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Time travelling - Einstien's revolution

  1. May 23, 2004 #1
    I was wondering what you guys think about time travelling.
    I read Paul Davies's book called How to Build a Time Machine which
    left me more confused about this topic. What do you think :smile:
  2. jcsd
  3. May 23, 2004 #2

    I have not read Paul Davies' book. But what I learned from Einstein's theories of special and general relativity is that spacetime is absolute. Everything in the universe is a point in spacetime. This point is called an event. The path of motion of an event in spacetime is called the worldline. Simultaneous events are the intersection of worldlines. Can two worldlines really intersect? I am still in doubt. To travel in time, backward or forward need the worldlines to intersect.

    To go back in time, we need to turn around our existing worldline of a time machine and intersect a previous point of another worldline.

    To go ahead in time, we need to go superluminal speed to intersect a worldline that already contains a future event.

    My worldline started when I was born and it will end when I die. The atoms and molecules in my body will eventually generate other many worldlines. I am typing these words here but by the time you read them my worldline has progress far into the future. So it seem to you that you are reading the worldline of my past and not my present state of mind. Can our worldlines really intersect?
  4. May 23, 2004 #3
    einstein has proved issac newton to be wrong. he says time is relative to where you are. issac said time is absolute and universal. [eg. if an observer on planet X (which has twice the mass and is more compessed than earth) will experience time going to slower than an observer on Earth. He said if we were to tarvel at 99.99999% of the speed of light then we will be able to reach the future.

    i presume that u may have heard about the twin theory?
  5. May 23, 2004 #4
    Space by itself is relative. Time by itself is also relative. But spacetime is absolute.

    All modern theories (quatum field theories, superstring theories, M-theory, special relativity and general relativity) are based on the absoluteness of spacetime. And the speed of light in vacuum remains the maximum attainable speed for all physical processes.
  6. May 23, 2004 #5
    How does one 'experience' time going slower?

  7. May 23, 2004 #6
    spacetime is unalterable

    only the perception of space and time measurements are variable

    the mathematical model of Relativity Theory states that length decreases with velocity in the direction of travel

    this causes an illusion for the traveller, of space being stretched in the direction of travel

    since time is a temporal dimension at right angles to the spatial dimensions
    real time seems condensed (speeded up) for the traveller

    to a stationary observer the traveller is shrinking in one dimension
    and the traveller's clock is moving more slowly
    Last edited: May 23, 2004
  8. May 23, 2004 #7
    ok.......i meant in comparison to the observer on earth. :confused:
    if an observer cannot 'experience' the time going slower, a clock
    will 'slow' down.
  9. May 23, 2004 #8
    Take Einsteins example in hios bool "relativty" where he introduces loss of simultaneity. Without analyzing the whole problem the moving observer crosses the midpoint between two light sources that pulse on at that time. Taking this positon in space time as smultaneous, ie the lights pulse on for moving and stationary frames at the same time, say at t = 0.

    Later the moving observer records light from the forward light before the light arrives at the midpoint and later from th rear light source. Now when we place recording (detecting gea)r along the path of the moving platform and the observers make simultaneous observations of the pulses each event is simultaneous in space and time whether we use clocks or not.

    Is this not true?

    Now my question is, how does one get to the loss of simultaneity under Einstein's example if every event 'thing' is measured simultaneously? If the moving observer knows of the simultaneous mesurements will she later conclude that there were any events originally measured unambiguously simultaneous to both frames to have happened at diffeent times, or places by imposing RT?

    It seems this is what RT is all about: that observers may corrupt measurenments and observations by the imposition of postulational theories.

    A simple proof for the return of simultaneity wrongly discarded by a flawed theory. :smile:
  10. May 23, 2004 #9
    12345, where and when did Einstein prove Newton wrong? Just when and where was Einstein proved "right" in his theoretical postulations about anything?
  11. May 24, 2004 #10
    I was so dissapointed with this link. It starts by setting up the experiment, great, then talks about what each observer might see, ok, but then goes off on a ramble about what is physical reality or something etc etc (yawn) with confusing diagrams and unclear explanations to justify it all.

    If there is a flaw in the theory please show it concisely and clearly. If you have to resort to hand waving, on the other hand, you have no argument.

  12. May 24, 2004 #11
    geistkiesel,( i have only have an outline on this experiment) proof is that an experiment was conducted with a clock on earth, and a man flying.
    when the man landed with his plane back on earth, the clock which was on earth was 0.000057 seconds slower. the fraction of time difference might be small, but proves newton wrong.but they are also sending a spacecraft with four individual probes to space. if einstein is right then the probes will hopefully move positions. this will confirm his theory. :approve:
  13. May 24, 2004 #12
    baffledMAtt, your yawn is your problem. You misread the point, but then you can always use thaty for an excuse when someone splains it to ya later and ya wont have to be embarrassed. RT is a psychological encumberance. The point about physical reality is that observers coming along with theoretical tools do not altersthe physical reality. Sorry. Go back to sleep. You can always read Einstein's biography, if you ever wake up.

    However take comfort. You have all those others with comments except the one that damages the link. The link, baffkledMatt, flushed the consequences of "simultaneity' down the toilet. Go find a physicist, she'll explain it to you.
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