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B Few Questions from a hobbyist

  1. Oct 23, 2015 #1
    Hello, I'm not an Academic, I love physics as a casual hobby. So I have few questions that stuck in my mind. Here is the first one:

    By Einsteins General Relativity everything including us stuck to Earth by gravity. Earths mass bends the Spacetime. The gravity means: deformed space is pushing us down. So if we take Spacetime out of equation just to conduct an imaginary experiment, and leave people, buildings and everything on Earth with no Spacetime present, everything will float in weightlessness?

    Will there not be noticeable force between us and Earth?

    I'm open to corrections.
  2. jcsd
  3. Oct 23, 2015 #2


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    Since the things you mention (Earth, etc) exist in space-time, the concept of "taking away the space-time" is not a meaningful concept even in a thought experiment. It is not meaningful to ask "what would the laws of physics say about <insert nonsense of your choice> if the laws of physics did not apply".
  4. Oct 23, 2015 #3
    It's really just about using two different ways to model gravity. As a force or using a 4-dimensional spacetime geometry. They are just different models.

    In the spacetime geometry model it's not correct to say that space is pushing us down, because pushing would be the application of a force.

    Concerning the removal of spacetime, space and time are human inventions. Creations of the mind. I guess you can remove them from your mind. Doing so would not remove gravity because gravity is a naturally-occurring phenomenon. Humans didn't invent gravity, we just invented different ways of describing it.
  5. Oct 23, 2015 #4


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    I disagree completely. Space and time (space-time) are reality, not inventions of our minds. The ways we describe them are our inventions but they are pretty good and give reliable results regarding reality.
  6. Oct 23, 2015 #5
    Second question: If we hypothetically make a wormhole from the centre of the universe to the very edge, then pass an object through it. Will object pass through the wormhole literally instantly, or with a delay of measurable time?
  7. Oct 23, 2015 #6


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    Second question that is not meaningful because there IS no "edge" to the universe. Also, wormholes are most likely a mathematical fiction.
  8. Oct 23, 2015 #7
    I would like to thank you Mister T, and phinds for a reply in such a short time :-)

    Mister T I apologise if misunderstood you, but if I understand you correctly, then I would like to point out to you that there is an organisation in Britain that corrects time on Satellites because difference in time between orbit and Earth, caused by space being bent less at the orbit. Secondly I would mention gravitational lensing.

    Looking forward hearing from you.
  9. Oct 23, 2015 #8


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    I don't understand if there is a question in there somewhere but consider this:

    Time passage is a bit of a complex issue. Time on a satellite passes on the satellite at the same one second per second as does time here on Earth, BUT, the satellite is (1) farther outside the Earth's gravity well, so a compensation is required for gravitational time dilation and (2) traveling at a modest speed relative to us (unless it's a geosynchronous one) and so requires a compensation for time dilation due to relative motion.

    These concepts are crucial to the proper working of the GPS system since if they were not accounted for your GPS would have you driving into the sides of buildings and off into corn fields.

    As I recall, the specific compensations are -7 microseconds per day for motion and +45microseconds per day for gravity.

    Google the "Twin Paradox" for more on this kind of thing.
  10. Oct 23, 2015 #9
    Reply to second question. Let point B not be an edge of the universe but be 46 bil light years away - what they call the edge of an observable Universe. My question still remains same: Will object pass through the wormhole literally instantly, or with a delay of measurable time?

    Wormholes are not fact, but theoretically explainable as if we assume that Spacetime is flexible enough to bend, we can theoreticaly assume that under extreme theoretical force Spacetime will loose integrity, thus creating a hole. We could assume that in tunnel - hole is no spase hence nearly instant travel.

  11. Oct 23, 2015 #10
    Note that I didn't say they aren't real!

    All of the quantities in physics are things that we measure. Humans invented the tools we use to measure them. Without a way to measure them we have no way of defining them.

    My apologies to the OP, I didn't mean to hijack the thread. I just wanted to clear up the misconception embedded in the original post.
  12. Oct 23, 2015 #11
    No doubt! Without that kind of accurate time-keeping the GPS system wouldn't work. But those are part of the process needed to keep time accurately. To call them corrections implies that some prior errors were made. Yes, the engineers use the Einsteinian 4-dimensional spacetime model because the Newtonian force model is not adequate. The former is no doubt the better model. But it's still a model. It doesn't incorporate quantum theory and physicists seek a model that's better yet.

    Radar-ranging is another. Radar beams that graze the surface of the sun before and after bouncing off Venus are one of the best confirmations of Einstein's physics.
  13. Oct 23, 2015 #12
    Thanks phinds for describing the Time passage in more accurate way than I did.I skimmed through Wikipedia and read about time Gravitational time dilation.
  14. Oct 23, 2015 #13


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    sorry but what you said .....

    ....... couldn't be taken any other way and is completely incorrect

    Please be a little more careful in how you word things, it can lead people astray when they are still learning and don't recognise when something said is wrong :smile:

    many thanks
  15. Oct 23, 2015 #14
  16. Oct 23, 2015 #15
    There were no errors in what I said. Things that are human inventions are things that are real. The two are not mutually exclusive.
  17. Oct 23, 2015 #16


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    Space and time exist, they are NOT human inventions

    please stop compounding your error
  18. Oct 23, 2015 #17


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    Spacetime "bending" is another one of those English language translations of math that really don't serve reality well. It is a totally artificial analogy based on Euclidean Geometry rather than try to explain to laymen the Riemann Geometry that describes spacetime. Things that are described as "bent" or "curved" are so described because that description uses Euclidean Geometry but in reality those things are traveling in straight lines (technically, "geodesics") in Riemann Geometry and there is no "bending" involved.
  19. Oct 23, 2015 #18
    What makes you think that being an invention and existing are mutually exclusive?

    I explained that I made no error.
  20. Oct 23, 2015 #19
    I would like rephrase the first question: Is the Spacetime with it's deformed (imaginable) curvature deciding factor that causes gravity?

    Does mass of Earth play no other role than deforming Space time thus creating a Gravity well?

    Does Earth's matter (fundamental forces + energy of whole Earth) not play role in Gravitational attraction of us and everything on Earth?

    What is the official scientific way of describing Gravity as an effect? Could you please explain it to me in simpler terms understandable to Hobbyist.

    Thanks to all of you for your time.
  21. Oct 23, 2015 #20
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