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Science

Gravity Diluted By Multiple Dimensions? 234

Posted by emmett from the catchy-name dept.
SEWilco writes: "Why is gravity so weak? Maybe it isn't, but it's diluted by propagating through many dimensions. The theory provides a relatively simple explanation to several oddities of physics, and it should be relatively easy to test. Notice the links at the bottom of the story; one of them mentions that the concept doesn't have a catchy name yet...and we'll be reading more about it soon. Slashdot discussed extra dimensions before, but this concept involves gravity actually propagating into them." I think we should call it 'The Emmett Effect.' There's got to be some lab-coated brainiac out there than can make it happen.
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Gravity Diluted By Multiple Dimensions? More

Gravity Diluted By Multiple Dimensions?

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  • Re:Nonsense (Score:4)

    by fiziko ( 97143 ) on Wednesday July 19, 2000 @01:25AM (#922954) Homepage

    I mean how the hell can you compare two forces with completely causes? It is just as absurd as saying that 1 gram is more than 1 coulomb.

    That's right. They're comparing the values of the coupling constants, which are dimensionless quantities (ie. no units), so they can look at things on the same scale. The coupling constant determines the strength of the interaction. (It also has a really bad name; it turns out that it's not constant.)

  • >And the probability is yet again increased that humanity's last words will be, "It's working!"

    LOL! I always figured humanity's last word would be something like, "Oops."

    How about, "What do you mean, it doesn't have an 'off' switch?!?"

  • They don't give you the whole picture.

    A proton decays into a neutron by emitting a positron and an electron-neutrino. Welcome to conservation of lepton number, as well as possibly spin.

    Don't get your physics off of kiddie webpages.

    In this scenario, we have to conserve a few quantities.

    • Charge: this is why we have to have a positron, a proton can't just drop to a neutron, we have to conserve charge by kicking off a positron.
    • Baryon number: this is why the proton turns into a neutron (although, to do this, you have to add energy, protons mass slightly less than neutrons)
    • Lepton number: Leptons in equals leptons out. A positron has lepton number of -1, which is balanced by the +1 of the electron-neutrino.
    • Spin: Spin conservation is what led to first the hypothesis for, and then the eventual detection of, neutrinos.
    Only some of the conservations can ever be broken, like CP (this is the very slight violation that we think led to the predominance of matter in the universe, as opposed to a perfect balance of antimatter and matter). There's a good physics website out there that lists the current experimental conservation limits, some of them down to one part in a billion or so.

    Maybe we need a Particle Physics for Slashdotters webpage. Any suggestions?

  • Dimensions do not have a size. Objects have sizes in a set of dimensions.

    Of course dimension have a size, due to the fact that they are either limited in some extent or infinite. For instance time has a definite starting point and may be infinite in size (an open universe) or finite in size (a closed universe with a Big Crunch). Since the Universe isn't infinitely large the three spatial dimensions we're familiar with also have a size.

    In superstring theory the compactified dimensions have a size corresponding to the Planck length in usual models - approx 10^-33 metres. There are models in which the size of these dimensions could be much larger, as in the article, and in those the idea in the article could be made to mesh with superstring theory.

  • The earth is holding back millions of pins plus everthing else as well. It also doesn't seem to get any weaker however many things you put on the earth, or indeed how "heavy" they are.

    The problem is, you can't "concentrate" gravity on any one particular object. By its very nature, gravity is a distributed force. Furthermore, because of that distributed nature, gravity won't get weak no matter how much you throw at it. It may be holding down ten pins, or ten trillion pins - at any given distance from the center of mass, the force of gravity will be the same for the former amount of pins as it for the latter.

    For this instance, gravity is the same everywhere on the surface of the planet (oversimplifying). So whether you take that pin to Guatemala, Madrid, Tokyo, or Minneapolis, gravity will still exert the same amount of force. Hence, it can be said that the entire force of the planet is holding that pin on the surface (as much force as Earth is going to exercise at any other point on Earth). So you have to consider the thought: an object the size of Earth, with it's hundreds or thousands of billions of tons (I don't know the figure off the top of my head), is holding a piece of paper. Yet, with a little rubbing on carpet, a balloon weighing maybe several grams, or a few dozen grams, can hold that paper up against the pull of the mass of the Earth.

    It even seems to be able to hold the moon in place too! In fact, it seems to me that it could hold lots of moons in place.

    But that has less to do with the force of gravity. I can put an arbitrary number of objects in orbit around the Earth. All I have to do is make sure that the rate at which gravity pulls them towards Earth is balanced by their motion around the Earth. At close distances, the object has to go really fast. At far distances, the object can go really slow. The strength of the gravity has nothing to do with how many objects can orbit around Earth, only with how far away those objects have to be.

  • In fact, the magnet *does* sometimes win the
    fight over the 2-ton hunk of iron. Ask anybody
    who runs a junkyard.

    Chris Mattern
  • I recently finished reading the widely popular book "The Elegant Universe" (here's an Amazon link [amazon.com]) by Brian Greene. It starts with the simplest of Newtonian physics, heads over to Einstein and quantum mechanics and then takes a sharp left into string theory, and eventually m-theory. I'm just an amateur, but this book is very readable (someone else mentioned the ants on a garden hose analogy, which is used in this book) and understandable. It generally avoids the intricate math involved and concentrates on getting the reader to grasp the concepts rather than the details. It takes some perseverence to make it through the 400 or so pages, but I highly recommend it.
  • Whoops, sorry about that. I even previewed the thing before I posted. That's what I get for typing before I've had Mountain Dew.
  • Sure, having some arbitrary dimensions and fundamental particles entangled in them does seem far fetched. But remember, these are just models. There probably aren't little teensy rings of dimensions upon which some force particles are "caught". It's something so our poor 3-dimensional biased minds can understand reality. Perhaps you're right, and "dimensions" are actually a continuum, instead of cut and dried orthogonal measurements. But I think the human mind needs some model it can innately understand.

  • Re:Gravity is weak? (Score:3)

    by phil reed ( 626 ) on Wednesday July 19, 2000 @02:55AM (#922963) Homepage
    In large part, the difference in the examples you give is not so much gravity, but other issues. For the insect, their fall is governed primarily by aerodynamic drag - in a vacuum it will plummet directly to the ground, same as the horse. In all cases, the amount of damage sustained is controlled primarily by the 'square-cube' law - the strength of the body's structural components goes up as the square of the size, but the mass goes up as the cube of the size. This means the strength to weight ratio gets worse the larger you get, so the larger, hence heavier objects will suffer worse damage.


    ...phil

  • Is the correct answer the German???

    I'd put up my proof of how I solved it to prove it wasn't a wild guess, but I don't want to spoil the fun...

  • Hoagland already mentions this in his physics i think.. Try www.enterprisemission.com [enterprisemission.com]
  • multiple dimensions, huh how about the "Buckaroo Bonzai Effect" now there's a pretty catchy name

    Gentlemen, you can't fight in here...this is the war room!!
  • Actually, I often refer to protons as fundamental particles.

    Well, guess what: they are not. And it is not nitpicking, it is absolutely essential to be precise when discussing technical issues.

    If experiments reveal smaller particles for which gravity is more important than other forces, then maybe it would be wrong to diss gravity so much.

    Ah, so I need to prove to you by experiments the existence of other particles.
    However when the article mentions dimensions wrapped inside other dimensions with gravity diffusing from one dimension to another and everything being ~1mm in size you are willing to take their word for it.
    And you know why? Because you really are short sighted and insecure. Insecure because these mumbo-jumbo theories only serve to protect other flawed theories which you believe in so firmly. And you are willing to believe anything that will give those theories another chance, because your world would collapse if someone proved them wrong.

    We already know that we don't know everything about physical law.

    Yes we do. But you also believe that the things we know are correct, whereas I don't make any such assumptions.

    What on earth are you complaining about?

    The technical inaccuracies of the article.
  • Science Fiction has a lot of Science in it. And has been the inspiration for many inventions (more recently voice-recognition software, which in the 80's was considdered completely impossible)

    I guess you never watched Knight Rider.

    $ cat < /dev/mouse

  • In large part, the difference in the examples you give is not so much gravity, but other issues
    Indeed - that's certainly the case. However, the point i was making is that gravity only seems strong to us because it dominates our behaviour. Different entities' behaviours are dominated by other effects.

    I don't think your argument:

    In all cases, the amount of damage sustained is controlled primarily by the 'square-cube' law - the strength of the body's structural components goes up as the square of the size, but the mass goes up as the cube of the size.
    is applicable - the square/cube law is certainly true, but its implication for animals is that their supporting structure size must increase - so a horse is as strong as an insect, but because its fall is dominated by gravity, its impact speed is such that it's a much greater force than it normally experiences.

    See here [lightandmatter.com] for more.

  • It would seem that dimensions also shift with respect to each other, so the gravitational force acting through a set space within our dimension doesn't act through a constant number of other dimensions. It's related to the alignment of the sun and earth with respect to the set space. If the sun is on the opposite side of the planet, some of the extra dimensions are drawn away, only gradually returning as the alignment changes. While there are less dimensions occupying the space, the apparent gravitational force, relative to our dimension, is increased. And this is why it's so hard for me to get out of bed on a morning.

    Troll? Me? Never...

  • Uh, I just went to a nice presentation on the Casimir effect about two months back. By people who spend years doing it, with Ph.Ds.

    The Casimir effect is NOT negative energy.

    Nor is it a bottomless source of energy, as people seem to assume.

    Just because two plates fall towards each other, that doesn't mean that it is negative energy. Potential energy is not negative energy. Otherwise, you could say that potential energy from gravitation is negative energy (hey, stuff falls down, right?)

    Also, amusingly, the two plate thing creates an "attraction," but, depending on the geometry of the two surfaces, you can also get a repulsion, where the two surfaces would push apart. The math is really, really ugly, though.

    So, again, Casimir effect is NOT negative energy. Also, all of my previous stuff stands. Negative net energies would cause all kinds of things to happen that we just do not see.

    Casimir effect is a purely QM phenomenon. In a very weird way, it's like the Van Der Waals forces. I'm not sure if you've ever done the basic blackbody stuff, but, imagine a box, say the size of the universe, with two metal plates floating in the midst of it. You can have all kinds of allowable, full wavelenghts of photons (virtual, hey, this is QM) on either side of the plate. Big wavelengths, light-years long. Little ones, nanometers long. Anyway, the possible push that QM allows on the plates is just a little bit bigger than the push generated by the possible push between the plates, thus generating what appears to be an attraction (really just unbalanced pushing from both sides).

  • Yet even EM doesn't match gravity's uniquely far reaching ability to bend space and time.

    The jury's still out on that one.

    Well...

    As I understand it, QED (Quantum ElectroDynamics, which is the basis of quantum EM theory) makes the assumption that EM propagates through space as a background, not affecting the metric through which it travels. In other words, it assumes that EM doesn't bend space and time.

    QED's prediction of the EM coupling constant has been verified out to at least a dozen decimal places as far as I know, and that was over a decade ago. If EM does have any effect on the local space-time metric (aside from the fact that photons have energy, which equals mass, which means they should generate gravity in sufficient concentration), certainly nobody's been able to detect it as of yet.

    Part of the reason that nobody's been able to come up with a workable Quantum GravitoDynamics theory is that gravity does affect the local metric of space and time. This means one of the basic simplifying assumptions goes right out the window. EM may have gravity's range (the other two fundamental forces use massive particles as intermediaries, and so don't have an infinite range), but it doesn't affect the underlying structure the same way. At least, not to any significant degree.

    -- Bryan Feir

  • Dimensions do not have a size. Objects have sizes in a set of dimensions.

    Saying a dimension has a "size" is an unfortunate wording born in an attempt to reach a broader audience. Dimensions have scales. I'm a little fuzzy on this part, since I'm in particle physics and not cosmology, but the idea is that the other dimensions could be "curved in" on themselves in such a way that their existance would be masked from our perceptions. I have yet to find a decent layperson's explanation for this, but I'll keep looking. The mathematical gymnastics in the theory do lead to characteristic length scales.

  • OK, the statements are wrong, but they were still taught to me when I was starting Physics.

    It's true of the entire field - even early on the laws of motion were taught at such a level to be considered wrong 2 years later futher up the school.

    The point is that the simplefications work to a degree - look at the law of gravity that we are looking at just now - it worked fine for ages till astronomers realised that Mercury didn't quite fit the formula. Years later (in sixth form :-) an expansion brought in relativity and everyone was happy again.

    What I'm trying to say is that while over simplification can be interperated as 'wrong' it can also help a beginner understand the basics of what is going on.

    just my lil bit,
    Avendit22

  • The four forces, in order from weakest to strongest, are

    • gravity
    • sex
    • death
    • guilt

    Sex. death and guilt were unified early in the 1800's. Gravity remains ununified.


    ----

  • When I calculate, I do. However, using it here would defeat the purpose of relating things to constants people know from high school physics.
  • I don't have the answer to your question, but maybe this will help: They say if you travel far enough you will eventually meet yourself.

  • Re:Gravity is weak? (Score:5)

    by com ( 151723 ) on Wednesday July 19, 2000 @01:31AM (#922978)

    The formula for calculating the gravity between two objects from Newton is:
    Fg = G * m1 * m2 / d^2

    Fg - is the force

    G - is a constant that is very small (about 10^-11)

    m1 and m2 - are two masses of objects attracting

    d - is the distance between objects

    Gravity acts between every two objects in space. Even between you and me. But because G and our "weight" is so small, we can't notice the gravity. It is very weak force.

    But when gravity acts between the Earth and you, the Earth's mass is very very big and the gravity is noticable. If the gravity would be a strong force, then you'd probably change into a pancake.

    We rearrange this equation:
    Fg=(G*m1/d^2)*m2

    (G*m1/d^2) = g ~ 10 m/s

    So we get the good old (and very simplified) equation:
    Fg= g * m

    But the word weak is very relative. You must compare gravity with the other forces. And relatively it is very weak.

  • Ehm, excuse me but doesn't the phrase "comparing apples to oranges" come to mind here? I mean how the hell can you compare two forces with completely causes? It is just as absurd as saying that 1 gram is more than 1 coulomb.
    Gravity is related to mass, and electromagnetic forces on charge. How can someone compare the mass of the earth with the charge in the atoms in a magnet? They are totally different things

    Not quite: you can compare the gravitational force of an electron or proton to the electric force effecting it. If you compare the repulsive force between two electrons to the gravitational force between them, you'll get around 10^40 ratio.

    The notion sounds deceptively simple: besides the familiar three dimensions of space there may be other dimensions, too small to see yet perhaps as large as a millimeter.

    Dimensions do not have a size. Objects have sizes in a set of dimensions.

    It is true by your perception of a dimention it doesn't have size, since you're used to think about infinite dimentions. However, imagine a dimention is wrapped around another dimention, and thus creates a loop - this loop have a limited size - after one milimeter of movement along this dimention you return to your initial point. So this is how dimentions may have size.


    Sela

  • > So while gravity allows us to detect the presence of other universes, they do not merge with ours because no strong, weak or electromagnetic interactions can occur across universal boundaries.

    What would happen if a super-massive object in the other universe passed "near" the earth? Could the gravitational leakage cause us any problems? Could we get sucked into a black hole in the center of a galaxy a gazillion light-years away?

    --
  • Mass = energy
    Charge = energy

    Johan V. (who sometimes likes to cut away all the syntactic sugar generally referred to as English, although it's not a wise thing to do from a Karma point of view, but who cares about Karma anyway, enough rambling, I hope the message was clear and stuff)
  • The real odd question is that gravity is only weak at large distances, such as that which we see in every day life. Down on the subatomic scale, everything gets flipped over. Gravity becomes stronger than all of the other forces.

    This presents a problem for those who want to find what lies at the heart of matter (what comprises quarks, for instances) because no useful theory for how gravity behaves at those levels has been developed yet.

  • Normally, the photons are repelled from each other due to electromagnetism...

    I'm pretty sure you meant to type protons, just wanted to clarify, since photons have no charge to repel each other with, and it was a little confusing. :) It must have been Win2k.

  • You don't get it. The article is basically comparing the mass of the magnet to the mass of the earth. The mass of the magnet is irrelevant: it's the charge that matters. And the article doesn't say how much charge the magnet has, just how much mass it has. So it's a totally stupid argument.
    ---
  • Oh come on !

    Semi mystical garbage ?

    Listen to yourself ? Ever heard of the Einstein/Rosen Bridge efect ? The theory of parallel universes, based on the concept of multiple dimensions was an Einstein theory !

    I really get ticked of when people try to hide their ignorance behind other peoples genius. Are you aware that Einstein divided by zero in the orriginall theory of relativity, something that was only discovered 30 years later by a 2nd year physics student (sorry, can't remember his name) Einstein acknowledged throughout his life that he is not infallible, and expansions upon his theories had always done him proud. What makes it sacrosanct now ?
    Here is a litle something else for you, in 1891 Jules Verne (One of the Godfathers of SCI-FI) wrote a story called Paris, which his publisher rejected because "it was too unbelievable"
    He described Paris in the 20th century as a city where everbody has electric lighting (back then the lightbulb had yet to be invented) and cars (which was a brand new invention). The manuscript made headlines a few years ago when someone decided to publish this, pitty Verne could not live to see it. Get the point ?

    Science Fiction has a lot of Science in it. And has been the inspiration for many inventions (more recently voice-recognition software, which in the 80's was considdered completely impossible)
    And frankly this theory tends to make sense, even to someone who doesn't understand the maths behind it. Yeah, I admit where my knowledge falls short - try it sometime.

    PS. I would like to propose the name "Chrighton Efect" I'm sure Michael will be writing a story about this soon, and thereafter make a sucky movie version.

  • Yes, particles do have mass. And what's gravity, kids? Come on, I know you know! YES IT'S A FUNCTION OF MASS.


    fuckhead

  • It was Win2K combined with the "it's not even 8am yet" factor!
  • a force is (in newtonian terms) mass*acceleration and acceleration is the rate that speed changes over time so forces don't equate to speed. look at a car that has a 0-60 in 4 secs this means that it is accelerating at a rate of 60 mph/4sec which would mean that it exerts a force of its mass times that acceltation.
  • Don't mention it. :) I'm a physics student now, but I plan to work in Academia. I enjoy teaching (informally, and as a lab TA), so I take every chance I get to practice for the times when it's my job to make sure someone understands something.

    Besides, I don't see the point in flaming someone because they took different classes than I did in high School and University. What's the point? If you're asking questions now, you're trying to learn. Why should I discourage that?
  • The article talks about how we see the effects though gravity...it mentions that this could explain cold dark matter which by definition can only influence other matter through gravitational effects or by very very rare collisions with other matter

  • While in three spatial dimensions, gravity obeys an inverse square law -- if you halve the distance between masses, the gravitational attraction between them quadruples; cut the distance to a third, and the force increases nine times -- in four spatial dimensions, gravity increases or falls off as the inverse cube of the distance. With each additional dimension, the inverse law increases.

    oh yeah? so in 2-D it's the 'inverse law' (1/dist^1) and in 1-D the 'constant law' (1/dist^0 = 1)??
    This is nonsense!

    It all depends on what norm you are using. What tells you that in these other dimensions - if they exists - the Euclidean norm should be used??


    Two extra dimensions need only extend about a millimeter for gravity to be comparable in strength to the other forces.

    It really hurts to read this stuff: "two dimensions extend a millimeter". WTF??? since when have dimensions got lengths? Some dimensions aren't even measured in centimeters (->time).

    Da Warez D00d
    living in the 5th dimension of Software
  • Actually, no its not nonsense. Gravity and the Electrstatic force are both measured in Netwons(N) -- that is, (kg)(m)(s)^(-2). Or, kilogram-meters per second-squared. Thus, they can be compared. However, I see your point. I believe what you are concerned about is the density of force -- that is, force per size, etc. Well, if you take an electron in the hydrogen atom, it is a valid comparison to compare the electrostatic force attracting the electron to the nucleus with the gravitational force attracting the electron to the nucleus. The electrostatic force attracting the electron to the nuclues is: (k)(q1)(q2)(r)^(-2). The gravitational force attracting the electron to the nuclues is: (G)(m1)(m2)(r)^(-2). Both an electron and a proton have an absolute value in Coulombs of ~1.602EE-19 Coulombs. An electrons mass is on the order of 10^(-31). A protons, on the order of 10^(-27). [I don't know the precise values off the top of my head]. k is an electrostatic constant. G is a graviational constant. Thus, the net electrostatic force attracting the electron to the nuclues is much smaller than the net graviational force attracting the electron to the nuclues. However, you may still accuse me of making an invalid comparison, if you carefully look at the two equqations: F(electromagnetic) = (k)(q1)(q2)(r)^(-2) F(graviational) = (G)(m1)(m2)(r)^(-2) In my example, the electron in the Hydrogen atom, the product of q1q2 was not equal to the product of m1m2. Thus, the comparison may be said to be invalid. However, even if such hair-splitting is employed, it is still obvious that Gravity is an inherently 'weaker' force than electromagnetism. Let us say that we have an object of 1kg and 1 Coulomb; and another of 1kg and -1 Coulomb. Let us say they are 1m appart. These two objects would be attracted to eachother by both the graviational and the electrostatic force. F(g) = (G)(1kg)(1kg)(1m)^(-2) F(g) = (6.67E-8 Nm^2/kg^-2)(1kg)(1kg)(1m)^(-2) F(g) = 6.67E-8 N F(e) = (k)(1C)(-1C)(1m)^(-2) F(e) = (8.99E9 Nm^2/C^2)(1C)(-1C)(1m)^(-2) F(e) = 8.99E9 N Clearly, even given a perfectly level playing ground in terms of the absolute magnitude of the mass/charge, the graviational force is much weaker. It is interesting to note that both these forces approach infinity as the radius -- that is, the distance between the two object's centres -- approaches zero. This is the concept behind a black hole. Because a black hole -- or singularity -- is essentially a large mass concentrated at a singular point, the gravity is very strong round that point. For example, being 100 meters above the surface of the earth you would feel little force. But being 1000 meters above the "surface" of a singularity, you would be stretched out like a sphagetti. This is because with the earth, you are farther away from its center. Such also shows why it is *impossible* to dig through the moon. As one starts digging down into the moon, the gravity becomes much stronger, as one is approaching its center(at the center of the moon, gravity is infinite). Eventually, as one digs down to the center, the gravity becomes too much to bear: it will crush one's body like you would squash a bug, turn your bones into dust, and do other unpleasant torturous things to you.
  • Does antimatter have negative mass?

    No, antimatter has normal mass.

    "Antimatter" is a misnomer. It isn't a different form of matter, really, and it isn't a true mirror image of "normal" matter. What makes antimatter different is that an antiproton simply has the opposite charge from a proton. A proton has a charge of +1, an antiproton has a charge of -1. In most other respects, protons and antiprotons are identical. Certainly, they are both massed objects.

    What happens to all the energy that is released in a matter-antimatter collision? Since mass cannot just appear out of nowhere, (1st Law of Thermodynamics?) and can only be converted from energy or energy to matter, wouldn't it stand to reason that since the matter got converted to energy, that the anti-matter got converted to anti-energy?

    No. All the energy that is released in a matter-antimatter collision is given off in a burst of light and heat (mostly heat).

    The weird thing is is that if there is no such thing as anti-energy, what happened to the antimatter?

    It is simply destroyed, with the mass of the antimatter and the matter (the antiproton and the proton) being converted into the light and heat energy given off by their collision. The first law of thermodynamics.

  • The part in the article that bothers me the most is the claim that gravity hasn't been measured at distances smaller than a millimeter.

    I remember reading about an effect that could be measured with a table-top setup. Take to plates and put them really close together. At some distance, they are pushed together without any added force. The explanation was that the photon pressure (or was it some quantum effect?) on the outside surfaces of the plates was larger then the force pushing against the inside surfaces because the gap between the plates was smaller then the wavelength of the ( particle | force ).

    Why not measure gravity at sub-millimeter distances by taking two plates, placing them inside a vacuum chamber that is electromagnetically shielded, including light. If you have a mechanism to very slowly push the plates together, you could put something like springs on each plate and measure the pull the springs are exerting(sp). Taking into account any friction, the force used to move the plates closer and the tension the springs create, shouldn't you be able to measure the tension on the springs to see if the plates pull on the springs with extra force at small distances?
    A millimeter is about how thin a dime is. It's small but we have micrometers that can measure much smaller then that, surely we have devices that can measure very small forces like tension on a spring. All you would need to know for this experiment would be the tension created by the spring along the same distance without the plates to compare with the tension created by the springs with the plates.

    Kelly

    Ideas? Questions? Rants? Raves?
    rants > /dev/null 2>&1
  • I got karma to burn, so I'm not afraid to go -1 offtopic....

    It was a pretty good original post [slashdot.org]. But the downside is that the record companies and artists wouldn't make as much money as they normally do now (unless of course someone wants to buy the song at a few million).

    I also must agree about the moderation. There's no way to stop it. Most people moderate only new articles, and then only moderate other posts that have been moderated up (me-too syndrome).

  • ...the Slashdot Effect, already known to dissipate the strength of powerful servers.


    --
  • And the probability is yet again increased that humanity's last words will be, "It's working!"

    LOL! I always figured humanity's last word would be something like, "Oops."

  • Gravity is weak? (Score:3)

    by Bedemus ( 63252 ) on Wednesday July 19, 2000 @01:00AM (#923002) Homepage
    Could someone give me some background on what precisely makes gravity weak? I never thought of it as anything but normal before. :)
    --
    NeoMail - Webmail that doesn't suck... as much.
  • I believe that these extra dimensions have already been proven to exist through large-scale, multi-decade global experimentation.

    Unfortunately, at this point all 7 other dimensions are filled with unpaired socks, lost keys, and pocket change.

  • Perhaps it didn't have its weetabix?

  • Re:Gravity is weak? (Score:3)

    by cot ( 87677 ) on Wednesday July 19, 2000 @01:03AM (#923012)
    I think it is in comparison to the other forces (Strong, Weak, and electromagnetic) that gravity is weak.

    If you take a proton and an electron, the force between them is going to be completely dominated by the electromagnetic force.

    I forget the ratio of the two, but the gravitational attraction is MUCH weaker than the electromagnetic.
  • Love is surely stronger. Does that propogate through different dimensions? :)
  • That's true. I've heard of cases where test audiences in 1970's sci-fi movies thought something was wrong with the print because there was no sound in space. Hollywood chose to run with the most common misconceptions rather than correct them, and now they propogate them. "Sound in space" is the most forgivable error. Nothing like the old Star Trek "he won't remember what happened when we beam him back to the past because it wouldn't have happened yet" cop-out. The sad thing is, Lois & Clark ripped that off thirty years later, in the episode where H. G. Wells built a time machine and came to visit.
  • Although the prospect of such a exciting new approach to gravity and the dark (or rather 'transparent' since it does not absorp light) matter problem, it needs to be stressed that lack of theories and ideas is not the problem.

    The actual limit on progress in this field is lack of relevant data, obtained either from super colliders or from deep cosmological observations. Currently it is possible to make many models consistent with the observational constraints because it is these constraints themself which are so loose.

    Everybody knows the US killed the giant supercollider program, and the state of affairs in observational cosmology learns that it is very difficult to calibrate measurements of (dark) matter.

    To so something more about the last point, since I've researched this last year, it is far from trivial to yield reliably answers on galactic cluster potentials via dynamic or gravitational lens measurements, especially because you need to go into the Infrared to observe (optical) light emitted by stars in the deep universe. Only recently with instruments like ISAAC [eso.org] on one of the VLT telescopes we are able to obtain high quality near-infrared data. For the far infrared imaging space based missions like the NGST [nasa.gov] are required, because of the polluting thermal radiation from the earths atmosphere. The NGST is still under study and not expected to be launched until 2010!

    Until then we can only speculate aboute the nature of dark matter.

    Ivo

  • Re:Nonsense (Score:3)

    by Darchmare ( 5387 ) on Wednesday July 19, 2000 @01:40AM (#923025)
    ---
    Gravity is related to mass, and electromagnetic forces on charge. How can someone compare the mass of the earth with the charge in the atoms in a magnet? They are totally different things.
    ---

    Exactly. A person could make the opposite argument - that you can place a rock on the ground and it will stay there, and yet remain stationary when you move a magnet over it.

    Or even plop down a 2 ton chunk of solid iron. It's a lot easier to keep it on the ground than to lift it with a magnet.

    - Jeff A. Campbell
    - VelociNews (http://www.velocinews.com [velocinews.com])

  • Re:Quantum String theory? (Score:3)

    by fiziko ( 97143 ) on Wednesday July 19, 2000 @01:42AM (#923028) Homepage
    String theory requires 10 dimensions. It's been effectively replaced by membrane theory, which requires an 11th dimension. They weren't brought in to make the math easier, they were brought in to make it possible. String theory didn't quite pan out, but membrane theory is gaining strength.

    Part of the string theory problem was that there were five totally separate formulations for the theory. Membrane theory allows all five to be related by "gauge transformations."

    A gauge transformation is essentially a freedom within the math. When calculating the potential energy of an object, we need a reference height, generally the height of the lowest place it can go. This is totally optional; we can set "ground level" to be the ground, the ceiling, or the basement. As long as we use the same ground level in all calculations, anything that we can measure or observe will be correctly predicted by the theory.

  • Cross Dimensional Stellar Effects? (Score:4)

    by Effugas ( 2378 ) on Wednesday July 19, 2000 @01:42AM (#923029) Homepage
    I have a simple question.

    Suppose for a moment that, indeed, many universes inhabited this specific multiversee.

    Also suppose that certain extreme events would lead to cross universal leakage.

    We wouldn't need to wait for a particle accelerator to be built to witness such effects--those stellar furnaces known as stars should be a constant source of evidence for reactions so extreme that they violate the bounds of this 3D environment.

    In fact, stellar reactions should be the most mysterious, because they'd contain the most missing energy by far. It's not unimaginable, to be sure. Where I think some things start to break down is that, if there *is* leakgage, the events that cause such things as Gamma Ray bursts would *need* to involve cross universal effects.

    A bigger problem actually with cross universal gravity is that it would cause real problems for universal integrity. In order for multiple universes to to exist in parallel to eachother without any kind of "reinforced wall" between those universes, they must grow in parallel to one another and never blur together. But if gravitation in one universe can extend out towards another, there'd be no way for the parallel universes to remain separate--particularly if the forces equated at short distances, the universes would draw together into one.

    Thoughts?

    Yours Truly,

    Dan Kaminsky
    DoxPara Research
    http://www.doxpara.com

    "Little Caesars? You do pizza?"

  • There's a great collection of essays by a fellow by the name of Michael R. Feltz who describes the possibility that the three-dimensional universe we live in may be built upon a fourth spatial dimension which is expanding. This could also explain gravity if matter is "dragging behind" in this expanding fourth dimension.

    Feltz's essays are located at http://www.cyburban.com/~mrf/ [cyburban.com]. It's really worth checking out, as it gives you some great ways to visualize the fourth spatial dimension, and some interesting insight into the possibilities of the structure of our universe.

    Sometimes the math gets a bit heavy, but the discussion is worth reading.

  • But if gravitation in one universe can extend out towards another, there'd be no way for the parallel universes to remain separate--particularly if the forces equated at short distances, the universes would draw together into one.

    Not necessarily. There has been some recent speculation that the universe is a 3-brane (a 3 dimensional membrane from string theory's big brother M theory). If the universe is a 3-brane, then there could be an infinite number of other 3-brane universes in the multiverse. And since the 3-branes are "atomic" in nature (they can't merge, but may interact), I don't think there's much chance of other universes drawing together. This may be the origin of the above article, because part of the 3-brane premiss was that all the forces except for gravity were confined to our 3-brane universe, but gravity was not.

  • That is the strong force, carried by the 'gluons', which have been around for quite some time now, cant exactly remember how long though.

    Gluons have most certainly existed since the beginning of the universe. Sorry, I couldn't resist... :-)

    Normally, the photons are repelled from each other due to electromagnetism, since like charges repell. But at small distances (like you mentioned) the strong, attractive nuclear force between the particles overpowers the electromagnetic repulsion. So, if you slam two protons into each other at high energies, they tend to stick. In fact, they release energy in the process by losing the potential energy inherent in their separation (similar to a brick losing potential energy when it falls). That's a rough way of putting it but you get the idea.
    The process I just described is two hydrogen ions (aka protons) fusing into one helium ion (2-proton nucleus), which releases the energy of nuclear fusion-- it takes a lot of energy to cause it but you get more energy out than what you put in. That's why if you use a fission bomb as the detonator for a hydrogen (fusion) bomb, it can release 100X the energy of the fission bomb by itself.
    Hopefully that wasn't more background information than you needed...
    Disclaimer: any inaccuracies in my description of the physics are due to me typing this in Windows2K.

  • several comments (Score:3)

    by jetson123 ( 13128 ) on Wednesday July 19, 2000 @09:19AM (#923042)
    • This is science by press release again. There's no link from the press release to any technical report, and the language of the press release seems to be written to attract attention.

    • There are several papers by Arkani-Hamed on arXiv [arxiv.org], if you want to get technical details (although it's hard to tell whether the work referred to in the press release actually has already been published).

    • Modeling the universe with more than 3+1 dimensions to account for the various forces has been common since the 20's, and it's already a big part of string theory. If the press release reflects what's in the papers, it appears, however, that Arkani-Hamed and co-authors are claiming that the extra dimensions are spatially extended.
  • Newton predicting weakening through dimensions? Yeah cool!

    Well, as I said I not arguing against theory itself. I'm arguing against the fact that the article shows a clear distinction between three-four dimensions and two more. There is some sort of strange dessimetry in this story. Gravity weakens due to unseen dimensions. And the other three "feed up the boy"???? What the Hell is this? Physics? Einstein is jumping in his grave man. What tells you that one dimension "strenghts" and other "weakens"??? Third Law and similar stuff to the trashcan? And why it looks like that our dimensions strengthen gravity while the two poor "unseen" weaken it? White-necks, niggers, and red-skins in Physics? Too human for the Universe...

    Well I like a lot of these theories of multi-dimensional worlds. But such idea of "dividing" dimensions the way it is shown in the article is rather ridiculous.
  • So I see that there's this sort of incoherent "Ask Slashdot" question [slashdot.org] that has some insight behind it, and as I'm thinking about the question, it hits me: The way we can do away with copyright's more draconian features without hurting the artists, inconveniencing the consumer, or even putting the record executives out of business. Everybody wins. I mull it over in my head, and it still seems to make sense. I post [slashdot.org] my idea, and go on with trying to figure out why gcc thinks "test" is a char *, but foo() ? "test" : "test" is a const char *. Just about as the sun is coming up, I check my users page, eagerly waiting for (a) huzzahs of praise and increased karma, (b) an enlightening explanation of why my idea is crap, or (c) "Yeah, there's a website like that at..." I find that my post is still (Score: 1). Forgotten. Ignored (with the exception of one AC kind enough to feed my ego). With heavy head and anguished heart, I remind myself that I don't care, because I am not a karma whore. I repeat it to myself about thirty times, start to believe it, check this article, post something that pops into my head, and take a shower. I come back and it's at +3! The slashdot crack speed-moderation team has been busy eating raw methamphetamine, ignoring my other post (the good one), and waiting for me to slip up and post some random brain-fart so they can use up all their points on it, and I fell right into their clever plan! You bastards! You'll never take me alive! You'll never take me alive!

    Jesus. I need to sleep or get laid as soon as possible. This computer shit is bad for your head.

  • Where are the mice? (Score:3)

    by Lonesmurf ( 88531 ) on Wednesday July 19, 2000 @01:43AM (#923050) Homepage
    What I'm wondering, is what this has to do with mice? I mean, since it is Science and it was posted on /., it HAS to have a mouse that was genetically engineered, right?

    RIGHT?

    --

  • Re:Nonsense (Score:2)

    by Anonymous Coward
    The notion sounds deceptively simple: besides the familiar three dimensions of space there may be other dimensions, too small to see yet perhaps as large as a millimeter.


    Dimensions do not have a size. Objects have sizes in a set of dimensions.

    In this description of the universe, some dimensions do have a size. You are perhaps familiar with the idea that the universe is closed -- ie, travelling along a geodesic will take you to where you started. You can imagine a 2d closed universe as a donut with n holes (n=0 gives a sphere) .

    But you don't need to have all dimensions closed. You could have some dimensions curl up on themselves (topological compactification) and others that stretch out into infinity. The 2d example of this is a very long paper towel tube.

    And finally, you can have some dimensions curl up much more tightly than others. 2d example again: the hula-hoop. A 2d scientist living on a hula hoop might not realize he is in a 1-holed donut shape, since part of the curvature tensor is so tight. Instead, he may think he is a 1d scientist living in a circle.

    That is what this idea is all about. Using scary mathematics you can imagine any number of additional tightly curled dimensions to our apparently 3d universe. The question of what effect these extra dimensions would have, and how we can test for them, is what people are working on.

    So far it is an exciting idea, but there have been no huge breakthroughs lately. I am much more interested in lattice QCD computation, but that is more personal prejudice than anything else.
  • Maybe the problem is that the force of gravity is a differential effect where em is a direct one?

    So far I've never need a decent case presented that says gravity pulls and isn't a push effect. Of course that would be as hard to prove as the differnce between gravity and acceleration.

    For example the early theory of gravity involves being puhsed from all sides. This has been proven to be infeasable (One of Fynmans books makes a good but flawed case of this) Think about a field pushing (like the wind), now imagine a wind from the other direction and then all directions. Where does an object get pushed? Now model it like you've got gravity particles moving at c that have a 1/bignum chance of hitting and interacting with something with "mass". Now go model that. If the things move at c you end up with a model that does a number of spooky thigns as v -> c. You get measurable time dialation in clocks. You also get the infinate mass problem, can equate acceleration to gravity and kill all the "true black holes" while explainging some strange activity out of massive objects. But its just a theory and has apparently been disproved.

    I figure G isn't a constant because we have spiral galaxys and you can't do that if G is a constant.

  • It's testable (Score:3)

    by Animats ( 122034 ) on Wednesday July 19, 2000 @09:33AM (#923056) Homepage
    The important thing about this theory is that it makes testable predictions. Scientists are already working on testing those predictions. We'll know in a few years.

    If this checks out, it could lead to a new era of physics research as productive as the first half of the 20th century. Too much of recent work in physics has revolved around explaining cosmology or developing theories that involve energy levels far beyond our reach. But this gravity theory leads to something that can be worked on. That's where new technology comes from.

    Science is prediction, not explaination. - Fred Hoyle.

  • Leptons refer to the "light" particles. There are six leptons known of today, the electron, the muon, the tauon, the electron-neutrino, muon-neutrino, and tauon-neutrino.

    Their are six flavors of quarks, the combination of them produces the mesons and hadrons. The mesons are particles like Kaons, they are the middle particles composed of two quarks. Protons and neutrons are examples of hadrons, or heavy particles composed of three quarks.
    The 6 flavors of quarks are:
    Up
    Down
    Charm
    Strange
    Bottom (originally called beauty)
    Top (originally called truth)

    Each of these quarks have their respective anti-quarks. The proton has the combination of Up Up Down, and the neutron has Up Down Down. Quarks are always found in groups of two or three, the search for a single quark is being conducted but many believe that it will never be found. The last quark to be found was the Top quark, and it was theorised many years before it was actually found. There is a lot of research still be conducted on Top quarks because they are so new to the playing field.

    There are a couple other fundemental particles that no one has mentioned. Those are the force particles and the Higgs Boson Field particle.

    Both quarks and leptons are considered fermions, which is the classification of any particle with spin 1/2, 3/2, 5/2... The fundemental force particles, the photon, Z, W, gluon, and, assuming it exists, the graviton are considered bosons, or those with integer spin. All of those, except the graviton have spin 1, while the graviton has spin 2. The Higgs Boson is the really wierd one, is theoretically has spin zero, and is the fudge factor for giving particles mass in the standard model (its existance also breaks the standard model because it would technically have infinite mass).

    There are theories out there like Supersymmetry which believe that at high energies all fundemental particles and forces have a supersymmetric partner. This supersymmetric partner has +/- 1/2 spin off of the low energy particle/force, so a fermions supersymmetric partner is a boson, and a bosons partner is a fermion. If Supersymmetry is true then we will roughly double the number of elementary particles.

    If you want to learn more about particle physics then go to the particle data group site [lbl.gov].

  • I often used what's known as Cp, or the CausticPuppy constant, which is unitless.

    It's not a universal constant, since its value changes from problem to problem, but it is a constant within the scope of any one problem.

    Cp is the value by which you multiply your answer in order to equal the answer given in the back of the book (or the "expected result.")

    It's best used if you bury it somewhere in the middle of the math, because hopefully the TA who's grading the papers won't follow too closely.
  • One theorem I read about tried to explain dark matter with a similar concept:

    "Dark Matter" is of course the name given to some substance that has mass, but neither absorbs nor reflects light. According to many calculations, the visible universe should weigh much more than what we can account for with telescopes.

    This theory stated that "Dark Matter" may be a manifestation of mass sitting outside of our three (four?)-dimensional universe, undetectable to all of our instrumentation. The idea is that the gravitron is the only subatomic particle that's capable of jumping through dimensions, and therefore makes its presence felt even though we can't find any mass to associate with it.

    All this is way beyond me.

  • We wouldn't need to wait for a particle accelerator to be built to witness such effects--those stellar furnaces known as stars should be a constant source of evidence for reactions so extreme that they violate the bounds of this 3D environment.

    Except that the reactions inside stars are not that energetic on a particle-by-particle basis. To study these effects, we need huge energies in a single collision, not a bunch of (relatively) low energy collisions that happen next to each other.

    As far as the accelerators go, they've already far exceeded the energy of events that happen in a star. In fact, a single collision in today's accelerators is of comparable energy to a single collision a fraction of a second after the Big Bang. That's still not quite enough energy to test this. The SSC would have been nice, with its 17TeV (I think) collision energy, but that's been mothballed. However, the 14TeV proposed collision energy for the LHC at CERN (under construction at this very moment) is going to break a lot of new ground.

  • Re:Gravity is weak? (Score:4)

    by Chops ( 168851 ) on Wednesday July 19, 2000 @01:51AM (#923075)
    Moreover, if the force of gravity increases dramatically at short distances, it may be possible for the next generation of accelerators -- such as Europe's Large Hadron Collider scheduled to begin operation in 2005 -- to create black holes, regions smaller than the radius of the extra dimensions where gravity is so strong that nothing can escape.
    And the probability is yet again increased that humanity's last words will be, "It's working!"
  • We can laugh, but there are a lot of people who ask this question seriously every time physicists push the envelope a bit further. (Last time I checked we didn't collapse into a Bose-Einstein Condensate or become a strange(r) planet.)

    For people who are worried about micro black holes, remember two compensating factors:

    <ul>
    <li>Hawking radiation should quickly evaporate it
    <li>Even if it doesn't, this black hole would be so small that the earth would look as empty as interstellar space to it. It would quietly orbit within the earth and very, very, very, very rarely hit a proton (or quark?!) head-on.
    </ul>

    David Brin (astrophysicist by training) discussed this in _Earth_. I don't recall the mass of a black hole which could ultimately consume the earth, but it's a lot heavier than you would expect - equivalent to small mountains (or larger!)
  • Actually, no.

    The "we just haven't found it" argument has many flaws, not the least of which is that you can look as long as you like on Earth, you're not going to stumble across a unicorn.

    Also, let's talk about what negative mass entails: If you go for negative mass, I'll use the kiddie E=mc^2 and point out that negative mass would lead to having negative energy (don't confuse this with potential energy, or a negative differential).

    Now, if negative energy was an "allowable" number, we would see all kinds of very odd things in quantum mechanics that we do not see, at all, and we'd expect to see them quite easily. They haven't been observed yet. Basically, think about the creation of two particles, one with positive energy, one with negative energy. This wouldn't violate any conservation laws (assuming you made one a baryon and another an anti-baryon, charges opposite, blah blah). We would then see particles simply appearing out of nowhere and staying there, all the time. The vacuum would blaze up and be, well, solid particles. We don't see this, ergo, no negative energy, ergo, no negative mass.

    Now, you could "decouple" the two numbers and say, "perhaps the 'mass' in gravitational attraction doesn't have to do anything with the 'mass' in E=mc^2." Unfortunately, that's also a problem if you look at anything in General Relativity.

    As for the "other forces," we keep looking. Every so often they'll revive a fifth and sixth force routine, I think the last time I remember that happening was circa 1990, but it has yet to pan out.

    Also, only in EM fields do the same charges repel. In strong, they hook to each other, there's no real analogue of "charge" there, unless you count baryon number. Weak I'm not so sure about, you have to start talking about neutral currents and stuff my profs never got to when I got my degree.

  • Also suppose that certain extreme events would lead to cross universal leakage. Hmm. This explains the weird phenomena that accompany downhill mountain-biking, street luge, and bungee jumping.

  • >Ehm, excuse me but doesn't the phrase "comparing apples to oranges" come to mind here? I mean how the hell can you compare two forces with completely causes? It is just as absurd as saying that 1 gram is more than 1 coulomb. Gravity is related to mass, and electromagnetic forces on charge. How can someone compare the mass of the earth with the charge in the atoms in a magnet? They are totally different things

    Gravitation coupling constant = 2piKM^2/hc = 5.3*10^-38.
    electromagnetic = e^2/2hc = alpha = 1/137
    weak = G_F8piM^2c/h^3 = 1.02 * 10^-5 (even though weak and electro are the same thing)
    strong = alpha_s =~ 1

    Hence gravitation is extremely weak
    Also, they are all charges, just difference kinds of charges, gravitation is carried by the graviton, and is the gravitational charge, strong is the colour charge, weak is the weak charge, and electro is the electric charge -- they are all analagous.

    >Dimensions do not have a size. Objects have sizes in a set of dimensions.

    Since I am only a 3rd year uni student, I cant comment much on on this, but I know the article is correct however.

  • Okay, I've got my asbestos on, so flame away.

    Here's what I think is really going on. Gravity isn't us being pulled toward the earth, it's us being pushed towards it. Why do I think this? The Zero Point Energy field. It's everywhere. Einstein always said there was more than enough energy in the space occupied by a coffee cup to vaporize all of Earth's oceans. He wasn't talking about the strong nuclear force, you know, the one that makes the wonders of atomic weapons possible. No, he was talking about the energy inherent in space-time itself. It's everywhere -- not only in pure vacuum, through which it constantly streams unobstructed, but also both inside and outside every object, every atom, every *thing* that exists. It's what keeps the negatively-charged electrons orbiting an atom's nucleus instead of spiraling right down into it, attracted there by the positively-charged proton. Because it's everywhere, it exerts a force in every direction. This force extends outward without bound, its strength decreasing with distance. It also interacts with matter, which "blocks" it somewhat. And what happens when a force meets resistance? It tends to push that resistance in the same direction as its force vector; at the same time, some of its energy is consumed by the work it does (moving the matter it hit). But what happens when this force is pushing on an object from *every* direction at once? You might think it'd crush it. Nope. Remember; to be crushed, there would have to be a "pressure" or force differential between the object's inside and outside and, as explained previously, the force is equally pressing from both within and without the object. This is analogous to our own very observable situation on earth. We exist under a rather thick layer of atmosphere. Right now, there are millions, if not billions, of tons of force pressing down on your head from the weight of the air above you. Why aren't you crushed under all that weight? Because there's an equal force balancing it from the opposite side. (Just trust me on this one.) Same thing with the ZPE field.

    So here we have this great big giant ball of matter we lovingly refer to as "Earth." It, being made of matter, presents resistance against the force of the ZPE field, and it dissipates some of that force before it gets all the way through the earth to the other side. Now, because all the energy coming from every side of the earth interacts with the earth's matter in the same way, with resistance, it doesn't push the earth in any one direction -- just like the air above your head doesn't push you right into the ground. But think now of something sitting ON the earth, something that can be considered part of its matter. Something like you, sitting there at your computer. You too have ZPE energy coming at you from all sides; up, down, inside, outside, left, right, etc. But because the earth, in interacting with it, is shielding some of that energy by absorption during its travel through the earth (some comes from beyond the other side of the earth from you, some comes from 12 feet under your chair, some comes from .001 millimeters under your butt sitting on the chair, etc, but all of it is absorbed in some way by passing through matter), there is NOT a net zero ZPE force acting upon you. There is in fact more of it pushing you down from the relatively unshielded "Up" direction than there is from the highly shielded "Down" direction; therefore, you are pushed down towards the center of the earth, and the force with which you are pushed is in direct correlation to your mass and the earth's mass. Does that sound familiar? :)

    Now think of a black hole. Eerie, scary things. They are of course extremely dense collections of matter, where even the electrons can't orbit because it has been crushed so competely. In ordinary matter, there is LOTS of empty space; a neutrino could pass all the way from your forehead to the sole of your right foot without even touching any of the matter that makes you up. That's why only a very very small percentage of the ZPE energy interacts with you in a direction that isn't balanced from the other side (ie, through the earth) -- because there's very little there to interact WITH. But what about a black hole? Very very dense, trillions of trillions of trillions of trillions of trillions of tons of matter all smashed into a tiny ball -- there isn't ANY free space inside it; it's all matter. So what does that mean? Yep; ALL the ZPE energy gets absorbed by interacting with it, from every direction, and so the energy flowing from behind you, through you, and towards the black hole isn't balanced by anything pushing back FROM the black hole -- and you are completely crushed into it.

    This is also why there is such a thing as the Gravitational Constant. It refers to the amount of interaction between the ZPE energy force and matter. It is very very small, and is multiplied by the mass of two objects to determine the amount of gravitational attraction between them (the GxM1xM2/d^2 formula). That number, "G", is literally how much of the energy in the ZPE field gets absorbed by passing through one kilogram of matter. Let's get into a bit of math here...

    The gravitational force, in Newtons, between objects having masses of M1 and M2, in kilograms, and separated by a distance of d, in meters, is the product of the two masses divided by the square of the distance between them... multiplied by G, which is 6.673e-11 Newton-meters squared per kilogram squared (the odd units associated with G are there so they cancel out all the units in the formula other than the result, which is in Newtons). Two 1-kg objects separated by 1 meter would yield Gx1x1/1x1 Newtons, or 6.673e-11 Newtons. Not very much. This means that most of the ZPE energy passes through these objects unobstructed. But how much doesn't? Literally, "G" doesn't... thus, 0.000000006673% of the energy gets absorbed and translated into "motion" by pushing the matter in the direction in which it is imbalanced. I may have said it before, but it's worth repeating: Nature doesn't abhor a vacuum. Nature abhors imbalance. All things will seek balance. That's how you can siphon gas out of your gas tank, and that's why you get pushed to the earth.

    Let's take a more realistic example: you and the earth. You have a mass of, let's say, 80 kg (176 pounds); the earth's mass is 5.974e24 kg (rather a lot of pounds). The distance from you to the earth isn't 0, as you might think; it's the distance from your center of mass to the earth's center of mass, which is roughly 3,185,500 meters. So plugging all that crap into the formula, we get 4.71e+13 * G, which makes 3,142.83 Newtons of force pushing you to the earth. G is the percentage of "gravitational" energy that gets absorbed or deflected by its interaction with the matter making up you and your body.

    I haven't completely worked out ALL the math yet, but something tells me this is right. It answers all the unknown things about gravity, it explains momentum and inertia, it explains what keeps atoms from just collapsing into themselves... hell, it might even be the definition OF matter. So come on; let's see you armchair physicists blow some holes in my theory...


    "The best weapon of a dictatorship is secrecy, but the best weapon of a democracy should be the weapon of openness."
  • Nope. If gravity pushes in a mostly uniform way in all directions but can be blocked slightly by mass, the observable results would be exactly the same.

    The only reasonable proof is based on the fact that if gravity pushes, it would slow down everything which observing things in deep space appears isn't happening but space probes with very good clocks are slowing down. The GPS sats are slowing down and they are missing their predicted orbits by a few meters a day. Gravity probe-b should help quatitize these issues as well as adding a gps recivers on the new gps sats.
  • I have been watching sci-fi shows and movies for a number of years about parallel dimensions, during that time you tend to develop your own theories about 4th dimensions.
    From what I have gathered, for every choice we make there is an infinite amount of possibilities and from those possibilities an inifinite amount of alternate universes are created. Each universe is unique. And the theroy of a paradox, a loop error (example: I go back in time and kill my mother before I was born, I was never born, but then how could I have killed my mother...endless loop), is in fact only half true. If you make a change in the past you begin to exist in an alternate reality and you would continue on. (Reference in Back to the Universe: "...it would destroy the entire universe, however it would probably be limited to our own galaxy"....almost true; you'd never return to that universe (but it would continue on as normal without your existence.)

    Now getting back to the gravity theory. If in fact gravity is a constant and you could effect changes in one universe and affect anothers, then it would make the above theory false. There would have to be a universe that would not be affected by the action of creating that change. It'd be as if you created a paradox in every other universe (affected some change that should not have happened because they did not do it).

    I believe this gravity theory to be false
  • From a Newtonian perspective Gravity acts instantly. If the Earth needed to wait 8 minutes for the suns gravity to hold it in orbit we would spin off out of the galaxy. A physician named Laplace postulated this in 1825.

    I would imagine that the best place to measure the propagation of gravity would be in an event such as a supernova. There are tremendous energy to mass conversions that would effect the gravity between the supernova and an observer on Earth. If Gravity propagates instantly you would get a different event observed on Earth than if gravity is limited by the speed of light and a "gravity wave" traveling at the speed of light is unable to overtake and slow down or blue shift the radiation traveling towards Earth from the supernova. When you ask what is the speed of gravity is from this perspective you are really asking how accurate is your stopwatch.

    Physics according to Einstein uses the speed of light as a limit to gravity propagation non locally. The relativistic calculations work for many applications, but they are not very easy to use for doing things like calculating satellite orbits.

    I guess it all depends on what you want to do with a calculation. When I go to a restaurant and need to calculate a tip it is easier for me to move the decimal point in my mind than try to do it out on paper. I have friends that make their children do it out longhand on paper for the practice.

  • I propose... (Score:5)

    by MupwI ( 152455 ) on Wednesday July 19, 2000 @01:08AM (#923121)
    Hyperspatially Orthogonal Transmission of Gravitational Rays In Twisted Space, or HOTGRITS for short...
    Damn...I think I've just used up my day's supply of long words...
  • No.

    Definitely not right.

    Never confuse equality of quantity with equality of property. Example: A dollar buys me two dollars. However, apples are not the same thing as dollars. Apples are tender, dollars are legal tender. Apples are round, dollars are rectangular and flat.

    Conversion may occur under some limited conditions, as well.

    For example, I may not transform an electron directly into energy. You gasp! No, I'm not kidding. I have to have an electron and a positron to do that. Nor can I convert a photon into just an electron.

    Saying that "mass=energy" and "charge=energy" ignores all kinds of basics, like conservation of baryon number, conservation of lepton number, conservation of charge, etc.

    Matter and energy are not the same two things. You may exchange one for another, under limitations, but don't think that they are in any way identical.

  • I think it is in comparison to the other forces (Strong, Weak, and electromagnetic) that gravity is weak.

    You're right. The difference is a factor of about 10^-15, IIRC. This is just in terms of the "coupling constants", and doesn't depend on the charge of the body. (The coupling constants are related to Coulomb's "k" and Newton's "G". Also, "charge" usually means electric charge, but it could be any charge. A gravitational charge is mass.)

  • One of the reasons we feel more noticeably the effects of gravity is our size. We are (in the scheme of things) really rather large, and have an exact balance of electric charge, so we don't conciously "feel" any electromagnetic pull.

    Different size animals have their world dominated by different effects. To paraphrase something i read somewhere: if you drop each of these animals from a height of 5m:

    • an insect flutters to the ground very slowly
    • a mouse is unharmed
    • a cat is unharmed - if it lands correctly
    • a man breaks his legs
    • a horse splatters
    There are other effects dominating other animals - eg. insects that live on the surface of water are so small that gravity is (for them) irrelevant compared to the effects of surface tension.

  • Re:why not electromagnetism (Score:2)

    by Anonymous Coward
    In the original proposal [arxiv.org], they suggested that the reason why only gravity can see the extra dimensions is because all of the Standard Model gauge fields are "trapped" on a subsurface of spacetime, either due to topological defects or string theory effects. (The latter I think is because in string theory, gauge fields can be confined to branes.)

    As for experiments... well, the article discusses experiments to test for the existence of these "large" extra dimensions, but "small" (Planck-scale) effects are much harder to see.

  • Re:Nonsense (Score:5)

    by stevelinton ( 4044 ) <sal@dcs.st-and.ac.uk> on Wednesday July 19, 2000 @02:06AM (#923137) Homepage
    Actually this is a perfectly sensible and serious theory, which has been around for 10 or 15 years, in various guises, it has just suffered from abbrevation and simplification.

    Regarding the comparisons, if you take any fundamental particle in the universe which actually has both mass and charge and place an identical particle at rest 1m away from it, the electrostatic force between them exceeds the gravitational by many orders of magnitude. If you want a theory that explains both electromagnetism and gravity as aspects of the same thing (which is generally considered desirable) then it has to explain this huge discrepancy.

    Regarding the dimensions, imagine a 1mm^2 two-dimensional creature living on the outer surface of a garden hose. It has two very different dimensions: along, which is practically infinite (althoiugh explorers may claim to have reached the mythical "tap" and "spout") and around, in which you can go only a few dozen body-lengths before you get back to your starting point.

    Actually an even closer analogy would be to imagine creatures living on the hose big enough to actually wrap round it in places. Fundamental particles are supposed to be entangled with the extra dimensions in this way.

  • So far I've never need a decent case presented that says gravity pulls and isn't a push effect.

    I'm not sure what you mean by a "push" effect. There are two possible interpretations I can think of. First (and least likely), you mean gravity can be repulsive. Repulsive gravity has never been observed. The second (and more likely) interpretation is that the interaction of gravity involves mediating particles that push instead of pull. ie. When body A is gravitationally attracted to body B, A is in between B and the mediator, rather than have the mediator in the middle.

    This is a little tricky. You probably learned that energy and momentum is always conserved. Well, that's not quite true. (I don't want to get too wordy here; when I say "true", I mean "consistent with the theories currently accepted by the people doing this research.") In fact, Heisenberg's Uncertainty Principle allows the Universe to cheat. Particles produce fields around them, full of whatever particles mediate the forces that particle can feel. These mediators are created from nothing; energy is borrowed from the Universe. They can do this, as long as they can't get caught. Heisenberg's principle gives conditions under which this energy violation can never be measured. As long as it can't get caught, it can break any rule it wants.

    This lies at the heart of the current explanations of forces. Mediating particles appear and disappear, and transfer energy and momentum from one particle to another. These can act to repel or attract two objects, according to their charges. The electromagnetic force has infinite range because its mediator is a photon; light has no mass. Massless mediators can have arbitrarily low energy, and can therefore live an infinite amount of time. The weak nuclear force, on the other hand, can choose any of three mediating particles, but they all have mass. Since mass and energy are equivalent (as shown by Einstein), there is a minimum amount of energy needed to conjure up that much mass. That's why the weak force has an effective range on the order of a few Angstroms.

    The current proposal for gravity involves a massless mediator that has never been observed. (The mediators for all the other forces have been produced in particle accelerators.) Having the mediators go around the object to come in from behind means it has to live longer, which reduces the amount of energy it can have. Nothing prohibits it, but the most efficient mediators will take the shortest path between bodies A and B.

  • Gravity is weak (Score:3)

    by Inoshiro ( 71693 ) on Wednesday July 19, 2000 @02:34AM (#923142) Homepage
    Because G is small.
    The equation for measuring the gravitation force between two objects is the same as the equation for measuring the electromagnetic force between two objects, except for the constant.

    If you want to figure out why gravity is weak, figure out why G is small. There are a lot of "magic numbers" used in physics that were measured through experimentation, but which have no explanation. As a programmer, I find the situation intollerable :-) I'd like to know why G constant is the way it is.. what does it stand for? The number of angels who can dance of the head of a pin? The number of massless spin 2 bosons which can fit into a 3x3 room which has a 2.5 people in it?

    Once we know where the magic numbers come from, we'll have a better chance of understand how things work on the lowest (i.e.: quantum) levels where they likely originate.
    ---
  • Gravity is an attractive force because the "gravitational charge" - mass - is always positive.

    Doesn't quite cut it - if that were the point, then you could always say that humans simply haven't discovered the "negative charge" yet. But all particles known to man have the same kind of "charge", and the force pulls them together whereas with all the 3 other forces, objects with the same charge are pulled apart!

    And that is the fundamental difference between gravity and the other forces, besides its weakness.

    Interesting idea: if gravity didn't have the "same chrage attracts" property and there were different charges, it would be so weak as to be immeasurable. Perhaps there are dozens of yet undiscovered forces that are as weak as gravity but follow the "different charges attract" principle?

  • Took me about 30 minutes or so. Pretty sad if 98% of people can't do it.

    Rob: We need a spoiler tag!!!

    House 1: Norweigan, Yellow, Dunhill, Water, Cats.

    House 2: Blue, Horses, Blends, Dane, Tea

    House 3: Milk, Red, Brit, Pallmall, Birds

    House 4: German, Coffee, Green, Prince (THIS IS THE FISH!)

    House 5: White, Beer, Bluesmasters, Swede, Dog.

  • Somebody else posted a cool link, but I don't have moderator points to bump it up. I do, however have karma to burn, so here [corepower.com] it is.

  • Re:Gravity is weak? Yes. (Score:3)

    by sela ( 32566 ) on Wednesday July 19, 2000 @01:14AM (#923157) Homepage

    Gravity IS the weakest of all known forces of nature. If you compare the force of gravity to the other forces: weak&strong nuclear force and electro-magnetic force, than gravity is far far behind.
    The fact gravity is felt strong to us is just because any other force is balanced on large scale, and thus we feel only "residual" force. There are positive and negative electric charges, whereas the strong nuclear force is created by three-color quarks that balance each other.
  • Yes, I read this, but the article doesn't explain what basis they really have to say that the other natural forces have a reason to be compared to gravity. As I said, I'm no scientist, but wouldn't they need some basis other than the old Sesame Street line of "One of these things is not like the other?"
    --
    NeoMail - Webmail that doesn't suck... as much.

  • Nonsense (Score:5)

    by garnier ( 204518 ) on Wednesday July 19, 2000 @01:16AM (#923163)
    Anyone with a good scientific background can see that this article is very flawed. Here are some examples:

    Although we think of gravity as strong -- we can get hurt if we fall down -- compared to electromagnetism, gravity is astonishingly weak. It takes the gravity of the whole Earth to hold a pin on a tabletop; a toy magnet can lift it easily.

    Ehm, excuse me but doesn't the phrase "comparing apples to oranges" come to mind here? I mean how the hell can you compare two forces with completely causes? It is just as absurd as saying that 1 gram is more than 1 coulomb.
    Gravity is related to mass, and electromagnetic forces on charge. How can someone compare the mass of the earth with the charge in the atoms in a magnet? They are totally different things.

    The notion sounds deceptively simple: besides the familiar three dimensions of space there may be other dimensions, too small to see yet perhaps as large as a millimeter.

    Dimensions do not have a size. Objects have sizes in a set of dimensions.

    I hope Sla
  • Alcohol must have some sort of local effect on gravity. It has been my experience that the more I drink, the more inconsistent gravity becomes. Alcohol must cause these little nano-blackholes to come into existence. That would explain why doing simple things like trying to walk a straight line, or setting a bottle on a table, are so difficult when completely blasted. Other intoxicants like pot or acid or nitrous oxide don't have this effect. Yeah, it must be the alcohol.

  • Re:ts.ts.... (Score:3)

    by streetlawyer ( 169828 ) on Wednesday July 19, 2000 @01:18AM (#923167) Homepage
    Perhaps you should have turned round and asked the doctorate in physics, behind you.

  • Gravity bombs (Score:3)

    by slickwillie ( 34689 ) on Wednesday July 19, 2000 @07:47AM (#923168)
    Does this mean that we will be able to build gravity bombs so we can preemptively defend ourselves from invasion from those other dimensions? "Let's 'grav' those suckers before they decide to come over here and take our stuff."
  • This is starting to sound too much like the Seth books. In one of the books (don't remember which one) he claims matter is time-shared between dimensions. So we get our little time slice, then we are suspended and some other dimension gets a chance to "run". (He didn't mention what happens if our swap space gets corrupted though.)
  • When I was reading through some topology book when I was in high school it seemed to make perfect sense to me that if folds of the universe were sufficiently "close" to each other (perhaps even *overlapping) that they could have some sort of interaction. In fact, this is what wormholes are (supposed to be).

    Just imagine a tablecloth on a table. Now ruffle it up. The surface of the tablecloth is actually a three dimensional world. If you trace your finger accross the surface you are travelling in space. But what if you could "jump" through a ruffle, from the upslope of the ruffle to it's downslope (or vice versa). What if a magnet on one side of the ruffle attracted a piece of metal on the other side "through" the tablecloth. That is sort of what this theory is saying. Close folds are having a dampening affect on the local gravity. The best theories are the ones that just "make sense" in retrospect.
  • Comment removed based on user account deletion

  • Again we are the center of the Universe (Score:3)

    by Ektanoor ( 9949 ) on Wednesday July 19, 2000 @02:48AM (#923176) Journal
    It is quite an interesting article. However it shows an all-time stereotype that we are some sort of center. It seems that Relativity teached absolutely nothing to a bunch of monkeys that just came out of the trees.
    What if this, "our" Universe is just a projection of much larger structures? No we are not looking through 3-4 dimensions over two or five or seven more. We could be folded in three dimensions that result from something much larger and bigger. Or "our" Universe could be the result of the intersection of two or more "meta-Universes".

    You may argue quite strongly with this. Well I'm not pointing how the Universe is made. I'm pointing on how we look at the Universe. Imagine that our Universe is made of five dimensions. What tells you that you are "in the center of it"???? You could well be in the first three or last three. The two other you don't see, feel, taste. As much as what you see is just a 0,01% of what sorrounds you. Besides you see nothing. All what you "see" is the result of how your eyes and brain produce out of something beyond you. Forget about radio waves, infra-red, ultra-violet, X-rays, your sunglasses and your short-sightness and you can still say "I see the world" with the same success.

    When one talks about "other dimensions" should be very careful. Because it will be quite serious the problem on how we are positioned to them. I would wildly laugh if suddenly anyone found the "originator" of gravity in the dimension next to us. No one knows how exactly gravity is made of. And G is, until the biggest mistery of all. I consider that this article fails in this little thing. It considers gravity as "weakening" through dimensions. Could it be that gravity is born from "travelling" through them? We are talking about dimensions. This is not a thing that stays next door. It is in every quantum of our Universe. a dimension determines a section of the space. And we live in it.

    PS: Again about relativity. For the hard-thinkers. What is the correct theory: geocentrism or heliocentrism. Note: both are correct. The problem is that it is much simpler to calculate planet dynamics from a heliocentristic point of view. However if you are hard in maths we can do this from a geocentristic point of view. The problem is that you have to do a lot more of maths to achieve this. And be quite careful about forces and gravity. However it is done. Many observational tasks are made from a goecentristic point of view. Middle Age geocentrism failed because it ignored completely Dynamics and mixed everything in a mystical-religious-political pan. However you still can say with some success that you are in the center of the Universe. The problem is that you have to be a damn mathematician to do it...

  • Re:Gravity is weak? (Score:4)

    by fiziko ( 97143 ) on Wednesday July 19, 2000 @01:19AM (#923179) Homepage
    That's why it's only a proposal waiting to be tested. Scientists have been trying to combine all the forces of nature into one coherent picture for years. The electric and magnetic forces were combined in the last century, joined with the weak nuclear force twenty years ago, and joined with the strong force afterwards. Gravity is the only force that hasn't been pulled into a single, coherent view. Maybe it never will be brought in, but the idea of one force being completely independant of the others raises a whole new set of questions.

    Basically, there's no reason for it to be the same, and there's no reason for it to be different, so scientists are checking out all the options.

  • Hi. Read this: http://www.kuro5h in.org/?op=displaystory&sid=2000/7/18/122257/231 [kuro5hin.org]. Please don't b-slap me; this is important!

    --

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