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I have a spacecraft that can trave to Alpha Centauri in 1 week

  1. Aug 17, 2012 #1
    Am I going to absorb 4 years of light data from Alpha Centauri or is it just going massively blueshift?
     
  2. jcsd
  3. Aug 18, 2012 #2

    Bill_K

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    Both. But not four years, eight years. The light that Earth is currently receiving left Alpha Centauri four years ago. And your spaceship will arrive there four years from now. So the signals you receive during your one-week trip will cover the entire eight-year span from -4 to +4. Hope you enjoy their programming!
     
  4. Aug 18, 2012 #3

    Dale

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    I think bad TV will be the least of your worries. I wonder how many g you will be pulling to make 4 ly in one week of proper time.

    EDIT: actually, I just did the numbers. That is a sustained acceleration of 411 g for 1 week, and that is assuming that you don't want to stop at Alpha Centauri, just fly by at a shade under c.
     
    Last edited: Aug 18, 2012
  5. Aug 18, 2012 #4
    Haha, ya it's a completely hypothetical question of course an abrupt stop or flyby is fine. But I was kind of curious how the kinetic time dilation equation interacted between Alpha Centauri and my Space Craft. With that kind of acceleration towards Alpha Centauri, Alpha Centauri's relative velocity towards us near's negative c and effectively becomes frozen in time according to the kinetic equation, or am I doing this wrong?

    This train of thought makes even more sense to me when I consider blue-shifting. Because rather than receive more photons at the same frequency, we instead receive the same amount of photons at a higher energy blue-shifted frequency.
     
  6. Aug 18, 2012 #5
    // Paraphrase of last post - thought it got lost somewhere, but I'll leave both up

    Hmmm, ok. I thought that as Alpha Centauri approached near negative c relative to your space crafts position that it's kinetic time dilation would be kind of almost frozen in time. Because the speed of light is constant, as we shrink our relative distance to Alpha Centauri instead of receiving more photons (although technically we would receive more by getting closer to their sun, but that's not what I mean), we simply would receive much higher energy, higher frequency, blue shifted photons.
     
    Last edited: Aug 18, 2012
  7. Aug 18, 2012 #6

    mfb

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    Well, you see the light Alpha Centauri emitted in 8 years of our time. If you take a clock with you in the spaceship, you will get a different value (4 years + 1 week). But I do not think this is a meaningful value - in the view of the spaceship, the star emits ultraviolet radiation in one direction and infrared in the other, for example.
     
  8. Aug 18, 2012 #7
    Isn't it true that the voyager probe feels less force from relative accelerations now that it's in deep space than it did closer to earth? I believe I read that somewhere. This tells me that time is kind of more like constant, but the forces in nature like gravity and the energy from our sun create little time-warp-zones that bind the action within them. Or to paraphrase, lightwaves are the fluid of time.
     
    Last edited: Aug 18, 2012
  9. Aug 18, 2012 #8
    Another supporting piece of science: Pulsars pulse at atomic clock precision, shouldn't there be a slight oscillation in pulse rate over the course of a year based on the rotation of the Earth depending on if we're swinging towards the star or away from the star?
     
  10. Aug 18, 2012 #9

    mfb

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    Relative to what? The gravitational force between the voyager probes and sun (and voyager probes and planets and everything else in the inner solar system) is lower than it was in the past.

    What?

    What?

    ???

    This is true, and it is already taken into account. You have to do the same for exoplanet searches and even position measurements of stars.
     
  11. Aug 18, 2012 #10
    Less centripetal and centrifugal force when completing the same maneuvers past pluto than there is nearer to Jupiter, Mars or Earth. Basically it would take more acceleration in deep space to feel "1 G force".

    These are test results returned from the Voyager probe.

    I don't know the numbers, but I assume it's something like 10.1m/s^2 or more acceleration to feel a G
     
  12. Aug 18, 2012 #11

    mfb

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    No, this would violate General Relativity.

    Please provide a source for this claim.
     
  13. Aug 18, 2012 #12
    K I will, just on my cellphone right now. I have to go through some NASA documentation.
     
  14. Aug 18, 2012 #13

    Bill_K

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    I suspect what Eirhead is referring to is the anomalous acceleration experienced by Pioneer 10 and Pioneer 11, which were launched in 1972 and 1973 on trajectories out of the solar system. All sorts of fanciful explanations had been advanced for the anomaly, including a departure from Newtonian gravitation. The effect was satisfactorily explained just last month as recoil from the emission of thermal radiation from the spacecraft.
     
  15. Aug 22, 2012 #14
    Ha, well done
    :)
     
  16. Aug 23, 2012 #15
    Sorry, that can't be right. 1 week on Earth's clocks -> less than 1 week on an on-board clock.
    Thus, an astronaut doesn't need to experience that much acceleration in order to reach a distant star in a reasonable amount of proper time.

    [ADDENDUM: Not 1 week but 4 years on Earth's clocks, strange that I forgot...]
     
    Last edited: Aug 23, 2012
  17. Aug 23, 2012 #16

    mfb

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    The "1 week" is the on-board clock and corresponds to 4 years on earth (and the rest frame of alpha centauri). The 4 years correspond to the 4 years before where the spaceship was at rest on earth.
     
  18. Aug 23, 2012 #17
    Ah yes of course! (I have not been drinking... could this be due to lack of sleep? :blushing:)
     
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