Scientific american article about the nature of gravity.

In summary, the conversation discusses a NASA probe that was sent out into the universe with no particular destination. The probe sent signals back to NASA and it was noticed that the farther it got from the sun, the slower it was going, causing concern and leading to the discovery that it defied gravity in some way. The conversation then delves into the possible causes of this observed slowing, with one person suggesting that it could be due to friction from matter in space and the other pointing out that there is no surface interaction in space. The conversation ends with the suggestion that more research is needed to determine the true cause of the probe's slowing.
  • #1
wasteofo2
478
2
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?
 
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  • #2
Originally posted by wasteofo2
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.

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?
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.
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?
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?

I'll bet the former is more likly to be true then the latter.
 
  • #3
Which issue of Scientific American?
 
  • #4


Originally posted by Integral
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.


http://www-ssg.sr.unh.edu/tof/Outreach/Interstellar/index.html?what1.html
matter of space, apparently, someone has detected it.

My point is that either there were a lot 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.
 
  • #5
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.
 
  • #6
Originally posted by Integral
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.

Well the article said this spacecraft 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.
 
  • #7
There is no friction acting on a spacecraft 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.
 
  • #8
Originally posted by Integral
There is no friction acting on a spacecraft 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.

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...
 
  • #9
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.
 
  • #10
Originally posted by Integral
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.

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.
 
  • #11
Originally posted by Nereid
Which issue of Scientific American?

yes, waste, wouldn't it be simpler if you just paste a link here so we can all read the article...
 
  • #12
Originally posted by Guybrush Threepwood
yes, waste, wouldn't it be simpler if you just paste a link here so we can all read the article...

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.
 
  • #13
Originally posted by wasteofo2
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.

Originally posted by Integral
My point is, that the obsevered slowing is after taking the laws of Newton into account.
 
  • #14
Originally posted by wasteofo2
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.

More likely neither one: the article just left out some of the details.


People at NASA sent out some sort of probe which was just intended to go out into the uiniverse with no particular destination.

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

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.

Yes.


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

2.) [...] 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.

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 modeled 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:

http://arXiv.org/find/gr-qc/1/AND+au:+anderson+ti:+pioneer/0/1/0/all/0/1
 
  • #15
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 http://spaceprojects.arc.nasa.gov/Space_Projects/pioneer/PNStat.html [Broken], 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.
 
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  • #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.
 
  • #17
LISA, Gaia, Microscope, BepiColombo

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

This site has an overview:
http://sci.esa.int/science-e/www/object/printfriendly.cfm?fobjectid=30467

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
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.
 
  • #20
Originally posted by wasteofo2
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.

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.
 
  • #21
MOND

If the sciam article referred to is Milgrom's, I found it an enjoyable read. It's good to see alternative ideas being discussed, particularly when they provide a good match to observational data that consensus physics has a tough time with.

IIRC (I don't have my copy to hand), Milgrom was careful to point out the limitations of MOND, and a separate panel article (by a different author) set MOND in a broader context.
 
  • #22
I read somewhere recently about light that passed through large concentrations of galaxies gaining frequency. The results are likely considered preliminary, but that got me to thinking that light could be the reason for the probe slow down. I'm not referring to light that hits the probe, but the light that does not.

The expectation in there test was that light would gain energy approaching the concentration of galaxies, and then lose energy leaving ..thereby canceling out. This was not the case. I was excited about this because it fit my model for light. My contention is that the light leaving the sun in the direction of the probe, is what's pulling the probe, and upon passing the distance of the probe the light has little effect toward accelerating it for a canceling effect.
 
  • #23
ISW?

Perhaps you are referring to the Integrated Sacks-Wolfe (ISW) effect? For example:
http://astro.uchicago.edu/~laroque/ISW.html

... and a claim that it has been detected, along with some characterisation of dark energy, in the cosmic microwave background as well as from galaxy clusters (combined WMAP and SDSS observations):
http://www.sdss.org/news/releases/20030721.darkenergy.html

If so, I rather doubt the ISW effect could account for the Pioneer anomoly; the scale is too short of expansion of the universe to leave a signal.
 
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  • #24
Perhaps you are referring to the Integrated Sacks-Wolfe (ISW) effect? For example:
Well yes - Thats part of the reference.
and a claim that it has been detected
Well no - Thier claiming that it is not being detected when expected. Thier claim is that dark energy is the culprit for the anomaly. I have no problem with this if dark energy does exist.

To be the devils advocate _ What if there is no dark energy. After all ... people have been searching for it for decades to no avail. I give no alternative for this, but offer the obvious in their survey - Light will gain energy when approaching consentrations of mass, and lose less than what's gained when leaving. If this is true - Then I can understand how light can have an effect on something like that of a spaceprobe. Energy is stolen from the probe by photons when approaching the probe from the sun. Upon passing - Less energy is given back to the probe then what was taken. The net effect is the spaceprobe slows down faster than expected.

I also have a problem with the idea of a gravity well effecting everything universally. I can accept this analogy and it's effect regarding masses, but not with photons. The survey is a telltale sign of this IMO.
 
  • #25
UltraPi1 wrote: To be the devils advocate _ What if there is no dark energy. After all ... people have been searching for it for decades to no avail.
Aren't you confusing 'dark matter' with 'dark energy'?

Dark matter has indeed been sought for decades, but, contrary to your summary, to very much avail!

Dark energy is but the leading contender to explain some very interesting observations that are now quite firmly established.

The first observations which put dark energy on the map were made to determine the distance-redshift relationship for high-z (redshift) galaxies, using Type Ia supernovae. This relationship plays a leading role in helping to determine which cosmological models work best.

Much to everyone's surprise, the data didn't fit any model, and seemed to show that the universe is expanding, at an ever increasing rate.

Since then, the first year's results from WMAP (which builds up a map of the cosmic background radiation, across the whole sky) fit nicely into models using 'dark energy' with parameters consistent with the distant supernovae work.
 
  • #26
Aren't you confusing 'dark matter' with 'dark energy'?
No - I'm pointing at dark energy.
Dark energy is but the leading contender to explain some very interesting observations that are now quite firmly established.
Yes - It's the leading candidate for some observations.

Once again - I'm being the devils advocate. I'll reject the concept of dark energy, and look at the data for what it is without this theory. The straight forward approach of the survey is that light gains energy moving through large concentrations of mass, and if this is so - I can understand the possibility of the opposite being true - That light can slow down craft like the probes. The same effect was seen to be so with another probe other than Pioneer 10. One constant here is the light from the sun. Each probe will get for the most part an equal share of light passing them. I'm not possitive about this, but I think the calculations are that the crafts would slow down in the neighborhood of 6 MPH over the course of 100 years. I see this estimation as a positive for light being the culprit.

If any of this turns out to be true - Light could be considered gravitational to a certain extent. It would be different in that it's effects are felt in the direction of it's motion, as oppose to a gravitational field where the effects are felt in all directions.
 
  • #27
Step by step

I'd like to take a step-by-step approach to your 'devil's advocacy' if I may.

First, what concerns do you have (if any) with the observations themselves? In particular:
a) the redshift-luminosity relationship from the combined distance supernovae studies?
b) the CMB map from WMAP?
c) the SDSS 'on the sky' distribution of galaxies by redshift?

Second, where are the flaws - in your opinion - in the work done to relate the observational results to cosmological models? In particular:
a) the construction of the models?
b) the methods used to estimate goodness of fit of the observations to the models (or the process used to determine the best-fit parameters in the models)?

Third, to be sure there's not something else being missed, what other observational results which (may) have a significant bearing on 'dark energy' are being overlooked?
 
  • #28
I'd like to take a step-by-step approach to your 'devil's advocacy' if I may.

First, what concerns do you have (if any) with the observations themselves? In particular:
a) the redshift-luminosity relationship from the combined distance supernovae studies?
b) the CMB map from WMAP?
c) the SDSS 'on the sky' distribution of galaxies by redshift?

Second, where are the flaws - in your opinion - in the work done to relate the observational results to cosmological models? In particular:
a) the construction of the models?
b) the methods used to estimate goodness of fit of the observations to the models (or the process used to determine the best-fit parameters in the models)?

Third, to be sure there's not something else being missed, what other observational results which (may) have a significant bearing on 'dark energy' are being overlooked?
I have no concerns for dark energy or the expansion of space. I tossed them in the trash by being the devils advocate. I give no alternative for what got tossed. If however light turns out to be the culprit for the probes slowing down - An alternative has to be put forth for expansion of space. Rest assured - this is no easy task, but if all this comes to fruition regarding the probes - Our current understanding of light is flawed too, and if so .. I would look to the new understanding of light for answers to the expansion of space issue.

Currently there is nothing out there to explain the probes slowing down (dark energy included). I merely give an alternative. There would be no surprise here if the alternative changes our understanding of everything else.

Many are questioning our understanding of gravity because of these probes. Why would it be a leap to question light, dark energy, and what ever else you so choose to? I'll answer that by saying - you must. In the process of doing a puzzle ... one must look on the task at different angles wherein the piece you are looking for is right before your eyes.
 
  • #29
Solar neutrino analogy?

Originally posted by UltraPi1
I have no concerns for dark energy or the expansion of space. I tossed them in the trash by being the devils advocate. I give no alternative for what got tossed. If however light turns out to be the culprit for the probes slowing down - An alternative has to be put forth for expansion of space. Rest assured - this is no easy task, but if all this comes to fruition regarding the probes - Our current understanding of light is flawed too, and if so .. I would look to the new understanding of light for answers to the expansion of space issue.

Currently there is nothing out there to explain the probes slowing down (dark energy included). I merely give an alternative. There would be no surprise here if the alternative changes our understanding of everything else.

Many are questioning our understanding of gravity because of these probes. Why would it be a leap to question light, dark energy, and what ever else you so choose to? I'll answer that by saying - you must. In the process of doing a puzzle ... one must look on the task at different angles wherein the piece you are looking for is right before your eyes.
LISA, we need you!

We'll both be following the next generation of space probes with great interest. Let's hope that it won't take as long as the solar neutrino puzzle to be resolved!
 
  • #30
Maybe this is a dumb question, but is it really possible to account for all the forces acting on the probe? The gravity of an object at a very far distance (planets in other galaxies) may be negligible when looked at alone, but when teh force from every single mass in the universe is put together it could be causing this deceleration. Also is there a possibility of some nearby mass they aren't aware of? (eg. small rock that has escaped it previous orbit.) But I've only done 3 months of Newtonian physics so I could be way off :D
 
  • #31
Originally posted by Sko
The gravity of an object at a very far distance (planets in other galaxies) may be negligible when looked at alone, but when teh force from every single mass in the universe is put together it could be causing this deceleration.

No. The gravitational force of all the other masses in the universe is negligible, for many reasons: they're too far away, they're isotropically and homogeneously distributed (so they all tend to cancel out), and they'd exert almost identically the same force on the rest of the solar system as they would on the probes so we wouldn't measure a difference anyway.

(They did try calculating gravity from the rest of the galaxy, and proved that it was much too small to account for this effect. The contribution from extragalactic sources would be even weaker.)

Also is there a possibility of some nearby mass they aren't aware of? (eg. small rock that has escaped it previous orbit.)

They made an attempt to detect small bodies in the solar system, primarily in the Kuiper belt. They didn't find anything.
 
  • #32
Originally posted by UltraPi1
Currently there is nothing out there to explain the probes slowing down (dark energy included). I merely give an alternative. There would be no surprise here if the alternative changes our understanding of everything else.

Many are questioning our understanding of gravity because of these probes. Why would it be a leap to question light, dark energy, and what ever else you so choose to? I'll answer that by saying - you must. In the process of doing a puzzle ... one must look on the task at different angles wherein the piece you are looking for is right before your eyes.
IMO the key is that the probes are made from earthly matter which is still connected by the spacetime layers with earth. Photons have this problems not because they are single. (not bound in a group to high mass levels). My approach predicts that the probes will come to a complete stop and be retracted to the sun. When this will happen depends from the stretchability of (gravity) spacetime layers. I don't like this idea at all (!) because it's like claiming that interstellar travel is not possible ... but there might be alternatives (related to decoupling-methodes of these earthly-originated gravity layers), and of course it depends of the powering of future probes. The actual probes are not powered anymore.

I suggest you look to the slowing probes like separate frames, and Einstein predicted 'frame dragging'.
 
  • #33
Simple question, have the accounted for gravitie's (possible) slowing (or speeding up) of the signal (itself) that communicates between probe, and earth?

After all, gravity bends 'spacetime', and might just have the signal following a more curved course, through space, then was previously thought.
 
  • #34
They have taken into account general relativity's effects on the signal.
 
  • #35
Originally posted by Ambitwistor
They have taken into account general relativity's effects on the signal.
Humm, yes I had figured that they would using the "known" manner of that, but is it possible that they 'miss evidence' because they believe that that part is figured out, but (perhaps) is actually flawed, inasmuch as, it isn't being accounted for in the manner in which it is "actually operating" as opposed to the way it has been believed to operate, which is how it is accounted for now, possible?
 
<h2>What is gravity?</h2><p>Gravity is a force of attraction between two objects with mass. It is responsible for keeping planets in orbit around the sun and objects on Earth from floating away.</p><h2>How does gravity work?</h2><p>Gravity works by bending the fabric of space-time around massive objects. This causes objects to follow a curved path towards the center of the mass, creating the force of gravity.</p><h2>What did the Scientific American article reveal about the nature of gravity?</h2><p>The Scientific American article discussed the theory of general relativity, which explains gravity as a result of the curvature of space-time. It also delved into the ongoing research and experiments being conducted to better understand the nature of gravity.</p><h2>Can gravity be manipulated or controlled?</h2><p>As of now, there is no known way to manipulate or control gravity. However, scientists are constantly exploring new theories and technologies that could potentially lead to the ability to control gravity in the future.</p><h2>How does gravity affect the universe?</h2><p>Gravity plays a crucial role in the formation and structure of the universe. It is responsible for the formation of galaxies, stars, and planets. It also governs the motion of celestial bodies and shapes the overall structure of the universe.</p>

What is gravity?

Gravity is a force of attraction between two objects with mass. It is responsible for keeping planets in orbit around the sun and objects on Earth from floating away.

How does gravity work?

Gravity works by bending the fabric of space-time around massive objects. This causes objects to follow a curved path towards the center of the mass, creating the force of gravity.

What did the Scientific American article reveal about the nature of gravity?

The Scientific American article discussed the theory of general relativity, which explains gravity as a result of the curvature of space-time. It also delved into the ongoing research and experiments being conducted to better understand the nature of gravity.

Can gravity be manipulated or controlled?

As of now, there is no known way to manipulate or control gravity. However, scientists are constantly exploring new theories and technologies that could potentially lead to the ability to control gravity in the future.

How does gravity affect the universe?

Gravity plays a crucial role in the formation and structure of the universe. It is responsible for the formation of galaxies, stars, and planets. It also governs the motion of celestial bodies and shapes the overall structure of the universe.

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