Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Where is the present?

  1. Apr 17, 2009 #1
    As a observer everything that I sense is the past, from the impulses sent within my body to the photons I see, do you think that makes the information processor I call my consciousness the present?

    Where is the present?
    Last edited by a moderator: Apr 17, 2009
  2. jcsd
  3. Apr 17, 2009 #2


    User Avatar
    Gold Member

    A modern day Zeno's paradox maybe?

    With a speed limit on information transmission it's impossible for anything to observe what we can mathematically construct as "the present."

    Even ignoring GR for the moment (and skipping the question of "whose present?"), I want to believe the limitations imposed on us by our own observational instruments shouldn't be what keeps us from experiencing "the present." But that is the conceited human in me. I am aware that there is a delay in everything I experience, but that doesn't mean I can get any closer to that mathematical construct. I treat all the information that I have most recently processed as "the present" and there's nothing else I can do.

    It's easy to observe when looking at the stars, or observing (discrepancy between light and sound) a distant explosion where the audible delay is quite noticeable and denote those events as "the past" even while it is part of MY "present." It becomes confusing to do so with the computer screen that sits 2 feet in front of me as I type this.

    I think I'm more confused after replying to this than when I started. The way I'm going to look at it is that the exact present is a useful tool for calculation, but applying that (and the inherant delay) to my experiences is not useful. I'm not sure if this is enough to serve as a distinction between the two, but that's what I'm doing.

    Please forgiven any shortcomings as I am not experienced or educated in Philosophy. This topic was intriguiging enough that I could not pass it up.
  4. Apr 17, 2009 #3
    In the almost-to-be observed just-past?
  5. Apr 17, 2009 #4

    There is no present,there is only the past, as far as we are concerned.
  6. Apr 17, 2009 #5


    User Avatar

    Staff: Mentor

    No we consider what we experience "now" as the present, even though it has already happened.
  7. Apr 17, 2009 #6


    User Avatar
    Gold Member

    Not all things that we experience are through our senses, thus not all we experience is in the past.

    Abstract thoughts, such as "I feel content" are not subject to events in the past. So, yes, I suppose our conscious thoughts are our present.
  8. Apr 18, 2009 #7
    Then it is the limit of the pas as it tends to the present.
  9. Apr 18, 2009 #8
    I think framing it in temporal terms is the problem. We and everything else is moving in relation to something which is what causes time to be perceived. So there is no now, only where we have been and where we are going.

    The present is whereabouts on that journey one finds oneself at the time of asking the question.
  10. Apr 28, 2009 #9

    True, we only observe one direction of space at a time, yet even a mathematical construct with a 360 view only exists in the minds eye of an observer in their present.

    Why skip this, its the only proof I can think of for the separability of time, other than as a mathematical construct.

    As far as we can see, maybe, because I am concerned in the present about the future. :rofl:

    How can you talk about the present with out doing so in temporal terms, naming a where instead of when maybe. Where does this leave the future?
  11. Apr 28, 2009 #10
    Actually that is just as much an observation of the past.
    One could feel contentment, but as soon as one acknowledges it or even understands it for what it is... that makes it self-reflective... which involves the past.

    We are most in the present when we are un-self-reflective, that is, just doing something without thinking about it.
  12. Apr 29, 2009 #11


    User Avatar

    If we are talking about the human brain I think in terms of this abstraction.

    First it's obvious that the brain can not store and hold (remember) only a limited amount of information, not all time history, as it actually happened. The brain needs to continously compress and store data selectively.

    So what strategy for this compression does the brain use?

    As seems hinted from som research, the brain is no optimized for remembering actual temporal sequences. Instead the brain remember the history in a form, optimized for the expected future. Ie. the brain remember what it THINKS, is of survival value. This is clearly more important than to remember irrelevant details. Only in some brain disorders(savants), does this utility get misdirected and the person gets almost supernatural skills at remembering details, like truly photographic memory. But the downside is that these people have poor skills at imagining the future, which is from the point of view of evolution and competition a disadvantage.

    Somehow the retained past induces a probably future, but given that each brain, formed by it's own history, is different, each brain "sees" a slightly different future.

    Similarly I think the story is with physical systems. A physical observer, can not hold an infinite amount of information, so at some point the past is about as uncertain as is the future. Clearly, from the survival point, it is more important to be able to predict the future, than to per see, remember the past.

    So maybe the present can be characterized as state of expectations on the future which determines the action of the system, implicitly determined by a retained compressed part of the past.

    So the present IMO is related to the definiteness of behaviour or action.

  13. Apr 29, 2009 #12


    User Avatar
    Gold Member

    If we think in terms of classical physics, the present is a point on the time-continuum, i.e. the factual state of affairs at a given instant. This picture works very well for many purposes, but doesn't correspond at all well to our internal experience of present time. Because what we experience in the moment is things happening and changing, the experienced present is sometimes said to have a certain duration. But that's a logical conclusion drawn from the classical picture, not really a good description of what it feels like to be in the moment. The moment we live in is always only this moment now, but it's also ongoing.

    In quantum physics, instead of a continually evolving set of determinate facts, we have a repeatedly updated set of possibilities. The moment is temporally complicated -- the past is built into it, because the current "shape" of possibilities is constrained by the factual situation inherited from previous events. Moreover, what the wave-function describes -- possibilities structured by limiting facts -- is only the "virtual" background for what actually occurs in the moment, when one system interacts with another and gets information from it -- i.e. one system becomes "present" to another. This is the so-called "collapse" of the wave-function, which selects certain possibilities as new facts, and so updates the ongoing possibility-structure of both systems.

    The quantum picture is far from clear, at this point, but I think it corresponds much more closely with the temporal structure of our experience. That is, at any given moment we're experiencing our factual surroundings (given by the past) in the context of all the possibilities we anticipate may happen. The world around us at any time is, in a way, a possibility-structure contrained by inherited fact. And that is the background for what we actually witness in the "now", i.e. the coming into being of new facts, in real-time interaction among things, updating the structure of what's possible.

    So in a way it's right to say that everything we experience is "the past" -- insofar as it consists of given fact -- but that doesn't really describe the full content of our experience in present time.
  14. Apr 29, 2009 #13


    User Avatar
    Gold Member

    This sounds much like what I was trying to say in the previous post...
  15. Apr 29, 2009 #14


    User Avatar
    Gold Member

    You seem to be asking about the psychological present. Brain processing takes time (around 200 ms for a habitual level response, 500 ms to evolve an attention level response). So there is always a mental lag behind reality.

    Except. The brain is actually an anticipatory device - a forward model in neural net terms. It actively predicts the future (and changes its running model in response to errors detected).

    So "in the present" you are busy predicting your future (while adusting that prediction on the basis of recent past information).

    For an animal mind, which runs pure, there is just this future orientation. The present in some sense does not exist. It is already being looked through to the future beyond. The animal would have a current state of orientation, but not a sharp psychological sense of this being "right now".

    Humans have language and so can scaffold their brain responses - steer things. We have developed the grammatical notion of past, present and future. The habit of thinking this way. Though we are still basically anticipatory machines (memories are anticipatory images of "what it might be like to be back there"). And focusing just on "the now" is pretty impractical, as Zen practices illustrate. You can kind of pretend to do it, but not really do it.

    So consciousness is about being a future oriented observer. Guessing and planning. The actual present is the located starting point - which we don't naturally see because it is where we stand to look. The past is irrelevant except to the extent it can bear on the impressions we are constructing about the arriving future.
  16. Apr 29, 2009 #15


    User Avatar
    Gold Member

    This also clearly relates to what I was trying to say above -- but what an interesting description you give! Many thanks.
  17. May 1, 2009 #16
    Maybe the "present" is a cognitive construction. If it refers to my experience of now, then it requires my mental processing of the concept.
  18. May 3, 2009 #17
    I think even though the information may be some ms old, we still experience that information consciously with no delay.
    I'm not gonna get into qualia, but what I mean is that all experience of qualia will be without delay, even though the information is older.
    This is kind of the definition of consciousness in a way, the fact that all that stimuli information and memory information, while a few ms old, will still be experienced consciously in a mental present..

    Odd world indeed..
  19. May 3, 2009 #18
    I define the present as right now :)
  20. May 4, 2009 #19
    I'm currently taking a Psychology of Consciousness course and this is the exact topic I've been wondering about.

    What is the present moment? In Special Relativity, 'now' theoretically depends on the reference point (without getting into hypotheticals involving quantum entanglement).

    Speaking of the cleverness of language, it seems that an above poster who was criticizing the concept of now as merely a construction of our brains is guilty of that as well, no?

    Modern physics relies on the physicality of time. so, can we easily backtrack and say 'time is an illusion?' Either time is or isn't. it's served as a good model for helping us to explain the mechanics of our univsere thus far...

    So, what causes me to be experiencing this post I'm typing as opposed to a post i will write 20 years from now? What I really would like to know, if possible, is if there is a way to physically describe the present moment (besides the cheeky t = 'now').

    conrads idea that 'now' is the the wave function collapsing (or at the point in space-time where quantum decoherence occurs) is very interesting. i think he may be onto something...

    time has always been a mystery to me. when i was a child, i got into physics because i wanted to build a time machine. 'now', I'm more interested in the physics of experience, whether the 'observer' is actually something that is real in the game of quantum mechanics, and exactly what places our consciousness at the point on the timeline that it is.

    this is a great conversation. please dissect my post and keep this conversation going.
  21. May 4, 2009 #20


    User Avatar
    Gold Member

    You are trying to map psychological time to some single certain physical model of time (of which there are quite a few views).

    The place to ground a discussion of psychological time would be in the classical time course of brain processes - nerve conduction goes so fast, there are x cortical areas to get across, the evidence from response times is, etc. Relativity and QM seem irrelevant here.

    But there are indeed plenty of BS quantum collapse approaches to the now of consciousness if you want to go down that route.
  22. May 5, 2009 #21
    yet, how can you get around this when all physical models themselves are constructions from the analytical mind?

    yes there are many 'views' as you say, but i guess the first real question is if time actually exists outside human consciousness. is the idea that time is the thing that "keeps everything from happening all at once," a logical idea, much like the laws of physics which keep order in the Universe?

    If so, then that would be a starting point. with the establishment of time as a real physical phenomenon, one can address the passage of time, the 'present' and how the human psyche relates to it.

    if not, then perhaps we should revise our physical models of the universe to not include concepts of time because the theories would be incomplete.

    i think that would, indeed, be part of the equation. again, you can't escape our minds working on the problem which might seem like a catch 22 :tongue2: it is non sequitor to the issue of 'now', and again relativity and QM are models we have constructed on the left side of our brains, so they may need to be taken a look at again, if our ideas of time are corrupt.

    but, as im writing this, i also get a sense that the 'present' is an idea to help us fit inside our concepts of time.

    i would only call them BS if they were disproved. I try to remain skeptical, yet open-minded. i think if we limit our consciousnesses from the realm of possibilities, we limit our scientific progress.

    as much as many want to irradiate human experience from science, it is impossible, because human experience is the building block of scientific thought, much to the points Immanuel Kant had brought up.

    this is all good stuff, though. i see more that 'now' is a subjective experience. and, perhaps we are inching closer to a more well-defined bridge between subjective and physical.
  23. May 7, 2009 #22


    User Avatar
    Gold Member

    This is exactly the issue I'm struggling with. My intuition is that both Relativity and Quantum Mechanics are describing the "world in real time" -- physics from the standpoint of each observer's present moment... and that the deep issues we run into trying to understand these theories (and how they fit together) come from our framing them in classical terms, where the present moment has no physical significance... it's just the point on the time-line where the world happens to be at a given moment, and all such moments are alike so far as physics is concerned.

    But the "now" we live in is nothing like a "point" on the timeline, like the frozen instant in a snapshot. It's ongoing... it doesn't vanish into the past, but stays here with us as the most constant feature of our existence, along with our point of view in space.

    But, because there are so many other issues involved in psychological time-perception, I don't feel I can get very far by thinking about our subjective experience in time. The question I want to pursue is -- IF we assume the physical present time each of us experiences is an important feature of the world's structure, what do Relativity and QM tell us about this?
  24. May 15, 2009 #23
    Relativity maps all events into the present via the observer, while QM tries to map the present without one.
  25. May 16, 2009 #24
    Thinking about the present actually makes me nervous. It's hard to think about a true 'now' because as far as my limited knowledge of physics extends, there isn't a time quanta. We're accustomed to thinking of time in terms of quanta such as seconds and minutes, but these quanta don't have an actual objective existence. If humans ceased to exist, so would minutes and seconds and any further quantifications of time. For the sake of argument, I'm going to say that the second is our smallest quantification of time. The second can thus be seen as sort of a made-up messenger particle, in the same way that the photon, a quanta of light, is the messenger particle of light, except of course for the fact that the photon has a real objective existence. When we look at point X on an object, we can say that a photon definitely was spatially present at point X, for we can see point X. We can thus truthfully label point X as a place where a photon was spatially present. Similarly, if we pass through point Y in time (where Y occupies one second/quanta), and point Y in time happens to be three seconds ago, we can also quite truthfully label three seconds ago as point Y in time. Then let's say that every sentient being on the planet is suddenly vaporized. Point X still exists, for this sudden vaporization had no effect on non-sentient objects or the spacial fabric. Point Y, however, no longer exists, for it only had existence in the minds of the humans. Point Y was based on a made-up quanta. But then one can easily argue that point Y really did have an objective existence, for that was the point in time during which a photon traveled 186000 miles, and that photon traveled that far exactly when another photon had traveled the maximum distance it could possibly have traveled since the beginning of the existence of photons. In that respect, point Y in time did uniquely exist, regardless of human consciousness and thought. But then another error still exists. We are still referring to point Y as a point. Point Y is not a point. It can be further divided. It has even smaller constituents. Point X, the light quanta, has no smaller constituents (as far as I know, anyway.). Point Y can be divided off into infinity. It has no spacial existence, no quanta; it's purely numerical. There is no smallest number; no numerical quanta--there is no shortest time; no time quanta. Thus, no point we can definably label 'here' or 'now'.

    In conclusion, 'now' doesn't exist. 'Now' is a quantitized point in time that we made up because it's convenient and it works. The element of being made-up doesn't affect our calculations because time is used only for comparison. I guess. I don't really know how to state what I meant there.
    Last edited: May 16, 2009
  26. May 16, 2009 #25


    User Avatar

    My current (pun intended) understanding is that there is really no such thing as the "present". I see it only as an illusion created by the cumulative experiences, stored in our memory cells, in each point of time.

    I would be very grateful to be proved wrong, since the concept of eternality does haunt me a bit.
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook