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

Is the time dimension expanding?

  1. Sep 8, 2006 #1
    A thought has been bother me for a while. Is the universe expanding in the time dimension? Let me explain. The future does not exist yet, the future is a concept, an artifact of the human mind. The past (from the time perspective) don't exist anymore, yet we can see the evidence of its passage all around us. The present is a Limit between the future and the past and our place of residence in the universe. From the "present' we can look back into the past and we can expect the future. As time passes, the past acumulates behind the present, so it is expanding.

    Is this an artifact of my current understanding or a physical reality?

    My knowledge of math is only at the first few weeks of calc 1, so this concept might be completly wrong, but I found it interesting and worthy of being tested against people of more knowledge than me. I tried to be clear and concise but it could be a little vague.
  2. jcsd
  3. Sep 8, 2006 #2
    Your impression of time expanding is an artefact caused by your belief that time is flowing. Think of time as another dimension, like space, and your position in time is just a point on the existing time axis like your position in space is a point on the existing space axis. When you travel in space you do not think of space expanding - so why should you think of time expanding when you "travel" in time?

    Best Regards
  4. Sep 11, 2006 #3
    Thanks for your reply. I've been going around the concept of time as a dimension just like space, but it is quite hard to visualize. Are there any links, or examples that can help me visulize it better? It is quite hard to stop seeing time as flowing.
  5. Sep 12, 2006 #4
    I agree, the notion of flowing time is a powerful intuition (a bit like the intuition that the earth is standing still and the sun is moving in the sky). I believe we have evolved to have this conscious intuition for survival reasons - we also intuitively believe the future is "open", not fixed, and that we can in some way create or influence the future in an absolute sense - and to support this intuition our consciousness also tells us that we are flowing from the past into the future (its the only way that we can consciously rationalise the notion that we are creating the future).

    The only way (imho) I think we can successfully visualise it is the following :

    (1) First you have to be prepared to accept that the future is every bit as "fixed" as the past (this has implications for free will, thus if you believe in free will in the philosophical libertarian sense you may be unable to accept this notion - in which case do not pass GO and do not collect $200).
    (2) Next imagine you can "step outside" the 4 dimensional spacetime world and view it as if you were a "god", with the ability to see all 4 dimensions simultaneously.
    (3) If you find step (2) difficult, then imagine instead that you are outside of and viewing a 3-D world (2 dimensions of space and one of time) - in this world beings would exist as 2D spatial entities inhabiting a 2D plane, with multiple 2D planes "stacked up" on each other in the 3rd (time) dimension. Of course these 2D beings cannot "see" their world as you can in 3D (just as you cannot see our own world in 4D), but from your vantage point you will effectively see their entire spacetime mapped out in a kind of "block" universe of spacetime.
    (4) Having done (3), just add one more spatial dimension - and you have our 4D "block" universe of spacetime.

    Wikipedia, as always, has some useful info


    and this one is interesting :

    http://urgrue.org/lib/mysterious-flow.html [Broken]

    Best Regards
    Last edited by a moderator: May 2, 2017
  6. Sep 12, 2006 #5
  7. Sep 12, 2006 #6


    User Avatar
    Science Advisor

    I think that's a natural interpretation. But, considering the 3D world you mentioned, which is composed of 2 spatial dimensions (x, y) and 1 time dimension (z), then, why would conservation of mass/energy be observed only within an (x, y) spatial plane? The time dimension can't be just like any other dimension. For example, consider the 3D world that you described, visualizing z as the time dimension. Suppose there is a sphere of radius 10 in this world, with center at (0, 0, 0). The sphere occupies 20 spatial planes spread out along the time dimension, from the plane at t=-10, to the plane at t=10.
    If we then move the sphere to be with its center at (40, 0, 0), i.e. moving it to the right on the x spatial dimension, then the 3D world still has the same amount of matter. Nothing has been gained or lost. We might say mass was conserved.
    On the other hand, while, in the beginning, the spatial (x, y) plane at t=0 contained some amount of matter (it was occupied by the sphere), now it does not, since the sphere no longer occupies it, so mass has been lost.
    So conservation of mass is not observed if the time dimension is considered as any other dimension, implying that, possibly, it is not like a spatial dimension to begin with, which you may or may not find suprising.
    Last edited by a moderator: May 2, 2017
  8. Sep 12, 2006 #7
    Sorry if I gave the impression the time dimension has identical prioperties to the spatial dimensions - that was certainly not my intent. Clearly the time dimension is very "special" in that it has properties quite different to the spatial dimensions we know (eg the so-called law of conservation of mass-energy applies, as you rightly point out, to slices through the time dimension, but not to slices through the spatial dimensions), but that doesn't change the argument that we can still "view" space and time as a set of 4 (dissimilar) dimensions.

    Best Regards
    Last edited: Sep 13, 2006
  9. Sep 12, 2006 #8
    absolutely brilliant!!!!! (even though I don't fully agree with some of the ideas suggested for properties above 4 dimensions!!!)

    Best Regards
    Last edited: Sep 12, 2006
  10. Sep 13, 2006 #9
    I think you meant "the spatial (y,z)".

    Either way whichever you meant. the 2d space at no point contained a sphere, it only contained a circle, and moving it along one axis doesnt not change the containance of any 2dimendional plane.

    According to our knowledge, Time is a pure geometrical dimension. and like other dimension we "should" be able to move freely in it, but we simply dont understand how.
  11. Sep 13, 2006 #10
    thanks very much!! Your writing was really interesting altough I have to admit , that I still have problem visualizing. I don't expect to change my whole notion of space and time in a couple of days of wacthing videos or reading. I imagine that during my formal education in math and physics I'll start having a better idea of it. Right?

    But while we are on it, how "certain"is this model? What level of skeptisism would you keep while learning math and physics? Should I keep my eyes open for alternate models while I learn this?
  12. Sep 13, 2006 #11
    I never believe in any scientific idea unless it is maths(but that isnt science), and yet i am the first to spout about it when explaining stuff.
    physics is a model and as the name suggest a model if but a way to understand reality and not reality itself. So if a better model comes along just change it like you would change shirt. So my advice is always keep an open mind towards any new model.
  13. Sep 14, 2006 #12

    Always be open-minded, but no so open-minded that your brain falls out.

    Best Regards
  14. Sep 14, 2006 #13
    I don't see how that follows at all. Any instance of "I" has a unique time-coordinate. The "I" of yesterday is not the same as the "I" of today. I cannot see any a priori reason for thinking that this "I" can be free to move about in time such that there is no longer any unique time-coordinate associated with it.

    I think the notion that the "I" should be able to move about in time is an illusion brought about by the intuition that time flows - once we believe that time flows then we may consider that the "I" can somehow step outside the flow (like stepping off a boat onto the shore) and then move to another part of the river of time. I don't see how this is coherent at all.

    Best Regards
  15. Nov 9, 2006 #14
    any diminute portion of our cosmological total volumetric can be ''involved or not'' in a process or in an event that will have a beginning and an end and is therefor only a fraction of our total cosmological volumetric.
    ageing is a relative to situation also.
    however i believe that diminute volumetrics with respect to themselves go through no ageing but form part of a process with a finite duration or are at a no process stage.
    i also believe that the sum of all posible processes is constrained due posibly to the idea that only so much of available diminute volumetrics exist.
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook