swansont Posted February 24, 2014 Posted February 24, 2014 All clocks proceed unevenly, within a tick cycle. Old fashioned chronometers proceeded with a series of small jerks forwards. More modern atomic clocks still run at uneven rates through their tick cycle, this can be modelled by SHM. Modern atomic clocks put out a signal at some frequency, typically 5 MHz or 100 MHz, which is used for comparisons, though some do have a 1 pps output as well. Clocks will update the output signal frequency at some interval, but the output is still analog. No "tick" per se. You count oscillations by counting zero-crossings of the analog signal.
studiot Posted February 24, 2014 Posted February 24, 2014 (edited) You count oscillations by counting zero-crossings of the analog signal. Yes I am aware of that and that this is your specialist field. What you are basically saying is the limit of resolution (nothing to do with Heisenberg) is the interval between two zero crossings. We have to assume that time itself flows evenly within this interval. And yes I am using 'tick' in the most general sense. This is somewhat akin to the limit of spatial resolution of various types of microscope. Edited February 24, 2014 by studiot
Lizzie L Posted February 24, 2014 Posted February 24, 2014 Well one of my underlying points, I guess, is that our models are only ever as good as their fit to the data, and the data is only as good as our measurements. So if we are going to have equations with measurable units in them (like seconds) we need at some point to operationalise that construct as a measure.
Dekan Posted February 24, 2014 Posted February 24, 2014 The OP asked for a basic understanding of "Time". And people seem to be assuming that "Time" is an actual "thing", which can be pinned down and defined. But surely it's only an abstract noun we've invented. I mean, in the English language we've got a word "time", That doesn't by itself create an actually physical entity Anymore than having the English word "beauty" creates some objective and measurable entity "Beauty". Also in this connection, people keep talking about time "flowing". And the "flow" of time. As if "flow" were a thing, Well, why not try to define "flow". What is "Flow"? Doesn't that make as much sense as asking, what is "Time"? Aren't we perhaps being led astray by language. We create a word "Time", then look for some "thing" to correspond to it. But there may not be one. It may be just a linguistic artifact.
Strange Posted February 24, 2014 Posted February 24, 2014 The OP asked for a basic understanding of "Time". And people seem to be assuming that "Time" is an actual "thing", which can be pinned down and defined. But surely it's only an abstract noun we've invented. That is true for the words "moon," "love" and "space" as well. I think we can all agree they exist. We create a word "Time", then look for some "thing" to correspond to it. Do you really think someone invented the word first and then tried to find something to apply it to? Really?
Lizzie L Posted February 24, 2014 Posted February 24, 2014 Well, all our words are ways of modeling the world. Some models are more precisely defined than others.
Endercreeper01 Posted February 24, 2014 Posted February 24, 2014 Reply - I wonder why the proportionality constant is c-squared. That seems to imply a kind of "Flatland"-style 2-D Universe. Whereas the actual Universe is 3-D. I mean light doesn't travel in a flat 2-D plane. It goes off in all three dimensions, Wouldn't that make a c-cubed constant, more what one would expect? The proportionality constant is [latex]c^2[/latex] because when you square the coordinate [latex]ct[/latex], you have to multiply the square of c and the square of t together, so it becomes [latex]c^2t^2[/latex]. It does not imply that we live in a 2 dimensional universe.
swansont Posted February 24, 2014 Posted February 24, 2014 The OP asked for a basic understanding of "Time". And people seem to be assuming that "Time" is an actual "thing", which can be pinned down and defined. But surely it's only an abstract noun we've invented. Abstractions are things, too. They just aren't physical objects, but then, I don't think that anyone has suggested that time is a physical object. Nature behaves an awful lot — one might say exactly — like time is a real phenomenon. I mean, in the English language we've got a word "time", That doesn't by itself create an actually physical entity Anymore than having the English word "beauty" creates some objective and measurable entity "Beauty". Also in this connection, people keep talking about time "flowing". And the "flow" of time. As if "flow" were a thing, Well, why not try to define "flow". What is "Flow"? Doesn't that make as much sense as asking, what is "Time"? Aren't we perhaps being led astray by language. We create a word "Time", then look for some "thing" to correspond to it. But there may not be one. It may be just a linguistic artifact. That's the problem of taking analogies and metaphors too literally: they stop working. The proportionality constant is [latex]c^2[/latex] because when you square the coordinate [latex]ct[/latex], you have to multiply the square of c and the square of t together, so it becomes [latex]c^2t^2[/latex]. It does not imply that we live in a 2 dimensional universe. Wrong context. The post in question was in regard to E=mc2
Dekan Posted February 24, 2014 Posted February 24, 2014 That is true for the words "moon," "love" and "space" as well. I think we can all agree they exist. Do you really think someone invented the word first and then tried to find something to apply it to? Really? Strange, the word "moon" obviously refers to a physical object. Either our own specific Moon, or in a more general sense, a moon or satellite of some other planet. Either way, the word corresponds to an actual object. "Space", is more doubtful. I suppose it corresponds to something that exists, but couldn't the noun "space" be replaced, in most contexts, by the preposition "from". For example, instead of saying "there's a space of 240,000 miles between the Earth and the Moon", we could say "the Moon is 240,000 miles from the Earth". "Love" I don't think exists any more than "Beauty" does - it's just a word describing what we humans experience and understand, but has no objective existence. As regards "Time", I don't think that has any objective existence either. It really means no more than "we experience, as humans, that things don't stay the same, they keep changing". You could replace the word "Time" by the word "Change", and wouldn't it convey the same meaning. Possibly, what makes us think of time as a separate entity is mainly our artifacts such as clocks, and calendars
studiot Posted February 24, 2014 Posted February 24, 2014 Dekan, have your heard of the terms abstract and concrete nouns? The moon is a concrete noun - it is made of 'stuff' Love is an abstact noun. They are often concepts. If you wish to deny love then there are plenty more eg anger, sorrow and so on that you cannot. It is a philosophical question as to whether something that consists of nothing itself but supports the existence of concrete nouns (space and time) is itself abstact or concrete. No classification scheme is perfect.
Dekan Posted February 24, 2014 Posted February 24, 2014 Thanks studiot, I seem to have heard of those terms. I would however respectfully dispute your suggestion that "Time" is a concrete noun. But as you say, no classification scheme is perfect. For example, "Love" can be used as a concrete noun, As in "Thanks, Love" .That reminds me of some old comedy sketch: "What is this thing called Love" versus Girl (in passionate clinch exploring boyfriend's nether regions):: "OOh, what's this thing called, Love?"
swansont Posted February 25, 2014 Posted February 25, 2014 "Love" I don't think exists any more than "Beauty" does - it's just a word describing what we humans experience and understand, but has no objective existence. Experience? Understand? You dismiss two abstract notions in favor of two other ones. It doesn't really bolster your position.
studiot Posted February 25, 2014 Posted February 25, 2014 Like I said no classification scheme is perfect. Peace and harmony certainly exist in concept , but sadly how much exist in reality is another matter.
Lizzie L Posted February 25, 2014 Posted February 25, 2014 What does appear to be true is that we tend to perceive time as going more slowly when the event rate is more rapid. Which means that rather than perceiving the speed of time as the rate of change, we have a normative idea of the rate of change, so that when things happen rapidly we perceive time slowing down. And when nothing happens, time seems interminable. The classic example is when people report their experience of a car crash as of things happening "in slow motion".
swansont Posted February 25, 2014 Posted February 25, 2014 Perception of time is a different beast. We aren't reliable. This is one reason we use instrumentation to do scientific measurements.
Lizzie L Posted February 25, 2014 Posted February 25, 2014 Definitely a different beast. Which is why I've been arguing that we operationally define time, for scientific purposes, in terms of clocks. There doesn't seem to be a more fundamental definition than that.
Strange Posted February 25, 2014 Posted February 25, 2014 It may be necessary to point out that when Einstein said, “Put your hand on a hot stove for a minute, and it seems like an hour. Sit with a pretty girl for an hour, and it seems like a minute. That's relativity”, he was joking... Definitely a different beast. Which is why I've been arguing that we operationally define time, for scientific purposes, in terms of clocks. There doesn't seem to be a more fundamental definition than that. The measurement of time, yes.
Lizzie L Posted February 25, 2014 Posted February 25, 2014 OK, so how would you operationally define time, independent of the method we use to measure it?
Strange Posted February 25, 2014 Posted February 25, 2014 OK, so how would you operationally define time, independent of the method we use to measure it? It is a dimension in GR.
studiot Posted February 25, 2014 Posted February 25, 2014 (edited) It is a dimension in GR. The so called 'block universe' is only one view or aspect of time I think the OOP and Lizzie L are trying to reconcile various views or aspects. Insisting upon one over all others is counterproductive IMHO. After all it was a great day for science when inertial mass was shown to be equivalent to gravitational mass. as was the day when the mechanical equivalent of heat was determined. That's progress. https://www.google.co.uk/#q=block+universe Edited February 25, 2014 by studiot 1
Strange Posted February 25, 2014 Posted February 25, 2014 The so called 'block universe' is only one view or aspect of time I think the OOP and Lizzie L are trying to reconcile various views or aspects. Insisting upon one over all others is counterproductive IMHO. I don't insist on one definition. But I will continue to use this (and muon decay) as an example that time does not have to be defined in terms of change. Although, of course, it can be for some purposes (such as measurement).
Implicate Order Posted February 25, 2014 Posted February 25, 2014 (edited) It's been a long thread. What is evident is that time as a notion is very hard to pin down and reach consensus on. It's getting late and I thought I would add a metaphysical addition to the mix just as a way to put this into perspective from an observers viewpoint. Obviously each one of us have a sense of what time is. It represents a personal notion to each one of us of a 'moving now'. We have memories of a past through a trace of causative progression and we are confident that that past is real to us and that we have ridden upon the moving now from the past to this present point in time. I carry my own personal clock with me at all times as a device to measure how my 'moving now' relates to all your apparent 'now's' or to the 'nows' of other seperated things in space that carry their own clocks. To relate my time to yours I don't actually recognise that I am always looking into my past when dealing with you all. When I communicate with you I assume you share the same moment in time ("moving now") as me but that is just illusory. You actually all exist in my past light cone as you are all seperated in space from me and it takes time for me to see you. The reason for this of course is that 'c' is finite from each observers frame of reference and does not travel between different points in space from a particular frame of reference 'instantaneously'. This 'illusion' in our minds is not obvious to us as we assume when communicating with you all that we share the same moving now and the same causal history, but this is actually not the case at all. Different frames of reference that are causally connected will only share a portion of the other frame of reference's light cone (hubble volume). The information available in each overlapped region is less than the total information available within each observers entire light cone. The closer you are to the other frame in spacetime, the greater overlap of causal histories but they are never exactly equivalent unless the frames of reference are located at the exact same point in spacetime. While this illusion is not evident, we are aware of something strange going on in the way that I perceive your clocks time and also if you are not comoving in space with me inertially, then your tick seperation is also different to mine when viewed from my frame of reference. This is actually necessary for me to possess a notion of a causative past. If from my frame of reference your clocks didn't show a different time when we were spatially seperated, or tick differently if our frames of reference were relatively moving, then there would not be a causative past for me at all. The reason for this difference in perspectives is due to the reduced amount of information available in each overalapping light cone region. This results in me seeing only a fraction of your causative history that is available to you. Assume I wish to get peace of mind that we all share the same 'instantaneous' moving now. To initially get all our clocks on the same footing I gather all your personal clocks you are all carrying and bring them to me to synchronise first before I then pass these clocks back to you. But I can't pass these clocks to you all seperated in space away from me 'instantaneously'. If I did so, your clocks from my frame of reference would all show the same time as mine and if you were moving relatively to me, would tick at a different rate. The best I can do however is send these clocks to you (say by a very fast transport device) in my past as it takes time to get these clocks back to you. As the transport device gets these clocks back to you, I have already moved on with my moving now and you get the clocks in my causative past. You won't of course see it this way as you are all ahead of me. What is sacrificed however in you living in my past is that from 'my frame of reference' the time on your clock will differ to mine even though they were initially synchronised. The reason for this is because you are now spatially seperated from me. It is further compounded if you are relatively moving in space with respect to my frame of reference. The degree of causative lag into my past will directly influence the way I measure the time of your clock. I am assuming there is no lag to give peace of mind to me that you share the same moving now and therefore will all a common notion of simultaneous causative events. The reality is that each observer will have a different viewpoint on where and when an event occurred but you won't sense this. The illusion that you all share the same moving now as me keeps my world ordered and makes me believe that we all share the same notion of simultaneity. However to share a sense of the exact same causative path as you, something has to give as you really are in my past, What does give is that your clocks will show a different time to me when I view yours and vice versa. The only way to get your clocks to show the same time as me is for you to catch up to my moving now. If you did so however I wouldn't see you in a simultaneous moving now, as I look to you in my past as you are in a different place that is spatially seperate. Now note that it seemed logical that because you exist in my past I should be able to 'sense' this. I do not sense this however as this requires a self-referential judgement from the point of view of the observer. As Godel demonstrated in his incompleteness theorem, self-reference gets an observer into trouble. What I do sense however is that 'your clocks' tick at a different rate to mine. This is because by the process of measurement the information I am receiving is actually information drawn from my past. What time 'actually is in my opinion, is how an 'illusory' causative past is created by the delay in information received by an observer (or a frame of reference) from the external surrounds seperated in spacetime. We don't sense this however as we assume we are all on the same moving now. It is a frame dependent notion based on the information acquired from our external surrounds (our past) as a basis to interpret where we are located in spacetime. The causative history of information therefore creates a sense of time moving in one direction always forward on a 'moving now'. As our light cone expands, more and more information (causative history) is incorporated into our hubble volume to give the sense that we are moving forward. We as observers use a light cone emanating from our point in spacetime to interrogate the surroundings and the information we receive is only ever about our past, never our future. This is why IMO we 'sense' an arrow of time. ...and just to push things a bit further before I hit the sack....... I perceive the causative history of unfolding events of my time from my frame of reference in a different way you or other observers perceive their's. For massless things such as photons (the carriers of the information) they can access the entire information in each observers hubble volume instantaneously as they are timeless from their own frame of reference. What we perceive as causation, being a delay in the receipt of this information, is, from a photons frame of reference instantaneously available. This smacks of a greater illusion still in relation to time. What we need to recognise is that, like the photon, we can actually see our entire causal history at an instant. All things from their own frame of reference travel at 'c'. It is how we measure things external to this frame that the appearance of time and space emerge. Just look up to the stars at night to see your own entire causal history in an instant. What we measure however of things external to our frame 'lags' and is not received instantaneously attributed to spacetime seperation of the frames of reference we are measuring. In Quantum Mechanics, the collapse of the information contained in the light cone to provide a 'causative history' for us as observers is 'instantaneous' to the photon.However we would use a Schrodinger wave function to describe how that information state unfolds in our terms of time (from our frame of reference). Just look at Wheelers delayed choice experiment if you have any doubts on that. Edited February 26, 2014 by Implicate Order 1
StringJunky Posted February 25, 2014 Posted February 25, 2014 What does appear to be true is that we tend to perceive time as going more slowly when the event rate is more rapid. Which means that rather than perceiving the speed of time as the rate of change, we have a normative idea of the rate of change, so that when things happen rapidly we perceive time slowing down. And when nothing happens, time seems interminable. The classic example is when people report their experience of a car crash as of things happening "in slow motion". Your challenge, I think, is to reconcile how time behaves objectively, as a physicist measures it and how you, as a psychologist, understand it relying more on human experiential and physiological data . 1
michel123456 Posted February 25, 2014 Posted February 25, 2014 (edited) (...) Here is some quotes from the recent Cambridge University book 'On Space and Time', edited by Professor Shahn Majid. The one thing that does seem clear is that time flows I disagree. (And I am not alone, see below) To me, time does not flow. What happens is that WE are "moving" in time. Etienne Klein wrote (sorry for my word-by-word translation from french) " We already said that when the language speaks about time, it does it often in the wrong way. What does it mean when, for example, we are repeating that time "flows", "passes through", "vanishes"? This way of talking which associates time with lability and escape, has become common. By the way, it is not neutral. First of all, it is a language abuse. Nobody is arguing that we may say that time is made from any thing that passes. But to deduct that it is time itself that passes through is making a shortcut and confusing content and container (“contenant et contenu”, which means also subject and object). The succession of the instants of time (past, present, future) is not the same thing that the evolution (“succession”) of time itself. They (the instants) pass, it (the time) does not. Then,, why is it more correct to say that time passes through than to say that the road is moving (“le chemin chemine”) or that a music book is singing? If we admit that any reality is temporal, saying that time is passing through is equal to say that, in reality, what is passing through is the sum of things and phenomenas that are containing by time. In a few words, it is the entire reality that passes through, and not time itself”From « DOES TIME EXIST? ( LE TEMPS EXISTE-T-IL?) » ed. Le pommier, 2002, pg 22,23. The smallest (and most condensated) book on my bookshelves. Etienne Klein is a physicist and phd in philosophy, working at CEA (French Commissariat a l’Energie Atomique) and professor at Ecole Centrale de Paris. Copy-pasted from an old long thread on the same subject. page 7 post#125. IMHO it is an important point about a basic understanding of time Edited February 25, 2014 by michel123456
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