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Proof that gravity exists?

  1. Nov 27, 2003 #1
    Could someone tell me what gravity is, and what is the proof that gravity exists?
  2. jcsd
  3. Nov 27, 2003 #2


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    Inb Newtonian physics gravity is the attraction between two massive bodies, in general relativty it is the curvature of space-time. The proof that it exists is the fact that when you posted the above post you were not floating upside down.
  4. Nov 28, 2003 #3
    gravity does not only exist as a pull from large objects however all objects pull on one another.
  5. Nov 28, 2003 #4
    I don't get it, how can light with no mass, or photons with no mass be affected by gravity?

    It is that gravity acts on all things including things with no mass?
  6. Nov 28, 2003 #5

    Well we know know light as both particle and wave or some would call it a "wavicle". The particle aspect of light allows gravity to play a role in affecting it. That's a simple way to put it.

    It was proven in the early 20th century during a solar eclipse off the coast of Africa when the gravity of the sun distorted the position of nearby stars.

    Also look up information on Gravity Lenses. A lot of deep space photography utilizes the gravity lensing effect. Very cool stuff.
  7. Nov 28, 2003 #6
    Yes. This is why gravity is referred to as the only "universal" interaction: it acts on everything.
  8. Nov 28, 2003 #7
    Re: Gravity

    Well, even in classical electromagnetism, where light is treated as a wave and not a particle, gravity still affects light.
  9. Nov 28, 2003 #8


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    Einstein's theory of general relativity describes gravitation as a result of the curvature of spacetime. All objects, even massless photons, move along the straightest possible lines in this curved space. The straightest possible lines in a curved space, however, and not "straight" like lines drawn on a plane.

    - Warren
  10. Nov 28, 2003 #9
    if Time is viewed as an interaction, couldn't this also be a universal determinate?
  11. Nov 29, 2003 #10


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    No, time is shown by experimentation to be variable.
  12. Nov 29, 2003 #11
    i dont understand the difference, what are some experiments to show this?
  13. Nov 30, 2003 #12


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    One of the simplest done is with two identical clocks. One is put into orbit around the earth, the other stays on the ground. The clock in orbit sends a signal to a computer on the ground which compares it to the clock on the ground. The clock in orbit loses time when compared to the clock on the ground. This fact (and correcting for it) is of the utmost importance in making the GPS system work.

    Experiments have also been done on clocks on towers: gravity affects the rate of the passage of time as well.
  14. Nov 30, 2003 #13
    Despite how many times i hear about that. (Gravity's effect on time) I still have trouble comprehending how it even begins to work...
    Any links on it as I have no clue what to search for.
  15. Nov 30, 2003 #14
    There are probably a gazillion links on the web about gravitational time dilation. You could search the WWW (www.google.com) or the Usenet newsgroups (groups.google.com) for keywords like "spacetime curvature time dilation".
  16. Dec 1, 2003 #15


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    Is it so much easier to understand how gravity affects something with mass?
  17. Dec 1, 2003 #16
    Yes, I would say that it is. Something that is matter is imagined easier if it has a mass, therefore it is a real thing or object. It is hard to understand how massless objects or the concept of photons exist. And gravity, which acts on everything; so does it also act on nothing? (or a thing with no mass?)
  18. Dec 1, 2003 #17
    DaveMan: so your problem isn't with gravity being able to affect massless things, it's about whether massless things exist at all.

    Why do you think mass is required for something to exist? Massless particles have plenty of other physical properties: energy, momentum, angular momentum, sometimes (gauge) charge, etc. A massless particle is hardly "nothing": it lacks mass, but it can exchange energy, exert a force (since it has momentum), interact via fields, etc.
  19. Dec 2, 2003 #18
    Oh yeh, I agree. A hypothetical question...
    In a sealed room is it possible to take the gravity out of the room, by using no external factors. - eg sucking the gravitons out of the room. and what would happen if it were possible?
  20. Dec 2, 2003 #19
    You can shield a room from electromagnetic effects, but you can't shield a room from gravitational effects.
  21. Dec 3, 2003 #20


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    Wasn't there some talk of BEC's shielding gravity? Thought I heard somrthing along those lines recently, though it still strains my credulity.
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