Solar System in a Can May Reveal Hidden Dimensions 251
dylanduck writes "A model solar system, made of tungsten and placed in space, could reveal hidden spatial dimensions and test alternative theories of gravity. If the system's 'planets' moved slightly differently to the way predicted by standard gravity, it would signal the presence of new physical phenomena." From the article: "Once at the Lagrange point, the artificial solar system would be set in motion inside the spacecraft. An 8-centimetre-wide sphere of tungsten would act as an artificial sun, while a smaller test sphere would be launched 10 cm away into an oval-shaped orbit. The miniscule planet would orbit its tungsten sun 3,000 times per year."
Gotchas, we got em (Score:3, Interesting)
Re:Gotchas, we got em (Score:4, Informative)
And the spacecraft components themselves would exert gravitational forces on the spheres. These forces could be minimised by making the spacecraft as symmetrical as possible and putting its heaviest components as far from the artificial solar system as possible.
"Such an experiment would be quite challenging to set up, but I don't think it is technologically impossible," says MOND expert Stacy McGaugh of the University of Maryland, US.
Not impossible can be quite a stretch to feasible, though.
Re:Gotchas, we got em (Score:5, Funny)
Re:Gotchas, we got em (Score:2, Funny)
Home on LaGrange (Score:3, Funny)
Re:Gotchas, we got em (Score:5, Insightful)
Re:Gotchas, we got em (Score:2)
Re:Gotchas, we got em (Score:2)
Re:Gotchas, we got em (Score:3, Informative)
Of course, the math for that is based on regular-old physics. It might not apply in higher-dimensional physics that these scientist hope to prove.
Of course, the article ignores the difficulty i
Re:Gotchas, we got em (Score:2)
Re:Gotchas, we got em (Score:3, Informative)
Um, I don't think so.
The effects cancel very nicely at the exact center, and nowhere else. As you get off-center, the attraction of the nearest wall exceeds the attraction of the oppo
Re:Gotchas, we got em (Score:4, Informative)
The proof, involving triple integrals, is left for the reader.
Of course, designing a spacecraft that is as spherically symmetrical and uniform in density as possible will be difficult. TFA refers to this, and before much money is spent on this project, one would hope some number-crunching is done to see how extreme the effect is.
Another problem will be microgravity. Orbital velocity is dependent upon the distance from the center of the object being orbited. In Earth orbit, even a few inches difference can produce a velocity gradient that can result in minute accelerations. At L2, some of these effects might be minimized, although again, number crunching should be done.
The late Robert L. Forward proposed a system of massive spheres that could flatten spacetime in a local region [aps.org]. To further minimize extraneous effects due to microgravity, a system like this might need to be used. One advantage would be that this same system might eliminate some of the problems due to assymetry in the spacecraft. One of the problems with this situation would be mass lofted, which currently tends to be expensive, and additional calculations that might be required to analyze the data.
Re:Gotchas, we got em (Score:2)
Re:Gotchas, we got em (Score:4, Informative)
Calculating the position of the moon throughout the month and deriving the orbit wasn't something I did until I got out of college. It's well within the capability of a Freshman physics student, so in theory we could have confirmed the inverse square law to a decent level of precision.
Tightening the exact value of that exponent (is it really -2?) further is the purpose of the proposed experiment.
If you know that gravity follows an inverse square law, then you know that inside a uniform sphere the gravitational acceleration will be zero.
You are correct. We never demonstrated experimentally for gravity that the net gravitational force inside a sphere was zero. Of course, I never said we did. The term "demonstrate" can, in fact, be used in a mathematical sense. When one of the kids on our dorm floor claimed the Ringworld was unstable, we had no trouble demonstrating that instability -- not that anyone had a Ringworld to work with.
Re:Gotchas, we got em (Score:2)
Any unexplained change, basically, is cause for more research.
Re:Gotchas, we got em (Score:2)
The net force exerted by nearby (distance to test system less than, say, 1000 times the distance between the test sphere and the 'sun') objects can be fairly trivially determined by measuring movement of the test sphere relative to some fixed point. After that, the effect of local gravitational attraction can be readily eliminated. Some measurement or calculation of gravitational noise c
Re:Gotchas, we got em (Score:2)
Re:Gotchas, we got em (Score:3, Funny)
Outside effects? (Score:2, Interesting)
Re:Outside effects? (Score:3, Informative)
Lagrangian Point [wikipedia.org]
Re:Outside effects? (Score:2, Insightful)
it's lagrangian for the earth/moon system... not for the rest of the planets...
with that force, and with the gravity from the spacecraft, how can any measurements be useful enough (i.e. free from otside noise) to show anything useful? one ide.... maybe they will model everything (spacecraft, and solarsystem) in a computer and compare to what really happens in the experiment. Even so... wont there be thermal considerations that eve
Re:Outside effects? (Score:2)
Re:Outside effects? (Score:2)
Re:Outside effects? (Score:2, Funny)
Re:Outside effects? (Score:2)
Re:Outside effects? (Score:2)
Re:Outside effects? (Score:2)
Re:Outside effects? (Score:2)
The effects of gravity drop off pretty quickly as the distances increase.
As others have mentioned, the bigger problem is the small amount of gravity caused by the ship itself.
It could be accounted for, especially if the ship was designed so that it's gravitational effects could be accounted for... but it's still a challenge in an experiment like this where precision is key, and the effects they're looking for might be very small.
Maybe they should consider using bigger orbs for the sun and
Yeah, but... (Score:2, Interesting)
Then you have to consider the gravitational effect of the asteroid belt. Do we know the mass of that, too? That might affect the model when put in use.
Any conclusions made from this experiment would be debated over endlessly because of this...
Re:Yeah, but... (Score:2)
Yeah, if they were trying to do a model of our solar system.
Re:Yeah, but... (Score:2)
Re:Yeah, but... (Score:2)
Re:Yeah, but... (Score:2)
What if (Score:5, Funny)
Re:What if (Score:5, Funny)
Suspect this is rubbish - NS has been had? (Score:3, Insightful)
What exactly are they thinking of putting into orbit around this thing?
Re:Suspect this is rubbish - NS has been had? (Score:2)
Re:Suspect this is rubbish - NS has been had? (Score:2)
Re:Suspect this is rubbish - NS has been had? (Score:5, Informative)
No doubt. The only reason there is any hydrogen on *Earth* is because it binds readily with more massive elements. Helium does not and, as a consequence, any helium released into the atmosphere will ultimately escape. My understanding is that the only reason we have any helium at all is due to radioactive decay from heavier elements
Re:Suspect this is rubbish - NS has been had? (Score:2)
Re:Suspect this is rubbish - NS has been had? (Score:5, Informative)
I calculated the escape velocity using the formula sqrt(2Gm/r) [yale.edu]:
sqrt((2)(6.6742x10^-11)(5.16)/0.4) = 0.00013m/s or 0.013cm/s
Re:Suspect this is rubbish - NS has been had? (Score:2)
> the same gravitational pull on any object 10cm away,
> regardless of the other object's mass.
Need a real physicist to answer this, but I'm half-guessing this is wrong; I think the greater the mass of an object, the more it is attracted to another object - but its mass in exact proportion cancels out the additional pull, by simple dint of being more massive and thus requiring more force to move.
This is why high and low mass objects fall at the same rate
at that speed... (Score:2)
Right?
A friend and I just did it.. (Score:2)
Amazing. I would have said it was impossible.
Re:Suspect this is rubbish - NS has been had? (Score:2)
Yes, but you're forgetting that the second object has a gravitational pull too; a larger secondary object will have a greater pull back, meaning a greater combined pull.
Re:Suspect this is rubbish - NS has been had? (Score:3, Interesting)
Re:Suspect this is rubbish - NS has been had? (Score:2)
Mass of 8cm-wide sphere: density * volume = 19250 kg/m^3 * (4/3 * pi * (4cm)^3) = 5.2 kg
Gravitational acceleration of negligible-mass object towards mass M at distance r: a = GM/r = G * 5.2kg / 10cm = 3.4e-9 m^2 s^-2
Acceleration of object rotating in a circle at speed w and distance r: a = r^2 w^2
Hence a = (10cm)^2 w^2 = 3.4e-9 m^s s^-2, so w = 0.0006 s^-1 (radians per second)
0.0006 rad/sec = 19000 rad/year = 2950 [google.com] orbits per year. Which is about 3000, as they say.
Black on black SHOULD be a crime (Score:2, Informative)
Flyboy 8v)
Re:Black on black SHOULD be a crime (Score:2)
Sounds like a fancy version of... (Score:3, Interesting)
The ultimate analog calculator (Score:2)
A link [wikipedia.org] for those too young to remember!
I am sure someone has thought of this already. (Score:2, Interesting)
Re:I am sure someone has thought of this already. (Score:3, Insightful)
Re:I am sure someone has thought of this already. (Score:2)
So, the number of dimensions there are depends purely on what you're calculating. Many dimensions may fold into fewer dimensions for some calculations (think, simplifying an equasion). There is likely, though,
Summary is incorrect. (Score:2, Informative)
This is MUCH MUCH less than 3000 times in year
Re:Summary is incorrect. (Score:2)
Re:Summary is incorrect. (Score:2)
For an oval orbit, to precess means that the oval of the orbit will also be rotating, and that rotation can be measured. That's precession. The planets in our solar system do this too. Precession is what makes this the Age of Aquarius [wikipedia.org].
Let the Sun shine in.
David
Forgive me but I have to nitpick (Score:2, Insightful)
"hide"
v. hid, (hd) hidden, (hdn) or hid hiding, hides
v. tr.
To prevent the disclosure or recognition of; conceal.
This fairly clearly implies intelligent action. I.E. something did the hiding. I.E. the dimensions we can't see (if they exist) are purposefully invisible to us because something chose for them to be, something intelligent. Invisible, as another word choice, would've been better.
Besides, something can't be hidden and
Re:Forgive me but I have to nitpick (Score:2, Insightful)
"Hidden" doesn't imply intelligent action. E.g. "The sun was hidden behind the clouds"
Besides, something can't be hidden and yet physically interact with the universe.
Yes it can. Sub atomic particles were hidden for most of history and yet they had no trouble physically interacting with the universe.
despite being able to probe to fundamental scales (planck, anyone?)"
No-one is poking around at those scales.
Simpson's... (Score:3, Funny)
Some sanity here (Score:3, Insightful)
This fails when considering some noise sources:
1. Accelleration felt by a "grain sized planet" due to a 5kg ball 10cm away is 1m/s/year.
2. Acceleration felt by same "planet" due to moon 1 million kilometers away: 130 times more
3. Accelleration felt due to spaceship: ?
4..? L2 orbit itself, light pressure, magnetic & other fields etc
This appears unfeasable by orders of magnitude.
I do not have much faith in statments like "Gravity leaks into other (higher) dimensions." Where does this come from? Efforts to make string theory models fit the real world?
Hmm... (Score:2, Insightful)
interesting but (Score:5, Insightful)
Such experiments, while useful, aren't practical when we have a real and current need to figure out how to get construction workers and ordinary people into space, so we can build a realistic presence there.
Once we're there, we could perform experiments like this at a fraction of the cost.
Ok, perhaps I'm thinking too fancifully, but it's real concern. Let's face it, every environment we've moved into only becomes liveable when the ordinary people who know how to build stuff and make things arrive. The larger the number of people, the faster things progress.
So long as it's only scientists and the 'elite' going into space and performing experiments progress will be very slow. That can't be good.
What we need is people going 'prospecting' for interesting asteroids/orbiting 'junk' that can be exploited, building commercial stations, setting up routine flights into space. In short, we need economic forces active in space.
Re:interesting but (Score:2)
Nevermind that, how about we start actually sending mostly scientists to space!
Currently, the vast majority of people visiting space come from regular militaries, and almost every mission has some military goal as its primary purpose, with the "science" aspect coming in only as an "oh yeah we can fit one of those things in there too".
Re:interesting but (Score:3, Insightful)
Yes, why play with twitching frog legs and your so called "electricity" when we have starving people and battling kingdoms to take care of?
Funnily enough, fancy abstract "basic research" often has benefits that greatly outweigh the relatively small costs of setting up "these experiments".
Too many uncertainties (Score:4, Interesting)
I wonder how they could conclude that a change of this magnitude would come from gravity leaking into other dimension and not from any of the other myriad of possible effects. It is a good idea, I just don't see how it could work.
Re:Too many uncertainties (Score:3, Informative)
The way any scientist would. List all known possibilities of your "myriad of possible effects". Then quantitatively estimate and calculate the magnitude of those effects on the orbit's precession. If all effects are less than the gravitional effect by some quantity greater than the experiment's margin of error, then you assume you
Wow... (Score:2, Funny)
High School Physics (Score:5, Informative)
Going with a circular orbit because they didn't specify the ellipse:
365.24*24*3600 = 31556736.00 seconds per year
1/. =
Pretty slow orbit. About that tungsten, 19250 kg/m3
3.1415926*(4/3)*.04*.04*.04 =
And let's say the planet is 8 mm in diameter,
3.1415926*(4/3)*.004*.004*.004 =
F = G m1 m2 / r^2 =
gravitational constant = 6.67300 × 10-11 m3 kg-1 s-2
=
Sounds reasonable to me. Assuming they can get a clean launch at exactly
Re:High School Physics (Score:2)
Re:High School Physics (Score:4, Funny)
Re:High School Physics (Score:2)
Re:High School Physics (Score:2)
It won't work. (Score:2, Insightful)
DO NOT PERFORM THIS EXPERIMENT! (Score:2)
So, they're going to use actual bodies as a computational model that measures the fit of a theoretical model to actuality? Sounds fishy. Using reality as a model of reality...couldn't that lead to some kind of infinite regress? A semantic gravitational collapse? Before we all disappear behind the denotational event-horizon, perhaps we should run a (safe) computer simulation modelling the idea of using reality as a way of testing our models of reality.
In any case, given the risks, I think they should ban t
semantics (Score:3, Interesting)
Lets review this. Lagrange point. Last I checked, a point is not a "region". So there's no way to put a titanium anything completely within a Lagrange Point. At the very best they might put the "sun" part of it centered at the LP, but then the "planetoids" would all be outside the LP, and however minorly, would be affected to varying degrees by the gravity of the earth and of the sun.
This test is invalid. The use of a LP is not going to nullify the effect of gravity of the earth, let alone of the sun. If they are going to do a test that is this sensitive, there is nowhere in the solar system they can hold it and get accurate results.
Just launch the experiment... (Score:2)
Re:I don't understand (Score:2)
Re:I don't understand (Score:2)
Re:I don't understand (Score:2)
Gauss's Law (Score:5, Informative)
Gauss's Law [wolfram.com] says that the gravitational acceleration of a body anywhere in an enclosed sphere is 0. At L4, L5 Earth and Sun graviational forces are balanced. The only accelerations that don't cancel out are the two body accelerations of interest. It is surprising to me that the bodies orbit as fast as 10 times per day. I wonder why they don't use heavier Uranium as the mass. It is an interesting side note that a body can stably orbit one of these points. They orbit with no body (!) at the focus. The Genesis Probe and WMAP missions have already taken advantage of this.
Re:Gauss's Law (Score:5, Informative)
Re:Gauss's Law (Score:2)
I found this [science.co.il]. You're right about Uranium. Platinum seems to be a good candidate. Maybe Tungsten is cheaper. Thanks.
Re:Gauss's Law (Score:2)
Think of all the Uranium you could buy with that!
Re:Gauss's Law (Score:2)
But the forces at Lpoints aren't perfectly balanced - there is always variation from the minute changes in orbits and masses of the primary bodies, small effects from other bodies, particle and photon impacts, etc.
I would think it'd be pretty difficult to take all those changes into account and keep them outside the instrument noise.
Am I missing something? (likely
SB
Re:Gauss's Law (Score:2)
The forces are certainly not perfectly balanced. I am sure Jupiter and Venus significantly perturb the L4/L5 points. Over the amazingly small scale of the experiment though I sure it can be subtracted out. I have always wondered how large a mass would be for me to observe gravitational motion in
Re:Gauss's Law (Score:2)
Short times scales, tho?
SB
Re:Gauss's Law (Score:2)
Assuming that over the duration of the experiment there is a meaningful average.
SB
Re:Gauss's Law (Score:5, Informative)
No it doesn't, re=read the law you linked to. It says the "surface integral of gravitational acceleration" will be zero over any arbitrarily-shaped closed surface, as long as that surface encloses zero mass. You cannot work backwards from this statement to assume that the local gravitational acceleration will be zero.
Simple example. Imagine a closed surface (say a small sphere) 20 feet above the ground (and also assume there's no air inside) such that the surface is closed. Since it encloses no mass, the net acceleration will be zero as summed over the whole sphere. However, any object placed within this hypothetical spherical surface (eg a brick) will fall to the ground.
Re:Confused physical reasoning (Score:3, Informative)
.
Read my first reply to my comment for more clarification if you want. But as per your comment here, the surface integral of the vector field (dot producted with its infinitesmal area element, of course) is identically zero for any surface enclosing zero net source/sink density (ie, masses or charges).
Re:I don't understand (Score:2)
Excellent point. As the article (and other posters) have said, this effect could be minimized in theory by designing the spacecraft to be as symmetric as possible, and by placing large masses as far away from the instrument as possible.
However, there may be another way to deal with this: the mass distribution of the spacecraft is known very well, since one has detailed m
Re:Why L2? (Score:5, Interesting)
So they've got that much of it thought out. But in regards to the mass of the spacecraft carrying this jar:
So while they're full aware of the problems the mass of the craft can cause, they seem to think it's possible to minimize the effects to a reasonable level.
My question is, aren't Lagrangian points going to start to get a bit crowded? There are only five to work with in our neighbourhood and who gets to say who uses which and for how long?
Re:Why L2? (Score:2, Informative)
The lagrangian points are not stable positions (L1 is only the more stable), especially L2. If you put a satellite there, it will eventually drift away. Space agencies are putting satellite in orbits "around" the lagrangian points (only L1 and L2 so far), and proceed regularly to orbit corrections. Here close means a few 10
Re:Why L2? (Score:2)
Re:Risky (Score:3, Funny)
Re:What's tungsten? (Score:2)
Re:What's tungsten? (Score:5, Funny)
Re:Hope they don't model our solar system (Score:2)
You wouldn't be able to scale the model to the diameters of the bodies involved unless the densities were the same.
Re:Hope they don't model our solar system (Score:2)
You can make a model using a different scale than the original.
That's what makes it a "model".
Re:It's Called a "Hill Sphere"... (Score:2)