Using Neutrons To Precisely Test Newton's Law of Gravity

NotSanguine writes with this excerpt from the BBC: "The neutrons are shot between two parallel plates, one above another and separated by about 25 micrometres — half a hair's width. The upper plate absorbs neutrons, and the lower plate reflects them. As they pass through, they trace out an arc, just like a thrown ball falling due to gravity. ... The new work by the ILL team has added what is known as a piezoelectric resonator to the bottom plate; its purpose is to jiggle the bottom plate at a very particular frequency. The researchers found that as they changed the bottom plate's vibration frequency, there were distinct dips in the number of neutrons detected outside the plates — particular, well-spaced 'resonant' frequencies that the neutrons were inclined to absorb. These frequencies, then, are the gravitational quantum states of neutrons, essentially having energy bounced into them by the bottom plate, and the researchers were able for the first time to force the neutrons from one quantum state to another. The differences in the frequencies — which are proportional to energy — of each of these transitions will be an incredibly sensitive test of gravity at the microscopic scale."

Comments

Newton's

[Dr. Spork]

Wow, my physics courses apparently forgot to mention that Newton's Law of Gravity had anything to say about the quantum states of neutrons. In fact, I was taught it's not a law; it's a falsified hypothesis.

Re:Newton's

[catchblue22]

Wow, my physics courses apparently forgot to mention that Newton's Law of Gravity had anything to say about the quantum states of neutrons. In fact, I was taught it's not a law; it's a falsified hypothesis.

Newton's Law of Gravity can be seen as an approximation of Einstein's theory. We have to be careful when we speak of "falsified". We haven't discovered that gravity is proportional to 1/r, or that gravity isn't attractive but repulsive. We have discovered that Einstein's models are better predictors of experimental results. We can still us Newton's models to send humans to the Moon. But Newton's model makes no sense when asking questions such as "what would happen to the Earth if the Sun suddenly disappeared. It doesn't predict the bending of light, nor does it properly describe certain orbital phenomenon.

Re:Newton's

[Hope Thelps]

In fact, I was taught it's not a law; it's a falsified hypothesis.

Tell it to the judge.

Re:Newton's

[dch24]

This is news to me too. In the BBC article, it says gravitational quantum states were only measured in 2002, in the parent experiment (the one where they didn't use piezo resonators -- just parallel plates).

Cool! Falsifiable experiments testing unified theories, like string theory!

Re:Newton's

[pclminion]

If you bother to read the article, you see that they are trying to see whether good old Newtonian gravity is a good approximation at extremely small length and mass scales (scales where the additional accuracy provided by general relativity is unnecessary). They're trying to see if when you make the experiment this sensitive, do you see some kind of quantum effect. The answer so far seems to be no. Yes, the neutrons behave in a quantum mechanical way. The question is, do they behave as you'd predict if Newton's/Einstein's gravity is true, or do they do something unexpected? This has nothing to do with Newton vs. Einstein.

Re:Newton's

[jd]

I disagree with the claim that it is falsified. All theories in physics come with two sets of conditions: the bounds in magnitude and the bounds in resolution. Newton's theory came with well-defined bounds - those of classical phenomena. You cannot extrapolate beyond those bounds and claim you are still working with the theory because the theory isn't defined beyond those bounds. Nor can you interpolate to the quantum level for the same reason - the theory isn't defined there.

Relativity didn't replace Newton's theory, it supplemented it. In computing terms, it's a third-party module you can add on. When you install the Relativity dynamic library, the combined theory applies to a much larger range of phenomena.

The only time a theory will actually be falsified is if QM's gravity or relativity can be patched to work within the other's range. They are contradictory and you cannot load both modules into Newtonian physics at the same time. Only one of these two will stand the test of time, the other will die. Whichever one wins will then merge with Newtonian mechanics to produce a universal law of gravity.

Re:Newton's

[pablomme]

I thought the same when I read this piece of news yesterday. Journalists like to fill their sentences with words that sound appropriate to them: "[Newton's Law of] Gravity", "8.1 magnitude [in Richter's scale]"... and often they make mistakes.

Re:Newton's

[catchblue22]

It doesn't predict the bending of light

Err...sorry. I should have said it doesn't predict the bending of light in gravitational fields.

Re:Newton's

[SoVeryTired]

Actually it does, but by half the amount predicted by general relativity. This was known to Cavendish in the late eighteenth century.

http://en.wikipedia.org/wiki/Tests_of_general_relativity#Deflection_of_light_by_the_Sun

Re:Newton's

[bcrowell]

I agree with the basic thrust of your post, but have one nitpick to make:

But Newton's model makes no sense when asking questions such as "what would happen to the Earth if the Sun suddenly disappeared.

Actually, general relativity doesn't answer this either, because GR has local conservation of mass-energy, so it doesn't allow the sun to disappear. A better example would be "What would happen to the Earth if the Sun suddenly zoomed away from us at nearly the speed of light." Admittedly I'm being totally pedantic here.

Re:Newton's

[Adult film producer]

so... what would happen ?

Re:Newton's

[nedlohs]

The energy required to make it happen would kill us all probably by turning all the inner rocky planets to molten balls of slag.

Re:Newton's

[blair1q]

How did Newton give light mass?

Or did he somehow grok that space itself is warped by mass?

Re:Newton's

[femtobyte]

You don't need to know what the mass of light is, you only need to treat it as a classical particle traveling at 3e8 m/s. From classical mechanics, objects follow the same trajectory in a gravitational field regardless of mass (different orbits depend only on different initial positions/velocities); a beam of light can be treated just like a very fast moving comet. The mass of the light would only be important if you were trying to calculate the reverse effect of how much a passing light beam would move a planet/star as it passed. The fact that light travels at a finite speed has been known for a long time.

Re:Newton's

[lennier]

Newton's theory came with well-defined bounds - those of classical phenomena.

I'm not sure that's correct. In Newton's time the word "classical" in the sense of either non-relativistic or non-quantum didn't exist. Gravity and the other mechanical forces are continuous and space is three-dimensional with independent time dimension in Newton's model. The entire idea of "bounds" in terms of relative speed and size where Newtonian mechanics don't apply was invented much later (both pretty much by Einstein) and would likely have seemed ridiculous to Newton.

The interesting thing is that Einstein's two brainchildren - quantised photons and general relativity - don't play well together.

Re:Newton's

[JamesP]

Exactly. There's no need to go to relativity for most of the cases.

But everyone that thinks otherwise is welcome to calculate sqrt(1 - v^2/c^2) for their experiment's velocity and see if the values vary significantly

Re:Newton's

[pclminion]

Two things. First: Newton knew that all objects (at least, all objects we've tested) accelerate toward the earth with a certain acceleration regardless of mass, depending only on their distance from the earth. If the law of gravitation is universal, then why wouldn't light also experience the same acceleration? Assuming that massless particles are an exception goes against Occam's Razor. Only if we observe that light does not deflect would we conclude our theory was wrong. Newton was unable to perform this experiment.

Second: Why would Newton automatically assume that light did not have mass? It seems perfectly obvious today, but is it obvious because everyone knows it or because it's obvious? I don't think it's obvious.

Re:Newton's

[Raenex]

This is a terrible apology for Newton's theory of gravity. Einstein's relativity isn't an "add on" module. It completely subsumes Newton's theory, and shows that is just a very good approximation at ordinary scales.

This in no way diminishes Newton's accomplishment, or even usefulness. However, we can say that his theory of gravity has been falsified.

Re:Newton's

[FrootLoops]

There's a big difference between today's conception of Newtonian mechanics and (what I presume was) the original conception of it. Today, we call it an approximation; originally, it was perfectly precise. The original idea has been falsified, but the newer version with supplemental error bounds is alive and well. The add on analogy is a little bit of a stretch, but I don't think it's awful. Loading the GR module would be akin to adding routines that could predict the impact of a black hole meandering through our solar system, for instance, in addition to improving the accuracy of the Newton module's routines. It entirely replaces the Newton module, which is where the stretch comes in. Quantum fits pretty well in the analogy, though.

Re:Newton's

[Anonymous Coward]

Great... Just what I need...

A Relatavistic DLL Hell....

Re:Newton's

[Roger W Moore]

You don't need to know what the mass of light is...

Actually you do because if the mass is zero there is no force according to Newton's law of gravity and hence no deflection. Cavendish did not know this in 1804.

Re:Newton's

[Roger W Moore]

Two things: First the question is what deflection does Newton's law of gravity predict for the deflection of light, not did Newton know that light was massless.

Two: Newton and Cavendish did not know that light was massless but we do and so Newton's law predicts no deflection i.e. Cavendish got it wrong but so would anyone else predicting the behaviour of a particle which was discovered about 100 years after he wrote his paper!

Re:Newton's

[ShakaUVM]

>>We haven't discovered that gravity is proportional to 1/r, or that gravity isn't attractive but repulsive.

Err, gravity *can* be repulsive.

Re:Newton's

[jd]

I'm not sure that you can say that it replaces the theory. You can use Newtonian mechanics exactly as Newton wrote them, without changing them one iota, but merely pass in the relativistic values rather than the classical ones. That doesn't sound like a replacement, that's a pre-processing routine at best. Gallilean addition of velocities is then modified by dividing the original result with a new result. A post-processing module.

In relativity, light still travels along straight lines but along a warped topology. The result is the appearance of light being bent by gravity, when it is space that is bent. Light is unaffected.

Where is the replacement?

Re:Newton's

[jd]

Just wait for Physics 3.0 - The Quantum DLLs can be both installed and not installed at the same time.

Re:Newton's

[jd]

The idea of physical theories being bounded was actually quite popular in Newton's time - hence the phrasing of Hooke's Law, the approximation of the motion of pendulums, etc. The laws were all quite specifically written in the form "provided these preconditions are true, this result WILL apply". Newton didn't change this in the slightest.

Indeed, that should be obvious from the description of gravitational attraction. Object X is pulled towards object Y because of the mass of object Y alone. However, it is equally true, by the same law, that object Y is pulled towards object X because of object X's mass. They are both pulled towards a common point. Newton was quite aware of this. If you jump up, you do not fall to the Earth, both you and the Earth move towards a common point. Because your mass is insignificant compared to that of the Earth (well, depending on how addicted you are to fast food), you can treat the Earth as in effect a stationary object.

Thus, although Newton's laws require you to apply the laws in both directions to get the "exact" result of his theory, you won't ever find that done in practice. By the time you get to objects of comparable size that can orbit each other you have to start factoring in relativity anyway. Even Newton never really considered the common center of gravity - he expressly confined himself to objects of significantly different mass such that the common center of mass is approximately the same as the center of mass of the larger object. There was never any attempt by Newton to extrapolate outside of that boundary.

There was an unwritten limitation also imposed on it. The addition law of vectors had to apply. This was a geometric property and there were certainly geometries known at the time in which the addition law did NOT hold. Thus, Newtonian Mechanics has the implicit precondition that you are working in a valid geometry. All QM and GR/SR geometries are invalid EXCEPT for special cases when both these theories reduce quite nicely to classical Newtonian Mechanics.

Re:Newton's

[Anonymous Coward]

Zeroes are troublesome in physics. If a light particle has zero mass, it would mean that any force at all would cause an infinite acceleration. Since it was known that light travelled at finite speeds, it's reasonable to assume that light particles did have a mass (of course, classically there's no such thing as rest mass)

Re:Newton's

[Woek]

Photons have mass, because they have energy. Furthermore, that photons have zero rest mass is still only an assumption in most models (ref)

Re:Newton's

[tyrione]

Correct! It makes me wonder if the Dr. originally posting his crap has the background to even comprehend basic Classical Mechanics.

Re:Newton's

[tyrione]

I'm not sure that you can say that it replaces the theory. You can use Newtonian mechanics exactly as Newton wrote them, without changing them one iota, but merely pass in the relativistic values rather than the classical ones. That doesn't sound like a replacement, that's a pre-processing routine at best. Gallilean addition of velocities is then modified by dividing the original result with a new result. A post-processing module.

In relativity, light still travels along straight lines but along a warped topology. The result is the appearance of light being bent by gravity, when it is space that is bent. Light is unaffected.

Where is the replacement?

Agreed and I will add that in 20 years or so we'll have new additions to Physics that augments Relativity and the exactness of what is actually going on with Force in a system will have a more complete picture, but we don't spit on the foundation of Newton and Einstein--we'll augment them.

Re:Newton's

[Nivag064]

[...]

But Newton's model makes no sense when asking questions such as "what would happen to the Earth if the Sun suddenly disappeared. It doesn't predict the bending of light, nor does it properly describe certain orbital phenomenon.

Actually, Newton's Gravitational laws _DID_ predict the bending of light by the Sun, but by a different amount!

There is a factor of 2 difference (can't remember which predicted the greater bending!).

Re:Newton's

[BlueParrot]

If you bother to read the article

Ahhhh. I love the smell of slahsdot in the morning.

Re:Newton's

[Dabido]

But Newton's model makes no sense when asking questions such as "what would happen to the Earth if the Sun suddenly disappeared.

Don't worry, I'm on that one. "It would get very dark." There, no need to worry about that now!

Re:Newton's

[Velex]

I think this is an appropriate link: http://chem.tufts.edu/AnswersInScience/RelativityofWrong.htm

Re:Newton's

[pclminion]

First the question is what deflection does Newton's law of gravity predict for the deflection of light, not did Newton know that light was massless.

No. The question was "How did Newton give light mass? Or did he somehow grok that space itself is warped by mass?" See parent of my post.

Re:Newton's

[FrootLoops]

That's a bit of an oversimplification of relativity. Some simple, highly idealized calculations can be done by just replacing an input with a modified version of it, or modifying the result of a Newtonian calculation. But, calculations involving significant gravity are far more complex. I would agree with you if we were talking about special relativity instead of general, or if the calculations were kept simple.

Re:Newton's

[blair1q]

Most models accept the data that say that photons are never at rest.

Re:Newton's

[FrootLoops]

What do you mean by the "addition law of vectors"? I've also never heard that Newton conceived universal gravitation as not necessarily universal and only applying in some limits. Newton actually said of Hooke's hypotheses on gravity that "without my Demonstrations, to which Mr Hook is yet a stranger, it cannot be beleived by a judicious Philosopher to be any where accurate"--Hooke's claims weren't sufficiently tested, either physically or mathematically, though Newton put his own similar/equivalent theory through its paces as best he could at the time. Newton did not confine himself to objects with significantly different masses, as you suggest: "I deduced that the forces which keep the planets in their orbs must [be] reciprocally as the squares of their distances from the centers about which they revolve...". It's very common to consider Newton's laws as they apply to a set of objects of roughly the same mass. See the 2-, 3-, or n-body problems.

I don't know what you mean when you talk about GR/SR geometries. SR is flat Minkowski space, and GR uses a pseudo-Riemannian manifold with metric given by the Einstein equations. One might be able to apply Newtonian gravity on, say, a sphere, with geodesic distance replacing regular distance in gravity computations. That seems a bit strange, though; I've never heard of it applied to anything besides standard Euclidean space.

Re:Newton's

[blair1q]

I think if Newton thought photons had 0 mass he'd have found it impossible to apply GMm/r^2 to them without getting the answer f=0 and deducing that photons did not curve in a gravity field.

But, what I failed to remember yesterday, is that Newton knew that light was particles. "How do I know that light is corpuscular? Because I grind my own lenses," or words to that effect. One of my favorite sayings, but apparently I only call it up when messing around with optics, not for gravity. He reasoned that since lenses are not infinitely smooth, because they are polished by successive reduction in the depth and width of scratches you make in them, waves would behave in a way that corpuscles do not.

Since he believed light was particles, he could easily assume they would have mass, and therefore react to gravity.

And then the tricky thing Einstein did was figure out that the mass of a photon is 100% relativistic. Which is good, because if the Higgs Boson is the charge carrier of mass, there's no room for it in a photon, and in fact no photon could reach the speed of light without sucking up all the energy in the universe. And if photons didn't move at the speed of light, a whole lot of our math would already be way off.

But the rub is, relativistic mass is only pseudo-mass, and its reaction to gravity is only due to relativistic effects, not to massiveness. So Newton's reason for believing that light would react to gravity is incorrect, and he gets a partially-correct result. Good thing he always showed his work. Half-marks.

Re:Newton's

[jd]

The addition law of vectors, as stated by Gallileo, is that the relative vector of two bodies is given by the sum of the vectors for each body. In other words, take the components in the X, Y and Z directions for the velocity of each of the two, then the relative velocity vector is (X1+X2, Y1+Y2, Z1+Z2).

The planets are a very different mass than the sun and there's no suggestion in his model of planetary motion that he considered the sun plus planets to be orbiting a shared center of gravity. Rather, he was quite clear that the sun should be regarded as static with the planets moving round it. The n-body problem is so bloody difficult to solve for similar masses because this breaks down. You can't do that approximation. This means that the center of gravity moves with each instant in time, which in turn means that unless you have a special case in which the center of gravity moves along a mathematically well-defined path, you HAVE to calculate the motion iteratively and you WILL accumulate error because you can't perform infinitely small steps. The solar system is sufficiently close to a special case (the mass of the planets is insignificant to the mass of the sun, so even when all lined up won't displace the center of gravity significantly) that numerical methods are just fine.

Applying Newton's laws as they stand and applying a transform to space instead actually works really well. There's a lot of evidence to suggest that this was, in fact, the early thinking Einstein used. It is also how some schools teach relativity today, since it's easier to teach Newton's laws and merely alter the shape of the space it is applied to than it is to substitute models as though they were urelated in any way and duck inevitable questions from students. The former fits with the standard concept of science as an evolutionary progression of ideas with very few real discontinuities and it allows students to feel as though they're progressing rather than treading water with ideas being replaced without explanation.

It doesn't get done a lot because schools prefer to teach to a syllabus and traditional syllabuses are based on what can be taught en-masse using cheap, throw-away textbooks and disposable teachers who teach a very narrow range of grades. The object for the teacher is to get the students to score highly (especially after the No Child Left Behind act), not to convey any level of understanding of the reasoning, methodology, history or even physics behind the models. With superior consequences for leaving students embittered about science but successfully passing the exams with a high score versus enthusiastic, knowledgable students who merely scrape by, naturally it is considered better to have students feel like nothing they learn is meaningful, useful or applicable - or even correct.

(Yes, I tend to get passionate on this subject.)

Re:Newton's

[Maritz]

Well to be fair, it's a thought experiment. It's not saying 'is it possible for the sun to vanish', it's saying, 'IF the sun DID vanish, what would we experience from Earth'? Not that I'm against your pedantry per se of course ;)

Re:Newton's

[Maritz]

What are you basing this on? Has it been demonstrated? I personally haven't heard of gravity ever being repulsive. If you're talking about gravitational forces 'ejecting' objects that come close to massive bodies on certain trajectories then it's a bit of a stretch to say you're talking about a repulsive force.

Re:Newton's

[Maritz]

For around 8 minutes nothing at all. Then we'd see the sun disappear, and we'd continue on a tangent from where we currently are in our orbit. At least that's my layman's understanding of things. Newton didn't appreciate that gravitational forces are not instantaneous, which is why you often hear the 'disappearing sun' thought experiment invoked when illustrating the differences between Newton and Relativity.

Re:Newton's

[ShakaUVM]

It's one of the theories of inflationary cosmology. You can read more about it here:
http://www.edge.org/3rd_culture/guth02/guth02_print.html

or a paper here: http://arxiv.org/abs/gr-qc/0001011

Re:Newton's

[pclminion]

I think if Newton thought photons had 0 mass he'd have found it impossible to apply GMm/r^2 to them without getting the answer f=0 and deducing that photons did not curve in a gravity field.

Remember also that Newton knew calculus, having invented much of it, which means he could have thought about it in terms of limits. F = ma = GMm/r^2. Take the limit of both sides as m goes to zero, and you get a = GM/r^2. No problem there. The burden is actually to come up with a reason why light wouldn't behave the same way as anything else.

Re:Newton's

[pclminion]

Gah. I didn't say that the right way, sorry. Intuitively, what I mean is that as m gets ever smaller and smaller the equality ma = GMm/r^2 continues to hold. In the limit as m goes to zero, both sides go to zero together, but that doesn't mean the acceleration must go to zero. I didn't state it right, I apologize.

Re:Newton's

[catchblue22]

What would happen to the Earth if the sun suddenly disappeared?

Under Einstein's Theory of Relativity, nothing can travel faster than light. If the Earth "disappeared", or some reasonable facsimile, it would take 7 - 8 minutes before we stopped receiving sunlight, since that is the time for light to travel from the Sun to the Earth. The Sun's gravity is what keeps pulling the Earth in a circular path...without it the Earth would travel in a fairly "straight line". If the Sun suddenly disappeared, its gravitational influence would also disappear. But Einstein's theory implies that nothing can travel faster than light, so the gravitational change caused by the Sun's disappearance cannot reach us sooner than 8 minutes, since otherwise this would imply that the gravity disturbance could exceed the speed of light.

Einstein's General Relativity implies that objects with mass cause distortions in space. It is these distortions that we experience as gravity. The distortions are rather difficult to visualize, however. To really see them in your mind, you have to be able to think in four spacial dimensions. The typical way of making spacial distortion easier to visualize is to reduce space to 2 dimensions. Then you can imagine that space is like a flat rubber sheet. Place a ball on the sheet, and it creates a distortion, as the ball pushes the rubber sheet down. The rubber sheet is still 2 dimensional, but to see the distortion we need to step back and look at it from our 3rd spacial dimension. Now extend space to 3 dimensions. Objects with mass have a similar distortional effect on 3 dimensional space, but to see the distortion, we have to step into the 4th spacial dimension.

If the Sun did disappear, the change in the spacial warping would radiate outwards from the former location of the Sun at the speed of light, kind of like a wave on a pond through 2 dimensional space, though actually in 3 dimensions, with the distortion really only "visualizable" by looking at space from a fourth dimension. It's tricky stuff...General Relativity, which is really Einstein's theory of gravity, is usually only studied seriously in grad school physics.

Re:Newton's

[Roger W Moore]

Photons have mass, because they have energy.

Wrong. Photons have energy because they have momentum, they have zero mass...and since mass is a Lorentz invariant that is always true in all inertial frames. Einstein's proper energy-momentum relationship is:

E^2 = p^2 c^2 + m^2 c^4

So next time you see someone with an "E=mc^2" T-shirt on when they are moving you can point out that their T-shirt is wrong!

Re:Newton's

[Roger W Moore]

it's reasonable to assume that light particles did have a mass

It was reasonable for primitive cultures to assume that the world was flat based on their available evidence. However that did not make them right!

Re:Newton's

[LifesABeach]

FTFA, the use of a "piezoelectric resonator" allowed a Neutron to be influenced by Earth's gravity. Could the same concept be applied to more complex atoms?

Re:Newton's

[FrootLoops]

I believe he did earth-moon calculations, and universal gravitation predicted an otherwise unobserved planet (Neptune?). Maybe Newton, in his calculations involving the sun, did always assume the sun was so much more massive than other planets that it was alright to assume it was at the center of mass of the solar system. That's a practical consideration that's different from what I understand you were saying in your first post, which was that Newton did not even theorize universal gravitation as applying to the solar system, instead fixing the sun at the center for some reason and making it necessarily immune to other body's gravitational pulls.

When I was taught special relativity, it was built up pretty much axiomatically. "Warped" geometry ended up falling out quite naturally from first principles (speed of light constant in all inertial reference frames, principle of relativity, continuous space, etc.). If they had instead just told me "apply this length contraction to space" I would have thought "well, that's completely random. Why would I do that?" Once in a while the evolutionary growth of science/math isn't the best pedagogically. A great example is quaternions, which were invented before vector analysis.

I still don't know what you mean about "other" SR/GR/QM geometries. Putting Newtonian mechanics on other geometries is clever, though.

Re:Newton's

[bcrowell]

so... what would happen ?

According to GR, the change in the gravitational field would propagate at the speed of light, so we wouldn't get any change in the gravitational field until 8 minutes later -- at the same time that the change became visibly detectable.

Assuming they weren't testing a plate resonance

[Ungrounded Lightning]

I hope they took into account the possibility that they were exciting a mechanical resonance of the plate, which would cause it to vibrate and as a result occasionally be positioned differently and possibly intercept the neutrons at slightly higher or lower locations, corresponding to higher or lower energy.

Resonant modes of the plate would also be a function of frequency.

Re:Assuming they weren't testing a plate resonance

[blair1q]

According to the second link, the resonance was at about 705 Hz.

The plate would have to be fairly wide and floppy to resonate at that frequency, but then it wouldn't have much gravitational attraction, so the plate is probably thick and chunky, and not very flexible. And it would have to be made of rubber to have any body resonance at that frequency.

Re:Assuming they weren't testing a plate resonance

[femtobyte]

Yes, we obviously need to be worried that the large team of scientists and engineers who designed and built this experiment have overlooked the most basic principles of freshman physics and mechanical design. Good thing we have the keen intelligence of Slashdot science critics to catch all these subtle flaws that would otherwise slip by the reviewers at Nature un-noticed. Should we also worry that the scientists are all part of the government conspiracy to cover up the true Time Cube four-side harmony perfection of gravity symmetry?

Re:Assuming they weren't testing a plate resonance

[T-Bone-T]

A Martian probe was destroyed by a mixup of SI and Imperial units so it seems safe to say they may have overlooked something basic.

Re:Assuming they weren't testing a plate resonance

[solarlux]

To be more specific, a Martian probe was destroyed because incompatible legacy software was used and the integration of it was not tested appropriately due to "faster, cheaper, better" funding cuts...

this is wrong

[circletimessquare]

the bible doesn't talk about neutrons

Re:this is wrong

[Anonymous Coward]

the bible doesn't talk about neutrons

You're holding it wrong.

Re:this is wrong

[140Mandak262Jamuna]

Come on. Bible does not talk about American Exceptionalism, nor our inherent right to bomb any nation into oblivion, not even why He buried our oil under their sand. Still we know these are all true.

Re:this is wrong

[Anonymous Coward]

That oil isn't under their sand... it's way, way, way under American soil. Drilling there is merely a shortcut.

Re:this is wrong

[Culture20]

It doesn't talk about gravity either.
Although regarding neutrons, some people speculate that the Ark of the Covenant was radioactive since plagues of tumors followed it. and people who looked into it quickly died.

Re:this is wrong

[Black Parrot]

the bible doesn't talk about neutrons

Try searching with the Bible Codes program.

Re:this is wrong

[Black Parrot]

Although regarding neutrons, some people speculate that the Ark of the Covenant was radioactive since plagues of tumors followed it. and people who looked into it quickly died.

Raiders of the Lost Ark explained it better, and without appealing to hocus-pocus such as gravity and radioactivity.

Now pay $18

[frovingslosh]

What a nice advertisement for an article that costs $18.

Re:Now pay $18

[pclminion]

It's a citation. Nobody said it has to be easy to get. If you think the article submitter is actually a shill for Nature trying to drum up funds by getting a bunch of Slashdotters to pay $18 for a copy of the article, well, you're a new kind of crazy I haven't seen before.

Re:Now pay $18

[MoonBuggy]

Not to mention that the majority of people wanting to read the paper itself (rather than the abstract and BBC summary) are likely to have institutional access anyway.

Re:Now pay $18

[Anne_Nonymous]

>> well, you're a new kind of crazy I haven't seen before.

I'm offering an article on the taxonomy of crazy for only $18, if you're interested.

Re:Now pay $18

[blair1q]

Actually, the links point to enough information that having the article could only help you replicate their setup exactly.

But it'd be better if you just replicated the idea in another fashion, to remove systematic bias their setup may have had.

So save your $18; you're going to need it to pay postage for your grant application.

Re:Gravitational quantum states of neutrons, eh?

[JonySuede]

You see, cars are attracted to other cars and there are some grooves on the road so a car usually stays jammed into one of them. While there it is both morphed a corresponding Transformer (the transfomer depending of the groove and the car) and the car but if you look at it you may see a car or you may see a transformer ex: Megateron. I hope that this clarify any doubts you had about gravitational quantum transformers.

Re:ummm

[multi io]

forgive me for this stupid question, but if neutrons have 0 charge, by what means does the upper plate attract them and the bottom plate repel them? Shouldn't the neutrons just ignore the presence of the plates and fall toward the center of the earth, aka down? or do we already have anti-gravity technology that i am not aware of

I didn't RTFA, but the "charge" for gravity is called "mass", which neutrons have, and the earth's gravity could be neutralized by setting up the plates vertically, so any movement of the neutrons towards the earth's center wouldn't coincide with a movement towards one of the plates. Oh, and both plates may attract the neutrons -- the summary only said that once the neutrons reached the plate surface, one of the plates would absorb the neutrons, and the other plate would reflect them.

Some of the Article Text

[catchblue22]

Here are a few paragraphs of the original article:

Spectroscopy is a method typically used to assess an unknown quantity of energy by means of a frequency measurement. In many problems, resonance techniques1, 2 enable high-precision measurements, but the observables have generally been restricted to electromagnetic interactions. Here we report the application of resonance spectroscopy to gravity. In contrast to previous resonance methods, the quantum mechanical transition is driven by an oscillating field that does not directly couple an electromagnetic charge or moment to an electromagnetic field. Instead, we observe transitions between gravitational quantum states when the wave packet of an ultra-cold neutron couples to the modulation of a hard surface as the driving force. The experiments have the potential to test the equivalence principle3 and Newton’s gravity law at the micrometre scale

Generally, a quantum mechanical system that is described by two states can be understood in analogy to a spin-1/2 system, where the time development is described by the Bloch equations, assuming two states of a fictitious spin in the multiplet, similar to spin-up and spin-down states. In magnetic resonance of a standard spin-1/2 system, the energy splitting results in the precession of the related magnetic moment in the magnetic field. Transitions between the two states are driven by a transverse magnetic radio frequency field. Similar concepts can be applied to any driven two-level system, for example in optical transitions with light fields. Variations are inherently connected to high-precision measurements such as atomic clocks6, atom interferometry7, nuclear magnetic resonance8, quantum metrology9 and the related spin-echo technique10. The sensitivity reached so far11 in the search for the electric dipole moment of the neutron is 6.8×1022eV, or one Bohr rotation every six days.

In this Letter, we demonstrate that energy eigenstates in the gravity potential of the earth can be probed using a new resonance-spectroscopy technique, using neutrons bounced off a horizontal mirror. This spectroscopy technique has in common the property that a quantum-system is coupled to an external resonator. Quantum mechanical transitions with a characteristic energy exchange between the coupling and the energy-levels are observed on resonance. A novelty of this work is the fact that the quantum mechanical transition is driven by an oscillating field that does not directly couple an electromagnetic charge or moment to an electromagnetic field. Instead, we observe energy transfer on resonance that is based on gravity-quantum states coupled to a modulator. We have named this technique gravity resonance spectroscopy, because the energy difference between these states has a one-to-one correspondence to the frequency of the modulator, in analogy to the nuclear magnetic resonance technique, where the energy splitting of a magnetic moment in an outer magnetic field is related to the frequency of a radio-frequency field. This is possible because of the feature of the quantum bouncing ball12, 13 that the levels are not equidistant in energy. The linear gravity potential leads to measured14, 15, 16 discrete non-equidistant energy eigenstates |nright fence. A combination of any two states can therefore be treated as a two-level system, as each transition can be addressed by its unique energy splitting or, in our case, by vibrating the mirror mechanically at the appropriate frequency. It has also been proposed to realize transitions between gravitational quantum states by means of oscillating magnetic gradient fields17. The physics behind these transitions is related to earlier studies of energy transfer where matter waves bounce off a vibrating mirror18, 19 or a time-dependent crystal20, 21. In the latter case the transitions are between continuum states, in the quantum bouncer the transitions are between discrete eigenstates. Optical dipole traps of atoms are reviewed in ref. 22.

Re:Some of the Article Text

[catchblue22]

It is only a small part of the article. Without graphs, and without without references. To anyone seeking to use this for academic purposes it would be largely useless. Still...

Re:ummm

[blair1q]

According to the links, one plate is smooth, and the other is rough. so a neutron will glide over the smooth plate or be scattered at small angles but if it hits the rough plate it will be scattered more, on average. Why the difference? So that they have a different effect and you can tell if perturbing their course causes more to hit the smooth plate or the rough one.

The neutron's course can be perturbed by gravity. In the steady state, this means the neutron just drops in a parabolic arc following gravity, which at these length scales (microns) can be more determined by massive nearby objects (1/r^2 is huge) than by the distant center of the Earth (1/r^2 is tiny). (You might even get a setup where the top plate gravity is equal and opposite to the Earth's gravity, for objects that are close enough.)

Moving one plate nearer or farther away makes the arc change shape, changing how many neutrons are scattered for a given beam intensity and launch angle. Moving the plate in an oscillating motion at a given magnitude should give you an oscillating scattering measurement with a fairly constant magnitude. You would expect the number of neutrons scattered to be irrelevant of the frequency, when averaged over many cycles of the oscillation, if you considered gravity to be purely Newtonian (i.e., Newtonian gravity, f = GmM/r^2, is monotonic with changes in r, even when r is changing with time).

But they don't see that. They see distinct frequencies of plate oscillation that result in bumps or sharp bends in the average scattering.

That says they're seeing non-monotonic, quantized, time-dependent effects that Einsteinian gravity suggests.

insert technobabble here ...

[Spectre]

Is it just me, or does that summary seem to be narrated by Geordi La Forge?

Re:Neutrons

[blair1q]

1. The neutrons hit the nuclei of the atoms in the plate.

2. When the nuclei are lined up nicely the neutrons are absorbed or glance-off in a more regular fashion; when the nuclei are in lumpy bumps, they are absorbed or glance off in more random fashion.

3. The piezo is only used as a motor to move the plate. The fact that it's piezoelectric is irrelevant and should have been left out. It could have been a servo or a twisted rubber band.

Stupid question of the day!!!

[Xaedalus]

Could gravity then be a function of resonance rather than mass?

Re:Neutrons

[femtobyte]

The way that the lower/upper plates "repel/attract" the neutrons is not to be due to familiar forces (e.g. electromagnetic, gravitational, weak, strong), but rather due to quantum scattering effects from the bulk of nuclei in the plate material (which can be either attractive or repulsive, depending on material composition) based on the Fermi exclusion principle (identical fermions, such as neutrons, cannot occupy the same quantum state, resulting in effective forces between them not caused by any other forces). While the statement (as is often true of science journalism for the general public) is unclear and confusing, it is somewhat true in the sense that the neutrons are not interacting through a mechanism that would show up on a list of "forces of nature".

Technobabble or Magic?

[ukemike]

Any sufficiently advanced science is indistinguishable from Star Trek technobabble.

It does NOT!

[Roger W Moore]

Actually it does, but by half the amount predicted by general relativity.

Actually it does NOT. Cavendish made suppositions without any clue to what light was - the date on Cavendish's paper was 1804, well before even Maxwell's equations let alone photons were known. Having no clue about light they supposed that it would follow a trajectory as any massive body does - quite reasonable not given any evidence to the contrary - but now we know better!

Newton's statement of his law explicitly states that the attraction is proportional to the masses of the bodies and, since a photon has no mass, there is no attractive force. So the prediction for light, composed of massless photons, is no deflection. Relying on Wikipedia articles quoting 19th century physics papers attempting to describing the behaviour of particles we discovered in the early 20th century is unlikely to be reliable!

Re:It does NOT!

[Celarent Darii]

Firstly you are wrong in saying that a photon has no mass. It has no rest mass, but it certainly has energy, and even momentum (hv/c). Force is not just m*a, but even more correctly described as the change of momentum dp/dt. Gravity is a force and therefore it causes a change of momentum.

There are many papers that speculate that is light is a particular, what must be the effect of gravity upon it, dating from several years before Cavendish even.

Here is a citation of a letter from John Michell, 1783, even predicting what we call black holes today:

http://books.google.pl/books?id=XpyvPTRwLoQC&pg=PA368&lpg=PA368&dq=Cavendish's+paper+on+gravity+and+light&source=bl&ots=EXGBWCHeYy&sig=g4vE442GKMsAtLsa0yH5ehiUIh8&hl=pl&ei=UEStTf2TGoPxsgaZ1c3XDA&sa=X&oi=book_result&ct=result&resnum=3&ved=0CCsQ6AEwAg#v=onepage&q=light%20gravity&f=false

The idea of photons, even if the name is recent in origin, is as old as light itself. Even Aristotle tried to reconcile several theories of light as being a "streaming substance" (a substance carrying some sort of energy, see de Anima), or as a "ray". The observation of motion of dust particules in a sunlight room does not date from last century.

The more you read the works of the ancient physicists, you will discover that they certainly were not people "without any clue", but often trying to wrap their minds around some serious observations. Whether they succeeded or not is another question, but they certainly had some clue.

Re:It does NOT!

[Roger W Moore]

Firstly you are wrong in saying that a photon has no mass. It has no rest mass, but it certainly has energy, and even momentum (hv/c).

Wrong. I am completely and absolutely correct to say that the photon has no mass. Mass is something called a Lorentz invariant and does not change - it is a common mistake which people often make. The gamma in p=gamma*m*v comes from the velocity (look up 4-velocity) and not the mass. Hence a photon has zero mass in all inertial reference frames regardless of its energy. Even Einstein warned that it was wrong to think of the mass as changing.

Force is not just m*a, but even more correctly described as the change of momentum dp/dt.

Under Newtonian mechanics, which is what we are talking about here, the two are identically equivalent for particles of constant mass. Since, even under relativity, photons have a constant mass this certainly applies. Since Newtonian gravity uses mass as the charge of the gravitational force any particle with no mass feels no force.

There are many papers that speculate that is light is a particular, what must be the effect of gravity upon it, dating from several years before Cavendish even.

True, in fact Newton was probably the first, but the key word here is speculate. They had absolutely no idea of the properties of the particle nor any evidence for it. Also none of these, to my knowledge, considered the effect on light if the light "corpuscles" (as Newton called them) had zero mass.

Re:It does NOT!

[Roger W Moore]

The more you read the works of the ancient physicists, you will discover that they certainly were not people "without any clue", but often trying to wrap their minds around some serious observations.

If you use hindsight to hand pick the wild speculations which happened to hit near the mark and ignore the rest then of course it seems like they had some amazing insights. For example, Newton was an amazing physicist and mathematician, he even speculated that light was made of particles. He was also an alchemist and believed that he could transmute lead into gold.

The more you read ALL the works the ancient physicists, and not the works which have been selected with modern hindsight, the more you will realize that, while they were brilliant people, when they were making wild speculation they really were doing just that - making wild speculations.

ATLAS/LHC

[Roger W Moore]

But everyone that thinks otherwise is welcome to calculate sqrt(1 - v^2/c^2) for their experiment's velocity and see if the values vary significantly

I'm not sure that works too well - my experiment is large and very stationary but the particles we collide in the middle have a gamma [which is 1/sqrt(1 - v^2/c^2)] of well over 3,500.

Re:ATLAS/LHC

[jd]

I think it's fair to consider the relativistic velocity* of the particles as being the key part of the experiment for ATLAS (much as it was for EUROGAM, the one I worked on). However, even if you consider the relativistic velocity of the detectors, it would be relative to the byproducts of the collision and not to the observing scientist. Thus, the velocity of the experiment is still not zero -- except in summation. (Although the relativistic velocity is very high, the resultant velocity is nearly zero.)

*In relativity, it is prohibited for any particle to observe another particle moving faster than C. In order for this to be true when a central observer sees two particles each closing in at near-C from opposite directions, you have to assume that you cannot simply sum up the velocities. You have to divide by 1 + vu/(c^2).

Re:ATLAS/LHC

[JamesP]

Well, I've heard about your experiment, and it's actually pretty fast, going at around 30 km/s around a large mass of hydrogen currently undergoing fusion! ;)

Re:ATLAS/LHC

[Roger W Moore]

That's nothing compared the the velocity of the large mass of hydrogen itself orbiting the centre of its galaxy.

Kernel Upgrade?

[Roger W Moore]

Perhaps a kernel upgrade would be a better analogy for slashdot? The core of the system has had a major improvement but the desktop GUI is not really affected. So, unless you are a kernel hacker/gravitational physicist there are not many noticeable changes!

a bit one-sided

[kubitus]

at least on the Authorship:

1.

Atominstitut, Technische Universität Wien, Stadionallee 2, 1020 Vienna, Austria

* Tobias Jenke,

* Hartmut Lemmel &

* Hartmut Abele

2.

Institut Laue-Langevin, 6, Rue Jules Horowitz, 38042 Grenoble Cedex 9, France

* Peter Geltenbort &

* Hartmut Lemmel

3.

E18, Physikdepartment, Technische Universität München, 85748 Garching, Germany

* Hartmut Abele

4.

Physikalisches Institut, Universität Heidelberg, Philosophenweg 12, 69120 Heidelberg, Germany

* Hartmut Abele

Re:anti-gravity machine?

[Muad'Dave]

Neutron != neutrino.

Re:Gravitational quantum states of neutrons, eh?

[The_Wilschon]

You may be able to wrap your head around the idea of the quantum states of an electron bound to a proton (that is, an electron in a hydrogen atom). The hydrogen atom is defined by having a particular potential energy that varies as a function of the distance from the proton. This is just like that, but instead of a potential energy that depends on the distance, r, from the proton like 1/r, we have a potential energy that varies as a function of the distance from the center of the earth, h, like m*g*h. This is actually a common and relatively elementary quantum mechanics problem that is commonly solved by undergrad physics majors in introductory quantum. The solution involves Airy functions.

Where it gets interesting: You put the lower, reflecting plate into the potential energy as an infinite potential at a particular h (the location of the plate). This makes a sort of triangular shape if you plot it as a function of h. The precise details of just exactly what happens in the potential down around the point of the triangle (does it stay pointy no matter how low you go, or does it smooth out as some scale, and if so, how?) can tell you a lot about how gravity works on very small scales. If you get a sensitive enough experiment, you might be able to test some theories of fundamental physics that involve large extra dimensions (string theories, Kaluza-Klein models, SUGRA, etc) and derive upper bounds on the size of those extra dimensions. You might also be able to learn something about the quantum behavior of gravity itself (as opposed to the quantum behavior of neutrons, which is comparatively much much more well understood).