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The nature of time. Which books to read?

  1. Jul 24, 2007 #1
    There is a discussion on the nature of time in the General Physics forum, originally titled "What is time?" I know that physicists have no firm conclusions on this issue, but I want to read about the various views that are taken seriously by physicists. Can anyone comment on the books/authors mentioned here in this discussion? (See post #42.)


    (I believe that replies should go in that forum, and not here, to avoid cross-posting.)


  2. jcsd
  3. Jul 24, 2007 #2
    A very well known and well respected book on this topic is called

    The Philosophy of Space & Time, Hans Reichenbach, Dover Pub

    I have another book I'm anxious to get around to reading but I can't find it right now and I forgot the exact name, something like The Nature of Time which is a collections of essays.

  4. Jul 25, 2007 #3
    Someone reccomended "A Brief History of Time", by Stephen Hawking, but this book is a mile wide, yet not deep. When it comes to discussing the nature of time itself, Hawking shows little knowledge of the great debates about this subject. He doesn't mention any of the mainstream ideas about what time is, or how we should understand it.







    I am distressed by the way that many physicists seem to have done little or no research on the very subjects that they write about. Even if a physicist somehow has come to disagree with the views of (apparently) every single philosopher, and all of their varied views, shouldn't the physicist at least briefly explain why?

    I'd like someone to point me to a book or article written by a physicist that is at least conversant with the subject, or writen by a philosopher who is conversant with modern physics.

  5. Jul 25, 2007 #4

    George Jones

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  6. Jul 25, 2007 #5


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    Philosophy is mostly irrelevant to physics. If you really want to talk about the philosophical aspects of time, try the philosophy forum.

    The fundamental difference between science and philosophy is that science makes testable predictions. This allows scientific arguments to eventually end, because one can actually go out and make a measurement that settles the question one way or the other.

    Purely philosophical questions, though, don't have any way to be tested. Because they can't be tested, they can't be proven wrong. They can't be proven right, either. This implies that philosophical arguments tend to go on forever. It also means that because they can't be tested experimentally, they are not in the domain of science.

    So, in short, as far as science is concerned (i.e not philosophy), the important aspects of time are the aspects that can be measured. This is why "Time is what you measure with a clock" is a good philosophy for physics, it keeps the focus on what can be measured, and it avoids the pitfalls of endless philosophical debate.
    Last edited: Jul 26, 2007
  7. Jul 26, 2007 #6
    Well I am pretty sure that time does not exist.

    Describing a system at a certain time t1 or at another time t2 makes no difference since there is a perfect reversible correspondance between these two descriptions.

    Why, then are we losing all our ... to solve the ...-dependent equations of physics?
    What do we gain by this difficult exercice?
    Nothing, the information is the same.

    Where is the flaw?
    Last edited: Jul 27, 2007
  8. Jul 26, 2007 #7
    Tine is defined so that all event don't happen at once. That's all you need.

    I agree that most philosophy of science has no baring on science itself. From what I have seen, most of it stems from the philosophers inability to properly understand quantum mechanics.
  9. Jul 26, 2007 #8
    Yeah, well I think the "why observation leads to wave-function collapse" is an endless philosophical debate, go tell all of them that they are wasting their time
    Last edited: Jul 26, 2007
  10. Jul 26, 2007 #9
    Why does there have to be a why? Things interact - all interactions occur at points so all interactions (including observations) collapse wavefunctions.
  11. Jul 26, 2007 #10
    I was referring to a specific thread, I guess your talking about the environmental decoherence theory... has that been worked out to everyone's satisfaction yet?
  12. Jul 26, 2007 #11


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    You are seriously asking what we gain by utilizing the concept of time in physics?
  13. Jul 27, 2007 #12
    Yes, but this is nearly a paraphrase of the title of this threat.

    I can safely say that all fundamental laws of physics are time-reversible.
    Then we can -indeed- ask ourself why time does play this big role in our lifes as well as in theoretical physics.
    We can ask ourself this question, even without considering the question of irreversibility, unless it would be essential for the answer.

    In other words, what are we doing with an "Heisenberg picture" of our world?
    The observables are functions of time, but the state of the system ignores time.
    Does that mean that time is only about our observations but not about the reality of the world?

    Sorry for expressing feelings instead of a rational point of view.
    Last edited: Jul 27, 2007
  14. Jul 27, 2007 #13

    I am trying hard to understand what are your "feelings" on the matter of time, but can't. Can you please try to explain them once more ?
  15. Jul 27, 2007 #14


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    Then how do you account for all those broken time reversible symmetry results? Example: M. Covington et al., PRL 79, 280 (1997). And what about the CP violating decay of Kaons? That in itself implies a T symmetry-violating event.

  16. Jul 27, 2007 #15
    Yes, I agree completely, but I ommit this aspect because I don't see how this may affect the discussion about the nature of time. In addition, I have never read about CPT violations. If this is right, the CP violation is not fundamental to discuss the nature of time.

    In our daily experience the T-violation obscures the T symmetry of most of the physics.
    Once the T symmetry is accepted as a basis for discussion, it is hard to understand why time is so fundamental.
  17. Jul 27, 2007 #16


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    How can it not be relevant since T reversal symmetry (or lack of it in certain situation) would imply an inherent characteristic of time? It is those small "exceptions" that is the source of a lot of new physics and understanding. Secondly, while there are no CPT violations (yet), the fact that CP (and T) symmetries are violated separately does not implie that these aren't "fundamental". In fact, broken time reversal symmetry is the KEY signatures of new merging phenomena. Remember, only when there's a broken symmetry somewhere do you get to see something "new". So such broken symmetry is extremely fundamental as signatures of a phenomenon. That is why such a thing is used in so many different studies. Broken gauge symmetry is a fundamental concept in our world and important enough that Phil Anderson got the Nobel prize for it.

    See my discussion above. Just because the symmetry can be broken has no connection with something being "fundamental" or not. I don't see anyone here arguing about space and charge not being "fundamental". Yet, I see lots of people arguing about "time" being such-and -such. I've yet to see someone come up with the complete dynamical description of a system without using time. Until that occurs, I consider time to be an essential ingredient, without which, you cannot completely describe any system. To me, that is ample evidence that time is essential and fundamental. There are no evidence so far to the contrary.

  18. Jul 27, 2007 #17

    I can only agree.

    But I like to take a classical physics point of view (first) on this question.
    Even in classical physics time is the main subject, without time there would probably be no object to physics.
    Yet, in classical mechanics all the information on a (autonomous) system is included in the initial conditions. Just as if the time evolution was simply a mystery for our conscience and a game for the physicists. I don't know if CP invariance could help in solving this paradox.
  19. Jul 27, 2007 #18
  20. Jul 27, 2007 #19


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    You still haven't addressed my question on why you seem to pick on 'time', yet you're leaving 'space' scot free. Can you define space in more "secure" terms than time? As far as I can see, the concept of space has the same importance and foundation as time, and GR/SR certainly treat them both as equals. So are you contradicting GR/SR? Why pick on time alone?

    Last edited: Jul 27, 2007
  21. Jul 28, 2007 #20
    You are right again:

    I think that for physics, space-time is a given stage.
    Since 1905 the shape of this stage is an experimental topic.
    Since more recently it seems that physics could go further in the investigations.

    Still, there is no detailled answer to the original question, in the sense that space-time cannot be reduced to other concepts, but it can be observed scientifically and that's the most important.

    Still, I think a huge number of people will never be satisfied with this answer: "space-time an ultimate concept that can be observed experimentally". Personally, I don't care much altough I can be interrested to learn.

    Further, I think that in all the space-time dimensions, time is the most mysterious for a majority of people including physicist. That's probably because space can be perceived at will by using vision, the sense of touch, or even by hearing. In contrast, time cannot be perceived at will, for example you cannot "walk back in time" to measure some lapse of time.

    Also, note that in SR, space has three components with signature 1, while time is unique with signature -1. Even in physics, time is apart.
    In thermodynamics too, time as a very special role, even though thermodynamics can also be formulated in a covariant way.

    In a local frame, time has its mysterious fingerprint that brings all these question.
    Last edited: Jul 28, 2007
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