Science The nature of perception of the past and present

Zatnikitelman

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I have been pondering certain aspects of human's perception of the present due to two things. The first is an alien race from Dr. Who known as "Silents:"
http://tardis.wikia.com/wiki/Silent
I haven't followed the continuity too deeply so my thoughts no doubt diverge, but they do pose an interesting question: is our perception of the present dependent on knowledge of the past? The way I see things is that there really is no present, only our very short-term memories of the very recent past. So let's say these critters exist where as soon as you look away, you lose ALL memory of them. Can you even perceive them?

The second aspect I've given thought to is a bit more complicated. I've had to have a good bit of dental work done recently, and fortunately there's the wonderful substance called Nitrous Oxide, unfortunately, I couldn't tolerate the procedures without it. Anyways, during my time in the chair with the gas, I tend to get philosophical and time loses meaning. I don't mean the same sense of playing a video game, and time seems to fly, I literally mean, it loses meaning. Some of the procedures actually lasted upwards of four hours, but I never felt that it took that long. The last time I was under the gas, I consciously (as best I could anyways :p) looked at my watch, then went back to doing nothing, then looked at my watch again a while later and tried to compare the experience to an experience while not under the gas, and they didn't compare in the slightest. I also thought of something, then immediately tried to think of it, and I did, but it seemed like a distant concept rather than something that was in my mind literally 5 seconds ago. I've also heard stories of people who have had general anesthesia where they're fully unconscious also lose perception of time unlike when they sleep. I'm not really sure where I'm going with this one, but it's an interesting phenomenon and I'm curious what others thoughts are on this oddness with the perception of time here.
 

Andy44

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I think about this sort of thing often, especially when I'm running or working out and my mind wanders to fight boredom.

Part of me wonders about time as a spacial dimension. The past to me seems like a place. I remember 1997 vividly; I was in a bar in Pennsylvania watching a rock band with some friends. That doesn't seem like a time to me; it seems like a place that I could go back to if only I could find a way, a map of some sort.

A person is born, lives, and dies within a specific time period (Heinlein called us "pink worms in 4 dimensions"). If you think of time as a spacial dimension, then that person is always there, living in that space between birth and death, even after we move on. Somewhere back there my younger self will always be in that club getting drunk and loving that music, and Armstrong will always be there stepping off that ladder, etc.

But it seems like a fairy tale at the same time. All of this is wrapped up in philosophy and is impossible for us to fully grasp since we are caught up in it.
 

Artlav

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Oliver Sacks, a neurologist and a writer, have several times described people who lost all ability to form memories.
Such a person thinks he's 18 and it's still 1945. You show him a mirror, he freaks out for a minute, but then forgets all about it and says hi to you again.
Interesting reading.
The book is called "The Man Who Mistook His Wife for a Hat and Other Clinical Tales", highly recommend it.

On the subject directly - the time is only meaningful relative to our perception.
You can reformulate the basic equations without including t (see timeless form of quantum mechanics, block universe, Julian Barbour's "The End of Time") if you extend the scope on the entire universe.

Simply speaking, an equation of motion for an object describes the change of position wrt time.
The change is caused by some interactions or lack of thereof.
If you include these, eventually you get to an equation of motion for that object that depends only on everything in the universe, instead of time.

So, when you perceive time, it's simply the fact that you can remember changes happening.
Lacking that memory or lacking the changes (i.e. sensory deprivation chamber or extremely repeatable lifestyle) your perception of time will disappear or go haywire.
 

Urwumpe

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You can't post this wisdom often enough:

The universe is, instant by instant, recreated anew. There is in truth no past, only a memory of the past. Blink your eyes, and the world you see next did not exist when you closed them. Therefore, the only appropriate state of the mind is surprise. The only appropriate state of the heart is joy. The sky you see now, you have never seen before. The perfect moment is now. Be glad of it.
 

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The moment is now. But we can savour the moment to come, based on patterns generated by pathways leading to moments of the past. Dependant upon the reliance of that activity which creates the moment of course. So we can manipulate the future, based on the past and dwell upon it in the present or at the moment prior to the moment to come. So are we being bi-dimentional as we can dwell in two universes. One of our recreation, existing in memory and in a tempory universe of the present whilst waiting for a new universe to be created for the new moment. :shifty:

Forget it.!!!

All I know, is the older I get, my perception of time has most certainly changed. Many of my friends at this time of year say "It isn't Christmas already.!!", or "Hasn't time flown.!!"
It does seen like 5 minutes since the last time I swapped tins of biscuits with relatives I'm only happy to see once a year, why.?
When we were kid's, time was a drag, slow and the moment never seemed to come. Now it's come and gone. Where has it gone? Where have they all gone? Will they ever come back?
Only if I make myself bi-dimentional and recreate the universe in my mind where they existed in or the universe the moment occoured in. Well, untill the key to that universe is lost due a faded memory or if alzheimer's kicks in.

When I was a child, the Romans seemed so distant, ancient. But now at almost half a century myself, it's not really that long ago given my changing perception of time. But one amazing thought is often replaced with another...
Yes it was ancient, is replaced with... how fast have we developed since then. Time has given me many things.

Funny how many of them are compensatory.
 

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is our perception of the present dependent on knowledge of the past?

Yes, because perception requires training. This is evident for instance from children which are born blind, but later receive surgery to make them see. Initially they don't know how to parse a visual scene, it's all a meaningless jumble of lines and colors which doesn't resolve into objects oriented in space. Only over the course of a few months, when they correlate visual impressions with what they know from touch and other senses they learn to see as we do.

The way I see things is that there really is no present, only our very short-term memories of the very recent past.

No, it is possible to see object and react to objects without being consciously aware of them, i.e. they never enter memory. That's apparent from people with certain kind of brain damage which prevents high level perception entering awareness - they don't experience vision, but they still have them - they can navigate an obstacle corridor just fine when asked to simply 'guess' where the obstacles are, but they can't see consciously.

There's more to the mind than conscious awareness, and that more has a present without having memories of a near past (at least in the sense you're probably using the word).

If you think of time as a spacial dimension, then that person is always there, living in that space between birth and death, even after we move on.

Except nature is not time-reversal invariant. Not in the macroscopic sense, here entropy has to grow in one direction, and not even in the microscopic sense, we know that subatomic physics breaks CP (charge-parity) invariance, and by a set of arguments which is very technical but basically unavoidable if you want to have anything like a sane universe, this means it must break T-invariance. So you can tell by looking at a 'movie' of subatomic processes happening whether you're watching it forward or backward in time - the two directions are not the same, and in that time is decidedly different from space.

If you include these, eventually you get to an equation of motion for that object that depends only on everything in the universe, instead of time.

I doubt that is correct as it's written. An equation of motion doesn't make any sense without time. I guess the statement is that if you know any infinite 3-dim hypersurface in the universe (for instance the equal time hypersurface of 3 spatial dimensions) then you know everything there is to know in the rest of the 4-d volume. And any surface will do - you can take two spatial surfaces and time. Causality places some restrictions on how things then connect. And general relativity messes the argument by allowing parts of the universe to be simply not accessible by a single surface - the topology of spacetime can be weird such that the general argument breaks, but weird topologies also mess with time, like in a black hole where space and time change meaning (in the same sense as outside of a black hole, time can only go forward, inside a black hole one spatial dimension becomes single-directional and can only go inward).

But I'm not really sure we truly understand these things.
 

N_Molson

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From an human (or maybe animal, or maybe extra-terrestrial) point of view, time is relative.

But let's assume there is no life in the Universe to perceive it. Does time still exists ? :hmm:
 

Andy44

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From an human (or maybe animal, or maybe extra-terrestrial) point of view, time is relative.

But let's assume there is no life in the Universe to perceive it. Does time still exists ? :hmm:

That's just a rewording of the old "if a tree falls in the woods and no one is there to hear it, does it make a sound?" argument.

Look up "[ame="http://en.wikipedia.org/wiki/Allegory_of_the_Cave"]Plato's Cave[/ame]" to get some insight on how humans model the world around them inside our heads, often erroneously or incompletely.
 

Urwumpe

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From an human (or maybe animal, or maybe extra-terrestrial) point of view, time is relative.

But let's assume there is no life in the Universe to perceive it. Does time still exists ? :hmm:

Well, if nothing is there to be influenced by time - can there be even a universe?
 

MattBaker

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But let's assume there is no life in the Universe to perceive it. Does time still exists ? :hmm:

Stars consume "themselves" every second (very, very simplified). The stars we know of in our understanding of physics have a limited lifetime (of cosmological length) until they end up in some new form, go nova, whatever, I never fully understood that part.
So I would say stars and their "states" would be a way to indicate how long they exist. Which would be a unit of time.


So I would say there is time when no life exists that perceives it (is able to perceive it). It might not be divided into seconds, minutes, hours etc. but it's there. From my understanding of the current understanding of physics, both might be incomplete.

Otherwise I would disprove your question by the opposition. If there isn't it would mean there has to be life so there is time. So when time was created in the beginning (alhough THAT's really a field where current physics has...trouble) there must have been life to perceive it. Who could survive the first milliseconds of the Big Bang? I find no place for a being unaffected or superior than cold hard physics, though some might disagree there.
 

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Well, if nothing is there to be influenced by time - can there be even a universe?

Another Heinlein quote, this time from "The Cat Who Walks Through Walls". I'll paraphrase: From my point of view, I have always existed, and always will. I cannot remember being conceived or born, and I have no idea what will happen to me in the future, so everything that happened before I became conscious, or which is yet to happen, is theoretical to me.
 

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But let's assume there is no life in the Universe to perceive it. Does time still exists ? :hmm:
Life is as much laws of physics in motion as rocks or stars or cosmic dust.
So, there is no difference.

To get time in a perception-less universe you need to define time as causality.

You have a chain of events, on one end of which is an intact star, on the other end a cloud of hot gas with all the elements in it.

If you trace the chain one way, you will get a sequence of very low probability events happening one after the other - big, stable atoms falling apart, gas getting more and more complex, distilling into a star.

If you trace the chain the other way, you will get a sequence of high probability events following each other - fusion of light atoms into stable ones, gas getting less dense and expanding into a less compressed cloud.

This allows you to derive a direction of time and describe events, specifically that a star went supernova.

In technical terms, one way the entropy increases, the other way it decreases.
The way time goes for us is the way entropy increases.

So, there still will be "time" in a universe without life, only there will be no one in there to talk about it.
 
E

ex-orbinaut

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This is probably nothing (I certainly hope so), but I noticed the title phrase you have just under your forum name. I am pretty sure your post is the tip of the iceberg of a kaleidoscopic myriad of thoughts along these lines.

I spent a great deal of time in my early teens (32 years ago) pondering these sort of subjects and filling up diaries with extrapolations of them. I still have a couple, which your post caused me me scan through. Nothing in them I feel like sharing, though in truth a lot of the "ideas" contained therein later seemed to appear (I noted), bit by bit, in some movies during the 90's and are sometimes mentioned (and I will add, better explained) by some "neo-physicists" these days.

But what causes me some "slight" concern; are you sure you are not teetering on a high-wire of melancholy or incipient depression and enjoying it, at the moment? Though I am probably off by a mile and your interest in the subject is probably "coldly clinical", so to speak, I know where they led me just a few years later, and what a self-dispassionate upheaval it eventually took to extricate myself from "there". Sorry, it might be a delicate subject, and I am no diplomat in broaching it. No "analysis" intended at all, mate, I just thought I perceived some analogous "thought experiments" that rang a bell; a bit of a warning bell.

As far as the subject itself goes, here is what I tell myself these days; time exists, and is manifested in formulae that represent the physical world. Just simple formulae, like speed, lift, drag, horsepower, etcetera. They do not work without a mensurable, non-distortion-able, time lapse. Now, that numbers used to represent these "quantities" of time, and even the "segmentation" of time being based solely on the division of our experience of orbiting around a star, are purely our own accommodated implementations to facilitate "explanations" is entirely another matter. I am not going there again. Numbers of all sorts are immensely useful at explaining what was once considered "phenomena", but are cold and meaningless, in reality. To attribute them characteristics, to try to integrate them into the why of distortions that are just "illusions" of enjoyment or not of a moment perceived and retained by a mechanism that is there to prevent us from putting our hands into a fire twice, or to simply say that I am "in love" with them, would be a fallacy.

Finally, to lighten up completely; it brings to mind of "The Langoliers", in Stephen King's "Four Past Midnight" collection.
 

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---------- Post added at 07:43 PM ---------- Previous post was at 06:39 PM ----------

is our perception of the present dependent on knowledge of the past? The way I see things is that there really is no present, only our very short-term memories of the very recent past.

Here's my :2cents:

In a "normally functioning" mind, perception of present is heavily influenced by memories of the past.

As you have observed yourself, the abnormally functioning mind tends to loose track of, or become lost, so to speak, within time.

My only counter argument for you is experiential, and therefore not measurable or recordable, but I have consumed more than my fair share of illicit psychedelics in my youth to share my bit of information. I do not encourage or endorse this behavior in any way.

In my experience, it is possible for a person to lose both a knowledge of the past and expectations for the future. When these are stripped from you, all that is left is the perception of the present. there are a couple things I can say about this state of mind:

1. it lasts "forever" until ... it doesn't
2. it is confusing and can be frightening
3. our minds are not set up to endure this type of thought for very long. If one were to remain in this state for a prolonged period (for whatever reason, i'm not suggesting they would stay this way, just that IF they did) onlookers would diagnosis psychosis or severe brain-damage.
4. "you" as a person, that is the collections of actions and things that allow people "know" you, "you" as a person cease to exist. By that i mean the person in this state of mind does not do things they would normally do, or say things they would normally say, if they are able to communicate at all.

So my opinion is that AS A CREATURE, humans are able to perceive the present as it happens.

In fact I would go so far as to say that this is probably the most basic form of perception. I would compare it to perhaps being the way that simple animals with rudimentary intelligence and eyes experience consciousness.

I believe that memory, learning, and planning are extremely advanced forms of thought, and that even the slightest glimpse we have at understanding time is one of the MOST VALUABLE aspects of our minds. We would be nothing without it, operating on genetic instinct alone. Do not take it for granted. I saw you mentioned an interest in mind altering substances. Do not be seduced into thinking that all experiences are worth having, or that all things to be known are worth knowing. It's pandora's box, and i don't mean that in a fun, mysterious, or light-hearted way. Like the flow of time that we are discussing, changes you make to yourself and your chemistry can be irreversible or in the worst case deadly.
 

Zatnikitelman

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This has certainly been an interesting discussion and has taken some interesting turns I really didn't expect. :)

@Keith: Unfortunately, you're partially right. The thoughts I have posted here are not something I really dwell on, just something I had noticed. I've always kind of been like that, posing odd questions. Where you're right however is where I am. I'm certainly not enjoying it, and melancholy doesn't quite describe it since there is cause, but you are quite perceptive otherwise.
 

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If you think of time as a spacial dimension, then that person is always there, living in that space between birth and death, even after we move on.

Not really. That's like saying that if you think of spatial dimensions as spatial dimensions, that person is everywhere. "Always" says something about the extent of something in time. If it does not extend infinitely in time, or at least from the beginning of time to the end, or is not outside of this universe (and thus time) entirely, you can't apply "always".

Now, the facts of a persons life are always true: Regardless of whether your own position in time makes "is", "was", or "will be" appropriate, if you're speaking true facts about their life, you'll always give the same days of birth and death, the same list of places they went, etc.

---------- Post added at 03:29 ---------- Previous post was at 02:52 ----------

Except nature is not time-reversal invariant. Not in the macroscopic sense, here entropy has to grow in one direction, and not even in the microscopic sense, we know that subatomic physics breaks CP (charge-parity) invariance, and by a set of arguments which is very technical but basically unavoidable if you want to have anything like a sane universe, this means it must break T-invariance. So you can tell by looking at a 'movie' of subatomic processes happening whether you're watching it forward or backward in time - the two directions are not the same, and in that time is decidedly different from space.

My understanding is that the laws of physics *are* microscopically time-reversal invariant and that we talk of CP or T symmetry violation because the equations we use were written at a time when we did not expect T reversal to implicitly mean CP reversal.

As I understand it, if you have a system consisting of a positron and an electron, you just know that you have a particle and its antiparticle, you don't know which is which or which way time is going. If you arbitrarily define a direction to be forward in time, you've defined which is the electron and which is the positron, and vice versa: If you declare that one particle is the electron, you've chosen a direction to call forward in time. But as long as you reverse both time and particle labeling simultaneously, you can choose either way and the dynamics will be exactly the same.
 

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As I understand it, if you have a system consisting of a positron and an electron, you just know that you have a particle and its antiparticle, you don't know which is which or which way time is going.

That's just the point of CP violation - you do know which is which, and you do know which direction time is flowing (provided you defined before what you mean by particle).

The weak interaction is maximally parity violating, so just by looking at weak decays and neutrinos you can tell which is particle and which is antiparticle, because it's always correlated with the handedness (projection of spin onto the momentum axis) - neutrinos are always left-handed, anti-neutrinos are always right-handed - unravel the rest from there.

CP violation is more subtle, it involves measuring difference between Kshort and Klong decays into multiple pions, but you can tell from that which direction time is running.

Replacing particles by antiparticles and reversing time doesn't work. Nature is CPT invariant, so if you mirror space, reverse time AND change particles by antiparticles, then you can't tell. But *only* the combination CPT is invariant, no other is. Especially just T or CT is not.
 
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ex-orbinaut

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This has certainly been an interesting discussion and has taken some interesting turns I really didn't expect. :)

@Keith: Unfortunately, you're partially right. The thoughts I have posted here are not something I really dwell on, just something I had noticed. I've always kind of been like that, posing odd questions. Where you're right however is where I am. I'm certainly not enjoying it, and melancholy doesn't quite describe it since there is cause, but you are quite perceptive otherwise.

Glad to hear it, and good luck with that dental work. You are not so alone, I am having quite a bit done myself, albeit minus the nitrous oxide. :cheers:

Not to make a completely off-topic post, [ame="http://en.wikipedia.org/wiki/Infinite_divisibility"]here's one topic[/ame] that intrigued me during those years, and applied to "time" you can extract at least one very spooky prospect. I used to freak out my class mates with it. Thinking back, it was only one phrase that triggered all this business with me; my math teacher - who in retrospect it seemed rather liked me, as she endured my company over many a lunch break when I should probably have been booting a ball around instead - once said "imagine if everything in the Universe was half its size every instant. Would you know?". I turned the idea of energy conservation around, in my block capital scribblings, and played around with the idea that maybe energy is eternally being destroyed, but as every existing atom was halved in dimensions, it gave the "illusion" of conservation. Quite a lot of that, with many now hilarious examples.

I know it is silly. You don't need to tell me. I was a kid playing around with rather eccentric thoughts, for 1982. What do you expect? :lol:
 

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Replacing particles by antiparticles and reversing time doesn't work. Nature is CPT invariant, so if you mirror space, reverse time AND change particles by antiparticles, then you can't tell. But *only* the combination CPT is invariant, no other is. Especially just T or CT is not.

Somehow I'd gotten it into my head that switching particles and antiparticles was a CP switch, not just C, though rereading the sources I'd gotten that from I see that that's not the case. Although so much of modern physics is just geometry that I do still kind of wonder whether flipping parity without flipping charge conjugation doesn't actually boil down to flipping parity inconsistently (flipping it on a large scale but not flipping it on a small scale). If this is the case then P would be "large scale parity" and C would be "small scale parity", and the combination CP would be "actual parity". An example of a case where this would be true would be if particles, rather than being point objects, had some spatial structure on a scale too small to measure, upon which their properties were somehow dependent, and if their antiparticles had the same structure with opposite handedness. In that case P would flip the handedness of that structure and

But that's all just speculation on my part that may be way off the mark. The point of my previous post was that unlike the macroscopic case, where entropy only ever increases, there's no variable in the microscopic case that moves in one direction only as the time coordinate increases, so there's no way microscopically to know whether this is a left-handed universe in which matter predominates and time runs forward or a right-handed universe in which antimatter predominates and time runs backward without making an arbitrary choice regarding the definition of time, handedness, or matter. Macroscopically you have entropy as a time arrow, matter being more common than antimatter, etc, to make those definitions for you.
 
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