What is reality?

[Pepsi]

link postat de alexx_tores

Special issue: What is reality? - New Scientist

despre limitele cunoasterii si realitate.uneori e surprinzator cat de putin stim.

WHEN you woke up this morning, you found the world largely as you left it. You were still you; the room in which you awoke was the same one you went to sleep in. The outside world had not been rearranged. History was unchanged and the future remained unknowable. In other words, you woke up to reality. But what is reality? The more we probe it, the harder it becomes to comprehend. In the eight articles on this page we take a tour of our fundamental understanding of the world around us, starting with an attempt to define reality and ending with the idea that whatever reality is, it isn’t what it seems. Hold on to your hats.


Reality: The definition





WHAT DO we actually mean by reality? A straightforward answer is that it means everything that appears to our five senses - everything that we can see, smell, touch and so forth. Yet this answer ignores such problematic entities as electrons, the recession and the number 5, which we cannot sense but which are very real. It also ignores phantom limbs and illusory smells. Both can appear vividly real, but we would like to say that these are not part of reality.
We could tweak the definition by equating reality with what appears to a sufficiently large group of people, thereby ruling out subjective hallucinations. Unfortunately there are also hallucinations experienced by large groups, such as a mass delusion known as koro, mainly observed in South-East Asia, which involves the belief that one's genitals are shrinking back into one's body. Just because sufficiently many people believe in something does not make it real.
Another possible mark of reality we could focus on is the resistance it puts up: as the science fiction writer Philip K. **** put it, reality is that which, if you stop believing in it, does not go away. Things we just make up yield to our wishes and desires, but reality is stubborn. Just because I believe there is a jam doughnut in front of me doesn't mean there really is one. But again, this definition is problematic. Things that we do not want to regard as real can be stubborn too, as anyone who has ever been trapped in a nightmare knows. And some things that are real, such as stock markets, are not covered by this definition because if everyone stopped believing in them, they would cease to exist.
There are two definitions of reality that are much more successful. The first equates reality with a world without us, a world untouched by human desires and intentions. By this definition, a lot of things we usually regard as real - languages, wars, the financial crisis - are nothing of the sort. Still, it is the most solid one so far because it removes human subjectivity from the picture.
The second equates reality with the most fundamental things that everything else depends on. In the material world, molecules depend on their constituent atoms, atoms on electrons and a nucleus, which in turn depends on protons and neutrons, and so on. In this hierarchy, every level depends on the one below it, so we might define reality as made up of whatever entities stand at the bottom of the chain of dependence, and thus depend on nothing else.
This definition is even more restrictive than "the world without us" since things like Mount Everest would not count as part of reality; reality is confined to the unknown foundation on which the entire world depends. Even so, when we investigate whether something is real or not, these final two definitions are what we should have in mind.
Jan Westerhoff is a philosopher at the University of Durham and the University of London's School of Oriental and African Studies, both in the UK, and author of Reality: A very short introduction (Oxford University Press, 2011)



Reality: The bedrock of it all



Can we explain reality purely in terms of matter and energy?




IS ANYTHING real? The question seems to invite only one answer: of course it is. If in doubt, try kicking a rock.
Leaving aside the question of whether your senses can be trusted, what are you actually kicking? When it boils down to it, not a lot. Science needs remarkably few ingredients to account for a rock: a handful of different particles, the forces that govern their interactions, plus some rules laid down by quantum mechanics.
This seems like a solid take on reality, but it quickly starts to feel insubstantial. If you take a rock apart, you'll find that its basic constituent is atoms - perhaps 1000 trillion trillion of them, depending on the rock's size. Atoms, of course, are composed of smaller subatomic particles, namely protons and neutrons - themselves built of quarks - and electrons. Otherwise, though, atoms (and hence rocks) are mostly empty space. If an atom were scaled up so that its nucleus was the size of the Earth, the distance to its closest electrons would be 2.5 times the distance between the Earth and the sun. In between is nothing at all. If so much of reality is built on emptiness, then what gives rocks and other objects their form and bulk?
Physics has no problem answering this question: electrons. Quantum rules dictate that no two electrons can occupy the same quantum state. The upshot of this is that, no matter how hard you try, you cannot cram two atoms together into the same space. "Electrons do all the work when it comes to the structure of matter we see all around us," says physicist Sean Carroll at the California Institute of Technology in Pasadena.
That's not to say the nucleus is redundant. Most of the mass of an atom comes from protons and neutrons and the force binding them together, which is carried by particles called gluons.
And that, essentially, is that. Electrons, quarks (mostly of the up and down variety) and gluons account for most of the ordinary stuff around us.
But not all. Other basic constituents of reality exist too - 17 in total, which together comprise the standard model of particle physics (see illustration). The model also accounts for the mirror world of antimatter with a complementary set of antiparticles.
Some pieces of the standard model are commonplace, such as photons of light and the various neutrinos streaming through us from the sun and other sources. Others, though, do not seem to be part of everyday reality, including the top and bottom quarks and the heavy, electron-like tau particle. "On the face of it, they don't play a role," says Paul Davies of Arizona State University in Tempe. "Deep down, though, they may all link up."
That's because the standard model is more than a roll call of particles. Its foundations lie in symmetry and group theory, one example of the mysterious connections between reality and mathematics (see "Reality: Is everything made of numbers?").
The standard model is arguably even stranger for what it doesn't include. It has nothing to say about the invisible dark matter than seems to make up most of the matter in the universe. Nor does it account for dark energy. These are serious omissions when you consider that dark matter and dark energy together comprise about 96 per cent of the universe. It is also totally unclear how the standard model relates to phenomena that seem to be real, such as time and gravity.
So the standard model is at best a fuzzy approximation, encompassing some, but not all, of what seems to comprise physical reality, plus bits and pieces that do not. Most physicists would agree that the standard model is in serious need of an overhaul. It may be the best model we have of reality, but it is far from the whole story.
Valerie Jamieson is New Scientist's features editor

[gerrard88]

De multe ori m-am intrebat daca realitatea pe care o traim nu e defapt o iluzie. Cand dormi si visezi, nu esti constient ca visezi, nu esti constient nici macar ca dormi, pentru tine realitatea e cea din vis. Daca realitatea e defapt un vis, un vis in vis?


Asta e o teorie in genul teoriei multiversurilor. Tot mai multi oameni de stiinta sustin ca defapt nu ar fi un singur univers ci ar fi vorba de multiversuri.

[Pepsi]

Reality: Is matter real?





It's relatively easy to demonstrate what physical reality isn't. It is much harder to work out what it is


NOTHING seems more real than the world of everyday objects, but things are not as they seem. A set of relatively simple experiments reveals enormous holes is our intuitive understanding of physical reality. Trying to explain what goes on leads to some very peculiar and often highly surprising theories of the world around us.
Here is a simple example. Take an ordinary desk lamp, a few pieces of cardboard with holes of decreasing sizes, and some sort of projection screen such as a white wall. If you put a piece of cardboard between the lamp and the wall, you will see a bright patch where the light passes through the hole in the cardboard. If you now replace the cardboard with pieces containing smaller and smaller holes, the patch too will diminish in size. Once we get below a certain size, however, the pattern on the wall changes from a small dot to a series of concentric dark and light rings, rather like an archery target. This is the "Airy pattern" - a characteristic sign of a wave being forced through a hole (see image).
In itself, this is not very surprising. After all, we know that light is a wave, so it should display wave-like behaviour.
But now consider what happens if we change the set-up of the experiment a bit. Instead of a lamp, we use a device that shoots out electrons, like that found in old-fashioned TV sets; instead of the wall, we use a plate of glass coated with a phosphor that lights up when an electron strikes it. We can therefore use this screen to track the places where the electrons hit. The results are similar: with sufficiently small holes we get an Airy pattern.
This now seems peculiar: electrons are particles located at precise points and cannot be split. Yet they are behaving like waves that can smear out across space, are divisible, and merge into one another when they meet.
Perhaps it is not that strange after all. Water consists of molecules, yet it behaves like a wave. The Airy pattern may just emerge when enough particles come together, whether they are water molecules or electrons.
A simple variant of the experiments shows, however, that this cannot be right. Suppose we reduce the output of the electron gun to one particle each minute. The Airy pattern is gone, and all we see is a small flash every minute. Let's leave this set-up to run for a while, recording each small flash as it occurs. Afterwards, we map the locations of all the thousands of flashes.
Surprisingly, we do not end up with a random arrangement of dots, but with the Airy pattern again. This result is extremely strange. No individual electron can know where all the earlier and later electrons are going to hit, so they cannot communicate with each other to create the bullseye pattern. Rather, each electron must have travelled like a wave through the hole to produce the characteristic pattern, then changed back into a particle to produce the point on the screen. This, of course, is the famous wave-particle duality of quantum mechanics.
This strange behaviour is shared by any sufficiently small piece of matter, including electrons, neutrons, photons and other elementary particles, but not just by these. Similar effects have been observed for objects that are large enough in principle to be seen under a microscope, such as buckyballs.
In order to explain the peculiar behaviour of such objects, physicists associate a wave function with each of them. Despite the fact that these waves have the usual properties of more familiar waves such as sound or water waves, including amplitude (how far up or down it deviates from the rest state), phase (at what point in a cycle the wave is), and interference (so that "up" and "down" phases of waves meeting each other cancel out), what they are waves in is not at all transparent. Einstein aptly spoke of a "phantom field" as their medium.
For a wave in an ordinary medium such as water, we can calculate its energy at any one point by taking the square of its amplitude. Wave functions, however, carry no energy. Instead, the square of their amplitude at any given point gives us the probability of observing the particle if a detector such as the phosphor-coated screen is placed there.
Clearly, the point where an object switches from being a probability wave, with its potential existence smeared out across space, and becomes an actual, spatially localised object is crucially important to understanding whether matter is real. What exactly happens when the wave function collapses - when among the countless possibilities where the particle could be at any moment, one is chosen, while all the others are rejected

First of all, we have to ask ourselves when this choice is made. In the example described above, it seems to happen just before the flash on the phosphor screen. At this moment, a measurement of the electron's position was made by a piece of phosphor glowing as the particle struck it, so there must have been an electron there, and not just a probability wave.
But assume we cannot be in the lab to observe the experiment, so we point a camera at the phosphor screen and have the result sent via a satellite link to a computer on our desktop. In this case, the flash of light emitted from the phosphor screen has to travel to the camera recording it, and the process is repeated: like the electrons, light also travels as a wave and arrives as a particle. What reason is there to believe that the switch from probability wave to particle actually occurred on the phosphor screen, and not in the camera?
At first, it seemed as if the phosphor screen was the measuring instrument, and the electron was the thing being measured. But now the measuring device is the camera and the phosphor screen is part of what is measured. Given that any physical object transmitting the measurement we can add on to this sequence - the camera, the computer, our eyes, our brain - is made up of particles with the same properties as the electron, how can we determine any particular step at which to place the cut between what is measured and what is doing the measuring?
This ever-expanding chain is called the von Neumann chain, after the physicist and mathematician John von Neumann. One of his Princeton University colleagues, Eugene Wigner, made a suggestion as to where to make the cut. As we follow the von Neumann chain upwards, the first entity we encounter that is not made up in any straightforward fashion out of pieces of matter is the consciousness of the observer. We might therefore want to say that when consciousness enters the picture, the wave function collapses and the probability wave turns into a particle.
The idea that consciousness brings everyday reality into existence is, of course, deeply strange; perhaps it is little wonder that it is a minority viewpoint.
There is another way of interpreting the measurement problem that does not involve consciousness - though it has peculiar ramifications of its own. But for now let's explore Wigner's idea in more depth.
If a conscious observer does not collapse the wave function, curious consequences follow. As more and more objects get sucked into the vortex of von Neumann's chain by changing from being a measuring instrument to being part of what is measured, the "spread-out" structure of the probability wave becomes a property of these objects too. The "superposed" nature of the electron - its ability to be at various places at once - now also affects the measuring instruments.
It has been verified experimentally that not just the unobservably small, but objects large enough to be seen under a microscope, such as a 60-micrometre-long metal strip, can exhibit such superposition behaviour. Of course, we can't look through a microscope and see the metal strip being at two places at once, as this would immediately collapse the wave function. Yet it is clear that the indeterminacy we found at the atomic level can spread to the macro level.
Yet if we accept that the wave function must collapse as soon as consciousness enters the measurement, the consequences are even more curious. If we decide to break off the chain at this point, it follows that, according to one of our definitions of reality, matter cannot be regarded as real. If consciousness is required to turn ghostly probability waves into things that are more or less like the objects we meet in everyday life, how can we say that matter is what would be there anyway, whether or not human minds were around?
But perhaps this is a bit too hasty. Even if we agree with the idea that consciousness is required to break the chain, all that follows is that the dynamic attributes of matter such as position, momentum and spin orientation are mind-dependent. It does not follow that its static attributes, including mass and charge, are dependent on in this. The static attributes are there whether we look or not.
Nevertheless, we have to ask ourselves whether redefining matter as "a set of static attributes" preserves enough of its content to allow us to regard matter as real. In a world without minds, there would still be attributes such as mass and charge, but things would not be at any particular location or travel in any particular direction. Such a world has virtually nothing in common with the world as it appears to us. Werner Heisenberg observed that: "the ontology of materialism rested upon the illusion that the kind of existence, the direct 'actuality' of the world around us, can be extrapolated into the atomic range. This extrapolation, however, is impossible... Atoms are not things."

[andreibc]

sa postezi un copy paste e similar cu a trimite un link catre Google

[alexx_tores]

@pepsi man,thanks de idee si de efort.nu mi-am dat seama cand am postat linkul ca este valid doar pentru abonatii siteului.oricum,este unul din articolele cele mai interesante citite in ultimul timp.chiar daca este cam lung,compus din 8 parti.sper ca fiecare din cei care il citesc sa aiba si mintea deschisa,sa zic asa,ca sa ii inteleaga fiecare nuanta.