Force of Gravity

Discussion in 'Science and Nature' started by NorseMythology, Apr 21, 2016.

  1. Okay so force of gravity is

    Fg=G(m1m2/r2)

    Fg is force of gravity

    G is gravitational constant

    m1 mass of object one

    m2 mass of object two

    r is radius/distance between bodies

    How do they calculate the gravitational lensing of photons when they have no rest mass and supposedly no diameter? They call it a point, not even a dimensional/physical mass.
     
  2. When photons are being bent by the gravity of an object, they're not at rest as they are traveling. It is important to note that the resting state of a photon mostly exists in thought. We've never been able to put a photon into rest, and if we did.. it'd no longer exist. If we did put a photon into rest and it continued to exist, then we would know that they do indeed have a minute amount of mass when at rest. Photons gain mass as they travel, relativistic mass.. but still mass.

    As for how to calculate the relativistic mass of traveling photons, no clue. I'm sure they can measure the lensing effect from an object, the mass of the object, and then work backwards to guesstimate the mass of the photons. I know they were looking to directly measure the mass.. but I don't think our technology is efficient enough to measure such a small increment yet.
     
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  3. The equation you are describing is derived from principles of newtonian physics, but the question you are asking pertains to general relativity. Newtonian physics cannot explain gravitational lensing of photons, etc...which is why Einstein did what he did. ;)
     
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  4. So is there another equation for relativity?
     
  5. Right there they assume the photon as a massed particle, which I think is accurate, but contradicts assumptions In other areas. If it has mass, and is travelling the speed of light, I think it would suggest the photon has infinite mass. This is why they say it is massless.
     
  6. I think they call the approach using gravity as naive for a reason (in the wiki I posted, I mean). Either photons have mass or how we understand mass at light speed is wrong, or there is something else at play.

    I haven't the slightest clue
     
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  7. They say it is massless because it has (should have) no mass when it is at rest. According to what I think I know about it all.. special relativity says that mass=energy, and that doesn't actually state that energy=mass.. but you can easily assume it. I do, because all energy has a pull, or push.. a system with the ability to do work. So in a way, energy can be looked at as mass.. and it's easy to walk away with a "everything is energy.." thought, but remember that it is relativistic mass. They call it massless because that's what science does, labels and classifies things with significant differences.. such as mass and energy. Yes.. at it's root it's all the same shit, but we need to differentiate them for scientific reasons. A photon is basically pure energy.. that's why the mass that is has can only be looked at as relativistic mass. Matter is basically condensed energy, so when it comes to traveling, it can never travel as fast as light.. because light is.. well lighter in terms of weight. A photon doesn't have infinite mass.. it doesn't even have infinite relativistic mass. In order for something to be able to have an infinite amount of mass.. it would also have an infinite amount of energy. Maybe in 10,000 years we'll be able to warp around like in Star Trek.. but for now infinite energy isn't possible. That is what it would take for us to be able to make something travel at, or faster, that speed of light.. an infinite supply of energy, at once. So a photon is massless because it is energy.. but the idea of something has zero mass is like saying it has zero energy. The relativistic mass gained by light happens in a moment.. it's not like a photon is created at 0 mph and speeds up with the speed of light, a photon is traveling at the speed of light the moment it is created. With all that.. I look at it like mass = energy, energy = relativistic mass, energy =/= mass.
     
  8. What is ever at rest?

    As far as energy and mass, as I have considered a response for about an hour now, I realize it comes down to metaphysical assumptions.

    The way I see it, mass is simply energy moving about an axis, powered by the flowing of energy, creating a 3D whirl.

    If we take it down to 2D, a particle spinning clockwise would have an up flow of energy/current on the left and a downflow on the right, thus sustaining the whirl, giving us a differentiation in the stream of energy.
     
  9. Well.. technically nothing is truly at rest. Rest is a frame of reference, a relative term. If you had a toy car sitting stationary on your dresser.. to your frame of reference it is at rest. To the universe, it is sitting on a planet that is rotating at thousands of mph.. while the planet travels around the sun, while the sun travels around the galaxy, while our galaxy moves within the local group, while the local group is moving. Our local group is cruising over a million mph towards an "attractor".. and depending on how objects travel through spacetime, it all might add up. Even if it did though, any relativistic mass gained by that movement is next to nothing.. and because of that, we can use that "rest" as our frame of reference. Kind of have to frame references when everything is relative.

    As for the mass/energy dilemma.. no metaphysical assumptions need be made. Physically, we know every is energy in one form or another. We know that mass is energy. We know that light is energy in its purest known form. If you want to look at everything in a quantized fashion, light is one of the smallest known bits. That's why anything that is made up of more than one "bit" can never travel as fast as light.

    With the visualization.. I can't say that it is incorrect.. but there are probably a million different ways one can visualize it since it is something that is beyond visualization. Fluid dynamics is probably the best thing we can use to try to visualize spacetime in its most primitive form.
     
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  10. #11 Dryice, Apr 27, 2016
    Last edited: Apr 27, 2016
    Bingo. I might be missing something from the convo (didn't see this mentioned when I skimmed), but massive objects curve space. It doesn't matter if the photon has mass or not, because the "channel" you were supposed to go through is now a warped/bent channel. It's not literally gravity pulling the photon away from its path, its the fact that gravity distorted the local space which affected the photons path.

    Also Einstein's field equations aren't nearly as eloquent as Newtons. It would be difficult for us to talk about it mathematically (as laypersons). Tensor analysis isn't that fun.
     
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  11. Idk if it's the main/standard model, but some hypothesize that gravity = bent space correct?

    Not even that gravity causes space to bend, but is bent space.
     
  12. I don't think I've heard that one, but I'd be curious how they justify it, and how it ultimately means something different from gravity curving space.
     
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  13. I could very well be wrong
     
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  14. I never personally cared for the curved space idea, but I am not an expert by any means.
     
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  15. I'm still young in my physics studies so anything I've learned is the traditional model of physics, nothing that speculative or theoretical so if it is something, I probably wouldn't have heard it anyways. :laughing:
     
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  16. I'm just having a hard time getting around the "6 vs half dozen" nature of the statement.
     
  17. Being reluctant in believing something I admittedly don't understand? I can see that.

    Having learned a bit about local astrophysics, just within our solar system, and the profound influence of electromagnetism and plasma, I get the sense the emphasis on gravity is an incomplete picture.

    So my opinion is based in much ignorance but not complete ignorance.
     
  18. This thread is out of my league.... I'm just gonna leave
     
  19. Well you can't beat yourself up over it cause we really don't know why gravity is gravity. I will say that the whole "6 vs half dozen" does seem to sum up the 'gravity bends spacetime and bent spacetime is gravity' thing. I personally don't like saying it is bent. To me, saying spacetime gets bent is like saying you can bend the flow of water while deep under the ocean.

    I think string threory will help solve the riddle of gravity. Imagine if you had a ball and literally stuck strings to it and had them all extended straight out. If you were to spin the ball, they would end up laying down on the surface.. and if you had another small object on the surface, the strings would fold over and hold it down. If string theory turns out to be more correct than not, it might help explain it.
     
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