinism," maintains that all of our actions are causally necessary and dictated by physics in the same way as a billiard ball's movement.

The Baron d'Holbach, a French philosopher, explained the stance:

"In short, the actions of man are never free; they are always the necessary consequence of his temperament, of the received ideas and of the notions, either true or false, which he has formed to himself of happiness; of his opinions, strengthened by example, by education, and by daily experience."

While physics and philosophy have both advanced since the enlightenment era, hard determinism still has supporters.

As some of you are probably thinking right now, quantum physics, with its uncertainties, probabilities, and general strangeness, might offer a way out of the determinism of classical physics. This idea, sometimes called "indeterminism," occurred to more than a few philosophers too, and variations of it date back to ancient Greece.

This stance holds that not every event has an apparent cause. Some events might be random, for example. Proponents of the perspective suggest that some of our brain functions might have random elements, perhaps caused by the fluctuations seen in quantum mechanics, that cause our choices to not be fully predetermined. Others suggest that only part of our decision-making process is subject to causality, with a portion of it under what amounts to the control of the individual.

There are issues with this stance being used to counter determinism. One of them is that having choices made randomly rather than by strict causation doesn't seem to be the kind of free will people think about. From a physical standpoint, brain activity may involve some quantum mechanics, but not all of it. Many thinkers incorporate indeterminism into parts of their models of free will, but don't fully rely on the idea.

Also called "compatibilism," this view agrees with causal determinism but also holds that this is compatible with some kind of free will. This can take on many forms and sometimes operates by varying how "free" that will actually is.

John Stuart Mill argued that causality did mean that people will act in certain ways based on circumstance, character, and desires, but that we have some control over these things. Therefore, we have some capacity to change what we would do in a future situation, even if we are determined to act in a certain way in response to a particular stimulus.

Daniel Dennett goes in another direction, suggesting a two-stage model of decision-making involving some indeterminism. In the first stage of making a decision, the brain produces a series of considerations, not all of which are necessarily subject to determinism, to take into account. What considerations are created and not immediately rejected is subject to some level of indeterminism and agent control, though it could be unconscious. In the second step, these considerations are used to help make a decision based on a more deterministic reasoning process.

In these stances, your decisions are still affected by prior events like the metaphorical billiard balls moving on a table, but you have some control over how the table is laid out. This means you could, given enough time and understanding, have a fair amount of control over how the balls end up moving.

Critics of stances like this often argue that the free will the agent is left with by these decision-making models is hardly any different from what they'd have under a hard deterministic one.

This is the stance with the premium free will people tend to talk aboutthe idea that you are in full control of your decisions all the time and that casual determinism doesn't apply to your decision-making process. It is "incompatibilist" in that it maintains that free will is not compatible with a deterministic universe.

People holding this view often take either an "agent-casual" or "event-causal" position. In an agent-casual stance, decision-makers, known as "agents," can make decisions that are not caused by a previous action in the same way that physical events are. They are essentially the "prime movers" of event chains that start with their decisions rather than any external cause.

Event-casual stances maintain that some elements of the decision-making process are physically indeterminate and that at least some of the factors that go into the final choice are shaped by the agent. The most famous living proponent of such a stance is Robert Kane and his "effort of will" model.

In brief, his model supposes an agent can be thought responsible for an action if they helped create the causes that led to it. He argues that people occasionally take "self-forming action" (SFA) that helps shape their character and grant them this responsibility. SFAs happen when the decisions we make would be subject to indeterminism, perhaps a case when two choices are both highly likely- with one being what we want and one being what we think is right, and willpower is needed to cause a choice to be taken.

At that point, unable to quickly choose, we apply willpower to make a decision that influences our overall character. Not only was that decision freely chosen, but any later, potentially more causally-determined actions, we take rely at least somewhat on a character trait that we created through that previous choice. Therefore, we at least partially influenced them.

Critics of this stance include Daniel Dennett, who points out that SFAs could be so rare as to leave some people without any real free will at all.

No, the question of free will is much larger than if cause and effect exist and apply to our decisions. Even if that one were fully answered, other questions immediately pop up.

Is the agency left to us, if any, after we learn how much of our decision-making is determined by outside factors enough for us to say that we are free? How much moral responsibility do people have under each proposed understanding of free will? Is free will just the ability to choose otherwise, or do we just have to be responsible for the actions we make, even if we are limited to one choice?

Physics can inform the debate over these questions but cannot end it unless it comes up with an equation for what freedom is.

Modern debates outside of philosophy departments tend to ignore the differences in the above stances in a way that tends to reduce everything to determinism. This was highlighted by neuroscientist Bobby Azarian in a recent Twitter thread, where he notes there is often a tendency to conflate hard determinism with naturalismthe idea that natural laws, as opposed to supernatural ones, can explain everything in the universe. .

Lastly, we might wonder if physics is the right department to hand it over to. Daniel Dennett awards evolutionary biology the responsibility for generating consciousness and free will.

He points out that while physics has always been the same for life on Earth, both consciousness and free will seem to have evolved recently and could be an evolutionary advantage of sortsnot being bound to deterministic decision making could be an excellent tool for staying alive. He considers them to be emergent properties we have and considers efforts to reduce us to our parts, which do function deterministically, to be unsound.

How to balance our understanding of causal determinism and our subjective experience of seeming to have free will is a problem philosophers and scientists have been discussing for the better part of two thousand years. It is one they'll likely keep going over for a while. While it isn't time to outsource free will to physics, it is possible to incorporate the findings of modern science into our philosophy.

Of course, we might only do that because we're determined to do so, but that's another problem.

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How philosophy blends physics with the idea of free will - Big Think

PennyLane is an open-source, cross-platform Python library for differentiable programming of quantum computers. Differentiable programming refers to a programming paradigm that leverages automatic differentiation. PennyLane tries to bridge the gap between quantum computing and machine learning. According to the projects GitHub page, PennyLane enables users to train quantum computers much like neural networks.

Xanadu, the company behind PennyLane, explained: Were entering an exciting time in quantum physics and quantum computation: near-term quantum devices are rapidly becoming a reality, accessible to everyone over the Internet. This, in turn, is driving the development of quantum machine learning and variational quantum circuits.

RELATED CONTENT: How quantum computing will impact software development

The projects key features include:

AWS recently announced it would be joining the projects steering council for variational quantum computing and quantum machine learning. Our goal is to help build better tools for developers and researchers by bringing together ideas and concepts from machine learning (ML) and quantum computing (QC). Together with our partner Xanadu, we want to continue to evolve PennyLane as an open, community-driven project, and we are inviting contributors from QC, ML, and other fields to join us, the company wrote in a post.

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SD Times Open-Source Project of the Week: PennyLane - SDTimes.com

Google and D-Wave Systems say theyve achieved a new milestone in the world of quantum computing.

In a press release, D-Wave says its quantum device has far outpaced a classical computer in a direct competition to complete a difficult computational problem.

The device successfully modeled the behavior of a spinning two-dimensional quantum magnet, and was able to complete the simulation at breakneck speed.

In collaboration with scientists at Google, demonstrating a computational performance advantage, increasing with both simulation size and problem hardness, to over 3 million times that of corresponding classical methods.

Notably, this work was achieved on a practical application with real-world implications, simulating the topological phenomena behind the 2016 Nobel Prize in Physics.

Quantum devices leverage the unique properties of quantum physics to perform certain calculations at revolutionary speeds.

D-Wave says its study proves that quantum computers can more efficiently and effectively tackle tough simulations.

What we see is a huge benefit in absolute terms, with the scaling advantage in temperature and size that we would hope for.

Quantum computing threatens to break the cryptographic algorithms that keep the internet and crypto assets secure. Ripple CTO Davis Schwartz, says he believes developers have about eight years to develop quantum-proof methods to keep digital infrastructures secure.

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Google Teams With D-Wave in Massive Quantum Computing Leap, Cracking Simulation Problem - The Daily Hodl

Reality is something of a subjective topic. It is actually very difficult (at least for me) to decide what it really is. It is abundantly clear to me that it isnt the way we experience it although a good argument can be made that if it is different from what we experience it doesnt really matter. Something along the lines of the question If a tree falls in the woods and no one is around, does it make a sound?

I think of this nature of reality question often as I ponder the nature of the universe. And ponder it is, as there is not much science that can illuminate it directly at this point; only science that hints at the bigger picture. This portion of science is more akin to philosophy than what we know as hard science. Something more like what you would have found 500 years ago as the alchemists worked in their labs far out at the edge of knowledge where there can only be speculation.

The best place to play in this subjective realm is on the scale of the universe where everything is writ large and not that much is actually known. You have to understand that weve only known that there is a universe for a few thousand years and it takes a lot of time to build the mathematical framework to have a hope of understanding something that large. So we are left with educated guesses that arent a lot different than philosophical arguments. The main difference between the two realms is that in science, asking the qualitative questions probably leads eventually to quantitative answers. Or at least should.

So as long as were asking big questions lets start with a doozie: Is there only one universe? It turns out that there are a number of scenarios where it is possible that there are many of them.

The simple version of this comes about if we postulate that the universe is infinite and that stuff is spread out evenly (as it appears to be). If it is, we can only see so far out because of the age of what we take to be the universe and the fact that light goes fast but at a finite speed. The universe as we know it is about 13.8 billion years old, give or take. That means you can only see to 13.8 billion light years out as it takes light that long to get here (by light, I mean anything that acts like it, visible or not). If there are other clumps of stuff out past that, we cant know that at this point so, for practical purposes, there would be multiple, disjoint universes. At some point, the light from these things would reach us and wed see it likely as an expanding universe because wed start seeing further out and it would be hard to tell the difference between expansion and just seeing further.

So what might be said if the universe is not infinite? A finite universe is what science is pointing to at this time. Current theories assume that our universe started out in space (in our 4 dimensional universe, it isnt helpful or even useful to ask what space would be at that point). At some near infinitely small spot in space, the energy there changed to matter (matter and energy are the same thing and entirely interchangeable) creating a huge explosion with things moving faster than light in the first fraction of a second (you can violate the laws of physics if you do it fast enough). This state of movement has been dubbed inflation and happens so quickly that the resulting fireball spreads the stuff of the universe out reasonably smoothly except for the randomness that happens (things are mostly random) which would give rise to small clumpiness to the results. We see these results today as the cosmic background radiation and it has been mapped in very fine detail and agrees with theory on this so it is quite likely that inflation is how we should look at our current state of the universe. It would, if you could get outside it, look essentially like an expanding balloon.

The thing is, if ours could come into existence because of probability, then there really isnt any reason that another one couldnt come into existence by the same mechanism. If it did, we couldnt see it because itd be racing the other way faster than we could ever catch up to it. Along the same lines, if you can create two of these, why cant you create any number of them? In fact, given the finite probability of it happening at all, we should be creating them all the time and if thats the case, our particular universe would only be one of countless others forming constantly, none of which could see each other.

This scenario would also help physicists with a sticky problem: There is a branch of physics that is an attempt to describe on one equation all of physics called String Theory. This is something of a Holy Grail of physics for some time now. The trouble with it is that it is a multi-dimensional equation (more than our four) and has an astronomical number of equally valid solutions, not just our particular physical laws. If there are a whole lot of other universes, then it could be possible that each is a separate solution to the problem a valid set of physics that is different than ours. This would neatly solve this puzzle.

There are other possibilities involving things like quantum physics and parallel sheets of universes operating in separate dimensions all of which satisfy some set of curiosities or other. In fact there appear to be more reasons why there should be multiple universes than there are suggesting we would be living in the only one.

Things to ponder as you look up into the night sky. Are we alone? Are we even what we think we are?

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