What is gravity?

What is gravity? Gear up for next week’s #Newtonmas  hangout on air with MinutePhysics with this  refresher inspired by Sir Isaac himself. Hangout RSVP:http://goo.gl/3sj7fi

Minute Physics: What is Gravity?

http://www.youtube.com/watch?v=p_o4aY7xkXg//cdn.embedly.com/widgets/platform.js

Join the Conversation

10 Comments


  1. What it is described in this video is basically what was thought of gravity two centuries ago (i.e., according to the Newtonian model of gravity).  It has little resemblance to description that is derived from the currently widely accepted relativistic model.


    I already objected about this misdescription of gravity as some kind of force in another video of the same YouTube channel: MAGNETS: How Do They Work? (6 min 26 s) It’s about time to throw away outdated models.


    Massive bodies, radiation and other non-massive particles aren’t attracted by a mysterious force emanating from matter itself. According to the relativistic model, what we call gravity is just the direct consequence of the curvature of space-time continuum.


    References:


    <>


    1. Geroch, Robert (1981). General relativity from A to B. University of Chicago Press. p. 181. ISBN 0-226-28864-1., Chapter 7, page 181


    books.google.com/books?id=UkxPpqHs0RkC&pg=PA181 


    << Gravity is treated very differently in Newton's and Einstein's theories. According to the general theory of relativity there is no gravitational force. The principle of equivalence says that the physical effects of permanent gravitational fields and those due to the acceleration or rotation of the reference frame are equivalent. >>


    2. Grøn, Øyvind; Hervik, Sigbjørn (2007). Einstein’s general theory of relativity; with modern applications in cosmology. Springer Japan. p. 256. ISBN 0-387-69199-5., Chapter 10, page 256


    books.google.com/books?id=COqUEa5M6O0C&pg=PA256 


    <>


     . . . 


    << Given that Einstein’s general theory does not involve the idea of gravity as a force, how does the gravitational “force” that is a feature of the Newtonian theory arise? We remarked in the Introduction that in a local inertial frame (a freely falling nonrotating reference system occupying a small region of space-time) the laws of physics are those of special relativity, an in particular free particles (those moving under gravity alone) follow straight-line paths with constant speed, so for these frames there is no acceleration and consequently no “force.” When discussing gravity in Newtonian terms, it is customary to insist that the frame used is nonrotating (so there are no centrifugal or Coriolis “forces”), but one does not normally use a frame that is freely falling, and it is this use of nonfreely falling frames that gives rise to gravitational forces. Just as the fictitious forces associated with rotation (the centrifugal and the Coriolis forces) can be transformed away (locally) by changing to a nonrotating frame, so can the fictitious force of gravity be transformed away by changing to a freely falling frame. >>


    3. J. Foster, J. D. Nightingale, J. Foster, J. D. Nightingale; J. Foster, J. D. Nightingale, J. Foster, J. D. Nightingale (2006). A short course in general relativity (3 ed.). Springer Science & Business. p. 55. ISBN 0-387-26078-1., Chapter 2, page 55


    books.google.com/books?id=wtoKZODmoVsC&pg=PA55 

    Like

Leave a comment

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out /  Change )

Google photo

You are commenting using your Google account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s

%d bloggers like this: