Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Scientific american article about the nature of gravity.

  1. Nov 26, 2003 #1
    Has anyone read this? Either the physicists interviewed in this article were ridiculously stupid or they're so smart that they go right over my head.

    People at NASA sent out some sort of probe which was just intended to go out into the uiniverse with no particular destination. It constantly sent signals back to NASA and they could tell how far it was from earth and the speed at which it was travelling. They noticed that the farther it got from the sun, the slower it was going, and this allarmed them greatly, and they said it defied gravity in some way.

    As I see it:

    1.) There's matter in space. When you travel through matter, you get friction and slow down.

    2.) Gravity impedes on inertia. If you throw a ball up into the air (away from earth's center of gravity) it will go fast, then slow down until it stops and comes back. It seems that's what the ship was doing, the initial inertia it got from being launched was being impeded upon from the gravity of the sun/planets.

    Now, are the scientists who thought this ship's movements just operating on such a level that I don't understand their logic, or am I smarter than them?
    Last edited: Nov 30, 2003
  2. jcsd
  3. Nov 26, 2003 #2


    User Avatar
    Staff Emeritus
    Science Advisor
    Gold Member

    What form does this matter have? Why have we not been able to detect it? Why didn't it effect other things we have launched such as the moon missions?
    So you are assuming that the teams of scientists who have mangaged to get a capsul out of the solar system do not know about the basic laws of Newton! Was it just luck that got them there?
    I'll bet the former is more likly to be true then the latter.
  4. Nov 26, 2003 #3


    User Avatar
    Staff Emeritus
    Science Advisor
    Gold Member

    Which issue of Scientific American?
  5. Nov 26, 2003 #4
    Re: Re: Scientific american article about the nature of gravity.

    matter of space, apparently, someone has detected it.

    My point is that either there were alot of things they considered and encorporated into their distress and didn't include into the article, or they're stupid. Didn't NASA once have a probe crash becuase some measurements weren't converted from metric to the american system of measurement? The article actually went on to dispute newton.

    Hopefully, I'm not smarter than NASA's scientists.

    It was a recent issue of scientific american, and it was the cover article, though on the cover it adressed the issue of dark matter more than this. The probe slowing down was just kind of used as an example of how the current understanding of is flawed and that dark matter may not exist due to this persons reasearch. it was probabally either october or november's issue.
  6. Nov 26, 2003 #5


    User Avatar
    Staff Emeritus
    Science Advisor
    Gold Member

    My point is, that the obsevered slowing is after taking the laws of Newton into account. I do not think that any sort of friction force with space will be the root cause. There is still much research to be done, until that is complete all else is speculation.
  7. Nov 27, 2003 #6
    Well the article said this space craft was far beyond pluto when it got out of range to send messages, so I don't see why you'd totally disregard friction as contributing to some of the slowing.
  8. Nov 27, 2003 #7


    User Avatar
    Staff Emeritus
    Science Advisor
    Gold Member

    There is no friction acting on a space craft in space. Friction is is a surface interaction, there is nothing in space to cause friction or even drag. Which is the term used in aerodynamics for air "friction". The density of particles in space is pretty well known, in fact the farther from the major planets you get the lower the density of particles becomes.

    You need to come up with something to cause this drag.
  9. Nov 27, 2003 #8
    From my viewpoint there's still the pull of the sun and our solar system in general which is responsible for the slowing. I just don't see how you can say there isn't friction between particles in space, even if it were ridiculously minute. Whenever you travel through matter, you're going to get resistance, it's just common sense...
  10. Nov 27, 2003 #9


    User Avatar
    Staff Emeritus
    Science Advisor
    Gold Member

    Once again, Believe it or not the people at NASA looking at this issue are familiar with the laws of gravity. The slowing that is seen is NOT within our current understanding of gravity. It is something else.

    This is not a new discovery, this slowing has been observed over the last several years. They have spend most of that time ruling out any thing aboard the craft itself which could possibly be causing the problem. They have found nothing.

    Why can we be pretty sure that it is not friction of some sort? If it were some sort of outside drag or friction there would be a corresponding warming of the skin or exposed surfaces of the craft. This would be detecable, I do not believe that they have observed any unaccounted for temperature varitations.

    If you wish to dream up some scifi friction which acts without effecting the surfaces of the craft then please take your ideas to the Theory Development fourm.

    For myself, I will continue to follow the developments as they are released, and not spin my wheels attempting to explain things that I cannot. I simply do not have acces to the necessary data to even begin a meaningfull analysis. This may turn into a revolution in our understanding of the universe or it may become a joke equivelent to cold fusion, only time will tell.
  11. Nov 27, 2003 #10
    Please explain to me why the slowing of this craft could not be due to the gravity of the sun and the planets in our solar system exerting a small pull on the craft.
  12. Nov 27, 2003 #11
    yes, waste, wouldn't it be simpler if you just paste a link here so we can all read the article......
  13. Nov 27, 2003 #12
    I read the article in late october in the school library. The school had already had 2 different copies of scientific american available and then taken them down, which leads me to believe it was the october or november issue. sciam.com does not have anything from their october or november 2003 issue available online yet.
  14. Nov 27, 2003 #13
  15. Nov 27, 2003 #14
    More likely neither one: the article just left out some of the details.

    Actually, they were planetary probes (Pioneer 10 and 11) that had already fulfilled their missions and continued travelling out of the solar system.


    They already calculated those effects and eliminated them, and found that there was still some deceleration that could not be accounted for by any known means.

    In their original paper, "the analyses were modelled to include the effects of planetary perturbations, radiation pressure, the interplanetary media, general relativity, and bias and drift in the range and Doppler", and they considered "gravity from the Kuiper belt, gravity from the galaxy, spacecraft `gas leaks', errors in the planetary ephemeris, and errors in the accepted values of the Earth's orientation, precession, and nutation".

    In short, they were very careful to make sure to consider all the non-gravitational causes they could think of.

    Some of their papers:

  16. Nov 27, 2003 #15


    User Avatar
    Science Advisor

    I'm pretty sure the probe you're talking about is Pioneer 10, Waste. That probe (as well as one of the Voyagers, I believe) is beyond the orbit of Pluto. It is indeed decelerating due to gravity from the Sun. However, it is decelerating faster than it should be if that were the only cause.

    The mission planners understand the influence of gravity so well that they are able to predict the deceleratrion of the probe with great accuracy. So great infact, that they are able to detect a discrepency of very small proportions. I'm not sure on the amount here, but I think the acceleration was on the order of 1mph over 6yrs, or something rediculously small like that.

    Anyhow, according to the Pioneer Homepage, it amounts to about 1/10,000,000 g. If you look through the link, you'll see a few of the things they tried to apply to account for the acceleration, none of which worked. So far, it is still unnexplained.

    It also mentions the SciAm artical, which was December 1998, if anyone wants to look that up.
  17. Nov 27, 2003 #16
    OK now that makes more sense. The way the article had been written, it seemed that the craft was expected to stay at a totally constant speed throughout its whole mission and that any decceleration was totally unexpected.

    So, my fault for being arrogant and thinking that NASA didn't realize our solar systems gravity and the author of the article's fault for not saying that it was more decceleration than expected.
  18. Nov 27, 2003 #17


    User Avatar
    Staff Emeritus
    Science Advisor
    Gold Member

    LISA, Gaia, Microscope, BepiColombo

    ... are all European Science Agency (ESA) planned missions.

    This site has an overview:

    LISA - scheduled for launch in 2011 - is an ambitious project to search for gravitational waves. It is also sensitive enough to not only detect the 'Pioneer anomaly', if it's as large as the work cited by Ambitwistor suggests, but also characterise it in some detail. The others may also detect it, if its parameterisation is in certain ranges.

    The site says, of the Pioneer anomaly, "The same behaviour has now been detected on NASA's Galileo and the joint ESA-NASA Ulysses spacecraft". However, I've not found any other references to such detections.
  19. Nov 27, 2003 #18
  20. Nov 27, 2003 #19
    So, has anyone actually read this article I'm talking about? The person the article mainly focused on came up with some theory about gravity which would explain the unusual movement of celestial bodies without the use of dark matter, and made some sort of modification to newtons theories. It went well over my head, but I'm sure some of the people here who could actually understand it would find it interesting.
  21. Nov 27, 2003 #20
    I haven't read the article, but it sounds like it may have been talking about Milgrom's MOND (MOdified Newtonian Dynamics) theory. But there are a few papers that mostly killed that theory.
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?

Similar Discussions: Scientific american article about the nature of gravity.
  1. Nature of gravity (Replies: 56)