Dec 13 2012

What is Time?

You are currently browsing comments. If you would like to return to the full story, you can read the full entry here: “What is Time?”.

Share

33 responses so far

33 Responses to “What is Time?”

  1. tmac57on 13 Dec 2012 at 11:42 am

    Can two spatially separated events be said to have occurred at the ‘same time’ ?

  2. korin43on 13 Dec 2012 at 11:48 am

    It’s funny that you just posted this. I’m in the middle of reading a book called “The End of Time”, which argues that time doesn’t exist..

  3. Eric Thomsonon 13 Dec 2012 at 11:52 am

    tmac that’s the problem: try to answer in one paragraph in a way that includes special relativity, in which the view of time expressed above would need some heavy revision. Revision that is *very* hard to do in a single paragraph. E.g., this view that there is this universal “now” is pre-relativistic.

  4. AdrianGon 13 Dec 2012 at 12:10 pm

    Here is a very good talk about time travel by Sean Caroll. He gives an interesting way of thinking about time : Time Cones.
    http://vimeo.com/11917849

  5. tyroon 13 Dec 2012 at 12:56 pm

    The long and the short of it is this: time is what clocks measure.

    It’s not a very satisfying answer, but it’s actually got interesting implications. It leads to the relativistic idea of time moving at different rates (because light-based clocks appear to tick slower) in a fairly straight-forward way.

  6. Jerry in Coloradoon 13 Dec 2012 at 5:28 pm

    Years ago, I overheard a 8 yr old explain “time” to his 6 yr old sister: “Time happens when you get older”.

  7. BobbyGon 13 Dec 2012 at 7:08 pm

    It’s always “now” anyway.

  8. ccbowerson 13 Dec 2012 at 9:37 pm

    “In my opinion these moments are tremendous opportunities to engage a young mind with everything that is awesome about science and intellectualism itself.”

    Nearly as important is that these are moments that can allow us to deepen our understand by forcing us to clarify our own thoughts enough to communicate them to a young mind. To be able to distill a concept down to a basic explanation, while maintaining the important components and structure of the concept is a great mental exercise.

  9. Blair Ton 14 Dec 2012 at 3:15 am

    I always thought time was simply movement. That is, there are 3 spacial dimensions (3D) and the 4th dimension is movement within the 3 spacial dimensions. No movement, no time. No time, no movement.

  10. BillyJoe7on 14 Dec 2012 at 4:58 am

    tmac57: “Can two spatially separated events be said to have occurred at the ‘same time’ ?”

    Yes, if the same gravitational forces act on them and they are not in relative motion.
    Because of the finite speed of light, they will mostly be observed to have occurred at different times, but all observers can make the calculation that tells them that the two events occured simulataneously.

  11. BillyJoe7on 14 Dec 2012 at 5:31 am

    korin43: “I’m in the middle of reading a book called “The End of Time”, which argues that time doesn’t exist.”

    Does the author explain this on the basis that time and space are illusions of the overlying reality that we call spacetime? Everything, including light, travels through spacetime at the same rate. The illusions of space and time are like the shadows on the backdrop of a theatre, whilst spacetime is the actual passion play.
    Am I close?

  12. BillyJoe7on 14 Dec 2012 at 5:34 am

    BobbyG: “It’s always “now” anyway.”

    Well, that’s the solipsists view anyway.

  13. BillyJoe7on 14 Dec 2012 at 5:38 am

    BlairT: “No movement, no time. No time, no movement.”

    In most of universe there is an absence of movement.
    Does time not exist there?

  14. quen_tinon 14 Dec 2012 at 8:51 am

    I think time is a terrible subject for this challenge, while flame was a very good one.

    Scientists know very well what flames are and our conception of flames will probably not be updated by any new scientific theory (even if our knowledge of fundamental particles happens to be completely revised, which change the way we think of atoms, the way atoms play in combustion will probably not be revised). Flames are not a matter of scientific or philosophical debate today (they don’t involve existential problems or the like). This makes of it the perfect subject to be explained to children: you can be clear and objective.

    For time, this is all the contrary: time plays a key role in the problem of unification of relativity and quantum physics, so future theories will probably change drastically how we think about time. Its very status (whether it is an “illusion”, whatever that means) is a matter of philosophical debates (presentism, eternalism, …) which encompass science rather than fall within the scope of science. Time is an existential question. I am pretty sure this “flame challenge” on time will turn into either pieces of hardcore scientism, or bad “woo” philosophy — metaphysical positions in either cases.

    An honest and cautious answer to the question could be: “You know just as much as us on time (=nothing). However we are able to measure and compare cyclic phenomenons, and on this I can tell you a bit more”. I truly hope that the winner will choose this approach.

  15. BillyJoe7on 14 Dec 2012 at 3:05 pm

    quentin,

    “Its very status (whether it is an “illusion”, whatever that means)”

    It simply means that time is not what it seems to be.
    (Like the colour of those two squares in the checkerboard illusion)
    Time does not seem to be something that changes according to relative motion or the effects of gravity.
    Time does not seem to be something that can interchange with space.
    Yet science has shown that this is the case.
    Therefore, the one thing that can be said about time is that it is an illusion.

    There is just a widespread misunderstanding about what an illusion is.
    Illusions are not delusions. They exist. They just aren’t what they seem to be.

  16. maineiac48on 14 Dec 2012 at 5:08 pm

    In most of universe there is an absence of movement.

    Not so. Everything is in motion. The universe itself is expanding. Particles and subparticles are in motion. Motion never stops. Curiously, if motion were to cease, such cessation would be impossible to prove without the use of “time”.

  17. locutusbrgon 14 Dec 2012 at 5:15 pm

    Time is the ability to understand that there is a past, present and future. For creatures that have only “now” time is meaningless.

  18. quen_tinon 14 Dec 2012 at 5:53 pm

    @BillyJoe

    I was not intending to have a philosophical debate, I was just pointing out that it *is* a matter of debate.

    When time is said to be an illusion, usually the flow of time is refered (not its relativity). This refers to a philosophical doctrine called eternalism, which some think is favoured by the relativity of time, but other don’t.
    By the way, time is not “interchangeable” with space… Both hold in the same representation but time-like intervals are distinct from space-like intervals.

  19. quen_tinon 14 Dec 2012 at 5:56 pm

    @BillyJoe

    Actually, saying that the flow of time is an illusion is a stronger statement than mere eternalism, and I am not sure it makes sense at all.

  20. Rikki-Tikki-Tavion 14 Dec 2012 at 8:03 pm

    I like tyro’s answer, and I would elaborate from there.

    Time is what clocks measure. Sorry, if that doesn’t seem satisfying to you, but we don’t really know what time is. But hold on, we know lots of cool stuff /about/ time … twin paradox, curved space-time, gravity and time, etc.

  21. BillyJoe7on 15 Dec 2012 at 12:06 am

    “By the way, time is not “interchangeable” with space… Both hold in the same representation but time-like intervals are distinct from space-like intervals.”

    Yes, “interchangeable” was the wrong word.
    I was trying to be succinct.

  22. ccbowerson 15 Dec 2012 at 9:36 am

    “Children may highlight this fact by innocently asking questions that are free of assumptions we didn’t know we had. Every parent has likely faced these questions.”

    I wonder if this is how children lose some of their curiosity as they age (or is this perception a myth- I may be more curious than when I was younger). If adults dismiss their questions, because they don’t know or don’t feel like answering a simple question with a complicated answer- does this discourage them from being curious about the world around them? My children may have the opposite problem of not asking me a question, because I will try too hard to answer them, but I’d rather err on the side of TMI

  23. tmac57on 15 Dec 2012 at 10:53 am

    ccbowers-You pose an interesting question about why or whether children lose their curiosity as they grow older.One possibility,is that as you age,you do learn things about the world that ‘answer’ (rightly or wrongly) the questions that you have,so those are done.Some people see further questions within the answers that they get,but others are satisfied with (and really want) a simple answer (even if it is incomplete or on shaky ground).
    One of the characteristics of skeptics,seems to be that when they discover “answers” that they have previously believed to be correct are in fact wrong,they are energized to go on a quest to not be fooled again,and try to understand how we can come to truly understand our world by the most rational methods.
    Credulous people will instead grasp on to the first explanation that ‘feels right’ in their gut,and cling tenaciously to it.These might be the type of people who lost their desire for questioning early on,and perhaps were discouraged from asking questions.

  24. tyroon 15 Dec 2012 at 12:12 pm

    @Blair T

    No movement, no time. No time, no movement.

    As I understand it, the reason that we have time dilation and other weird GR effects is that our movement through time and space is always a constant, c (the speed of light). When our movement through space is 0, our movement through time is at a maximum. That’s why when particles are moving through space close to the speed of light, their movement through time is very low. So ironically, as intuitive as your statement sounds it’s actually backwards.

  25. tyroon 15 Dec 2012 at 12:17 pm

    I’ll be very interested to see what sort of answers people come up with. For flames, the forces and particles involved are accessible to children and there are day-to-day analogues. As Feynman once said about magnets, some forces don’t have any analogies and have to be taken as they are and intuitive understanding may be elusive. I think that despite the simplicity of the question, time doesn’t have any analogues so it simply isn’t something that can intuitively understood. I suspect the best answers for children will have to emphasize the complexity and our lack of (non-mathematical) understanding.

  26. BillyJoe7on 15 Dec 2012 at 3:41 pm

    Tyro,

    That was a pretty clever response and entirely accurate. Everything in the universe travels through spacetime at the same rate in all reference frames. That includes light. In fact, it is the reason that the speed of light is the same in all reference frames. The time dimension of light’s spacetime is zero, so all of it’s spacetime is taken up in the space dimension. This also shows why the constancy of the speed of light is not really all that special.

  27. Jared Olsenon 16 Dec 2012 at 4:39 am

    I’m inclined to agree with quen_tin on this one. The best Einstein could do was “what a clock reads”, as quoted above. If anyone really knows what time is, I think explaining it to a child is next to impossible. Why not ask ‘what is quantum entanglement?’. That being said, I think it is a fruitful exercise, if not for the askers, then at least for the answerers (as the posts above show :-) ).

  28. BillyJoe7on 16 Dec 2012 at 6:03 am

    Jaded,

    There is a retired high school teacher in Australia, who has gone back to teach physics to primary school children in grades 3 and 4. He uses diagrams and models and the kids seem to be engaged and interested. At another school in Western Australia, children in grades 5 and 6 are being taught relativity.

    http://www.abc.net.au/7.30/content/2012/s3647537.htm

  29. selfificationon 16 Dec 2012 at 11:42 am

    “Let us say that you had the ability to view the entire universe at once. As you watched it, you make not of the randomness or the messiness of the universe. We say that “positive time” has passed if your see more randomness overall (like milk mixing in water to become a uniformly watered down mixture). We say that “negative time” has passed if you see less randomness overall (like a broken vase re-arranging itself). We use devices called clocks that give us a measuring stick so that we may talk to one another about amounts of time. Now, we know that how quickly you are running around, where you and how close you are to other big objects and things affects how a clock works. There is no standard clock – everything is based on your own clock. But for people on earth, the changes are tiny and we still manage to mostly get along with crude measurements like seconds, minutes and hours.”

  30. Jared Olsenon 17 Dec 2012 at 3:15 am

    Nice link, BillyJoe. Inspirational. The little girl talking about filled electron shells…wow. Not a helluva lot of deep abstraction though, which I think would be required for the ‘time’ question.
    BTW Jaded? Was that a typo??

  31. BillyJoe7on 17 Dec 2012 at 4:59 am

    Maybe it was the iPad autocorrect function. Let’s see:
    Jarred
    Nope, must have been a typo, sorry.

  32. roadfoodon 18 Dec 2012 at 11:28 am

    “Time. Time. What is time? Swiss manufacture it. French horde it. Italians want it. Americans say it is money. Hindus say it does not exist. Do you know what I say? I say time is a crook.”

    
–Peter Lorre
 in the movie “Beat the Devil”

  33. rchapraon 19 Dec 2012 at 9:38 am

    What we call time is the process by which we organize our perception of movement.

Trackback URI | Comments RSS

Leave a Reply

You must be logged in to post a comment.