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I woke up wondering

  1. Sep 18, 2011 #1
    When is now?

    The further away an object is, the further back in time it appears to be. So does this mean the closer an object is, the more closer it is to now?

    Which brought up another question, as i lapsed between dreamland and the noise of the dogs barking and running around with squeeky toys! If there are 2 objects of equal size travelling towards each other at equal velocity (i imagined 2 spheres), and at the same time decreasing in size, at the same rate... would they ever meet?

    As you probably guess by the simplicity and probably ignorant questions... I'm new to physics (as in, I've never studied or read anything about the subject). But I just had to ask these questions before they fried my brain. This seems to be the best place to ask.

  2. jcsd
  3. Sep 18, 2011 #2
    about those spheres, just assume some radius and velocity and calculate urself if they will reach each-other....
  4. Sep 18, 2011 #3
    For your first question, both time and distance are considered to be dimensions, but distance has two directions whereas time only has one (i. e., "time's arrow").

    For your second question, this appears to be a variation on Zeno's First Paradox. Google on it for some interesting discussions.

    By the way, questions like these will not fry your brain. They will stretch it!
  5. Sep 18, 2011 #4
    A bit vague. Are you referring to the fact that light that reaches you from far away is "old light" in the sense that is was sent off a time of [itex]\frac{\textrm{distance}}{\textrm{speed of light}}[/itex] seconds ago?
  6. Sep 18, 2011 #5
    For the spheres problem, they will meet. Just replace either of sphere with a point particle. Two point particles traveling head on towards each other will meet if their velocities are equal, opposite in direction and constant.

    The reason I am considering point particles here is that if the spheres keeps decreasing, they will eventually approach the size of a point particle.
    Last edited: Sep 18, 2011
  7. Sep 18, 2011 #6


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    Consider these two points;

    -I've I post a letter to you and you receive it three days later am I three days in the past?
    -Two balloons are blown up then released without having a knot tied in them. They are propelled towards each other expanding air as they go. What will happen?
  8. Sep 18, 2011 #7


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    All news is old news. It takes time for all information to travel from A to B so, whatever you find out about what's happening somewhere, it's really information about how things were some while ago. Even for a spacing of 1m, there is a delay of about 3ns.
    Take that Supernova that 'we' observed last week. IS it happening as we watch? One could say so - the same as when we watch a feature film. The action we see on the film is 'happening' now, for us.
  9. Sep 22, 2011 #8
    Some interesting and mind boggling stuff to consider. Thank you. I'm still not sure if I'm further from, or nearer to the answers.
    When we measure the light distance from the furthest galaxies... is this the measure of how old the universe is?
    If the universe were to shrink, at what point would everything become nearest the point of now? At the point of were galaxies are the size of particles?
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