Newton's Second Law, Revisited

eldavojohn writes "Dust off your fundamental physics books, an aspiring astrophysicist by the name of Alex Ignatiev has published a paper that proposes testing special cases of Newton's Second Law on earth's surface. His goal is sort of ambitious. The time he has to test his theory is only 1/1000th of a second, twice each year, in either Greenland or Antarctica. What would he look for? Spontaneous motion. From his interview with PhysOrg: 'If these experiments were to take place, Ignatiev says that scientists would look for what he calls the SHLEM effect. This acronym stands for static high latitude equinox modified inertia and would be noticed in a condition where the forces of the earth's rotation on its axis, and of the orbital force of the earth as it moves around the sun, would be canceled out ... In the end, if Newton's Second Law could be violated, he would be forcing physicists to reevaluate much of what we understand derived from that law — which is quite a bit.'"

A bit early for April Fools?

[lecithin]

Or is it?

Reminds me of what Patrick Moore did:

Stolen from

http://en.wikipedia.org/wiki/Patrick_Moore [wikipedia.org]

Eccentric personality

Due to his long-running television and xylophone playing career, eccentric manner, distinctively rapid speech delivery and in later years his ever-present monocle, Moore is widely-recognised and well-respected in the United Kingdom, even by those with no interest in astronomy. This was used to great advantage for a 1976 April Fool's joke on BBC Radio 2, when Moore announced that at 9.47 am a once-in-a-lifetime astronomical event was going to occur: Pluto would pass behind Jupiter, temporarily causing a gravitational alignment that would reduce the Earth's own gravity. Moore informed listeners that if they could jump at the exact moment that this event occurred, they would experience a temporary floating sensation. The BBC later received hundreds of phone calls from listeners claiming to have felt the sensation.

Moore joined the Flat Earth Society as an ironic joke though many have taken this seriously.

Finding holes in the theory...

[RyanFenton]

Yes, it only takes one demonstration to a render invalid a scientific theory. But that does not validate any other theories by doing so, unless they can accurately carry the same predictive weight as the previous theory, plus comply with the improved observations.

A hole in Newtons second theory in any case doesn't mean scientists throw out their physics books, it generally means they add and exception to the theory and work on finding a more unified algorithm to describe the newly revised observations. Here's hoping this somewhat exotic set of observations leads eventually to a stronger set of theories, rather than just more false controversy about 'mavericks' and 'closed minded skeptics' - everyone's a skeptic AND a maverick, closed minded and radical - focusing only on the extremes of that, especially in terms of science sort of ignores the whole point of science, to use biased viewpoints to paint a larger picture.

Ryan Fenton

the era precision cosmology

[bcrowell]

I think it's odd that MOND's enthusiasts are so eager to push it as an alternative to dark matter, now that we've entered the era of high-precision cosmology. We know a hell of a lot about cosmology that we didn't know ten years ago. We know the age of the universe to two significant figures. We know that the universe is expanding at an increasing rate. We know the spectrum and angular distribution of the cosmic microwave background to high precision. We've found out that neutrinos have mass. I can see how MOND would have some appeal back in 1981, when it was first proposed, but so much has changed in the last 26 years. The evidence has accumulated that we live in a universe that's much stranger than we'd believed. I think that's cool.

Hammer, Feather, Freefall on the Moon: Revisited

[Anonymous Coward]

"Fall heavy towards the moon, and the moon falls also towards you." -- Nietzsche

Hammer and feather are dropped simultaneously from equal heights (as measured by distance from the center of the moon), separated laterally by a distance substantially less than the moon's diameter. Both hammer and feather experience force from the moon's gravity proportional to their mass, and hence both accelerate at the same rate. Meanwhile, the moon is also accelerating towards the other two objects, but unevenly so: the hammer exerts a greater gravitational pull due to its greater mass. The moon is therefore subject to a torque, causing it to accelerate more rapidly towards the hammer.

The hammer is first to hit the ground.

Anyone who denies this truth is a spatially absolutist lunocentric whose refusal to recognize the validity of hammer/feather mechanics places him wholly beyond the help of Galilean metaphysics. Such hammer/feather rejectionists ought to be banished from planetary space, for their own good and for the good of not only hammers and feathers but all subjugated smaller objects, everywhere, who find themselves victims of this scientifically perpetrated emassculation.

--
a756f345ec354225c08ff1a10a43162a

Speed of Light Breaks it Already, Doesn't It?

[BlackGriffen]

I mean, NSL only applies in the case of slow moving/low acceleration objects because it assumes infinite propagation speed of the force carrier.

If he finds this it will be interesting not because of NSL concerns but because it would be an observation of the finite propagation speed of gravity. A fact that would serve as indirect (or perhaps direct) evidence of gravitational waves.

Why Not in Space?

[vertigoCiel]

Am I missing something, or would this be a hell of a lot easier to do in space? From TFA I gather that he's looking for an instance of no outside force, and, since orbit is essentially free-fall, this would be easily accomplished on the ISS. Granted, I might be missing the point entirely, or I don't get his strange "I've got to do this on the surface of the Earth!" fetish.

Wonder how much testing this is worth

[ThanatosMinor]

So for this thousandth of a second in a remote location at 80 degrees of latitude, is he proposing that we build an entire testing facility to see if an uncharged particle wiggles a little bit for some reason by some mechanism that no one has really figured out?
Are we also to believe that because the mathematical calculations work out such that all first- and second-order gravitational forces are cancelled, if we observe some motion, that motion is a clear violation of Newton's Second Law by assuming that there is zero force on the particle?
Wouldn't it be just as reasonable to claim that there were another force involved rather than saying that the Law has been debunked?

Laws aren't exactly "broken" in physics

[thrawn_aj]

What laypersons should realize is that when a flaw is discovered in a well-established physical theory, it usually reduces the domain of validity of the theory, but RARELY makes that theory useless as a calculational tool (it just tells us when the theory will break down, as ALL current theories eventually do - the triumph of modern physics is to push those breakdown points to the farthest reaches of the imaginable). In this, physics has been an unqualified success - a fraction of the predictive power that we have today would have been enough to condemn several "soothsayers" to a grisly demise at one point in history :P. To digress for a moment here, it amuses me greatly that people can be obsessed with psychics and the contemptible Nostradamus while taking such exquisitely detailed predictions as tomorrow's weather for granted. It's rather like being impressed with a mythical flying superman while thinking of an airplane as mundane.

An example to illustrate the breakdown of theories: the Special theory of Relativity modified Newtonian mechanics on a fundamental level. However, for speeds much less than the speed of light (which is what most of us experience in daily life), it is STILL Newtonian mechanics that we use, even in several cutting edge research fields. The rule of thumb in research is: never use a full model when an approximate one is just as accurate in the domain of interest. In much the same way, even if MOND were true, any deviations from Newton would kick in at EXTREMELY LOW accelerations (of the order of 10^-20 m/s^2 which is about 10^-21 g, something next to impossible to duplicate in a lab because of ambient vibrational noise which is usually MUCH higher (say, about 10^-9 g is a VERY quiet environment)). This is the reason why the paper (which attracted our group's attention a few weeks ago) proposes an experiment at such well-defined times and locations. To put it bluntly, this is an ad-hoc modification in the sense that there is just no justification for the modification. Of course, I don't even think MOND would replace the Dark Matter hypothesis. One might even argue that this modification is simply a way of expressing the effect of Dark Matter (just a thought).

Re:Does this mean...

[TheManifold]

Newton's laws are just very very good approximations of reality. Einstein's theories of general/special relativity are still even more accurate versions of reality.

An article in the New Scientist talks about 'Quantum Reality', where everything we see is just an approximation of the quantum world. I won't elaborate further, but I hope you get my gist.

These theoretical astrophysicists are getting good

[Phroon]

These theoretical astrophysicists are getting good at what they do.

The submitter of this article (and the populace of Slashdot as a whole) doesn't get the point of this article. Ignatiev isn't suggesting this experiment out of thin air, he's suggested a novel earth-based experiment to help explain the anomaly in galactic rotation (ie. Dark Matter). To explain this anomaly some theoretical astrophysicists modify Newtonian dynamics in a small way so that the galactic rotation calculations come out correct. Others introduce Dark Matter, or alter gravitation itself.

He basically wants to observe an object smaller than 7 cm x 40 cm x 40 cm at the precise moment and the precise location on the earth such that it would experience an acceleration that is much smaller than the extra acceleration it would experience as proposed by the modified Newtonian dynamics. So any extraneous acceleration observed at this moment had to have come from modified Newtonian dynamics.

The interesting thing about this article is that it isn't just a wild claim by a crackpot scientist, it's the proposition of an extremely accurate measurement using the most advanced technologies we have available. Of particular interest to me was that the proposed effect was two orders of magnitude larger than that observable by LIGO, a gravitational wave detector, suggesting that such an experiment is actually possible.

Re: Relativistic 2nd Law

[blank axolotl]

You're right that you can still use an equation that looks like F = dp/dt in GR, but I still think the original second law is wrong with all the quantities defined as they were. Writing it your way, it is then the definition of momentum which is wrong (or going on, the definition of velocity as dx/dt not dx/dTau). (Also in GR F= dp/dTau, not dp/dt if t is the time coordinate). The symbols in GR just happen to look and act quite like the newtonian symbols, but are interpreted differently.

Anyway, it is the error in predicted motion that is interesting here, where 'F=ma' gives the newtonian motion,
but this becomes like 'F = ma + m Gamma Vi Vj' in GR. You can't clearly see the different motions each theory gives in F = dp/dt.

Re:Both Sun and galaxies centers are accelerating

[ThosLives]

I don't think it has to do with acceleration of galactic centers. I think it has to do more with the effective radius used in the calculations.

For instance, in a traditional central-body problem, you have a very basic set of equations that says the path of any body around another body will be a conic section, with modifications due to more than two bodies in a system.

What I've never seen in literature, and I've seen the plot of angular velocity versus radius that "flattens out" for galaxies, is just what that angular velocity is? Is it angular velocities for individual stars, or an average?

If it is just an average, then I wonder is it an effect due to observation. What I mean is this: when looking at a gas here on earth, the average temperature is a good measure for its properties. However, only a small portion of the individual molecules in the gas actually have that exact temperature. The same for a stream of exhaust from a jet - the jet has a general average velocity, but each individual particle has some other velocity that contributes to the bulk average velocity.

I am wondering if the aggregate motion of a galaxy is like gas temperature or velocity; that is, it may be a superposition of the individual accelerations of the individual starts and nebulae in the galaxy. That is, is it possible to generate a system only with particles that obey classical (relativistic) gravity but can appear, in aggregate, to disobey the mass proportionality of Newton's Second Law? I suspect that 'galactic' measurements are like measuring bulk properties of a gas rather than looking at the kinetic model. Something perhaps like the recent storm on Saturn / water in a spinning bucket articles where simple motion of individual particles gives rise to more complex aggregate behavior.