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If a tree falls observerless events

  1. Jun 21, 2004 #1
    many qsnts : unchanging light, time not time, &more

    I may be about to make myself look like a total ass, but, please, be merciful (my knowledge of physics and math is slight --> but I want to change that). I have been reading, albeit somewhat topically, about relativity. I have a BUNCH questions :

    1) events with observers : in the barn-pole paradox (in which the barn has only one door --> you have a runner approaching the open door near the speed of light, and a person standing by the door, whose goal is to trap the runner in the barn for a brief period by closing the door as soon as she is inside --> the result, from what I can gather, is that the runner will perceive herself breaking throug the far side of the barn and then the door closing, while the door-closer will perceive himself closing the door and then the runner bursting out the other side), if you took a picture from the pole perspective and at the same moment, a picture from the barn perspective, would one (from the barn perspective) show the barn intact and all doors closed and the other (runner perspective) show the runner bursting through the barn and the door not yet closed ? Can the barn be both intact and sealed as well as broken and unsealed at the same time ? Isn't that a violation of logic ? (now to make myself look like a bigger moron : I also read that part of the problem with Newtonian physics was that they built on our experiences up to that point, that is, they conformed to those experiences, which have been limited in that people have not experienced the extremes of the universe (ie, we have never moved near the speed of light). Thus, when we considered the extremes, the physics had to change. Is the same true with logic ? We have built it up from the norms of our experience, but now as it becomes clear that those norms are not representative of the universe, the logic must expand and change, possibly fundamentally, in order to encompass new data ?)

    2) Events without observers : ok, so everything is relative and depends on the (sentient) observer. What if there is no observer ? ie, in the barn-pole example, what if everyone was miles away from the barn when they fired the pole at the barn (note : the barn would have to have a timer on it that opened the door at the right moment to allow the pole through and then tried to close them again just as quickly) and then no one had any sensory data about the event, either form the barn's perspective or from the pole's ? What would happen ? Would the pole morph ? the barn ? or would everything be like it would in an objective universe, such that nothing expands or contracts, and the pole just doesn't fit in the barn, ever ? This seems like an impossible question, since obviously it cannot, by definition, ever be confirmed by experiment. Or am I completely misunderstanding this (I am guessing that the correct answer would be that I am misunderstanding the idea of perspective. It is not that a person or thing has to see it or record it, but just the pole has a perspective, or, orientation or situation in the universe, and so does the barn and even without an observer, things will happen as before -- that is, both things (the pole shortening from the barn persepctive and the barn shortening from the pole persepctive) will happen)

    3) When it is said in relativity that, for example, from the barn's perspective, the pole becomes shorter, do the physical properties of the pole actually change ? Is it actually shorter than when it started out ? If so, then it seems that the runner's pole and the barn-perception's pole cannot be the same pole even though they are in the same place. However, if the pole is not actually shorter, then how could it fit in the barn (ie, if the shortness is only a trick of light or of perception, then obviously the pole would not fit) ? So, if the conclusion then is that the pole held by the runner must be both X long and Y long, where X does not equal Y, then how is that logical ? Are the two perceivers (barn and runner) actually even perceiving the same things ? Can they even be said to be in the same universe (if they are, then two different poles must be in the same place at once)

    4) How do you reconcile the seemingly different universes in which everything now seems to exist (ie, the barn universe which is not busted until after the door closes, and the pole universe where the barn (the same barn ? a different barn ? is there no barn to begin with (all this does seem to support a mind-only view of the universe) is busted before the door closes) ?

    5) if space movement + light movement = speed of light, then light cannot be moving through time. If it cannot move through time, then it cannot change. but, if it cannot change, then it cannot move through space. if it cannot move through space then it must move only through time. if it moves only through time then it cannot exist spatially. if it cannot exist spatially, how do we see it ? If light is timeless, how can it change ?

    6) if someone in a very long glass spaceship which is moving right along a line set two robots to wind their internal clocks as soon as he dropped a flag, what would happen ? someone observing from outside would say that the robot on the left started his internal clock first. That person, on the outside, would have a watch moving faster than the clocks on the ship and he would say, for example, that the robot on the left started his internal clock at 12:05 by the outsider's watch, while the one on the right started it at 12:06 (a very, very long ship moving very, very fast) by the outsider's watch. Thus, according to the outsider, the two robot clocks should be one minute apart. However, on the ship, the robots started at the same exact time, so their clocks are not different at all. When you actually check the two robot clocks, who is right ? It will, I think, be the robots. The outsider is wrong. Couldn't you say then that the true thing that happens (ie, the real, objective event) is the thing in the frame of reference of the happening, while everyone outside that frame is merely experiencing a delusion ?

    7) if a watch would really slow down when going very fast, and a watch does NOT measure time but just ticks off motion, then in fact, what happens when moving very fast through space, is that motion slows down ? The watch does not actually measure the passage of time; it is not locked into time as a ruler is locked into space (ie, watches cannot actually measure a thing called time). it only measures its ability to keep up a constant motion. so if high speed slows down a watch, it must actually be slowing down motion. How can you be moving really fast but slower than everything else ? is it a frame of reference thing ? Like a shoebox with a bunch of lazy ants in it. the shoebox is rocketed really fast through space, but the ants in it continue to move very slow. Doesn't this support the idea that time is ONLY a measure of motion and so that space-time is really just space (what changes when moving really fast is NOT time as it effects people like an individual force, but rather the ability of things moving very fast to move themselves within their frame of reference ? you just don't notice it because in your frame of reference, everything appears normal) Time is a construct of ability to move in space. Is this why light needs no medium to move (ie, it never actually moves --> it exists and everything moves around it) ? What then about turning on a light ? How is light created and spread if it CANNOT CHANGE ?

    8) a standard example is a person standing outside a fast moving thing who witnesses something happening in that thing and has a different interpretation of it (ie, watching a glass spaceship pass and seeing light from the center hit one side first). However, what if the observers is actually moving faster than the thing being observed ? If I am moving just under the speed of light and I see a glass spaceship going spaceship speed, and watch a light emitted from the center, will I still think it hits one or the other side first ?

    thanks and sorry if these are dumb questions,

    P.S. : could anyone recommend a good book for a beginner who is interested in this stuff ?

    P.P.S. : I'm sorry if something funky happens with the text of this message. I hit some combo of keys (I can't remember what) and all of a sudden, the font, size and style changed. Go figure.
    Last edited: Jun 21, 2004
  2. jcsd
  3. Jun 23, 2004 #2
    Seems to me that the main problem you're having is that you're trying to reconcile 'thought experiments' in Special Relativity with everyday life.

    None of these thought experiments (e.g. Barn-pole paradox) are actually do-able ... man running at 3/4 speed of light into barn, then decelerating, etc ...

    It will probably do you more good to just think about moving rods and static clocks and take the 'man' out of things. Otherwise, it is very easy to get confused with 'who's universe' and other such questions.

    Try to understand the Classical Principle of Relativity (Gallileo) as applied to spatial dimensions, before tackling Special Relativity, which brings in the time dimension. Then you must just accept that, experimentally, the speed of light in any particular medium remains constant regardless of the speed of the measuring instrument.

    From these two principles (which cannot be proved) the whole of SR comes.

    Come back if you need help with any of the above.
    Last edited: Jun 23, 2004
  4. Jun 23, 2004 #3
    Hmm I have had similar questions about relativity, I understand that the physical properties do change. I understood that the pole would increase in mass and decrease in volume, however I also dont understand this, I cant see how the pole could get in the barn or get stuck. I was going to post a similar thread but i may aswell tag along with this one, rather than clutter up the forum. When clarifying relativity could someone perhaps explain what speed object B is moving from object A, if A is travelling at two thirds the speed of light one way and B is travelling two thirds the speed of light the other way. Sorry for the intrusion, hope you dont mind!

    P.S. A good book on physics that I am enjoying at the moment is Before the Begining Our Universe and Others by Martin Rees
    Last edited: Jun 23, 2004
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