Experiment Finds That Gravity Still Works Down To 50 Micrometers (arstechnica.com) 63
An anonymous reader shares an excerpt from a report via Ars Technica: To make small-scale gravity measurements, researchers rely on conceptually simple experiments: measure the changes in rotational speed of an oscillating disc that is subject to a periodically changing gravitational force. The periodic force is supplied by a spinning disc. Both discs have wedges cut out so that the force due to gravity varies as the gaps spin past each other. The two discs are arranged right on top of each other. One is attached to a thin cable and is set in motion by twisting the cable, while the other rotates at a constant rotational speed. As the oscillating disc changes its direction of rotation, it is still subject to a periodic torque from the rotating disc. These torque changes are highly periodic and can be measured very accurately. The wedged disc design gives a set of three rotational frequencies, so the instrumentation errors can be filtered out by examining changes that are common to all three frequencies. The researchers have gone through several iterations to slowly improve their sensitivity over the last decade. Their experiment eliminates -- so far as possible -- all forces due to electrical and magnetic fields. The researchers have a set of three test masses that sit on top of the experiment to allow them to calibrate their analysis against a larger signal.
The major improvement, however, was in the analysis. To extract the force due to gravity, careful modeling is required. The researchers changed the design of the pattern cut out of the test mass so that analytical solutions to the model were obtainable for the torques involved. This eliminated many of the uncertainties due to computer modeling. This and many other experimental refinements have allowed them to measure gravitational attraction down to a distance of just 52 micrometers. Once they add additional stabilization against vibration, they will be able to measure at even smaller separations. In the meantime, they have verified that the inverse-square law holds for distances shorter than 50m, and therefore we have no New Physics. The findings have been published in the journal Physical Review Letters.
The major improvement, however, was in the analysis. To extract the force due to gravity, careful modeling is required. The researchers changed the design of the pattern cut out of the test mass so that analytical solutions to the model were obtainable for the torques involved. This eliminated many of the uncertainties due to computer modeling. This and many other experimental refinements have allowed them to measure gravitational attraction down to a distance of just 52 micrometers. Once they add additional stabilization against vibration, they will be able to measure at even smaller separations. In the meantime, they have verified that the inverse-square law holds for distances shorter than 50m, and therefore we have no New Physics. The findings have been published in the journal Physical Review Letters.
Sure... (Score:3)
...but falling down 52 micrometers doesn't hurt.
Re: (Score:3)
That depends on how massive the object attracting you is.
Re: (Score:3)
Re: (Score:2)
Re: (Score:2)
A black hole of 3 Inches is a pretty big mass. I wouldn't want to fall unto that. That's about 8 to 9 times the mass of earth.
So it would attract you 9 times harder than earth does to you, at a single 3 inch point. This will probably go through you like a knife trough butter.
Or your atoms would spaghettify-sucktion into the 3 inches.
Re: (Score:2)
Even a microscopic black hole would be devastating because of tidal disruption.
https://en.wikipedia.org/wiki/... [wikipedia.org]
Amoeba late night TV (Score:1)
..."I fell down and can't squirm back up!"
It takes all kinds (Score:3)
Re: (Score:2)
Yet nobody knows if the light really goes off when you shut the refrigerator.
I do. I turned on the video recording on my cell phone and put it in the fridge. Then I watched the recording.
The light goes off.
Re:It takes all kinds (Score:4, Interesting)
But does it turn off when you're NOT observing it?
Re: (Score:3)
Re: (Score:2)
"Schroedinger's refrigerator*
You locked your cat again in the fridge?
Re: (Score:2)
Re: (Score:2)
Re: (Score:2)
Re: (Score:2)
Re: (Score:2)
Re: (Score:2)
But does it turn off when you're NOT observing it?
The photo-sensitive film behind the slits in the double slit experiment is recording the 'outcome' of the photons' impacts, yet isn't 'observing' them.
So, does being filmed on a 'dumb', or perhaps non-conscious, recording device such as GP's cell phone, count as observation? Nope. The observation happens when he looks at the footage. Too late for the light to have decided not to switch off...
If that's not a convincing argument then perhaps we'd need to move to a proxy measurement instead. Agree that we neve
Summary of the summary (Score:2)
This test is very simple: (insert the most complex thing you have ever read, full of sciency terms and complex descriptions of interacting things that are basically impossible for normal people to follow)
See? Simple! What's wrong with you? You aren't stupid, are you?
Re: (Score:2)
This fact persists only because manufacturers have cleverly continued to wrap them in a Faraday shield. What else are they trying to hide? (Ever seen a propane refrigerator? They're using *heat* to *cool* something? *Yeah, right.* What's the real interdimensional source they're tapping?)
Very useful experiment (Score:4, Insightful)
There are various gravity theories that predict a deviation from inverse square law behavior at small distances. This is a very nice result. Its always useful to try to push basic physics measurements into new conditions.
Re:Very useful experiment (Score:5, Interesting)
String Theory predicts that gravity should start falling off faster than 1/r^2 over very short distances as it begins propagating through the "rolled" dimensions - just how short is an open question, but I suspect it would be MUCH larger than Plank-scale, or the granularity would interfere with curvature. I believe several of the other semi-related N-dimensional theories expect similar behavior.
Every time we push down the maximum size of those dimensions we make those theories slightly less plausible, and help alternatives gain a little traction. Alternately, if they had found a discrepancy, it could be the first real supporting evidence those theories had found, and exploring the exact characteristics might be extremely enlightening. It is one of the only places that ST predicts different behavior than more traditional quantum theories.
Re: (Score:2)
We're not talking about the strings - they'd indeed be at quantum-particle scales. We're talking about the space that the strings occupy, which must have at least 10 dimensions for the strings to be able to resonate at all the frequencies needed to create the fundamental particles.
String theory make NO predictions about the size of the extra dimensions themselves* - it would be perfectly consistent with a universe in which all 10 dimensions were exactly like the "normal" 3 - but that would drastically alte
Re: (Score:2)
No, it's not. String theory, in conjunction with historical observations, predicts that gravity will start deviating from 1/r^2 at small distances.
It makes absolutely no prediction as to how small those distances will be - it could be just barely below the current limits tested, or it could be subatomic. There's not one shred of theory to suggest one the one is any more likely than the other.
Re: (Score:2)
Nobody is claiming it does. *Testing* gravity at ever smaller scales is useful, primarily because it may discover those discrepancies we're looking for. Failing to find them is disappointing, but also kind of useful since narrowing the plausible size range makes it (slightly in this case) less like that those theories are correct, and lends more momentum to competing theories. Much as (dramatically) narrowing the size range of black holes that could be dark-matter candidates has caused them to largely b
Re: (Score:2)
String theory is the phlogiston of the modern age. It's a complex set of theories conjecturing physical structures with contradictory characteristics which keeps being refuted by elegant simple experiments with very careful measurements. Verifying gravitational behavior by spinning disks is as interesting and elegant as the original measures of the speed of light, also measured by spinning disks with gaps, and the Michelson Moreley experiment, also measuring interference patterns to look for significant co
Re: (Score:2)
You misunderstand the role of "theory" in physics. No experiment exists in a theory vacuum. They all make presumptions of one theory or another, even when they are testing a theory. Let there be myriad theories, that's how we think of new physics for which to test.
That doesn't excuse the ST bandwagon. Physics theories should not become bandwagons.
Re: (Score:2)
How is this not understood? (Score:2)
Re:How is this not understood? (Score:5, Interesting)
Re: (Score:2)
And /. has no (Score:2)
In the meantime, they have verified that the inverse-square law holds for distances shorter than 50m, and therefore we have no New Physics.
That should be 50µm but slashcode is stuck in 1999.
Re: (Score:2)
That, and the difficulty typing it, is why "um" is so frequently used instead of using the letter mu
Re: (Score:2)
Why not ""?
Re: (Score:2)
Yup even ASCII dies on ./
Re: (Score:1)
Apparently the real excuse is there was a unicode troll problem with people putting in fun control codes to do stuff like reverse text. Don't think sticking to extended ASCII is the best solution though.
I'm puzzled (Score:2)
Re:I'm puzzled (Score:4, Informative)
I believe the challenge is measuring the result amidst the other attractive forces. You have to get the centers of mass to within 50 microns, and yet have enough of an effect to actually measure, which is generally going to mean thin disks or some other arrangement where the surface area of the objects in close proximity is high. Large flat surfaces close to one another are affected by a variety of forces. A tiny amount of charge in this poor-man's capacitor would utterly dominate gravity. Van der Walls force is quite small for objects that aren't actually touching, but compared to gravity? I believe the challenge is in controlling the experiment, so that what you measure is actually gravity, and that get progressively harder as distance falls.
Re: (Score:2)
Re: (Score:2)
Re:I'm puzzled (Score:4, Insightful)
String Theory and many other N-dimensional physics theories predict that gravity propagates through many more dimensions of space that loop back on themselves, so that once you measure it at scales below the size of the largest looped dimension it will begin falling off much more rapidly. A force propagating through 4-D space for example would fall off with the inverse cube, instead of the inverse square.
However, they make absolutely no prediction on the size of these other dimensions, except that historical observations set the maximum at less than a few mm. And I suppose this has pushed it down by another factor of 10 (I'm assuming that things get a lot less conclusive as you approach the limits of the data.)
Re: (Score:2)
Re: (Score:2)
Do we have some reason to believe the Higgs field is involved with gravity? My understanding is that the Higgs field is theorized to provide inertial mass, but that we still have no theoretical explanation for the fact that gravitational mass always seems to be the same as inertial mass. And we're not even certain of that much, as we haven't yet directly measured the effect of gravity on antimatter, which might have a different polarity or even more unexpected characteristics.
Nice (Score:2)
Re: (Score:2)
I think the biggest driver for gravitational experiments at ever-smaller scales is probably looking for evidence that there are more than 3 spatial dimensions in the universe, as required by String Theory, etc. Gravity is generally predicted to propagate through those other dimensions (*especially* if it's a property of space itself), so once you start measuring gravity over distances shorter than the circumference of the largest extra dimension you should see gravity falling off faster than it does in our
Re: (Score:3)
I think the biggest driver for gravitational experiments at ever-smaller scales is probably looking for evidence that there are more than 3 spatial dimensions in the universe, as required by String Theory, etc. Gravity is generally predicted to propagate through those other dimensions (*especially* if it's a property of space itself), so once you start measuring gravity over distances shorter than the circumference of the largest extra dimension you should see gravity falling off faster than it does in our larger (effectively) 3-D universe. For example, we'd expect gravity to fall off as 1/r^3 in 4-D universe.
1/r^10 in 11 space?
Re:Nice (Score:4, Insightful)
Exactly.
As a monopole force (light, gravity, electrostatic charge, etc.) propagates through space, the intensity of the force at a given distance is inversely proportional to the surface area across which it's spread. And the surface of a (hyper) sphere, or any other shape really, has one fewer dimensions than the space its volume occupies. E.g. spray butter through a hole so that it perfectly covers a piece of toast - and if you move the toast 2x as far away, the same angular spray "pyramid" will cover a 2x2 arrangement of toast in size (same amount of butter, over r^2 the area =1/r^2), while the pyramid itself is a space-filling phenomena that will be also be affected by the distance being 2x as far, for 2x2x2 the volume
The same pattern extends to lower dimensions as well - conduct experiments where force propagation is confined to a plane, and it will fall off as 1/r instead of 1/r^2. You can get a similar effect in 3D space by using an "infinite" rod as your source rather than a point. Since the angular length of the rod is independent of your distance, it essentially "erases" that dimension from consideration. Long florescent tubes are probably the most common example - so long as you're much closer to the tube than its length, the light intensity falls off as roughly 1/r (And yes, using an infinite plane source means *no* falloff with distance. Which is one of the cool properties of large panel lights, speakers, microphones, etc.)
Re: (Score:2)
Re: (Score:2)
I suppose it would - but at such short distances from a fissioning rod, I doubt anything would survive long enough to care. And since a rod spreads out the material you'd need a *lot* more of it to maintain near-critical density - the rod would probably have to be almost as thick as the sphere it's replacing.
Re: (Score:2)
And since a rod spreads out the material you'd need a *lot* more of it to maintain near-critical density.
I think you mean "maintain near-critical mass," as almost any mass can be driven to critical density with properly applied force. And the massive force of the plasma induced in the secondary by the primary x-rays would crush any amount of plutonium in the cylindrical "sparkplug" to critical density.
Excellent (Score:2)
That is one science that is not satisfied with half-baked theories and coarse measurements. They really want to know.
Gosh, that's way too close! (Score:2)
Re: (Score:2)
lies (Score:2)
How does measuring things down to 52 micrometers prove that the inverse square law holds down below 50? Below 50 micrometers gravity is controlled by microscopic smurfs working in an inverse cubed law, go ahead prove me wrong ;)
That's Actually Pretty Big (Score:2)
For SAE/USCU people, 50 microns is about 0.001270"