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What is time?

  1. Nov 25, 2010 #1
    I recently realized that we use this concept constantly but I have absolutely no idea how I would answer this. Never in any school physics lesson or university lecture I've attended has anyone even mentioned this. It's just sort of taken for granted because we all have experience of it passing. This a pretty open ended question, just thought I'd throw it out there. So, how would you define this quantity we call time?
  2. jcsd
  3. Nov 25, 2010 #2


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    Tim is change/ movement. If there is no movement/ change in a system (and I mean at the deepest possible level), then practically, there is no time flowing. And it works backwards - no time= no change/ movement.
    Jap.. this is the best I have :P

    And yes - this is a very good and fundamental question that is bugging me for some time now..
  4. Nov 25, 2010 #3
    I would agree. "Time" is just a concept that involves "change"
    Without change there can be no time.

    However, one has to be a little careful with this.
    That is, just because something may not change internally does not mean that it doesn't change with respect to its external environment.
    Movement of an internally, non-changing object through space is an example.

    In short, "time" is a measurement of change, specific on perspective frame.
  5. Nov 25, 2010 #4
    that's kind of unsatisfying I think. I mean, we could be sat in an enclosed room with no windows just staring at a wall, and be unable to detect any movement of anything, but we'd have no reason to suppose that time had stopped just because we couldn't see any of its effects. we could assume the world outside was still going about its business. am I missing the point here?
  6. Nov 25, 2010 #5
    You see the effect of time because you are still living. The fact your heart is beating is an indicator of time.

    Time is obviously relative, however, and people might not agree on the simultaneity of a specific event.
  7. Nov 25, 2010 #6
    My favorite textbook definition for time is :

    "If the internal state of a particle or a localized object is changing, its successive states define a continuum,which we call the time of that particle"
    Classical Mechanics, Volume 1 A. Desloge

    Whether that is enough for you is another issue.
  8. Nov 25, 2010 #7
    "Time is what happens when nothing else does." --Feynman Lectures
  9. Nov 25, 2010 #8
    The difficulty with time, I think, has to do with perception. We receive data from photons that consist of changes of velocity with respect to time. Moving down theoretically, it means that changes of distance with respect to time are not constant, they vary. I know that you know this. My point is that if we return to considering the data, and, recognize that we use it to form a visualization of what may be happening in the outside world, then visualizing distance and not visualizing time is a matter of interpretation. Time is not less real than is distance. Distance does not gain credibility leaving time to be an effect just because one is visualized and the other is not. (Gravity is not visualized either).

    The cause of changes in distance are not known. The cause of time is not known. That is because, we do not know what cause is. Theoretical physics is necessary in order to substitute imagined causes for that which we cannot know. We can imagine something that we choose to generically call force to account for changes of position of an object; but, we cannot imagine something that causes time to move on. Force causes acceleration; but, that same imagined cause cannot cause time to accelerate. It is rather inferred from theory. Inferring is not satisfactory for explaing what time is. So, without an obvious clear answer, it is sometimes put forward that the motion of objects causes time. In other words, time is an effect.

    Relativity theory seems to support this idea, so, it continues to be put forward. My point to this is that everything we observe is an effect. We never observe cause. Therefore, that which we observe objects to do may relate to time, but, cannot be shown to be the cause of time. The 't' in physics equations is always about a non-constant standard of cyclic activity. When that 't' varies it does not tell us what time is doing, it tells us what that cyclic activity is doing. If we discovered a measure of duration in time that was constant everywhere, at all time, in the universe, then we would know that time is not an effect of motion. However, that discovery would also necessitate doing away with Relativity Theory alltogether. Perhaps the most interesting possibility of an existing natural constant standard of time is that as a universal constant it should already appear in today's theories. Its interpretation may be incorrect; but, it should be already recognized by us under a different name.

    Everything we learn comes from observing patterns in changes of velocity. There are two clearly fundamental properties that we cannot put into containers. We cannot isolate them in order to experiment on them. Neither one experiences changes of velocity. Those two properties are space and time. Since we cannot push or pull either of them, we cannot make measurements of rates of change for either. We only experiment on objects. We only know what it is that objects do. Objects are always things that exist in space and during time. Objects cause other objects to change that which they were doing. Objects causing effects that we observe to occur to other objects do not tell us about either space or time.

  10. Nov 25, 2010 #9
    The simplest of question yet one of the most elusive!
    Wasn't the question of time's uni-directionality one of the causes for physicist's to attempt to formulate a theory of everything? For in order to examine the nature of time, one must go back to the beginning. And once physicists mathematically examined the beginning with the two main theories of the time, the maths turned out to be nonsense.
    And i dont think that the implication that if an entity is living, time is passing. A virus is considered 'dead' outside of a host. Surely time doesnt stop for the virus? How would it's metabolism kick in once it found its way into a host? How would it know, if time ceased for the virus?
  11. Nov 25, 2010 #10
    Time is a measure of our Planet's 24 hour segment. Other planets and star system will naturally differ. We have even calculated light-years based on our conception of the Speed of Light, but it may differ within other systems. Bottom Line: Time is a measure.
  12. Nov 26, 2010 #11
    I think of time as a sort of ether which is repelleded by mass, energy. and by objects moving through space. Thus it might be a particle, and maybe is represented by what we call dark energy. Figuring this out is way outside my pay grade...

  13. Nov 26, 2010 #12
    The question is the deepest (physical) question I know. I spend several years on this one (basically as the guiding question of a masters and then PhD thesis in philosophy and the philosophy of physics).

    Here is my favourite answer:

    Time is God's way of keeping everything from happening at once...

    Okay, and a little more explicative:

    Time in physics actually has somewhere on the order of 14 flavours. For example in quantum physics, there are at least 10 different and even inconsistent definitions of time. Relativity theory, Quantum Gravity, etc. all do weird things with time. Coming back to classical physics, even here it has several variants. There is time the measure used in a laboratory and time the theoretical metric used to describe the evolution of classical systems. And there are some ways it has been used to talk about entropy and even be defined in terms of entropy (thinking to Prigagine for example).

    On thing in all of this to keep in mind. All notions of “flow” are strictly non-physical. In fact, this sort of “time” has been traditionally called “psychological time”. Now what I will add is that if you think this through, you will see that there is still a pretty serious mystery behind all this: What is flow? This was the question I was addressing in the context of my graduate work—very subtle stuff. There is not theory in physics that even hints at what this could conceivably be, with the possible exception of certain variations of quantum gravity that treat the wave collapse as a genuinely “real” or ontological phenomenon. Even then, it requires something of a conceptual dance to tease out the semantic features that would make flow flow (pun intended).

    If anyone is interested, write me and I will forward a copy of one of my papers that has a fair amount of background of all this stuff in it. (In other words, even if you don't like my approach to the problem, you get a taste of who else has said what about the issue).
  14. Nov 26, 2010 #13
    I have a theory which can explain time, dark matter, dark energy and the expansion of space easily.

    First, I do not have a background in mathematics or physics. I was pursuing a pre-engineering degree before I got derailed by life stuff and will not be going back anytime soon.

    Second, how can I go about getting taken seriously? Where is a place that I could honestly begin?

    This is an honest inquiry and no I will not share this information publicly.

    Thank you.
  15. Nov 27, 2010 #14
    I'd post your thoughts here. People on PF are pretty open-minded for the most part. Just be prepared for criticism - especially if your views are highly speculative and go against the grain of accepted theories.
  16. Nov 27, 2010 #15


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    No, if your views are highly speculative and go against the grain of accepted theories, then it's against the rules of this forum to post your thoughts here:

    Unfortunately, without a background in mathematics or physics you will have great difficulty in being taken seriously anywhere else. For people to take your theory seriously, they will expect you to have a good understanding of existing theories. (E.g. see the Independent Research Guidelines referred to above.)
  17. Nov 27, 2010 #16
    It is not really that highly speculative, all it really is is a change in perspective of how the current theories are currently viewed. It is just one thing or idea that can explain a bunch of these things we scratch our heads at, more than just specified above.

    I have a good understanding of existing theories, I just do not have the schooling to go with it. Well read, just can't do the math, by myself that is. I would love to work with somebody that does possess those qualities, but I have no idea how to go about finding somebody willing to come down to my level (little math).

    I don't just want to throw the idea out there however, especially on a message board. It is not because I am worried about criticism, that is expected.
  18. Nov 27, 2010 #17
    Well, that must be "earned"
    That is, you must prove yourself right(or reasonably so) WITHOUT any DEMAND that others MUST prove you wrong.

    In other words, try not to have an attitude like "well, you can't prove me wrong so I must be right"
    That just goes nowhere really fast, and makes one look like a babbling idiot.

    So, with a speculative theory, I would approach it by first asking reasonable, specific questions. Allow yourself to be educated by the responses.
  19. Nov 27, 2010 #18
    That is not an issue. I am trying to bring this information humbly, I know where I stand. I am at the bottom rung of the ladder pretty much when it comes to credentials.

    I have seen plenty of people raise their hands triumphantly saying THEY HAVE THE ANSWER only later to be seen with their tail between their legs. I do not have THE ANSWER. What I have may possibly be an answer, but I don't have the means or the methods to verify this by myself.
  20. Nov 27, 2010 #19
    OK, well, that's perfectly fine, so what are your questions or statements regarding your theory? Let's start with that.
  21. Nov 27, 2010 #20
    I am not quite sure where to begin, honestly. Like I stated earlier, I don't wish to put everything out on a message board.

    I guess the expansion of space is as good as any.

    Space isn't expanding, all of the material within 'space' is getting smaller. The more mass and volume something has the quicker this takes place. This is why everything around us is redshifting.

    Go ahead and ask your questions, I will do my best to answer them.
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