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Thread: Is it possible ..

  1. #1
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    Is it possible ..

    I hope Iíve come to the right place - not sure if my question fits here.

    Here goes:
    Is it possible to have an object (man made) traveling in interstellar space, come to a complete hold? Taking the expansion of the Universe into consideration obviously. Not by having it crash into anything, explode or otherwise - But if object had thrusters, would it be possible? Why/why not? And how? ..

    Iím by no means a scientist .. So I guess thatís why I ask.
    Excuse my misspellings if there are any

    /Kat

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    Hi iMarvel, welcome to CQ. And yes, this is an OK place; our Q&A section would also work.

    What do you mean by "a complete hold"? Do you mean it stops moving? That is actually a little tricky to answer. There is no absolute coordinate system in space, so if you ask can you stop moving, the reply will be "relative to what".
    At night the stars put on a show for free (Carole King)

    All moderation in purple - The rules

  3. #3
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    Hi Swift,

    It’s a tricky question to phrase to be honest. I mean ‘stop moving’ yes.
    Say you had 3 or 4 hypothetical, 100% identical solar systems in equal distance from a center, all moving the same way at the same speed in the universe - and the object was moving freely, not affected by gravity or otherwise, towards the center of these systems. At the exact moment it hit that center, could you suspend the object there and have it stay there in reference to the systems (moving with the center of them), without ever having to correct?

    Just starting to learn about relativity and newt mechanics,
    appreciate the answer!

  4. #4
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    You say interstellar space and thrusters allowed, so relative to the nearby star or stars you could accelerate or decelerate to rest relative to at least one to enjoy the view. Whether you then need continuous thrust depends on the local gravity field which would be quite small when a long way from any star.
    sicut vis videre esto
    When we realize that patterns don't exist in the universe, they are a template that we hold to the universe to make sense of it, it all makes a lot more sense.
    Originally Posted by Ken G

  5. #5
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    The short answer is: depends on how picky you are.

    You are phrasing it in absolutes: "without ever having to correct", which suggests you might be looking for 'very picky'.

    There are a few confounding factors to the whole setup before even dealing with the spaceship:
    - it is very unlikely to have four stars in a stable configuration - but it is theoretically possible to have them all orbit a common centre (Klemperer Rosette).
    - "ever" is indeed a long time. Long enough to have other stars intrude and interfere with the stable system you've got set up.

    Finally, if you parked a spaceship at the centre of those stars, it would be in an unstable configuration. Any motion away from that point will only increase.

    But very slowly. The spaceship is still - for all practical purposes - stopped. You'd have to be be patient just to wait for the drift to get big enough to even measure.

    From one or several light years away from just a single star, it could take millenia for the ship to fall deeply into its well. With a stable configuration of four stars - all light years away - the net pull toward any particular star will be orders of magnitude smaller. It could take a long time - perhaps many millennia - before the ship might need to be brought back to its location.
    Last edited by DaveC426913; 2018-Nov-21 at 11:24 PM.

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    Quote Originally Posted by profloater View Post
    You say interstellar space and thrusters allowed, so relative to the nearby star or stars you could accelerate or decelerate to rest relative to at least one to enjoy the view. Whether you then need continuous thrust depends on the local gravity field which would be quite small when a long way from any star.
    He did say "without ever having to correct".

  7. #7
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    I'm really summarizing, but I think the answer is, if you use thrusters, you could certainly stop your motion relative to the earth. But eventually you would start drifting in some direction, depending on the specific conditions, and you would have to make corrections.
    As above, so below

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    The gravitational pulls and tugs of surrounding objects will be different in each part of space. And stars move constantly in every which direction. So any object at rest relative to one body, will be constantly if slowly drifting off under the influence of other bodies.

    The closest you can practically get to your scenario, would be two objects in a tide-locked orbit of each other in an intergalactic void. To an observer on the surface of one, the other object would seem to hang motionless in the sky.
    "I'm planning to live forever. So far, that's working perfectly." Steven Wright

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    Quote Originally Posted by Noclevername View Post
    The closest you can practically get to your scenario, would be two objects in a tide-locked orbit of each other in an intergalactic void. To an observer on the surface of one, the other object would seem to hang motionless in the sky.
    ??
    Why would the bodies have to be tidally locked? All that matters is the spaceship in the middle.

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    Quote Originally Posted by DaveC426913 View Post
    He did say "without ever having to correct".
    fair enough but then it becomes a question of how close to another object the spacecraft is, and the general case must be drift I suppose. The question of whether there is ever a point in space time that is static is almost philosophical or requires more assumptions about the model of the universe you wish to use.
    sicut vis videre esto
    When we realize that patterns don't exist in the universe, they are a template that we hold to the universe to make sense of it, it all makes a lot more sense.
    Originally Posted by Ken G

  11. #11
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    So, I was thinking in absolutes and so am concluding that the answer is a ‘no’. It’s possible to hold it very still for a very long time, but not in the manner that I was thinking about. I thank you for your answers Good Sirs. I’ll be back with more weird questions.

    Kat

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    Quote Originally Posted by DaveC426913 View Post
    ??
    Why would the bodies have to be tidally locked? All that matters is the spaceship in the middle.
    A spaceship in the barycenter would be unstable, and would fall into an orbit.
    "I'm planning to live forever. So far, that's working perfectly." Steven Wright

  13. #13
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    To put this in time perspective, suppose we park a spacecraft at a gravitationally neutral point in interstellar space somewhere in our vicinity. While it will be unstable in the long run, it will appear to stay in place for a very long time, just as the "fixed" stars have done throughout recorded history.

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    Quote Originally Posted by Noclevername View Post
    A spaceship in the barycenter would be unstable, and would fall into an orbit.
    Do you mean that, if the two bodies are not spherical, they will perturb the spacecraft as they revolve about their axes? I can't think of another reason why tidal locking would come into play.

    And, if the OP allows four four identical stars, then surely he'll allow for two smooth spherical bodies.

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    Quote Originally Posted by DaveC426913 View Post
    Do you mean that, if the two bodies are not spherical, they will perturb the spacecraft as they revolve about their axes? I can't think of another reason why tidal locking would come into play.

    And, if the OP allows four four identical stars, then surely he'll allow for two smooth spherical bodies.
    Tidal locking is there to preserve the observation of relative immobility.
    "I'm planning to live forever. So far, that's working perfectly." Steven Wright

  16. #16
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    Quote Originally Posted by Noclevername View Post
    Tidal locking is there to preserve the observation of relative immobility.
    Even more confused.
    The OP's question is about a spaceship staying stationary wrt to the masses. Don't see anything about observers on those masses.

  17. #17
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    Quote Originally Posted by DaveC426913 View Post
    Do you mean that, if the two bodies are not spherical, they will perturb the spacecraft as they revolve about their axes? I can't think of another reason why tidal locking would come into play.

    And, if the OP allows four four identical stars, then surely he'll allow for two smooth spherical bodies.
    if in this thought experiment those four stars are stationary, that surely answers the OP? And if they are moving that is the other answer. In the general case the stars are moving (and also changing their masses ) relative to each other and the spaceship so stationary without thrusters is not possible.
    sicut vis videre esto
    When we realize that patterns don't exist in the universe, they are a template that we hold to the universe to make sense of it, it all makes a lot more sense.
    Originally Posted by Ken G

  18. #18
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    You could use gravity assists in more dramatic ways
    https://www.centauri-dreams.org/2012...tional-assist/

    I think someone once said that a spacecraft in front of a massive body moving quickly towards it might accelerate with no propellant. Large objects creating some kind of push...

    Related?

    I have heard that phonons have negative gravity
    https://www.sciencealert.com/physici...-all-around-us
    https://phys.org/news/2018-01-device...nd-lasers.html

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