Solar System in a Can May Reveal Hidden Dimensions

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."

Comments

What's tungsten?

[Bin Naden]

Read more about tungsten here

Re:What's tungsten?

[Anonymous Coward]

Naked wiki link gets +2 Informative. Sad. I could write a bot to do the same.

Re:What's tungsten?

[JourneyExpertApe]

Read more about bots here.

Re:What's tungsten?

[jdbartlett]

I for one welcome our infinitesimal Wolframium overlords.

Re:What's tungsten?

[Shads]

Naked wiki link to a wiki link gets +2 funny. Sad. I could write a bot to do the same.

Re:What's tungsten?

[Anonymous Coward]

Modded offtopic? didn't the mod even read the article?

Re:What's tungsten?

[Anonymous Coward]

Learn more about funny here.

Re:What's tungsten?

[Ginger Unicorn]

learn more about goatse here

Re:What's tungsten?

[DaltonRS]

Read the topic? On Slashdot?! You must be new here.

Gotchas, we got em

[Ancient_Hacker]

This sounds mighty dubious. The gravitational attaction of the spacecraft is likely to be much larger than the effect looked for.

Re:Gotchas, we got em

[andrewman327]

I was wondering the same thing. Hopefully the isolation sphere or whatever contains the experiement contains large mass that is evenly distributed.

Re:Gotchas, we got em

[d34thm0nk3y]

FTA:
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

[pilgrim23]

the old L5 Society wanted to place a module they called a High Orbital Mini-Earth there... sort of a H.O.M.E. on LaGrannge.....

Re:Gotchas, we got em

[Anonymous Coward]

How to design a space mission:

(X) tests fundamental physics
(X) requires a fancy metal
(X) resides at a Lagrangian point
( ) no obvious flaw

Let's hope they can go forward with only 3/4 on their scoresheet.

Re:Gotchas, we got em

[ceoyoyo]

They mentioned that would have to be taken into account. Scientists measure the gravitation attraction between human scaled objects on Earth all the time, yet that's dwarfed by Earth's gravity.

Re:Gotchas, we got em

[Anonymous Coward]

You either deserve a medal, or to be shot for that...
the worrying thing is, I'm not sure which!

Re:Gotchas, we got em

[Bad D.N.A.]

Every time I turn around someone is trying to launch balls into space. First we had those balls that were suppose to detect gravitational waves, now we have these balls that are suppose to rotate around each other. What's next, balls on the moon, mars, and beyond?

Re:Gotchas, we got em

[Anonymous Coward]

RTFA. They have a whole paragraph on the issue of the spacecraft's own gravitational forces influencing the experiment.

Re:Gotchas, we got em

[KFury]

Since it's not explicitly stated in the article or these replies, gravitational effects precisely cancel inside a uniform shell. So if the spacecraft's mass was evenly distributed on a spherical shell there would be zero effect on items inside the shell, even when those items are close to the shell's interior surface.

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 in clearing out L2. Legrange points, as 'stable equilibrium' points in space, are likely littered with debris, even if this debris doesn't directly impact the experiment, it will exert its own gravity that could prove problematic.

Re:Gotchas, we got em

[Anonymous Coward]

The net gravitational force on any point within a hollow sphere is 0, not counting things that aren't the sphere. All they have to do is make the shell as spherical as possible.

Re:Gotchas, we got em

[Rob Carr]

In Freshman physics, it's common to demonstrate the net gravitational or electrical attraction inside a uniform sphere is zero. Any force with an inverse-square law will exhibit this peculiarity. If you want the details, there's a Wiki article on the Divergence theorem of vector fields.

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. 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

[Ruff_ilb]

Perhaps, but the gravitational attraction of the spacecraft would be accounted for... even if, at first, it might be subtle, the eventual results of the gravitational force of the spacecraft would definitely be noticeable.

Any unexplained change, basically, is cause for more research.

Re:Gotchas, we got em

[sharkey]

I hear they gotta lotta nice girls.

Re:Gotchas, we got em

[ottffssent]

But any external gravitational forces will act very nearly identically upon both the tungsten 'sun' and the test sphere.

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 caused by such things as orbiting satellites, people moving about, etc. would provide a baseline for how strong an effect would have to manifest to even be considered as evidence of some unknown phenomenon.

Things farther away won't interfere with the test much at all. The magnitude of interference is not proportional to the mass of the interfering object, since any force which acts equally on both the 'sun' and test sphere will have no impact on the results. The farther away an interfering object is, the smaller the difference in gravitational attraction between the 'sun' and test sphere would be. It is that difference, rather than the absolute magnitude of attraction, which would interfere with results.

Re:Gotchas, we got em

[DarrinWest]

I'd bet that static charges on the spacecraft and bodies would have a bigger effect than gravity.

(Are they going to light this tung-sun? No. I'm thinking of Magnesium.)

Re:Gotchas, we got em

[Tony Hoyle]

Damn. I'm sure there's a spaceballs joke there somewhere...

Re:Gotchas, we got em

[athmanb]

Only L4 and L5 are stable over astronomical time scales. Orbits around L2 decay over a few years so the point is just about free of natural objects.

Re:Gotchas, we got em

[Goaway]

Oh wow, they must not have thought of that! It's a good thing you set them straight, or they'd have launched the mission for nothing!

Re:Gotchas, we got em

[professorhojo]

reminds me of douglas adams fairy cake theory a little:

To explain: since every piece of matter in the Universe is in some way affected by every other piece of matter in the Universe, it is in theory possible to extrapolate the whole of creation - every sun, every planet, their orbits, their composition and their economic and social history - from, say, one small piece of fairy cake.

Re:Gotchas, we got em

[nacturation]

Show me a home... where the buffalo roam,
and I'll show you a home full of shit...

Re:Gotchas, we got em

[Ohreally_factor]

I think that the experiment will have at least one protocol governing researchers shuffling their feet on the carpet.

Re:Gotchas, we got em

[trixillion]

In Freshman physics, you demonstrated that the net gravitatinoal attraction inside a uniform sphere is zero? Are you sure you did this experimentaly and not just on paper? Maybe the state of Freshman physics has improved since my days, but color me sceptical.

Re:Gotchas, we got em

[Anonymous Coward]

Someone has been reading their R.A.W.

Re:Gotchas, we got em

[Rob Carr]

We demonstrated that forces that follow an inverse square law follow this rule. We demonstrated that a charged sphere followed that rule in a lab by charging the sphere and then measuring the electrical force inside the sphere and out. We demonstrated that electrical forces follow the inverse square law in the lab. I'd argue that stable orbits demonstrate inverse square law for gravity, and we did visit the telescope and look at the moon in Freshman physics. We also calculated G using the old torsion technique.

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

[tonsofpcs]

Still a problem: The Lagrange point is just that, a POINT. Anything drifiting just a bit from this point, especially on a smaller scale, will be drawn away.

Re:Gotchas, we got em

[dargaud]

the article ignores the difficulty in clearing out L2. Legrange points, as 'stable equilibrium' points in space, are likely littered with debris

Aren't there already some satellites at some of the Lagrange points ? I recall some solar observer or somesuch...

Re:Gotchas, we got em

[zippthorne]

Incorrect. L1-3 work like that for in-plane perturbations, but nearly-stable orbits can be designed for them using minimal propellent. see SOHO for the textbook example. L4 and L5 are stable. The problem there is accumulation of dust. One wonders why the article said they'd be protected from insolation though, since L4,5 are 60 degrees ahead and behind the earth.

Re:Gotchas, we got em

[stjobe]

Well, I hear it's fine if you got the time and the ten to get yourself in. And I hear it's tight most every night, but now I might be mistaken.

Ah have mercy.

Re:Gotchas, we got em

[Ancient_Hacker]

>Since it's not explicitly stated in the article or these replies, gravitational effects precisely cancel inside a uniform shell. So if the spacecraft's mass was evenly distributed on a spherical shell there would be zero effect on items inside the shell, even when those items are close to the shell's interior surface.

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 opposite wall.

Re:Gotchas, we got em

[cluckshot]

A variant of this happens with the Gravity B Experiment

The whole problem we have here is that the data keeps having to be fudged to try and keep Einstein in the catbird's seat. Simply stated the data isn't there. Special Relativity is a theory. It is a theory that now can be shown to have glaring flaws and gaping holes. I know this upsets some people but is simply is true.

Whenever someone dares question the Einstein religious nuts and their "universal facts", they get attacked and modded down. How about a little science for a change. I think it might be useful. The whole system that the Einstein bunch has constructed is coming apart in the face of more and more data that does not support it. The Neutreno's are missing, The energy is missing, the Matter is missing so we have to invent ever more funny things like dark matter and dark energy and .... to get this to work. We have to fill our universe with all sorts of objects that have never been observed and believe in them in order to keep this theory set working.

These guys ignore the EM force which is 10^39 times stronger than gravity. These guys ignore the plasma that fills space. These guys ignore the evidence that is all around us of the electrical universe. The mod down anybody who speaks up on slashdot. In university they destroy careers of those who speak up. These guys are religious zelots who destroy heritics.

Good Science would listen for a change. It would also follow the scientific method and throw out a theory set that is so flawed that it requires these exotic patches as does special relativity. To be fair here the guys have some fact and some reality and some data that is valuable. I don't throw out good things. It is just time for Special Relativity to be sent to the Phlogisten and Phrenology pile. It isn't right.

Re:Gotchas, we got em

[Anonymous Coward]

Dust accumulates in a sealed can? Why should we trust anything else you say?

Re:Gotchas, we got em

[As_I_Please]

Sorry, you're wrong. The gravitational force due to a hollow sphere is exactly zero everywhere inside that sphere.

Proof

Re:Gotchas, we got em

[Ancient_Hacker]

Dang, sometime intuition fails!

I'm still somewhat puzzled as to how one could make a usable spacecraft with the required precision of symmetry. You'd probably need better than one part per thousand precision, which would rule out anything tha wasnt very very homogenous. Consumables, like reaction fuel would be a problem.

I don't understand

[n8d06]

Help me out...wouldn't the mass of the "spaceship" affect the experiment? Could this be reliably accounted for in this type of experiment?

Re:I don't understand

[ceoyoyo]

Yes. You need to build a very precise spaceship. Starting with a sphere might be easiest as gravity cancels out everywhere inside a sphere. You'd probably need thrusters and things (although maybe you could make them detach and leave the scene after you were done with them) but you'd measure them very carefully so you could account for their effect.

Re:I don't understand

[dnoyeb]

Why not build any ole spaceship and then measure the gravity present at the location of the experiment before you begin the experiment?

Re:I don't understand

[Tempete]

"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."

From the article.

Re:I don't understand

[ceoyoyo]

The only way to measure gravity is to take a test mass and see what it does in the field. You're right, you could build any old spaceship and figure out what the contributions of the ship should be. The problem is, if you have a big mass on one side your miniature solar system might end up stick to the side of your ship rather than happily floating inside it.

Re:I don't understand

[ClickOnThis]

Help me out...wouldn't the mass of the "spaceship" affect the experiment? Could this be reliably accounted for in this type of experiment?

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 mechanical schematics of it, and the properties (density, heat expansion coefficients, etc.) of the materials used in its construction are well-known. So, one could determine the gravitational effect of all the spacecraft parts on the experiment using existing theory and subtract these effects from the instrument measurements. If, after doing this, there is still a discrepancy from existing theory in the processed results, then one has disproved the null hypothesis: a new feature of gravity has been discovered.

Re:I don't understand

[AdmiralSpearmint]

It might, unless you built the spacecraft correctly. According at least to current theories of gravity, the net gravitiational force anywhere inside a sphere is zero. It is not nearly as simple as that, after all, you need propultion and some mechanism for observing the experiement, but it is possible to keep outside gravitational effects to a minimum.

Outside effects?

[Clazzy]

If the minature solar system is sent into space, then would it also come under the effect of the gravity of the actual solar system? Granted the effect will be very small (considering one object is very small and is far away anyway) but surely it would cause enough of an effect to make a difference? I'm sure they're trying their best to cancel out these forces, but they'd need absolutely minute amounts of gravity or (impossibly enough) none at all for a good reading.

Re:Outside effects?

[Compholio]

If the minature solar system is sent into space, then would it also come under the effect of the gravity of the actual solar system?

Lagrangian Point

Re:Outside effects?

[Anonymous Coward]

i imagine that the means of detection (lasers?) of the positions of the spheres would also introduce significant perturbations at that scale. ain't uncertainty a bitch...

Re:Outside effects?

[ceoyoyo]

Despite the misleading title they're not trying to make a model solar system. They want to put one metal sphere in orbit around another one and then watch to see if its orbit precesses the way they predict.

Re:Outside effects?

[Anonymous Coward]

It's been learned long ago that the solar system has more than 2 objects in it.

Re:Outside effects?

[HelloKitty]

even the lagrangian point feels miniscule effects from other planets...

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 even a computer can't predict? the point at which you launch the ball, photons hitting the ball, etc...

Re:Outside effects?

[HelloKitty]

>> It's been learned long ago that the solar system has more than 2 objects in it.

what he said...

Re:Outside effects?

[Breakfast Pants]

What's wrong with studying the moon's orbit?

Re:Outside effects?

[Clazzy]

Fair enough, I didn't quite know what a Langrangrian point was, but it will still be nowhere near perfect, will it? The point isn't a specific area, it's an exact point and anywhere else will be just off and will have a slight pull from either the Earth or the Sun, slowly setting it out of alignment. If it's going to be watched for a year, this will become a bigger and bigger difference, accelerating away until it's strongly in one planet's pull.

Re:Outside effects?

[ceoyoyo]

The moon and Earth have irritating imperfections like mountains. Plus there are all kinds of other significant influences like other planets and the sun. It's actually not possible to predict the moon's orbit accurately very far into the future because the other bodies in the solar system make it semi-chaotic. The moon doesn't orbit the Earth 3000 times a year either, so you'd have to wait longer to see the same magnitude of precession.

Re:Outside effects?

[nelsonal]

Heritic, the rest of the objects aren't there. The gravity is just there to test your faith.

Re:Outside effects?

[vistic]

F = G * (m1*m2)/r^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 planet... and make the ship some sort of larger inflatable low-mass thing, so that it's gravity would be negligible by comparison.

Re:Outside effects?

[Ohreally_factor]

Bah. Everyone knows that the experimental miniature solar system will be weightless in space.

Re:Outside effects?

[GTMoogle]

For different reasons, the grandparent post and I would both argue you should attend mass. :)

Re:Outside effects?

[Ohreally_factor]

Are you implying that I'm dense? =)

Yeah, but...

[jamestheprogrammer]

You would need to be extremely precise for that to work. The masses of the model planets would have to be PERFECTLY scaled. Do we actually know for a fact the masses of all the other planets, and can we make something that precise?

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...

[necro2607]

"The masses of the model planets would have to be PERFECTLY scaled."

Yeah, if they were trying to do a model of our solar system.

Re:Yeah, but...

[heinousjay]

Oh, sure, just blithely bring facts into the discussion. I won't stand for it, no sir.

Re:Yeah, but...

[ArieKremen]

...how do you inject a tiny planet in an elliptical orbit around a tiny sun? I find that most models (physical and theoretical) fail at getting the setup to work.

Re:Yeah, but...

[exp(pi*sqrt(163))]

The masses of the model planets would have to be PERFECTLY scaled

I'd love to know what is going through your mind at this point. Are you imagining these experimenters are planning to place nine little spheres in position around one big one and that we're going to see them orbit because of the gravitational forces between these spheres?

Re:Yeah, but...

[Darundal]

They aren't attempting to model our solar system, or any existing one for that matter. What they are attempting to do is create a model of their own design, calculate positions, velocities, etc... and compare the numbers they get with the actual values for those after a long period of time.

Re:Yeah, but...

[Breakfast Pants]

Being that Sol refers specifically to our sun, what other 'solar system' are you talking about?

Re:Yeah, but...

[eipipuz]

You just let gravity do its share.
Imagine you roll a tube in space. It would continue rolling if there's no friction. Now substitute endpoints with the spheres. If they have the same mass, one could define a fixed point around which both rotate at equal distances. Now, if one had a bigger mass, that fixed point would be nearer to it. If the proportion is great enough, one can assume the tiny one is orbiting around the big one. There you have a circular motion.

Now just let the tiny one have a small acceleration. Any vector in the orbit plane would suffice to make an elliptical orbit, so long as you don't give too much energy, in other words, don't give more than escape velocity. Voila!

Or you could just setup a motionless sun and shoot near it. If you send it right, the gravity of the big sphere will hook the tiny planet! Just like we got Halley, I guess...

Re:Yeah, but...

[Ohreally_factor]

The model system in the experiment, in which one body will orbit another body. TFA mentions nothing about a "scale model" of our solar system.

Re:Yeah, but...

[1iar_parad0x]

That's pretty much what theoretical physicists do anyways.

Re:Yeah, but...

[Breakfast Pants]

Did you read my post? Solar system is 'our solar system' implicitly. That is what the sol in solar means.

What if

[Raindance]

I wonder if our universe is just a hidden spacial dimension test for a super-advanced alien civilization... still trying to figure out string theory.

Re:What if

[Anonymous Coward]

The answer is 42.

Re:What if

[sjs132]

Funny... This was my first thought when I read it, the whole "what if our existance is just some lab experiment that is next in the termination schedule." idea... Makes you wonder when you go to sleep if you'll see the next sunrise, or if this experiment will be decleared a failure. :)

Re:What if

[stunt_penguin]

Tom Cruise seems to think so.

Re:What if

[Anonymous Coward]

Dude, quite bogarting that J.

Re:What if

[ichigo 2.0]

Re:What if
(Score:1, Informative)
by Anonymous Coward on 5:18 8th July, 2006 (#15681003)
Dude, quite bogarting that J.

Did I miss something?

Re:What if

[ConceptJunkie]

In America, movie stars act in goofy science fiction movies.

In Scientology, movie stars believe goofy science fiction is real.

Re:What if

[flappinbooger]

Wasn't there a simpsons episode somewhat along those lines?

Re:What if

[Anonymous Coward]

OK... OK... what if our universe... is like an atom... part of a bigger universe... you know, man? Woah, that's so deep. Pass the corn chips, dude.

Re:What if

[Anonymous Coward]

Yeah, but when's the last time he was wrong?

Suspect this is rubbish - NS has been had?

[Toby The Economist]

A tungsten sphere 10cm in diameter would have such a tiny gravitational field that I suspect even a hydrogen atom at the ambient temperature of local space would possess escape velocity.

What exactly are they thinking of putting into orbit around this thing?

Re:Suspect this is rubbish - NS has been had?

[kimvette]

Read the summary again - nowhere is a 10cm sphere mentioned.

Re:Suspect this is rubbish - NS has been had?

[erice]

A tungsten sphere 10cm in diameter would have such a tiny gravitational field that I suspect even a hydrogen atom at the ambient temperature of local space would possess escape velocity.


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?

[wealthychef]

Holy crap, it says 8cm, big deal. The GP is still right -- what can orbit around an 8cm ball of tungsten? Wow. The article doesn't say.

Re:Suspect this is rubbish - NS has been had?

[Anonymous Coward]

The ambient temperature on the Earth is much higher than that in space, hence the hydrogen and helium atoms have much higher thermal velocities. Even in the vicinity of our sun the ambient temperature isn't much above the 2.7K of the CMB.

Re:Suspect this is rubbish - NS has been had?

[Anonymous Coward]

Well yea, no kidding. Seeing as how the average temperature of a hydrogen gas molecule at any reasonable temperature is quite large. That could be why they aren't going to use hydrogen molecules.

Instead they are going to use tungsten, which is quite heavy. And a very slow orbit - it works out to about 8 revs per day or about 0.06 millimeters/second. That's just from their statement of an orbital radius of 10 cm and 3000 rev/year. I don't have the time to work out the orbit at the moment, but it doesn't sound to outlandish to me.

Re:Suspect this is rubbish - NS has been had?

[mazarin5]

If they we trying to approximate Jupiter, then they would just use an 8mm ball of tungsten. If it was earth, then it would be a little bigger than 1mm.

Here's this.

Re:Suspect this is rubbish - NS has been had?

[Jeff DeMaagd]

Not only that, Lagrange points aren't necessarily stable. The article mentions L2, which is one of the unstable lagrange points, meaning that it requires station keeping (occasional thruster firing), I'd think that would interfere with this experiment.

Re:Suspect this is rubbish - NS has been had?

[Anonymous Coward]

What's really odd is that New Scientist can't spell the word "minuscule."

Re:Suspect this is rubbish - NS has been had?

[Cecil]

Actually, an 8cm tungsten sphere would exert the same gravitational pull on any object 10cm away, regardless of the other object's mass. It would have an escape velocity of 0.013 cm/s or 1.3 microns per second -- which, while very slow, is certainly within the realm of feasability. Your hard drive heads move accurately with tolerances significantly smaller than that.

I calculated the escape velocity using the formula sqrt(2Gm/r):

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?

[Toby The Economist]

> Actually, an 8cm tungsten sphere would exert
> 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 when dropped; the heavier mass object MUST be feeling a greater attraction or it would not be able to move at the same rate as a lower mass object.

To put it another way, all the atoms in the tungsten sphere pull upon all the atoms in the remote sphere; if the remote sphere has more atoms, then there is more pull. However, because there *are* more atoms, the remote object is more massive and this exactly matches the additional pull.

Re:Suspect this is rubbish - NS has been had?

[njchick]

Fortunately, thermal velocities of macroscopic objects are much lower than those of atoms.

Re:Suspect this is rubbish - NS has been had?

[Excors]

Density of tungsten: 19250 kg/m^3
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 orbits per year. Which is about 3000, as they say.

Re:Suspect this is rubbish - NS has been had?

[solitas]

...an escape velocity of 0.013 cm/s or 1.3 microns per second ... sqrt((2)(6.6742x10^-11)(5.16)/0.4) = 0.00013m/s or 0.013cm/s...

Um: sqrt(2 * 6.6742e-11 * 5.16 / 0.4) = 4.1496e-5 = .000041496

???

Re:Suspect this is rubbish - NS has been had?

[Anonymous Coward]

It's 0.04... so

sqrt(2* (6.6742*10^-11) *(5.16/(0.04)))

But yeah you get 0.00013m/s.

Re:Suspect this is rubbish - NS has been had?

[Anonymous Coward]

Yep, they mention L2, but advocate L4, which is very stable.

Re:Suspect this is rubbish - NS has been had?

[Anonymous Coward]

Escape velocity can be just thought as the kinetic energy required to overcome the gravitional potential energy. So we can let the velocity remain constant since the larger the mass the more energy is required to reach that velocity.

KE = (1/2)m(v^2)
v = sqrt(KE/((1/2)m))

So yes greater mass results in more gravitational energy. But also more energy is required to reach escape velocity.

Re:Suspect this is rubbish - NS has been had?

[Anonymous Coward]

Lets assume you're not trolling...

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

No, IAARP but Newton gravity is defined as accerelation, 1G ~= 9.8 m/s^2. So the earth attracts objects by adding 1 m/s to it's velocity each second, regardless its mass.

This is why high and low mass objects fall at the same rate when dropped; the heavier mass object MUST be feeling a greater attraction or it would not be able to move at the same rate as a lower mass object.

Actually the dropped object attracts the earth (eg the moon makes the earth wobble a little bit) but usually the relatively small mass (compared to earth's mass) makes this unnoticable.

Re:Suspect this is rubbish - NS has been had?

[x2A]

"Actually, an 8cm tungsten sphere would exert the same gravitational pull on any object 10cm away, regardless of the other object's mass"

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?

[Quantum Fizz]

You are correct that helium, given its Maxwellian velocity distribution at Earth's temperature, has a significant-enough fraction of it above escape velocity, so yes, helium gas on earth eventually escapes. So does diatomic hydrogen gas (but not hydrogen compounds eg water and hydrocarbons).

But we DO have alot of helium gas on Earth because much of it is trapped in pockets inside the Earth's crust. It's mined when the oil companies dig for oil and natural gas. In fact, these companies used to release it because it's not economically feasible to capture and sell it. But at least here in the USA the NSF set up some kind of deal with local oil companies to capture and sell the helium gas for cryogenics and other industries.

In this regard, the USA is pretty wasteful with helium gas, filling up balloons at kids parties, venting helium to the atmosphere in laboratories, etc. I've heard about (but not visited) cryogenics labs in other countries where helium is more scarce so they recycle it. In fact, early in grad school before knowing all this, I was also surprised when talking to some Russian students that told me they heard a rumor that breathing helium makes your voice get high. But this is somethign that just about every American kid has tried when they were little.

Re:Suspect this is rubbish - NS has been had?

[CrimsonAvenger]

an escape velocity of 0.013 cm/s or 1.3 microns per second

I calculated the escape velocity using the formula sqrt(2Gm/r):

sqrt((2)(6.6742x10^-11)(5.16)/0.4) = 0.00013m/s or 0.013cm/s

0.013 cm/s is 130 microns per second. Wherever did you get the notion that there are 100 microns per cm?

Re:Suspect this is rubbish - NS has been had?

[Excors]

a = GM/r
...
acceleration ... 3.4e9 m^2 s^-2

Uh, sorry, that's what I get for posting at 3am and not bothering to check the equations and units. But I got the expected answer and it was dimensionally consistent, even if the intermediate calculations were rubbish. Isn't that what physics is all about?

A more correct version:
Density of tungsten: 19250 kg/m^3
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^2 = G * 5.2kg / (10cm)^2 = 3.4e-8 m s^-2
Acceleration of object rotating in a circle at speed w and distance r: a = r w^2
Hence a = 10cm w^2 = 3.4e-8 m s^-2, so w = 0.0006 s^-1 (radians per second)
0.0006 rad/sec = 19000 rad/year = 2950 orbits per year.

Re:Suspect this is rubbish - NS has been had?

[kimvette]

The article DOES say: a smaller sphere of tungsten. They did not specify the diameter of the smaller sphere. I'm sure that is part of the experiment - determining the mass of what is required to achieve such an orbit vs. what their math predicted.

Why L2?

[Capt'n Hector]

Though the article didn't say, I'm guessing the reason for an L2 orbit is to minimize solar cosmic rays, using the earth as a shield of sorts. Any other ideas?

Re:Why L2?

[addie]

Well actually the article did say:

A spacecraft placed there would stay fixed in space, relative to Earth, making it easier to monitor. The Earth would also shield it from the Sun's radiation, which pushes gently on any objects it shines on. Any such push could change the spacecraft's position relative to the tiny "planets" held inside it.

So they've got that much of it thought out. But in regards to the mass of the spacecraft carrying this jar:

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.

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?

[DamnStupidElf]

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.

The simplest thing to do is simply put the expiriment in deep space, start it up, then move the craft away and monitor it from a distance.

Re:Why L2?

[mcmaddog]

Actually, in the 7th paragraph of the article...

A spacecraft placed there would stay fixed in space, relative to Earth, making it easier to monitor. The Earth would also shield it from the Sun's radiation, which pushes gently on any objects it shines on. Any such push could change the spacecraft's position relative to the tiny "planets" held inside it.

Re:Why L2?

[HarveyTheWonderBug]

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?

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 10s of kilometers quite enough to avoid collisions.

Re:Why L2?

[philovivero]

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?

Well, that's easy. Disney gets to use the Langrangian points for their newest Disneyuniverse rides. And they get to use them until their copyright on Mickey Mouse runs out.

mmmm....

[panchoguayaba]

I think someone is just doing this to justify his his childhood dream of playing marbles in space.

Hope they don't model our solar system

[CarlJagt]

Hope they don't model our solar system... at 8.0cm for a 'sun' the earth would be 0.7mm in diameter (don't breathe) and yet have an orbital radius of 8.5m! Pluto would be almost 340m away! Talk about one big ass spacecraft...

From HHGttG: "Space is big. Really big. You just won't believe how vastly, hugely, mind-bogglingly big it is. I mean, you may think it's a long way down the road to the chemist, but that's just peanuts to space." -- Douglas Adams, HHGTTG "

Still, hope we actually get to test this out.

Re:Hope they don't model our solar system

[Anonymous Coward]

it's obviously not our solar system it's being modelled after because the planet will be orbitting 3,000 times in 1 Year our time. It would be painful to try to make scientific measurements of a system with the same angular velocity as ours.

Re:Hope they don't model our solar system

[dbowden]

To make the angular velocity the same, the models would have to have a 1:1 ratio, which would take up somewhat more space than they're planning to use.

You can make a model using a different scale than the original.

That's what makes it a "model".

Re:Hope they don't model our solar system

[dbowden]

I don't think they're trying to model our Solar System, but even if they were, the orbits described by the "planets" would be governed by the mass of the bodies, not their sizes.

You wouldn't be able to scale the model to the diameters of the bodies involved unless the densities were the same.

Soup

[Eightyford]

Man that Chunky Soup tasted a little strange!

Dude, you just ate the solar system!

EVERYOONE LEAVE! I have to poop...

Yay! Zonk's been suckered again!

[Anonymous Coward]

Hey Zonk, wanna buy this really awesome bridge I have for sale?

Black on black SHOULD be a crime

[flyboyfred]

I got black text on a mostly black background. Sheesh! The printable page reads a lot better.

Flyboy 8v)

Re:Black on black SHOULD be a crime

[bigtrike]

But everything goes with black!

Re:Black on black SHOULD be a crime

[Xtravar]

Except slavery. That's so out of style.

Sounds like a fancy version of...

[exp(pi*sqrt(163))]

...Cavendish's classic experiment. I look forward to seeing the results.

Thank you, Captain Obvious

[Anonymous Coward]

If the system's 'planets' moved slightly differently to the way predicted by standard gravity, it would signal the presence of new physical phenomena.

Wow, really? Who would have guessed?

The ultimate analog calculator

[cagle_.25]

Boy, this puts the old RLC calculators to shame ...

A link for those too young to remember!

Re:The ultimate analog calculator

[1iar_parad0x]

What would be really sad is if they do some sort of calculations in a computer to analyze the results.

Risky

[Anonymous Coward]

I wonder if they accidently create a miniature black hole and will be never heard from again.

Re:Risky

[ScrewMaster]

No big deal, plenty more scientists where they came from. I'd be more concerned about them creating a great big black hole, and us never being heard from again.

I am sure someone has thought of this already.

[wickedsteve]

But can anyone explain to me why gravity would be the only force bleeding into other dimensions? Or is it the only one? Also is there any evidence of extra dimensions already? I would think there would already be some evidence since it does not sound very scientific to me to base the very popular string theory on imaginary notions with no basis in reality. If we are just gonna make up dimensions to make the math work isn't that just as bad as making up Thor to explain the thunder and lightning?

Re:I am sure someone has thought of this already.

[The Living Fractal]

"If we are just gonna make up dimensions to make the math work isn't that just as bad as making up Thor to explain the thunder and lightning?"

Yes.

Re:I am sure someone has thought of this already.

[Btarlinian]

Except for the fact that Thor just came from well...someones mysterious mind, and the extra dimensions come from math.
This is how general relativity came about in the first place too.
The real world wasn't fitting the math of Newton's theory, so Einstein had his moment of genius, so now you get GPS.

Re:I am sure someone has thought of this already.

[particle_fizax]

You have to understand that to a theoritician, having a "basis in reality" is a vague phrase. We have these equations, and they work really well for certain things that have been troubling the physics community for quite some time. They happen to require more than 4 dimensions. The theoretician says, "Oh well, find the other dimensions!" It's not a strange concept to make up new physics to "make the math work out". Quarks were hypothesized, then as each quark pair was discovered, we knew how many pairs of quarks there should be and knew roughly where we needed to look for the rest of them. You could say someone "made up" the top quark to "make the math work". But it turns out that it worked pretty well. Also, don't even get me started about the Schrodinger equation... ever seen the derivation? Yeah... it's more of a "here's a couple theoretical ways the equation _could_ be derived... maybe...

Re:I am sure someone has thought of this already.

[x2A]

A "dimension" is just a variable in an equasion, not as much of a physical property as connotations of the word imply, but a property of the physical 'stuff' that an equasion is describing. Any of the dimensions that we see may actually be functions of more than one dimension for certain calculations.

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, a maximum number of dimensions that would be required to describe anything. Many believe this is where string theory lies. They just need to figure out what all of the variables actually represent in the physical world.

(roughly)

Re:I am sure someone has thought of this already.

[Anonymous Coward]

according to string theory the particles that carry gravity (gravitons) are made up of strings that do not adhere at either end to the brane of our universe.

the short version: the math says that everything but gravity is stuck to the 4 dimensions we know.

Re:I am sure someone has thought of this already.

[Oligonicella]

Math describes something. That something can be imaginary. Anyone using a flight simulator simulating reverse gravity can "experience" it. So, those extra dimensions ultimately came from someone's mind, not observations of the real world.

And don't lay that old canard about the dimensions only being some attribute of something. String theorists themselves jump far too readily into extrapolating alternate universes for that to be the underlying reason.

Re:I am sure someone has thought of this already.

[ademaskoo]

Don't forget magnetic and electric fields. There is no "particle emission" like the hypothetical "graviton". These two forces bend space similar to the way gravity does, except gravity seems to trump them all: gravity can affect the path of electro-magnetic radiation.

Re:I am sure someone has thought of this already.

[Anonymous Coward]

I can't answer the first question, nor the second, but I can tell you this: stable solar systems are only possible in three spatial dimensions. 1, 2 or 4+ and every system will eventually fall apart. My guess is that they want to study the behaviour of the orbit: if the miniature solar system destabilizes, while other influences than 'another spatial dimension' can be excluded, that is an indication another spatial dimension might exist. If they can quantify the difference with 'normal' behaviour, they might even be able to tell you how many extra dimensions there are, though I do not know whether they actually have the theory to do that.

Re:I am sure someone has thought of this already.

[Anonymous Coward]

stable solar systems are only possible in three spatial dimensions. 1, 2 or 4+ and every system will eventually fall apart.

Hmmmm? Planets orbit stars in a plane, and satellites/moons orbit their planets in a plane, although the planes do precess.

A 1D solar system would be a straight line, and any orbiting object would smack right into the "Sun" not more than halfway through its orbit.

a 4D solar system would be interesting. In a 3D viewpoint, planets and satellites would disappear and reappear on a regular basis.

Nice toy

[compilator]

Why use it for science when it could be marketed as "you very own tungsten-solar-system-in-a-box"?

Summary is incorrect.

[MindStalker]

Article states the orbit would be 1/3,000 degree in year.
This is MUCH MUCH less than 3000 times in year

Re:Summary is incorrect.

[MindStalker]

Sorry I screwed up summary is correct, the 1/3000 degree is the estimated change or something to that effect.

Re:Summary is incorrect.

[Anonymous Coward]

No, that would be the deviation if one of the theories is correct.

Re:Summary is incorrect.

[dbowden]

The article says the system may precess by 1/3600 degrees in a year, while still orbiting 3000x/year.

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.

Let the Sun shine in.

David

Forgive me but I have to nitpick

[The Living Fractal]

I don't like the word choice "hidden". Hidden is the past participle of hide.

"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 yet physically interact with the universe. I believe if a thing interacts with the universe on any degree then we should be able, generally speaking as intelligent beings, to see it. And if we can't see the interaction, despite being able to probe to fundamental scales (planck, anyone?), then, forgive me again but, so fucking what?

So to me the word is not only implying an intelligent purpose, but is furthermore illogical in choice from the very point of view of physics.

Maybe I'm full of shit, I probably am. I guess the real reason I write this is that I'm really starting to get tired of people throwing around buzzword catchphrases like 'hidden dimensions' to get attention. You might as well say the UFO's made them. Anyway, explain to me how something that can be measured via our three standard directional dimensions manages to slip into the realm of 'hidden dimensions'? /endrant

TLF

Re:Forgive me but I have to nitpick

[c0bw3b]

eh, I don't think the terminology implies intelligence behind the hiding at all. The sun becomes "hidden" behind the moon during a solar eclipse, but that doesn't mean someone put the moon there. I think the only intelligence implied is that of the observer so.. oh wait, you have a point. Yes, no intelligent life here.

Re:Forgive me but I have to nitpick

[Lorkki]

This fairly clearly implies intelligent action. I.E. something did the hiding.

I suppose they could rephrase it as "directly imperceptible" but I fail to see the necessity. The term "hidden variable", for instance, no more implies that some mischievous students played a prank on their unsuspecting professor.

Popularised science in general uses imprecise language to stay within the constraints of our usual hairless monkey terms. After all, it's intended to appeal to people who aren't familiar with the established terminology of a field, where the use of that terminology may even differ from its use in a more common context. Just take note of how many things are claimed to "fly" or "fall" in outer space.

If you insist on being objective and precise, there's painstaking long-hand and mathematical notation, but I'd guess that doesn't really make for an interesting read to many non-astrophysicists.

Re:Forgive me but I have to nitpick

[Anonymous Coward]

That's a stupid objection. Clouds may hide the sun, but there's no intelligent action there.

Re:Forgive me but I have to nitpick

[Joebert]

Quick sombody get in there ! Truman's getting ideas !

Re:Forgive me but I have to nitpick

[Tomfrh]

This fairly clearly implies intelligent action.

"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.

Re:Forgive me but I have to nitpick

[Anonymous Coward]

Yes, yes you are full of shit. Anyone that takes one definition out of many to prove (an incorrect) pedantic point is exactly that.

Re:Forgive me but I have to nitpick

[phageman]

there was an excellent Scientific American article several months back about the theory of gravity leaking into a higher dimension. The idea was that this is an alternate explanation to dark energy to explain the accelerating expansion of the universe, i.e. there isn't some unknown energy forcing the universe apart, gravity just gets weaker at extremely long distances because some of it is leaking.

Re:Forgive me but I have to nitpick

[Anonymous Coward]

Weaker gravity doesn't explain acceleration at a large distance.

Re:Forgive me but I have to nitpick

[Xiroth]

"hide"
v. hid, (hd) hidden, (hdn) or hid hiding, hides
v. tr.
To prevent the disclosure or recognition of; conceal.

There's your problem. Use the adjective application of the word instead - it makes much more sense in this context.

Re:Forgive me but I have to nitpick

[Anonymous Coward]

I doubt you can see ultraviolet light, or any other electromagnetic radiation besides that of visible light. However, it still interacts with the physical world. Just because you can't see gravity or another dimension doesn't mean it doesn't exist.

Re:Forgive me but I have to nitpick

[Anonymous Coward]

well, if we've been around for 100,000 years as a species (anything older was another species, go look it up) and are only now thinking that these other dimensions are there, then they have been 'hidden' from us up until now. secondly if we have been unable to detect them until now then they have been concealed from our perception.

also note that the usage of such terminology has long since ceased to solely imply any sort of active and purposeful attempt by some sort of sentience to create such a state.

while true, the way the words are conjugated implies a transition into that state, the way the language is used it is not necessary that something be placed into 'hiding' to be hidden, the word 'hidden' i believe can properly be used to describe something that has always been in that state.

and if you dont like the fact that i dont use capital letters you really should complain about e.e. cummings before you let into me. i say if a man can become a respected poet witout using capitals, then i can post to slashdot in the same fashion.

anyways, not to belittle you, but the way the language is setup, we really dont have (that i can think of) a way to describe something in a state that would imply an infinite existence in such state, instead of having been put there from another state.

Simpson's...

[grumling]

"Well, we're running an experiment to see the effects of gravity on these little screws."

NS strikes again

[Iron Condor]

Oh, look, it's the New Scientist again. The Weekly World News of science reporting.

Really: anybody who makes reference to this rag is decidedly not interested in science, reality, or truth.

Re:NS strikes again

[Anonymous Coward]

Frick, what did they do, make you waste a half day on an interview and then not run the story or something? The article, the experiment, and the researchers are all legitimate, you make it sound like this was a UFO sighting or someone sticking a piece of metal in their arm and calling themselves a cyborg or something.

Re:NS strikes again

[Slashcrap]

Frick, what did they do, make you waste a half day on an interview and then not run the story or something? The article, the experiment, and the researchers are all legitimate, you make it sound like this was a UFO sighting or someone sticking a piece of metal in their arm and calling themselves a cyborg or something.

You've never read New Scientist have you? I'm guessing you're in the US and that you assume it's similar to Scientific American. You are mistaken. The only reason a real scientist would read it is for the job adverts, which make up approximately 50% of the magazine.

Go and read the article if you haven't already. That's not some cut-down summary for the web. That's the whole article from the print edition. Lots of the stories in the Slashdot section come from New Scientist. You can tell from the way that half the comments are along the lines of "Where's the fucking details?".

Solar System in a Can

[slowbad]

Churchill was right ... the whole world is just swirling around, ready to go into the shitcan.

Some sanity here

[viking2000]

The key question is: What is the ratio between signal and noise here? The article does not mention this at all except talking about lagrange points, solar wind, etc. I assume placing it at L2 is to get the S/N ratio >1.

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...

[muzammal]

Would the fact that this little universe would be enclosed in a spaceship have any effect on it?

Re:Hmm...

[Eric604]

And if they find no deviation from the real solar system, would that mean that our solar system is inside a gigantic spacecraft?

Gauss's Law

[amightywind]

Gauss's Law 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

[bbaskin]

If I had a nickel for everytime I heard someone suggest replacing a tungsten weight with uranium, I'd have a buck or so. Uranium (238 anyway) isn't denser than tungsten. Tungsten is the densist material for semi-practical applications. It's more available than iridium or osmium, and far less expensive than platinum, three more dense elements. For a few reasonably obvious reasons, neptunium and plutonium aren't really good alternatives to tungsten if you just want a dense lump of metal.

Re:Gauss's Law

[shadowbearer]

  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

[amightywind]

If I had a nickel for everytime I heard someone suggest replacing a tungsten weight with uranium, I'd have a buck or so.

I found this. You're right about Uranium. Platinum seems to be a good candidate. Maybe Tungsten is cheaper. Thanks.

Re:Gauss's Law

[amightywind]

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

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 a little experiment apparatis. It is surprisingly small.

Re:Gauss's Law

[phageman]

It's that level of noise that determines how small a difference can be reliably identified out of the noise. When the researchers say that rate of precession is a "reasonable" quantity to measure, it's because they expect to be able to identify this signal above the noise. Also, the longer the experiment runs, the more data can be averaged and the noise will cancel out.

Re:Gauss's Law

[Anonymous Coward]

Dumb OT question: with all the hooplah about depleted uranium ammunition, if tungsten is just as dense, why don't they use that instead? Seems like it would be a lot less toxic, and cheaper to boot.

Re:Gauss's Law

[grammar fascist]

If I had a nickel for everytime I heard someone suggest replacing a tungsten weight with uranium, I'd have a buck or so.

Think of all the Uranium you could buy with that!

Re:Gauss's Law

[shadowbearer]

  Assuming that over the duration of the experiment there is a meaningful average.

SB

Re:Gauss's Law

[shadowbearer]

  Short times scales, tho?

SB

Re:Gauss's Law

[Quantum Fizz]

Gauss's Law says that the gravitational acceleration of a body anywhere in an enclosed sphere is 0.

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:Gauss's Law

[aonic]

um... unless i fell asleep during AP physics, gauss's law describes the gravitational/electrical _flux_ at any point in the sphere. that says nothing for the gravitational acceleration, only that "gravitational flux in" = "gravitational flux out". there's nothing preventing an asteroid from zooming by, knocking a microplanet out of its orbit, and ending the experiment. that being said, orbital perturbations are easy to calculate for given known objects in the area (sun, moon, earth, mir, dr. evil, etc)

also, L4 and L5 are the stable lagrange points, meaning that objects will naturally fall into them. in fact, the jupiter-sun L4 and L5 have clumps of asteroids that just hover there. L1, L2, and L3 are the ones you have to orbit, as the gravitational field at the points are zero, but deviate just slightly and you'll fall away from the point.

Re:Gauss's Law

[CodeBuster]

Seems like it would be a lot less toxic, and cheaper to boot.

Tungsten is not cheaper and it does not combust like DU does when it impacts at high speed. The performance of the weapon is not based soley on the density of the penetrator.

Re:Gauss's Law

[Quantum Fizz]

Just one clarification. I re-read your post and see that you mentioned "inside a sphere". That constraint can even be extended to any hollow spherically-symmetric massive object, to yield zero acceleration inside the cavity (only by virtue of the symmetry). But that's assuming that there are no other massive objects in the universe (or of significance nearby). Including any massive objects outside the sphere.

However, if there were any thrusters attached to the sphere, or asteroids or other junk outside the cavity, then these WOULD contribute to the gravitational field inside the cavity. But yes, if the engineers were somehow able to make a perfectly spherically-symmetric container that is jettisoned, and send far enough away from all other masses, then that container's gravitational field should be negligible inside its inner cavity.

And since the L4 and L5 Lagrange points are unstable points, there shouldn't be much space junk at those points. However, any craft that will stay at those points for an extended time will need to have some kind of orbit-adjustment system (eg thrusters) to keep it at the Lagrange point. I'm too lazy now to determine the time scale of how long a passive object (ie, a perfectly spherical shell without thrusters) would remain at the Lagrange point before drifting too far away to significant gravitational fields (assuming reasonable initial conditions). But presumably it would be longer than the lifetime of this experiment.

But still, the technological engineering challenges are pretty difficult. Even if the container were passive, the engineers would need to build in system sensors and telemetry into the enclosure, probably destroying the spherical symmetry, but they could account for these perturbations in the orbits, if they know the precise locations and density distributions, etc.

Re:Gauss's Law

[Tim C]

The gravitational acceleration anywhere within a uniform sphere is zero. Any areas of higher or lower density in the sphere will cause a stronger/lower field at that point, and thus a net force within the sphere.

Given that the craft needs to do useful things (eg send and recieve radio signals, manoeuvre into and maintain position, etc) it's likely to have stuff bolted to it (radio equipment, engines) and so is unlikely to be uniform. Doubtless this will be taken into account and compensated for, but it's not as easy as making it a uniform sphere.

Re:Gauss's Law

[bbaskin]

As a poster comments below, DU dust does burn. I don't know about tungsten. Tungsten is hard to work with, melts at a higher temperature and can't really be cast easily. Most tungsten products are sintered instead of cast and then forged, I think. The other issue is the government has tons of DU laying around with few other obvious uses.

Re:Gauss's Law

[Anonymous Coward]

Feel free to correct me if I'm wrong here but my understanding was that uranium, in addition to being relatively cheap, especially for the military who has tons lying around, is also not only heavy but ridiculously hard. The hardness also contributes to it use as armor piercing ammo.

Re:Gauss's Law

[Anonymous Coward]

That's the lamest admission of complete factual error that I think I've seen. Good points for actually admitting the error though.

Re:Gauss's Law

[Anonymous Coward]

At L4, L5 Earth and Sun graviational forces are balanced.

It's not so simple. What's "balanced" is that L4/L5 are stable minima of the effective potential, which includes centrifugal pseudoforces (the angular momentum barrier). The Earth/Sun gravitational forces don't actually "cancel".

[...] The Genesis Probe and WMAP missions have already taken advantage of this.

Incorrect. Genesis was at L1 and WMAP at L2, both unstable Lagrange points.

Re:Gauss's Law

[Anonymous Coward]

It doesn't even have to be symmetrical: the calculus is a little easier if it's rectilinear rather than spherical (since the bit about the area being proportional to the force is true for even finite areas, rather than just infintessimal areas as in a sphere), and since the distance from any two opposite points doesn't matter, it doesn't have to be a cube, or pyramid, or any other fancy Platonic solid; it could be in the shape of a rectangular prism or a semisphere or anything convex, but I'm not sure about a solid shell with some concave parts.*

*Whoo one sentence.

Re:Gauss's Law

[yndrd1984]

He answered the question posed by the post he replied to. If you want to nitpick:

Gauss's Law leads us to the conclusion that the gravitational acceleration of a body anywhere in a sphereically symetric shell, due to the shell, is 0.

Your example with the brick has nothing to do with the origional question - "wouldn't the mass of the "spaceship" affect the experiment?". As a physics TA, I'd have given you a 'A' for understanding the math of Gauss's Law, but a 'C' for missing the point.

Re:Gauss's Law

[Quantum Fizz]

Great-Grandparent asked the worthwhile question about the spaceship's own gravitational field affecting the experiment. The Grandparent said "Gauss's Law [wolfram.com] says that the gravitational acceleration of a body anywhere in an enclosed sphere is 0."

.

First, re-read my own reply to my first comment for clarification (posted long before your comment here). Secondly, the grandparent is implying that merely having a spherically-symmetric shell implies the field inside is zero. And this is only true in the absence of any masses outside. Which in reality would include thrusters, communications, etc. I comment on all of this in my response.

So yeah, the grandparent responded to the grandparent by assuming some kind of ridiculous hypothetical experiment, while ignoring the actual reality of building a self-contained ship with sensors, telemetry, possibly thrusters, and simultaneously making this entire thing have a spherically-symmetric mass density. So in that sense I'd say my responses are well justified.

Regarding your grading methods, you seem to be one of those physics TA's that merely looks at the final answer and deducts significant points for minor arithmatic errors, despite having a 10 page solution with the correct method (eg a problem from a typical Jackson level E&M class).

Re:Gauss's Law

[yndrd1984]

Regarding your grading methods, you seem to be one of those physics TA's that merely looks at the final answer and deducts significant points for minor arithmatic errors, despite having a 10 page solution with the correct method (eg a problem from a typical Jackson level E&M class).

Oddly enough, that's my mental image of you! The guy who keeps jumping in to correct the minor errors of other students. The original answer had all of the correct parts, and I think it was rude of you to suggest that he doesn't know what he talking about.

As for the "ridiculous hypothetical experiment", I'll ignore the ridiculous part, at the moment we are talking about a hypothetical experiment - frictionless pulleys, massless strings, perfect spheres and all.

Secondly, the grandparent is implying that merely having a spherically-symmetric shell implies the field inside is zero. And this is only true in the absence of any masses outside.

First: The origional question was "Help me out...wouldn't the mass of the "spaceship" affect the experiment?". The answer was "Gauss's Law says that the gravitational acceleration of a body anywhere in an enclosed sphere is 0.". Because the question focuses only on the spaceship, that answer is basicly correct, as far as I'm concerned.

Second: He says "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.", which implys that outside bodies can cause acceleration, but in this particular case, bodies other than the spacecraft don't matter. He covered his ass there quite well.

while ignoring the actual reality of building a self-contained ship...

I'm not going to argue that it would be easy to carry out this experiment. But the answer to the original question has to remain "At least in theory the spaceship can be made in a way that will keep it from affecting the experiment with gravitational forces".

at that speed...

[YesIAmAScript]

There's no way it would orbit 3,000 times a year, right? It'd have to go very slowly to keep from escaping the gravity well of the tungsten sphere and at that speed, it couldn't cover much ground (even less than 2*pi*10cm*3000 per year).

Right?

interesting but

[rucs_hack]

Since we're not able currently even to build a spaceship capable of making it to the moon (having mothballed all the relevent tech and gone for the technical nightmare that is the shuttle, and the hidiously expensive disaster that is the ISS), why bother with these types of experiments?

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

[pla]

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.

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

[hawfizzle]

jesus man, if you believe the numbers, 10% of defense budget spending could fund nasa for centuries

Re:interesting but

[Kopretinka]

Since we're not able currently even to build a spaceship capable of making it to the moon [snip] why bother with these types of experiments?

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".

Re:interesting but

[Jeff DeMaagd]

Since we're not able currently even to build a spaceship capable of making it to the moon

What? NASA and other space agencies routinely send probes to the rest of the solar system, what is so hard about the moon? Cassini-Huygens was the size of a bus and it went to Saturn.

You seem to suggest that this needs a manned mission, but the article doesn't suggest this. Human operations would probably interfere with the experiment, if it was possible.

Re:interesting but

[rucs_hack]

My point is that, even though it risks the occasional loss of life, we *must* have a routine and large scale presence in space.

Re:interesting but

[nleaf]

The article isn't all that descriptive of the methods to be used for this experiment, but from what I gather it has nothing to do with space exploration. It has everything to do with testing predictions of theory. While both are important, and often overlap, this experiment really has no direct relation to the ISS, the shuttle program, or the moon missions.

You may be right about being able to perform such experiments for less with a solid presence in space, but that is a very long way down the road yet, and is likely dependent on the very advances in theoretical physics that you claim should be de-prioritized. Plus, I really doubt there's enough grant money for everybody to be working on a space presence, to the rest of the physicist need something to keep them busy. ;)

Re:interesting but

[rotenberry]

...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....Ok, perhaps I'm thinking too fancifully...

I don't know what is more frightening: that he considers realistic engineering goals more fanciful than this proposed search for hypothetical extra dimensions, or that (given the current political climate) I agree with him.

Too many uncertainties

[mcguiver]

It seems to me, after reading the article, that there are just too many influential factors to be able to conclude anything by such a test. From the article If gravity is leaking into extra dimensions, the slight change in its force should cause the planet's oval-shaped orbit to rotate, or precess, slowly... the orbit would precess by 1/3600 per year - "a reasonable quantity to try and measure," they say.
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

[Quantum Fizz]

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.

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 can measure this and run the experiment.

If the experiment doesn't give you the values you expect, then you find a flaw in either your theory, your experiment, or your assumptions of the possible effects, etc. If it does give you the values you expect, then you have another good data point in the MOND or similar graviational theory. In any case, you either learn something useful, and further solidify our understanding of known physics.

Wow...

[Jugalator]

I nominate this for the strangest news article title of 2006.

High School Physics

[Soong]

Ok, some orbital mechanics.

Going with a circular orbit because they didn't specify the ellipse:
365.24*24*3600 = 31556736.00 seconds per year
./3000 = 10518.912 seconds per orbit
1/. = .00009506686623103225 orbits per second
.*.14*3.1415926*2 meters per orbit =
.0000836 meters per second
.*1000 = .0836 millimeters per second

Pretty slow orbit. About that tungsten, 19250 kg/m3
3.1415926*(4/3)*.04*.04*.04 = .000268 m^3
.*19250 = 5.16 kg
And let's say the planet is 8 mm in diameter, .004 m in radius
3.1415926*(4/3)*.004*.004*.004 = .000000268 m^3
.*19250 = .00516 kg

F = G m1 m2 / r^2 =
gravitational constant = 6.67300 × 10-11 m3 kg-1 s-2
.00000000006673000000 * 5.16 * .00516 / (.1*.1)
= .00000000017767262800 Newtons of force, resulting acceleration on the smaller body of
./.00516 = .00000003443267984496 m/s = .00003443267984496 mm/s

Sounds reasonable to me. Assuming they can get a clean launch at exactly .0836 millimeters per second everything should be fine!

Re:High School Physics

[redphive]

Was your calculations based on 8mm or 8cm diameter center mass? I thought the article said 8cm.

Re:High School Physics

[Ctrl-Z]

Shhh... he's trying to show off his big brain.

Re:High School Physics

[njchick]

See .04? That's the radius of the central mass in meters. Convert is to furlongs, multiply is by 2 to get the diameter, then convert it to centimeters. You'll get approximately 8 cm.

Re:High School Physics

[redphive]

ah looked right at the last one... good to know i was paying attention to this post as much as I was paying attention in 12th grade physics.

Re:High School Physics

[Napoleon The Pig]

They don't specify the eccentricity of the ellipse however they do specify the period and the material that makes up their "sun". From a few simple calculations you can figure it out:

T=3000 rev/year => 9.5066x10^-5 rev/s
take the inverse
P = 10519.007s (some rounding error)

mu is known as the standard gravitational parameter, and can be found by multiplying the mass of the object by the universal gravitational constant:

mu = G*m

to find the mass take the volume of a sphere of diameter 8cm (FTA) and multiply it by the density of tungsten:

m = V*rho

V = (4/3)*pi*r^3 = (4/3)*pi*(4cm)^3
    = 268.08 cm^3

rho = 19.25 gm/cm^3

m = (268.08 cm^3)(19.25 gm/cm^3)
    = 5160.589gm
    = 5.160 kg

mu = G*m
      = (6.6742x10^-11 m^3*s^-2*kg^-1)(5.16 kg)
      = 3.443 m^3/s^2

Using mu and the period P, we can find the semimajor axis a:

P = 2*pi*sqrt(a^3/mu)

solving for a:

a = (P^(2/3)*(2*mu)^(1/3))*(2*pi^(2/3))^-1

plugging all those fun numbers in:

a = 212.838 m

from there we can find the eccentricity by the formula:

e = 1-(r_p/a)

r_p is the radius at the periapsis of the orbit (the closest point in the orbital path to the mass it is orbiting).

FTA the "planet" will be launched 10cm away into an oval shaped orbit. For an arbitrary assumption, we'll take 10cm to be the periapsis of this orbit.

That would put the eccentricity at e=.99953, which is extremely close to the eccentricity of a parabolic trajectory of e=1, so 10cm is most likely not the periapsis of the orbit.

However since the semimajor axis of the orbit is so large compared to the initial given value of 10cm, it wouldn't make sense for it to be at any other point in the orbit. So essentially, from the numbers given in the article we have an extremely large system (total orbital diameter is 2a = 425.676m) which would be impractical to create and launch to the legrange point.

Unfortunately I believe we have yet another case of not enough actual details in the article to come to a reasonable conclusion about the physics behind the story.

As always, if there's something wrong with the analysis or any of my calculations please point them out. It's been a while since I've done any of this stuff and mistakes do happen.

Achooo

[xamomike]

So what happens when some idiot lets out a sneeze and throws 3 years worth of experiments down the drain? Or god forbid a fart?

Cheese in a can

[Cisko Kid]

Is that like cheese in a can? If that is the case I do not want any.

It won't work.

[DolomiteZipper]

Wouldn't the space ship exert its own gravity on the system and ruin the whole experiment?

A friend and I just did it..

[YesIAmAScript]

Assuming the "10cm" orbit number is altitude from the surface of the tungsten sphere, it actually would orbit 6,000 times a year. It would move at 1.66E-4 m/s, or 1 cm/minute. The orbital path is about 90cm around (14cm*pi), so it would orbit about every 90 minutes, meaning 16 per day * 365 days or about 6,000 a year.

Amazing. I would have said it was impossible.

DO NOT PERFORM THIS EXPERIMENT!

[BorgCopyeditor]

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 this kind of experiment until further simulations can be run.

What a load of shit.

[Anonymous Coward]

"To hide" is both a transitive and intransitive verb, your selective quoting of dictionary definitions notwithstanding.

Since it can be an intransitive verb, it does not imply an actor. You're not nitpicking, you're being a fucking idiot. Every fucking conversation about science does not have to include ID-bashing just for the sake of it. ID is as big a load of bullshit as your post, but there was no reason to give it a venue by bringing up retarded criticisms disguised as pedantry. Pedantry is bad enough, but what you present is total fucking nonsense.

semantics

[v1]

Once at the Lagrange point

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.

Re:semantics

[phageman]

What's the basis for that assertion? All they need is enough of a signal to detect above the noise caused by all these other factors. I assume that they have crunched the numbers and determined that a change of 1/3500 degree would be above this threshold.

or voodoo

[Anonymous Coward]

What if a small asteroid collides with the voodoo solar system? LaGrange points are really the intercies of ley lines.

Peanut Brittle !

[Joebert]

Solar System in a Can May Reveal Hidden Dimensions

I'm going to go ahead & take their word for this one, you guys feel free to take a look inside that can though...

It's Called a "Hill Sphere"...

[Blackbird_Highway]

and it's the measure of the size of the gavitational influence of a body. Outside the Hill Sphere, the gravitational effects of other bodies dominate. The Hill Sphere of this 8cm tungston "sun" is extremely tiny, actually smaller than its' own radius, unless you place it far out in deep space, well outside the orbit of Neptune. Don't believe me, go look it up on Wikipedia for yourself!

Re:It's Called a "Hill Sphere"...

[Quaoar]

Except that the two outside forces which would have a noticeable effect on the experiment, the Sun and the Earth, are in equal and opposite directions at the Lagrange point. The Hill sphere does not matter in this situation.

Just launch the experiment...

[posterlogo]

...and place it at the Lagrange point between the Moon and the Earth. There, external forces may be minimized, and some productive observations could be made. Any experiment which tries to measure "extra dimensions" or whatever would have to have such a low margin of error that yes, it would be IMPOSSIBLE to acheive within a space craft. Don't believe everything you hear -- the fundamental laws of physics are still the most important considerations at the scale of observation currently possible.

read Flatland again

[Ardipithecus]

we would not be able to see in the direction of the other dimensions, or, they could be so tiny we couldn't see them either hth

The mighty butt of commerce

[EEDAm]

In other news, the mission will be sponsered by Magic Knickers with the slogan "Feel inspired to miniaturize Uranus".....

In related news...

[fahrbot-bot]

Since announcing their experiment, the designers Varun Sahni and Yuri Shtanov have been barraged with crank phone calls asking if they have, "Prince Albert's solar system in a can"? They are reportedly unamused.

The actual Paper

[Anonymous Coward]

IAAPM (that physics major) and have heard about a similar experiment.

I looked up and found a paper in the arxiv preprint library that appears to be what the new scientist article is about. Its at: http://arxiv.org/abs/gr-qc/0606063

Quickly reading through the paper and based on some previous reading of another older paper at http://arxiv.org/abs/gr-qc/0002088 I think that both the ideas proposed are with in the realm of possibilities. Obviously there would be many technical measurement challenges but that's expected. And any such challenges are likley surmountable.

Re:The actual Paper

[Savantissimo]

Some info on the linked paper:

APSIS - an Artificial Planetary System in Space to probe extra-dimensional gravity and MOND [MOdified Newtonian Dynamics]

Authors: Varun Sahni, Inter-University Centre for Astronomy and Astrophysics,
Post Bag 4, Ganeshkhind, Pune 411 007, India
Yuri Shtanovm, Bogolyubov Institute for Theoretical Physics, Kiev 03143, Ukraine

13 pages

        A proposal is made to test Newton's inverse-square law using the perihelion shift of test masses (planets) in free fall within a spacecraft located at the Earth-Sun L2 point. Such an Artificial Planetary System In Space (APSIS) will operate in a drag-free environment with controlled experimental conditions and minimal interference from terrestrial sources of contamination. We demonstrate that such a space experiment can probe the presence of a "hidden" fifth dimension on the scale of a micron, if the perihelion shift of a "planet" can be measured to sub-arc-second accuracy. Some suggestions for spacecraft design are made.

Gauss's Law does not apply

[Anonymous Coward]

Your application of Gauss's law is flawed- all those formulas only tell you about the total strength of the field generated by objects inside them (Hence enclosed). Otherwise, your argument could be used to show that no electric or gravitational fields exist anywhere except inside the objects that produce them, since you could otherwise always arrange the volume integral to not include any charged objects, making q or g enclosed = 0.
The fact that your comment was modded +5 Informative suggests that more slashdotters need to go back to introductory physics courses. And you call yourself nerds...

Another use of this experiment

[Anonymous Coward]

This experiment may also have another use: a more precise measurement of the gravitational constant (G). The 2002 CODATA recommended value of G has a relative standard uncertainty (RSU) of 1.5e-4. Compared to other constants such as Planck's constant (RSU of 1.7e-7) or the mass of an electron (RSU of 1.7e-7), this is a very high relative uncertainty. (Source of numbers: http://physics.nist.gov/cuu/Constants/)

This experiment could almost certainly determine G to a higher precision than possible with Earth-bound experiments. On Earth, there is gravitational "noise" generated by things such as active geology. In interplanetary space, there are less noise sources and they are more predictable. The experiment is almost like a super Cavendish torsion balance experiment in that the gravitational attraction between non-astronomical (ie. not "very large") objects is what is being measured.

The high relative uncertainty of the gravitational constant makes things such as some astronomical measurements hard. Conversion of SI units to natural units (Planck units) involves high uncertainties due to G appearing as a factor in nearly all of the conversions. At the very least, determining G to a higher precision would allow astrophysicists to reduce uncertainties in cosmic gravitational "experiments" (eg. tests of general relativity).

Home on LaGrange

[Anonymous Coward]

Oh, give me a locus where the gravitons focus
Where the three-body problem is solved,
Where the microwaves play down at three degrees K,
And the cold virus never evolved.

Home, home on LaGrange,
Where the space debris always collects,
We possess, so it seems, two of Man's greatest dreams:
Solar power and zero-gee sex.

We eat algea pie, our vacuum is high,
Our ball bearings are perfectly round.
Our horizon is curved, our warheads are MIRVed,
And a kilogram weighs half a pound.

Home, home on LaGrange,
Where the space debris always collects,
We possess, so it seems, two of Man's greatest dreams:
Solar power and zero-gee sex.

If we run out of space for our burgeoning race
No more Lebensraum left for the Mensch
When we're ready to start, we can take Mars apart,
If we just find a big enough wrench.

I'm sick of this place, it's just McDonald's in space,
And living up here is a bore.
Tell the shiggies, "Don't cry," they can kiss me goodbye
'Cause I'm moving next week to L4!

Home, home on LaGrange,
Where the space debris always collects,
We possess, so it seems, two of Man's greatest dreams:
Solar power and zero-gee sex.

Re:Home on LaGrange

[SimplyI]

Funny... but not what was alluded to.

ZZ Top - La Grange

Rumour spreadin a-round in that texas town
bout that shack outside la grange
And you know what Im talkin about.
Just let me know if you wanna go
To that home out on the range.
They gotta lotta nice girls.

Have mercy.
A haw, haw, haw, haw, a haw.
A haw, haw, haw.

Well, I hear its fine if you got the time
And the ten to get yourself in.
A hmm, hmm.
And I hear its tight most evry night,
But now I might be mistaken.
Hmm, hmm, hmm, hmm.

Have mercy.

Re:Gotchas, we got em (naah, you haven't)

[Richard Kirk]

Okay - it may not be perfect but it is better than the only alternative. What's the alternative? The traditional methods of measuring gravitational forces on earth involve measuring tiny motions of suspended weights towards each other. Suspending the weights ought to mean the degrees of freedom for the weights lie perpendicular to the ambient gravitational field. Well, that works, but the ambient gravitational field is many billions of times greater than the little attraction you are trying to measure. You have to isolate the experiment from external vibrations, movements of mass, electric and magnetic fields, tidal effects, ageing and grain growth in the support cables, yada, yada, yada.

Sticking the whole experiment up in space gets rid of most of these problems. No wire, no vibrations, no air currents (vacuum out there is very much better than lab vacuums). The gravity is now by far the biggest force. If you stick the whole experiment in a symmetric tin, then Gauss' theorem (old school gravitational theory, but still pretty accurate) says it the net gravitational field inside is zero. The tin could keep out the solar wind, though it might need a small ion motor to keep it motionless with respect to the experiment inside.

I am not sure of the need to go to the Lagrange point. That is a precious point in space and we don't want to go cluttering it with time-expired junk. Probably just getting into high orbit would get us much better results than on earth. Shoving the experiment out of earth's orbit altogether might be better still.

Anyhow, we ought to do it because it's cool. That's what Space stuff is for: to be cool. The space shuttle sort-of misses the point of Space these days.

Re:Gotchas, we got em (naah, you haven't)

[Ancient_Hacker]

> says it the net gravitational field inside is zero.

I can see this happening at the exact center, but is it true everywhere inside the sphere? If you're closer to one side, doesnt that side extert more force on you than the side farther away?

If, if, if.

[WhatDoIKnow]

' "If the system's 'planets' moved slightly differently to the way predicted by standard gravity, it would signal the presence of new physical phenomena." ' Uh huh. And if a frog had wings it wouldn't have to land on it's ass whenever it jumped.

"Noise" is random

[mangu]

1. Acceleration 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. Acceleration felt due to spaceship: ?
4..? L2 orbit itself, light pressure, magnetic & other fields etc

These perturbations are all predictable and can be taken into account. The calculations would be rather complex, but feasible, astronomers do that all the time. The problem is in random perturbations, like solar radiation which changes slightly due to flares and sunspots. That's why the system is set in the Earth's L2 point, which is not exposed to direct sunlight.

Re:"Noise" is random

[viking2000]

These pertubations are bigger than the escape velocity of the system. They would throw the "grain sized planet" out of orbit. Probably hitting the wall in the spaceship.

You would need a lot of complex calculation to compensate for "bouncing off wall of spaceship" every week.

Confused physical reasoning

[amightywind]

Your trivial example ignores the problem by not enveloping the entire acting mass with a Gaussian surface. You have made no point. My original post simply states well known result of Gauss's law that says the gravitational or electric field within a hollow sphere is 0. Jackass.

Re:Confused physical reasoning

[Quantum Fizz]

Do you even understand Gauss's law? My example did envelop the mass with a "Gaussian surface", the fact you don't understand that and yet resort to namecalling only makes you look both naive and immature.

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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). Just because this surface integral (ie, a continuous sum) is zero doesn't imply the local vector field at any point on or within the surface will be zero. As perfectly exemplified by my brick example.

And finally, the gravitational field within a hollow sphere is zero only if the gravitational field is also zero in the absence of that sphere.

Asleep in AP physics

[amightywind]

I guess you were asleep in AP physics then N00b. Gauss's law is a relationsip for any conservative field, G or E with mass (m) or charge (q).

To stake out and claim the Lagrange point?

[Traf-O-Data-Hater]

How about this for an idea - the 'experiment' could be a cover to stake out one of the Lagrange points. By placing a piece of space junk there first they not only claim the space but would it not make a second comer more wary about crashing into the first, and thus not risk it? From what I've read the Lagrange points will become strategically important to space-based defence in decades to come.

Well enough

[amightywind]

Do you even understand Gauss's law?

Well enough to apply it and simply answer original parent's question. Why you are jacking off on tangents I don't know.

Re:Well enough

[Quantum Fizz]

Why you are jacking off on tangents I don't know.

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The so-called 'tangents' directly follow from your original erroneous implications of Gauss's law, along with your further accusations of "confused physical reasoning" to demonstrate that you are in fact the confused party.

comments on probes

[Anonymous Coward]

The experiment they are talking about would have to be unmanned. You can't have astronauts moving about messing up your gravity experiment. 99% of space exploration is unmanned and goes largely unnoticed by the public. (Men will get to go to space when there is a reason for them to be there. Any sooner is a waste of money.)

There have been several probes sent to Lagrange points. (For instance to Wilkinson Microwave Anisotropy Probe that has been running for a while at the earth sun L2 Lagrange point.)

The difficulties to overcome would be things like how are you going to prevent your spacecraft from disturbing your experiment. How are you going to measure the positions of your spheres to the desired degree of accuracy. Presumably you would keep them in vacuum and in the dark. Maybe they would be outside and away from the probe in the probes shadow, but there might be some better way to do it.

Re:Gotchas, we got em (naah, you haven't)

[Richard Kirk]

If you have an inverse square gravitational field, then a uniform shell will balance itself out exactly. If you are outside the shell, it will behave as though there was a point mass at the centre.

Roughly it goes like this. If you approach one side, then you have a small region that is very close to you on that side, and a much bigger region on the other side that isn't attracting you as strongly. The area goes as the square of the radius. The attraction per unit area goes as the inverse square. So they ought to be able to balance out, and in fact they do exactly.

Enclosing space ship unnessesary?

[Anonymous Coward]

Why would the system want to be enclosed? It will be impossible to make a spaceship perfectly symmetrical so why not just have the spheres float free in space with the spaceship observing from a distance. When gravity acts from a distance the lines of force on the spheres will appear practically parrallel. All the spheres will together be influenced by the observer so in relation to each other they will see no influence.

Shout out

[StikyPad]

Nice to see my old shop teacher on New Scientist.. recognizable from the missing ring finger tip, of course. Keep up the good work Mr. Daly!

nonono.

[TheLink]

You got your priorities all wrong.

Think about the benefits to the _entire_world_ if we start actually sending mostly _politicians_ to space.

One way.

Start some Reality TV show ala Survivor. And the most disliked politician gets voted off the planet...

My friend hasn't quite got round to it so www.voteofftheplanet.com isn't up yet ;).