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Gravitation Anomaly Measured
Rob Riggs writes "Is there a hole in Einstein's Theory of Relativity? A story in The Economist talks about an apparent gravitation anomaly recorded during solar eclipses. According to Chris Duif at the Delft University of Technology, the 'Allais effect' is real, unexplained, and could be linked to another anomaly involving a the Pioneer spacecraft. More detailed information can be found in the paper he has just posted on arXiv.org."
Yes. Syzygy is when the Earth, moon, and the sun are all lined up. Spring tides occur at this time. Spring tides are unusally high tides that occur during syzygy.
as i understand it it's the other way round - one of the possibilities mentions the moon "blocking" gravitation from the sun during an eclipse.
I would highly doubt that Einstein's theory is flawed, but then again, they did not study the effects of gravity during a solar eclipse back then.
Not only is this comment not "insightful" but it is just plain wrong. One of the original PROOFS for relativity involved measuring the amount that light is bent during a -- pay attention now -- solar eclipse. To quote the article you so carefully did not read, it was "observations taken during a solar eclipse (of the way that light is bent when it passes close to the sun) which established General Relativity in the first place."
Next.
Actually, it was Eddington's observations of a solar eclipse that provided the first concrete evidence of General Relativity. Those observations are nowadays regarded as having been less than reliable, but they were crucial at the time for establishing GR's credibility.
The "three-body problem" is that there is no known general closed-form solution to Newton's laws if more than two gravitating bodies are involved. In short, you can't derive an equation that will give you the positions of all three objects at any arbitrary point in time.
Instead, iterative solutions are used: given the current masses, positions, and velocities of the objects involved, figure out where they'll be a short time from now. Lather, rinse, repeat. The problem with this is that over long timespans (tens of millions of years), errors build up.
"They redundantly repeated themselves over and over again incessantly without end ad infinitum" -- ibid.
Photons are massless, but having energy, they do gravitate. However, if you work out the magnitude of the gravitational effect of the photons from the Sun that reach the Earth, it's much smaller than even the purported effect in the article.
"Photons have mass. "
They don't. They do have momentum though.
I wonder if Gravity Probe B will be able to measure this effect if it is still in working order next time an eclipse rolls around.
(Side note-- I never heard of this probe until I saw it in a magazine. Why not?)
MOND evidently has problems; while dark matter can explain both galactic rotation curves and cosmological behavior, MOND is hard to make consistent with both. (And it's also, I've heard, extremely hard to make consistent with any relativistic theory of gravity.)
As for the "apparent need" for FTL expansion in the early universe, by which I assume you mean inflation, some very specific predictions of inflation are now verified by WMAP, including the structure of the acoustic peaks in the CMBR angular power spectrum.
Wacky as they may seem, dark matter, dark energy, and inflation are the mainstream theories right now for a reason: the alternatives so far simply don't work as well.
Light can be slowed down in a medium, but c is by definition the speed of light in vacuum. The presence of charged matter can slow down light, but not speed it up, so the speed of light in vacuum is as fast as you can get.
The easy explanation as I was given to understand is that the photons propagate in spacetime, ie the wave that they are does. Spacetime is curved by gravity, hence the photons/waves curve with them. According to General relativity, they cannot have mass since they propagate at light speed. Any object with mass obtains infinite mass upon attaining lightspeed, which is impossible. Hence a photon has no mass. Of course, solar sails work so photons can exert pressure which might lead one to suppose they have mass. In sense they do, as energy and matter are equivalent. In the case of a solar sail, it is impulse that is being transferred. It depends on how you measure the presence of the photon. By the way, note that Duif does not cast doubt upon Einstein's theories per se. Rather, he invokes the presence of dark matter (although no one has ever demonstrated its presence unequivocally).
----- One learns to itch where one can scratch.
Given that light can be slowed down, what reason have we to assume that c is not some slowed-down light speed?
It is. You can get a very slight boost in the speed of light by suppressing quantum vacuum fluctuations (the Casimir effect).
"They redundantly repeated themselves over and over again incessantly without end ad infinitum" -- ibid.
The Economist is probably the best source of general news available. It is in the same category as Time, Newsweek, US News & World Report, except that where those magazines tend to be 10-20% real news and 80-90% pab, the Economist is the inverse with 80-90% real hard news.
They know it too, and consequently it is very hard to find much of a discount on subscription pricing -- if you can pick it up for under $100/yr you are doing very well. All those other rags can typically be found for pennies on the dollar if you look.
In case you can't tell, I get all my news online - no tv news, no newspaper, maybe a dab of NPR when I'm tired of listening to my music in the car and no magazines, except the Economist. Which I get full access to online by virtue of paying for a paper subscription.
According to modern definitions, the unqualified word "mass" refers to invariant mass (which for massive particles is called "rest mass", although that term makes no sense for photons which can never be at rest). Thus, photons are referred to as massless particles.
The kind of mass you're talking about is nowadays referred to variously as "mass-energy", "effective mass", "relativistic mass", or just "energy" when people feel like slurring the difference.
Apparently, you've never seen a scrabble word. (There are only two 'y's in Scrabble).
Photons are both influenced by gravity, and can influence gravity.
To understand how they are influenced by gravity, one must understand that according to general relativity, spacetime is curved, and bodies follow paths called geodesics which are paths of minimal distance. (Geodesics on a spherical surface, for example, are segments of great circles.) Photons travel along a special class of geodesics called "null geodesics" (Which don't exist in ordinary Euclidean spaces, but do in spacetime. They are essentially paths of zero "length" where length is defined a bit differently for spacetime.) Anyhow, massive bodies influence matter around them by curving spacetime. In curved spacetime, geodesics are no longer straight lines, but curved paths. Photons trajectories can thus be bent by massive object even though they have no mass, in contrast to Newton's theory of gravity which holds that massless objects do not participate in gravity.
Additionally, photons can influence gravity themselves. According to Einstein, it is not just mass, but momentum and energy that curve spacetime. (This is through a quantity called the stress-energy tensor, T, which can be represented by a 4x4 matrix). Since photons, although massless, have momentum and energy (this is allowed by special relativity, forbidden by Newtonian mechanics) they can gravitate as well.
If I can be modded down for being a troll, can I be modded up for being an orc, or a balrog?
Well, it's yer space-time warping by large gravitational fields innit.
r s/961102.html for a pretty good explanation.
Check out http://imagine.gsfc.nasa.gov/docs/ask_astro/answe
Once I was a four stone apology. Now I am two separate gorillas.
This is just wrong. The Newtonian prediction gave an angle of deflection which is half that of the Einstein prediction. The experimental prediction decided in favor of Einstein.
The General Theory of Relativity consists of sixteen coupled differential equations that can be reduced to ten, which when just written out would take hundreds of pages. It is so complex that there are research programs just categorizing possible solutions.
Analytical solutions only exist for two cases: the overall case that describes a homogeneous universe, and the Schwartzschild case that describes a spherical body. There is also a linear approximation that gets gravity waves.
It's a bit premature to say that GR has a hole in it, because nobody has ever explored it fully. Perhaps this will lead to a solution of GR for this case, or perhaps not.
The term "spring tide" has nothing to do with the seasons. The word "spring," means "to rise up." Therefore, the water is rising up above about its normal level during a spring tide. (Neap tide is opposite, for your information.)
On second check, it's worth less than 25 points, because a standard Scrabble set comes with only two Y tiles, meaning a blank must be used for the third, decreasing the possible score to a mere 21 points.
You can never go home again... but I guess you can shop there.
I'm inherently skeptical of any paper first heard of via a website. Call me old fashioned, but I'd rather wait for peer review to run its course and read this in something like the Journal of the AAS. Having said that, I read the paper and it's considerably less sensational than the summary suggests. The author considers it possible, if not probable, that the effects can be ascribed to a combination of experimental error and theorists not having taken into account the circumstances of the situation. He suggests that further research would be useful, but I've never read a paper that didn't...
"'I pass the test,' she said. 'I will diminish, and go into the West, and remain Galadriel.'"
- JRR Tolkien.
Tips for successful karma-whoring: #63 if you're going to reuse an ancient joke that was dodgy the first time round, at least try not to post it directly in reply to the exact same joke....
"'I pass the test,' she said. 'I will diminish, and go into the West, and remain Galadriel.'"
- JRR Tolkien.
pay attention now
Quit trolling. The OP was speaking in the context of measuring pendulums during an eclipse. Context creates "they did not study the effects of gravity on a pendulum during a solar eclipse".
+++ATHZ 99:5:80
IIRC, the gravity/acceleration equivalence is only supposed to be true at a point anyway. Thus, your objection, as well as the other common one, that gravity is spherical while acceleration is flat, says nothing about relativity.
Media that can be recorded and distributed can be recorded and distributed.
-kfg
You obviously aren't a subscriber or a regular visitor to their website. The Economist is simply the best weekly news print magazine in the world. For example, it's the only news magazine which never makes me cringe when they cover technical subjects I know well like Linux or computing. Same with their culture section, world news, etc. They've been doing this since 1843 and they are bad ass. I highly recommend it to anyone looking to read just one print magazine a week to learn about world news.
:-)
And no I don't work for them.
Wow, does that mean if the human seismic/mass hypothesis in the original paper hold true, that a flash mob near a high-energy physics facility could lead to mass devastation?
There's a much easier way. It only takes around 50 people to make a large office block sway. All they have to do is push on opposite sides at the right rate and they can use the resonant frequency of the building to build up amplitude.
Alternatively, you can do what Tesla did, and attach a Tesla oscillator onto one of the iron beams of a 10 story steel structure, and allow the resonance to build up. He managed to create a mini-earthquake.
And if you could get around 4.55 x 10^28 humans to form a flash mob, you could create an all-human black hole.
Vintage computer adverts: http://www.vintageadbrowser.com/computers-and-software-ads
Proponents of Process Physics claim that Einstien's original case for general relativity was built on a misinterpretation of critical 19th century experimental data and contend that the consequential abandonment of the ancient notion of Æther was wrong headed.
From their perspective, gravity should not be seen as a force field but rather as the cummulative effect of all massive bodies continuously absorbing/dissipating Æther. Locally the earth sucks most of the Æther and we experience the resulting downwards pressure.
-- Our systemic servants do not good masters make.
Wow, Syzygy really is a word. Somehow, I don't remember that one from the decade-old high school science corner of my brain. That's almost as good as Xyzzy.
-jim
"Pay attention... pendulums on earth fall towards the EARTH, NOT THE SUN."
Like hell they don't. The sun is the most massive hunk of anything in the star system and its gravity, by definition, has an effect on everything. Accurately measure the period of that pendulum and you will find that it has a tendency to move faster during the night (earth and sun pulling in the same direction) as it does during the day (earth and sun pulling in opposite directions). The question this anomally brings up is how much faster?
After all, by your view of the solar system we shoudln't even have tides, since the oceans "fall towards the earth, not the sun" or the moon.
(Then there's the fact that we're all falling towards the sun. It's just that we keep missing.)
I've read many of the old (and new) 'push' gravity theories, the ones that theorize a particle carrier for gravity (I'll call them gravitons here). Where there are less gravitons, e.g. next to a body and more so between two bodies), you experience a lop-sided 'push' from areas of high graviton density.
With two bodies, you wouldn't be able to tell the difference - the absorption of gravitons would be measurable as though they were an appropriate pull.
Where you'd see a difference is in three bodies in a line, as the gravitons have to pass through two bodies on their way to the third, as the density (well, the flux) would already be minutely lower, hence a gravitational "shielding" effect (which would actually be more gravitational pushing from the other side).
These 'push' theories of gravity have waxed and waned in appeal over the past century or so (they're often called LeSagian theories, after Georges-Louis LeSage.) Part of the appeal is that they provide a mechanism for gravity, which GR does not truly provide (the theory of following geodesics in GR may explain paths objects take, but not why spacetime curves in that manner - what 'pulls down' on the 'fabric'?) There's a good collection of papers in Pushing Gravity which show some of the strengths and weaknesses of eight or so of the current push-gravity theories, and possible explanations of things like the anomalous in-track (and seemingly periodic) accelerations satellites can undergo.
Our theories may flip-flop a fair bit over time, but we do collect more data that needs explaining over time, and the anomalies do much more to further our understanding than the same ol'-same ol' ever did ;)
- Ritchie
Binary geeks can count to 1,023 on their fingers
I consulted my professor (he's a General Relativity guy, but works in quantum field theory, too) and he said that he sees no reason for the increase, as long as you stick to linear electrodynamics.
This 'negative energy' argument would be valid in classical mechanics, where the decrease of potential energy gives increase in kinetic energy (since their sum is conserved).
I did an arXiv search (which IMHO is better suited for scientific lookups than google) and found only one article referring to the concept. Not a lot for a theory sound enough to be brought up on slashdot? The articles is written by the authors of the concept themselves and was published in 1999. It does not give the impression of being written by proffessional scientists (no academic affiliation) and the authors base the concept on another hypothesis of their own (stuffed in the lengthy appendix). This concept is just a hypothesis, not a proven scientific theory. The authors explicitly state that their postulate violates Special Relativity. Special Relativity is not a Bible, but you really should think twice before attempting to tear it down. I did not read the article line by line, and I am by no means an authority on the subject, but I think I have enough evidence to say that the concept in question (of the increase of light speed between plates) is risky and presenting it as a fact to the general public is, in my opinion, dishonest.
"Long run is a misleading guide to current affairs. In the long run we are all dead." (John Maynard Keynes)