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Thread: Is there anyplace in the universe where there's no gravity?

  1. #1
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    Is there anyplace in the universe where there's no gravity?

    Silly question???
    I know that I know nothing, so I question everything. - Socrates/Descartes

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    No. Mass is everywhere.

    Information about American English usage here and here. Floating point issues? Please read this before posting.

    How do things fly? This explains it all.

    Actually they can't: "Heavier-than-air flying machines are impossible." - Lord Kelvin, president, Royal Society, 1895.



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    Quote Originally Posted by DaCaptain View Post
    Silly question???
    Nope. Gravity fields are IIRC not limited in range, only in detectability. There's always going to be some gravity present, even at great distances from mass.
    "I'm planning to live forever. So far, that's working perfectly." Steven Wright

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    To add what others have said, gravity is an inverse square law, so if you double the distance the gravity is four times as weak. What that means of course is that it can never reach zero, only come close to it.


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    Indulging in a license for pedantry - there are arrangements of masses which can give arbitrarily low gravitation acceleration over finite areas. Robert Forward described such an arrangement in a technical paper as well as his novel Dragon's Egg. Doing this over big regions near an astronomically significant mass starts to take a lot of well-controlled mass.

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    I suspect that gravity is like everything else. It is the difference that counts. We don't understand the quantum of gravity. We don't understand, if there are two quantum of gravity, next to each other, would they have gravity between them, or gravity as a unit.
    The moment an instant lasted forever, we were destined for the leading edge of eternity.

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    Quote Originally Posted by Copernicus View Post
    I suspect that gravity is like everything else. It is the difference that counts. We don't understand the quantum of gravity. We don't understand, if there are two quantum of gravity, next to each other, would they have gravity between them, or gravity as a unit.
    Copernicus

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    The gravity at the center of the earth is zero, but that does not include everything else pulling on that center, like the sun, other planets etc. https://www.quora.com/Why-is-gravity...entre-of-earth
    The moment an instant lasted forever, we were destined for the leading edge of eternity.

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    Quote Originally Posted by Copernicus View Post
    The gravity at the center of the earth is zero, but that does not include everything else pulling on that center, like the sun, other planets etc. https://www.quora.com/Why-is-gravity...entre-of-earth
    Interesting. So there's really no where were there's no gravity. You can equalize the gravitational effects of nearby masses by equal and opposite masses. But there will still be gravitational pull in all directions. Gravity can't be blocked or cancelled. It's simply omnipresent.
    Last edited by DaCaptain; 2018-Sep-25 at 06:05 PM. Reason: typo
    I know that I know nothing, so I question everything. - Socrates/Descartes

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    Quote Originally Posted by Copernicus View Post
    The gravity at the center of the earth is zero, but that does not include everything else pulling on that center, like the sun, other planets etc. https://www.quora.com/Why-is-gravity...entre-of-earth
    The gravity at the centre of the Earth is high. You would be able to detect time dilation.
    But its force cancels out, since it's pulling from all directions equally.

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    Quote Originally Posted by DaveC426913 View Post
    The gravity at the centre of the Earth is high. You would be able to detect time dilation.
    But its force cancels out, since it's pulling from all directions equally.
    Does gravity come from the center of earth??? Or is it more the combined force of all earths mass? So it wouldn't be it's center but somewhere offset from center but directly below you.
    I know that I know nothing, so I question everything. - Socrates/Descartes

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    Quote Originally Posted by DaCaptain View Post
    So it wouldn't be it's center but somewhere offset from center but directly below you.
    I don't understand this statement. The center of mass is where all the gravity balances out.
    "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
    I don't understand this statement. The center of mass is where all the gravity balances out.
    Oops, my mistake. Not sure what I was thinking. Guess I was thinking that if I was standing on earth that there would be more mass between me and the center than on the other side of earths center. Not true.

    But then it brings up the thought if gravity is zero at the center, why are so many heavy elements gathered there?
    I know that I know nothing, so I question everything. - Socrates/Descartes

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    Quote Originally Posted by DaCaptain View Post
    Oops, my mistake. Not sure what I was thinking. Guess I was thinking that if I was standing on earth that there would be more mass between me and the center than on the other side of earths center. Not true.

    But then it brings up the thought if gravity is zero at the center, why are so many heavy elements gathered there?
    Because the gravity is not really zero. It's like a Trojan point, matter tends to collect there.
    "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
    Because the gravity is not really zero. It's like a Trojan point, matter tends to collect there.
    No the gravity is zero at the center of earth. There is no time dilation.
    The moment an instant lasted forever, we were destined for the leading edge of eternity.

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    Quote Originally Posted by Copernicus View Post
    No the gravity is zero at the center of earth. There is no time dilation.
    DaveC426913 directly contradicted that. Post 10.

    So it comes down to, who's got citations?
    "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
    DaveC426913 directly contradicted that. Post 10.

    So it comes down to, who's got citations?
    I'm sure that somebody who actually understands this can clarify. But I believe that DaveC426913 is correct, because it is the gravitational potential rather than the actual felt gravity that is important. But as I said, I'll wait until someone with an actual grasp of physics chimes in!
    As above, so below

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    It would require that portion of the universe to be so distant from all matter and energy that the point would exist at the center of an absolutely empty sphere around 14 billion light years in radius.
    Except quantum mechanics would laugh at this and make at least one particle appear in there by now.
    On the one hand the universe could be infinite, but on the other there is no reason to assume such a large void is possible out of any origin theory we have.

    And Copernicus, gravity doesn't effect itself, I asked this question in astronomy in college long ago because otherwise black holes would roll inward as gravity couldn't escape itself.

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    Quote Originally Posted by JCoyote View Post
    And Copernicus, gravity doesn't effect itself, I asked this question in astronomy in college long ago because otherwise black holes would roll inward as gravity couldn't escape itself.
    Please explain, gravity doesn't effect itself.
    I know that I know nothing, so I question everything. - Socrates/Descartes

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    Quote Originally Posted by JCoyote View Post
    It would require that portion of the universe to be so distant from all matter and energy that the point would exist at the center of an absolutely empty sphere around 14 billion light years in radius.
    Except quantum mechanics would laugh at this and make at least one particle appear in there by now.
    On the one hand the universe could be infinite, but on the other there is no reason to assume such a large void is possible out of any origin theory we have.

    And Copernicus, gravity doesn't effect itself, I asked this question in astronomy in college long ago because otherwise black holes would roll inward as gravity couldn't escape itself.
    I don't know where, "gravity doesn't effect itself came from. As I stated before. The gravity at the center of the earth is zero, with respect to the earth. It obviously is not the exact center because there are variations in density and shape of the earth. The time dilation comes from outside the center of the earth. The strongest gravity is at the surface of the earth. The ideal graph is shown in the following link.

    https://www.google.com/search?q=grav...jN5Zbxxp0T5YM:

    This does not mean there is not gravity at the center of the earth, because there is gravity from all over the universe.
    The moment an instant lasted forever, we were destined for the leading edge of eternity.

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    I am seeing enough errors and misunderstandings in this thread that it is hard to tell where to start. Let me address the readership at large.

    As far as we can tell, there is matter everywhere, so there is gravity everywhere. Even if we come to a place beyond which there is no matter, the gravitational effects of the matter that is elsewhere will extend without limit, according to our prevailing theory.

    At the center of a uniformly spherical planet the gravitational action of the surrounding matter acts equally in all directions, thus cancelling out so there is no net acceleration of an object at that point.

    At the surface of that planet the resultant gravity is the same as if it were all at the center. Newton found the means to calculate that as an exercise in calculus. I would not say that the gravity is coming from the center. It comes from all over the planet and merely gives the same net result as if it came from the center.

    Suppose the planet is transparent so we can see a clock at the center from afar. That clock is not being accelerated but it is still at the bottom of a gravitational well and would appear time-dilated relative to a clock on the surface. Likewise the surface clock will be time dilated compared to one above the surface. The latter has been observed with clocks aboard airplanes and satellites.

    I could go on and on but I think this is enough for now. These are my understandings and as always don't take them as gospel. If any of you think I am mistaken or missing something, please speak up.

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    As regards to time. Time will move fastest at the center of the earth. Gravity slows down time. Where the field strength is highest, time moves slowest.
    The moment an instant lasted forever, we were destined for the leading edge of eternity.

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    Quote Originally Posted by Copernicus View Post
    As regards to time. Time will move fastest at the center of the earth. Gravity slows down time. Where the field strength is highest, time moves slowest.
    It looks like I am wrong about this.
    The moment an instant lasted forever, we were destined for the leading edge of eternity.

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    Quote Originally Posted by Hornblower View Post
    ..... Suppose the planet is transparent so we can see a clock at the center from afar. That clock is not being accelerated but it is still at the bottom of a gravitational well and would appear time-dilated relative to a clock on the surface. Likewise the surface clock will be time dilated compared to one above the surface. The latter has been observed with clocks aboard airplanes and satellites.....
    Wow, so what would happen if we could place that same clock at the center of a black hole? Would we would be seeing into the future or into the past?
    Last edited by DaCaptain; 2018-Sep-26 at 11:30 PM.
    I know that I know nothing, so I question everything. - Socrates/Descartes

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    Yeah. Time is dilated (slower) at the centre of a massive object, as viewed from higher in the g-well.

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    Quote Originally Posted by DaCaptain View Post
    Wow, so would happen if we could place that same clock at the center of a black hole? Would we would be seeing into the future or into the past?
    Neither.

    We cannot observe such a clock, as no light could escape the BH to reach us.

    What would happen is that, when we dropped the clock into the BH, from a distance, it would fall toward the event horizon. As it did so, it would appear to slow down, and it would also red shift.
    No matter how long we observed it, that's all we would see. It would get closer and closer the EH, getting slower and slower, as well as redder and redder and dimmer and dimmer, until we could no detect enough photons coming from it to even call it an image. We would never see it cross the EH, even if we waited forever.

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    Quote Originally Posted by DaCaptain View Post
    Wow, so what would happen if we could place that same clock at the center of a black hole? Would we would be seeing into the future or into the past?
    You can't see the inside of a BH from the outside. No light escapes. That's why it's black.
    "I'm planning to live forever. So far, that's working perfectly." Steven Wright

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    Forget about the "light cannot. . . " diversion. What about a "clock" that was generating gravitational waves? Would it appear to be faster, slower, or non-existent compared to a similar "clock" outside the BH?

    <edited to change the word choice>
    Last edited by mkline55; 2018-Sep-27 at 12:20 PM.
    Depending on whom you ask, everything is relative.

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    Quote Originally Posted by mkline55 View Post
    Forget about the "light cannot. . . " diversion. What about a "clock" that was generating gravitational waves? Would it appear to be faster, slower, or non-existent compared to a similar "clock" outside the BH?
    A gravitational wave travels at the speed of light, so it won’t escape any better than a photon. The gravitational waves we see are of things collapsing into black holes, not black holes themselves.


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    The only things that escape from black holes are our hopes and expectations.


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