Follow Slashdot stories on Twitter

 


Forgot your password?
Close
typodupeerror
×
Science

Reflected Gravitational Waves 329

Posted by kdawson from the could-prove-useful dept.
WSOGMM sends in an arXiv blog post about reflecting gravity waves. The speculation is that reflected gravity could go some ways toward explaining the odd readings being returned by Gravity Probe B. "In the couple of weeks since he introduced the idea that superconducting sheets can reflect gravity waves, Raymond Chiao from the University of California, Merced, has been busy with a couple of buddies working out how big this effect is... Chiao and co. ask how big the effect of a gravitational wave on a thin superconducting sheet is compared to the effect on an ordinary conducting sheet. The answer? 42 orders of magnitude bigger."
This discussion has been archived. No new comments can be posted.

Reflected Gravitational Waves More

Reflected Gravitational Waves

Comments Filter:

  • We now know the question to the answer... (Score:4, Funny)

    by Anonymous Coward on Tuesday March 24, 2009 @04:35AM (#27309315)
    Douglas Adams gave us that answer forever ago.

  • This can't be a coincidence (Score:3, Funny)

    by saibot834 ( 1061528 ) on Tuesday March 24, 2009 @04:39AM (#27309325)

    The answer? 42 orders of magnitude bigger.

    Either that's a scientist's prank or Douglas Adams really was right [wikipedia.org]!

  • Cue the Douglas Adams references! (Score:4, Funny)

    by bonch ( 38532 ) on Tuesday March 24, 2009 @04:40AM (#27309333)

    Attention wannabe comedians:

    There is a 42 reference in this story. This your cue...this is your chance..the spotlight is on you to bring humor to the world and make countless references to Douglas Adams. Because he mentioned the number 42 in a book!

  • ...how many superconducting sheets do I need to make a hoverboard?

    • Re:So... (Score:5, Informative)

      by strawberryutopia ( 1301435 ) on Tuesday March 24, 2009 @05:06AM (#27309459) Homepage

      Nine thousand and one

    • Re:So... (Score:5, Informative)

      by Yvanhoe ( 564877 ) on Tuesday March 24, 2009 @05:17AM (#27309511) Journal
      IANA Physicist but my understanding is that while gravitational waves can be reflected, it does not affect gravity at all. It is akin to having a grid reflect waves on the sea but still letting water flow through it (yes I know, these metaphors suck)
      • no, in this case gravity waves = gravity. It is like light waves and superconducting sheet being mirror.

      • Re:So... (Score:5, Informative)

        by FTWinston ( 1332785 ) on Tuesday March 24, 2009 @06:13AM (#27309755) Homepage
        IAAP (ok i used to be), and I commend this distinction - its important to realise that gravitational waves are not the same thing as gravity.

        Gravity is (from one point of view) just the curvature of spacetime. Its the large sagging indentation in the rubber sheet of spacetime that a massive body creates. Gravitational waves are fluctuations in this curvature, not gravity itself.

        The distinction is somewhat akin to acceleration and velocity - consider a car (hurrah!) travelling with a very high velocity, which accelerates very slightly for a short period. If you could reflect the velocity, it would turn around instantly. Reflecting the acceleration however, causes no immediately obvious change. The car's still travelling bloody fast, in the same direction.

        The gravitational waves caused by the earth's motion & rotation are so minute that gravity probe b's measurements, taken over a whole year, still took many months of processing before they could even be detected. Gravity waves are far too weak to have any practical purposes, and certainly not in "anti gravity".

        • Re: (Score:3, Interesting)

          by locofungus ( 179280 )

          We then have to ask what happens if you vibrate the semiconductor in a non-uniform but static gravitational field.

          The ultimate success would be a gravity shield where we could setup standing waves that nulled out the gravitational field. Even if it turned out that the energy required to do this matched the gravitational potential energy of any object that had it's gravity nulled it would make a fantastic addition to a space elevator, the climbers would now only need to carry enough energy to overcome fricti

        • I never got that, nor did my physics teacher (who started out as a real physicist.) If we imagine gravity as a deflection in a rubber sheet, why does the object "fall" into it? Because it would only do so if there was an external gravitational field parallel to the deflection. In the absence of that field the object would presumably travel through the space time deflection with unchanged velocity, whereas the analogy requires it to change path so as to lose potential energy and gain kinetic energy as a resu

          • Re:"Indentation in rubber sheet" (Score:4, Insightful)

            by vegiVamp ( 518171 ) on Tuesday March 24, 2009 @07:21AM (#27310151) Homepage

            This is what's commonly referred to as "overthinking it".

            You're given an analogy so you don't have to understand the entire ruleset. If you then attempt to apply the ruleset that the analogy was trying to keep you away from, well...

          • Re:"Indentation in rubber sheet" (Score:5, Informative)

            by Anonymous Coward on Tuesday March 24, 2009 @07:31AM (#27310227)

            "Indentation in rubber sheet" I never got that, nor did my physics teacher (who started out as a real physicist.) If we imagine gravity as a deflection in a rubber sheet, why does the object "fall" into it?

            The answer is, it doesn't fall onto it. It's called an analogy.

            You are thinking of this rubber sheet as existing in our 3 dimensions, when it would better work as a dimension of its own.

            If analogies don't work for you, then the technical answer is the objects mass causes the indentation or the 'falling into it' as you say. This mass causes a warp in spacetime, and the warping itself is what we SEE as gravity, not what gravity is however, since that is a force of nature that results from mass (or so it seems) which we can't directly observe yet, we can only observe its effect on things with mass.

            Now, WHY mass causes gravity (or the indentation on the sheet, or for the body to 'fall' into said sheet), to give us an effect we can see, we don't know yet. Hopefully this discovery can help us get closer to that understanding.

            But the biggest mistake is to think of the object 'falling into' a sheet, since that description itself uses gravity as both the description of the event, and the event itself. They are not at all the same, so there is no magic 2nd gravity field. That 2nd field you are thinking of results 100% from the poor analogy and of course doesn't exist, it just helps some people wrap their mind around the effect in a visual way.

            Basically, the falling on a sheet visual seems more helpful to right-brained people, while the maths itself is more helpful to the left brained people.
            Neither representation (visual or the maths in the theory) is complete or correct at this point, so both are bound to cause confusion if you are looking for the end-answer.

          • Re:"Indentation in rubber sheet" (Score:4, Insightful)

            by Anonymous Coward on Tuesday March 24, 2009 @08:49AM (#27310999)

            That's from people avoiding hurting their brains. It's also the cause of why people have this image of a black hole being this really deep funnel thingie rather than the actuality (which hurts the brain).

              Think Flatland and curved space for a moment.

            Mass bends space. The analogy is trying to get you to picture why going in what is to you a straight line is actually following that curve. An extreme example might be thinking about that flatlander finding themself in an extremely curved portion of space- deep within the above funnel for example- and what it would do to their "straight line path."

            The hard part is moving that warping from two dimensions to three, and imagining it accurately. That's where the brain hurt comes in. That's why they resort to dragging out that rubber sheet and bowling ball example. There's no invisible gravity analogue making the ball "drop" into the well: it's the ball rolling along in what it thinks is a straight line, only the "floor" it's rolling on is warped, curving it's path.

          • The cells on the grid. (Score:5, Informative)

            by DrYak ( 748999 ) on Tuesday March 24, 2009 @09:00AM (#27311111) Homepage

            Disclaimer : IANAP, IAAMD. And we doctors aren't very renown for our skill in physics...

            the analogy requires it to change path so as to lose potential energy and gain kinetic energy as a result of the perpendicular field. So the thought experiment seems to gravity as a deflected rubber sheet into which things fall because of another gravity in an external dimension. To make things worse, the rubber sheet is effectively 2D in a 3D universe.

            Well, that's a way to interpret the rubber sheet metaphor and as you point out, it requires a sheet in a higher dimensional space and an additional perpendicular force. As it is enough to have a mental image of beads making turns on a sheet, it seem to be enough when taught in school.

            From what I understand, the importance isn't the higher dimensional shape, it's the shapes of the cells on the grid that represent the rubber sheet on the illustration.

            Physical bodies aren't bead rolling *on* the sheet. The sheet is the space-time itself. Physical bodies are travelling inside the sheet, crossing cells of the grid.

            In the absence of that field the object would presumably travel through the space time deflection with unchanged velocity

            And that's what happens. An object is simply going straight ahead, moving from one grid's cell to the next one.
            But the 2D universe grid isn't regular as on a flat sheet. Big masses "wrap" the space around them and cells have strange deformed shapes.
            It's just handy to paint those deformed cells as a bump.
            And the object is simply following the same path as before, but as the cells it "crosses" are weirdly shaped, the point where the object leaves one cell isn't in line with the points where the object left the previous cells.
            It follows a straight path, but as the terrain isn't even, the net result is a curve.

            In our 3D universe, what form does the curvature take?

            It's still a grid. It's now a 3D grid. Composed of small cubic cells. Except that, around big masses, the cells all of sudden aren't perfectly cubic anymore.
            Thus if an object was following a subjectively straight path from on cell to the next, seen from the "outside" the path will be curved, because the cells have non-cubic shapes.

            I've actually seen one exposition (for 100th anniversary of Einstein's annus mirrabilis) where it was indeed shown that way.

            This model is nice because it helps understanding why massless thing such as light still recieve an effect (gravitational lensing) from big masses :
            - on the high dimensional rubber sheet it won't work as they won be affected by the perpendicular "extra-gravity".
            - but on the grid, they just run straight ahead in the cells and the cells happen to have been shaped into a curve. Thus "seen from far away", the resulting path is a curve. Massless light particle just happen not to make any curve around them on their own.

          • Re: (Score:2)

            by reiisi ( 1211052 )

            I am way too sleepy to be doing this, but here's how I resolved it in my mind.

            Think of a graph of density of the sun versus radius from center.

            Turn the rubber sheet upside down and take a cross-section. Now it looks like your graph of density, except it extends out along the x axis in both directions.

          • I believe the easiest way for you to maintain the analogy of the rubber sheet (although nobody says that's strictly necessary), is to accept that there is no 3rd dimension in the analogy.

            The analogy makes sense to us because we are 3D creatures (ignoring time) and the idea of something falling into a funnel or depression is rather easy and intuitive to understand.

            But to complete the analogy, once you've got the idea of a ball rolling around, you have to take the next step and realize nothing (NOTHING) is "o

          • Re: (Score:2)

            by morcego ( 260031 )

            To make things worse, the rubber sheet is effectively 2D in a 3D universe. In our 3D universe, what form does the curvature take?

            I'm not a physics , but even I can spot that one.

            4D universe, please. We are talking "space-time" here. Any 3D based analysis will be wrong, so you just can't do it and expect to have realistic results.

            Yes, I know they use a 2D sheet to represent/illustrate the concept, but that is the only option we have right now.

            So I would venture to say that your physics teacher was having a p

        • Re: (Score:3, Interesting)

          by master_p ( 608214 )

          I understand the difference (the wave is simply a fluctuation of the medium), but are we really sure that gravity is only a curvature? the speed of gravity is not infinite, (IANAP, but from what I have read from various articles) it is the speed of light, so could it be that gravity is a sort of a particle, undetected so far, with properties similar to a photon? i.e. no rest mass, with only kinetic energy.

          • Re: (Score:2, Informative)

            by Famous Moose ( 41402 )

            Yes, as with all classical field theories, when you quantize it you get a gauge boson. In this case it's called the graviton and current (incomplete) quantum gravity formulations have it pop out as spin-2 and massless. Remember kits fields are classical, gauge bosons are quantum mechanical.

            • Re: (Score:2)

              by jambox ( 1015589 )
              So if the graviton is massless, how does it interact with matter? I vaguely recall reading something about quantum gravity a while ago and I got the impression that there was meant to be a a sort of universal sea of gravitons, dashing around an exerting an equal pressure on all massive objects. The observed effect of gravity is only apparent when you are "shielded" by another massive object to one side of you, causing a pressure imbalance which moves you towards that object (and vice versa).

              If the gravito

              • Re: (Score:3, Insightful)

                by Abcd1234 ( 188840 )

                So if the graviton is massless, how does it interact with matter?

                Well, given a photon is massless [ucr.edu], yet still interacts with matter, I'm really not sure where the problem is...

              • Re: (Score:3, Insightful)

                by Luyseyal ( 3154 )

                Well, the strong force mediators -- the gluons -- are massless too, as are photons (electromagnetism). It turns out mass is not necessary to interact with matter. This is why physicists are so taken with "fields". You can define a number of fields in which a particle participates which are mutually exclusive, but all add up to define where a particle is and what it's doing.

                This is why Higgs is so exciting. It's the Higgs field which is supposed to give baryons (normal matter) mass. The general idea is that

                • Re: (Score:2)

                  by jambox ( 1015589 )

                  It turns out mass is not necessary to interact with matter.

                  POP! Sorry that was my head exploding. In all seriousness - thanks for a very good answer to a very dumb question! I'm going to go read some books, or something.

        • Re: (Score:2)

          by Orne ( 144925 )

          Doesn't a wave effect imply an impulse change at the source?

          A wave is an oscillating change, therefore a gravity wave means that a change in a (point source) gravity.

          Right now, we believe that mass is the only thing that creates gravity. A slow accumulation or decrease in a (point) mass such as a star or black hole would have an even smaller change as a waveform. If a star goes nova, from a macro perspective, isn't the same amount of mass/energy conserved but now dispersed over an area?

          What is it out ther

        • Re: (Score:2)

          by Yvanhoe ( 564877 )
          I wonder... What would happen if a "gravitational-wave-insulated" box was closed at, say, Moon's surface and brought back to Earth. Would its interior behave like it was under Moon's gravity ?

      • Re:So... (Score:5, Interesting)

        by hasdikarlsam ( 414514 ) on Tuesday March 24, 2009 @06:21AM (#27309791)

        While that is definitely true, and an important caveat, the fact that there is a connection at all between electromagnetism and gravity was somewhat unexpected - physicists did expect to eventually unify the theories, but probably not in a way where one affects the other like this. Don't underestimate the importance of this discovery.

        Plus, there may be corresponding interactions between, I don't know, petahertz-level magnetic or electric waves (not plain old photons, mind) that have larger, more useful effects on gravity. Maybe. At any rate, the possibility is open now; we're allowed to hope.

        • Re: (Score:3, Insightful)

          by evanbd ( 210358 )
          How, precisely, do petahertz EM waves differ from photons? Visible light is ~ 1PHz. All EM waves are photons; the only distinction is how obvious it is, which is an artifact of your observation technique and not the photon itself.

      • Re: (Score:2)

        by nmg196 ( 184961 )

        If you're reflecting gravity waves, is there not a change of momentum involved? If so, why wouldn't reflecting it reduce the gravity on the object concerned?

  • Possible correlation? (Score:5, Insightful)

    by ma11achy ( 150206 ) on Tuesday March 24, 2009 @04:46AM (#27309359)

    From the article:
    "If there were an obvious interaction between a superconducting films and gravitational waves, wouldn't Gravity Probe B have picked them up somehow?.....As it turns out, the experiment has been throwing out anomalous results ever since it was launched......The team has puzzled over them for years now....."

    I really do love those moments in science when something you have puzzled over for years may have an elegant answer after all.

  • Superconducting spheres (Score:3, Interesting)

    by MichaelSmith ( 789609 ) on Tuesday March 24, 2009 @05:05AM (#27309455) Homepage Journal
    Just like the concentric rotating benzels in Carl Sagans book Contact. Maybe he had a gravitational wave resonance thing happening there.

  • Gravity Shielding (Score:2, Interesting)

    by chr1sb ( 642707 )
    Eugene Podkletnov has been claiming for some time to have produced gravity shielding using levitated superconducting disks. The scientific community has mostly rejected his work, although NASA was for a time attempting to reproduce it. There's an article [wired.com] on it from a few years back on wired:
    • This is about gravitational waves, not about gravitational fields.

      • Re: (Score:2)

        by dargaud ( 518470 )

        This is about gravitational waves, not about gravitational fields.

        I understand that when you agitate or rotate a mass (= gravitational field), you get gravity waves. But admitting that this effect is real and that you can reflect/refract gravity waves, could you use it to make a gravity field ?

    • Gravity Shielding => Perpetual Motion Machine => Violation of Conservation of Energy

      If I can shield gravity, I can put half a wheel over my shield and the wheel will spin, even if the effect is only a couple percent. Hurray, for free energy! Now, if there was a power input requirement that was directly related to the amount of mass that was being lifted by the purportedly blocked gravity, it might work; but nothing that I've ever seen on the subject of rotating super-conducting disks has mentioned a

  • Truly Amazing (Score:5, Interesting)

    by Lifyre ( 960576 ) on Tuesday March 24, 2009 @05:33AM (#27309599)

    This theory has implications that could revolutionize scientific thought across numerous fields. It may even provide some direction for the unified theory people to look in that isn't horribly complex and require inventing 1700 dimensions to make the math work.

    Also if people don't understand how large 42 orders of magnitude really is 10 is one order of magnitude. 1,000,000,000,000,000,000,000,000,000,000,000,000,000,000 is 42 orders of magnitude... Granted the numbers they are dealing with are very very small to start with and even 42 magnitudes larger is still pretty damn small this change in scale is mind boggling and shows much more we have to learn about the universe in general and the properties of superconductors in particular.

    -Lify

    • But then this paragraph says:

      Chiao and co ask how big is this effect of a gravitational wave on a thin superconducting sheet compared to the effect on an ordinary conducting sheet. The answer? 42 orders of magnitude bigger.

      So if the affect of a conducting sheet is next to nothing then the affect of a superconducting sheet is 10^42 times as much but this may still be next to nothing. The article doesn't say that there will be no gravity inside the sphere.

    • Re: (Score:2, Informative)

      by dottedlinedesign ( 754366 )

      This theory has implications that could revolutionize scientific thought across numerous fields. It may even provide some direction for the unified theory people to look in that isn't horribly complex and require inventing 1700 dimensions to make the math work.

      Nassim Haramein has put forth a unified field theory which doesn't rely on made up science: http://theresonanceproject.org/ [theresonanceproject.org]

      • Re: (Score:2)

        by Lifyre ( 960576 )
        Mod + Informative. I got out of the physics game when strings where the big popular thing... Thanks, I think, for enough reading material for the rest of the deployment.

  • Gravity wave detectors. (Score:5, Insightful)

    by Therefore I am ( 1284262 ) on Tuesday March 24, 2009 @05:51AM (#27309661)
    Doesn't this discovery also lead to the possibility of building super-sensitive gravitational wave detectors that really work....... Remember this - If you can't measure a phenomena, you have little hope of truly understanding it.

  • This is a-posteriori explanation of GP-B issue (Score:5, Interesting)

    by Zdzicho00 ( 912806 ) on Tuesday March 24, 2009 @06:12AM (#27309743)
    Martin Tajmar also posits an a-posteriori explanation for the anomalous data from Gravity Probe B based upon Cooper-pair mass in Niobium superconductors in: arxiv.org/abs/0707.3806 [slashdot.org]
    Heim Theory [wikipedia.org] predicted such effects in 1950s already. Droscher & Hauser have suggested mechanism based on Heim Theory which was a-priori prediction as commented in the cover story of New Scientist Jan 2006 [newscientist.com], 3 months before Tajmar's announcement on the ESA homepage [esa.int].

    Here is the latest paper [hpcc-space.de] from Droscher & Hauser which gives explanation for outcome of both Tajmar and GP-B experiments.

    Personally I like this part:
    Numerous experiments by Tajmar et al. were carried out since 2003, and first published in 2006 report on the generation of gravitomagnetic (spacetime twisting) and gravity-like fields (acceleration) in the laboratory. The gravitational effects measured were about 18-20 orders of magnitude larger than predicted by the Lense-Thirring effect of GR. In other words, the rotating niobium ring, having a mass of some 100 grams as utilized by Tajmar et al., produces a gravitational effect similar to the mass of a a white dwarf.

    /Joss

  • Reflected gravitational waves can be useful (Score:3, Insightful)

    by Anonymous Coward on Tuesday March 24, 2009 @06:41AM (#27309883)

    If you can reflect it, you can make a curved "mirror" to concentrate it to a single point in space.
    If you can concentrate it, you can amplify it.
    And if you can amplify it, then maybe you could directly measure its effects (something that has not been done yet)
    And once you measure its effect directly, you can compare your results to the various theories (there are plenty)
    If you compare results, you can refute some of the current theories, and maybe create others.
    Then maybe you can use reflected and concentrated gravitational waves for long-distance communication? or for detecting matter in the farthest reaches of the galaxy...

  • Something which reflects gravity? That's cavorite [wikipedia.org]!.
  • I think this means that it might be possible to build a gravitational wave telescope. I get first dibs on a patent/prior art if the big corporations don't completely emasculate the USPTO's ability to grant patents to the little guys. [slashdot.org]

    P.S. I also get first dibs on the 'gravitational wave sterling engine, powering devices on earth from colliding black holes out there!'

  • Is arxiv actually legit? (Score:4, Interesting)

    by tjstork ( 137384 ) <todd@bandrowsky.gmail@com> on Tuesday March 24, 2009 @07:48AM (#27310387) Homepage Journal

    There's a couple of proofs that P=NP, gravity waves, all these holy grails are in there. I wonder if they should rename this site: "Popular Mechanics Research"

  • Maybe we can soon get sub-etha radios and communicate across the universe to hail a passing star ship?

  • Possible applications (Score:4, Insightful)

    by Stoutlimb ( 143245 ) on Tuesday March 24, 2009 @09:27AM (#27311459)

    If gravitational waves can shake a superconducting sheet, will shaking a superconductive sheet create gravitational waves? Wouldn't that open things up to some amazing experiments?

  • Maybe the bulb just burnt out? (Score:3, Funny)

    by illegalcortex ( 1007791 ) on Tuesday March 24, 2009 @11:44AM (#27313635)

    Oh Gravity Probe B, why can't you be more like Gravity Probe A?

Slashdot Top Deals

In practice, failures in system development, like unemployment in Russia, happens a lot despite official propaganda to the contrary. -- Paul Licker

Close