What are the accepted theories for the source of gravity?

  1. I have very little knowledge of physics so the simpler you can keep your replies the better for me.

    Newton put forth a gravity theory that essentially said that there is a force that pulls on us to keep people on the earth and this is gravity.

    Einstein came along and included in his theory of relativity that there is not a force that pulls on us but that because massive objects such as the earth bend/warp space that there is no pull on us but space is pushing us toward the earth.

    I'm not generally a skeptical person and so put it to my lack of knowledge as the reason I don't really believe space is pushing me toward the earth. But I am not here to argue that Einstein is wrong but to understand this part of his theory better.

    Did Einstein's theory about gravity make Newton's obsolete and so no longer valid nor used?

    Are there other theories on what the source of gravity is?

    Who is it that first thought that everything with mass has gravity?
     
  2. jcsd
  3. HallsofIvy

    HallsofIvy 40,932
    Staff Emeritus
    Science Advisor

    Both Newton and Einstein developed theories that told how to calculate the force of gravity. Neither said anything ablut "the source of gravity" nor does any modern theory. (Some theories deal with "gravitons" but that still does not say anything about the source of gravitons.)
     
  4. I thought that Einstein indicated that he believed that space pushes us toward the earth. Is that wrong? And that is what I took to indicate the source of gravity in the case of his theory.

    I do remember from a documentary about Newton that he believed gravity was a pulling force without saying where that pulling source came from.

    Is there a specific theory name that I could look up that would explain more about these graviton's? I've come across reference to graviton's once or twice in the few weeks I've been researching physics.
     
  5. russ_watters

    Staff: Mentor

    Yes, that's wrong. The warping of space isn't really meant to indicate that space is a "thing" that pushes on matter.
    Yes.
    Just googling for gravitons will get you a lot of info. Starting with the wiki: http://en.wikipedia.org/wiki/Graviton
     
  6. That is incomplete. It's not just space that warps but space-time. Absent any forces, everything has a constant velocity through space-time. If you are sitting still, all your velocity is in the time direction. If you move through space you move less through time. Gravity is the twisting of the space-time framework so that forward in time is also downward. Slightly downward in the case of the earth, straight down in the case of a black hole. Please note that this is an extreme simplification. Einstein would likely be appalled, but it's the best I can do in 1 paragraph.
     
  7. Thanks. This gives me more to think about and more to research. I didn't quite think of Einsteins theory in that way.

    And I still need to read more about gravitons.

    Are both Newtons and Einsteins equations to calculate gravity still in use? Or did Einsteins replace Newtons?
     
  8. WannabeNewton

    WannabeNewton 5,862
    Science Advisor

    Newton's equations are still used ubiquitously in physical applications.
     
  9. Newton's equations are used in almost all instances because they are much simpler then Einstein's and almost as accurate. NASA uses Newtonian gravity to plan it's mission.

    Einstein's equations are used mostly for theoretical work dealing with extreme circumstances like the BB, black holes, etc. The differences do become significant in extreme circumstances.

    The 1 exception that I can think of is the GPS system which must take gravitational time dilation into account in order to achieve the extreme accuracy of time keeping necessary to make it work. Each 0.000000003 seconds of error in time keeping represents about a meter in position.
     
  10. mrspeedy "The 1 exception that I can think of is the GPS system which must take gravitational time dilation into account in order to achieve the extreme accuracy of time keeping necessary to make it work."

    There does exist another significant exception: in the case of nuclear submarines which must spend long periods of time on the ocean floor, closer to the center of the earth. They are
    required to modify their clocks due to the stronger gravity there, so that the delicate missile behaviours can be accurate. Sending a missile to the wrong place would be a 'no-no' , no?
     
  11. Thanks! You're answers help me to understand better as to how both could be in use when I was thinking it should be one or the other.

    What level of calculus would I need to understand the formula's you posted. I know I took the first year of calculus but don't remember mention of its use in gravity calculations and of course I remember almost none of it now since I haven't used it in more than 20 years.

    What does BB stand for?
     
  12. sophiecentaur

    sophiecentaur 14,135
    Science Advisor
    Gold Member

    Big Bang. :smile:

    You need to be careful when trying to establish the "why"s that are involved in Science. Unless you are going to postulate a 'God' who set up a load of rules then all you can ever really hope to do is to devise models that predict the way things will work within certain limits. Newton was no more wrong than Einstein and Einstein was not ultimately 'right'. There's no end to it.

    It is easy to feel superior to our scientific predecessors who assumed that there were actual 'Laws', literally, at work but 'they' were building on top of their religion and trying to improve on Genesis 1 etc.. We have loads of questions that will always be unanswerable without using further 'shells' of understanding which, themselves, will throw up more new questions.
     
  13. Now I feel dumb not realizing that BB was for the big bang. Thanks for giving me the meaning!

    I am actually curious to see what aspects of physics is found in the scriptures and how much is similar and how much is different. I don't remember reading anything about gravity in the scriptures but that could be because I was never really focused on that whereas now I am. I remember reading things in the site rules about religion and am not sure how much of what I believe concerning God and the laws of physics I am allowed to discuss here.

    In fact I was very worried that my first question here would suffer the fate of other questions mentioned in the rules and sticky threads.

    I am convinced there are questions we may never find the answer too, but was hoping that the source of gravity was not one of those and that I was simply missing something because I didn't know what terms to use in a search or because there was so much info that I'd have a lot of trouble finding what I am looking for.
     
  14. Drakkith

    Staff: Mentor

    Your best bet is to simply not talk about scriptures at all. I've been on the site for almost 3 years now and not once have I ever seen a productive thread that had any mention of religion in it. Also, to my limited knowledge, there is absolutely nothing that could be considered "accurate physics" in any religious text. Otherwise we wouldn't have had to start from scratch all those years ago.


    Why stop at gravity? There are four total fundamental forces, and we don't know the "source" of any of them. But, as has been explained, there really isn't an end to the "why" question. You can keeping asking why forever, as each time you answer one question a new one immediately pops up.
     
  15. A driving force for my interest in gravity is to better understand it so that a science fiction book I am writing may be more realistic. That is at least what sparked my interest but there seems to be more to it than that at this point and so I keep reading and listening to documentaries and such on you tube. So I haven't tried to investigate the other forces but have come across them while trying to learn about gravity.

    And up until you said that, I didn't realize the other forces also had unknown sources.

    I've read and listened to more about gravitons and while it is interesting and difficult to understand for me at first they still leave me with questions.

    Is there any person or people that are credited with a theory that includes gravitons? Like Einstein is credited with developing the theory of relativity.
     
  16. Drakkith

    Staff: Mentor

    What are you going to do with this knowledge in your book? Just use it to make things more realistic, or are you delving into explaining gravity in some way?

    As I said, the question of "Why" something works or what's the "source" of something is never ending. For example, if I asked you why things have mass, how would you explain it? The only possible answer anyone can give you is "They just do." This goes for all sorts of properties. From spin, to charge, and any other fundamental property or force there is.

    I don't know, sorry.
     
  17. I just read a thread here about artificial gravity and depending on how I decide to do things this knowledge could help me make a different kind of artificial gravity. However, my initial reason for trying to understand it was so that I can have a feasible way for a large object to shut off its natural gravity and/or have gravity function differently than what we know here on earth.

    And you just hit on another problem I am starting to delve into which is about mass. I don't have enough knowledge to know why things have mass but I am going to investigate differences in mass and get a better understanding of mass also.
     
  18. Drakkith

    Staff: Mentor

    There is no feasible way for that to happen. Period.
    However, that's why it's Science Fiction and not Science Fact!

    I'll tell you why things have mass.
    They just do.
     
  19. sophiecentaur

    sophiecentaur 14,135
    Science Advisor
    Gold Member

    If you really want to feel good about any small increase in your understanding of the World, that involves getting down to some real Rigour. The pleasure you can get from learning absolute basics and using that to derive even the most fundamental 'new thing' (that is 'new for you') is just incredible. It beats all that arm waving and mystical phoney Science. In the end it's down to nuts and bolts and getting the lamp to light up or the solution to change colour as you predicted. All the rest is metaphysics and philosophy - angels on pinheads etc.. Try to swim around out of your depth in Science and you'll drown before you get anywhere. (Imho, of course)
     
  20. To use Newtonian gravity you should have a basic understanding of integration. When I took calculus I had 1 semester of differentiation and 1 semester of integration. If your course was similar then you've probably been exposed to all the calculus you need for Newton, though you'll probably need some refreshment after 20 years
    To use Einstein's equations you need a solid understanding of tensor calculus. This is beyond my abilities right now and apparently it's pretty advanced stuff. When I first discovered I needed to learn it I asked my father to teach me because he has a masters degree in mathematics. He didn't know what a tensor was. (In his defense it has been 40 years since he graduated)
     
  21. Ah but if I remember correctly from a documentary I listened to, at the quantum level they believe they can do teleportation. If that can be done at a larger scale then mass could be teleported elsewhere temporarily, thus shutting off gravity because of the reduced mass and then teleported back.

    Also what if in the CERN collider they discover a graviton and then learn how to create them consistently. They may be able to create artificial gravity that way by generating enough gravitons.

    I intend to do experiments as a way to gain experience that I won't get by just talking about physics but I have not done many at this point as I want a bit more knowledge first.

    Thanks! I'll have to review integration calculus and then move on to tensor calculus. Can I safely ignore differentiation calculus if I am only interested in Newton's gravity equations?
     
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