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gzhpcu
2017-Dec-01, 06:18 AM
I know I am probably opening a can of worms here, but I have a rather simplistic question which has bugged me since childhood.

The old model of the universe was that the universe always existed, will always exist for eternity. Problem here, I never could understand how we could ever reach the present, since the past was eternally long.

Then the theory of the Big Bang showed up, and the question was what was before t=0? How could it start up?

Now we speak of multiverses, bubble universes, branes colliding to create the Big Bang for our universe, etc. So these extend back infinitely (back to square one)

So the question is: how could we ever have reached the (elusive, constantly changing) present if the past is infinite? :confused:

cosmocrazy
2017-Dec-01, 09:38 AM
I wouldn't say there is anything simplistic about the question, its rather a difficult one to answer, since we don't really know. The model of the big bang suggests that there was "nothing" before the start of the universe we observe today. That doesn't mean that it is certain there was nothing. "How could it start up?" a question that I mull over a lot myself. I think we are so accustomed to cause and effect it's difficult for us to conceptualise a situation where something could just happen from nothing, not even time.


If the universe always existed, what do we mean by the "universe". The observational evidence strongly suggests that the universe we live in had a beginning and quite possibly will have an end. But is what we observe just a spec in an infinite ocean of universe/s? we don't know, and might never know.


I think when we try to conceptualise infinity, especially infinite time, it raises questions about what time really is, what it means. Why is there an arrow of time? or is this just a point of view? We experience/measure time to follow a direction at a constant rate relative to our own frame of reference. But each frame of reference may experience/measure different rates of time relative to other frames. So if there is no universal time frame reference then this takes us right back to the question of what does this mean for time regarding the "start" of the universe?

For example, a photon of light experiences no time or space. Therefore for the photon does the universe exist yet? Is there a start or an end?

Shaula
2017-Dec-01, 11:17 AM
The model of the big bang suggests that there was "nothing" before the start of the universe we observe today.
No it does not. The model says that the observable universe expanded from a hot dense state a finite time ago. And that is all it says.


For example, a photon of light experiences no time or space. Therefore for the photon does the universe exist yet? Is there a start or an end?
This is an extrapolation of SR concepts into an invalid domain.

gzhpcu
2017-Dec-01, 11:50 AM
Our physics breaks down as we approach t=0 for the start of the big bang. Steven Weinberg in his book, "The First Three Minutes" uses this as a starting point, since going back closer is not possible, it leads to a singularity and infinity in our current theories.

FrankWSchmidt
2017-Dec-01, 01:07 PM
I think the theory "How to get from an infinite past to the present" is not a problem. It's just like a variable t which could be any negative value, or zero, or any positive value - it doesn't "get from there to here", it just is.

Problems would be practical problems: If stars use up their hydrogen in fusion, then all across the universe there'd be less and less hydrogen compared to other elements over time. But right now we observe there's still plenty of it, so the fusion couldn't have started an infinite time ago.

gzhpcu
2017-Dec-01, 01:11 PM
I think the theory "How to get from an infinite past to the present" is not a problem. It's just like a variable t which could be any negative value, or zero, or any positive value - it doesn't "get from there to here", it just is.

Problems would be practical problems: If stars use up their hydrogen in fusion, then all across the universe there'd be less and less hydrogen compared to other elements over time. But right now we observe there's still plenty of it, so the fusion couldn't have started an infinite time ago.Except we are not talking about abstract mathematics. Saying it just is, I do not find satisfying...

profloater
2017-Dec-01, 01:46 PM
Except we are not talking about abstract mathematics. Saying it just is, I do not find satisfying...

yes but the whole idea is based on a maths model isn't it? You cannot expect to get a feel for time in that model of the distant past if you don't believe the maths as a backwards prediction model. Most of what we have to work on is observation of stars using the electromagnetic spectrum and then maths to form a model of how they got there. Then we add particle work here on Earth but it's mostly looking at stars and maths.

Strange
2017-Dec-01, 01:57 PM
I can't really see a problem. There are an infinite number of integers, but 5 still exists. And the universe might be spatially infinite, but we are still "here". We didn't have to get here from an infinite distance away.

gzhpcu
2017-Dec-01, 03:17 PM
yes but the whole idea is based on a maths model isn't it? You cannot expect to get a feel for time in that model of the distant past if you don't believe the maths as a backwards prediction model. Most of what we have to work on is observation of stars using the electromagnetic spectrum and then maths to form a model of how they got there. Then we add particle work here on Earth but it's mostly looking at stars and maths.Math does not help me. I am talking about existence, not abstract symbolisms created by the mind.

Ken G
2017-Dec-01, 03:20 PM
The way I would put it is, time is not a thing, it is a concept that we have developed because it has worked for us. This does not imply it must always work for us in every situation-- there may be situations in which we need to replace the notion with something else. This always happens, it's how science advances. So we have two ways to frame questions like:
1) What existed before the beginning of time?
or
2) When time has a beginning, can it be the same time that we normally think of, or do we need a new concept there?
I rather feel the second question is the one more likely to bear scientific fruit, but of course experimental verification is quite tricky in this area!

Just as an example of the kind of thing I'm talking about, relativity already forced us to radically change our concept of time. We used to think time was universal, ticking along for all things in the universe just the same way. That turns out to be completely wrong when objects pass each other at speeds near c. Instead, each object has its own proper time. However, in the very early universe when the energy scales were ghastly large, there were not "things" that could survive, they were constantly appearing and disappearing, destroyed in timescales shorter than what we would normally regard as a tick of a clock. So if there are no things that could have a proper time, then there is not proper time, the whole notion essentially dissipates. And of course photons don't have proper time in the first place. So a Big Bang model that invokes an initial singularity (which you need to be able to talk about "before" the "beginning") already invokes an invalid use of the time concept at that singularity, just by virtue of how fast the particles are moving and how shortlived they are-- even when we stick to the concept of time that has been found to work in high-energy experiments. One might even be tempted to conclude that in the limit as all particles are highly relativistic, the clocks we can imagine for them all cease to tick-- so we have a "beginning" to time right there, it is born from a state of extreme time dilation, almost like the proverbial caveman coming out of deep freeze.

Strange
2017-Dec-01, 03:21 PM
Maybe if you don't think of time as something that "flows" or something we move through, but just as a set of coordinates then it is no more problematical that were are "now" than that we are "here". Neither requires us to have come from an infinite distance.

grapes
2017-Dec-01, 04:00 PM
I can't really see a problem. There are an infinite number of integers, but 5 still exists. And the universe might be spatially infinite, but we are still "here". We didn't have to get here from an infinite distance away.
An infinite number of integers in both directions, too


Math does not help me. I am talking about existence, not abstract symbolisms created by the mind.
But, if you can abstractly manage the mathematical example, doesn't it give you a good handle on the actual?

gzhpcu
2017-Dec-01, 04:04 PM
Theories apart, subjectively, time passes for me. I remember yesterday, when I graduated, when I went to elementary school... a chain of events. That is what I am alluding to. Not mathematical concepts.

Strange
2017-Dec-01, 04:22 PM
Theories apart, subjectively, time passes for me. I remember yesterday, when I graduated, when I went to elementary school... a chain of events. That is what I am alluding to. Not mathematical concepts.

You can start from "now" and work back as far as you like. You didn't have to start from infinity to get here though.

profloater
2017-Dec-01, 04:32 PM
Theories apart, subjectively, time passes for me. I remember yesterday, when I graduated, when I went to elementary school... a chain of events. That is what I am alluding to. Not mathematical concepts.

Do you find memories have time and date attached to them or do you have milestones like you know the year you graduated as a separate fact? Some people do seem to have tagged memories, others are ordered by intensity with no strong sense of how long ago or indeed sequence. A chain of events as a chronicle has no intergral evidence attached until we allocate cause and effect with time, that every effect has to have an earlier cause. This simple idea breaks down if you ask about a beginning.

Ken G
2017-Dec-01, 04:33 PM
Theories apart, subjectively, time passes for me. I remember yesterday, when I graduated, when I went to elementary school... a chain of events. That is what I am alluding to. Not mathematical concepts.
You just described a concept. Are you saying it only counts as such if it is not mathematical? Besides, what I said applies equally to the description you just gave-- none of those things you said would make any sense at the beginning of the universe, so your own concept of time doesn't make sense there either, nor does the experimentally verified one.

Look more closely at your logic here. You are saying that you have found the concept of a "chain of events," pieced together using a mental capacity you call memory, is a useful way to build a concept of time. That is certainly true, we've all found that to be the case. But we build our concepts based on what works, just as you did here, we don't tell the universe what has to make sense first, and then require that it must obey. That isn't what you did when you built the concept you just described, so it is also what you should not do when you talk about the evidence that the universe had a beginning, or a singularity, or just a period of extreme difference from now, however you like to look at it.

The key point I'm making here is that, over and over in the history of science, we have found that our own experiences, those we use to get a sense of "what is" on an everyday basis, sample an extremely tiny corner of what actually is, even if you hold that the concept of "what actually is" makes sense independently of what we can experience and how we can make sense of that. As such, in science we constantly find that we need to update "what is" when our awareness extends to new spheres well outside common experience. You have a tendency to discount everything that is not in your common experience, labeling it as "mathematical" in nature, but why would you think that your own tiny corner of experience has some kind of monopoly on how reality works? It seems to me that one of the first steps of science is to adopt a stance of not knowing, rather than a stance of pre-knowing. You didn't pre-know anything when you were born into this world, why start now?

Don't get me wrong, I agree that saying it took an infinite time to "get here" is a problematic notion, I don't think that would have ever been a working concept of time. But neither should we expect our everyday notion to apply universally. We always need to be ready to throw out a model, any model no matter how fundamental, when we reach the domain where it just doesn't make sense any more, or is found to disagree with observations, or where we cannot even provide operational definitions for what we are talking about. That's if we will use science as our tool, and no sharper one exists.

gzhpcu
2017-Dec-02, 07:14 AM
Do you find memories have time and date attached to them or do you have milestones like you know the year you graduated as a separate fact? Some people do seem to have tagged memories, others are ordered by intensity with no strong sense of how long ago or indeed sequence. A chain of events as a chronicle has no intergral evidence attached until we allocate cause and effect with time, that every effect has to have an earlier cause. This simple idea breaks down if you ask about a beginning.
Look: my grandparents were born, my parents were born, I was born. A clear sequence.

gzhpcu
2017-Dec-02, 07:47 AM
You just described a concept. Are you saying it only counts as such if it is not mathematical? Besides, what I said applies equally to the description you just gave-- none of those things you said would make any sense at the beginning of the universe, so your own concept of time doesn't make sense there either, nor does the experimentally verified one.
I am speaking from my point of view. From what I experience. Things which have a time sequence in my life. I am saying I do not need math for this simple example.


Look more closely at your logic here. You are saying that you have found the concept of a "chain of events," pieced together using a mental capacity you call memory, is a useful way to build a concept of time. That is certainly true, we've all found that to be the case. But we build our concepts based on what works, just as you did here, we don't tell the universe what has to make sense first, and then require that it must obey. That isn't what you did when you built the concept you just described, so it is also what you should not do when you talk about the evidence that the universe had a beginning, or a singularity, or just a period of extreme difference from now, however you like to look at it. Are you questioning the red shift of galaxies, pointing towards the Big Bang?


The key point I'm making here is that, over and over in the history of science, we have found that our own experiences, those we use to get a sense of "what is" on an everyday basis, sample an extremely tiny corner of what actually is, even if you hold that the concept of "what actually is" makes sense independently of what we can experience and how we can make sense of that. As such, in science we constantly find that we need to update "what is" when our awareness extends to new spheres well outside common experience. You have a tendency to discount everything that is not in your common experience, labeling it as "mathematical" in nature, but why would you think that your own tiny corner of experience has some kind of monopoly on how reality works? It seems to me that one of the first steps of science is to adopt a stance of not knowing, rather than a stance of pre-knowing. You didn't pre-know anything when you were born into this world, why start now?I naturally assume when I am looking at my wristwatch observing that the second hand is moving that time is passing for me. When I look at the moon and see it moving during the night, I assume time is passing. I go play tennis: I toss the ball in the air and hit a serve. Time passing. I learned all this as I grew up. I had no pre-knowledge. It is experience.


Don't get me wrong, I agree that saying it took an infinite time to "get here" is a problematic notion, I don't think that would have ever been a working concept of time. But neither should we expect our everyday notion to apply universally. We always need to be ready to throw out a model, any model no matter how fundamental, when we reach the domain where it just doesn't make sense any more, or is found to disagree with observations, or where we cannot even provide operational definitions for what we are talking about. That's if we will use science as our tool, and no sharper one exists.

If everything I observe and experience, reinforces my concept of time, then I will grow to accept it. Quite obviously, I am talking about our macro world.

Stephen Hawking posited three arrows of time:
1) psychological time: things we remember are in the past.
2) Entropic time: universe moves from a state of order to a state of disorder.
3) cosmological time: arrow of time moves forward in inflationary state

He argued that the first two are the same: To create memories neurons align themselves in a certain way. This requires energy, which results in our body heating up a little bit, which means total entropy increases. Our memory only increases when entropy increases. So the two arrows must point in the same direction.

He argued that these two notions are the same.

profloater
2017-Dec-02, 03:23 PM
I know I am probably opening a can of worms here, but I have a rather simplistic question which has bugged me since childhood.

The old model of the universe was that the universe always existed, will always exist for eternity. Problem here, I never could understand how we could ever reach the present, since the past was eternally long.

Then the theory of the Big Bang showed up, and the question was what was before t=0? How could it start up?

Now we speak of multiverses, bubble universes, branes colliding to create the Big Bang for our universe, etc. So these extend back infinitely (back to square one)

So the question is: how could we ever have reached the (elusive, constantly changing) present if the past is infinite? :confused:

I suppose you are thinking of infinity as a number too big to think about. When I was younger I always though infinity of the past was more satisfactory than a beginning. So when the Big Bang was proposed I preferred to see that as a stage, a node if you like. If you think of a solar system it could be timeless cycling around for ever or it could be evolving out of dust, but the whole universe is a big thing to arrive out of nothing, but that is not what the current model says. The BB is a singularity in the maths or a point beyond which we cannot see backwards.

grapes
2017-Dec-02, 03:49 PM
I am speaking from my point of view. From what I experience. Things which have a time sequence in my life. I am saying I do not need math for this simple example.

Need math? Math is just a tool that can aid in understanding. It's a powerful tool, too, if you reject it you're just limiting your understanding.


Stephen Hawking posited three arrows of time:
1) psychological time: things we remember are in the past.
2) Entropic time: universe moves from a state of order to a state of disorder.
3) cosmological time: arrow of time moves forward in inflationary state

He argued that the first two are the same: To create memories neurons align themselves in a certain way. This requires energy, which results in our body heating up a little bit, which means total entropy increases. Our memory only increases when entropy increases. So the two arrows must point in the same direction.

He argued that these two notions are the same.

Of course they're the same by that description. The second is a physical law, the first is described by a physical process. If it is a physical process, which I have no reason to doubt right now.

gzhpcu
2017-Dec-02, 04:03 PM
Need math? Math is just a tool that can aid in understanding. It's a powerful tool, too, if you reject it you're just limiting your understanding.

Of course they're the same by that description. The second is a physical law, the first is described by a physical process. If it is a physical process, which I have no reason to doubt right now.
Guess I did not make myself clear. I just said that I do not math in this instance, i.e., sequencing my memories...

01101001
2017-Dec-02, 05:18 PM
Executive summary: Everything has a beginning -- unless it doesn't.

Ara Pacis
2017-Dec-02, 05:32 PM
Anchor points. Even if time and space are infinite, anchor points give us both an orientation and a reference for reckoning. Unless one posits that time is infinitely indivisible (i.e. Zeno's Paradox) in such a way that there is no fixed scale from moment to moment (ignoring Planck Time), time can still be counted at a rate of 1 second per second. Just because something is infinite, doesn't mean it's infinitesimal. For all we know, it's not infinite, but merely looks that way.

Think of it as a treadmill. You see the belt rotate over the front roller, and if you look behind, you can see it disappear over the rear roller, and if you see markings on the belt, you can discern both sequence and rate. However, you may not know how long the belt is. It could be a simple loop that connects back to the front roller using the shortest path possible, or it could be many yards longer, supported by more wheels and motors that allow it to support its movement. It could have loops and rollers that are much larger and much smaller, allowing the speed to appear faster or slower to other entities on that part of the treadmill, but you don't know about that since you can't see it. All you see is the treadmill between the rollers in front of and behind you, and its rate. For all you know, the markings are painted on just before it comes into view and erased as soon as it disappears, but that doesn't make it any less real, to you at least.

Or think of it as industrial baking. If you've ever watched "How It's Made," you'll understand. A dough mixing machine pours a continuously made dough onto a conveyor. It goes under various hoppers, and gets stuff added to it. Then it goes through a cutter, is baked, and is then cooled and packaged. To someone at a certain point on the conveyor, it looks like the dough is never ending. However, when we look at the bigger picture, we realize it's being part of a cycle that is discrete and non-infinite.

Ken G
2017-Dec-02, 05:42 PM
Are you questioning the red shift of galaxies, pointing towards the Big Bang?Quite the opposite, I'm describing the logical ramifications of those redshifts.


I naturally assume when I am looking at my wristwatch observing that the second hand is moving that time is passing for me. I know, that's what I said.

When I look at the moon and see it moving during the night, I assume time is passing. I go play tennis: I toss the ball in the air and hit a serve. Time passing. I learned all this as I grew up. I had no pre-knowledge. It is experience.That's all what I just said, read it again. Here is what you are doing. You have all the experiences you just named, and you built a concept of time from them. None of them occurred anywhere near the beginning of the universe, and among many other things, none of them hold a candle to the extreme energy scales of those early times (based on interpretation of galactic redshifts). In particular, as I said, there were no objects we have ever observed that existed for a "proper time" long enough to rise to the level of what you call "existence" when you are talking about moons and tennis balls. What's more, you had no "pre-knowledge" of moons or tennis balls when you were born, you built that knowledge from experience. But then, you take your construction, and you extrapolate it into realms you have not experienced, yet you are surprised when your constructions seem to fail you. I'm saying you should never find that experience particularly surprising-- that's what you have experienced your whole life, a need to rebuild your concepts when exposed to a whole new set of situations. This is also what physics had to do, when it discovered that the Earth is not the only thing that is responsible for gravity, when it discovered that motion does not need a cause to continue in friction-free environments, when it discovered that particles and waves share similar rules of behavior, and when it discovered that time does not tick along universally for all objects-- but instead every object has its own time, if indeed it exists long enough to support a notion of the passage of time for that object. The question that the early moments of an energy density singularity force us to ask is, how long must a particle exist before we can apply a concept of the passage of proper time to that particle? And when every particle has a different proper time, does anything you've ever experienced in your life, that contributed to your concept of time, apply at all?


Quite obviously, I am talking about our macro world. But that's just it, you're not talking about our macro world. Look back at your OP, and notice that you asked a question that involves t=0, so why do you think that is about our macro world?


Stephen Hawking posited three arrows of time:
1) psychological time: things we remember are in the past.
2) Entropic time: universe moves from a state of order to a state of disorder.
3) cosmological time: arrow of time moves forward in inflationary state
Ah, but that is quite a bit more than just three arrows of time, those are three very different types of time! In particular, they are not at all the same thing. The first is a mental construct that is not measured with a clock at all. The second applies to large systems that can support a concept of proper time for the whole system, like a functioning timepiece, which of course is quite a bit different from the elapsed proper time of all the components of that system (like people, if the system is a universe). The third engenders a set of operational definitions that cobble together a host of different reference frames into a mathematical entity called the "comoving frame" in cosmology. Above all, it seems quite likely that all three of those concepts of time lose their operational support as one approaches t=0.
He argued that the first two are the same: To create memories neurons align themselves in a certain way. This requires energy, which results in our body heating up a little bit, which means total entropy increases. Our memory only increases when entropy increases. So the two arrows must point in the same direction.

Now, the important thing is that all three of those "types" of time play well together in the context of our own experiences, so we suffer no existential angst around the issue of "which is the real time." But we don't have to stress these notions very far before disconnects do appear, and we find they cannot all be the same. The natural conclusion is that none of them are the "actual thing that time is," they are all just useful mental constructs that we call "time", analogous to all the useful mental constructs we call "a computer" or "a phone," or any of the other countless useful constructs we invoke every day that are not "the actual thing that a computer is" or "the actual thing that a phone is."


He argued that the first two are the same: To create memories neurons align themselves in a certain way. This requires energy, which results in our body heating up a little bit, which means total entropy increases. Our memory only increases when entropy increases. So the two arrows must point in the same direction.
Yes, the arrows are the same, but the times are not. The arrow is a tiny component of the concept of time.
He argued that these two notions are the same.I doubt he argued the notions are the same, because it is very easy to find counterexamples. If you've ever heard the expression "time flies when you're having fun," that's an obvious counterexample to the claim that the notion of psychological time is the same as the notion of entropic time.

Ken G
2017-Dec-02, 05:44 PM
Executive summary: Everything has a beginning -- unless it doesn't.Or put this way: the concept of a beginning is a useful notion for everything-- except when it isn't. What's more, sometimes sticking too literally to that notion actually becomes a barrier to understanding. I can ask anyone-- when did you begin? Is finding a literal answer to that question useful to your understanding of yourself, or an impediment to it?

Chuck
2017-Dec-02, 10:55 PM
We don't know that there was a beginning of the universe. Maybe the diameter of the universe was Ĺ a Planck length 1 second before the the Big Bang, ľ of a Planck length a second before that, ⅛ of a Planck length a second before that, etc. Then it would have been doubling in diameter every second until it got big enough for us to theorize about. Since for each second before that it would have been half the size that it was a second later, there would have never been a time when its diameter was zero. There need not have been a beginning.

I think there's a problem with the universe being infinitely old only if it had a beginning. Then infinite time would have had to have passed between two events, the beginning and now. We would never have gotten to this point in time. But if there was no beginning then only finite time would have to have passed between any two events. Just like on a number line with infinite numbers, the difference between any two numbers is finite.

gzhpcu
2017-Dec-03, 07:26 AM
Or maybe to put it another way: how can I get to the present from the past?

Ken G
2017-Dec-03, 08:05 AM
Indeed, how do you know you are "in" the present in the first place? How much time is in a "now", such that you could have "gotten there" in some perceptual sense? If you say that "now" is an instant, then it's pretty clear "you" aren't there, as "you" don't do anything in an instant. Or if you say "now" is whatever period of time it takes for you to formulate the concept you call "now", then one "now" cannot "turn into" another, as there are no lines drawn in those shifting sands, flowing through the hourglass. These concepts are always much more vague than we tend to admit to ourselves, but they work for us-- as long as we don't take them too literally.

gzhpcu
2017-Dec-03, 10:03 AM
The present is a moving target. It is like frames of a motion picture. Now is dynamic. I can not freeze the present, the clock moves constantly. The present is what I am currently experiencing. But in terms of the universe, I could approximate it and say it is today, using our calendar as a reference point. One rotation of our planet.

slang
2017-Dec-03, 11:01 AM
The present is a moving target. It is like frames of a motion picture. Now is dynamic.

Not to a photon, at c. So why should time adhere to your description or our perception when we reach another limit, where t reaches zero and speed might cease to have meaning?


If you've ever heard the expression "time flies when you're having fun," [...]

I heard it as "times are fun when you're having flies", but the one expressing it was a bit green.

Copernicus
2017-Dec-03, 01:54 PM
42

Ken G
2017-Dec-03, 02:59 PM
The present is what I am currently experiencing. So you're saying "the present" requires whatever elapsed time necessary to have an experience, right? I mean, I think we can agree you cannot experience anything in an arbitrarily short time, so when you say the present is what you are experiencing, then it must last long enough for you to have that experience. And, no doubt you realize that some kinds of experiences take longer than others, I don't know the physiology of it but the nervous system has various different timescales for various different types of signals to move around. Perhaps a complex thought, say an insight, requires more time than a simple sensation. So by your meaning, even "the present" cannot be regarded as lasting a given amount of time, it must be more fluid than that. Hence the various expressions about psychological time ("appreciate your kids now, the time will fly by until they grow up," or, "a watched pot never boils", etc.). So we see the psychological time may have the same arrow as the time a clock is capable of measuring (which depends on the oscillator it uses for its precision), but it cannot be the same thing. Indeed, the Heisenberg uncertainty principle establishes quite fluid limits on how well we can establish a time interval, based on the situation. So "the present" means various different things in different situations, and it's not a stretch to imagine its meaning at the origin of the universe is different than the one you defined above.

gzhpcu
2017-Dec-03, 03:46 PM
Not to a photon, at c. So why should time adhere to your description or our perception when we reach another limit, where t reaches zero and speed might cease to have meaning?

Well, not being a photon, I am referring only to time as we perceive it. The time I am referring to in this discussion is that which we experience. Am not referring to QM extremes..

Jens
2017-Dec-04, 09:50 AM
Or maybe to put it another way: how can I get to the present from the past?

It seems like the paradoxes that Zeno brought up. And about the original problem, I agree itís troublesome. But I think thereís another way to look at it. Suppose you have an infinite timeline. The chance of you being at a certain spot approaches zero, but at the same time you have to be somewhere...

grapes
2017-Dec-04, 01:37 PM
Guess I did not make myself clear. I just said that I do not math in this instance, i.e., sequencing my memories...
No one needs math :)

If you refuse to consider it, in relating experience to math as an analogy for instance, you're just admitting defeat. There is no other area of human thought has dealt with the infinite more thoroughly.

However, the problem you're considering is not unique to the time dimension--space extends out forever in all directions. We don't know the limits of that extent, in any direction, of space or time, and if there are limits how those limits occur, how the limits keep us from beyond those limits.

Ken G
2017-Dec-04, 02:08 PM
The time I am referring to in this discussion is that which we experience. Am not referring to QM extremes..But that's exactly the problem I'm pointing out. You are applying a non-extreme notion of time to highly extreme conditions (t=0), and then seem surprised that leads to inconsistencies. you should only be surpised if it didn't!

Copernicus
2017-Dec-04, 02:27 PM
I know I am probably opening a can of worms here, but I have a rather simplistic question which has bugged me since childhood.

The old model of the universe was that the universe always existed, will always exist for eternity. Problem here, I never could understand how we could ever reach the present, since the past was eternally long.

Then the theory of the Big Bang showed up, and the question was what was before t=0? How could it start up?

Now we speak of multiverses, bubble universes, branes colliding to create the Big Bang for our universe, etc. So these extend back infinitely (back to square one)

So the question is: how could we ever have reached the (elusive, constantly changing) present if the past is infinite? :confused:

No one knows the answer to this question. I think it is a great mystery. That is why I wrote, "The moment, an instant, lasted forever, we were destined for the leading edge of eternity."

gzhpcu
2017-Dec-04, 04:15 PM
So you're saying "the present" requires whatever elapsed time necessary to have an experience, right? I mean, I think we can agree you cannot experience anything in an arbitrarily short time, so when you say the present is what you are experiencing, then it must last long enough for you to have that experience. And, no doubt you realize that some kinds of experiences take longer than others, I don't know the physiology of it but the nervous system has various different timescales for various different types of signals to move around. Perhaps a complex thought, say an insight, requires more time than a simple sensation. So by your meaning, even "the present" cannot be regarded as lasting a given amount of time, it must be more fluid than that. Hence the various expressions about psychological time ("appreciate your kids now, the time will fly by until they grow up," or, "a watched pot never boils", etc.). So we see the psychological time may have the same arrow as the time a clock is capable of measuring (which depends on the oscillator it uses for its precision), but it cannot be the same thing. Indeed, the Heisenberg uncertainty principle establishes quite fluid limits on how well we can establish a time interval, based on the situation. So "the present" means various different things in different situations, and it's not a stretch to imagine its meaning at the origin of the universe is different than the one you defined above.
Sorry, but in the context I am speaking about, I do not need to revert to QM or philosophy. I am talking about the pure and simple, every day context of the present, as the man in the street understands it. As I type, I am aware of the flow of time as my fingers type the words I am thinking about. I am not talking about Planck time units, I am talking about the simple flow of minutes.

gzhpcu
2017-Dec-04, 04:19 PM
But that's exactly the problem I'm pointing out. You are applying a non-extreme notion of time to highly extreme conditions (t=0), and then seem surprised that leads to inconsistencies. you should only be surpised if it didn't!I am only referring to the Big Bang have occurred about 13.8 billion years ago. If I run my film backwards, I approach t=0. Yes, I know, QM and GR breakdown here...

grapes
2017-Dec-04, 05:57 PM
Sorry, but in the context I am speaking about, I do not need to revert to QM or philosophy. I am talking about the pure and simple, every day context of the present, as the man in the street understands it. As I type, I am aware of the flow of time as my fingers type the words I am thinking about. I am not talking about Planck time units, I am talking about the simple flow of minutes.


I am only referring to the Big Bang have occurred about 13.8 billion years ago. If I run my film backwards, I approach t=0. Yes, I know, QM and GR breakdown here...
Your original question was


So the question is: how could we ever have reached the (elusive, constantly changing) present if the past is infinite? :confused:
This is not a problem that is even talked about, much less solved, in the street! Not that anybody else has solved it...

Darrell
2017-Dec-04, 05:57 PM
Going by all your refutations of all the suggestions and explanations other people have responded with, in context with your opening question, I can't understand what it is you are looking for. Though I suspect that any answer that would satisfy you would involve everything from cosmology to cognitive science. Whatever it is you are asking it probably is unanswerable at this time because we don't know enough. But I think if you considered some of the other comments further you might find that they address misunderstandings that have contributed to your question.

Ara Pacis
2017-Dec-04, 06:10 PM
Dude, infinity could have started last Thursday, for all we know.

gzhpcu
2017-Dec-04, 06:19 PM
Your original question was

This is not a problem that is even talked about, much less solved, in the street! Not that anybody else has solved it...
Yes, sorry if I was unclear. I was contrasting the old universe is infinitely old theory to the original Big Bang theory. Just saying both seem unsolvable (to us). I know there is no answer provided by our current level of science.

gzhpcu
2017-Dec-04, 06:21 PM
Going by all your refutations of all the suggestions and explanations other people have responded with, in context with you opening question, I can't understand what it is you are looking for. Though I suspect that any answer that would satisfy you would involve everything from cosmology to cognitive science. Whatever it is you are asking it probably is unanswerable at this time because we don't know enough. But I think if you considered some of the other comments further you might find that they address misunderstandings that have contributed to your question.Actually, I did not expect an answer. Was just expressing frustration at the current state of affairs.

gzhpcu
2017-Dec-04, 07:38 PM
Dude, infinity could have started last Thursday, for all we know.Yeah, we covered that in the (shudder) reality thread... :)

profloater
2017-Dec-06, 06:05 PM
What is frustrating is that you ask a question about a difficult aspect of time, then insist on an answer that relates to,our perception of time passing. Well I can tell you the rate of perceived time depends on the rate of information received. Neither constant nor predictable because our brain can supply its own information! But none of that helps with cosmic time questions even if some people find meditation has cosmic implications for them. Perceived time is a psychological question. Time during the Big Bang is a theoretical physics question.

Jeff Root
2017-Dec-06, 08:38 PM
I think that almost everything said here misses the point of the
original question, but Jens addressed it in post #34. It just
seems impossibly weird that a single point on an infinite line
could be special or unique or "now", but it is.

-- Jeff, in Minneapolis

gzhpcu
2017-Dec-07, 07:10 AM
What is frustrating is that you ask a question about a difficult aspect of time, then insist on an answer that relates to,our perception of time passing. Well I can tell you the rate of perceived time depends on the rate of information received. Neither constant nor predictable because our brain can supply its own information! But none of that helps with cosmic time questions even if some people find meditation has cosmic implications for them. Perceived time is a psychological question. Time during the Big Bang is a theoretical physics question.Why do I insist on an answer that relates to our perception of time passing you ask? Because it is relevant to our being and we are constantly confronted with it. From our perspective, if we could move backwards in time, would anything change? As a hypothetical entity impervious to the forces of gravity as we approach the Big Bang...

Am not talking about the clock pertaining to photons or elementary particles approaching the speed of light.

Darrell
2017-Dec-07, 02:32 PM
Am not talking about the clock pertaining to photons or elementary particles approaching the speed of light.

But, I think you are. You ask questions like this . . .


From our perspective, if we could move backwards in time, would anything change? As a hypothetical entity impervious to the forces of gravity as we approach the Big Bang...

Which are questions about the nature, the properties of time and how they result in human perception of time. It is as if you want to skip right to the answer, which is perfectly understandable, but not practical. The answer you're looking for will include all of what modern science has discovered about time. You may not need to be informed of all that to have some understanding of the answer, but the answer can only be arrived at by understanding and building on what science has previously discovered about time. Unfortunately, modern science has not yet discovered enough about time to answer your questions beyond some degree of informed speculation. And it is all based on the currently "known" properties of time. Like how it is relative, for example.

Ara Pacis
2017-Dec-07, 09:30 PM
Why do I insist on an answer that relates to our perception of time passing you ask? Because it is relevant to our being and we are constantly confronted with it. From our perspective, if we could move backwards in time, would anything change? As a hypothetical entity impervious to the forces of gravity as we approach the Big Bang...

Am not talking about the clock pertaining to photons or elementary particles approaching the speed of light.

Is moving backwards in time the same thing as visiting the past? I think there are distinctions. If you move backwards in time at the rate of 1 second per second, you'd be standing still, freezing time from your perspective. You'd have to move backwards at a faster rate. However, does that create physical effects, such as occupying space and creating gravity? A lot of people get around this by moving forward in time through a shortcut, such as a wormhole or traveling really fast backwards in space where there is presumed to be less mass to interact with, or by claiming to use some sort of field effect to create a bubble that acts as a discontinuity.

Come to think of it, the simplest answer is yes, you can go back in time as easily as forwards, but it merely rewinds the tape and you walk backwards and lost the information you learn. In other words if you could move backwards, you wouldn't be able to remember it.

As for the rest of the question about why is one moment special? Perception. All moments are special, we just choose some to be more special to us than others. We choose these to be landmarks and count the time elapsed since then.

gzhpcu
2017-Dec-08, 07:20 AM
The duration of the present is infinitesimally small, it is the boundary between the past and the present. We use the word present in a much looser, broader sense...

Ara Pacis
2017-Dec-08, 05:00 PM
The duration of the present is infinitesimally small, it is the boundary between the past and the present. We use the word present in a much looser, broader sense...

I thought it was limited to discrete units of Plank Time.

The human nervous system has a finite speed (~60 MPH, IIRC), so we're all living in the past. Perceptions take time to be processed, and our bodies know this, hence the evolution of ganglia that trigger reflexes before the brain is aware of a stimuli. New research in human thought using MRI suggests there is an internal debate about how to understand perception, memories, processed results, etc. This may indicate that the brain itself is aware of the passing of time even while it is stuck thinking about events. Perhaps this is the base reason why our perception of time and the present is "a looser, broader sense."

Luckily for us, we're the top predator and have the luxury of wasting time lost in thought. Prey animals have to react more quickly. Also, we're a large animals, so our movements are slower than smaller animals, and our proprioception may inform our sense of time as well. Smaller animals also have less distance for neural impulses to move, so they can react more quickly. The speed of small animals and insects compared to our own may also inform our prolonged sense of time. Our ability to play catch, tossing a ball into the air and preparing to intercept the parabolic arc power by gravity of a huge planet may also prolong our sense of time, since the motion can seem slow to us even though it is powered by forces much more massive than us (whether it be Earth's gravity or some cosmic entity).

gzhpcu
2017-Dec-09, 07:31 AM
Yes, right, assuming time is quantized.

Shaula
2017-Dec-09, 08:35 AM
I thought it was limited to discrete units of Plank Time.
Nope. In current theories the Planck time has not been shown to have any physical significance at all. There is lots of speculation about it but it is just that - speculation.

Strange
2017-Dec-09, 09:52 AM
The human nervous system has a finite speed (~60 MPH, IIRC), so we're all living in the past.

Worse than that, we are living in multiple pasts. When you pick up a cup of coffee, the visual signal of your hand and the cup reach the brain in a few milliseconds but the touch sensation takes 100s of milliseconds. The brain has to make these both appear to be "now".

profloater
2017-Dec-09, 12:35 PM
indeed the ability to predict which muscles to fire to throw a ball or walk, have to be learned and form an intricate set of predictions to achieve smooth performance. The ability to catch a ball for example is amazing when you consider the twin predictions of the incoming flight from vision and the coordination of muscles which are driven by neurons at quite slow speeds. So the brain can work in the future to do that but our sense of now stays continuous. If we try to think about it the automatic system falters, like the adage that if you want to ruin a golfer's swing, ask her to explain exactly how she does it.

Copernicus
2017-Dec-09, 02:29 PM
indeed the ability to predict which muscles to fire to throw a ball or walk, have to be learned and form an intricate set of predictions to achieve smooth performance. The ability to catch a ball for example is amazing when you consider the twin predictions of the incoming flight from vision and the coordination of muscles which are driven by neurons at quite slow speeds. So the brain can work in the future to do that but our sense of now stays continuous. If we try to think about it the automatic system falters, like the adage that if you want to ruin a golfer's swing, ask her to explain exactly how she does it.

I have often thought that our hands actually have visual receptors.

Ara Pacis
2017-Dec-09, 03:49 PM
I have often thought that our hands actually have visual receptors.

Insofar as heat is thermal photons, they kinda do.

gzhpcu
2017-Dec-09, 08:36 PM
Nope. In current theories the Planck time has not been shown to have any physical significance at all. There is lots of speculation about it but it is just that - speculation.Isn't Planck time the time needed to cross the Planck length, so defacto the smallest time measurement possible?

gzhpcu
2017-Dec-09, 08:46 PM
Apparently Saint Augustine once said "I know what time is until you ask for a definition about it, then I can't give it to you"-

Chuck
2017-Dec-09, 10:02 PM
Time is distance divided by speed.

Jeff Root
2017-Dec-09, 10:36 PM
If you are reading this thread, then you need to read this web page:

http://www.pitt.edu/~jdnorton/Goodies/What_is_time/

His answer to that question includes my own, which I'll state in my
own words: A definition or explanation describes an unfamiliar thing
in terms of things that are familiar. Time is familiar to everyone.
We all experience it all the time. Nothing that is in any way similar
to time is as familiar to us as time is. So it is not possible to define
or explain or describe time in terms of things that are more familiar.
Time is one of those things that can only be understood through
experience. Like color, amusement, happiness, or love.

The quote from book 11 of Augustine's 'Confessions':

https://harpers.org/blog/2009/03/augustine-on-the-illusion-and-reality-of-time/

-- Jeff, in Minneapolis

Ken G
2017-Dec-10, 03:56 AM
If you are reading this thread, then you need to read this web page:

http://www.pitt.edu/~jdnorton/Goodies/What_is_time/

His answer to that question includes my own, which I'll state in my
own words: A definition or explanation describes an unfamiliar thing
in terms of things that are familiar. Time is familiar to everyone.
We all experience it all the time. Nothing that is in any way similar
to time is as familiar to us as time is. So it is not possible to define
or explain or describe time in terms of things that are more familiar.
Time is one of those things that can only be understood through
experience. Like color, amusement, happiness, or love.

The quote from book 11 of Augustine's 'Confessions':

https://harpers.org/blog/2009/03/augustine-on-the-illusion-and-reality-of-time/

-- Jeff, in MinneapolisYet that answer is not a scientific one, as it is not the scientist's goal to prejudge time, but rather to test it. In science, we can only allow operational definitions, which do not look like "I know it when I see it," as that dictates to nature. Instead, operational definitions look like instructions for doing a quantitative measurement, which allows nature to talk to us instead. So in science, time is something that can be measured with a clock, and although the clock is something we know when we see (it is something that exhibits the necessary consistencies that allow time to be a scientific notion in the first place), time itself is not something we know when we see. Indeed, the concept of time used in relativity is not at all like anything we've seen. No doubt St. Augustine would have been quite shocked by how time "actually works," which is more or less the reason we had to invent science in the first place!

Hence, whenever one asks "what is time," one can mean a lot of things. One can mean, "what is time in science," and that's a very different question from "what is the notion of time that I think I know already from my daily life." Indeed, in science, the latter question really doesn't make any sense, even if one imagines it does, but of course science need not be all things to all people. Many people think they already know the Earth is flat, for example, and they don't think they need science to tell them otherwise. They are not listening anyway.

The philosopher you quote felt that the scientific definition of time, that which a clock measures, is insufficient to answer what is time, but actually I think a very good answer is this: "time is our name for the recognition that it is possible to have clocks." It is because the concept of a clock makes sense and the engineering of a clock is straightforward that we have a notion of time, and any and all precision that comes with that notion stems from clock precision, whereas all informal elements stem from more informal versions of clocks. It is an observation about clocks, that's what the time concept is, and like so many scientific concepts, once defined, we discover it is way different than we imagined when we look at it more closely. This is the key fact that "I know it when I see it" thinking misses, although one also needs a version more of that ilk to cover all the unscientific needs for the notion. It is always a choice to think scientifically, and it is always necessary to notice if that choice is being made-- or not.

gzhpcu
2017-Dec-10, 07:37 AM
No matter how time is defined, one thing is common: it moves forward, not backward. That is why the question arises: How did we get to the present?

Copernicus
2017-Dec-10, 07:50 AM
As far as I can tell time is events recorded relative to the number of revolutions of a periodic object. One revolution can define an interval, but that is all that we are saying. 1000 intervals, a zillion intervals etc. It has no absolute meaning.

Jens
2017-Dec-10, 07:50 AM
No matter how time is defined, one thing is common: it moves forward, not backward. That is why the question arises: How did we get to the present?

I was trying to address that in post 34. Iím afraid I canít give you anything more satisfying, but do you see the point?

profloater
2017-Dec-10, 09:45 AM
No matter how time is defined, one thing is common: it moves forward, not backward. That is why the question arises: How did we get to the present?

If you want to take that line, then I do not see your problem. your time has moved forward from the past to now. Yesterday is passed, today is the present. But you are not right about "however it is defined" . "How did we get to the present? is a question full of assumptions as has been teased out already.

Ara Pacis
2017-Dec-10, 04:07 PM
No matter how time is defined, one thing is common: it moves forward, not backward. That is why the question arises: How did we get to the present?

Common in what sense? To all humans? To all sapient species, including potential aliens? To all physical systems? And what is "it": Does time move around us, or do physical objects move through time? And what do you mean by defined: How it is designed/evolved to work, how it is observed to work, or how it is explained/theorized to work? And when you say backwards, you you mean an unwinding of cause-effect, or moving forward in an opposite direction?

Is there something you think is unique about the present? Even on an infinite plane, a finite object takes up a finite area. It has to be somewhere. Is the issue more a Cognitive Dissonance between human ego and the Copernican Principle?

gzhpcu
2017-Dec-10, 09:30 PM
Common in what sense? To all humans? To all sapient species, including potential aliens? To all physical systems? And what is "it": Does time move around us, or do physical objects move through time? And what do you mean by defined: How it is designed/evolved to work, how it is observed to work, or how it is explained/theorized to work? And when you say backwards, you you mean an unwinding of cause-effect, or moving forward in an opposite direction?

Is there something you think is unique about the present? Even on an infinite plane, a finite object takes up a finite area. It has to be somewhere. Is the issue more a Cognitive Dissonance between human ego and the Copernican Principle?
Time moves forward. Forget theories on exotic oarticles. The present is a moving target, but it moves forward on the macro level. What is pertinent is what affects us. Sure you could have a model of slices of spacetime layered upon one another. Why so complicated? What is pertinent to us is how we experience it. Abstract mathematical models are fine, but they do not neccesarily reflect what things really are. They are models to use to make predictions and need not be taken literally.

Chuck
2017-Dec-11, 03:56 AM
Time is what makes me either bored or late for something.

grapes
2017-Dec-11, 11:38 AM
Isn't Planck time the time needed to cross the Planck length, so defacto the smallest time measurement possible?
But, the Planck mass is a small insect egg, about a fiftieth of a milligram. I'm not sure you can say anything is the smallest possible.