Science world: AUSTRALIAN PHYSICISTS PROVED TAHT TIME TRAVEL IS POSSIBLE


Scientists from the University of Queensland have used photons (single particles of light) to simulate quantum particles travelling through time. The research is cutting edge and the results could be dramatic!

Their research, entitled “Experimental simulation of closed timelike curves “, is published in the latest issue of Nature Communications. The grandfather paradox states that if a time traveler were to go back in time, he could accidentally prevent his grandparents from meeting, and thus prevent his own birth.

However, if he had never been born, he could never have traveled back in time, in the first place. The paradoxes are largely caused by Einstein’s theory of relativity, and the solution to it, the Gödel metric.

How relativity works

Einstein’s theory of relativity is made up of two parts – general relativity and special relativity. Special relativity posits that space and time are aspects of the same thing, known as the space-time continuum, and that time can slow down or speed up, depending on how fast you are moving, relative to something else.

Gravity can also bend time, and Einstein’s theory of general relativity suggests that it would be possible to travel backwards in time by following a space-time path, i.e. a closed timeline curve that returns to the starting point in space, but arrives at an earlier time.

It was predicted in 1991 that quantum mechanics could avoid some of the paradoxes caused by Einstein’s theory of relativity, as quantum particles behave almost outside the realm of physics.

“The question of time travel features at the interface between two of our most successful yet incompatible physical theories – Einstein’s general relativity and quantum mechanics,” said Martin Ringbauer, a PhD student at UQ’s School of Mathematics and Physics and a lead author of the paper.

“Einstein’s theory describes the world at the very large scale of stars and galaxies, while quantum mechanics is an excellent description of the world at the very small scale of atoms and molecules.”

Simulating time travel

The scientists simulated the behavior of two photons interacting with each other in two different cases. In the first case, one photon passed through a wormhole and then interacted with its older self. In the second case, when a photon travels through normal space-time and interacts with another photon trapped inside a closed timeline curve forever.

“The properties of quantum particles are ‘fuzzy’ or uncertain to start with, so this gives them enough wiggle room to avoid inconsistent time travel situations,” said co-author Professor Timothy Ralph. “Our study provides insights into where and how nature might behave differently from what our theories predict.”

Although it has been possible to simulate time travel with tiny quantum particles, the same might not be possible for larger particles or atoms, which are groups of particles.

What Is Space?


It’s not what you think.

Ask a group of physicists and philosophers to define “space” and you will likely be stuck in a long discussion that involves deep-sounding but meaningless word combinations such as “the very fabric of space-time itself is a physical manifestation of quantum entropy concepts woven together by the universal nature of location.” On second thought, maybe you should avoid starting deep conversations between philosophers and physicists.

Is space just an infinite emptiness that underlies everything? Or is it the emptiness between things? What if space is neither of these but is a physical thing that can slosh around, like a bathtub full of water?

It turns out that the nature of space itself is one of the biggest and strangest mysteries in the universe. So get ready, because things are about to get … spacey.

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Space, It’s a Thing

Like many deep questions, the question of what space is sounds like a simple one at first. But if you challenge your intuition and reexamine the question, you discover that a clear answer is hard to find.

Most people imagine that space is just the emptiness in which things happen, like a big empty warehouse or a theater stage on which the events of the universe play out. In this view, space is literally the lack of stuff. It is a void that sits there waiting to be filled, as in “I saved space for dessert” or “I found a great parking space.”

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If you follow this notion, then space is something that can exist by itself without any matter to fill it. For example, if you imagine that the universe has a finite amount of matter in it, you could imagine traveling so far that you reach a point beyond which there is no more stuff and all the matter in the universe is behind you.1 You would be facing pure empty space, and beyond that, space might extend out to infinity. In this view, space is the emptiness that stretches out forever.

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Could Such a Thing Exist?

That picture of space is reasonable and seems to fit with our experience. But one lesson of history is that anytime we think something is obviously true (e.g., the Earth is flat, or eating a lot of Girl Scout cookies is good for you), we should be skeptical and take a step back to examine it carefully. More than that, we should consider radically different explanations that also describe the same experience. Maybe there are theories we haven’t thought of. Or maybe there are related theories where our experience of the universe is just one weird example. Sometimes the hard part is identifying our assumptions, especially when they seem natural and straightforward.

In this case, there are other reasonable-sounding ideas for what space could be. What if space can’t exist without matter—what if it’s nothing more than the relationship between matter? In this view, you can’t have pure “empty space” because the idea of any space at all beyond the last piece of matter doesn’t make any sense. For example, you can’t measure the distance between two particles if you don’t have any particles. The concept of “space” would end when there are no more matter particles left to define it. What would be beyond that? Not empty space.

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That is a pretty weird and counterintuitive way of thinking about space, especially given that we have never experienced the concept of non-space. But weird never stood in the way of physics, so keep an open mind.

Which Space Is the Place?

Which of these ideas about space is correct? Is space like an infinite void waiting to be filled? Or does it only exist in the context of matter?

It turns out that we are fairly certain that space is neither of these things. Space is definitely not an empty void and it is definitely not just a relationship between matter. We know this because we have seen space do things that fit neither of those ideas. We have observed space bend and ripple and expand.

This is the part where your brain goes, “Whaaaaat … ?”

If you are paying attention, you should be a little confused when you read the phrases “bending of space” and “expanding of space.” What could that possibly mean? How does it make any sense? If space is an idea, then it can’t be bent or expanded any more than it can be chopped into cubes and sautéed with cilantro.2 If space is our ruler for measuring the location of stuff, how do you measure the bending or expanding of space?

Good questions! The reason this idea of space bending is so confusing is that most of us grow up with a mental picture of space as an invisible backdrop in which things happen. Maybe you imagine space to be like 
that theater stage we mentioned before, with hard wooden planks as a
 floor and rigid walls on all sides. And maybe you imagine that
 nothing in the universe could bend that stage because this abstract frame is not part of the universe but something that contains the universe.

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Unfortunately, that is where your mental picture goes wrong. To make sense of general relativity and think about modern ideas of space, you have to give up the idea of space as an abstract stage and accept that it is a physical thing. You have to imagine that space has properties and behaviors, and that it reacts to the matter in the universe. You can pinch space, squeeze it, and, yes, even fill it with cilantro.3

At this point, your brain might be sounding “what the #@#$?!?!” nonsense alarms. That is totally understandable. Prepare to bear with us, because the real craziness is yet to come. Your nonsense alarms will be exhausted by the time we’re done. But we need to unpack these concepts carefully to understand the ideas here and appreciate the truly strange and basic mysteries about space that remain unanswered.

Space Goo, You’re Swimming in It

How can space be a physical thing that ripples and bends, and what does that mean?

It means that instead of being like an empty room (a really big room) space is more like a huge blob of thick goo. Normally, things can move around in the goo without any problems, just like we can move around a room full of air without noticing all the air particles. But under certain circumstances, this goo can bend, changing the way that things move through it. It can also squish and make waves, changing the shape of the things inside it.

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This goo (we’ll call it “space goo”) is not a perfect analogy for the nature of space, but it’s an analogy that helps you imagine that the space you are sitting in right now at this moment is not necessarily fixed and abstract.4 Instead, you are sitting in some concrete thing, and that thing can stretch or jiggle or distort in ways that you may not be perceiving.

Maybe a ripple of space just passed through you. Or maybe we are being stretched in an odd direction at this moment and don’t even know it. In fact, we didn’t even notice until recently that the goo did anything but sit there, goo-ing nowhere, which is why we confused it with nothingness.

So what can this space goo do? It turns out it can do a lot of weird things.

First, space can expand. Let’s think carefully for a minute about what it means for space to expand. That means things get farther apart from each other without actually moving through the goo. In our analogy, imagine that you are sitting in the goo, and suddenly the goo started growing and expanding. If you were sitting across from another person, that person would now be farther away from you without either of you having moved relative to the goo.

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How could we know that the goo expanded? Wouldn’t a ruler we use to measure the goo alsoexpand? It’s true that the space between all the atoms in the ruler would expand, pulling them apart. And if our ruler was made out of extra-soft taffy, it would also expand. But if you use a rigid ruler, all of its atoms would hold on to one another tightly (with electromagnetic forces), and the ruler would stay the same length, allowing you to notice that more space was created.

And we know that space can expand because we have seen it expanding—this is how dark energy was discovered. We know that in the early universe space expanded and stretched at shocking rates, and that a similar expansion is still happening today.

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We also know that space can bend. Our goo can be squished and deformed just like taffy can. We know this because in Einstein’s theory of general relativity that’s what gravity is: the bending of space.5 When something has mass, it causes the space around it to distort and change shape.

When space changes shape, things no longer move through it the way you might first imagine. Rather than moving in a straight line, a baseball passing through a blob of bent goo will curve along with it. If the goo is severely distorted by something heavy, like a bowling ball, the baseball might even move in a loop around it—the same way the moon orbits the Earth, or the Earth orbits the sun.

And this is something we can actually see with our naked eyes! Light, for example, bends its path when it passes near massive objects like our sun or giant blobs of dark matter. If gravity was just a force between objects with mass—rather than the bending of space—then it shouldn’t be able to pull on photons, which have no mass. The only way to explain how light’s path can be bent is if it’s the space itself that is bending.

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Finally, we know that space can ripple. This is not too far-fetched given that we know that space can stretch and bend. But what is interesting is that the stretching and bending can propagate across our space goo; this is called a gravitational wave. If you cause a sudden distortion of space, that distortion will radiate outward like a sound wave or a ripple inside of a liquid. This kind of behavior could only happen if space has a certain physical nature to it and is not just an abstract concept or pure emptiness.

We know this rippling behavior is real because (a) general relativity predicts these ripples, and (b) we have actually sensed these ripples. Somewhere in the universe, two massive black holes were locked in a frenzied spin around each other, and as they spun, they caused huge distortions in space that radiated outward into space. Using very sensitive equipment, we detected those space ripples here on Earth.

You can think of these ripples as waves of space stretching and compressing. Actually, when a space ripple passes through, space shrinks in one direction and expands in another direction.

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This Sounds Ridic-goo-lous. Are You Sure?

As crazy as it may sound that space is a thing and not just pure emptiness, this is what our experience of the universe tells us. Our experimental observations make it pretty clear that the distance between objects in space is not measured on an invisible abstract backdrop but depends on the properties of the space goo in which we all live, eat cookies, and chop cilantro.

But while thinking of space as a dynamic thing with physical properties and behaviors might explain weird phenomena like space bending and stretching, it only leads to more questions.

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A Nonlinear History of Time Travel

I doubt that any phenomenon, real or imagined, has inspired more perplexing, convoluted, and ultimately futile philosophical analysis than time travel has. (Some possible contenders, determinism and free will, are bound up anyway in the arguments over time travel.) In…READ MORE

For example, you might be tempted to say that what we used to call space should now be called physics goo (“phgoo”) but that this goo has to be in something, which we could now call space again. That would be clever, but as far as we know (which to date is not very far), the goo does not need to be in anything else. When it bends and curves, this is intrinsic bending that changes the relationships between parts of space, not the bending of the goo relative to some larger room that it fills.

But just because our space goo doesn’t need to sit inside of something else doesn’t mean that it is not sitting inside something else. Perhaps what we call space is actually sitting inside some larger “superspace.”6 And perhaps that superspace is like an infinite emptiness, but we have no idea.

Is it possible to have parts of the universe without space? In other words, if space is a goo, is it possible for there to be not-goo, or the absence of goo? The meaning of those concepts is not very clear because all of our physical laws assume the existence of space, so what laws could operate outside of space? We have no idea.

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The fact is that this new understanding of space as a thing has come recently, and we are at the very beginning of understanding what space is. In many ways, we are still hobbled by our intuitive notions. These notions served us well when early men and women were hunting for game and foraging for prehistoric cilantro, but we need to break the shackles of these concepts and realize that space is very different from what we imagined.

Straight Thinking about Bent Space

If your brain is not yet hurting from all these gooey space-bending concepts, here is another mystery about space: Is space flat or curved (and if it’s curved, which way does it curve)?

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These are crazy questions, but they are not 
that hard to ask once you accept the notion 
that space is malleable. If space can bend around 
objects with mass, could it have an overall curvature to it? It’s like asking if our goo is flat: You know that it can jiggle and deform if you push any point on it, but does it sag overall? Or does it sit perfectly straight? You can ask these questions about space, too.

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Answering these questions about space would have an enormous impact on our notion of the universe. For example, if space is flat, it means that if you travel in one direction forever you could just keep going, possibly to infinity.

But if space is curved, then other interesting things might happen. If space has an overall positive curvature, then going off in one direction might actually make you loop around and come back to the same spot from the opposite direction! This is useful information if, for example, you don’t like the idea of people sneaking up behind you.

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Explaining the idea of curved space is very difficult because our brains are simply not well equipped to visualize concepts like these. Why would they be? Most of our everyday experience (like evading predators or finding our keys) deals with a three-dimensional world that seems pretty fixed (although if we are ever attacked by advanced aliens that can manipulate the curvature of space, we hope we, too, can figure it out quickly).

What would it mean for space to have a curvature? One way to visualize it is to pretend for a second that we live in a two-dimensional world, like being trapped in a sheet of paper. That means we can only move in two directions. Now, if that sheet we live in lies perfectly straight, we say that our space is flat.

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But if for some reason that sheet of paper is bent, then we say that the space is curved.

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And there are two ways that the paper can be bent. It can all be curved in one direction (called “positive curvature”) or it can be bent in different directions like a horse saddle or a Pringles potato chip (this is called “negative curvature” or “breaking your diet”).

Here is the cool part: if we find out that space is flat everywhere, it means that the sheet of paper (space) could potentially go on forever. But if we find out that space has a positive curvature everywhere, then there’s only one shape that has positive curvature everywhere: a sphere. Or to be more technical, a spheroid (i.e., a potato). This is one way in which our universe could loop around itself. We could all be living in the three-dimensional equivalent of a potato, which means that no matter which direction you go you end up coming back around to the same spot.

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In this case, it turns out that we do have an answer, which is that space does appear to be “pretty flat,” as in space is within 0.4 percent of being flat. Scientists, through two very different methods, have calculated that the curvature of space (at least the space we can see) is very nearly zero.

What are these two ways? One of the ways is by measuring triangles. An interesting thing about curvature is that triangles in a curved space don’t follow the same rules as triangles in flat space. Think back to our sheet-of-paper analogy. A triangle drawn on a flat sheet of paper is going to look different than a triangle drawn on a curved surface.

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Scientists have done the equivalent of measuring triangles drawn in our three-dimensional universe by looking at a picture of the early universe  and studying the spatial relationship between different points on that picture. And what they found was that the triangles they measured correspond to those of flat space.

The other way in which we know that space is basically flat is by looking at the thing that causes space to curve in the first place: the energy in the universe. According to general relativity, there is a specific amount of energy in the universe (energy density, actually) that will cause space to bend in one direction or the other. It turns out that the amount of energy density that we can measure in our universe is exactly the right amount needed to cause the space that we can see to not bend at all (within a margin of error of 0.4 percent).

Some of you might be disappointed to learn we don’t live in a cool three-dimensional cosmic potato that loops around if you go in one direction forever. Sure, who hasn’t dreamed of doing Evel Knievel–style spins around the entire universe on a rocket motorcycle? But instead of feeling disappointed by the fact that we live in a boring flat universe, you might want to be a little intrigued. Why? Because as far as we know, the fact that we live in a flat universe is a gigantic cosmic-level coincidence.

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Think about it. All the mass and energy in the universe is what gives space its curvature (remember that mass and energy distort space), and if we had just a little bit more mass and energy than we have right now, space would have curved one way. And if we had just a little bit less than we have right now, space would have curved the other way. But we seem to have just the right amount to make space perfectly flat as far as we can tell. In fact, the exact amount is about five hydrogen atoms per cubic meter of space. If we had had six hydrogen atoms per cubic meter of space, or four, the entire universe would have been a lot different (curvier and sexier, but different).

And it gets stranger. Since the curvature of space affects the motion of matter, and matter affects the curvature of space, there are feedback effects. This means that if there had been just a little too much matter or not quite enough matter in the early days of the universe, so that we weren’t right at this critical density to make space flat, then it would have pushed things even farther from flat. For space to be pretty flat now means that it had to be extremely flat in the early universe, or there has to be something else keeping it flat.

This is one of the biggest mysteries about space. Not only do we not know what exactly space is, we also don’t know why it happens to be the way it is. Our knowledge in this matter appears to fall … flat.

The Shape of Space

The curvature of space is not the only thing we have deep questions about when it comes to the nature of space. Once you accept that space is not an infinite void but rather a maybe-infinite physical thing with properties, you can ask all kinds of strange questions about it. For example, what is the size and shape of space?

The size and shape of space tell us how much space there is and how it is connected to itself. You might think that since space is flat, and not shaped like a potato or a horse saddle (or a potato on a horse saddle), the idea of the size and shape of space makes no sense. After all, if space is flat, it means that it must go on forever, right? Not necessarily!

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Space can be flat and infinite. Or it could be flat and have an edge to it. Or, even stranger, it could be flat and still loop around itself.

How can space have an edge? Actually, there’s no reason why space can’t have a boundary even if it is flat. For example, a disc is a flat two-dimensional surface with a smooth continuous edge. Perhaps three-dimensional space also has a boundary at some point thanks to some strange geometric property at its edges.

Even more intriguing is the 
possibility that space can be flat
 and still loop around itself. It
 would be like playing one of
 those video games (like Asteroids or Pac-Man) where if you move 
beyond the edge of the screen 
you simply appear on the other side. Space might be able to connect with itself in some way that we are not completely aware of yet. For example, wormholes are theoretical predictions of general relativity. In a wormhole, two different points in space that are far apart can be connected to each other. What if the edges of space are all connected together in a similar way? We have no idea.

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Quantum Space

Finally, you can ask whether space is actually made up of tiny discrete bits of space, like the pixels on a TV screen, or infinitely smooth, such that there are an infinite number of places you can be between two points in space?

Scientists in ancient times might not have imagined that air is made up of tiny discrete molecules. After all, air appears to be continuous. It acts to fill any volume and it has interesting dynamical properties (like wind and weather). Yet we know that all these things we love about air (how it brushes gently against your cheek in a cool summer breeze or how it keeps us from asphyxiating) are actually the combined behavior of billions of individual air molecules, not the fundamental properties of the individual molecules themselves.

The smooth space scenario would appear to make more sense to us. After all, our experience of moving through space is that we glide through it in an easy, continuous way. We don’t jump from pixel to pixel in a jerky fashion the way a video-game character does when it moves across the screen.

Or do we?

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Given our current understanding of the universe, it would actually be more surprising if space turned out to be infinitely smooth. That’s because we know that everything else is quantized. Matter is quantized, energy is quantized, forces are quantized, Girl Scout cookies are quantized. Moreover, quantum physics suggests that there might be a smallest distance that even makes sense, which is about 10−35 meters.7 So from a quantum mechanical perspective, it would make sense if space was quantized. But, again, we really have no idea.

But having no idea hasn’t stopped physicists from imagining crazy possibilities! If space is quantized, that means that when we move across space we are actually jumping from small little locations to other small little locations. In this view, space is a network of connected nodes, like the stations in a subway system. Each node represents a location, and the connections between nodes represent the relationships between these locations (i.e., which one is next to which other one). This is different from the idea that space is just the relationship between matter, because these nodes of space can be empty and still exist.

Interestingly enough, these nodes would not need to sit inside a larger space or framework. They could just … be. In this scenario, what we call space would just be the relationships between the nodes, and all the particles in the universe would just be properties of this space rather than elements in it. For example, they might be vibrational modes of these nodes.

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This is not as far-fetched as it sounds. The current theory of particles is based on quantum fields that fill all of space. A field just means there is a number, or a value, associated with every point in that space. In this view, particles are just excited states of these fields. So we are not too far from this kind of theory already.

By the way, physicists love this type of idea, where something that seems fundamental to us (like space) comes out accidentally from something deeper. It gives them the sense that we have peeked behind the curtain to discover a deeper layer of reality. Some even suspect that the relationships between nodes of space are formed by the quantum entanglement of particles, but this is mathematical speculation by a bunch of overcaffeinated theorists.

The Mysteries of Space

If
 you have read this far and either understood it deeply or just turned your nonsense alarm to mute, then we should not hesitate to explore the craziest concept about space (yes, it gets crazier).

If space is a physical thing—not a backdrop or frame—with dynamic properties such as twists and ripples, perhaps even built out of quantized bits of space, then we have to wonder: What else can space do?

Like air, perhaps it has different states and phases. Under extreme conditions, maybe it can arrange itself in very unexpected ways or have weird unexpected properties in the same way that air behaves differently whether it’s in liquid, gas, or solid form. Perhaps the space we know and love and occupy (sometimes more than we’d like) is only one rare type of space and there are other types of space out there in the universe just waiting for us to figure out how to create and manipulate them.

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The most intriguing tool we have to answer this question is the fact that space is distorted by mass and energy. In order to understand what space is and what it can do, our best bet is to push it to extremes by looking carefully at places where cosmically huge masses are squeezing and straining it: black holes. If we could explore near black holes, we might see space shredded and chopped in ways that cause our nonsense alarms to explode.

And the exciting thing is that we are closer than ever to being able to probe these extreme deformations of space. Whereas before we were deaf to the ripples of gravitational waves moving through the universe, we now have the ability to listen in to the cosmic events that are shaking and disturbing the goo of space. Perhaps in the near future we will understand more about the exact nature of space and get at these deep questions that are literally all around us.

So don’t space out. And save some space in your brain for the answers.

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Jorge Cham is the creator of the popular online comic Piled Higher and Deeper, also known as PHD Comics. He earned his Ph.D. in robotics at Stanford.

Daniel Whiteson is a professor of experimental physics at the University of California, Irvine, and a fellow of the American Physical Society. He conducts research using the Large Hadron Collider at CERN.

Source:http://nautil.us

Reality Doesn’t Exist Until We Measure It, Quantum Experiment Confirms


Australian scientists have recreated a famous experiment and confirmed quantum physics’s bizarre predictions about the nature of reality, by proving that reality doesn’t actually exist until we measure it – at least, not on the very small scale.

That all sounds a little mind-meltingly complex, but the experiment poses a pretty simple question: if you have an object that can either act like a particle or a wave, at what point does that object ‘decide’?

Our general logic would assume that the object is either wave-like or particle-like by its very nature, and our measurements will have nothing to do with the answer. But quantum theory predicts that the result all depends on how the object is measured at the end of its journey. And that’s exactly what a team from the Australian National University has now found.

“It proves that measurement is everything. At the quantum level, reality does not exist if you are not looking at it,” lead researcher and physicist Andrew Truscott said in a press release.

Known as John Wheeler’s delayed-choice thought experiment, the experiment was first proposed back in 1978 using light beams bounced by mirrors, but back then, the technology needed was pretty much impossible. Now, almost 40 years later, the Australian team has managed to recreate the experiment using helium atoms scattered by laser light.

“Quantum physics predictions about interference seem odd enough when applied to light, which seems more like a wave, but to have done the experiment with atoms, which are complicated things that have mass and interact with electric fields and so on, adds to the weirdness,” said Roman Khakimov, a PhD student who worked on the experiment.

To successfully recreate the experiment, the team trapped a bunch of helium atoms in a suspended state known as a Bose-Einstein condensate, and then ejected them all until there was only a single atom left.

This chosen atom was then dropped through a pair of laser beams, which made a grating pattern that acted as a crossroads that would scatter the path of the atom, much like a solid grating would scatter light.

They then randomly added a second grating that recombined the paths, but only after the atom had already passed the first grating.

When this second grating was added, it led to constructive or destructive interference, which is what you’d expect if the atom had travelled both paths, like a wave would. But when the second grating was not added, no interference was observed, as if the atom chose only one path.

The fact that this second grating was only added after the atom passed through the first crossroads suggests that the atom hadn’t yet determined its nature before being measured a second time.

So if you believe that the atom did take a particular path or paths at the first crossroad, this means that a future measurement was affecting the atom’s path, explained Truscott. “The atoms did not travel from A to B. It was only when they were measured at the end of the journey that their wave-like or particle-like behaviour was brought into existence,” he said.

Although this all sounds incredibly weird, it’s actually just a validation for the quantum theory that already governs the world of the very small. Using this theory, we’ve managed to develop things like LEDs, lasers and computer chips, but up until now, it’s been hard to confirm that it actually works with a lovely, pure demonstration such as this one.

Source: Nature Physics.

Physicists Leak Evidence That Approve Elon Musk’s Theory – The Universe Is A “Computer” Simulation


Philosophers have long proposed that given that any civilization of remarkable intelligence and size would likely create simulations of other universes, and likely a great number of simulations), it may be that there are more simulated universes than real, and consequently more simulated worlds than real.

And now, some physicists say, we just may have the evidence that our universe is just one such simulation.

A team of researchers led by Silas Beane at Germany’s University of Bonn, have just released a paper titled “Constraints on the Universe as a Numerical Simulation,” in which they make the argument that any such simulation of a universe must, by nature of a simulation, put limits on the physical laws of that universe.

As Technology Review explains, making the same point, “the problem with all simulations is that the laws of physics, which appear continuous, have to be superimposed onto a discrete three dimensional lattice which advances in steps of time.”

For example, if a simulation, there would be clear limits on the amount of energy particles within the program can contain. And, researchers say, there’s evidence of exactly such limits in our universe.

In particular, we can consider what is known as the Greisen-Zatsepin-Kuzmin, or GZK cut off – which is a clear limit to the energy an cosmic ray particle can hold. Scientists argue this is the result of interactions with cosmic background radiation. Beane’s research team, however, argues that it is also exactly what you would expect from a simulation’s limits.

Of course, you should read the paper yourself to get a better feel for the science – but the argument is certainly an interesting one, and will only fuel more philosophers’ arguments about the nature of our world.

For more, consider what Elon Musk has to say about the theory in the video below:

Sources:

In a World-First, Scientists Have Achieved ‘Liquid Light’ at Room Temperature


A Frankenstein mash-up of light and matter.

For the first time, physicists have achieved ‘liquid light’ at room temperature, making this strange form of matter more accessible than ever.

This matter is both a superfluid, which has zero friction and viscosity, and a kind of Bose-Einstein condensate – sometimes described as the fifth state of matter – and it allows light to actually flow around objects and corners.

Regular light behaves like a wave, and sometimes like a particle, always travelling in a straight line. That’s why your eyes can’t see around corners or objects. But under extreme conditions, light can also act like a liquid, and actually flow around objects.

Bose-Einstein condensates are interesting to physicists because in this state, the rules switch from classical to quantum physics, and matter starts to take on more wave-like properties.

They are formed at temperatures close to absolute zero and exist for only fractions of a second.

But in this study, researchers report making a Bose-Einstein condensate at room temperature by using a Frankenstein mash-up of light and matter.

“The extraordinary observation in our work is that we have demonstrated that superfluidity can also occur at room-temperature, under ambient conditions, using light-matter particles called polaritons,” says lead researcher Daniele Sanvitto, from the CNR NANOTEC Institute of Nanotechnology in Italy.

Creating polaritons involved some serious equipment and nanoscale engineering.

The scientists sandwiched a 130-nanometre-thick layer of organic molecules between two ultra-reflective mirrors, and blasted it with a 35 femtosecond laser pulse (1 femtosecond is a quadrillionth of a second).

“In this way, we can combine the properties of photons – such as their light effective mass and fast velocity – with strong interactions due to the electrons within the molecules,” says one of the team, Stéphane Kéna-Cohen from École Polytechnique de Montreal in Canada.

The resulting ‘super liquid’ had some strange properties.

Under normal conditions, when liquid flows, it creates ripples and swirls – but that’s not the case for a superfluid. 

As you can see below, the flow of polaritons is disturbed like waves under regular circumstances, but not in the superfluid:

liquid liquid lightThe flow of polaritons encounters an obstacle in non-superfluid (top) and superfluid (bottom). Credit: Polytechnique Montreal

“In a superfluid, this turbulence is suppressed around obstacles, causing the flow to continue on its way unaltered,” says Kéna-Cohen.

The researchers say the results pave the way not only to new studies of quantum hydrodynamics, but also to room-temperature polariton devices for advanced future technology, such as the production of super-conductive materials for devices such as LEDs, solar panels, and lasers.

“The fact that such an effect is observed under ambient conditions can spark an enormous amount of future work,” says the team.

“Not only to study fundamental phenomena related to Bose-Einstein condensates, but also to conceive and design future photonic superfluid-based devices where losses are completely suppressed and new unexpected phenomena can be exploited.”

Source:Nature Physics.

After 100 years of debate, hitting absolute zero has been declared mathematically impossible.


The third law of thermodynamics finally gets its proof.

After more than 100 years of debate featuring the likes of Einstein himself, physicists have finally offered up mathematical proof of the third law of thermodynamics, which states that a temperature of absolute zero cannot be physically achieved because it’s impossible for the entropy (or disorder) of a system to hit zero.

While scientists have long suspected that there’s an intrinsic ‘speed limit’ on the act of cooling in our Universe that prevents us from ever achieving absolute zero (0 Kelvin, -273.15°C, or -459.67°F), this is the strongest evidence yet that our current laws of physics hold true when it comes to the lowest possible temperature.

 “We show that you can’t actually cool a system to absolute zero with a finite amount of resources and we went a step further,” one of the team, Lluis Masanes from University College London, told IFLScience.

“We then conclude that it is impossible to cool a system to absolute zero in a finite time, and we established a relation between time and the lowest possible temperature. It’s the speed of cooling.”

What Masanes is referring to here are two fundamental assumptions that the third law of thermodynamics depends on for its validity.

The first is that in order to achieve absolute zero in a physical system, the system’s entropy has to also hit zero.

The second rule is known as the unattainability principle, which states that absolute zero is physically unreachable because no system can reach zero entropy.

The first rule was proposed by German chemist Walther Nernst in 1906, and while it earned him a Nobel Prize in Chemistry, heavyweights like Albert Einstein and Max Planck weren’t convinced by his proof, and came up with their own versions of the cooling limit of the Universe.

 This prompted Nernst to double down on his thinking and propose the second rule in 1912, declaring absolute zero to be physically impossible.

Together, these rules are now acknowledged as the third law of thermodynamics, and while this law appears to hold true, its foundations have always seemed a little rocky – when it comes to the laws of thermodynamics, the third one has been a bit of a black sheep.

“[B]ecause earlier arguments focused only on specific mechanisms or were crippled by questionable assumptions, some physicists have always remained unconvinced of its validity,” Leah Crane explains for New Scientist.

In order to test how robust the assumptions of the third law of thermodynamics actually are in both classical and quantum systems, Masanes and his colleague Jonathan Oppenheim decided to test if it is mathematically possible to reach absolute zero when restricted to finite time and resources.

Masanes compares this act of cooling to computation – we can watch a computer solve an algorithm and record how long it takes, and in the same way, we can actually calculate how long it takes for a system to be cooled to its theoretical limit because of the steps required to remove its heat.

You can think of cooling as effectively ‘shovelling’ out the existing heat in a system and depositing it into the surrounding environment.

How much heat the system started with will determine how many steps it will take for you to shovel it all out, and the size of the ‘reservoir’ into which that heat is being deposited will also limit your cooling ability.

Using mathematical techniques derived from quantum information theory – something that Einstein had pushed for in his own formulations of the third law of thermodynamics – Masanes and Oppenheim found that you could only reach absolute zero if you had both infinite steps and an infinite reservoir.

And that’s not exactly something any of us are going to get our hands on any time soon.

This is something that physicists have long suspected, because the second law of thermodynamics states that heat will spontaneously move from a warmer system to a cooler system, so the object you’re trying to cool down will constantly be taking in heat from its surroundings.

And when there’s any amount of heat within an object, that means there’s thermal motion inside, which ensures some degree of entropy will always remain.

This explains why, no matter where you look, every single thing in the Universe is moving ever so slightly – nothing in existence is completely still according to the third law of thermodynamics.

The researchers say they “hope the present work puts the third law on a footing more in line with those of the other laws of thermodynamics”, while at the same time presenting the fastest theoretical rate at which we can actually cool something down.

In other words, they’ve used maths to quantify the steps of cooling, allowing researchers to define set speed limit for how cold a system can get in a finite amount of time.

And that’s important, because even if we can never reach absolute zero, we can get pretty damn close, as NASA demonstrated recently with its Cold Atom Laboratory, which can hit a mere billionth of a degree above absolute zero, or 100 million times colder than the depths of space.

At these kinds of temperatures, we’ll be able to see strange atomic behaviours that have never been witnessed before. And being able to remove as much heat from a system is going to be crucial in the race to finally build a functional quantum computer.

And the best part is, while this study has taken absolute zero off the table for good, no one has even gotten close to reaching the temperatures or cooling speeds that it’s set as the physical limits – despite some impressive efforts of late.

“The work is important – the third law is one of the fundamental issues of contemporary physics,” Ronnie Kosloff at the Hebrew University of Jerusalem, Israel who was not involved in the study, told New Scientist.

“It relates thermodynamics, quantum mechanics, information theory – it’s a meeting point of many things.”

Source: Nature Communications.

New Research Shows That Time Travel Is Mathematically Possible


IN BRIEF

Physicists have developed a new mathematical model that shows how time travel is theoretically possible. They used Einstein’s Theory of General Relativity as a springboard for their hypothetical device, which they call a Traversable Acausal Retrograde Domain in Space-time (TARDIS).

BENDING TIME

Even before Einstein theorized that time is relative and flexible, humanity had already been imagining the possibility of time travel. In fact, science fiction is filled with time travelers. Some use metahuman abilities to do so, but most rely on a device generally known as a time machine. Now, two physicists think that it’s time to bring the time machine into the real world — sort of.

The Future According to H. G. Wells [INFOGRAPHIC]

“People think of time travel as something as fiction. And we tend to think it’s not possible because we don’t actually do it,” Ben Tippett, a theoretical physicist and mathematician from the University of British Columbiasaid in a UBC news release. “But, mathematically, it is possible.”

Essentially, what Tippet and University of Maryland astrophysicist David Tsang developed is a mathematical formula that uses Einstein’s General Relativity theory to prove that time travel is possible, in theory. That is, time travel fitting a layperson’s understanding of the concept as moving “backwards and forwards through time and space, as interpreted by an external observer,” according to the abstract of their paper, which is published in the journal Classical and Quantum Gravity.

Oh, and they’re calling it a TARDIS — yes, “Doctor Who” fans, hurray! — which stands for a Traversable Acausal Retrograde Domain in Space-time.

FEASIBLE BUT NOT POSSIBLE. YET.

“My model of a time machine uses the curved space-time to bend time into a circle for the passengers, not in a straight line,” Tippet explained. “That circle takes us back in time.” Simply put, their model assumes that time could curve around high-mass objects in the same way that physical space does in the universe.

For Tippet and Tsang, a TARDIS is a space-time geometry “bubble” that travels faster than the speed of light. “It is a box which travels ‘forwards’ and then ‘backwards’ in time along a circular path through spacetime,” they wrote in their paper.

Unfortunately, it’s still not possible to construct such a time machine. “While is it mathematically feasible, it is not yet possible to build a space-time machine because we need materials — which we call exotic matter — to bend space-time in these impossible ways, but they have yet to be discovered,” Tippet explained.

Image credit: Tippet and Yang

Indeed, their work isn’t the first to suggest that time traveling can be done. Various other experiments, including those that rely on photon stimulation, suggest that time travel is feasible. Another theory explores the potential particles of time.

However, some think that a time machine wouldn’t be feasible because time traveling itself isn’t possible. One points to the intimate connection between time and energy as the reason time traveling is improbable. Another suggests that time travel isn’t going to work because there’s no future to travel to yet.

Whatever the case may be, there’s one thing that these researchers all agree on. As Tippet put it, “Studying space-time is both fascinating and problematic.”

Metallic Hydrogen Is The Holy Grail Of High-Pressure Physics, And One Team Says They’ve Made It


For more than 80 years, physicists have dreamed of the ability to produce metallic hydrogen. In 2016, one team claimed to have finally done it. To understand why science wants metallic hydrogen so badly—and why the 2016 announcement caused so much drama—you have to first understand the potential of this elusive material.

The heart of a diamond anvil cell.

To Infinity And Beyond

 We all know hydrogen: it’s the first element on the periodic table, and the most abundant in the universe. It appears most commonly as a gas. If you cool it to very low temperatures, as rocket scientists are wont to do, it becomes a liquid. Liquid hydrogen makes great rocket fuel because it’s light and it burns with extreme intensity. Specifically, when you combine it with something like liquid oxygen, liquid hydrogen yields the highest specific impulse—efficiency, basically—of any rocket fuel.

You can imagine, then, what you could accomplish if you squeezed hydrogen with enough pressure to turn it into a metal. High-pressure researchers first predicted this was possible in 1935. They theorized that not only would metallic hydrogen conduct electricity (that’s what metals do, after all) but it might do it without resistance, which would mean it was a superconductor. What’s more, it could do that at room temperature—no supercooling necessary for this supermaterial! But that’s not all it could help accomplish, as Nature’s Davide Castelvecchi points out: “By making metallic hydrogen, physicists might also be able to explore planetary science at their lab bench: gas-giant planets such as Jupiter are theorized to have metallic hydrogen in their cores, which would perhaps explain how they can sustain a magnetic field.”

More Like Metallic Hy-Drama

 In October of 2016, two physicists announced that they had actually squeezed hydrogen between diamonds at such low temperatures and high pressure that it turned metallic. As Gizmodo reports, “As the scientists cranked up the pressure, they observed transparent hydrogen turn black. Finally, at a pressure 5 million times our own air pressure, the hydrogen turned reflective. The researchers presented this as proof that the hydrogen atoms had arranged into a regular, 3D structure like a metal.” Other physicists did not take this lying down. “I don’t think the paper is convincing at all,” French physicist Paul Loubeyre told Nature. “We express a doubt that [the physicists] were even in a close vicinity of the claimed pressure,” wrote Carnegie Institute staff scientist Alexander Goncharov in a response paper.
Why are other scientists so skeptical? There are a few reasons. For one thing, there’s little evidence that the material was even hydrogen in the first place; it could have been the aluminum oxide that coats the tips of the diamonds themselves. The researchers also took just a single measurement of the sample at its very highest pressure, which makes it hard to see how the pressure changed as the hydrogen turned metallic. Worst of all, further testing led them to lose the sample. “Basically, it’s disappeared,” team leader Isaac F. Silvera told ScienceAlert. “It’s either someplace at room pressure, very small, or it just turned back into a gas. We don’t know.” And you thought losing your keys was rough.

Metallic Hydrogen Is The Holy Grail Of High-Pressure Physics, And One Team Says They’ve Made It


For more than 80 years, physicists have dreamed of the ability to produce metallic hydrogen. In 2016, one team claimed to have finally done it. To understand why science wants metallic hydrogen so badly—and why the 2016 announcement caused so much drama—you have to first understand the potential of this elusive material.

The heart of a diamond anvil cell.
 We all know hydrogen: it’s the first element on the periodic table, and the most abundant in the universe. It appears most commonly as a gas. If you cool it to very low temperatures, as rocket scientists are wont to do, it becomes a liquid. Liquid hydrogen makes great rocket fuel because it’s light and it burns with extreme intensity. Specifically, when you combine it with something like liquid oxygen, liquid hydrogen yields the highest specific impulse—efficiency, basically—of any rocket fuel.

You can imagine, then, what you could accomplish if you squeezed hydrogen with enough pressure to turn it into a metal. High-pressure researchers first predicted this was possible in 1935. They theorized that not only would metallic hydrogen conduct electricity (that’s what metals do, after all) but it might do it without resistance, which would mean it was a superconductor. What’s more, it could do that at room temperature—no supercooling necessary for this supermaterial! But that’s not all it could help accomplish, as Nature’s Davide Castelvecchi points out: “By making metallic hydrogen, physicists might also be able to explore planetary science at their lab bench: gas-giant planets such as Jupiter are theorized to have metallic hydrogen in their cores, which would perhaps explain how they can sustain a magnetic field.”

More Like Metallic Hy-Drama

In October of 2016, two physicists announced that they had actually squeezed hydrogen between diamonds at such low temperatures and high pressure that it turned metallic. As Gizmodo reports, “As the scientists cranked up the pressure, they observed transparent hydrogen turn black. Finally, at a pressure 5 million times our own air pressure, the hydrogen turned reflective. The researchers presented this as proof that the hydrogen atoms had arranged into a regular, 3D structure like a metal.” Other physicists did not take this lying down. “I don’t think the paper is convincing at all,” French physicist Paul Loubeyre told Nature. “We express a doubt that [the physicists] were even in a close vicinity of the claimed pressure,” wrote Carnegie Institute staff scientist Alexander Goncharov in a response paper.

Why are other scientists so skeptical? There are a few reasons. For one thing, there’s little evidence that the material was even hydrogen in the first place; it could have been the aluminum oxide that coats the tips of the diamonds themselves. The researchers also took just a single measurement of the sample at its very highest pressure, which makes it hard to see how the pressure changed as the hydrogen turned metallic. Worst of all, further testing led them to lose the sample. “Basically, it’s disappeared,” team leader Isaac F. Silvera told ScienceAlert. “It’s either someplace at room pressure, very small, or it just turned back into a gas. We don’t know.” And you thought losing your keys was rough.

Did Scientists Really Make Metallic Hydrogen?

Scientists: “We Have Detected the Existence of a Fundamentally New State of Matter”


IN BRIEF

Scientists have discovered a fundamentally new state of matter: 3D quantum liquid crystals. These have the potential to advance microchip technology and quantum computing.

3D QUANTUM LIQUID CRYSTALS

Caltech physicists at the Institute for Quantum Information and Matter have discovered the first 3D quantum liquid crystal. This is a new state of matter they expect will have applications in ultrafast quantum computing, and the researchers believe this discovery is just the “tip of the iceberg.”

The molecules of standard liquid crystals flow freely as if they were a liquid, but stay directionally oriented like a solid. Liquid crystals can be made artificially, like those in display screens of electronic devices, or found in nature, like those found in biological cell membranes. Quantum liquid crystals were first discovered in 1999; their molecules behave much like those in regular liquid crystals, but their electronsprefer to orient themselves along certain axes.

Watch the video. URL:

The electrons of the 3D quantum liquid crystals exhibit different magnetic properties depending on the direction they flow along a given axis. Practically speaking, this means that electrifying these materials changes them into magnets, or changes the strength or orientation of their magnetism.

QUANTUM APPLICATIONS

The research team expects that 3D quantum liquid crystals might advance the field of designing and creating more efficient computer chips by helping computer scientists exploit the direction that electrons spin. The 3D quantum liquid crystal discovery could also advance us along the road toward building quantum computers, which will decrypt codes and make other calculations at much higher speeds thanks to the quantum nature of particles.

Achieving a quantum computer is a challenge, because quantum effects are delicate and transient. They can be changed or destroyed simply through their interactions with the surrounding environments. This problem may be solved by a technique requiring a special material called a topological superconductor — which is where the 3D quantum liquid crystals come in.

“In the same way that 2D quantum liquid crystals have been proposed to be a precursor to high-temperature superconductors, 3D quantum liquid crystals could be the precursors to the topological superconductors we’ve been looking for,” Caltech assistant professor of physics David Hsieh, principal investigator on the new study, said in an interview for a Caltech press release.

“Rather than rely on serendipity to find topological superconductors, we may now have a route to rationally creating them using 3D quantum liquid crystals,” Hsieh lab postdoctoral scholar John Harter, the lead author of the new study published in Science, said in the press release. “That is next on our agenda.”

Source:futurism.com