Bewegen door de tijd?
Geplaatst op 09 juni 2004 - 22:38
Geplaatst op 10 juni 2004 - 18:28
Heeft dit niet iets te maken, over hoe je zelf over de wereld denkt?
Bewegen we door de tijd, of is alles er al op ieder tijdstip?
Denk je bijvoorbeeld dat alles al is vastgelegd?
Geplaatst op 11 juni 2004 - 09:20
Ons denken vindt plaats in de richting van de entropiepijl. De tijd verloopt eveneens in die richting. Als we als waarnemer niet één toestand van onszelf als referentiepunt beschouwen, maar onszelf als dissipatief systeem dat verandert in de tijd, ja, dan reisen we inderdaad door de trijd.
Zoals je kan lezen dus een definitiekwestie.
Geplaatst op 11 juni 2004 - 11:30
Als we als waarnemer niet één toestand van onszelf als referentiepunt beschouwen, maar onszelf als dissipatief systeem dat verandert in de tijd
Wat bedoel je met een dissipatief systeem (zijn er wel andere systemen ? )
Geplaatst op 11 juni 2004 - 11:58
Ons denken vindt plaats in de richting van de entropiepijl. De tijd verloopt eveneens in die richting.
Staat hier niet 2 keer hetzelfde? Tijdverloop is een illusie van ons denken. Tijd zelf is geen illusie. Door de entropiepijl LIJKT de tijd van verleden naar toekomst te verlopen. Maar eigenlijk ligt alles al vast en bestaat alles al op ieder moment. Maar nou weet ik niet zeker wat entropie precies betekent, kun je het ook verstrooiing noemen?
Geplaatst op 11 juni 2004 - 15:09
Er bestaan anders systemen waarvan het bekendste voorbeeld de wereld binnen de waarnemingshorizon van een zwart gat is. Deze wereld bereiken vereist een transeindige, dus causaal niet verbonden tijd door de tijdvertraging in de buurt van de warnemingshorizon.
Wat bedoel je met een dissipatief systeem (zijn er wel andere systemen ? )
Maar inderdaad, voor verreweg de meeste systemen heb je gelijk.
Ik bedoelde: systeem dat informatie uit de buitenwereld kan ontvangen en door de invloed hiervan van staat wijzigt. (is dus dissipatief).
Geplaatst op 11 juni 2004 - 21:13
Maar nou weet ik niet zeker wat entropie precies betekent, kun je het ook verstrooiing noemen?
entropie betekent wanorde....
de tweede hoofdwet van de thermodynamica zegt dat een fysisch proces slechts kan verlopen als de totale entropie, dat is de entropie van het systeem en die van de omgeving, toeneemt of op zijn minst gelijk blijft.
alleen met een fysisch proces kan er orde (minder entropie)gecreerd worden...
waardoor de orde uiteindelijk altijd af zal nemen in het heelal
Het is hierdoor onmogelijk dat de entropie afneemt in het heelal
waardoor het onmogelijk is dat alles er altijd is zoals het nu is....
dus we bewegen door de tijd....
Geplaatst op 11 juni 2004 - 21:51
Geplaatst op 24 september 2004 - 13:37
Geplaatst op 24 september 2004 - 17:59
New Scientist vol 182 issue 2445 - 01 May 2004, page 34
No wonder physicists can't explain past, present and future. The passage of time is just an illusion that we can't live without, says Marcus Chown
DEEP in the Amazon rainforest, a tree frog sits on a log watching a fly. A genetic fluke has furnished the frog with a brain that perceives its surroundings as they were a second ago. When the fly comes within range, the frog lunges. But, with its out-of-date observation, it misses. Weakened by a rarely sated hunger, the frog falls off the log and dies.
It's a sad story. But if you think it is completely fanciful, think again. There is nothing in the laws of physics that says all creatures have to process data about their environment in the same way as we do. A "behind the times" perception like that of our deceased frog is only ruled out by the handicap it imposes. "Natural selection has equipped people and frogs to experience the world in the most effective way for their survival," says James Hartle of the University of California, Santa Barbara. "A frog that calculates the trajectory of a fly from the most recent data, eats; one that doesn't, starves."
Perhaps this seems mere common sense. In a way it does to Hartle too. So why is this heavyweight cosmologist - his collaborators include Stephen Hawking, Murray Gell-Mann and Steven Weinberg - worrying about frogs?
Because he believes it goes to the very heart of why we perceive time as we do. The constraints that evolution imposes on our perception of time could help us understand time's true nature. "Our powerful sense that there is a 'now' and that time 'flows' from the past, through the present, to the future, has survival value," he says. "It is the only plausible explanation, since none of these concepts actually appear in Einstein's special theory of relativity, our most fundamental physical description of space and time."
After many years of worrying about time, Hartle has put aside a little of it to consider what evolution might tell us about past, present and future. After adding in the concerns of a few alien civilisations and constructing a robot that has premonitions, he believes things are starting to become clearer. Really, he does.
Even a little thought reveals that the idea of a "flow of time" is a nonsense, Hartle says. "Something which flows, changes with time," he points out. "But how can time change with time? It's a logical impossibility." This is made explicit in special relativity. According to Einstein, space-time is essentially a four-dimensional landscape (with three dimensions of space and one of time) in which all the events in the history of the universe - from the big bang into the far future - are laid out exactly as if they are pre-ordained. Nothing flows.
But, even if the flow of time does not appear in our description of reality, surely it is still possible to agree on what we all mean by past, present and future? "Sadly, no," says Hartle.
It is a well-documented, if rather strange, facet of relativity: time is not an independent phenomenon, but inextricably linked with space. And if people within this "space-time" are moving through space relative to one another, the distinction between space and time becomes blurred: they cannot agree on what "now" means. "In Einstein's universe, there can be no such thing as a universally agreed past, present and future," Hartle says. "Within the context of space-time, the very concepts are meaningless."
So, how to make sense of it? The answer, he says, lies in the concept of information: it is information - and the way we process it - that gives us a sense of past and future.
Hartle reached this conclusion by considering what he terms a subsystem of the universe, defined as something that gathers and uses information. Human beings, both individually and collectively (as members of civilisations), fit into this definition, as do frogs, and even robots. It was the physicist Gell-Mann who gave these subsystems a name - he called them "information gathering and utilising systems" (IGUSs).
The mechanism behind the IGUS has turned out to be a surprisingly useful concept (see Diagram). First, information from its environment is held in an input register. But this register has a limited capacity, and as more information comes in from the environment, the information is passed to a memory register to clear space for new input. The IGUS might have many memory registers, along which it can shuffle the past information. Eventually though, it will have to be dumped.
Of course, to dump this past information without using it in any way would be a waste, so before that happens it is passed to other parts of the information processing system. In addition to the registers, the IGUS has a "schema", a simplified model of its environment with rules culled from its past experience, which tells it how to behave in particular circumstances. It also has a computer that works out how it should react to its surroundings, based on the rules stored in the schema. The computer carries out two distinct kinds of computation: conscious, which makes decisions; and unconscious, which updates the schema.
There are many ways in which information can pass between all these components, Hartle points out, and they create very different behaviours in the IGUS. The most familiar idea - what we would consider normal - is to allow conscious to focus on the present (the input register), and unconscious on the past. "This distinction is important because it is the suggested reason we consciously experience the present but remember the past," Hartle says. He contends that this simple set-up mimics some of the key features of human perception. For a start, because an IGUS focuses its attention on the most recently acquired image, the present is a specific thing with a special immediacy.
It is the passage of images between registers, until they are erased and "forgotten" that creates the impression of a flow of time. "Something analogous to the flow of information from register to register happens in our brains, and this is what ultimately gives us our sense of time passing," Hartle says. The perception of time as flowing is perfectly compatible with Einstein's space-time as long as the "flow of time" is in fact a "flow of information". Furthermore, he says, for an IGUS the past and future are qualitatively different, in that the past in the registers is "remembered" while the future is "predicted" as the output of computation.
Equipped with this set-up, Hartle imagines what happens when an IGUS observes an object in its environment - when an image of a cheeseburger appears in the input register, for example. "The computer consults the schema, which has abstracted rules from a previous experience - previous visits to burger restaurants, for example - and realises 'Hey, I like cheeseburgers'," Hartle says. "The IGUS therefore decides to buy a cheeseburger. Or perhaps the schema contains information on the fat content of burgers, which overrides the liking of burgers, so the computer decides not to buy a cheeseburger."
This seems reasonable and familiar, showing that we use past information to inform decisions to be made in the present that might change the future. But what about the problem of the common now; what about the fact that, in space-time, it is not always possible for observers moving relative to each other to agree on the past-future ordering of events? That doesn't fit with our experience; on Earth we IGUSs define "now" quite easily.
Well, says Hartle, imagine two or more of the IGUSs embedded in 4D space-time. In this situation, although there can be no universally agreed "now" in space-time, there can nevertheless be an approximate, "local now", given three restrictive conditions. The first condition is that the observers are separated by a short distance compared with the distance light can travel in the time of the observed events. The second condition is that the observers must be moving relative to each other at significantly less than the speed of light. And the last condition is that the time for perception - that is, for processing the new information in the input register - must be short compared with the time over which interesting features of the environment change. "That is probably necessary for a creature to function," Hartle says. "A frog would have a hard time if it took longer to perceive a position than for the fly to move."
All three conditions are easily satisfied for human beings on Earth, but Hartle points out that the first condition would not be satisfied for an IGUS that comprised an alien civilisation spread across a whole galaxy. "There would be no point in defining a 'now' on a planet at the centre of the galaxy when light would take 60,000 years to take knowledge of it to a planet on the periphery," he says. "Clearly, such a civilisation would need to organise its time differently from us."
And that's when the robots come in. Hartle imagined building robot IGUSs according to his own peculiar blueprints; because they are so flexible in their set-up, they can help determine whether there are other ways in which creatures could organise their experience of time - ways that are still consistent with the basic laws of physics. "It is possible to imagine an IGUS that organises its experience much like we do," he says. "But, importantly, it is also possible to imagine IGUSs which organise their experience in quite different ways."
To explore this, Hartle has come up with three variations on his basic IGUS. The "split-screen" robot focuses on not one but two moments of time, 10 seconds apart, so it has two "nows". The "always-behind" robot, like our poor deceased frog, sees the world as it was a few seconds ago. And the "no-schema" robot must calculate its next move from the contents of all its registers, because they all feed directly into the conscious computation.
"Would any of these be viable?" Hartle asks. Well, perhaps, but they all seem to have problems - to us, at least. The split-screen robot would be wasting valuable conscious focus on inessential information in the past. As we have seen, the always-behind robot would starve to death. And the no-schema robot would waste its computational resources.
Hartle concludes that such variant ways of organising experience, should they ever arise, would be promptly weeded out by natural selection. "Our time sense is determined not by physics alone but also by biology," he says. "If this is right, any extraterrestrials we meet will experience the world the same as us, sharing concepts of past, present and future, and the idea of a flow of time."
He points out, however, that if the laws of physics were different they would have given rise to creatures that organised their experience differently from us. "Say the force on a body depended on its position now and 10 seconds ago," he says. "Natural selection would favour the evolution of a split-time creature."
But, though natural selection based on the laws of physics has made humans process information in the way we do, there must be other possibilities beyond what he has imagined so far. After all, we are free to build robots any way we like.
Indeed, the satellites that make up the Global Positioning System could be considered as an IGUS that is programmed to perceive time in a peculiar way. People using the GPS rely on receiving signals from clocks on the satellites. By comparing the different amounts of time the various satellite signals take to reach it, the user's receiver then determines its position on Earth. The system depends on the satellite clocks being synchronised but, since they are all accelerating and moving at high speeds relative to the receiver, relativity dictates that they all have different perceptions of "now". For the system to operate, the GPS engineers had to design a particular meaning of "now", adjusting each of the satellite clocks' ticking rates, and programming receivers to perform the necessary relativistic corrections. In other words, they tinker with the system's perception of time.
But engineers could push things further, Hartle suggests. It might even be possible to build a robot which organises its experience back-to-front, one that remembers the future and predicts the past. "Though it is difficult, it is not impossible in principle," he says.
To create a robot with a reversed perception of time, Hartle simply has to reconstruct information records about the robot's environment that have been destroyed, and then feed them through the robot's registers backwards in a way that would make it look - to the robot at least - as though information was coming from the future. Because it travels through the memory registers, it would seem like a memory of the future.
Imagine, for example, a time-reversed robot observing an egg falling to the ground. In the usual time order, the record of the destruction of the egg is erased some time after the egg hits the floor. How would a reversed robot and egg look to us? We would see the record unerase and then, later, the egg fall. "Thus, in between, the robot has records of the future," Hartle says.
In practice, Hartle points out, achieving this would be much more tricky even than sticking the contents and shell of a broken egg back together. The robot would have to operate in an environment showing this reversed entropy: that would mean reversing the velocity of every particle of matter and photon of energy in the robot's neighbourhood. "Since we have a system of matter interacting with light, it would be necessary to deal with every molecule and photon within a radius of 60,000 light years," Hartle says. "We lack the technology to do that."
And so, for the moment, he is contenting himself with the conclusion that every creature that we know about is likely to organise its time in the same way as we do. But maybe, out there in the far reaches of space, some highly intelligent beings are doing things differently, reversing time's flow in their locality. Perhaps manipulating the interactions of light and matter is the best way to establish intragalactic communications over 60,000 light years, for example. Or, of course, it may just be fun. "More advanced civilisations might find this amusing," Hartle says. "Who knows?"
Geplaatst op 24 september 2004 - 21:21
ja eigenlijk vindt ik gen vamn beiden opties passen. Maar ik kies door we bewegen in de tijd, het ligt eraan hoe jezelf erover denk
Geplaatst op 17 juli 2009 - 10:11
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