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Thread: The dumb questions thread

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    Veteran Member Wiploc's Avatar
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    My new theory is that they took the picture from underneath.

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    So I was pondering about faster than light speed travel. And two questions came to mind (ignoring whether FTL speed is possible).

    1) Can you steer when going faster than light? (I suppose this applies to any really fast speed approaching a fraction of c)
    Someone showed me a YouTube link about using a blackhole's gravity to slingshot a laser around it, to hit your ship and go very very fast. I had a few concerns about that, but the one I'm asking about is vectors. If you are going really really really fast... is it possible to modify your trajectory? We are struggling with theories about how to change the course of a meteor heading towards earth at pathetically low speeds relative to light. So I was wondering, you shoot yourself into a direction at a mammoth speed... is your trajectory set in stone? How can you apply any force in a lateral direction to change your trajectory?

    2) Can you navigate when going faster than light? When you go faster than light, doesn't light do the Star Trek thing, kind of like how water drops appear to be going horizonal when you drive the car? It might be as simple as some math, but from an engineering point of view, wouldn't it be hard to know where you are exactly when going faster than light? Yes, you have velocity (though to what precision) and time, but is there certainty in direction? Is it also possible to use stars for navigational beacons when going faster than light?

  3. Top | #723
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    Quote Originally Posted by Wiploc View Post
    Post a link, or an image of an upside down crater, if you would.
    Here's the first footprint on the moon. Since I was a little kid, I've always thought it was weird, because it looks inverted, but I never heard anyone else mention it or give an explanation for it. I guess its the same effect we're discussing here?


  4. Top | #724
    the baby-eater
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    Quote Originally Posted by Jimmy Higgins View Post
    So I was pondering about faster than light speed travel. And two questions came to mind (ignoring whether FTL speed is possible).

    1) Can you steer when going faster than light? (I suppose this applies to any really fast speed approaching a fraction of c)
    Someone showed me a YouTube link about using a blackhole's gravity to slingshot a laser around it, to hit your ship and go very very fast. I had a few concerns about that, but the one I'm asking about is vectors. If you are going really really really fast... is it possible to modify your trajectory? We are struggling with theories about how to change the course of a meteor heading towards earth at pathetically low speeds relative to light. So I was wondering, you shoot yourself into a direction at a mammoth speed... is your trajectory set in stone? How can you apply any force in a lateral direction to change your trajectory?
    You can't travel faster than light. c is a fundamental speed limit. You can't just ignore that.

    If you are travelling at a fraction of c, acceleration still works the same way as it does at low speeds. If you rely on Newton's third law and use a rocket engine, you'll need a very large amount of ejection mass in order to change your trajectory by any meaningful amount. In practice, you would probably want to point yourself in the right direction before you start accelerating, rather than wasting your thrust travelling in the wrong direction.

    The reason it's hard to shift a meteor is because a meteor has a lot of mass, therefore a lot of inertia, and it's hard to attach a thruster that's big enough and lasts long enough to impart any meaningful acceleration on it.

    Quote Originally Posted by Jimmy Higgins View Post
    2) Can you navigate when going faster than light? When you go faster than light, doesn't light do the Star Trek thing, kind of like how water drops appear to be going horizonal when you drive the car? It might be as simple as some math, but from an engineering point of view, wouldn't it be hard to know where you are exactly when going faster than light? Yes, you have velocity (though to what precision) and time, but is there certainty in direction? Is it also possible to use stars for navigational beacons when going faster than light?
    Sci Fi relies on adding extra rules to the universe, like wormholes and hyperspace. If you want to know how physics works in these universes, you have to read the fictional source material or ask the creators.

    Faster than light travels breaks the rules of relativity so badly that you descend into absurdities pretty quickly. Spaceships travelling faster than c would somehow have negative mass, experience time in reverse, see everything back to front and upside down, and everyone on board would have green skin and goatees.

  5. Top | #725
    Veteran Member skepticalbip's Avatar
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    I always enjoy FTL travel. It saves me the hassle and worry of being late because every time I travel FTL I always get to where I am going before I start out.

  6. Top | #726
    Nut Case George S's Avatar
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    Quote Originally Posted by Jimmy Higgins View Post
    So I was pondering about faster than light speed travel. And two questions came to mind (ignoring whether FTL speed is possible).

    1) Can you steer when going faster than light? (I suppose this applies to any really fast speed approaching a fraction of c)
    Someone showed me a YouTube link about using a blackhole's gravity to slingshot a laser around it, to hit your ship and go very very fast. I had a few concerns about that, but the one I'm asking about is vectors. If you are going really really really fast... is it possible to modify your trajectory? We are struggling with theories about how to change the course of a meteor heading towards earth at pathetically low speeds relative to light. So I was wondering, you shoot yourself into a direction at a mammoth speed... is your trajectory set in stone? How can you apply any force in a lateral direction to change your trajectory?
    There is one FTL in which the spaceship distorts space itself so the space behind ages faster than that in front. The spaceship never exceeds c in space; it need not move at all in space. However, the spaceship may appear to an observer to have reached its destination faster than light which did not also go through the distorted patch in space. This method "warps" space and is, therefore, a "warp drive." If one of the paths -- your slingshot around a massive object -- from A to B (as in an Einstein Ring) did not have the warped space you could see your spaceship before you turned the warp drive on viewing on a different path.


    2) Can you navigate when going faster than light? When you go faster than light, doesn't light do the Star Trek thing, kind of like how water drops appear to be going horizonal when you drive the car? It might be as simple as some math, but from an engineering point of view, wouldn't it be hard to know where you are exactly when going faster than light? Yes, you have velocity (though to what precision) and time, but is there certainty in direction? Is it also possible to use stars for navigational beacons when going faster than light?
    Navigation would involve changing the direction of the distortion -- a technology requirement to get the direction of the warp in the first place. The Star Trek visual effect would not happen.

    ____________
    Gravity happens for exactly that reason.


    (View video on YouTube)

    But also see (by same physicist).


    (View video on YouTube)
    Last edited by George S; 06-19-2019 at 11:58 AM.

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    Veteran Member Wiploc's Avatar
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    Quote Originally Posted by thebeave View Post
    Quote Originally Posted by Wiploc View Post
    Post a link, or an image of an upside down crater, if you would.
    Here's the first footprint on the moon. Since I was a little kid, I've always thought it was weird, because it looks inverted, but I never heard anyone else mention it or give an explanation for it. I guess its the same effect we're discussing here?

    It looks right to me. But if you perceive the light as coming from the left, then it should be inverted for you.

  8. Top | #728
    Veteran Member Wiploc's Avatar
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    Quote Originally Posted by Wiploc View Post
    Quote Originally Posted by thebeave View Post
    Quote Originally Posted by Wiploc View Post
    Post a link, or an image of an upside down crater, if you would.
    Here's the first footprint on the moon. Since I was a little kid, I've always thought it was weird, because it looks inverted, but I never heard anyone else mention it or give an explanation for it. I guess its the same effect we're discussing here?

    It looks right to me. But if you perceive the light as coming from the left, then it should be inverted for you.
    Ah, I got it! Right now it looks like it's sticking up out of the ground. And, yes, I'm seeing the light as from the left.

  9. Top | #729
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    High speed space travel is problematic if you are in what we would call normal space.

    The structural reaction forces in the structure for turns or stops would be enormous. I expect the result would also be heat.
    STNG got around it with 'structural integrity fields' and 'inertial dampers'. I giggle a bit whenever Picard orders 'full stop'.

    Heat rejection on the shuttles and on the ISS are problematic even with the relatively small loads. The only way to reject heat is radiation. The shuttles could not stay up if the cargo bay doors were not opened exposing radiators.

    Whatever space ship is created, the propulsion will mot be 100% efficient and a lot of heat would be created.

    Even at 99.999999 % efficiency the terawatt generator on Enterprise would cook the crew. A ship in space is like a Thermos vacuums bottle.


    There is a theory of FTL that creates a bubble around the ship such that the ship appears to not go fast. The problem in the theory it needs energy with a negative sign.

    There is also the problem of non empty space. There are pictures of micrometeorite damage on the space shuttles. Dust and gas would abrade the ship as speed increased.

  10. Top | #730
    Veteran Member Wiploc's Avatar
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    Quote Originally Posted by Jimmy Higgins View Post
    1) Can you steer when going faster than light? (I suppose this applies to any really fast speed approaching a fraction of c)
    ... If you are going really really really fast... is it possible to modify your trajectory? We are struggling with theories about how to change the course of a meteor heading towards earth at pathetically low speeds relative to light. So I was wondering, you shoot yourself into a direction at a mammoth speed... is your trajectory set in stone? How can you apply any force in a lateral direction to change your trajectory?
    All motion is relative. You are always stopped relative to yourself. Your controls will always seem normal to you. Even though you are traveling very near to c relative to, say, a cosmic ray, your handles normally. It is not affected by its speed relative to other objects.

    But suppose we look at your vehicle from another point of view, rather than from your own. Suppose you start from the earth, and accelerate until you are at .99 c relative to the earth. And suppose you want to reach .995 c (again, relative to the earth). If you are watching from inside your ship, acceleration will seem normal. But if we are watching from earth, your acceleration will seem slow and costly.

    But, of course, that's nothing new. That's how it looks now--as viewed by a cosmic ray--when you accelerate your car.

    If there are tachyons around, you can still maneuver your car normally, even though you are going faster than light relative to the tachyon.

    Now suppose you are traveling at 1.5 c, relative to the local stars, and you discover that you are heading right at one, and there is no way you can slow down in time to avoid it. You can still turn. The relativistic distortions are in the direction of relative travel. So even though you can't effectively brake, you still ought to be able to turn normally. Because your speed to the right or left of the obstacle is zero, which isn't fast enough to generate relativistic distortions.




    2) Can you navigate when going faster than light? When you go faster than light, doesn't light do the Star Trek thing, kind of like how water drops appear to be going horizonal when you drive the car? It might be as simple as some math, but from an engineering point of view, wouldn't it be hard to know where you are exactly when going faster than light? Yes, you have velocity (though to what precision) and time, but is there certainty in direction? Is it also possible to use stars for navigational beacons when going faster than light?
    Let's do an analogy with water waves. Suppose waves travel at (to make up a number) two miles an hour. And suppose you're in a boat going four miles an hour. Do you still encounter waves even though you're going faster than them? Yes. You keep striking (or being struck by) waves no matter what speed or direction you go. (Unless you match speed and direction with the waves.)

    So, yes, you can still learn from the waves anything that you could learn from them if you were stopped relative to the shore.

    Now if we consider light, there is no such thing as matching its direction and speed. So you'll still encounter peaks and troughs (or photons, if you prefer) so you can still see things.

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