Is Gravity Faster than Light?

Discussion in 'General Science & Technology' started by Bowser, Jan 18, 2018.

  1. Bowser Right Here, Right Now Valued Senior Member

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    Again, I was watching YouTube videos and came across an idea regarding the use of gravity as a means of interstellar communication. Unfortunately, it was just a basic idea and didn't offer any details. My first thought was, how fast is gravity? Also, does it move in waves or is it a constant throughout space?

    It's a curiosity that seems worth exploring. Unfortunately my understanding of the science is limited, and I am open to any insight you might have.
     
    justtestingthings likes this.
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  3. Q-reeus Valued Senior Member

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    This link was posted months ago in Astronomy...etc. sub-forum: http://news.mit.edu/2017/ligo-virgo-first-detection-gravitational-waves-colliding-neutron-stars-1016
    By the time you get to read it all the answer should be obvious. In fact before even starting on the main body of text.
     
    Bowser likes this.
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  5. Q-reeus Valued Senior Member

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    PS: Owing to the extraordinarily weak coupling between gravity and matter, there is zero chance of ever being able to communicate via GW's. As opposed to 'merely' detecting those given off by massive inspiralling binaries etc.
     
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  7. DaveC426913 Valued Senior Member

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    It has recently been demonstrated that gravitational waves move at the speed of light.

    Gravity does not travel; it is a field (or a property of space-time) that is always present, everywhere. It is only changes in gravity that move.
     
    nebel, youreyes and Vociferous like this.
  8. Bowser Right Here, Right Now Valued Senior Member

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    Much like waves on water?
     
  9. DaveC426913 Valued Senior Member

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    Loosely, yes.
     
  10. Q-reeus Valued Senior Member

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    The widespread references in even prestigious journal articles to GW's 'stretching' & 'squeezing' space are wrong. Stretching and squeezing of a media is appropriate to acoustic analogues - such as sound waves traveling through water (surface water waves are even further removed as fitting analogue). A closer analogue would be pure shear waves generated in a solid - since then the transverse character of GW's is better illustrated. But still not perfectly by any means.
    Instead, GW's are fundamentally different - simultaneously creating and destroying space in orthogonal directions. Giving the illusion of objects e.g. LIGO mirrors, moving further and closer apart as GW's pass through. There is alternately more and less space between the mirrors, yet each mirror remains perfectly still i.e. zero proper acceleration owing to passing GW's.
    That conclusion was summarized my 3rd para here: http://www.sciforums.com/posts/3450810/
     
    Last edited: Jan 19, 2018
  11. Bowser Right Here, Right Now Valued Senior Member

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    This is interesting stuff. I appreciate your participation in this thread. I suppose my next question would be, is there more space or less space around a high gravity object, such as a black hole?
     
  12. Q-reeus Valued Senior Member

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    Thanks.
    More space - a sort of TARDIS situation. This is evident by inspection of the standard Schwarzschild metric chart:
    https://en.wikipedia.org/wiki/Schwarzschild_metric
    In that representation, the radial spatial metric is compressed wrt the gravity-free case. That is, it takes more distance to travel between an outer circumference and an inner one than Newtonian physics predicts.
    Also - unlike the GW situation, it IS appropriate in that static gravity case to speak of space (more generally spacetime) being 'squeezed' anisotropically.
     
  13. Bowser Right Here, Right Now Valued Senior Member

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    A little too heady for me, but I appreciate the offer.
    I think I understand. But I'm assuming the difference is minimal, unless we are referring to super massive objects, such as a black hole.

    Once again, I appreciate your input.
     
  14. Q-reeus Valued Senior Member

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    Sure. Even for relativel massive planet Earth, the fractional difference between the Newtonian and GR case is of the order of R_s/R.
    Where R_s is the 'Schwarzschild radius' of Earth ~ 0.9cm, and R is Earth's mean radius ~ 6.4x10^6m. Giving R_s/R ~ 1.4x10^-9.
    See: https://en.wikipedia.org/wiki/Schwarzschild_radius

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  15. Bowser Right Here, Right Now Valued Senior Member

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    Revisiting the Wiki page, I think my assumptions incorrect. Possibly my understanding of black holes also incorrect. One thing leads to another, I suppose.
     
  16. Q-reeus Valued Senior Member

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    I chose to work exclusively from within GR earlier. Viable alternate gravity theories generally give the same gross results but may vary in interpretation for weak gravity cases - and even drastically re predictions for extreme gravity situations. Don't intend on fleshing that out here....we are already well into the usual SF sidetracking thing. Witness what's happened to the Tabby's Star thread for instance!

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  17. amber Registered Member

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    I think you need to stop watching videos if you are going come up with such stupid questions.
     
  18. Michael 345 Bali in Nov closer Valued Senior Member

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    Think you need to reevaluate your participation in forums if you criticises but not debate or contribute

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  19. amber Registered Member

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    Photons have a velocity, Gravity causes a velocity, it is an idiot question.
     
  20. Xelasnave.1947 Valued Senior Member

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    Does that mean it takes an idiot to answer?

    So you roll in guns blazing and you sound so grumpy you should fit right in...

    What is your deal?

    Think you are better than every body or trying to manage an inferiority complex?

    In any event welcome to the site what interest brought you here.

    What do you like to discuss?

    Alex
     
  21. Michael 345 Bali in Nov closer Valued Senior Member

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    Exactly how does gravity cause a velocity?

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  22. amber Registered Member

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    It means that it is an idiot question, attempts to answer an idiot question is being , well..........

    I am sick of reading rubbish ideas that get more discussion than the better ideas.

    I suffer from Dunning and Freddy Krugger syndrome , I think I am smarter than all of you and I will give you nightmares.

    Thank you for the welcome, I like to discuss most things , I will have a think and open a starter thread on something.
     
  23. amber Registered Member

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    The force of attraction between masses causes the velocity, Gravity is just a name we give this force of attraction. We at this moment in time do not know the actual cause and mechanics behind the process of gravity. There is some hypothesis and speculation of what it is, but nothing factual as yet.
     

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