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Why don't they fall?

  1. Aug 22, 2012 #1
    Does space have some kind of buoyancy that prevents stuff from falling down? for instance, why doesn't the Sun fall downward eternally? Like, it is clear why the moon doesn't fall out of the sky but what is holding the Sun up in space? If you say the galaxy what is holding it up? what is the support structure for this stuff ... dark matter? Else it seems everything is just floating in space. is the entire universe everywhere filled with this support structure to prevent everything from falling?

    Or is everything falling in the same frame of reference and it appears to be static? what happens if the support structure fails or becomes too diluted due to expansion?
     
  2. jcsd
  3. Aug 22, 2012 #2

    K^2

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    In what direction should it be falling?
     
  4. Aug 22, 2012 #3
    Things only "fall" the way you're talking about because of gravity. Don't think of a model of the solar system as little balls you have to hold up, because then you'll make the mistake of implicitly thinking there is gravity you hold them up against. Presumably, there is a fairly even distribution of matter in space meaning the solar system is being attracted in many different directions, and this could balance out to hold it in place.
     
  5. Aug 22, 2012 #4

    LJW

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    Why should it "fall"? Where would it fall to? Things fall when you drop them due to gravity. These aren't small objects near the surface of the Earth, they're massive objects in space.

    Though, everything is moving outwards from a point of origin- as proven by red shift. Gravitational pull does attract the objects to one another, though it is very weak.
     
  6. Aug 22, 2012 #5
    Ok, but I am not referring to gravity. There has to be some kind of scaffolding to hold the stars in position. Just seems wierd that they are just sitting out there. what happened to their momentum maybe they should be falling in that direction.
     
  7. Aug 22, 2012 #6

    LJW

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    Yes, you are. You're used to living with gravity- and a lot of it, constantly. They aren't just sitting out there- they are moving apart from a central point. But they are certainly not "falling" as you suggested.
     
  8. Aug 22, 2012 #7

    davenn

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    You need to wrap your head around the idea that there is no falling in space. There is no specific up, down, left or right. Its all relative to you as an observer.

    Imagine being in a geostationary orbit over the Earth's equator ( like the satellites in those positions) And your feet were in the direction of the south pole and your head towards the north pole. Now because you are used to thinking your feet and anything "below" them is down... you may say that south pole is below you.
    But here I am in orbit beside you, but I am orientated the opposite way so we are looking at each other's feet .... I would argue with you that, UP is towards the south pole and down is towards the north pole. !! :)

    There is no up, down, left, right .... nothing needs to be suspended.

    Dave
     
  9. Aug 23, 2012 #8

    davenn

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    ..... and on from that, whilst you are positioned there over the equator, rotate your body length through 360 deg, At 0deg feet to the Spole, at 90deg feet/body parallel to the equator, at 180 deg feet now towards the north pole, at 270 deg feet/ body parallel to the equator again.

    NOW ... you tell me which one of those orientations is up or down etc ? ;) you cant

    Dave
     
  10. Aug 23, 2012 #9
    The closest thing to a scaffolding that I can think of is space-time. Gravity is an attractive force causing all masses to "fall" towards each other.
    Red shifting evidence indicates that masses are actually "moving" further apart and this is attributed to dark energy.
    There may very well be a scaffolding of some sort that the electroweak force doesn't interact with so it has yet to be discovered (unless you just think of it as space-time)...
     
  11. Aug 23, 2012 #10
    The sun actually IS moving at quite a good clip around the center of the galaxy. I've heard something like 500,000 mph. But I've also heard ~52,000 mph. Maybe we don't know, but suffice to say that it's NOT standing still. It just seems liek it to us. If the sun somehow put on the brakes, then it would "fall" gravitationally towards the center of the galaxy.

    Of course the center of the galaxy itself is not standing still either. However, IF something was standing still and there was no gravity acting on it, then it would indeed just chill there. Why would it move if there's no force on it?
     
  12. Aug 23, 2012 #11
    Yep, it's gravity holding everything in orbit. Learning about UCM (uniform circular motion) may help you understand why the Earth doesn't fall to the centre of the solar system.

    Anyway, as per SR, it's meaningless to ask whether we're standing still. From our point of view, we're standing still, obviously. From the point of view of someone sitting at the centre of the galaxy (ignoring the fact that it's pretty near impossible to survive there,) we're going pretty fast. And so on.
     
  13. Aug 23, 2012 #12

    mfb

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    ~220km/s relative to the center of the galaxy (about 9 million miles per hour), which corresponds to one orbit per ~250 million years.
    Without this relative velocity, the solar system would begin to fall towards the central area.

    All stars have some velocity relative to the center of the galaxy, and most of them are orbiting around it in some way.
     
  14. Aug 24, 2012 #13
    I think you got a conversion factor wrong. 220 km/s is about 500,000 mph.

    Here's where I was reading about the slower speed:

    http://www.redorbit.com/news/space/1112533286/speed-of-the-sun-shockingly-slower-than-believed/

    But they seem to have omitted some key information in the article. I'm guessing from info that I've pieced together that the solar system is actually travelling through some intersellar cloud, and 52,000 mph is the speed it's moving through this thing.
     
  15. Aug 24, 2012 #14
    It used to be thought that the stars & planets were in a medium called luminiferous aether, sort of like how a fish lives in a medium called water http://en.wikipedia.org/wiki/Luminiferous_aether
    Experiments showed that luminiferous aether does not exist http://en.wikipedia.org/wiki/Michelson–Morley_experiment

    In a sense you are right, the stars & planets are rushing away from eachother but nothing is "holding them up". This started at the big bang & is called the expansion of space http://en.wikipedia.org/wiki/Metric_expansion_of_space
     
    Last edited: Aug 24, 2012
  16. Aug 24, 2012 #15

    mfb

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    Hmm, you are right, probably some typo in my WolframAlpha query.


    That is the interstellar medium
     
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