I think the factor 1/c^6 plays its part in making gravitational radiation considerably weaker. The first astronomical objects to show promise for probing GR directly were the millisecond pulsars and in particular those in a tight orbit with another compact object.
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Manchester has also found a double pulsar with both components detectable which opens up new avenues.
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Caltech have a bit on the sort of gravitational wave radiation power output a 1 tonne steel bar on the verge of disintigrating would produce and it is around 10^36 times below their detection limit see
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I think it would take something going down the plughole in our part of the galaxy before they stand a chance of detection. They are somewhat more optimistic.
On a sunny day (Fri, 10 Dec 2010 18:39:46 -0800) it happened John Larkin wrote in :
I dunno about recent, but several years ago somebody did some math and experiments, and the jury was still out if the was c or anything else. One problem with relatitvitiests is that they correct anything they measure for Einstein's, so that usually gives a very complicated result in conformance with relatitvitiests's assumptions, I think the word was 'epicycles'. 'Epicycles' described the motion of the sun around all the planets IIRC with great precision, the math was hard to comprehend, only a a few 'specialists' could do it, but it was the status quo. I think some people were murdered who disagreed. But they did not have Usenet then. hehe
On a sunny day (Fri, 10 Dec 2010 18:17:13 -0800 (PST)) it happened George Herold wrote in :
LIGO is about job securty. Heaven beware they build something that detects something. that would be the end iof the project. Same for ITER and CERN. Mandate for an other 10 years of 'searching'. Sign of times.
On a sunny day (Fri, 10 Dec 2010 18:45:00 -0800) it happened John Larkin wrote in :
atomic clocks,
relative
the pendulums get larger.
in the motion.
oriented vertically.
spectral width from an atomic clock.
Even better than that, they recently did measure it between first and upper floor of a building. This is not about a formula, math is not 'the reason why', math is a very limited abstraction of observation of nature. A mechanism is what will bring us forward. Ein's Tit-Vity is like Ohms law without the electrons. It does not always hold when you expect, and it does not solve or create any thing. Math starts where understanding ends. This is what you usually see in physics, somebody measures some effect, and a whole bunch of mathemagicians begin a long task of division by zero and multiplication, sponsored by public money, on and off the job, with or without preservatives, leading to more mathemagicians doing more multiplications in the sense of: A half full bottle = half an empty bottle. Multiply by 2 and now we have proved that a full bottle is an empty bottle. So, well, I think my Le Sage explanation of why time changes up there versus down here is a more sane way to look at things, cheaper, faster better, and avoid you falling in a wormhole, or becoming a singularity. Call it normalisation if you want.
On a sunny day (Fri, 10 Dec 2010 19:36:41 +0000) it happened Martin Brown wrote in :
Oh what a fool you are. The operation of the GPS sat is set by the DIGITAL DIVIDER in it for the atomic clocks, NOT by a THEORY. There can be many theories that explain the faster moving clock up there relative to a slower moving one on earth. For example in a Le Sage theory it could go like this: The higher you get up, the more intense the particle flux, the more atoms and their sub-particles are compressed, the shorter the pendulums, the faster they move. And close to earth a lot of Le Sage particles are intercepted (shadowed), and the pendulums get larger. Now I just explained it in the form of a mechanism, and PREDICT an asymmetry in the motion. So atoms close to earth moving horizontally should move different from those oriented vertically. Now lets see how long before this is confirmed, could show up as a change in spectral width from an atomic clock.
The higher speed of the clock travelling eastwards makes it tick more slowly than one at rest due to special relativity but being 35,000 feet up in the air makes it tick quicker than one on the ground travelling at the same speed. The kinematic correction wins out in this case.
Here is a brief description of the 1971 experiment you refer to on Wiki:
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Many institutions have replicated the experiment since.
For GPS satellite clocks the GR correction is significant:
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What are you talking about? The extent of the errors in spacecraft flybys are usually due to US aerospace speaking only foot/pounds and BTus whilst NASA specify thrust in Newtons. Units conversions, hardware failures and software errors account most failed planetary probes.
Flybys to do slingshots are done pretty routinely now with very high accuracy. It is a way to get extra acceleration without using fuel. The occasional trajectory adjust thruster doesn't always shut off as cleanly as one might like but that is engineering not physics.
There is a miniscule apparent sunward acceleration of around 8x10^-10 m/s^2 of the Pioneer probes that is unaccounted for and might signal new physics. It could be as mundane as helium or heat leaking from the RTGs or non luminous material perhaps eevn dark matter is clumped round the sun in the solar system. There is also a possibility that it is a clue that the inverse square law is not quite right at long range and that what we presently call dark matter on galactic and intergalactic scales is an artefact of our present formulation of physics. Time will tell when better gravitational probes fly that are designed to test whether the effect observed is real or illusory.
The latest review paper on the Pioneer anomaly is on arXiv
The December issue of Physics Today came Today. There is a blurb about LIGO. They are shutting down for an upgrade and might even move one of the detectors to Austrailia. To quote... ".... Advanced LIGO originally involved increasing the sensitivity at those sites up to ten times, thus expanding by 1000 fold the volume of accessible universe. The improvement can be summed up as going from a predicted single event in 30 years to an event every week or so."
Of course increasing sensitivity by an order of magnitude may be no small task.
=A0>It isn't correct to say that a light wave is 'made up of photons', at
ch
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hread...
That's an interesting perspective. Thank you Phil. (I think I've been watching too many Feynman videos. A man who loved his photons.)
I don=92t need to quantize the EM field (photons) and I can think of the quantization as being only in the interaction between EM and electrons.
Is that right?
I=92ve always been a bit bothered when people say that the shot noise caused by light shinning on a detector is an indication of quantization of the photons. To me it always just looked like quantization of the electrons. (How could one untangle the two?) After all it=92s not much different than the shot noise in a forward biased diode. In that case it=92s random thermal excitation of the electrons.
It's fuzzy for non-avalanche photodiodes at visible wavelengths, where one photon tends to create less than one photoelectron. With, say, xray photons and the right detector, you might get a lot of electrons per photon, and the statistics would more clearly demonstrate the photon quantization. As in showing a current blip for each single photon.
PMT shot noise is like that. It's clearly big pulses, each with lots of electrons, per incoming photon.
Hmm, never less than one electron. But probablity of absorption is less than one.
In all cases the detection process starts with the interaction with a single electron.
OK if the EM field (I'm going to try not using the term photon... which I use all the time.) has more energy it can ionize a bunch of electrons.
Yeah but the beginning of the chain is the interaction between a single electron and the EM field. Everything else is just gain. There are vaccum tube photodiodes, (as I assume you know.) that's how Schottky first saw shot noise.
On a sunny day (Mon, 13 Dec 2010 08:51:47 -0800 (PST)) it happened George Herold wrote in :
Is not there a plan for launching some spacecrafts with a laser connection in-between them, to do the same thing over much longer distances? With the same zero result of course :-)
I have been posting an April one joke to sci.physics every year for the last few years that says that LIGO detected something, they are getting used to it now...
On a sunny day (Mon, 13 Dec 2010 09:27:33 -0800) it happened John Larkin wrote in :
No I do not see it that way, I think Mr Planck got misunderstood. What he said was that you need a specific amount of energy to get an electron lose from an atom. That one electron then causes the avalanche of electrons and subsequent output pulse in the PMT. So I prefer to look at the atom, with it's sort of orbiting electron, as being influenced by the incoming *WAVE*, and at a specific frequency (say 'energy') the electron shakes out of orbit. Now here people call me wrong, but there are sensors that detect less than one photon, or so I'v read. I think this is all set by De Broglie's wavelength.
So to put it very simply, there is a threshold, but light comes in ever smaller quantities or energies.
But if you specify 'photon' as 'h.v' then the math is correct, but reality does not care. fun fun fun.
Called LISA. On of the cool things about LIGO, (if they get the advanced version up and running.) is that it's a whole sky 'detector', you don't have to point it.
ast few years
Well since the 'expected' detection rate was once per 30 years, it's not that surprizing that they say nothing. Of course there is always the unexpected!
cut Photomultiplier. In our lab somebody had one wired up, and covered the tube with about twenty layers of black cloth. The tube was connected to an audio amplifier and a loudspeaker. A very nice demo. Lifting slightly a corner of 2 or 3 layers of cloth, let you hear a loud click for each photon. Starting at some clicks per second, and changing to a machinegun rattle when lifted to far.
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