1. PF Contest - Win "Conquering the Physics GRE" book! Click Here to Enter
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

If light is a constant then gravity is also right?

  1. Oct 29, 2009 #1
    Ok so if gravity is a constant then what relation does it have to mass? Is mass also a constant? Like mass will act the same way every time I assume... So what is the constant for mass? My only guess is it has something to do with the size of the object. Like if something displaces xyz amount of space it will have xyz qualitys. I would also assume the shape of the mass might play a role. Thoughts?
  2. jcsd
  3. Oct 29, 2009 #2


    User Avatar

    Staff: Mentor

    Huh? Could you reword that because it doesn't make any sense.

    Perhaps you are trying to comment on these two facts/observations: The speed of light is constant to all inertial observers. Changes in gravity propagate at the speed of light.
  4. Oct 29, 2009 #3
    Light itself is not a constant. Maybe you're thinking of c, the speed of light. Gravity is not a constant either. Maybe you're thinking of G, the gravitational constant.
  5. Oct 29, 2009 #4
    No im pretty sure light is a constant and that is the reason for why c is a constant. And same for gravity. Provide some evidence to the opposite if you really want to convince me im wrong. Here is the underlying thought behind this... ...If you run a test exactly the same way multiple times you will get exactly the same results. Basicaly what im saying is that light made in the same way will act the same always and that its probably possible that light is basicaly always made in the same or at least very similar ways thus it acts like light even when its made in say a different star or whatever.
  6. Oct 29, 2009 #5
    Careful, I've seen threads get locked for statements like that. :)
    But really, if you're so sure you're right then why should you expect anyone to waste their time trying to change it?
  7. Oct 29, 2009 #6
    You can make a very good estimate of mass (in grams) if you count the number of protons and the number of neutrons in it, and divide by the number of protons in a gram (hint: it's 6E23). Electrons don't count for much.
    Bob S
  8. Oct 29, 2009 #7
    I really dont expect anyone to actualy try to convince me of anything. But I do like personal growth so I challenge myself constantly. I'm kinda just hoping someone who doesnt agree and mostly gets what im saying will help me to get a better understanding of it myself. I dont think people should "try" to convince others generaly more just make convince themselfs and find out the truth as best they can.
  9. Oct 29, 2009 #8


    User Avatar

    Staff: Mentor

    That phrase is gibberish. Light is not a property. It isn't a value that can be constant or not constant.
    You're going to have a very hard time learning anything in this world with an attitude like that. It is much easier to learn by starting with a blank slate and filling it with knowledge than it is to start with a completely baseless assumption or logic pulled out of thin air and then have others try to change your mind.

    More to the point: we don't care! If you want to learn, fine, if not, fine. You're here by choice and we are not at your beck and call.
    Ok.....but that has nothing to do with the gibberish you posted above!
  10. Oct 29, 2009 #9

    Gravitation is the result of a distortion of space-time within a particular region. It is caused by a massive object. The degree of distortion depends on the mass of the object, the more massive the object is the more the space-time around it will be distorted regardless of the shape of the object. Gravitation accelerates all massive bodies toward a central point. Every massive body has its own gravitational field and thus exerts force in this manner on every other massive body in the universe via the inverse square law. Gravitational fields have the additional effect of time dilation, in which the path of light follows the distortion and causes events to appear slower when viewed from less distorted frames of reference. In summation, gravity increases with mass but does not depend on shape and causes acceleration along the y axis and dilates time.

    One additional comment: saying that light itself is constant has no meaning, it is the way light interacts with matter which is constant.
    Last edited: Oct 30, 2009
  11. Oct 29, 2009 #10
    Now THIS is gibberish.
  12. Oct 30, 2009 #11
    Please try and listen with an open mind. I can't speak for everyone else, but I'm open to a little criticism of how I conduct myself, and so I hope you will be too.

    The problem is, you're assuming that we're all in the same boat, and none of us understands the subject better than any other. This is not the case. Most of the people who responded to you understand the subject very well. You seem to be a beginner. And that's fine! Great, even. Beginners are very much welcome here. But you aren't going to learn anything if you take the attitude that no one should try to convince you of anything, but instead we should somehow "try to use your question to understand it better ourselves". You aren't saying anything insightful enough to revolutionize our world, and you're being a little arrogant for thinking that you are. It's not that beginners never ask questions that insightful; sometimes they do, but yours isn't one of them. Sorry if that's disappointing. It shouldn't be.

    Based on your question, it sounds like maybe you aren't 100% sure what the concepts you're trying to talk about "look like". We can try to help you understand them better, but you're going to have to trust us. And you're going to have to try to think more clearly and precisely, because, unlike art, physics is a clear and precise subject. Unlike the arts and humanities, the sciences cannot be understood vaguely or clumsily. The details are *everything*.

    You need to make an effort to phrase what you're trying to say clearly enough that someone can tell what you're trying to say. The effort of trying to do that, in itself, will actually give you a better, more detailed understanding of what you're saying. Sometimes, someone answers their own question just by finding a more precise way of phrasing it!

    A constant is a number that doesn't change. More specifically, it doesn't change when you change something else. If "A is constant with respect to B," that means that "changing B doesn't change A". Light and gravity are not numbers. You might be trying to say that light doesn't change as it moves through space, but even that isn't totally right, because it does actually spread out as it moves. The same is true for gravity. Mass IS actually a number, but it certainly isn't constant. Weight yourself two weeks in a row and you'll see that your mass changes! Now, it is true that mass is conserved can't be created or destroyed, if that has anything to do with what you're trying to think about. But that doesn't have anything to do with constancy of the speed of light.
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook